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

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.