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Sheet Weaver

Sheet weaver

Dubiaraneinae
Erigoninae
Linyphiinae
Micronetinae
Mynogleninae
Stemonyphantinae Linyphiidae is a family of spiders, including nearly 4,250 described species in over 550 genera worldwide. This makes Linyphiidae the second largest family of spiders after the Salticidae. New species are still being discovered throughout the world, and the family is poorly known. Because of the difficulty in identifying such tiny spiders, there are regular changes in taxonomy as species are combined or divided. Spiders in this family are commonly known as sheet weavers (from the shape of their webs), or money spiders (in the United Kingdom, from the superstition that if such a spider is seen running on you, it has come to spin you new clothes, meaning financial good fortune). There are six subfamilies, of which Linyphiinae (the sheetweb spiders), Erigoninae (the dwarf spiders), and Micronetinae, contain the majority of described species. Common genera include Neriene, Lepthyphantes, Erigone, Eperigone, Bathyphantes, Troglohyphantes, the monotypic genus Tennesseellum and many others. These are among the most abundant spiders in the temperate regions, although many are also found in the tropics. The generally larger bodied members of the subfamily Linyphiinae are commonly found in classic bowl and doily webs or filmy domes. The usually tiny members of the Erigoninae are builders of tiny sheet webs. These tiny spiders (usually 3 mm or less) commonly balloon even as adults and may be very numerous in a given area on one day, only to disappear on the next. Some males of the erigonines are very strange, with their eyes set up on mounds or turrets. This reaches an extreme in some members of the large genus Walckenaeria, where several of the male's eyes are placed on a stalk taller than the carapace! A few spiders in this family include:
- Bowl and doily spider, Frontinella communis
- Filmy dome spider, Neriene radiata
- Blacktailed Red Sheetweaver, Florinda coccinea

External links

- [http://research.amnh.org/entomology/spiders/catalog81-87/index.html Platnick, N.I. 2003. World Spider Catalog]
- [http://www.marion.ohio-state.edu/spiderweb/SpiderPictures/Linyphiidae/Frontinella%20pyramitela%20web.htm Frontinella pyramitela web (photo)]
- [http://www.andtan.newmail.ru/list/ Linyphiidae of the world, huge list of genera and species]
- [http://tolweb.org/tree?group=Linyphiidae ToL on Linyphiidae]

Gallery

Image:Frontilla_close.jpg|Bowl and doily spider, Frontinella communis Image:Florinda_coccinoa.jpg|Blacktailed Red Sheetweaver, Florinda coccinoa Image:Florinda_coccinoa_eyes.png|Florinda coccinoa eyes Category:Spiders

Erigoninae

Many; see text. Dwarf spiders are sheet weavers in the subfamily Erigoninae. They are the most numerous of the sheet weavers, with more than 2,000 described species. They are very small (some less than 1 mm) spiders. They balloon both as spiderlings and adults. Some males have bizarre projections on their carapaces. The function of these projections is little understood, but is presumed to be involved with courtship. These spiders probably are more important as members of the beneficial complex of predators in agroecosystems than is generally known. One species, Atypena formosana lives in colonies in wetland habitats. They build nets just above the water line in rice fields to hunt planthopper nymphs. The most well-known genus is Erigone.

External reference

- [http://www.cpitt.uq.edu.au/software/riceipm/keys/Html/Atypena.htm Atypena] Category:Spiders

Spider

Araneomorphae
Mesothelae
Mygalomorphae
See the taxonomy section for families Spiders are invertebrate animal(s) that produce silk, have eight legs and no wings. More precisely, a spider is any member of the arachnid order Araneae, an order divided into three sub-orders in newer systems: the Mygalomorphae (the primitive spiders), the Araneomorphae (the modern spiders) and the Mesothelae, which contains the Family Liphistiidae, rarely seen burrowing spiders from Asia. The study of spiders is known as arachnology, although it is often included in the more general term entomology. Many spiders hunt by building webs to trap insects. These webs are made of spider silk, a thin, strong protein strand extruded by the spider from spinnerets on the end of the abdomen. All spiders produce silk, although not all use it to spin elaborate traps. Silk can be used to aid in climbing, forming smooth walls for burrows, cocooning prey, and for many other applications.

Morphology and development

Spiders, unlike insects, have only two body segments instead of three; a fused head and thorax (called a cephalothorax or prosoma) and an abdomen (called the opisthosoma), supported by a hard exoskeleton composed mainly of chitin. chitin Spiders also have eight legs (insects have six), no antennae, and their eyes are single lenses rather than compound eyes. Additionally spiders have pedipalps (or just palps), which are two appendages next to their mouths that aid in manipulating food and are used by the males in mating.

Respiration and circulation

Spiders have an open circulatory system, meaning they don't have true blood or veins for it to travel in. Rather, their bodies are filled with haemolymph, which is pumped through arteries by a heart into spaces called sinuses surrounding their organs. organsSpiders have developed several different respiratory anatomies, based either on book lungs, a tracheal system, or both. Primitive mygalomorph spiders generally have only a pair of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allows air to enter and diffuse oxygen. Modern araneomorph spiders often have a single book lung in addition to spiracles which deliver air into the tracheae, where oxygen is then diffused into the haemolymph. In the tracheal system oxygen interchange is much more efficient, enabling cursorial hunting (hunting involving rapid pursuit) and other advanced characteristics.

Vision

Spiders usually have eight eyes in various arrangements, a fact which is used to taxonomically classifiy different species. Sometimes one pair of eyes is better developed than the rest, or there are only six pairs, or no eyes at all. Several families of hunting spiders have developed good to excellent vision, such as wolf spiders and jumping spiders. However most spiders that lurk on flowers, webs and other fixed locations waiting for prey have very poor eyesight, but possess extreme sensitivity to vibrations for hunting.

Defense

Some primitive spiders, like the tarantula, have a patch of urticating hairs on their abdomens for defense, which are generally absent on modern spiders. Certain other species have specialized defense tactics. For example, the Golden Wheeling spider of the desert escapes Tarantula Wasps (a species of wasp that lays it's eggs in a paralyzed spider so the larvae have enough food when they hatch) by flipping onto its side and cartwheeling away.

Life cycle

The spider life cycle progresses through three stages: the embryonic, the larval, and the nympho-imaginal (Foelix, 1996). Between the time an egg is fertilized and the spider begins to take the shape of a spider is referred to as the embryonic stage (Foelix, 1996). As the spider begins to look more like a spider it enters the larval stage (Foelix, 1996). It enters the larval stage as a prelarva and, through subsequent molts, it reaches its larval form, a spider-looking, non self-sufficient animal feeding off its yolk supply (Foelix, 1996). After a few more molts, also called instars, body structures become differentiated; all organ systems are complete and the animal begins to hunt on its own; it has reached the nympho-imaginal stage (Foelix, 1996). This stage is differentiated by two sub-stages: the nymph, or juvenile stage and the imago, or adult stage (Foelix, 1996). A spider does not transition from the nymph to the imago until it has become sexually mature (Foelix, 1996). Once a spider has reached the imago stage, it will remain there until its death. Many spiders may live only about a year, but a number will live two years or more, overwintering in sheltered areas (the annual influx of 'outdoor' spiders into houses in the fall is due to this search for a nice warm place to spend the winter).

Reproduction

Spiders reproduce by eggs laid in silk bundles called egg sacs. egg Spiders often use elaborate mating rituals (especially in the visually advanced jumping spiders) to allow the male to approach close enough to inseminate the female without triggering a predatory response. Assuming that the approach signals are exchanged correctly, the male spider must make a timely departure after mating to escape before the female's normal predatory instincts come back into operation. Unusually, sperm transmission is an indirect process. When a male is ready to mate, he will spin a web pad onto which the contents of the abdominal reproductive organs are discharged. He then dips his palps (also known as 'palpi'), the small, leg-like appendages on the front of his cephalothorax, into the sperm, absorbing it. Mature male spiders characteristically have swollen bulbs on the end of their palps for this purpose, and this is a useful way to identify the sex of a spider in the field. With his palps thus 'charged' he then goes off in search of a female. The act of copulation occurs when the male inserts one or both palps into the female's genital opening, known as the epigyne. He transfers his sperm into the female by contracting his palps. Very unusual behaviour is seen in spiders of the genus Tidarren, as the male amputates one of his palps before maturation and enters his adult life with one palp only. The palpi constitute 20% of its body mass, and since this weight greatly impedes its movement, the spider detaches one of the two to gain mobility. In the Yemeni species Tidarren argo, the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In the meantime the female feeds on the palpless male. (Journal of Zoology (2001), 254:449-459 Cambridge University Press )

Do female spiders eat their mates?

