COS 6-10 - Functional composition of large terrestrial herbivore regimes as a driver of continental vegetation distribution

Monday, August 7, 2017: 4:40 PM
C125-126, Oregon Convention Center
Daniel Gorczynski, Vanderbilt University, Nashville, TN and Maria Luisa Jorge, Earth & Environmental Sciences, Vanderbilt University, Nashville, TN

Large terrestrial herbivorous mammals have a major impact on their ecological systems through interactions with the plant community and with the general landscape. These mammals are particularly influential due to their size, feeding habits and home range breadth, and have been shown to have a significant influence on vegetation type in grassland ecosystems. Studies have shown that functional grouping of herbivores simplifies analyses of their interactions with the environment and can reveal broad-scale trends in herbivory when applied spatially. This study groups the large herbivorous mammal genera of the Neotropics by their ecosystem function using five trait variables: weight, diet, sociality, water dependence and gut type. The study then relates the presence of the functional groups to each other across the Neotropics, categorizing the landscape based on the relative abundances of each functional group and the overall quantity of mammalian herbivores. These “herbivomes” are correlated with climactic variables to ascertain the origin of emergent trends in herbivore community structure and vegetation type. The goal of this work was to understand how groups of mammalian herbivores are distributed across the Neotropics, and how these spatial distributions may be affecting vegetation distribution, particularly in tropical savannah/dry forest complexes.


The analyses resulted in the production of five herbivore functional groups (social omnivores, small solitary frugivores, social non-ruminant grazers, large solitary water-dependents, and semi-social ruminant grazers) and four herbivomes (Ruminant Grazer, Herbivore Deficient, Proto-forest Coalition, and Forest Coalition) within the Neotropics. Our study suggests that a coalition of forest-dwelling herbivore functional groups in the center of the South American continent contributes to the persistence and expansion of forest vegetation in areas of high temperature and moderate to low precipitation. This is accomplished through high functional group diversity and high herbivore biomass seen nowhere else on the continent. The process of forest perpetuation is likely encouraged by various ecosystem functions performed by the forest-dwelling groups including seed dispersal, seedling regulation, and soil overturn. A notable deficiency of grazing ungulates in this region also seems to reinforce forest vegetation. This trend stands in stark contrast with what is seen on the African continent, where areas of high temperature/moderate to low precipitation are dominated by grassland-dwelling ungulate functional groups that propagate a large-scale grassland environment. This study calls for further investigation to understand why these different trends emerge on the two continents and what ecosystem functions are most responsible for herbivore-vegetation feedbacks.