Population biology of social insect conservation

Abstract

Pamilo, P. and Crozier. R.H., 1997. Population biology of social insect conservation. Memoirs of the Museum of Victoria 56: 411-4 I 9. Social insects, especially ants and termites, are keystone species in most non-arctic ter­ restrial ecosystems, but their special features have received little attention in conservation discussions. Both plants and other animals arc aff ected by social insects as keystone species. Despite the abundance of species it may be that rather few in any one location are critical to understanding the ecosystem, because of the mosaic nature of the distributions of the dominant species. Social insects present a wide array of life patterns within the broad sway of sociality, varying in having colonies which are annual or perennial, multi-or single-nested, and multi-or single-queened. Populations of social insects may often be much more vul­ nerable than they appear on the basis of numbers of individuals: the reproductive division of labor means that the effective population size may be small for a species of apparently reasonable abundance. Factors increasing eff ective population size occur in many species, especially rare ones, but it is uncertain these represent adaptations to rareness. In eusocial Hymenoptera, many species. probably most, show inbreeding depression of a special kind due to the production of sterile males caused by homozygosity at the sex locus. In many termites, on the other hand, colonies pass naturally through cycles of inbreeding and out­ breeding. Socially parasitic ants which habitually inbreed appear to have evolved a diff erent means of sex-determination and do not show inbreeding depression. Diff erences in the mode of colony formation between species also lead to difference in the longevity of col­ onies. dispersal abilities, and the robustness of populations to disturbance. The greatest threats to social insects, apart from humans, are other social insects, and this applies also to invading ant pest species, which tend to have particularly strong impacts on native species. Social insects thus form a vital part of ecosystems, but also impel the need to accept long­ term studies because of the slow pace at which their populations change.