Quantifying insect responses to
elephant carcasses in a semi-arid savanna
Insect communities play a vital, yet often unappreciated, role in terrestrial ecosystems. They can control plant biomass and species composition, they can regulate ecosystem nutrient cycling, buffer soil communities from extreme environmental changes, serve as prey for predators, and can also engineer the ecosystem to look completely different. Yet we only know the broad strokes of what insects do in ecosystems - our understanding of their importance lags far behind our understanding of mammalian herbivores.
One important question is how insect diversity is maintained in time and space. Insects respond quickly to changes in plant nutrient content. If elephant carcasses enrich vegetation with essential nutrients like nitrogen, phosphorus, or even calcium, then carcasses could serve as hotspots for insect diversity to accumulate, or could cause a change in diversity over time as insects increase their growth and reproduction because of high-quality vegetation.
We aim to:
1. Establish spatial patterns in insect diversity throughout Kruger National Park in relation to rainfall and vegetation.
2. Determine whether carcass sites are hotspots for insect abundance or biodiversity.
3. Investigate whether changes in plant nutrient content at carcass sites is attractive to herbivorous insects, such as grasshoppers and katydids.
In the Field:
In each field campaign, we sample insects using drop nets and sweep nets both in the center of the carcass site and 15-20 m away from the carcass center. We collect all grasshoppers and katydids found within the site for genetic analysis to help with identification, because field guides for South African grasshoppers are sparse and do not have full coverage!
We then collect plants from the middle of the carcass site and in the matrix surrounding the carcass, as well as grasshoppers from a nearby area. We then bring the grass and insects back to conduct feeding experiments. Insects are fed grass from only the matrix site or the carcass site to determine palatability. We then offer insects a choice between matrix grass and carcass grass, which helps us determine whether insects prefer to feed on carcass-grown grass. Grass is then sent away for nutritional analyses.