No abstract

Tropical montane organisms are vulnerable to climate change because of elevational specialisation, but little is known of the variability in elevational specialisation across tropical insects. We assessed elevational specialisation across several insect taxa comprising four trophic groups 80–2263 m up an elevational transect in Brazilian Atlantic Rainforest, using community‐based and species‐based approaches. We sampled 697 species, of which 32% were found only in the top and 45% only in the bottom half of the transect. Considering only the 182 species with at least five individuals recorded, the percentage of species found exclusively in the top or bottom half drops to 16% and 24%. Across four vegetation belts (lower montane forest, montane forest, upper montane forest and Campos de Altitude) the Eumolpinae (herbivores) were more specialised than Scarabaeinae (saprotrophs), or Lampyridae (predators). This result was robust to the treatment of rare species, and the difference was most marked at higher elevations. Lampyridae lacked upper montane forest specialists. Using all species sampled, specialisation to the upper or lower half of the transect was greatest among Chrysomelidae, Curculionidae (both herbivores) and Lampyridae, and lowest among Tiphiidae (parasitoids) and Coccinellidae (predators). Considering only better sampled species, however, Lampyridae were the most specialised and Braconidae the least specialised. Trophic groups also varied consistent with these findings. Our findings suggest high elevational specialisation and concomitant extinction risk in Brazilian Atlantic Rainforest insects. Differences in elevational specialisation between taxonomic groups may alter the functioning of insect communities under climate change.

Context The species-area relationship (SAR) is one of the main patterns in Ecology, but its underlying causes are still under debate. The random placement hypothesis (RPH) is the simplest one to explain the SAR: larger areas are more likely to contain more individuals and, as a consequence, more species. However, it is still unclear the degree to which the RPH is supported for different taxa and regions globally. Objectives We performed the first global synthesis on the RPH to investigate which variables mediate variation in the degree of support of this hypothesis across taxa and regions. Methods We conducted a review of the global SAR literature and created a new integrative metric to estimate the degree of support of the RPH. This metric takes into account the coefficient of determination, the intercept, and the slope of the relationship between observed (empirical) and predicted (according to the RPH) species richness. We analyzed the relationship between this metric and different geographic and ecological factors. Results We found a total of 52 independent tests of the RPH. About 42% of these tests confirmed the RPH. Using the new metric, we found that the degree of support of the RPH was significantly higher for plants than animals, and increased consistently with latitude. Conclusions Simple probabilistic processes are important to determine SARs, especially for sessile organisms and at higher latitudes. Further tests of the RPH, especially using the new metric introduced here, will be vital to understand the processes underlying the SAR and to advance Landscape Ecology.