The Cape Floristic Region (CFR) of South Africa is rich in biodiversity and comprises steep environmental gradients that span multiple terrestrial biome types. The CFR contains more than 9000 plant species in an area of about 90,000 km2, 67% of which are endemic. These factors make it an ideal location to examine functional trait by environment relationships, and to draw inferences regarding the role of these relationships on plant community assembly. Further, with both high values of species richness ( diversity) and turnover of species in space ( diversity), and the ubiquitousness of several major clades, whose members comprise a large amount of this diversity, across separate regions in physical and environmental space, this region offers an ideal location for a deep investigation of how trait by environmental relationships vary across scales of space and taxonomy. We used existing vegetation survey data to guide extensive field collections of plant functional traits for over 1000 species. We applied regression analyses to measure trait by environment relationships for individual plants, individuals aggregated by clades, and community aggregations across multiple spatial scales.
We found large influences of changing scales on the resulting trait by environment relationships. All major clades were observed in each of the regions within the CFR where data was collected. The range of observed functional trait values greatly overlapped from region to region, despite substantial difference in environmental conditions. However, trait by environment relationships were often regionally specific. Further, trait by environment relationships varied among different biomes within and across regions at botht the individual and community level. We also found evidence for dramatically different trait by environment relationships across major clades, when comparing between genera or families. An important question in community ecology studies is what levels of information aggregation yield useful results for interpreting ecological (and evolutionary) processes? At very course scales, there is abundant evidence of functional trait by environment relationships, but at finer scales, these relationships break down, suggesting some degree of neutrality. Our results suggest that trait by environment associations vary dramatically based spatial and taxonomic scales of aggregation. In many cases, finer scale aggregations yield contrasting relationships across clades and/or space. Ignoring these scaling issues could lead to interpretations that ignore the ecological fallacies apparent in our data.