Huge Animals, Huge Impact

Depletion of megafauna – animals that weigh over a ton or more – is one of the most damaging ecological consequences of human activity on Earth. Of great concern is the African Forest Elephant, an animal whose population has declined 60% in the last decade and now inhabits less than a quarter of its previous range. While some may view extinction of one elephant species as an unfortunate, but small consequence of human activity, the reality is that megafauna loss likely impacts the entire ecosystem and the sustenance of both people and the environment. Substantial gaps in knowledge exist as to the full impact of megafauna loss in general, and loss of the African Forest Elephant specifically. To fully evaluate the impact of megafauna loss, the ecosystem must be viewed in totality, understanding that when species depletion starts with the largest animals, that depletion likely causes a chain reaction that dramatically shapes the outcome of remaining flora and fauna. Dr. John Poulsen understands that elephants, as large browsers, has significant effects on vegetation, by breaking and killing plants often at later life stages. In the absence of these browsers, vegetation turnover is disrupted, and fungal and insect-based plant pathogens are left unchecked. These plant ‘enemies’ create open space for other plant species to establish and grow. Further, elephant-mediated seed dispersal, seed predation, and seedling predation are substantially altered in their absence, with largely unknown consequences for tree recruitment and their allied ecosystem functions. Using the African Forest Elephant as a model of megafauna depletion, Dr. Poulsen is characterizing the effects of defaunation on tree species recruitment to enable predictions of the resulting changes to the composition and structure of tropical forests. Dr. Poulsen is assessing the relationship among host plant, elephant, insect vector and pathogen over plant life stages. By doing so, he can quantify the degree to which defaunation alters plants, insect vectors, and pathogens. By generating individual based models to simulate population dynamics of elephant-dispersed tree species, he can compare extinction probabilities in simulated populations with and without elephants.

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