Landscape variation in the larval density of a bromeliad-dwelling zygopteran, Mecistogaster modesta (Odonata: Pseudostigmatidae)

Abstract

In the premontane rain forests of northwest Costa Rica, patches of secondary forest can contain high densities of large Vriesea spp. bromeliads. Such patches contain an average of 6,470 ± 1,080 (s.e.) larvae ha-1 of the bromeliad-dwelling pseudostigmatid, Mecistogaster modesta, ca 36x higher than larval densities that we previously reported for adjacent primary forest. Using a new method to partition landscape variation in populations, we show that secondary forest has higher larval densities than primary forest because of higher bromeliad abundance (13% of effect), greater bromeliad size (33%), and greater larval abundance in bromeliads of similar size (54%). The last effect reflects additional effects of forest type after accounting for differences in the quantity of larval habitat. We use surveys of prey communities in bromeliads and adult densities in the two forest types to show that these additional effects of forest type are more likely due to adult behaviour, not larval resource limitation. This study demonstrates that certain areas of secondary forest can be disproportionately important for M. modesta populations, and has implications for estimating effects of forest loss and conversion on M. modesta.