Macroecological Patterns of Plant Species and Anthropogenic Activities

Abstract

The study of macroecology not only identifies patterns in the distribution and abundance of species at large spatial and temporal scales, it also gives insight into the processes underlying those patterns. The contribution of this work is not limited to helping develop the field of ecology per se, but also provides important insights into the understanding of large scale processes like climate change, the spread of introduced species, pest control and how increasing pressure from anthropogenic activities threatens biodiversity and ecosystem services. During the first decade following its formal inception, most of the progress in macroecology was made through studies of animal species, and research into plant species continues to lag far behind. This thesis contributes to the study of the macroecology of plant species by examining some selected macroecological patterns that have been studied only for animal species and by including an important issue that might have significant effects on diverse macroecological patterns, namely anthropogenic activities. The second and third chapters of the thesis address the generalised individuals-area relationship (GIAR) and the patch individuals-area relationship (PIAR), two macroecological relationships not previously explored for plant species. I show for the first time the existence of negative GIARs at the intraspecific and interspecific levels in plant species, similar to those documented for animal species. Unlike animal species, I did not find a broadly consistent intraspecific PIAR in plant species; more than half of the tested species showed negative PIARs. The resource concentration hypothesis may help explain those positive PIARs that were observed. The fourth chapter considers the effect of past human activities on current patterns of plant species richness at a landscape scale. Using a detailed database on the historical anthropogenic activities for Cornwall, U.K., I examine the relationship between species richness and the area covered by each historical land-use at two different spatial resolutions (10km x 10km and 2km x 2km). I find that at the 10km x10km scale human activities carried out since the 17th and 19th centuries explain an important proportion of the variation in current plant species richness. In contrast, a model at 2km x 2km scale with upland woods and the total land area of a grid cell explain only 5% of the variation. The fifth and sixth chapters focus on how artificial light at night (ALAN), which has increasingly come to attention as a significant anthropogenic pressure on species, is interacting with the distributions of plant species. In the fourth chapter, I consider the plant family Cactaceae to determine the proportion of the global distribution ranges of species that is being influenced by ALAN, and how this changes with the size of these distribution ranges and over a 21-year period (1992 to 2012). I found that >80% of cacti species are experiencing ALAN somewhere in their distribution range, and that there is a significant upward trend in ALAN in the ranges of the vast majority of species. For the sixth chapter, I consider similar issues for the threatened plant species of Britain, exploiting new remote sensing imagery of nighttime lighting at a very fine spatial resolution (c.340x340m2). Only 8% of Britain is free of artificial light at night and in consequence a high number of threatened plant species have a high proportion of their range under some influence of ALAN.