Document: AND-3-39-9

Predicting the impacts of harvesting using structured population models: An example based on tropical trees.

WATKINSON, A.* and R.FRECKLETON

University of East Anglia, Norwich, UK ¹

Abstract:
Structured population models are often used to predict the long-term behaviour of populations of economic or conservation interest. Such models, however, rarely include density-dependence and are typically parameterised with respect to fixed census points within the life cycle. We analyse a model for the harvesting of adults of the edible palm Euterpe edulis in the Atlantic Forest of Brazil for which the role of density-dependence has been clearly defined. Harvesting adult plants for the MISSING CHARACTER ENTITY: graveheart of palmMISSING CHARACTER ENTITY: accent or palmito leads to the death of plants and consequently has a major impact on population structure and abundance. Size structures are typically linear or slightly L shaped in harvested populations, contrasting with the reverse J shape that is characteristic of unexploited populations. It is shown, if density-dependence is not included, that predictions of population responses to harvesting are erroneous and highly misleading. Moreover we show that the timing as well as the intensity of harvesting are important in determining population behaviour. In particular, it is shown that population growth rates may lie within a range of values for a given level of harvesting, depending on how the timing of mortality relates to the structure of the model. Our analyses suggest that the essentially static nature of most existing analyses of the impacts of harvesting on populations can lead to misleading or uninformative predictions on the impacts of harvesting on abundance and the levels of harvesting that can be sustained.

Keywords: matrix models, density-dependence, harvesting, tropical trees, population dynamics

This abstract is being presented at: 2:15 PM in session:
Oral Session #51: Disturbance Ecology: Harvesting, Grazing and Roads.