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We investigated the relationship between abundance and geographic range structure of 258 North American landbirds. For this purpose we used six measures of range structure based upon fractal geometry and geostatistics, and three ecological characteristics that can influence avian distribution. Permanent residents (PRs) that were abundant showed little fragmentation of their abundance surface at the periphery of their breeding range. Conversely, common Neotropical migrants (NTMs) exhibited low fragmentation of their central populations. The abundance surface was smoother for PRs than NTMs or short-distance migrants (SDMs), indicating that changes in abundance occurred more gradually across space for this group. The areas of high abundance for grassland species were had little demographic fragmentation, but other populations showed little spatial autocorrelation in abundance. Species breeding in late-successional forests were relatively rare compared tospecies breeding in other habitat types. Among carnivores, PRs had ahigher average abundance than either NTMs or SDMs. Although carnivores had more distributional gaps within their ranges than other trophic groups, the number of gaps did not differ between rare and abundantspecies, indicating that increased abundance did not change significantly influence their presence/absence distribution maps. Knowledge of patterns and variations of geographic range structure among speciesmay provide insights into processes that shape and maintain the biodiversity of a continent. [ABSTRACT FROM AUTHOR]

Island communities are generally viewed as being more susceptible to invasion than those of mainland areas, yet empirical evidence is almost lacking. A species-by-species examination of introduced birds in two independent island-mainland comparisons is not consistent with this hypothesis. In the New Zealand-mainland Australia comparison, 16 species were successful in both regions, 19 always failed and only eight had mixed outcomes. Mixed results were observed less often than expected by chance, and in only 5 cases was the relationship in the predicted direction. This result is not biased by differences in introduction effort because, within species, the number of individuals released in New Zealand did not differ significantly from those released in mainland Australia. A similar result emerged in the Hawaiian islands-mainland USA comparison: among the 35 species considered, 15 were successful in both regions, seven always failed and 13 had mixed outcomes. In this occasion, the results fit well to those expected by chance, and in only seven cases was the relationship in the direction predicted. I therefore conclude that, if true, the view that islands are less resistant than continents to invasions is far from universal. [ABSTRACT FROM AUTHOR]

There has been a recent resurgence of interest in documenting and explaining patterns of species' range sizes with the goal of determining if general patterns exist. Much recent debate has centered on whether Rapoport's rule, the tendency for range size to increase with increasing latitude, is a general rule or a local effect. I calculated the sizes of turtle species ranges from distribution maps and used published natural history data to examine how range size varies with latitude, and to determine if differences in range size exist among continents, and if correlations with body size, available land area, habitat and diet breadth exist. The distribution of turtle range sizes extended over six orders of magnitude and formed a lognormal distribution with many species having moderate or small ranges and few species having large ranges. Range size was positively correlated with available land area, habitat breadth, diet breadth, and body size. Multiple regression accounted for only 39% of the variance in range size indicating that other important factors remain unknown. At both global andcontinental scales, range size is largest near the equator and decreases with increasing latitude, the opposite of Rapoport's rule. However, range size did increase latitudinally above 25-30 deg. N in both the Neararctic and Palearctic suggesting that the pattern would be more accurately considered a local effect than a general rule. Larger range sizes at low latitudes may occur because more land area in the tropics provides much suitable habitat for ectotherms and there are few large scale physical barriers to dispersal. Rapoport patterns result from the occurrence of a small number of wide-ranging cold tolerantspecies that have reinvaded northern latitudes after Pleistocene glaciation. Patterns of the longitudinal and latitudinal extents of species ranges and their positions illustrate the importance of climate, mountain ranges, deserts, and coastlines, as barriers potentially affec [ABSTRACT FROM AUTHOR]

Extinction and artificial reduction in the size of geographical ranges of many species have occurred extensively across the globe becauseof human activities. In particular, Australian mammals have sufferedheavily in the last two hundred years, with the highest number of reported cases of mammal extinctions anywhere. In the present study, weinvestigated the extent to which human impact has affected contemporary macroecological patterns in Australian terrestrial mammals. Afterexamining patterns relating to body size and range size among the contemporary mammal fauna, we removed the effects of the last two hundred years of human impact by exploring patterns in the pre-European assemblage. This permitted us to determine whether contemporary macroecological patterns are distortions of pre-European patterns. In contrast to the expected pattern of a significant positive relationship between body size and range size, our results showed no significant association for the complete fauna in both cross-species and phylogeneticanalyses, even when data were corrected for species extinctions and range reductions. Analyses within families and among species with thesame trophic strategy revealed three significant positive relationships (Macropodidae, Peramelidae, and herbivores) and one significant negative relationship (insectivores) within the contemporary assemblage that disappeared when the pre-European assemblage was analyzed. A positive relationship also emerged in the pre-European assemblage for the Vombatidae that was not apparent in the contemporary fauna. Thus,correcting for human impact revealed important distortions among contemporary macroecological relationships that have been brought about by human-induced range reduction and extinction. These findings not only provide further evidence that the Australian continent presents aunique and valuable opportunity with which to test the generality ofmacroecological patterns, but they also have important ramificationsfor the a [ABSTRACT FROM AUTHOR]