It is often said that the male (usually significantly smaller than the female, down to 1% of her size for Tidarren sisyphoides), is likely to be killed by the female after the coupling, or sometimes before intercourse has occurred. This supposed propensity is what gave the Black Widow Spider, Latrodectus mactans its name. However, the three species of North American black widows do not seem usually to kill the male (although they may) and males can sometimes live in the web of a female for a while without being harmed. The male Latrodectus hasselti dies after it inserts its second palpus in the female genital opening even if the female does not eat it. However, despite these examples, and many other similar reports, the story of the 'sacrificial male' has become greater than the truth. Mating of spiders is not invariably followed by cannibalism. Rainer F. Foelix, (1982), says "The supposed aggressiveness of the female spider towards the male is largely a myth... only in some exceptional cases does the male fall victim to the female.". Michael Roberts (1995) says "It is rare for a fit male to be eaten by the female..." However, there has been speculation on why this sacrifice of male mates might occur at all. One theory is that once the male has mated, if he is unlikely to mate again then further extension of his life serves no evolutionary purpose, while the sacrifice of the male may help increase egg production through increased nutrition for the female. Having more offspring would give the male an advantage of having his genes passed on over other males that were not eaten. This would be consistent with the hypothesis (Roberts, 1995) that old or unfit males get eaten, whilst younger and fitter ones may survive to mate again.

Ecology

nutrition Spiders have a great range of variation and lifestyle, although all are predatory. While spiders are generalist predators, in actuality their different methods of prey capture often limits the type of prey taken. Thus web-building spiders rarely capture caterpillars and crab spiders that ambush prey in flowers capture more bees, butterflies and some flies than other insects. Groups of families that tend to take certain types of prey because of their prey capture methods are often called guilds. A few spiders are more specialized in their prey capture. Dysdera captures and eats sowbugs, pillbugs and beetles, while pirate spiders eat only other spiders. Bolas spiders in the family Araneidae use sex pheromone analogs to capture only the males of certain moth species. Despite their generally broad prey ranges spiders are one of the most important links in the regulation of the populations of insects. Every day on a meadow they devour over 10 g/m² of insects and other arthropods. insect]]

Predatory techniques

insect There are many families of spiders, and the ways that they catch prey are diverse. But whether they catch insects, fish, small mammals, small birds, or some other small form of life, as soon as a spider makes contact with its prey it will attempt to bite. Spiders bite their prey, and occasionally animals that cause them pain or threaten them, to do two things. First, they inflict mechanical damage, which, in the case of a spider that is as large as or larger than its prey, can be severe. Second, they can choose to inject venom through their hollow fangs. Many genera, such as the widow spiders, inject neurotoxins that can spread through the prey's entire body and interfere with vital body functions. Other genera inject venom that operates to produce tissue damage at the site of the bite. Genera such as that of the brown recluse spider produce a necrotoxin. The necrotoxin is injected into prey where it causes the degradation of cell membranes. In the larger victims that do not die from these attacks, painful lesions over a fairly wide area of the body can remain active for fairly long periods of time. Digestion is carried out internally and externally. The spiders secrete digestive fluids into their prey from a series of ducts perforating their jaws. These digestive fluids dissolve the prey's internal tissues. Then, the spider feeds by sucking the partially digested fluids out. Spiders consume only liquid foods. Many spiders will store prey temporarily while this process of external digestion is going on. Web weaving spiders that have made a shroud of silk to quiet their envenomed prey's death struggles will generally leave them in these shrouds and then consume them at their leisure. prey

Spider webs and prey capture

Main article: Spider web Some spiders spin funnel-shaped webs, others make sheet webs, and still others make the spiral "orb" webs which are most commonly associated with the order. These webs may be made with sticky capture silk, or with "fluffy" capture silk, depending on the type of spider. Webs may be in a vertical plane (most orb webs), a horizontal plane (sheet webs), or at any angle in between. Most commonly found in the sheet-web spider families, some webs will have loose, irregular tangles of silk above them. These serve to disorient and knock down flying insects, making them more vulnerable to being trapped in the web below. They may also help to protect the spider from aerial predators such as birds and wasps. The spider, after spinning its web, will then wait on, or near, the web for a prey animal to become trapped. The spider can sense the impact and struggle of a prey animal by vibrations transmitted along the web lines. Other species of spiders do not use webs for capturing prey directly, instead pouncing from concealment (e.g. Trapdoor spiders) or running them down in open chase (e.g. Wolf spiders). Spiders do not usually adhere to their own webs. However, they are not immune to their own glue. Some of the strands of the web are sticky, and others are not. For example, if a spider has chosen to wait along the outer edges of its web, it may spin a non-sticky prey or signal line to the web hub to monitor inter-web movement. The spiders have to be careful to only climb on the non-sticky strands. The ability to spin webs allows a spider to catch prey without having to expend energy by running it down. Thus it is a very efficient method of gathering food. However, constructing the web is in itself an energetically costly process due to the large amount of protein required, in the form of silk. In addition, after a time the silk may lose its stickiness and thus become inefficient at capturing prey. It is not uncommon for spiders to eat their own web daily to recoup some of the energy used in spinning. The silk proteins are thus 'recycled'. The spider, in the middle of the web, also makes for a highly visible prey for birds and other predators. Many day-hunting orb-web spinners reduce this risk; for example, by hiding at the edge of the web with one foot on a signal line from the hub, or by appearing to be inedible or unappetizing. The Net-casting spider balances the two methods of running and web-spinning in its feeding habits. This spider weaves a small net which it attaches to its front legs. It then lurks in wait for potential prey and, when such prey arrives, lunges forward to wrap its victim in the net, bite and paralyse it. Hence, this spider expends less energy catching prey than a primitive hunter such as the Wolf spider. It also avoids the energy loss of weaving a large orb-web. Some spiders manage to use the 'signalling snare' technique of a web without spinning a web at all. Several types of water-dwelling spiders will rest their feet on the water's surface in much the same manner as an orb-web user. When an insect falls onto the water and is ensnared by surface tension, the spider can detect the vibrations and run out to capture the prey.

Types of spiders and the severity of their bites

Over 37,000 species of spiders have been identified, but because of their great ability for hiding, it is believed that about 200,000 species exist. All species are venomous (with the exception of the family Uloborus), but only 30 species are known to be potentially deadly to humans. Key to bite severity:
- Extremely dangerous: Bite (assuming successful envenomation) may cause death in a healthy adult without emergency medical treatment.
- Very dangerous: Bite may cause death in children, the elderly, the infirm without prompt medical treatment; and/or may cause debilitating injury. Prompt medical attention is required.
- Dangerous: Bite unlikely to cause death/no known deaths reported; bite may cause significant local or systematic reaction. Medical attention is generally required to limit scope of symptoms.
- Painful bites: Venom may inflict localized pain (similar to a bee sting) but does not have any dangerous or long-term side effects. Medical attention generally not required.
- Not dangerous: Spider is unable to puncture human skin, and/or venom does not cause any significant reaction in humans.
- No venom: This species does not produce venom. The only true Family of spiders in this category is the hackled orb-weavers; other Arachnids often confused with spiders, such as the harvestman, also do not produce venom. A couple of things should be noted when considering the amount of danger posed by spider bites. First, it is often the case that a spider bite is "dry"--the skin may be pierced, but little or no venom injected into the victim; thus reducing or eliminating any harmful effects. Second, there have been reports of spider bites (by spiders considered otherwise harmless) causing allergic reactions in some individuals, up to and including anaphylactic shock, a life-threatening condition (much the same as a sting from an ant, bee, or wasp). Third, many spiders listed as dangerous are seldom encountered, or have dispositions that make them unlikely to bite despite the high toxicity of their venom. Finally, little is known about the toxicity of many spiders, due to infrequent encounters with Man; the list of venomous spiders is limited to those who are linked to medical events in humans or who otherwise have been extensively studied. It should also be noted that for healthy adults, a bite by even the most toxic spiders on the list will require hours before death ensues; if timely appropriate emergency medicine is administered, victims should be expected to recover. The scenario given in movies such as Arachnophobia, where bite victims die within minutes, does not occur. One exception to this is with very small children; there is at least one recorded case of a small child dying within 15 minutes of a bite from a Sydney funnel-web spider; that occurred before the development of an antivenin.

