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Britnell, J.A.; Yichun Zhu; Kerley, G.I.H; Shultz, S., 2023. Ecological marginalization is widespread and increases extinction risk in mammals. PNAS 120 (3) e2205315120: 1-8 -

Location: Africa
Subject: Distribution
Species: All Rhino Species

Original text on this topic:
Habitat loss has led to widespread range contraction and population declines across taxa. The impact of range contraction on niche occupancy is rarely, if ever, incorporated into conservation assessments. We evaluate range loss in 4,785 terrestrial mammals and changes in niche parameters of range-contracted species. Range contraction results in more homogenous ranges and reduced niche sizes. Some species become restricted to ecologically extreme habitats at the periphery of their historic niche. This ecological marginalization increases extinction risk. Marginalization can result in a “double whammy” where poor performance in marginalized relict populations exacerbates population declines. This phenomenon is an underappreciated global conservation threat that may partially explain the failure of protected areas to buffer species from further decline.
Human land-use results in widespread range change across taxa. Anthropogenic pressures can result in species’ realized niches expanding, shifting, or contracting. Marginalization occurs when contraction constrains species to the geographic or ecological extremes of their historic niche. Using 4,785 terrestrial mammal species, we show that range contraction results in niche space and habitat diversity loss. Additionally, ecological marginalization is a common consequence of range contraction caused by human land use change. Remnant populations become located in the climatic and topographic extremes of their historic niche that are more likely to be at the periphery of their historic niche at greater distances from historic niche centroids. This ecological marginalization is associated with poor performance and increased extinction risk independent of geographic range loss. Range loss and marginalization may create a “double whammy” in vulnerable groups, such as large-bodied species and species with small geographical range size. Our results reveal a hitherto unrecognized conservation threat that is vital to incorporate into conservation assessment and management.

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