Evol Ecol Res 4: 937-950 (2002)     Full PDF if your library subscribes.

Relating species rarity to life history in plants of eastern Australia

Brad R. Murray,* Peter H. Thrall and Brendan J. Lepschi

Centre for Plant Biodiversity Research, CSIRO, Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia

Address all correspondence to Brad Murray, Institute for Water and Environmental Resource Management, Department of Environmental Sciences, University of Technology Sydney, Gore Hill, NSW 2065, Australia.
e-mail: brad.murray@uts.edu.au


We examined species rarity in relation to life history in plants of eastern Australia. Correlated-divergence analysis (using phylogenetically independent contrasts) and cross-species analysis (exploring patterns across present-day species) were employed in a complementary fashion to test the hypothesis that rare and common species differed with respect to life history. Two measures of rarity, threat of extinction and geographical range size, were investigated for relationships with growth form, longevity, pollination mode, mating system, dispersal and seed mass. Species threatened with extinction had, on average, significantly smaller seed mass than non-threatened species. This emerged in both correlated-divergence and cross-species analyses, independently of the effects of the other life-history traits. In cross-species analysis, but not as phylogenetic contrasts, a significant number of species with short life spans were less likely to be threatened with extinction. This arose because most short-lived species not threatened with extinction diverged from long-lived species threatened with extinction at a major node deep in the phylogenetic tree (where monocotyledons diverged from dicotyledons). Mating system was significantly related to geographical range size in correlated-divergence analysis, but not across present-day species. There was evidence that evolutionary divergences for dioecy have been significantly correlated with the occupation of a wide geographical range, although this relationship has not been maintained across present-day species. Growth form, pollination mode and dispersal could not account significantly for variation in either threat of extinction or range size. Because relationships for plants of eastern Australia were found to differ considerably from those emerging for other species assemblages on other continents, support is provided for the notion that associations between species rarity and life history are highly dependent on geographical context and the species assemblage under scrutiny.

Keywords: evolutionary divergence correlation, geographical range size, phylogenetic regression, threat of extinction.

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