Tangleweb spiders (Theridiidae)

Characterized by irregular, messy-looking, tangled, three-dimensional (non-sticky) webs, generally low and anchored to the ground or floor and wall. Commonly found in or near buildings; some build webs in bushes. The spider generally hangs in the center of the web, upside-down. Prey is generally ground-dwelling insects such as ants or crickets, in addition to small flying insects. Widows (Latrodectus spp.) - a large, cosmopolitan group; all with relatively dangerous bites. These are relatively large (about the size of a nickel), 'burly-looking' house spiders; generally dark, often with a red mark on the glossy, smooth abdomen, either above or below. examples:
- Black widow spider (very dangerous)
- Latrodectus tredecimguttatus, known as the European or Mediterranean Black Widow, the Malmignatte spider, or the Karakurt spider (very dangerous)
- Red-back spider (very dangerous)
- Red Katipo and black katipo spiders (very dangerous)
- Button spider (very dangerous)
- Brown widow spider (dangerous; venom is less severe than the black widow)
- Red widow spider (believed to be very dangerous; less is known about the effects of red widow envenomations on humans due to the limited range of this spider). Steatoda--a large genus which includes the false black widows; these are sometimes mistaken for widows, but have more flattened abdomens, and abdominal markings are generally white stripes or dots rather than red dots. None of these is truly dangerous but some of them are medically significant:
- S. grossa (possibly dangerous); bite resembles a very minor widow bite.
- S. nobilis (painful bites)
- S. paykulliana (painful bites) others - the common "yuck!" spiders - large, globular abdomen, thin, spindly legs. Often rather non-descript patterns in gray or brown and white. examples:
- American house spider (not dangerous)

Orb web spiders (Araneidae)

American house spider These spiders spin the familiar spiral snare that most people think of as the spider web. They range in size from quite large (6+ cm) to very small (<1 cm), but all are quite harmless to humans, beyond the shock entailed from walking into a face-height web and having a large spider dangling from your nose. Many of the day-time hunters have a 'ferocious' appearance, with spines or large 'fangs', but they are almost invariably inoffensive, preferring to drop on a drag-line to the ground when disturbed, rather than bite.
- St Andrew's Cross spider (an Argiope) (not dangerous)
- Long-jawed orb weaver Tetragnathidae (not dangerous)
- Cyclosa conica (not dangerous)
- Golden silk orb-weaver (not dangerous)
- European garden spider (not dangerous)
- Australian garden orb weaver spider (not dangerous)
- Jewel Spider (not dangerous)
- Spiny Micrathena (not dangerous)

Other forms of webs

Spiny Micrathena] This is a "catch-all" category, comprising members of several different groups that spin non-sticky webs in a variety of structural styles. Some (the Linyphiidae) make various forms of bowl- or dome-shaped web with or without a flat sheet or a tangled web above or below. Some make a flat platform extending from a funnel-shaped retreat, with generally a tangle of silk above the web. The common northern hemisphere 'funnel-web', 'house' or 'grass' spiders are only distantly related to the notorious Sydney funnel-web spider, and are generally considered to be quite harmless (with one notable exception - the Hobo spider, below). Some of the more primitive group Atypidae may make tubular webs up the base of trees, from inside which they bite insects that land on the webbing. These spiders look quite ferocious, but are not generally considered to be particularly dangerous to humans.
- Sydney funnel-web spider (Atrax robustus) (extremely dangerous)
- Bowl-and-doily spiders (Linyphiidae) (not dangerous)
- Hobo spider (Tegenaria agrestis) (dangerous)
- Grass spiders (Agelenidae) (not dangerous)
- Filmy dome spider (Linyphiidae) (not dangerous)
- Hackled orb-weaver (no venom)
- Net-casting spider

Hunting spiders

Net-casting spider
- Brazilian Wandering Spider (extremely dangerous)
- Brown recluse spider (very dangerous)
- Huntsman spiders (painful bites)
- Jumping spiders (not dangerous)
- Lynx spiders (not dangerous)
- Nursery web spiders (not dangerous)
- Spitting spiders (not dangerous)
- Tarantulas (painful bites; some species like the Chinese bird spider may be dangerous)
- Wolf spiders (Lycosidae) (not dangerous)
- Yellow sac spider (painful bites - may produce effects like a milder form of Recluse venom)

Spiders which ambush their prey

This is another catch-all category that includes a diverse collection of spiders. Some actively lure prey (the Bolas spiders) and may capture them with a sticky ball of silk on a line; others wait in a high-traffic area and directly attack their prey from ambush.
- Six-eyed sand spider (Sicariidae) (extremely dangerous)
- Trapdoor spider (painful bites)
- Crab spiders (Thomisidae) (not dangerous)
- Bolas spiders (Araneidae) (not dangerous)

Others

Bolas spiders
- Camel spider, not actually a spider at all, but rather a Solifugid (also commonly called Sun-spiders or Wind-scorpions). Very well-known as the source of many urban legends (no venom)
- Kimura-gumo (Heptathela kimurai, a member of the Family Liphistiomorphae) (not dangerous)
- Spruce-fir moss spider, Microhexura montivaga
- Tooth cave spider, Neoleptoneta myopica
- Bird Dropping Spider, Celaenia excavate

Spider bites

Most spiders are unlikely to bite humans because they do not identify humans as prey. Spiders, even small ones, may however bite humans when pinched. For instance, a common jumping spider (Family: Salticidae), around 3/8 inch (1 cm.) long, when pinched between the folds of a human's palm may inflict a bite that is about as painful as a bee sting. Dangerous spiders in the United States include widow spiders, brown recluse spiders, hobo spiders, and yellow sac spiders. None of these spiders will intentionally "come after you," but they should be removed from one's house to avoid accidental injury. Many authorities warn against spraying poisons indiscriminately to kill all spiders, because doing so may actually remove one of the biological controls against incursions of the more dangerous species by ridding them of their competition. If dangerous spiders are present in your area, then be mindful when you move cardboard boxes and other such objects that may have become the shelter of a poisonous spider. There is no need to be fearful; just do not grab a spider.

Black widows

The Black widow spider is one of a number of widow spiders (genus Latrodectus) that carry a neurotoxic venom. Like many spiders, widows have very poor vision (jumping spiders and wolf spiders being notable exceptions), and they move with difficulty when not on their web. Widow spiders are large, strong-looking house spiders (but still have relatively spindly legs and deep, globular abdomens). The abdomen is dark and shiny, and has one or several red spots, either above or below. The spots may take the form of an hourglass, or two triangles, point-to-point. Male widows, like most spiders, are much smaller than the females, and may have a variety of streaks and spots on a browner, less globular abdomen. The males are generally considered to be much less dangerous (if at all) than the females. Widows tend to be quite non-aggressive, but will bite if the web is disturbed and the spider feels threatened. The venom, although rarely life-threatening, produces very painful effects including muscle spasms and 'tetanus-like' contractions. A serious bite will often require a short hospital stay. Children, elderly, and ill individuals are at most risk of serious effects.

Brown recluse spiders and hobo spiders

wolf spider Brown recluse spiders, (or "Violin Spiders" from the dark violin-shaped marking on the cephalothorax) Loxosceles reclusa, are slow-moving, retiring spiders which wander about in dim areas and under things, and so are more easily trapped against one's skin by clothing, bed sheets, etc. Even so, most encounters with this spider occur from moving boxes or rooting about in closets or under beds. The range of this spider in the US is approximately the lower 2/3 of the country by the eastern 3/4 of the country. A number of related Recluse spiders (some non-native introductions) are found in southern California and nearby areas, as well. The hobo spider, Tegenaria agrestis, may wander away from its web, especially in the fall, and thus come into contact with people and bite. This spider is found in the northwestern United States and throughout much of Europe. Oddly enough, in Europe it is considered a harmless outdoor relative of the common House Spider (Tegenaria domestica). The yellow sac spiders, Chiracanthum sp., take shelter in silk tubes during the daytime and generally come out to hunt at night. These pale yellow or whitish spiders are often found in houses at the top of walls, or wandering across ceilings. They are also commonly found outdoors on foliage. The drag-lines they leave while hunting are one of the most common "cob-webs" that are removed with broom and vacuum cleaner. People may unintentionally make contact with them in the dark and so be bitten. However, most people will live their entire lives in close proximity to them and never suffer a bite. Brown recluse spider bites can produce very severe local symptoms, death of tissue around the wound, and, sometimes, severe systemic symptoms, including organ damage. The bites of hobo spiders and yellow sac spiders can cause both pain and necrosis (tissue death). Typically, all these bites are characterized by open, sore-like wounds that heal very slowly and may leave scarring. It has been suggested that steroid treatments may speed healing and reduce scarring. It is believed that many spider bites which are attributed (often by physicians and other medical personnel) to the brown recluse are in fact caused by the hobo spider (if caused by a spider at all). Many brown recluse bites are reported in the U.S. west coast states (Washington, Oregon, and northern California) where populations of brown recluse spiders have not been found. There are other species of spider in the genus Loxosceles which are found in southern California and other southwestern states; most of these species live in remote areas and are rarely encountered by humans. Bites of Loxosceles spiders found in South America are more serious in their consequences than their North American relatives.

Huntsman spiders

The huntsman spiders have a worldwide reputation for scaring people. They are large, defend their nests, and may move toward people and make threat displays. They frequently enter houses and hunt over the walls and ceilings where they may run rapidly for long distances without pausing. When they actually do bite people, the bites are very unpleasant, but these spiders are not regarded as dangerous. They are quite common in parts of Australia. Australian huntsman spiders are typically non-aggressive except when defending their nests or their young. There is one spider in California and Japan, probably a huntsman (tentatively identified as a member of the Sparassidae family, Heteropoda venatoria), that might run over and bite your finger if you touch the wall that it is clambering over. That behavior may well occur because its eyesight is good enough to see movement and general shape, but not sufficient to avoid mistaking something else for its natural prey.

