Traditional studies of biodiversity are mainly concerned with patterns of taxonomic richness. In neontology, particularly conservation biology, the focus is generally at the species level (Reid, 1998; Mittermeier et al., 2005), while in paleontology, the genus and family levels are often used as proxies (Sepkoski, 1988; Bambach et al., 2004). However, there are of course other aspects to diversity, including genetic diversity (e.g. Petit et al., 2003) and phylogenetic diversity (Faith, 1992). A further type of diversity that has generated some interest over the past decade or so is morphological diversity, often referred to as disparity (Gould, 1991; Foote, 1997). This kind of diversity, which, importantly, does not necessarily covary with richness measures, takes as its study the variation in morphology or morphological types in a study group at a particular time or place. The focal level is generally a higher taxonomic category, such as a Family or Order, but can also be a non-monophyletic adaptive category such as carnivore or herbivore, as the object is not in the first instance to trace the evolution of a specific clade, but to investigate the range of adaptations realised by a group of organisms in a particular setting, or, in other words, the totality of their context-specific ecomorphology.
Such studies of ecomorphology can be used to investigate differences in ecological structure in time and space and help differentiate between processes such as selective or random extinctions. It leads to a much fuller depiction of biological diversity than richness alone. Ecomorphology and analysis of disparity has been used at various scales to study the diversification of vertebrates (Van Valkenburgh, 1989, 1994; Jernvall et al., 1996; Werdelin, 1996; Wesley-Hunt, 2005), invertebrates (Foote, 1994, 1997; Wills et al., 1994; Wills, 1998; Roy et al., 2001), and plants (Lupia, 1999) over their evolutionary history.
Ecological morphology (ecomorphology) is a powerful tool for exploring diversity, ecology, and evolution in concert (Wainwright, 1994, and references therein). Alpha taxonomy and diversity measures based on taxon counting are the most commonly used tools for understanding long-term evolutionary patterns and provide the foundation for all other biological studies above the organismal level. However, this provides insight into only a single dimension of a multidimensional system. As a complement, ecomorphology allows us to describe the diversification and evolution of organisms in terms of their morphology and ecological role. This is accomplished by using quantitative and semi-quantitative characterisation of features of organisms that are important, for example, in niche partitioning or resource utilisation. In this context, diversity is commonly referred to as disparity (Foote, 1993). The process of speciation, for example, can be better understood and hypotheses more rigorously tested if it can be quantitatively demonstrated whether a new species looks very similar to the original taxon or whether its morphology has changed in a specific direction. For example, if a new species of herbivore evolves with increased grinding area in the cheek dentition, it can either occupy the same area of morphospace as previously existing species, suggesting increased resource competition, or it can occupy an area of morphospace that had previously been empty, suggesting evolution into a new niche. This example illustrates a situation where speciation did not just increase the number of taxa, but also morphologic and ecologic diversity. In turn, this quantitative information can be used to test speciation hypotheses in the extant fauna as well as the fossil record suggested by previous studies using molecular data and habitat reconstruction (Gaubert and Begg, 2007).
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