Threatened arthropods are defined here as any of a number ofspecies within thephylumArthropoda, whoseextinction is likely in the foreseeable future. Estimating the number of threatened arthropod species is extremely difficult, primarily because a vast number of the species themselves are not yet named or described. Furthermore, according to Deyrup and Eisner,[2] "The rate of destruction and degradation of natural habitats is currently so great that there are not nearly enough biologists to even catalog thearthropod species that are suddenly on the edge of extinction." In any case, independent estimates indicate that there are millions of undocumented arthropods on Earth.[3]
Arthropods as a group have been very successfulorganisms on this planet, comprising over half of all the higherlife forms. However the expansion of human activities has led to demise of many arthropod species through the mechanisms ofdeforestation, conventionalfarming,slash-and-burn methods in the tropics,habitat fragmentation via urban development, excessive use ofpesticides and even the success offorest fire suppression.
The social/political practice whereby a species is given a formal designation as "Endangered" or "Protected" is a different matter, called "Conservation status", and discussed elsewhere; seeEndangered Species List for theUnited States, andIUCN Red List for international purposes. Only a tiny fraction of the planet's endangered arthropods are formally recognized as such, as no one has ever evaluated the conservation status of the vast majority of arthropod species.
It is difficult to estimate the total number of endangered arthropod species, since many of the taxa themselves have not been recorded. For example, inNorth America the estimated number of insect species exceeds 163,000, of which only about two thirds are taxonomically known.[4] An even greater discovery awaiting, over 72 percent of North Americanarachnids are yet to be named and described.[4]
The total number of living arthropod species is probably in the tens of millions.[3] One conservative estimate puts the number of arthropod species intropical forests alone at six to nine million species.[5] As a consequence of all of the above, most published estimates of the total number of endangered insects and arachnids are probably low by at least an order of magnitude.[4] Conservatively at least eighty percent of all living animal species are arthropods.[6]
Since arthropods constitute the majority of the faunal biomass on Earth, their role is vital to the survival of large numbers ofinsectivores and other animals that prey upon arthropods. This includes enormous numbers ofmammals,avafauna,fishes,reptiles andamphibians; in addition, arthropods constitute the bulk of faunalpollinators, so that the survival ofcrops as well as millions of naturalflora species depend on robust andbiologically diverse arthropod populations.[7]
The survival of diverse arthropods is essential to propagation of higher animals on thefood chain, e.g. those species who prey upon the insectivores and other taxa that consume arthropods. Even if constant arthropod total biomass results after certain arthropod extinctions, the ecosystem stability is compromised by reduction in species numbers. Thus extinction of arthropods species threaten to make extinct hundreds of thousands, if not millions, of higher order birds, amphibians, reptiles and mammals.[citation needed]
Most endangerment of arthropod populations is fromhabitat destruction by growing human populations and related human activities such as agriculture, construction and transportation.[citation needed]
Agriculture, in particular has a number of direct effects: amonocultures fromintensive practices cannot support thebiodiversity nurtured by the predecessor natural environment.[citation needed] Normally arthropods represent the largest number of species that are displaced by such farming. In tropical regions the major threat isslash-and-burn agricultural techniques pursued by indigenous peoples in their sometimes only available method of subsistence.[citation needed]Pesticide use is also a major threat to arthropod species survival. Pesticides may have an intended effect of killing specified insects in a farming environment; however, considerable pesticide applications kill unintended species by the lack of specificity of most chemical formulations; moreover, much of the insect mortality arises from pesticiderunoff enteringsurface waters or from transportingtoxicchemicals to downgradient environments.[citation needed]
Habitat fragmentation has special methods of endangerment beyond the amount of land consumed by the fragmenting agent. As an example, consider the construction of ahighway, whose width is an effective barrier to arthropod migration. Many arthropods never migrate more than about 200 feet from their place of birth, so afreeway ordual carriageway effectively fragments many arthropod colonies such that they cannot interact. Studies have shown the greater vulnerability to extinction where habitats are fragmented.[8]
The following is a very small fraction of the potentially hundreds of thousands of endangered arthropods, limited to species which have been formally recognized as to their special conservation status:
| IUCNRed List |
| ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Bytaxa | |||||||||||||||||||
| Conservation | |||||||||||||||||||
1 Pre-2001 categories and subcategories shown initalics. | |||||||||||||||||||