Redback jumping spiders

Some people have reported being bitten by redback jumping spiders (Phidippus johnsoni). Most reports seem to be from California. These relatively large, alert jumping spiders have bright red abdomens (the females have a black stripe), and should be clearly visible. It is unclear how the bites occur. Accidental contact seems rather unlikely since jumping spiders have excellent vision and could easily avoid being brushed by a human hand. It is also unlikely that they would mistake a human finger for their natural prey. One source suggests that since they are quite attractive children may try to pick them up and in that way elicit a defensive bite. Fortunately, the worst consequences reported have been three to four days of discomfort, with no permanent damage. Like most of the larger spiders, the consequences of a bite seem little different than a wasp or bee sting. Since they do not frequent human habitations it should ordinarily be easy to avoid unpleasant contact with them.

Brazilian wandering spiders and Australian venomous funnel-web spiders

The Brazilian wandering spider (a ctenid spider) and the Australian venomous spiders such as the Sydney funnel-web spider (a mygalomorph only distantly related to the araneomorph funnel-web spiders) frequently bite people and are regarded as among the most dangerous in the world. They are quite aggressive spiders, and are prone to biting when confronted, rather than running away. The Sydney funnel-web spider, a large, bulky, dark-colored spider, is restricted to a relatively small area around Sydney, Australia. There are other dangerous species related to this spider in surrounding parts of Australia, including Tasmania. The males in this case have somewhat more potent venom than females and they also wander, making them more likely to be encountered. The Brazilian wandering spider is a large, brown spider rather like a North American Wolf spider in appearance. It, like several other more harmless spiders, may hitch a ride in clusters of bananas. As a result, any large spider appearing in a bunch of bananas should be treated with due care. Oddly, many of the bites of this species are dry bites and no venom is released. The spiders are as large as some small tarantulas and have fairly long fangs. While venom from either spider can be deadly to children and the infirm, since the development of antivenin to the venoms of both were developed (the funnel web spider in the mid-1980's and the wandering spider in 1996), no humans have died from their bites. Nevertheless, any large spider which makes a threat display (raising front legs, rearing back to display fangs) when encountered should be treated with caution - especially in areas where these two types of spiders may be expected.

Taxonomy

antivenin] antivenin antivenin antivenin antivenin ]] Suborder Araneomorphae
- Agelenidae (araneomorph funnel-web spiders)
- Amaurobiidae (tangled nest spiders)
- Anyphaenidae (anyphaenid sac spiders)
- Araneidae (orb-weaver spiders)
- Caponiidae (two-eyed spiders)
- Clubionidae (sac spiders)
- Corinnidae (corinnid sac spiders)
- Ctenidae (wandering spiders)
- Cybaeidae (water spiders)
- Deinopidae (ogre-faced spiders)
- Desidae (intertidal spiders)
- Dictynidae (dictynid spiders)
- Diguetidae (coneweb spiders)
- Dysderidae (woodlouse hunter spiders)
- Eresidae (velvet spiders)
- Filistatidae (crevice weavers)
- Gnaphosidae (ground spiders)
- Hahniidae (dwarf sheet spiders)
- Hersiliiidae (tree trunk spiders)
- Hypochilidae (lampshade spiders)
- Leptonetidae (leptonetid spiders)
- Linyphiidae (sheet weavers or money spiders)
- Liocranidae (liocranid sac spiders)
- Lycosidae (wolf spiders)
- Mimetidae (pirate spiders)
- Miturgidae (long-legged sac spiders)
- Nesticidae (scaffold web spiders)
- Oecobiidae (wall spiders, six-exit tent spiders)
- Oonopidae (oonopid spider)
- Oxyopidae (lynx spiders)
- Palpimanidae (palp-footed spiders)
- Philodromidae (philodromid crab spiders)
- Pholcidae (daddy long-legs spiders)
- Pisauridae (nursery web spiders)
- Plectreuridae (plectreurid spiders)
- Salticidae (jumping spiders)
- Scytodidae (spitting spiders)
- Segestriidae (tube-dwelling spiders)
- Selenopidae (wall crab spiders)
- Sicariidae (recluse spiders)
- Sparassidae (huntsman spiders)
- Tengellidae (tengellid spiders)
- Tetragnathidae (long jawed spiders)
- Theridiidae (tangle web spiders)
- Theridiosomatidae (ray spiders)
- Thomisidae (crab spiders)
- Titanoecidae (titanoecid spiders)
- Uloboridae (hackled orb-weavers)
- Zodariidae (zodariid ground spiders)
- Zorocratidae (zorocratid spiders)
- Zoropsidae (zoropsid spiders) Suborder Mesothelae
- Actinopodidae
- Arthrolycosidae (primitive spiders)
- Arthromygalidae (primitive spiders)
- Barychelidae
- Idiopidae
- Liphistiidae (primitive burrowing spiders)
- Microstigmatidae
- Migidae
- Nemesiidae
- Paratropidae Suborder Mygalomorphae Mygalomorphae
- Antrodiaetidae (folding trapdoor spiders)
- Atypidae (atypical tarantulas)
- Ctenizidae (trapdoor spiders)
- Cyrtaucheniidae (wafer trapdoor spiders)
- Dipluridae (funnel-web tarantulas)
- Hexathelidae (venomous funnel-web tarantulas)
- Mecicobothriidae (dwarf tarantulas)
- Theraphosidae (tarantulas)

Symbolism

The spider symbolizes patience, for its hunting with web traps. Some fictional and mythological characters are related to spiders:
- Arachne, a weaver turned spider in Greek mythology.
- Kwaku Ananse, the West African trickster.
- Aunt Nancy, its American version
- Anansi the Spider is a superhero in the Static Shock animated series.
- Spider-Man, the Marvel superhero with spider-like powers, and his avatars:
- Pavitr Prabhakar, his Indian version.
- Yu Komori, his manga version
- Many techniques (fictional and otherwise) of ninja are named after spiders, usually due to involving spiderlike movement or other traits. The Italian dance and music tarantella is related to tarantulas, either as a folk remedy for bites or from its vigorous movements.

References

- The World of Spiders, by W. S. Bristowe Collins (New Naturalist), London 1958
- The Life of the Spider, by John Crompton. Mentor, 1950.
- How to Know the Spiders, by B. J. Kaston. Dubuque, 1953.
- Biology of Spiders, by Rainer F. Foelix, 1982 and second edition, 1996
- The Book of the Spider, by Paul Hillyard, Random House, New York 1994
- Spiders, by Barbara York Main, Collins (The Australian Naturalist Library), Sydney 1976
- Spiders of Britain and Northern Europe, by Michael J. Roberts, Collins, London 1995
- Spiders of North America: an Identification Manual, by Darrell Ubick, Pierre Paquin, Paula E. Cushing, and Vincent Roth, American Arachnological Society 2005 Wise, David H. "Spiders in Ecological Webs." Cambridge University Press. Great Britain: 1993.

External links

- [http://www.arachnology.org/Arachnology/Pages/Araneae.html Arachnology Home Pages: Araneae]
- [http://www.dearge.de/english.php Deutsche Arachnologische Gesellschaft e. V. - German Arachnologic Society (EN/DE)]
- [http://www.xs4all.nl/~ednieuw/Spiders/InfoNed/The_spider.html Spider info by Ed Nieuwenhuys]
- [http://www.britishspiders.org.uk/html/info.html List of spiders found in Great Britain]
- [http://delta-intkey.com/britsp Watson, L., and Dallwitz, M.J. 2004 onwards. The families of spiders represented in the British Isles.] http://delta-intkey.com
- [http://research.amnh.org/entomology/spiders/catalog81-87/index.html Platnick, N.I. 2005. World Spider Catalog]
- [http://www.cannabis.net/weblife.html Webs made by spiders fed on drug-dosed flies]
- [http://www.surviveoutdoors.com/reference/spiders/index.asp Pictures of Spiders]
- [http://www.surviveoutdoors.com/emergency/spiderbites.asp Spider Bites]
- [http://spiders.ucr.edu/dermatol.html University of California evaluations of spider bite severity]
- [http://www.camel-spiders.net Camel Spiders]
- [http://www.macro-photo.org/species-checklist-arthropods-insects-birds-avians/spiders-araneae-macro-photo-images-gallery.htm Macro Photography - Pictures of spiders, image gallery]
- Category:Araneae als:Webspinne ko:거미 ja:クモ

Species

In biology, a species is the basic unit of biodiversity. In scientific classification, a species is assigned a two-part name in Latin. The genus is listed first (and capitalized), followed by a specific epithet. For example, humans belong to the genus Homo, and are in the species Homo sapiens. The name of the species is the whole binomial not just the second term (the specific epithet). The binomial, and most other purely formal aspects of the biological codes of nomenclature, were formalized by Carolus Linnaeus in the 1700's and as a result are called the "Linnaean system". At that time, species were thought to represent independent acts of creation by God, and were therefore considered objectively real and immutable. Since the advent of the theory of evolution, the conception of species has undergone vast changes in biology, however no consensus on the definition of the word has yet been reached. The most commonly cited definition of "species" was first coined by Ernst Mayr. By this definition, called the biological species concept or isolation species concept, species are "groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups". However, many other species concepts are also used (see other definitions of species below). The scientific name of a species is properly typeset in italics. When an unknown species is being referred to this may be done by using the abbreviation "sp." in the singular or "spp." in the plural in the place of the second part of the scientific name. Note that the word "specie" is not the singular of "species". It refers to coined money.

