The ecology of plant populations: their dynamics, interactions and evolution.

Abstract

What regulates the size and distribution of plant populations? What determines whether a population of plants will increase in size or decline? What allows some species to become aggressive invaders of exotic habitats, and what prevents this from occurring? When do individuals from different species exclude each other from a community by competition, and when do their interactions facilitate coexistence? These are just a few of the questions that arise when one contemplates the ebb and flow of plants across our landscapes, the magnificent diversity one finds in some habitats, or the tendency of one species to exclude all others in habitats that would appear to be very similar. This Special Issue brings together 15 articles presenting recent research bearing on these and other questions that have become, or continue to be, hot topics in the study of plant populations. The topics covered in this issue range from the epigenetic inheritance of characters that influence defence traits to the abiotic factors and biotic interactions that contribute to community assembly and the coexistence of plant species. Several of the studies consider the ecology and evolution of invasive species. Others address questions about the evolutionary ecology of local adaptation and differentiation in lifehistory traits, including differentiation between the sexes of dioecious plants. With this breadth, it is perhaps not sensible to look for themes that unite all the papers ‐ beyond the common concern with plant populations. Nevertheless, one theme does echo hither and thither between the contributions made: that ecological interactions take place between organisms that vary genetically, and that the extent of genetic, indeed phylogenetic, divergence between interacting populations can matter. The integration of a formal phylogenetic perspective into comparative functional ecology represented an important step in the field of plant ecology (Harvey and Pagel, 1991; Silvertown et al., 1997). The point is a simple one: traits may be associated among species either because they are functionally related, or simply because traits are inherited together from common ancestors (or both). It is now accepted that failure to account for the latter possibility is tantamount to pseudoreplication, because species are not independent units, and can lead to spurious conclusions about function. In phylogenetically corrected analyses, trait associations between more closely related species are effectively downplayed in relation to those found between more distantly related species (Felsenstein, 1985; Grafen, 1989; Harvey and Pagel, 1991). But how distant is distant, in an absolute sense? In this Special Issue, two papers incorporate a phylogenetic perspective into their analyses, the second of which considers