The relative role of climate and biotic interactions in shaping the range limits of a neotropical orchid

Abstract

Aim The centre‐periphery hypothesis (CPH) explains the decline of species abundance towards range limits and how this is driven by increasing ecological marginality. So far, most studies testing the CPH have focused on abiotic factors contributing to marginality, while the role of biotic interactions in limiting species distribution has been neglected. Here, we investigate both drivers' roles in restricting an orchid's range along a broad environmental gradient. Location Atlantic Forest and Pampas grasslands (south and southeastern Brazil). Taxa Sand dune orchid Epidendrum fulgens (Orchidaceae). Methods We integrated empirical data on geographical distribution, pollinator richness and genetic diversity along the entire range of the species to investigate whether range limits match niche limits and whether habitat suitability declines towards low‐ and high‐latitude species ranges. We performed niche models to predict niche limits and used polynomial and linear regression models to investigate the associations between ecological niche and species range as well as to test the relationship between genetic‐derived metrics and the geographical and ecological distances. Results Ecological conditions become more marginal towards the edges of the E. fulgens range, with an abrupt variation in precipitation. While pollinator richness increases habitat suitability of E. fulgens in the low‐latitude edge range, climate has primarily shaped the species' high‐latitude limit. Genetic diversity within populations decreases, while genetic differentiation increases towards both margins, although with a more consistent pattern for the low‐latitudinal component. Main Conclusions This study corroborates the predictions of CPH regarding ecological and genetic patterns of variation in space and highlights distinct factors limiting geographical distribution at the opposite margins of a latitudinal and narrowly distributed species. This improves our understanding on how biotic and abiotic variables limit species distribution ranges along latitudinal gradients in an extremely diverse and vulnerable tropical ecosystem, with potential for informing conservation practices.

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