MEGAHERBIVORE ECOLOGY PROJECT
Depletion of megafauna, animals that weigh 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, whose population declined 62% in the last decade and 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, megafauna loss likely affects entire ecosystems with widespread repercussions for the environment and humanity. Elephants, as large browsers, break vegetation and kill saplings, opening up the forest understory; but they also consume fruits and disperse seeds, facilitating reproduction of some tree species - the duality of their impact conceivably stabilizes forest dynamics. Substantial gaps in knowledge exist with respect to the full impact of megafauna loss. To close this gap, we are using the forest elephant as a model to study how the loss of megaherbivores alters the structure, composition and diversity of forest ecosystems.
ELEPHANT MOVEMENT ECOLOGY
Movement ecology can provide insights into species' resource requirements food, water, and space and elucidate temporal and spatial patterns of habitat use. Studies of forest elephant movement are relatively rare because of the difficulty of collaring elephants in dense forests and, until recently, the challenge of reliably transmitting GPS signals through the canopy. The Gabon Parks Agency recently GPS-collared over ~100 forest elephants; we are collaborating with the Agency to determine the drivers of variation in elephant home ranges, movement behavior and distance.
Our goal is to combine elephant movement data, field data, and expert and local knowledge to propose management and land zoning recommendations for elephant conservation that can be integrated into national land use planning.
Seasonal movement patterns of an elephant between two forest areas.
ELEPHANT BEHAVIOR
The degree to which individuals can live in social groups is limited by ecological constraints such as food availability and distribution. Individuals are constrained in the amount of time and energy they can spend foraging, which increases with larger group sizes. Fission-fusion group dynamics, like those of forest elephants, have been rarely described in response to anthropogenic disturbance, such as hunting or deforestation. Using a framework of ecological constraints, we seek to determine how African forest elephants adaptively respond to anthropogenic disturbances.
We are examining forest elephant social dynamics in the presence and absence of human disturbance and determine areas conducive to social interactions. Our goals are to: 1. determine forest elephant social group size and within group relatedness, and assess the environmental drivers of group size and relatedness in space and in time; 2. describe how forest elephant social groups are organized; and, 3. evaluate the effect of human disturbance, such as poaching and roads, on forest elephant group size and dynamics.
ECOLOGICAL EFFECTS OF ELEPHANTS
SEED DISPERSAL
Forest elephants are known to be effective seed dispersers because they are highly mobile and consume many species of fruit. Patterns of seed dispersal by elephants depend on two key variables: how elephants move and the average amount of time a seed spends in an elephant gut - gut passage time (GPT). We are using a combination of new technologies to measure GPT in order to model how elephants influence forest composition, diversity, and structure through this plant-animal interaction.
HERBIVORY
Megaherbivores, in particular, have big effects on vegetation: through browsing of saplings and breaking of trees, elephants are major drivers of vegetation structure and community composition in woodlands. But the extent to which elephants shape tropical forests through browsing is largely unknown. We are employing exclosures to experimentally assess the strength of browsing on the forest plant community.
