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Habitat selection of aquatic organisms across gradients of forest canopy coverage.
Binckley, Christopher *,1, Resetarits, William1, 1 Old Dominion University, Norfolk, VA, U.S.A.
ABSTRACT- Many species segregate amongst aquatic habitats that differ in resource abundance. Two mechanisms, differing primarily in assumed colonization strategies used by species to select habitats, could explain these field patterns. The first mechanism emphasizes differential mortality within habitats after a random colonization of all habitat types. A second mechanism emphasizes nonrandom colonization of habitats (e.g. habitat selection) based on habitat specific fitness consequences. We tested the strength of this second mechanism by conducting two experiments that quantified the abundance and species richness of colonizing aquatic beetles. In the first experiment we established 24 experimental ponds with 12 placed 3m into the forest (closed canopy) and 12 placed 3m out from the forest edge (open canopy). Beetles were collected weekly for 6 weeks and mean abundance and species richness were both significantly higher in open canopy ponds. In the second experiment we established 24 experimental ponds as in experiment 1, but utilized a split-plot design with canopy as the whole plot factor and nutrient addition (0, 30, or 60 g) as the sub-plot factor. For both response variables there was no significant canopy by nutrient interaction or significant nutrient effect as beetles again strongly avoided closed canopy ponds. Behavioral avoidance of particular habitats resulted in a greater degree of spatial co-occurrence than would occur if ponds were chosen randomly, suggesting that habitat selection is one primary mechanism structuring aquatic communities.
Key words: dispersal, colonization, oviposition, aquatic