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.
Mountains are interesting systems for studying patterns of diversity distribution and the role of environmental filters and competition on community assembly. According to the phylogenetic niche ...conservatism theory, the co-occurrence of closely related species might indicate that environmental filters are more important than competition when structuring communities in time and space. We investigated the patterns of phylogenetic diversity and the influence of environmental filters in the Brazilian rocky grasslands and tested the influence of phylogenetic niche conservatism. We placed 180 plots of 1 m² in five sites along an altitudinal gradient at the Cipó Mountains (Espinhaço Range, southeastern Brazil) and surveyed all vascular plant species and edaphic variables. We assessed the phylogenetic diversity of the communities by calculating the phylogenetic species variability and phylogenetic species richness. These measures were related to altitude and the edaphic variables through a principal component analysis and regressions. Phylogenetic species variability decreased towards higher altitudes and less fertile sites, whereas phylogenetic species richness increased. Thus, the number of species and the degree of phylogenetic clustering increased with increasing altitude, suggesting that the intensity of abiotic factors acting as environmental filters increased with altitude and could be constraining species in the community to a smaller number of clades.
Abstract Environmental stress is a fundamental facet of life and a significant driver of natural selection in the wild. Gene expression diversity may facilitate adaptation to environmental changes, ...without necessary genetic change, but its role in adaptive divergence remains largely understudied in Neotropical systems. In Amazonian riparian forests, species distribution is predominantly influenced by species' waterlogging tolerance. The flooding gradient delineates distinct wetland forest types, shaping habitats and species characteristics. Here we investigated the molecular basis of environmental stress response in a tropical ground‐herb species ( Ischnosiphon puberulus ) to environmental variation in Amazonian riparian forests. We compared environmental variables and gene expression profiles from individuals collected in two forest types: Igapó and Terra firme in the Amazonian riparian forests. Predictable seasonal flooding poses a significant challenge in Igapó compared to Terra firme environments, with the former presenting higher water column height and longer flooding duration. Our findings suggest that contrasting environmental conditions related to flooding regimes are important drivers of population genetic differentiation and differential gene expression in I. puberulus . Enriched gene ontology terms highlight associations with environmental stresses, such as defence response, water transport, phosphorylation, root development, response to auxin, salicylic acid and oxidative stress. By uncovering key environmental stress response pathways conserved across populations, I. puberulus offers novel genetic insights into the molecular basis of plant reactions to environmental constraints found in flooded areas of this highly biodiverse neotropical ecosystem.
