Relationships among species traits: Separating levels of response and identifying linkages to abundance

We test the idea that species interactions and environmental tolerances translate constrained traits to patterns of species distribution and abundance through a series of trade-offs. First we suggest a framework to classify relationships among traits at different levels of organization. We then synthesize experiments to quantify relationships at these multiple levels for a group of I I prairie plant species that characterize different disturbance regimes. Finally we identify linkages among traits at these different levels and examine how these linkages relate plant traits to patterns of species composition following gap creation. Linkages were evident between all levels of response, lending credence to the idea that relationships among organismal traits can shape dynamics of species interactions and thereby translate into abundance patterns. Interestingly the important trade-offs and translators for the set of species we examined were not always the ones predicted by conceptual models. For instance, we found evidence of trade-offs between measures of competitive and tolerance (to soil compaction) abilities, but little evidence of negative correlations between competitive abilities in different environments or between colonization and competitive abilities. Tolerance (to defoliation, shade, drought) and colonization abilities, rather than competitive ability, appeared to be important translators that linked organismal traits to abundance patterns. In addition growth rates of the species under field conditions, but not other measures of demographic success (e.g., survival, seedbank density), were related to the species distributions due to soil disturbance. Although our results support the idea that trade-offs scale across several levels of organization, specific predictions of several well-known hypotheses are not borne out along all levels of organization and other, less emphasized trade-offs appear to be as important in our study system.