Habitat and seasonality as niche axes in an odonate community.

Focuses on the coexistence of the dominant larval populations among 46 odonate species found in Bays Mountain Park, Sullivan County, Tennessee, using an index to estimate niche specialization (breadth^-1) and overlap on habitat and seasonal axes, both separately and simultaneously (two dimensional analysis). This enables evaluation of 2 possible mechanisms of coexistence: resource partitioning (differing time-averaged patterns of resource utilization among competitors) and ecological shift (nonevolutionary change in resource utilization in response to competition). Three results support the resource-partitioning mechanism: 1) Competition coefficients, obtained by dividing niche overlap values by the appropriate niche specialization values, are all less than one; this indicates that each population should inhibit its own access to a limited food supply more than it inhibits the access of the other populations. 2) The two-dimensional competition coefficients are slightly smaller on average than the product of single-axis means, suggesting two-dimensional complementary. 3) There are about the same number of consistent 3-yr trends in specialization and overlap as would be expected by change, suggesting a relatively persistent arrangement of odonate niches in niche space. The ecological shift mechanism may nevertheless be operating within or between those populations that do exhibit consistent 3-yr trends in specialization or overlap. The 6 populations that comprise the detritus-submersed macrophyte guild account for most of the larval biomass. The dominant population within the guild (and the community as a whole) is the semivoltine anisopteran Tetragoneuria cynosura. A particularly intense interaction is between the abundant zygopterans Enallagma traviatum and E. signatum; unusually high specializations and overlap were observed for the rush-dwelling zygopterans Ischnura verticalis and I. posita.-from Authors