Читать книгу Practical Field Ecology - C. Philip Wheater - Страница 70

A gridded pitfall trap baited with cow dung.

Scarabaeinae, or true dung beetles, comprise one of the most species‐rich groups of coprophagous insects with almost 7000 species found globally. Dung beetles have a widespread distribution, which is centred around the species‐rich tropics, with diversity gradually declining in higher latitudes. This ubiquity means that dung beetles are often used as indicators of habitat quality and barometers of habitat change due to species' associations with habitat types, and reductions in diversity when habitats are negatively affected by disturbance. One of the benefits of using dung beetles as an eco‐indicator is the ease with which large data sets can be gathered in a short timeframe, and consequentially used to form a rapid impact assessment (Bicknell et al. 2014). However, there are many challenges one may encounter when used baited pitfall traps.

Collection of dung beetles from a baited pitfall trap ready to be sorted for identification.

One major issue with pitfall trapping is obtaining an accurate relative sample of dung beetle diversity. Without adequate sampling effort, dominant species are often over‐represented and rare species may be missed entirely. Traps frequently generate large numbers of common species over a short time period, but longer trapping periods of up to one month may be needed in species‐rich tropical locations where dung beetle niches are smaller. Factors such as the quantity of moonlight, or seasonal shifts in temperature could determine if rare species are detected or not. Another common issue when using baited pitfall traps is trap disturbance by other animals. Once traps are set, they are left unattended until the observer returns. This allows inquisitive species such as hyenas (Crocuta crocuta), or animals such as mongooses (e.g. Mungos mungo) which like to feed on captured beetles, ample time to disrupt trapping effort and consume valuable data.

Once trap data have been collected, the samples need to be sorted and identified to species or morphospecies. This typically requires a high‐powered microscope and access to many intricately written identification keys. Identifying dung beetles to species level requires time and tenacity, and access to existing collections to verify identifications can be beneficial. This can be challenging when collecting species internationally, but can be circumnavigated by using collections belonging local or national museums.