Interspecific carnivore competition and ungulate predation correlate with predator species richness

Competition for resources underlies the development of ecological community structure and function. Niche compression occurs when species reduce resource use due to competition, and niche complementarity posits resource competition should occur sequentially among habitat, time, and food. Within this context, interspecific predator competition can be influenced by prey characteristics and landscape attributes. We examined drivers of interspecific competition among carnivores using a database of North American ungulate cause-specific mortality published during 1970-2021. We used weighted logit-linked beta-binomial generalized linear mixed models to assess the influence of seven predator species, ungulate age class, and landscape characteristics (i.e., human footprint, terrain ruggedness, and forest cover) on ungulate predation mortality. We predicted that (1) predation by individual predator species would decrease with increasing predator species richness mediated by predator size, (2) landscape characteristics would mediate predation by individual predator species, and (3) juvenile ungulate predation would increase with increasing predator species richness. As predator species richness increased, the proportions of predation attributed to individual predator species decreased, but the overall proportion of ungulate mortality attributed to predation increased. Juvenile ungulates experienced greater predation mortality than adults, with smaller predators predating proportionally more juveniles than larger predators. Landscape metrics altered observed predation patterns among caribou (Rangifer tarandus), wherein predation corresponded to terrain ruggedness but not predator species richness, and mule deer (Odocoileus hemionus), wherein predation increased with greater forest cover. We provide evidence for niche compression and complementarity using a top-down predator-centric approach by showing compression in prey resources and increased predation mortality with increasing predator species richness. However, landscape characteristics had limited effects on predator competition at large spatial extents, which counters niche complementarity. Collectively, our results support the importance of large predators to ecosystem structure and efforts to conserve and restore predator guilds.