OOS 26-2
Spatial niches influence biodiversity during adaptive radiation
Variation in environmental conditions over time and space provides temporal and spatial niche opportunities for co-occurring species, potentially allowing more species to coexist than predicted by classic ecological theory. While several empirical studies have examined the role of temporal niches in promoting species coexistence and diversity, empirical tests of spatial niche theory have been extremely rare. In particular, we know virtually nothing about how spatial niches contribute to biodiversity patterns over evolutionary timescales. We experimentally explored how the presence of spatial niches influences adaptive radiation, using the rapidly evolving bacterium Pseudomonas fluorescens SBW25 as the model organism. P. fluorescens undergoes rapid adaptive radiation under the static condition where specialized niches are available for new phenotypes to utilize, but not under the shaking condition where such niches are absent. By taking advantage of these characteristics, we constructed laboratory metacommunities each containing two local microcosms, incubated either under the same (shaking or static) conditions, or under different conditions. In addition, we also manipulated species dispersal, either allowing or not allowing exchange of individuals among the local communities.
Results/Conclusions
Our results showed that spatial niches and dispersal interactively affected P. fluorescens diversity. When there was no dispersal, spatial niches had little effect on either alpha-diversity in local microcosms or beta-diversity among microcosms. By contrast, when dispersal was present, spatial niches increased alpha-diversity but reduced beta-diversity. The spatial storage effect was responsible for the observed biodiversity patterns. Adaptation of P. fluorescens to different incubation conditions increased the niche difference between its phenotypes, promoting frequency-dependent selection among them in metacommunities with spatial niches. Such frequency-dependent selection facilitated phenotypic coexistence but weakened priority effects, resulting in the highest alpha-diversity and lowest beta-diversity in metacommunities characterized by both dispersal and spatial niches. These results highlight the importance of spatial niches in maintaining biodiversity in evolving metacommunities.