Definitions of species

The definition of a species given above as taken from Mayr, is somewhat idealistic. Since it assumes sexual reproduction, it leaves the term undefined for a large class of organisms that reproduce asexually. Biologists frequently do not know whether two morphologically similar groups of organisms are "potentially" capable of interbreeding. Further, there is considerable variation in the degree to which hybridization may succeed under natural and experimental conditions, or even in the degree to which some organisms use sexual reproduction between individuals to breed. Consequently, several lines of thought in the definition of species exist: ; Typological species : A group of organisms in which individuals are members of the species if they sufficiently conform to certain fixed properties. The clusters of variations or phenotypes within specimens (ie: longer and shorter tails) would differentiate the species. This method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, we now know that different phenotypes do not always constitute different species (e.g.: a 4-winged Drosophila born to a 2-winged mother is not a different species). Species named in this manner are called morphospecies. ; Morphological species : A population or group of populations that differs morphologically from other populations. For example, we can distinguish between a chicken and a duck because they have different shaped bills and the duck has webbed feet. Species have been defined in this way since well before the beginning of recorded history. This species concept is much criticised because more recent genetic data reveals that genetically distinct populations may look very similar and, contrarily, large morphological differences sometimes exist between very closely-related populations. Nonetheless, most species known have been described solely from morphology. ; Biological / Isolation species : A set of actually or potentially interbreeding populations. This is generally the most useful formulation for scientists working with living examples of the higher taxa like mammals, fish, and birds, but meaningless for organisms that do not reproduce sexually. It does not distinguish between the theoretical possibility of interbreeding and the actual likelihood of gene flow between populations and is thus impractical in instances of allopatric (geographically isolated) populations. The results of breeding experiments done in artificial conditions may or may not reflect what would happen if the same organisms encountered each other in the wild, making it difficult to gauge whether or not the results of such experiments are meaningful in reference to natural populations. ; Mate-recognition species : A group of organisms that are known to recognise one another as potential mates. Like the isolation species concept above, it applies only to organisms that reproduce sexually. Unlike the isolation species concept, it focuses specifically on pre-mating reproductive isolation. ; Phylogenetic / Evolutionary / Darwinian species : A group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, members may diverge from one another: when such a divergence becomes sufficiently clear, the two populations are regarded as separate species. ; Microspecies : Species that reproduce without meiosis or mitosis so that each generation is genetically identical to the previous generation. See also apomixis. In practice, these definitions often coincide, and the differences between them are more a matter of emphasis than of outright contradiction. Nevertheless, no species concept yet proposed is entirely objective, or can be applied in all cases without resorting to judgement. Given the complexity of life, some have argued that such an objective definition is in all likelihood impossible, and biologists should settle for the most practical definition. For most vertebrates, this is the biological species concept, and to a lesser extent (or for different purposes) the phylogenetic species concept. Many BSC subspecies are considered species under the PSC; the difference between the BSC and the PSC can be summed up insofar as that the BSC defines a species as a consequence of manifest evolutionary history, while the PSC defines a species as a consequence of manifest evolutionary potential. Thus, a PSC species is "made" as soon as an evolutionary lineage has started to separate, while a BSC species starts to exist only when the lineage separation is complete.

Importance in biological classification

The idea of species has a long history. It is one of the most important levels of classification, for several reasons:
- It often corresponds to what lay people treat as the different basic kinds of organism - dogs are one species, cats another.
- It is the standard binomial nomenclature (or trinomial nomenclature) by which scientists typically refer to organisms.
- It is the only taxonomic level which has empirical content, in the sense that asserting that two animals are of different species is saying something more than classificatory about them. After thousands of years of use, the concept remains central to biology and a host of related fields, and yet also remains at times ill-defined and controversial.

Implications of assignment of species status

The naming of a particular species should be regarded as a hypothesis about the evolutionary relationships and distinguishability of that group of organisms. As further information comes to hand, the hypothesis may be confirmed or refuted. Sometimes, especially in the past when communication was more difficult, taxonomists working in isolation have given two distinct names to individual organisms later identified as the same species. When two named species are discovered to be of the same species, the older species name is usually retained, and the newer species name dropped, a process called synonymization, or convivially, as lumping. Dividing a taxon into multiple, often new, taxons is called splitting. Taxonomists are often referred to as "lumpers" or "splitters" by their colleagues, depending on their personal approach to recognizing differences or commonalities between organisms (see lumpers and splitters). Traditionally, researchers relied on observations of anatomical differences, and on observations of whether different populations were able to interbreed successfully, to distinguish species; both anatomy and breeding behavior are still important to assigning species status. As a result of the revolutionary (and still ongoing) advance in microbiological research techniques, including DNA analysis, in the last few decades, a great deal of additional knowledge about the differences and similarities between species has become available. Many populations which were formerly regarded as separate species are now considered to be a single taxon, and many formerly grouped populations have been split. Any taxonomic level (species, genus, family, etc.) can be synonymized or split, and at higher taxonomic levels, these revisions have been still more profound. From a taxonomical point of view, groups within a species can be defined as being of a taxon hierarchically lower than a species. In zoology only the subspecies is used, while in botany the variety, subvariety, and form are used as well.

The isolation species concept in more detail

In general, for large, complex, organisms that reproduce sexually (such as mammals and birds), one of several variations on the isolation or biological species concept is employed. Often, the distinction between different species, even quite closely related ones, is simple. Horses (Equus caballus) and donkeys (Equus asinus) are easily told apart even without study or training, and yet are so closely related that they can interbreed after a fashion. Because the result, a mule or hinny, is not usually fertile, they are clearly separate species. But many cases are more difficult to decide. This is where the isolation species concept diverges from the evolutionary species concept. Both agree that a species is a lineage that maintains its integrity over time, that is diagnosably different to other lineages (else we could not recognise it), is reproductively isolated (else the lineage would merge into others, given the chance to do so), and has a working intra-species recognition system (without which it could not continue). In practice, both also agree that a species must have its own independent evolutionary history—otherwise the characteristics just mentioned would not apply. The species concepts differ in that the evolutionary species concept does not make predictions about the future of the population: it simply records that which is already known. In contrast, the isolation species concept refuses to assign the rank of species to populations that, in the best judgement of the researcher, would recombine with other populations if given the chance to do so.

The isolation question

There are, essentially, two questions to resolve. First, is the proposed species consistently and reliably distinguishable from other species? Secondly, is it likely to remain so in the future? To take the second question first, there are several broad geographic possibilities.
- The proposed species are sympatric—they occupy the same habitat. Observation of many species over the years has failed to establish even a single instance of two diagnostically different populations that exist in sympatry and have then merged to form one united population. Without reproductive isolation, population differences cannot develop, and given reproductive isolation, gene flow between the populations cannot merge the differences. This is not to say that cross breeding does not take place at all, simply that it has become negligible. Generally, the hybrid individuals are less capable of successful breeding than pure-bred individuals of either species.
- The proposed species are allopatric—they occupy different geographical areas. Obviously, it is not possible to observe reproductive isolation in allopatric groups directly. Often it is not possible to achieve certainty by experimental means either: even if the two proposed species interbreed in captivity, this does not demonstrate that they would freely interbreed in the wild, nor does it always provide much information about the evolutionary fitness of hybrid individuals. A certain amount can be inferred from other experimental methods: for example, do the members of population A respond appropriately to playback of the recorded mating calls of population B? Sometimes, experiments can provide firm answers. For example, there are seven pairs of apparently almost identical marine snapping shrimp (Altheus) populations on either side of the Isthmus of Panama, which did not exist until about 3 million years ago. Until then, it is assumed, they were members of the same seven species. But when males and females from opposite sides of the isthmus are placed together, they fight instead of mating. Even if the isthmus were to sink under the waves again, the populations would remain genetically isolated: therefore they are now different species. In many cases, however, neither observation nor experiment can produce certain answers, and the determination of species rank must be made on a 'best guess' basis from a general knowledge of other related organisms.
- The proposed species are parapatric—they have breeding ranges that abut but do not overlap. This is fairly rare, particularly in temperate regions. The dividing line is often a sudden change in habitat (an ecotone) like the edge of a forest or the snow line on a mountain, but can sometimes be remarkably trivial. The parapatry itself indicates that the two populations occupy such similar ecological roles that they cannot coexist in the same area. Because they do not crossbreed, it is safe to assume that there is a mechanism, often behavioral, that is preventing gene flow between the populations, and that therefore they should be classified as separate species.
- There is a hybrid zone where the two populations mix. Typically, the hybrid zone will include representatives of one or both of the 'pure' populations, plus first-generation and back-crossing hybrids. The strength of the barrier to genetic transmission between the two pure groups can be assessed by the width of the hybrid zone relative to the typical dispersal distance of the organisms in question. The dispersal distance of oaks, for example, is the distance that a bird or squirrel can be expected to carry an acorn; the dispersal distance of Numbats is about 15 kilometres, as this is as far as young Numbats will normally travel in search of vacant territory to occupy after leaving the nest. The narrower the hybrid zone relative to the dispersal distance, the less gene flow there is between the population groups, and the more likely it is that they will continue on separate evolutionary paths. Nevertheless, it can be very difficult to predict the future course of a hybrid zone; the decision to define the two hybridizing populations as either the same species or as separate species is difficult and potentially controversial.
- The variation in the population is clinal; at either extreme of the population's geographic distribution, typical individuals are clearly different, but the transition between them is seamless and gradual. For example, the Koalas of northern Australia are clearly smaller and lighter in colour than those of the south, but there is no particular dividing line: the further south an individual Koala is found, the larger and darker it is likely to be; Koalas in intermediate regions are intermediate in weight and colour. In contrast, over the same geographic range, black-backed (northern) and white-backed (southern) Australian Magpies do not blend from one type to another: northern populations have black backs, southern populations white backs, and there is an extensive hybrid zone where both 'pure' types are common, as are crossbreeds. The variation in Koalas is clinal (a smooth transition from north to south, with populations in any given small area having a uniform appearance), but the variation in magpies is not clinal. In both cases, there is some uncertainty regarding correct classification, but the consensus view is that species rank is not justified in either. The gene flow between northern and southern magpie populations is judged to be sufficiently restricted to justify terming them subspecies (not full species); but the seamless way that local Koala populations blend one into another shows that there is substantial gene flow between north and south. As a result, experts tend to reject even subspecies rank in this case.

