When does competition matter at the large scales studied by biogeographers?

Submitted by editor on 28 October 2015. Get the paper!

Editor's choice article for November 2015

By William Godsoe

Competition occurs when different living things harm one another. It is common in nature. As one example, the grass in my lawn becomes less dense when weeds run amok. But it isn’t clear when competition shape species’ distributions at large spatial scales. Our new paper is an attempt to resolve this issue, by carefully applying what we know about coexistence among competing species. Coexistence occurs when competing species are present at the same location after many generations. To see why this impacts our understanding of species’ distributions, focus on a single location where two competitors could occur. If these species can coexist at this location, neither species influences the distribution of the other. However, if they can’t coexist, we would expect one species to out compete theother. As a result we would expect one species to be absent from that location.

Starting from this insight, we argue that species competition can matter a great deal at large spatial scales. We highlight examples from small scale community ecology where coexistence is impossible and illustrate mechanisms that would make coexistence more difficult at large spatial scales. As a result, there are cases where we’d expect competition to have more of an influence on species’ distributions at large spatial scales than would be predicted from looking at small scales. We offer a useful simplification, when competition becomes less important at large spatial scales we should see “regional coexistence” a special form of coexistence that depends on mechanisms such as dispersal and heterogeneous environments.


Figure 1. We expect competition among living things that live near one another such as these plants, it is less clear when biogeographers must consider competition’s effects. Photo credit: Ian Dickie.

Figure 2. Regional coexistence provides clues on when competition becomes less important at large spatial scales (from Godsoe et al. 2015).