Context and connectivity in plant metapopulations and landscape mosaics: does the matrix matter?

Recent reviews of evidence for plant metapopulation prevalence in nature have concluded that most species appear not to be arranged as metapopulations - hence other frameworks may be necessary for understanding large-scale, regional dynamics in plants. Separate but related paradigms from the disciplines of landscape ecology and metapopulation ecology exist for understanding patterns of regional population variation. The major models of both paradigms assume a binary landscape mosaic composed of "suitable habitat" and background "matrix." An important distinction between the two approaches is that metapopulation models essentially ignore features of the matrix. A binary approach to the landscape seems inappropriate for plants for several reasons. First, plants probably do not have a binary perception of the landscape, but rather respond to gradients of resource quality. Thus properties of patches, or the matrix per se, may be less important than the nature of the landscape mosaic, in particular as this is reflected in terms of connectivity. Secondly, many plants rely on a range of other agents for dispersal of pollen and seed, all of which are also affected by their environment in terms of connectivity. Furthermore the various components of the mosaic, including physical, spatial and functional elements can significantly influence plant movements. We review important effects of the matrix - via composition and configuration of habitat patches, extent of edges, patterns of land use, etc., upon plant populations. We describe evidence supporting a general integration of metapopulation and landscape ecological approaches for understanding regional dynamics in plants, emphasizing notions of connectivity (traditionally measured in very different ways by metapopulation and landscape ecologists), and context, an emerging concept describing components of variability in the landscape from a species-specific perspective. Finally, we describe a functional landscape mosaic approach that treats structural and functional features of the landscape and show how these interact to determine the fate of plant populations.