Aim

The center-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 potentially restricting an orchid's range along a broad environmental gradient.

Location

Brazilian Atlantic Forest and Pampas biomes (south and southeastern Brazil) Taxa Sand dune orchid Epidendrum fulgens (Orchidaceae).

Methods

We integrated empirical data on geographical distribution, pollinator richness, and niche models to investigate whether range limits match predicted niche limits and whether habitat suitability declines towards low- and high-latitude species ranges. In addition, we used genetic-derived metrics to test whether populations at range edges are indeed small and isolated, as predicted by the CPH.

Results

Our results show that ecological conditions become more marginal towards the edges of the E. fulgens range, with an abrupt variation in climate. We also found that the climate has primarily shaped the species' high-latitude limit, while pollinator richness increases habitat suitability of E. fulgens in the low-latitude edge range, likely explaining the species' persistence. Genetic diversity within E. fulgens populations decreases while genetic differentiation increases towards both margins, although with a more consistent pattern for the low-latitudinal component.

Main conclusions

Our results corroborate most of the predictions associated with CPH, highlighting distinct factors limiting geographical distribution at the opposite margins of this latitudinal and narrowly-distributed species. This study is a first step towards understanding the relative role of climate and biotic interactions in shaping the range limits of coastal species, with significant potential for informing conservation practices.