Abundance and vertical distribution of a bromeliad-dwelling zygopteran larva, Mecistogaster modesta, in a Costa Rican rainforest (Odonata: Pseudostigmatidae)

Abstract We compared the larval abundance of Mecistogaster modesta between bromeliads at ground level and canopy level in a primary tropical wet forest. Zygopteran abundance correlated strongly with bromeliad diameter at both levels. Although the per-bromeliad zygopteran abundance did not differ between vertical levels, M. modesta showed a strong vertical distribution in abundance owing to the variation in bromeliad size and density along a vertical gradient, with more and larger bromeliads closer to ground level than to the canopy. We predict M. modesta larval abundance to be 171 ± 65 (s.e.) per hectare, with >80% of larvae below halfway to the lower canopy limit. The total prey abundance or species richness did not differ between ground and canopy bromeliads, further suggesting that apart from bromeliad size, habitat quality for M. modesta was similar between vertical levels. Effects of habitat size on larval abundance patterns are addressed by comparing habitat volume and basal resource mass with diameter. Finally, larger-scale spatial patterns in zygopteran abundance are discussed with reference to bromeliad distributions.