Insects as bio-indicators for monitoring landscape biodiversity

Atlas Moth
Atlas Moth

One of the major crises we face today is the ever-growing mass extinction of living beings caused by human activities. Our knowledge of global biodiversity and extinction is very limited, but of the 5 to 50 million species believed to exist, conservative estimates points to about 17500 being lost each year, that is, 2 species every hour. Of these, the vast majority belongs to understudied groups like invertebrates, “the little things that run the world. Despite their fundamental roles in nature and potential in the definition of conservation priority areas, invertebrates have been systematically ignored in conservation studies. But how do we conserve species when we have very limited knowledge of which species are endangered or even how many species there are?

Estimates of the number of insect species thought to exist globally vary widely, but there are probably 4-6 million. We have perhaps named only 23-35% of these. As for their ecology and habitat requirements, the chances of elucidating even a small fraction of the myriad life histories and species interactions that exist within the invertebrate world are remote, especially in the hyper diverse tropics. This is despite the widely appreciated importance of arthropods to the diversity and function of terrestrial and freshwater ecosystems, at least among entomologists. The limitations associated with invertebrate conservation efforts are clearly manifested in the literature. Clark and May (2002) found deep taxonomic bias in conservation research, with vertebrate studies dominating (69% of papers versus 3% of described species) over plants (20% of papers versus 18% of species), and with invertebrates lagging far behind (11% of papers versus 79% of species).

The described taxonomic richness of insects is distributed unevenly among the higher taxonomic groups. Five orders stand out for their high species richness: the beetles (Coleoptera); flies (Diptera); wasps, ants and bees (Hymenoptera); butterflies and moths (Lepidoptera); and the true bugs (Hemiptera). Insects play a central role in all terrestrial ecosystems as herbivores, pollinators, for nutrient cycling, and as food and host organisms. Due to their sheer numerical preponderance herbivorous insects comprise a significant fraction of any insect fauna. Herbivorous insects are also expected to respond sensitively to deforestation and subsequent forest regeneration, since they have a close functional relationship with the vegetation they live in.

Lepidoptera are important herbivores, pollinators, and serve as food and hosts for multiple other organisms at higher trophic levels. They are the most diverse order of insects associated primarily with angiosperm plants and, with some 160,000 named species estimated that the world fauna is certain to exceed 350,000 species. In common parlance, Lepidoptera comprises the butterflies (some 20,000 species in two or three superfamilies) and moths (the great majority of species, spread among some 30 superfamilies). The largest families of moth each thus include more species than the whole of the butterflies. Another “working division” of the Lepidoptera, of considerable relevance to conservation, is that of so-called “macrolepidoptera” and “microlepidoptera”. The former includes the butterflies and larger moths and is by far the better documented group, largely because it includes the taxa which have traditionally attracted most attention from collectors and hobbyists. Nevertheless, the smaller moths are relatively poorly known, comprise a substantial proportion of most local lepidopteran assemblages, and in contrast with macrolepidoptera in that very few species have been considered widely as targets for conservation.

In general, the amount of information available on distribution and decline is limited, and substantial taxonomic difficulties remain in virtually all regional faunas. This division by size tends to mirror the “bridging role” of moths in practical conservation considerations- from the ability to focus constructively on single target species (mainly macrolepidoptera, for which the ecology of many species is reasonably well understood) to the twin topics of assemblage diversity and its changes in relation to patterns of land use or disturbance. The last usually involve either macrolepidoptera or all Lepidoptera, so using moths as indicators of environmental condition and possible surrogates of wider changes in biodiversity. Thus, many studies of moth assemblages include only macrolepidoptera. In many parts of the world this limitation simply reflects taxonomic expediency, because knowledge of most microlepidoptera does not yet enable them to be incorporated with equivalent confidence in many surveys where species-level determination is needed. However some microlepidoptera groups are very diverse and thus have potential to yield much relevant information on interest to land managers.

Written by: Dr. V.P. Uniyal
Affiliation: Wildlife Institute of India
Country: India


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