Closer to the rear edge: ecology and genetic diversity down the core‐edge gradient of a marine macroalga

<jats:p>A fundamental goal in ecology is to understand distribution and abundance of species. Peripheral populations inhabiting the trailing‐edge of a species' distribution may carry considerable ecological and evolutionary value yet being most threatened under predicted climate change scenarios. However, the nature of species distributional limits and the ecological and genetic implications of living at low latitude rear edges remain unclear. The assumption that population abundance declines towards range edges, where environmental selective pressure increases, is the basis of a wide range of ecological and evolutionary predictions. Empirical data have provided contrasting evidence about the consequences of living at low latitude distributional limits, raising concerns regarding their generality and highlighting the need for combined multidisciplinary tests. Here, we provide a long‐term, comprehensive evaluation of latitudinal patterns in genetic diversity, demographic, morphological and life history traits in the marine macroalga <jats:italic>Fucus guiryi</jats:italic>.</jats:p><jats:p>The center to edge transition was mirrored by increasing water and air temperature gradients, with sea surface temperature of coldest months being the most relevant influence on <jats:italic>F. guiryi</jats:italic> traits. Overall, we identified a strong correlation between ecological data, collected over one year at bimonthly intervals, and distance to the range center. We found decreasing population and individual size towards distributional margins. Similarly, reproductive capacity, threshold size for reproduction, density of reproductive population and recruitment rates showed a core to edge reduction. Temporal variability of individual reproductive effort and recruitment rates did not conform to the general pattern. In contrast, population genetic data did not show a core‐edge gradient, as gene diversity and allelic richness were not significantly lower at edge populations, contradicting predictions of higher drift and bottlenecks for smaller edge populations.</jats:p><jats:p>The contrasting support provided by genetic and ecological data highlights the need to combine multiple and cross‐disciplinary evidence for a comprehensive understanding of ecological and evolutionary mechanisms linked to species ranges.</jats:p>