Correlative, Experimental, and Comparative Evolutionary Approaches in Ecomorphology

This paper discusses questions, pitfalls, and constraints of ecomorphology, and proposes a step-wise approach to its study. Five broad and overlapping questions in ecomorphology are proposed and examples given. The questions address (1) the covariation between environmental factors and form, (2) performance testing in ecomorphology, (3) the optimization of the form-function faculty and constraints on optimization, (4) the ontogeny of ecomorphological relationships, and (5) direction of evolutionary change in ecomorphological relationships. Ecomorphological relationships are clouded by various factors, including (1) improper selection of morphological or ecological characters, (2) differing and/or improper methods of data analysis, (3) restricting the depth or scale of the analysis, either morphologically or ecologically, (4) lack of a proper null hypothesis against which to test ecomorphological relationships, (5) lack of knowledge of the life history of the species, and (6) lack of knowledge of the constraints acting on the ecomorphological relationship. Two general approaches to character selection, a priori and a posteriori, are examined. In either approach, character selection may be inappropriate, resulting in faulty conclusions. Historical (evolutionary) and current constraints that act against ecomorphological relationships are briefly listed. Finally, a practical, hierarchical approach to ecomorphology is put forward. The first step seeks correlations between form and environmental factors. Predictions are generated and tested with field and laboratory experiments to determine the biological role and performance of the form-function faculty and its optimal range. Comparative phyletic analysis of either closely or distantly related organisms may then elucidate parallel and divergent, or convergent evolutionary pathways, respectively.