Do habitat size and shape modify abiotic factors and communities in artificial treeholes?

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Community composition may be determined by a variety of factors, including habitat dimension, abiotic conditions, and biotic interactions. Habitat dimensions may influence abiotic conditions, thus modifying community structure or biotic interactions. We used six different mesocosm sizes, two depths crossed with three surface areas, to test hypotheses regarding the direct and indirect effects of habitat dimensions (depth and surface area) on dissolved oxygen concentration and insect communities in artificial water-filled treeholes. Containers were monitored for dissolved oxygen concentrations and insect community composition from June 2002 to November 2003. We predicted that deep mesocosms would have lower species richness and insect larval densities than shallow due to less dissolved oxygen at deeper depths, and that large surface area mesocosms would have greater species richness and abundance of insects than small. Larger surface area habitats may attract more insects because they are easier to find and perceived by ovipositing females to be more stable. Dissolved oxygen concentrations ([DO]) at depth were consistently lower in deep than shallow habitats, and mosquito densities and species richness were lower in those deep mesocosms compared to shallow mesocosms. We found higher insect richness at certain times of the year in large and medium than in small surface area mesocosms. By modifying abiotic factors such as [DO], dimensional aspects of the habitat, in this case depth, may affect community structure in ways not predicted simply by habitat size.