From individuals to communities: Contributions of stable isotope analysis to mechanisms of coexistence among African mammalian herbivores

Presenter: Daryl Codron (University of the Free State, South Africa)

Abstract: Ecological niche partitioning is well-known as a necessary, albeit insufficient, condition for multispecies communities to achieve stable coexistence. In large mammalian herbivores, an exceptionally diverse animal group given their large body size, the primary axis for partitioning is the diet niche, with species varying along a gradient from grazing to browsing. Statistical and experimental evidence for convergence in multiple morphophysiological traits supports the evolutionary stability of grazer-browser niche separation. Stable isotope analysis (SIA), however, reveals a clustered rather than uniform pattern of separation of diet niches, irrespective of prevailing habitat conditions and changes in specie’s niche positions across space, as well as the development of this form of community structure over geological time. Moreover, there is growing evidence that species’ niches tend to expand at high population densities, contrary to what is expected if partitioning is the only mechanism regulating community structure. This suggests that processes occurring at individual level are ultimately responsible for the niche breadths of populations and their influence on other members of the community, even if the details remain vague. Ultimately, such isotopic studies of herbivore communities can be used to parameterize models that potentially resolve the paradox of biodiversity, like Modern Coexistence Theory, but for which empirical explanations for component parameters are still lacking.

Bio: Daryl Codron is a South African scientist currently heading the Terrestrial Ecology laboratory at the Department of Zoology and Entomology, University of the Free State (UFS), Bloemfontein, South Africa. He has over 20 years research experience addressing various topics related to southern African wildlife ecology and conservation, as well as of the evolutionary and palaeoecological history of African mammalian fauna. He obtained a PhD from the University of Cape Town in 2006 for his research using stable isotope analysis to study dietary niche dynamics of large mammal herbivores over multiple spatial and temporal scales. He subsequently completed three post-doctoral fellowships (National Museum, Bloemfontein, South Africa, and two at the University of Zurich, Switzerland), during which time he studied processes driving non-linearity in consumer-resource isotopic relationships, the directional evolution of generalized to specialized dietary niches in multiple herbivore lineages through the Late Quaternary, and developed palaeocological models for studying the role of size-specific competition and predator-prey interactions in regulating dinosaurian as well as therapsid communities, and extinctions thereof. Emergent ideas about vertebrate evolutionary ecology were further informed by a series a experimental and comparative analyses that uncovered the functional value of multiple morphophysiological traits, including anatomical characteristics, metabolic and digestive physiologies, and reproductive strategies of mammals. His current research focuses on environmental controls that determine the levels of ecological organization, from individuals to communities, at which niche variance is most prominent, and how organismal interactions at these different levels combine as mechanisms supporting multispecies coexistence. 
 

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