The difference question

Obviously, when defining a species, the geographic circumstances become meaningful only if the populations groups in question are clearly different: if they are not consistently and reliably distinguishable from one another, then we have no grounds for believing that they might be different species. The key question in this context, is "how different is different?" and the answer is usually "it all depends". In theory, it would be possible to recognise even the tiniest of differences as sufficient to delineate a separate species, provided only that the difference is clear and consistent (and that other criteria are met). There is no universal rule to state the smallest allowable difference between two species, but in general, very trivial differences are ignored on the twin grounds of simple practicality, and genetic similarity: if two population groups are so close that the distinction between them rests on an obscure and microscopic difference in morphology, or a single base substitution in a DNA sequence, then a demonstration of restricted gene flow between the populations will probably be difficult in any case. More typically, one or other of the following requirements must be met:
- It is possible to reliably measure a quantitative difference between the two groups that does not overlap. A population has, for example, thicker fur, rougher bark, longer ears, or larger seeds than another population, and although this characteristic may vary within each population, the two do not grade into one another, and given a reasonably large sample size, there is a definite discontinuity between them. Note that this applies to populations, not individual organisms, and that a small number of exceptional individuals within a population may 'break the rule' without invalidating it. The less a quantitative difference varies within a population and the more it varies between populations, the better the case for making a distinction. Nevertheless, borderline situations can only be resolved by making a 'best-guess' judgement.
- It is possible to distinguish a qualitative difference between the populations; a feature that does not vary continuously but is either entirely present or entirely absent. This might be a distinctively shaped seed pod, an extra primary feather, a particular courting behaviour, or a clearly different DNA sequence. Sometimes it is not possible to isolate a single difference between species, and several factors must be taken in combination. This is often the case with plants in particular. In eucalypts, for example, Corymbia ficifolia cannot be reliably distinguished from its close relative Corymbia calophylla by any single measure (and sometimes individual trees cannot be definitely assigned to either species), but populations of Corymbia can be clearly told apart by comparing the colour of flowers, bark, and buds, number of flowers for a given size of tree, and the shape of the leaves and fruit. When using a combination of characteristics to distinguish between populations, it is necessary to use a reasonably small number of factors (if more than a handful are needed, the genetic difference between the populations is likely to be insignificant and is unlikely to endure into the future), and to choose factors that are functionally independent (height and weight, for example, should usually be considered as one factor, not two).

Historical development of the species concept

In the earliest works of science, a species was simply an individual organism that represented a group of similar or nearly identical organisms. No other relationships beyond that group were implied. Aristotle used the words genus and species to mean generic and specific categories. Aristotle and other pre-Darwinian scientists took the species to be distinct and unchanging, with an "essence", like the chemical elements. When early observers began to develop systems of organization for living things, they began to place formerly isolated species into a context. To the modern mind, many of the schemes delineated are whimsical at best, such as those that determined consanguinity based on color (all plants with yellow flowers) or behavior (snakes, scorpions and certain biting ants). In the 18th century Carolus Linnaeus classified organisms according to differences in the form of reproductive apparatus. Although his system of classification sorts organisms according to degrees of similarity, it made no claims about the relationship between similar species. At the time, it was still widely believed that there is no organic connection between species, no matter how similar they appear; every species was individually created by God, a view today called creationism. This approach also suggested a type of idealism: the notion that each species exists as an "ideal form". Although there are always differences (although sometimes minute) between individual organisms, Linnaeus considered such variation problematic. He strove to identify individual organisms that were exemplary of the species, and considered other non-exemplary organisms to be deviant and imperfect. By the 19th century most naturalists understood that species could change form over time, and that the history of the planet provided enough time for major changes. As such, the new emphasis was on determining how a species could change over time. Jean-Baptiste Lamarck suggested that an organism could pass on an acquired trait to its offspring, i.e., the giraffe's long neck was attributed to generations of giraffes stretching to reach the leaves of higher treetops (this well-known and simplistic example, however, does not do justice to the breadth and subtlety of Lamarck's ideas). Lamarck's most important insight may have been that species can be extraordinarily fluid; his 1809 Zoological Philosophy contained one of the first logical refutations of creationism. With the acceptance of the work of Charles Darwin in the 1860s, Lamarck's view of evolution was quickly eclipsed. It was not until the late 20th century that his work began to be reexamined, and took its place as a fundamental stepping stone to the modern theory of adaptive mutation. Lamarck's long-discarded ideas of the goal-oriented evolution of species, also known the teleological process, have also received renewed attention, particularly by proponents of artificial selection. Charles Darwin and Alfred Wallace provided what scientists now consider the most powerful and compelling theory of evolution. Basically, Darwin argued that it is populations that evolve, not individuals. His argument relies on a radical shift in perspective from Linnaeus: rather than defining species in ideal terms (and searching for an ideal representative and rejecting deviations), Darwin considered variation among individuals to be natural. He further argued that variation, far from being problematic, actually provides the explanation for the existence of distinct species. Darwin's work drew on Thomas Malthus' insight that the rate of growth of a biological population will always outpace the rate of growth of the resources in the environment, such as the food supply. As a result, Darwin argued, not all the members of a population will be able to survive and reproduce. Those that did will, on average, be the ones possessing variations—however slight—that make them slightly better adapted to the environment. If these variable traits are heritable, then the offspring of the survivors will also possess them. Thus, over many generations, adaptive variations will accumulate in the population, while counter-adaptive will be eliminated. It should be emphasized that whether a variation is adaptive or non-adaptive depends on the environment: different environments favor different traits. Since the environment effectively selects which organisms live to reproduce, it is the environment (the "fight for existence") that selects the traits to be passed on. This is the theory of evolution by natural selection. In this model, the length of a giraffe's neck would be explained by positing that proto-giraffes with longer necks would have had a significant reproductive advantage to those with shorter necks. Over many generations, the entire population would be a species of long-necked animals. In 1859, when Darwin published his theory of natural selection, the mechanism behind the inheritance of individual traits was unknown. Although Darwin made some speculations on how traits are inherited (pangenesis), his theory relies only on the fact that inheritable traits exist, and are variable (which makes his accomplishment even more remarkable.) Although Gregor Mendel's paper on genetics was published in 1866, its significance was not recognized. It was not until 1900 that his work was rediscovered by Hugo de Vries, Carl Correns and Erich von Tschermak, who realised that the "inheritable traits" in Darwin's theory are genes. The theory of the evolution of species through natural selection has two important implications for discussions of species -- consequences that fundamentally challenge the assumptions behind Linnaeus' taxonomy. First, it suggests that species are not just similar, they may actually be related. Some students of Darwin argue that all species are descended from a common ancestor. Second, it supposes that "species" are not homogeneous, fixed, permanent things; members of a species are all different, and over time species change. This suggests that species do not have any clear boundaries but are rather momentary statistical effects of constantly changing gene-frequencies. One may still use Linnaeus' taxonomy to identify individual plants and animals, but one can no longer think of species as independent and immutable. The rise of a new species from a parental line is called speciation. There is no clear line demarcating the ancestral species from the descendant species. Although the current scientific understanding of species suggests there is no rigorous and comprehensive way to distinguish between different species in all cases, biologists continue to seek concrete ways to operationalize the idea. One of the most popular biological definitions of species is in terms of reproductive isolation; if two creatures cannot reproduce to produce fertile offspring, then they are in different species. This definition captures a number of intuitive species boundaries, but nonetheless has some problems, however. It has nothing to say about species that reproduce asexually, for example, and it is very difficult to apply to extinct species. Moreover, boundaries between species are often fuzzy: there are examples where members of one population can produce fertile offspring with a second population, and members of the second population can produce fertile offspring with members of a third population, but members of the first and third population cannot produces fertile offspring. Consequently, some people reject this notion of species. In recent years we have witnessed the drastic reduction in the size of breeding populations and the geographical range of many physically large mammals. In earlier times it was assumed that every species existed in at least a few thousand living individuals, except very rare relic, isolated groups. In the present, many well know mammal & bird species are so stressed by habitat loss, and other effects of the modern world, that only a very few breeding males may contribute the genetic material to a small number of breeding females. In these highly stressed conditions, the likelihood of change is very much greater. Mammals may become smaller, have darker fur, more stripes, more cautious behavior, even over time learn to co-exist with the human world. Very likely, evolution is radically accelerated, and we are only beginning to notice it. Species in transition before our eyes. It is possible that this severe stress is essential to the creation of new species, and may have been a prime factor throughout biological history, from other population reducing influences. Richard Dawkins defines two organisms as conspecific if and only if they have the same number of chromosomes and, for each chromosome, both organisms have the same number of nucleotides (The Blind Watchmaker, p. 118). However, most if not all taxonomists would strongly disagree. For example, in many amphibians, most notably in New Zealand's Leiopelma frogs, the genome consists of "core" chromosomes which are mostly invariable and accessory chromosomes, of which exist a number of possible combinations. Even though the chromosome numbers are highly variable between populations, these can interbreed successfully and form a single evolutionary unit. In plants, polyploidy is extremely commonplace with few restrictions on interbreeding; as individuals with an odd number of chromosome sets are usually sterile, depending on the actual number of chromosome sets present, this results in the odd situation where some individuals of the same evolutionary unit can interbreed with certain others and some cannot, with all populations being eventually linked as to form a common gene pool. The classification of species has been profoundly affected by technological advances that have allowed researchers to determine relatedness based on molecular markers, starting with the comparatively crude blood plasma precipitation assays in the mid-20th century and coming into full swing with Charles Sibley's ground-breaking DNA-DNA hybridisation studies in the 1970s. The results of the technique caused revolutionary changes in the higher taxonomic categories (such as phyla and classes), resulting in the reordering of many branches of the phylogenetic tree (see also: molecular phylogeny). For taxonomic categories below genera, the results have been mixed so far; the pace of evolutionary change on the molecular level is rather slow, yielding clear differences only after considerable periods of reproductive separation. Instances of hybridization can result in misleading molecular data, the Pomarine Skua - Great Skua phenomenon being a famous example. Turtles have been determined to evolve with just one-eighth of the speed of other reptiles on the molecular level, and the rate of molecular evolution in albatrosses is half of what is found in the rather closely related storm-petrels. The hybridization technique is however no longer considered a good technique and more reliable computational techniques for sequence comparison are now used for. Molecular taxonomy does not directly measure the evolutionary processes, but rather the overall change brought upon by these processes. The processes that lead to the generation and maintenance of variation such as mutation, crossover and selection are not uniform (see also molecular clock). DNA is only extremely rarely a direct target of natural selection rather than changes in the DNA sequence enduring over generations being a result of the latter; for example, silent transition-transversion combinations would alter the melting point of the DNA sequence, but not the sequence of the encoded proteins and thus are a possible example where, for example in microorganisms, a mutation confers a change in fitness all by itself.

