In the new Early View paper “Predator-mediated interactions between preferred, alternative and incidental prey in the arctic tundra”, Laura McKinnon and her colleagues used the Arctic Tundra in Canada as a natural laboratory to study predator-prey interactions.
Predators can have direct impacts on prey populations by decreasing survival and fecundity, and in turn, prey populations can also drive predator densities. These interactions between predator and prey can often lead to coupled cycles in population abundance, many studies of which have become classic textbook examples in ecology. More recently, these models have been expanded to incorporate multiple prey species and even multiple trophic levels in order to have a better understanding of the causes and consequences of predator prey interactions in more complex realistic environments. However, testing these models in complex ecosystems can become rather cumbersome due the sheer number of interactions between species. Luckily, there are some terrestrial ecosystems, such as the Arctic tundra which provide less complex natural laboratories in which to study trophic interactions between predators and multiple prey items. In our recent study, we took advantage of this natural laboratory to study indirect interactions between preferred, alternative and incidental prey.
In the arctic tundra, numerical and functional responses of predators to preferred prey (lemmings) affect the predation pressure on alternative prey (goose eggs) and predators aggregate in areas of high alternative prey density. Therefore, we hypothesized that predation risk on incidental prey (shorebird eggs) would increase in patches of high goose nest density when lemmings were scarce. By measuring predation risk on artificial shorebird nests in quadrats varying in goose nest density on Bylot Island (Nunavut, Canada) across 3 summers with variable lemming abundance, and monitoring quadrats for predator activity, we provide evidence that the abundance of preferred prey influences the indirect relationship between alternative and incidental prey. Predation risk on artificial shorebird nests increased in the presence of increasing goose nest densities, especially at low lemming abundance, as predicted. In addition to supporting our incidental prey hypothesis which suggests that when preferred prey decrease in abundance, short-term apparent competition via aggregative response can occur between alternative and incidental prey, these results also provoke interesting applied questions regarding the potential effects of increasing goose densities on incidental prey such as shorebirds.