SEEM EVOLUTION / John Silander / Ven. 13 déc. à 11:30 ISEM

Silander_lgJohn Silander ((University of Connecticut)
Going beyond correlative biogeography –using integral projection models to build demographically driven species distribution models: proteas of South Africa.

Abstract: Knowledge of species’ geographic distributions is critical for understanding and forecasting population dynamics, responses to environmental change, biodiversity patterns and the impacts of conservation plans.  While many descriptive, correlative occurrence models have been used to these ends, progress lies in understanding the underlying population biology processes that generate patterns of species range dynamics. Here, we show how using a limited amount of demographic data with integral projection models can yield informative, Demographically Driven Distribution Models (DDDMs). By modeling survival, growth, and fecundity in a regression context, integral projection models can interpolate across missing vital rates data and environmental conditions. DDDMs have a number of strengths: (1) they allow a mechanistic understanding of the demographic processes that generate spatial occurrence patterns; (2) this mechanistic understanding enables prediction of spatial and temporal variation in local population dynamics, (3) they can predict a variety of population statistics including  population growth rates, sensitivities/elasticities, stage passage times, reproductive values, etc.; and (4) they allow for more robust extrapolation under altered environmental conditions (e.g., changing fire regimes and climates). To illustrate these features, we constructed DDDMs for Protea repens a common, iconic perennial shrub widespread across the Cape Floristic Region of South Africa. We use both occurrence and abundance data to validate predictions of population growth rates. We find that the species’ persistence depends most strongly on adult survival rates. Since the species lacks a persistent soil seed bank, the main threat to future persistence of the species in most areas appears to be recurrence of fire before adults become senescent. While the models project higher population growth rates in the core of the range under projected climate for 2050, they also suggest that the species faces a threat at the arid interior margin of its range from the interaction of more frequent fire and drying climate. The models also indicate a critical dependence of different vital rates on environmental gradients – including adult survival dependence on rainfall, and interannual growth dependence on summer soil moisture. This points to the need for targeted, additional sampling along these environmental gradients to iteratively achieve refined model projections.

Vendredi 13 décembre 2013, 11:30 – 12:30
Salle Louis Thaler, ISEM, UM2, Bât. 22, 2ème étage

Contact : Ophélie Ronce

Séminaire d’Ecologie et Evolution