Holt RD., Bonsall MB.
Most species have one or more natural enemies – predators, parasites, pathogens, and herbivores, among others. These species in turn typically attack multiple victim species. This leads to the possibility of indirect interactions among those victims, both positive and negative. The term “apparent competition” commonly denotes negative indirect interactions between victim species that arise because they share a natural enemy. This indirect interaction – which in principle can be reflected in many facets of the distribution and abundance of individual species, and more broadly govern the structure of ecological communities in time and space – emerges in studies of a wide variety of natural and managed systems, with the latter including agricultural pests, harvesting, the conservation of endangered species, and emerging diseases. At one end of the scale of life, apparent competition also characterizes intriguing aspects of dynamics within individual organisms – the immune system is akin in many ways to a “predator” that can induce negative indirect interactions among different pathogens. At intermediate scales of biological organization, the existence and strength of apparent competition depends upon many contingent details of individual behaviour and life history, as well as the community and spatial context across which indirect interactions play out. At the other broadest scale of macroevolution, apparent competition may play a major, if poorly understood, role in the evolution of species’ geographical ranges and adaptive radiations.