We investigated patterns of community structure in the water-bodies on the islands of Lake Huron’s Georgian Bay, the world’s largest freshwater archipelago. These habitats offer a unique opportunity to use the naturally patchy and nested structure of ponds situated on islands that vary in their level of isolation to determine the relative contributions of processes at local and regional scales to community structure. Animal communities were sampled across a diverse set of water-bodies and islands to assess the relationship between community structure, local habitat conditions, and habitat isolation. We sampled 128 water-bodies on 31 different islands. Invertebrates were preserved and later identified to the lowest level feasible while vertebrates were identified to the lowest taxonomic level possible in the field and released alive. Habitat conditions were also measured including the size (length, width, and depth) and water chemistry (temperature, conductivity, and pH) of each water-body. Habitat isolation was measured by measuring distance to the mainland and by quantifying connections to surrounding islands at varying buffer distances (1 to 8km).
Results/Conclusions
Community structure in these pools was affected by factors across all scales measured including local conditions, island conditions, and habitat isolation with different taxa showing responses to different scales. Pool-level conditions had strong effects on community structure with smaller pools having lower diversity and a restricted set of species compared to those found in larger pools. Small pool communities are characterized by species that rapidly recolonize pools that have re-filled following drying and habitat stability may be the major limiting factor on diversity in these communities in these sites. At the island scale there was a positive relationship between the variation in pool size on an island and the total diversity of invertebrates and amphibians on that island, suggesting a greater range of available habitat types supports more species on islands, regardless of island isolation. Surprisingly, island isolation, measured as distance to the mainland, was positively associated with amphibian richness on islands. Our results suggest that community structure in these habitats is affected by multiple processes acting at different scales and that taxa may be differentially affected by processes based on their mobility.