Species communities in habitat patches fluctuate over time in response to local extinction, dispersal between patches, environment, and interactions between species. There is a strong need to test metacommunity theory at field scales relevant to conservation questions, and ephemeral ponds (EPs) provide ideal sites for study. EPs flood in the spring and dry completely during at least some years. We assessed plant communities in 57 wetlands within Wisconsin’s Chippewa Moraine region in order to determine the relative importance of environment, space (dispersal), and environmental variation across space in structuring plant community variation. Twenty-five wetlands were permanently-flooded, while 32 were EPs. We hypothesized that metacommunity structure would be detectable in this system and that it would vary by plant functional guild (annual, graminoid, forb perennial, woody), with annual plants displaying more null and mass effects and woody plants impacted more by species sorting. In addition, we thought that U.S. Army Corps of Engineers wetland indicator status would affect metacommunity structure. Indicator status assigns each plant species an environmental tolerances ranging from obligate wetland (OBL) to upland (UPL). We hypothesized that OBL plants are more strongly structured by null and mass effects than plants with drier requirements due to the patchy nature of the wetlands in the landscape.
Results/Conclusions
Variance partitioning of principle coordinates of neighborhood matrices demonstrated that 87.9% of variation in the plant communities of all wetlands (both permanent and EP) can be explain by variables that we measured. 31.82% of structure is explained by environment, 37.13% by environmental variation across space, and 16.38% by space alone (P < 0.05). These results indicate that species sorting, null model, and possibly mass effects play a role in structuring wetland metacommunities. Annual species were more strongly structured by null model processes than perennials and woody plants. The subset of plants that were categorized as facultative-wet and drier were more strongly spatially structured (space alone = 27.8% of variance, P = 0.030) than the OBL plants (space alone = 16.1%, P = 0.591). Because OBL plants are wetland specialists, they are more strongly affected by species-sorting mechanisms than plants that have more flexible habitat requirements. The facultative plants may be more structure by neutral processes due their lack of strong niche requirements. These results indicate that species with different environmental tolerances may be structured by different metacommunity processes.