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A Thunbergia atacorensis adult plant showing a characteristics purple flower in one of our study sites in Benin (West Africa). The species is found in gallery forest along the Atacora mountain chain

A Thunbergia atacorensis adult plant showing a characteristics purple flower in one of our study sites in Benin (West Africa). The species is found in gallery forest along the Atacora mountain chain

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Understanding the ecological processes that govern species' range margins is a fundamental question in ecology with practical implications in conservation biology. The center-periphery hypothesis predicts that organisms have higher abundance at the center of their geographic range. However, most tests of this hypothesis often used raster data, assu...

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... While data on other abiotic factors that covary with elevation (e.g., soil type and fertility) were not collected in this study, abiotic factors have been shown to be important drivers of highly localized habitat differences, influencing the success of seed and clonal establishment, particularly in alpine environments where soil formation is poor and soilnutrient availability is limited (Potter and Bowman, 2020;Moutouama and Gaoue, 2022). However, it is also likely that responses to environmental change in populations of C. cordifolia across elevational bands will be largely driven by more localized variables (e.g., wetland response to climate change; Burkett and Kusler, 2000) than by factors that largely covary with elevation. ...
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Premise In mountain ecosystems, environmental conditions (e.g., temperature, ultraviolet radiation) covary with elevation, potentially limiting gene flow over steep gradients. We hypothesized that, (1) due to stark elevational differences in environmental factors, populations from dissimilar elevations (e.g., montane versus alpine) are more strongly differentiated than populations from similar elevations; (2) patterns of migration reflect downslope dispersal more than upslope dispersal; and (3) alpine populations at the cold edge show evidence of expansion, while montane populations at the warm edge have declined. Methods DNA polymorphisms in whole‐genome sequences were studied from 6–10 genotypes each in populations of Cardamine cordifolia found at three montane sites (ranging from 2200 to 2800 m a.s.l.) and three alpine sites (ranging from 3000 to 3500 m a.s.l.). Statistical analyses assessed patterns of population structure, genetic diversity, migration, and historical demography since the Pleistocene. Results Populations maintained very high levels of nucleotide diversity (π range: 0.062–0.071) and were weakly differentiated (pairwise F ST = 0.027) on average. Migration among alpine populations was also inferred, with no directionality of migration across elevation bands. Demographic inference suggests that both montane and alpine populations have declined in size since the Pleistocene. Conclusions Environmental differences across elevation represent diffuse barriers to gene flow. Recent polyploidy and clonal reproduction likely explain excess heterozygosity and high nucleotide diversity within populations. The genetic similarity of populations across elevation suggests highly connected refugia during the Pleistocene; such results may indicate that montane and alpine populations will respond similarly to changing environmental conditions associated with climate change.
... This distribution pattern is often explained by the expectation that the most favorable ecological conditions (biotic and abiotic) exist at the center of distribution. However, the geographic center of distribution does not necessarily coincide with species' optimal climatic conditions (Moutouama & Gaoue, 2022a). Therefore, species are not always expected to be most abundant at the center of their range, and this limits the generalization of the center-periphery hypothesis (Dallas et al., 2017;Pironon et al., 2017). ...
... The absence of decreasing population growth rate toward range periphery is not surprising given the greater relative importance of survival-growth to population fitness than fertility which is a typical trait of long-lived species. Consistent with our findings on population growth rates, our previous study on the same system showed no significant variation in population abundance between range center and periphery (Moutouama & Gaoue, 2022a). These convergent results of two different metrics (e.g., population abundance and population growth rate) must not be interpreted as if population abundance could be used as a surrogate measure of population growth rate. ...
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The center‐periphery hypothesis predicts a decline in population performance toward the periphery of a species' range, reflecting an alteration of environmental conditions at range periphery. However, the rare demographic tests of this hypothesis failed to disentangle the role of geography from that of ecological niche and are biased toward temperate regions. We hypothesized that, because species are expected to experience optimal abiotic conditions at their climatic niche center, (1) central populations will have better demographic growth, survival, and fertility than peripheral populations. As a result, (2) central populations are expected to have higher growth rates than peripheral populations. Peripheral populations are expected to decline, thus limiting species range expansion beyond these boundaries. Because peripheral populations are expected to be in harsh environmental conditions, (3) population growth rate will be more sensitive to perturbation of survival‐growth rather than fertility in peripheral populations. Finally, we hypothesized that (4) soils properties will drive the variations in population growth rates for narrowly distributed species for which small scale ecological factors could outweigh landscape level drivers. To test these hypotheses, we studied the demography of Thunbergia atacorensis (Acanthaceae), a range‐limited herb in West Africa. We collected three years of demographic data to parameterize an integral projection model (IPM) and estimated population level demographic statistics. Demographic vital rates and population growth rates did not change significantly with distance from geographic or climatic center, contrary to predictions. However, populations at the center of the geographic range were demographically more resilient to perturbation than those at the periphery. Soil nitrogen was the main driver of population growth rate variation. The relative influence of survival‐growth on population growth rates exceeded that of fertility at the geographic range center while we observed the opposite pattern for climatic niche. Our study highlights the importance of local scale processes in shaping the dynamics and distribution of range‐limited species. Our findings also suggest that the distinction between geographic distribution and climatic niche is important for a robust demographic test of the center‐periphery hypothesis.