Print PageSuccession is a central concept in community ecology, although the processes driving changes in species composition through time remain poorly understood. One proposed successional mechanism is a progression from abiotic filtering to biotic interactions as communities shift from being limited by species dispersal and establishment to being structured by competition for limiting resources. However, like most successional hypotheses, this mechanism is difficult to test because of the long time scales inherent in most communities. Changes in phylogenetic structure through successional time can be used to test predictions about biotic and abiotic filtering. Due to a shared evolutionary history, closely related species generally occupy similar niches. Consequently, they experience similar abiotic constraints, and compete more strongly for resources.
I analyzed phylogenetic relatedness in an old field-to-deciduous forest chronosequence in Ohio originally described by Vankat et al. (1991). Stand ages were 2, 20, 50, 90 and 200 years since disturbance. Using sequences obtained from Genbank, I assembled a maximum likelihood tree to calculate mean phylogenetic distance (MPD) and net relatedness index (NRI) for each stand.
Results/Conclusions
I found that no communities were significantly clustered or evenly spaced in their community structure as measured by NRI, but there was a significant positive relationship between MPD and age of the stand in the community. This pattern is consistent with the hypothesis that as the community matures, the dominant force structuring the community shifts from abiotic filters to competition and niche partitioning, which favors less-closely related species. These results agree with the findings of other studies that have analyzed changes in phylogenetic structure during tropical forest succession, but this is the first time it has been investigated in temperate forests, suggesting that this may be a common pattern across systems.
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