Abstract
Comparative analyses of extinction risk routinely apply methods that account for phylogenetic non-independence, but few analyses of extinction risk have addressed the possibility of spatial non-independence. We explored patterns of extinction risk in Banksia, a plant genus largely endemic to Australia’s southwest biodiversity hotspot, using methods to partition the variance in two response variables (threat status and range size) into phylogenetic, spatial, and independent components. We then estimated the effects of a number of biological and external predictors on extinction risk independently of phylogeny and space. The models explained up to 34.2% of the variation in range size and up to 9.7% of the variation in threat status, nearly all of which was accounted for by the predictors, not by phylogeny or space. In the case of Banksia, therefore, high extinction risk can be clearly linked with biological syndromes (such as a brief flowering period) or geographic indicators of human impact (such as extensive habitat loss), but cannot be predicted from phylogenetic relatedness or geographic proximity.
Highlights
Over the past few decades, numerous studies have used a comparative approach in an attempt to identify particular biological syndromes or ecological strategies that effectively distinguish extinction-prone from non extinction-prone plant species
As well as the need to account for the possible effects of phylogenetic and spatial autocorrelation in comparative analyses, it may be instructive to quantify their effects and compare the relative contribution of spatial and phylogenetic autocorrelation, intrinsic traits, environmental features, and threatening processes, on the variation in extinction risk among species. This would allow us to expand on the question of whether certain biological traits predict extinction risk, to ask a more general question: if two species have a similar level of extinction risk, is it because (1) they have similar biological traits; (2) they inhabit similar environments; (3) they are exposed to the same threatening processes; (4) they are closely related; or (5) they occur in the same region?. We explore this way of partitioning variation in extinction risk in the plant genus Banksia L.f
The spatial pattern of mean range size per grid cell shows a clear difference between the southwest and eastern/northern Australia, where many species are widely-distributed, but within each region shows little spatial pattern
Summary
Over the past few decades, numerous studies have used a comparative approach in an attempt to identify particular biological syndromes or ecological strategies that effectively distinguish extinction-prone from non extinction-prone plant species. It has been suggested that extinction-prone species should be characterized by specialized ecological requirements (e.g.[1]), small or highly variable population sizes While many studies have found support for such predictions, biological attributes usually explain very little of the variation in extinction risk across plant species. Their effects appear to be highly variable and contextdependent [1,5,6,7,8], and may interact in complex ways with external factors [9]. Variation in extinction risk among plant species seems to be associated with varying degrees of exposure to external threatening processes (e.g. habitat loss or overexploitation), mediated by species’ intrinsic biological traits, and by the environmental context in which species live.
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