Species abundance distributions in niche communities with trait-dependent carrying capacities

Background/Question/Methods

The species abundance distribution is a community metric that is shaped by underlying dynamics of interacting species. However, the extent to which it reflects processes that influence community structure is currently a topic of debate in ecology. Studies have explored differences between communities with neutral dynamics, which are based on demographic stochasticity and immigration, and those with niches, or clusters of species. We have previously reported on the importance of considering the dynamics that give rise to niches in nature, using a stochastic Lotka-Volterra model to show that there are distinct differences between neutral and niche community species abundance distributions when niches emerge due to competition that depends on trait differences. For simplicity, previous studies use a carrying capacity that is constant across traits. Here we use the stochastic Lotka-Volterra model to investigate how carrying capacities that depend on species traits specifically influence the shapes of the species abundance distributions of niche communities. We consider communities with varying numbers of niches and varying competition kernels that affect niche clustering patterns along the trait axis. We also compute the likelihood of detecting differences from neutral species abundance distributions in data.

Results/Conclusions

We show that the species abundance distributions of niche communities in which carrying capacities are Gaussian functions of traits exhibit a strong central peak and greater differences from neutrality than niche communities with constant carrying capacities. We also show that the detectability of differences from neutrality is stronger, and show specifically how detectability changes across varying numbers of niches in this case as well. This work builds on previous results to further build understanding of the complex relationship between community dynamics and the species abundance distribution. These results demonstrate that understanding how traits affect fitness is important in developing predictions of SADs in natural communities. Because we see patterns in this case with even greater departures from neutrality, this also supports the notion that the species abundance distribution could potentially reveal even more information than previously thought about the nature of underlying dynamics and niche structure in a community.