Competition and environmental filtering occur at different spatial scales: Determining spatial dependency in community phylogenetic and functional patterns

Background/Question/Methods

The spatial scale of phylogenetic and trait studies do not often match the eco-evolutionary processes of interest. While biotic interactions are thought to occur between individuals, studies instead examine patterns at the community scale, which may include dozens or hundreds of individuals. Moreover, environmental gradients are measured at the regional scale, when local environmental gradients may affect community composition. While the spatial context is known to affect trait and phylogenetic patterns, the exact spatial scales at which these patterns are detectable or shift remain unexplored. For a plant community in the Rouge Valley National Urban Park, Canada, we investigate: (a) how phylogenetic and trait patterns shift at fine-spatial scales; and (b) the spatial scales that best capture phylogenetic and trait patterns. In 2013, we sampled species’ identity and height for five 40-meter transects at 10-cm intervals; and recorded environmental data at a 1-meter scale. To assess the spatial autocorrelation of species’ phylogenetic and trait relationships across space, the partial Mantel correlogram correlated a distance matrix of combined trait and phylogenetic relationships with 400 geographic distance classes, while removing environmental effects. We determined the best spatial scales for trait and phylogenetic patterns with a Principal Coordinates of Neighbor Matrices analysis. 

Results/Conclusions

For each of the five transects, the partial Mantel correlogram was significantly negative at small distance classes meaning that at small scales individuals were phylogenetically and functionally over-dispersed. However, at a scale greater than 15 meters, individuals appeared to be phylogenetically and functionally clustered. Because we removed environment from the Mantel correlogram, biotic interactions between species (e.g., disease or competition) may largely drive our observed non-random patterns at small scales. The Principal Coordinates of Neighbor Matrices analysis determined the spatial scales of around 40 and 15 meters to best capture trait and phylogenetic patterns for our community. Future studies within community ecology that explicitly test hypotheses with trait and/or phylogenetic information therefore need to be conducted, at a minimum, at these spatial scales.