Communities of Small Terrestrial Arthropods Change Rapidly Along a Costa Rican Elevation Gradient

Biological diversity changes along montane slopes. Such changes are particularly stark in the neotropics due to the relative stability of abiotic variables (like temperature and precipitation) across elevation. While these relationships have been understood since the late 1960s, elucidating patterns of neotropical diversity along elevation is slowed by taxonomic impediments (including that most tropical arthropod species are not named) and by a general lack of quantified abiotic conditions (such as lapse rates) for specific neotropical mountains. In northwestern Costa Rica, in the Área de Conservación Guanacaste (ACG), we have worked to understand the elevational distribution of diverse leaf-litter fauna while collecting temperature data from coastal dry forest through rain forest into the cloud forest at the montane peaks of these volcanos. We found, the predictable pattern in the face of the climate crisis, that the cold, historically temperature invariant cloud forests are rapidly heating while the hot low elevation dry forests are not cooling off during the rainy season as they would have historically. To avoid the taxonomic impediment, we used DNA barcodes to focus on six taxa (Formicidae, Staphylinidae, Araneae, Collembola, Isopoda and the Microgastrinae) and found that the connection between alpha diversity and elevation was very dependent on the tax on in question (along elevation: some increased, some decreased, some displayed mid-elevational peaks and some no relationship). However, changes in betadiversity occurred with dramatic speed and were remarkably similar across taxa. To understand patterns of diversity and elevation in the neotropics we need to illuminate the biology of cryptic arthropod species. To communicate the sensitivity of neotropical elevation gradients to the climate crisis requires baseline data collection. Unfortunately, further study of these questions and collection of these data will not provide solutions to the underlying problems of the climate crisis in the neotropics. This requires (at least) three coincident strategies. Locally, increase the size of protected areas while concurrently maintaining and expanding long-term monitoring and expertise. Globally, accelerate and entrench strategies to reduce greenhouse gas emissions and transition to a low-carbon future.