Edge effects and diversity of understory and canopy cloud forest beetles

Habitat fragmentation results in edge effects— changes in diversity and community composition along high-contrast forest edges. To date, a study of edge effects on beetle diversity has not been performed in tropical cloud forests, and few studies compare communities at both understory and canopy levels. Using bottle traps, I sampled canopy and understory beetle communities in a tropical lower montane cloud forest of Monteverde, Costa Rica across three distances (edge- 15 m, middle- 100 m, far- 205 m) along an edge-to-interior transect into the forest. According to the Shannon-Weiner diversity index, the site with the most diversity was the middle understory, whereas the canopy at the edge was the least diverse. Out of all the understory sites, there was significantly less diversity at the far site. Within the canopy, the opposite was true, with more diversity further into the forest. Using a Linear Mixed Model and several post hoc tests, the results indicated that edge effects on beetle abundance and richness were stronger in the canopy than in the understory. In the canopy, there was a positive linear relationship between the number of individuals/morphospecies and distance into the forest, but no real trend in the understory. There were also differences in composition between heights and across distances, according to the Morisita Index. Overall, Curculionidae, Staphylinidae, and Chrysomelidae were the most species-rich families of beetles, and Curculionidae and Staphylinidae were the most abundant families. Differences in diversity and response to edges could be explained by the varying ecological traits of beetles inhabiting each site. The three most dominant families have very generalized diets and therefore can exist in a wide variety of habitats, even in canopy areas which are characterized by increased sunlight and wind, higher temperatures, and an increased risk of desiccation, similar to edge sites. In addition, tropical ecosystems have more specialists, which tend to decrease in abundance in human-disturbed areas. This could explain why abundance and richness was lower near the edge in my study, but higher near edges for other studies not in the tropics. Considering that insects are so small and large-scale changes in their diversity can easily go unnoticed, it is important to conduct studies like these to evaluate how habitat fragmentation is affecting them, and from that, make decisions about how best to conserve insect populations.