External links

- http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Speciation.html
- [http://www.sciencedaily.com/releases/2003/12/031231082553.htm 2003-12-31, ScienceDaily: Working On The 'Porsche Of Its Time': New Model For Species Determination Offered] Quote: "...two species of dinosaur that are members of the same genera varied from each other by just 2.2 percent. Translation of the percentage into an actual number results in an average of just three skeletal differences out of the total 338 bones in the body. Amazingly, 58 percent of these differences occurred in the skull alone. "This is a lot less variation than I'd expected", said Novak..."
- [http://www.sciencedaily.com/releases/2003/08/030808081854.htm 2003-08-08, ScienceDaily: Cross-species Mating May Be Evolutionarily Important And Lead To Rapid Change, Say Indiana University Researchers] Quote: "...the sudden mixing of closely related species may occasionally provide the energy to impel rapid evolutionary change..."
- [http://www.sciencedaily.com/releases/2004/01/040109064407.htm 2004-01-09 ScienceDaily: Mayo Researchers Observe Genetic Fusion Of Human, Animal Cells; May Help Explain Origin Of AIDS] Quote: "...The researchers have discovered conditions in which pig cells and human cells can fuse together in the body to yield hybrid cells that contain genetic material from both species... "What we found was completely unexpected", says Jeffrey Platt, M.D."
- [http://www.sciencedaily.com/releases/2000/09/000913211733.htm 2000-09-18, ScienceDaily: Scientists Unravel Ancient Evolutionary History Of Photosynthesis] Quote: "...gene-swapping was common among ancient bacteria early in evolution..."
- [http://plato.stanford.edu/entries/species/ Stanford Encyclopedia of Philosophy entry]
- [http://www.barcodinglife.org/ Barcoding of species] rank22 rank22 ms:Spesies ja:種 (生物) th:สปีชีส์

Genera

Genera was an operating system and development environment for Lisp machines developed by Symbolics off an earlier operating system originating on the MIT AI Lab's Lisp machines. It was closed in 1981. When Symbolics went bankrupt, Genera was rebranded in 1992 and developed for the DEC Alpha processor architecture as OpenGenera; rather than rewrite all (by this point) 1.5 million lines in Common Lisp or another Lisp, Symbolics instead wrote an emulator for Zetalisp, and runs OpenGenera on that. Reportedly, there are efforts to port it to the Macintosh G5. [http://home.hakuhale.net/rbc/symbolics/] Because Genera was largely a single mass of approximately 10,000 Lisp functions (written in ~500,000 lines of source code) which were called to form the actual programs and which could be called at any time, there is no hard or fast line between the actual IDE and the operating system per se; rather both or either are referred by the name "Genera". Genera was noted for its power, the integration of its tools, and its excellent documentation.

External links

- [http://www.symbolics.com/ Symbolics]
- [http://www.symbolics.com/Genera-1.htm Symbolics Genera Integrated Development Environment]
- [http://www.sts.tu-harburg.de/~r.f.moeller/symbolics-info/symbolics-tech-summary.html "Symbolics Technical Summary"]
- [http://lispm.dyndns.org/genera-concepts/genera.html "Genera Concepts"] - (Web copy of Symbolic's introduction to Genera)
- [http://www.sts.tu-harburg.de/~r.f.moeller/symbolics-info/development-environment/index.html A page of screenshots of Genera]
- [http://www.sts.tu-harburg.de/~r.f.moeller/symbolics-info/docex/docex.html Screenshots of the award-winning Symbolics Document Examiner] Category:Computing platforms Category:Operating systems

Taxonomy

Taxonomy (from Greek verb tassein = "to classify" and nomos = law, science, cf "economy") may refer to:
- the science of classification (see alpha taxonomy)
- a classification Initially taxonomy was only the science of classifying living organisms, but later the word was applied in a wider sense, and may also refer to either a classification of things, or the principles underlying the classification. Almost anything, animate objects, inanimate objects, places, and events, may be classified according to some taxonomic scheme. Taxonomies are frequently hierarchical in structure. However taxonomy may also refer to relationship schemes other than hierarchies, such as network structures. Other taxonomies may include single children with multi-parents, for example, "Car" might appear with both parents "Vehicle" and "Steel Mechanisms". A taxonomy might also be a simple organization of objects into groups, or even an alphabetical list. In current usage within "Knowledge Management", taxonomies are seen as slightly less broad than ontologies. Mathematically, a hierarchical taxonomy is a tree structure of classifications for a given set of objects. At the top of this structure is a single classification, the root node, that applies to all objects. Nodes below this root are more specific classifications that apply to subsets of the total set of classified objects. So for instance in common schemes of scientific classification of organisms, the root is the Organism (as this applies to all living things, it is implied rather than stated explicitly). Below this are the Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species, with various other ranks sometimes inserted. Some have argued that the human mind naturally organizes its knowledge of the world into such systems. This view is often based on the epistemology of Immanuel Kant. Anthropologists have observed that taxonomies are generally embedded in local cultural and social systems, and serve various social functions. Perhaps the most well-known and influential study of folk taxonomies is Émile Durkheim's The Elementary Forms of Religious Life. The theories of Kant and Durkheim also influenced Claude Lévi-Strauss, the founder of anthropological structuralism. Lévi-Strauss wrote two important books on taxonomies: Totemism and The Savage Mind. Such taxonomies as those analyzed by Durkheim and Lévi-Strauss are sometimes called folk taxonomies to distinguish them from scientific taxonomies that claim to be disembedded from social relations and thus objective and universal. A recent neologism, folksonomy, should not be confused with Folk Taxonomy (though it is obviously a contraction of the two words). Those who support scientific taxonomies have recently criticized folksonomies by dubbing them fauxonomies. The phrase enterprise taxonomy is used in business to describe a very limited form of taxonomy used only within one organization. The field of solving or best-fitting of numerical equations that characterize all measurable quantities of a set of objects is called cluster analysis; this is a form of taxonomy called numerical taxonomy or taximetrics.

