Macroecology depends heavily on a comparative methodology in order to identify large-scale patterns and to test alternative hypotheses that might generate such patterns. With the advent and accessibility of large electronic databases of species and their life history and ecological attributes, ecologists have begun seeking generalities, and examining large-scale ecological hypotheses involving core themes of range, abundance and diversity. For example, combinations of ecological, life history and phylogenetic data have been analysed using large species sets to test hypotheses in invasion biology. Analysis of regional species inventories can contribute cogently to our understanding of invasions. Here we examine several ways in which database analysis is effective. We review 19 studies of comparative invasions biology, each using >100 species of plants in their analyses, and show that invader success is linked to seven correlates: short life cycle, abiotic (mostly wind) dispersal, large native range size, non-random taxonomic patterns (emphasizing certain families or orders), presence of clonal organs, occupying disturbed habitats, and earlier time of introduction. These phylogenetically influenced, comparative analyses using regional species inventories are only just beginning and have much potential.

Doust, J. 2004. Context and connectivity in plant metapopulations and landscape mosaics: does the matrix matter? Á/ Oikos 105: 3 Á/14.Recent reviews of evidence for plant metapopulation prevalence in nature have concluded that most species appear not to be arranged as metapopulations Á/ 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 Á/ 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.

Aim We analysed spatial datasets of abundance across the entirety, or near entirety, of the geographical ranges of 134 tree species to test macroecological hypotheses concerning the distribution of abundance across geographical ranges.Location Our abundance estimates came via the USDA Forest Service Forest Inventory and Analysis Eastwide Database, which contains data for 134 eastern North American tree species. MethodsWe extracted measures of range size and the spatial location of abundance relative to position in the range for each species to test four hypotheses: (a) species occur in low abundance throughout most of their geographical range; (b) there is a positive interspecific relationship between abundance and range size; (c) species are more abundant in the centre of their range; and (d) there is a bimodal distribution of spatial autocorrelation in abundance across a species range. ResultsOur results demonstrate that (a) most species (85%) are abundant somewhere in their geographical range; (b) species achieving relatively high abundance tend to have larger range sizes; (c) the widely held assumption that species exhibit an 'abundant-centre distribution' is not well supported for the majority of species; we suggest 'abundant-core' as a more suitable term; and (d) there is no evidence of a bimodal distribution of spatial autocorrelation in abundance.Main Conclusions For many tree species, high abundance can be achieved at any position in the range, though suitable sites are found with less frequency towards range edges. Competitive relationships may be involved in the distribution of abundance across tree ranges and species with larger ranges (and possibly broader niches) may be affected more by biotic interactions than smaller ranging species.

Ecological niche modeling has become an increasingly important tool to address issues in many fields of basic and applied ecology. The ecological niche space occupied across the geographic range, particularly for wide‐ranging species, may vary for a variety of evolutionary and non‐evolutionary reasons. However, ecological niche models are often applied over large geographic areas without regard for the potential effects of regional variation in adaptation, environmental conditions and their interactions, and species responses, thus significantly reducing their accuracy and utility. We develop regionally partitioned ecological niche models, using GARP, for the wide‐ranging North American tree Gleditsia triacanthos (Fabaceae). Models were constructed based on known tree occurrences at peripheral and range‐centre locations, as well as across the geographic range as a whole. Our results suggest that the niche space occupied by G. triacanthos varies regionally and that between some regions in particular there may be a complete absence of niche overlap. In particular, while there is some overlap between the niche space occupied by trees in the western and central regions of the range, there appears to be virtually no overlap in the niche space occupied by trees in the south of the range and that occupied by western and central trees. This lack of overlap appears to be driven primarily by regional differences in abiotic conditions, rather than regional adaptation per se. The results of our study have several important implications for the future development of habitat suitability models over large geographic areas. Spatial partitioning of data is clearly necessary to improve predictions of models where regional niche variation occurs. For wide‐ranging species in particular, regional differences in ecological characteristics may cause apparent niche variation.

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Abundance and occupancy of populations at high- and low-latitude geographic range edges will be critically important in determining a species' response to climate change. Low abundance and occupancy at expanding (high latitude) edges of the range may limit a species capacity to migrate, and at trailing (low latitude) edges, may result in range erosion and regional extinction. We examined abundance-occupancy distributions across the geographic ranges of 102 eastern North American trees and looked for signatures reflecting capacity to respond to climate change. We found that 62% of species display a signature consistent with higher climatic suitability in the northern latitudes of their range. However, our results suggest that the most common response is likely to involve range erosion in the south and limited range expansion in the north, possibly leading to an overall reduction in range size for many species. In particular, species with smaller ranges centred at lower latitudes may not have the capacity to successfully track the current rate of climate change.

In colonizing species, high phenotypic plasticity can contribute to survival and propagation in heterogenous adventive environments, and it has been suggested as a predictor of invasiveness. Observation of natural populations of an invasive species, Lythrum salicaria salicaria, indicated extensive variation in its growth and reproductive traits. Phenotypic plasticity of different life history traits of L. salicaria was investigated using vegetative clones of each of 12 genotypes from one population in Ontario, Canada. We chose soil moisture as the treatment factor because of its importance in wetland species and raised all 12 genotypes in each of four soil moisture treatments. We examined an array of vegetative and reproductive traits, including root and shoot mass, shoot and inflorescence length, total seed set, floral mass, and morphometric variables. All observed vegetative as well as reproductive traits demonstrated significant phenotypic plasticity in response to soil moisture treatment. Even the stigma-anther separation involved significant genotype by environment interactions, suggesting that soil moisture may modify the relative positions of anthers and stigma. Compared to vegetative traits, most reproductive traits demonstrated crossing reaction norms, implying that the average differences in those traits among genotypes vary with the environment maintaining the genetic variation in a population.

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