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Functional groups of rare plants differ in levels of imperilment¹

² Harvard Forest, Harvard University, 324 North Main Street, Petersham, Massachusetts 01366-0068 USA ³ Florida International University 11200 SW 8th Street, Miami, Florida 33199 USA

ABSTRACT

Comparative examination of a large sample of plant species can reveal important aspects of life history that influence the ecology and distribution of taxa and their vulnerability to local extinction. We investigated whether functional groups of 71 rare plant species with contrasting life history traits differed in terms of population losses over time, regional range contraction, and range-wide levels of imperilment. Using town-level occurrence data from herbaria and Natural Heritage Program databases, we characterized species’ extents of occurrence as -hulls encompassing the centroids of New England towns that contained well-documented populations of these rare taxa. Family affiliation was used as a covariate in analyses to reduce phylogenetic bias. Disparate functional groups of plants differed both in proportions of populations lost and declines in range areas over time, with insect-pollinated taxa, upland (vs. wetland) taxa, species with localized seed dispersal modes, and taxa reaching their northern range boundary in New England significantly more imperiled than other functional groups. These techniques permit a broad comparative assessment of the distribution of large numbers of plant taxa, so that we can identify several functional groups that warrant more concerted conservation attention.

Key Words: biogeography • functional groups • GIS • guilds • herbarium collections • rarity • species ranges