Superstition

:For other senses, see superstition (disambiguation). A superstition is an irrational or invalid belief about the relation between certain actions (often behaviors) and other actions that is not true. The essence of superstition is not defined by the "truth" of the result, however, but recognized by the methods through which truth is searched for. The superstitious individual erroneously believes that the future, or the outcome of certain events can be caused or influenced by certain specified behaviors, despite the lack of a causal relationship in reality. Many superstitions emerged from the notions of "good luck" and "bad luck"; the notion of "luck", however, can itself be considered a form of superstition. Some popular superstitions are a result of misinterpreting correlations as causes, although many others are simply urban legends that have no rational justification whatsoever. Many things that were once considered scientific are now considered superstitious such as alchemy or astrology By its definition superstition is not based on reason and is not true. Many superstitions can be prompted by misunderstandings of causality or statistics. Others spring from unenlightened fears, which may be expressed in religious beliefs or practice, or to belief in extraordinary events, supernatural interventions, apparitions or in the efficacy of charms, incantations, the meaningfulness of omens and prognostications. Any of the above can lead to unfounded fears, or excessive scrupulosity in outward observances. Fanaticism, some argue, (citation needed) arises from this same displaced religious feeling, in a state of high-wrought and self-confident excitement. Such unquestioning loyalty can apply to politics and ideologies as well as religion; indeed, it can even be focused on sports teams and celebrities. See Baseball superstition for a series of such examples. Examples of superstitions include things like a gambler crediting a winning streak in poker to a "lucky rabbit's foot" or to sitting in a certain chair, rather than to skill or to the law of averages. An airline passenger might believe that it is a medal of St Christopher (traditional patron saint of travellers) that keeps him safe in the air, rather than the fact that airplanes statistically crash very rarely. Brides on their wedding day do not usually see their groom until the ceremony believing that to do so causes bad luck. Superstition is also used to refer to folkloric belief systems, usually as juxtaposed to another religion's idea of the spiritual world, or as juxtaposed to science. In the academic discipline of folkloristics the term "superstition" is used to denote any folk belief expressed in if/then (with an optional "unless" clause) format. IF you break a mirror, THEN you will have seven years of bad luck UNLESS you throw all of the pieces into a body of running water.

Superstition and behavioral psychology

The behaviorist psychologist B.F. Skinner placed a series of hungry pigeons in a cage attached to an automatic mechanism that delivered food to the pigeon "at regular intervals with no reference whatsoever to the bird's behavior". He discovered that the pigeons associated the delivery of the food with whatever chance actions they had been performing as it was delivered, and that they continued to perform the same actions: :One bird was conditioned to turn counter-clockwise about the cage, making two or three turns between reinforcements. Another repeatedly thrust its head into one of the upper corners of the cage. A third developed a 'tossing' response, as if placing its head beneath an invisible bar and lifting it repeatedly. Two birds developed a pendulum motion of the head and body, in which the head was extended forward and swung from right to left with a sharp movement followed by a somewhat slower return. ("'Superstition' in the Pigeon", B.F. Skinner, Journal of Experimental Psychology #38, 1947 [http://psychclassics.yorku.ca/Skinner/Pigeon/]) Skinner suggested that the pigeons believed that they were influencing the automatic mechanism with their "rituals" and that the experiment also shed light on human behavior: :The experiment might be said to demonstrate a sort of superstition. The bird behaves as if there were a causal relation between its behavior and the presentation of food, although such a relation is lacking. There are many analogies in human behavior. Rituals for changing one's luck at cards are good examples. A few accidental connections between a ritual and favorable consequences suffice to set up and maintain the behavior in spite of many unreinforced instances. The bowler who has released a ball down the alley but continues to behave as if she were controlling it by twisting and turning her arm and shoulder is another case in point. These behaviors have, of course, no real effect upon one's luck or upon a ball half way down an alley, just as in the present case the food would appear as often if the pigeon did nothing -- or, more strictly speaking, did something else. (Ibid.) Like the pigeons, many people associate behavior (head-turning or worship of God(s) ) with an external phenomenon (delivery of food or conquest by a foreign power) that was not necessarily connected in any way with personal behavior. Any misfortune could thus be interpreted as a sign of divine disfavor, whether or not the individuals who suffered bore direct responsibility.

Religious views on the subject of superstition

Superstition may be expressed in the terminology of religion, giving rise to skeptical thinkers' opinion that all religion is superstition. Greek and Roman pagans, who modeled their relations with the gods on political and social terms scorned the man who constantly trembled with fear at the thought of the gods, as a slave feared a cruel and capricious master. "Such fear of the gods (deisidaimonia) was what the Romans meant by 'superstition' (Veyne 1987, p 211). For Christians just such fears might be worn proudly as a name: Desdemona. The Roman Catholic Church considers superstition to be sinful in the sense that it denotes a lack of trust in the divine providence of God and, as such, is a violation of the first of the Ten Commandments. The Catechism of the Catholic Church states superstition "in some sense represents a perverse excess of religion" (para. #2110). The Catechism even appears to turn a bit of a critical eye on Catholic doctrine whenever certain practices become frivolous or scrupulous: :Superstition is a deviation of religious feeling and of the practices this feeling imposes. It can even affect the worship we offer the true God, e.g., when one attributes an importance in some way magical to certain practices otherwise lawful or necessary. To attribute the efficacy of prayers or of sacramental signs to their mere external performance, apart from the interior dispositions that they demand is to fall into superstition. Cf. Matthew 23:16-22 (para. #2111) Atheists and Agnostics often see all Religious belief as a form of superstition, and religious believers have seen other religions as superstition. Edmund Burke, the great Irish orator, once said, "Superstition is the religion of weak minds".

External links

- [http://www.infidels.org/library/historical/robert_ingersoll/superstition.html Superstition] by Robert Green Ingersoll
- [http://www.geocities.com/vaksam/supers.html The Science of Superstitions] by Dr. Sam Vaknin
- [http://skepdic.com/ The Skeptic's Dictionary]: A very handy and comprehensive online reference on all matters paranormal or dubious.
- [http://www.infidels.org/desk.html The Secular Web Reference Desk]
- [http://www.nobeliefs.com/problemswithbeliefs.htm Problems with beliefs]: These articles examine beliefs, faiths and superstitions to help become aware of their methodology and dangerous consequences.

Source

- Veyne, Paul. 1987 A History of Private Life: 1. From Pagan Rome to Byzantium. category:cognitive biases ko:미신 ja:迷信 th:ความเชื่อโชคลาง

Sheetweb spider

Frontinella
Neriene
Pityohyphantes
etc. The sheetweb spiders are a subfamily, Linyphiinae, of sheet weavers. There are more than 800 described species. In some taxonomies, the subfamily Micronetinae is classified within Linyphiinae as the tribe Micronetini. Category:Spiders

Dwarf spider

External reference

- [http://www.cpitt.uq.edu.au/software/riceipm/keys/Html/Atypena.htm Atypena] Category:Spiders

Sheet weaver

External links

Gallery

Erigoninae

External reference

Spider

Morphology and development

Respiration and circulation

Vision

Defense

Life cycle

Reproduction

Do female spiders eat their mates?

Ecology

Predatory techniques

Spider webs and prey capture

Types of spiders and the severity of their bites

Tangleweb spiders (Theridiidae)

Orb web spiders (Araneidae)

Other forms of webs

Hunting spiders

Spiders which ambush their prey

Others

Spider bites

Black widows

Brown recluse spiders and hobo spiders

Huntsman spiders

Redback jumping spiders

Brazilian wandering spiders and Australian venomous funnel-web spiders

Taxonomy

Symbolism

See also

References

External links

Species

Definitions of species

Importance in biological classification

Implications of assignment of species status

The isolation species concept in more detail

The isolation question

The difference question

Historical development of the species concept

See also

External links

Genera

External links

Taxonomy

See also

Superstition

Superstition and behavioral psychology

Religious views on the subject of superstition

See also

Books

External links

Source

Sheetweb spider

Dwarf spider

External reference

Erigoninae