The relative importance of stabilizing mechanisms of coexistence - ESA 2009

Stabilizing mechanisms of coexistence, by definition, cause a species to experience greater intraspecific competition than interspecific. This results in negative frequency-dependent growth rates for that species causing a negative relationship between its relative frequency in the community and its growth rate in the next year. The most crucial aspect of this negative relationship for persistence is that it enables a species to increase when rare. This has been empirically demonstrated for pairwise interactions. However, in species-rich communities, the effects of competition are not realistically pairwise. In cases where multiple species are competing for a resource, stabilizing mechanisms become increasingly important to ease the effects of that competition. Thus,  for rare species, increasing the strength of stabilization may be essential to their persistence in the community, or their ability to invade. A mathematical model of negative frequency-dependent growth is used to explore how the strength of stabilization affects a species’ ability to persist in a community. Increasing the steepness of the negative frequency-dependent growth relationship for rare species significantly increases their mean time to extinction in this simulated community. Significantly, the desert rodent community at the Portal LTREB site shows this predicted pattern, in which rare species experience stronger negative frequency-dependant growth relationships than the dominant species. This pattern may be a characteristic of species-rich communities, and thus have implications for the ability of those communities to maintain stable structure despite change (climate change, invasive species, habitat loss).