The roles of disturbance, topography and climate in determining the leading and rear edges of population range limits

Aim To identify the ecosystem features most important for differentiating leading edges from rear edges of plant population distributions, and for distinguishing both from contiguous-range sites. Location Eastern California, USA. Methods Habitats supporting multiple plant populations at their range edges were analysed, including 32 rear-edge, 32 leading-edge and 526 control sites within contiguous ranges. Multivariate modelling techniques, including general linear and additive modelling, ordination and classification trees were used to identify the biotic and abiotic factors that control range edges. Results Rear edges were associated with lower solar radiation and potential evapotranspiration, as would generally be expected as ranges shift in a warming climate regime. Leading edges were associated with lower topographical positions, such as canyon bottoms, and were characterized by recent disturbance and early successional stages. Rear edges occurred mainly in undisturbed sites. Main conclusions The interacting roles of biological and physical factors in determining population range limits have recently gained attention as the need to predict ecosystem shifts in a changing climate increases. Further understanding and recognition of disturbance in facilitating the expansion of native species' ranges and in conserving relict populations will enhance the ability of land managers to maintain biodiversity and ecosystem resilience as climate continues to change.