The decline of African large herbivores (>5 kg) can have strong effects on local communities of plants and smaller mammals. What are the cascading effects of these changes on plant-herbivore interaction networks? As keystone species that enhance local ecological heterogeneity and reduce dominance in plant communities, large herbivores could promote robust networks characterized by a high diversity and overlap of small-mammal diets. Another possibility is that by limiting the quantity of resources available to smaller herbivores, large herbivores could promote more specialized networks characterized by little dietary overlap (i.e., dietary niche partitioning). We tested these predictions within a diverse community of mammalian herbivores from an East African savanna using a large-herbivore exclusion experiment. We elucidated plant-herbivore interactions using DNA metabarcoding to identify plant species eaten by >30 large- and small-herbivore species (~2000 dietary samples). We tested for differences in the structure of plant-herbivore interaction networks (i.e., connectence, interaction diversity, specialization) involving small mammals in the presence and absence of large herbivores.
Results/Conclusions
Preliminary data reveal >175 plant taxa in the food webs. Understory plant abundance was ~2x greater and small mammal abundance was ~3x greater in the absence of large herbivores. The network of interactions between plants and smaller herbivores exhibited lower diversity but greater connectence and specialization in the presence of large herbivores. Large herbivores may not only suppress the local richness of plants and smaller herbivores, but also suppress the degree of dietary overlap among co-occurring small herbivores. Dietary samples from the most abundant and well-sampled species of small mammals also revealed minor effects of large-mammal exclusion on diet composition. Thus, in this system, large herbivore declines not only change the composition of plant and herbivore communities but also seem to rewire plant-herbivore interaction networks. The use of DNA metabarcoding reveals changes in local species-interaction networks following the decline of large herbivores. These changes may unexpectedly enhance food web robustness and mitigate further species loss.