EVOLDEM · Evolutionary Consequences of Demographic Perturbations in Plant Populations: A Theoretical Study

Final Activity Report Summary - EVOLDEM (Evolutionary Consequences of Demographic Perturbations in Plant Populations: A Theoretical Study.)

The genetic consequences of landscape alterations are a central concern in plant conservation biology. Both the FP6 thematic priority 'Sustainable Development, Global Change and Ecosystems' and the EU 6th Community Environment Action Programme explicitly encourage action to investigate the interaction between genetic resources and human activities, including the development of modelling and forecasting tools. This project aimed at developing a predictive model of evolution in plant populations subject to demographic perturbation. The main objectives were to explore how demographic heterogeneities (such as local density variation in space and local density fluctuations in time) may affect the processes effective gene dispersal and spatial genetic structuring of a plant population, relative to those expected in a uniform ideal distribution. We also aimed at testing a common method, commonly used by population geneticists and molecular ecologists, to estimate demographic and dispersal parameters from spatial genetic structure data. To achieve these goals, we developed a versatile simulation platform that allows investigating demo-genetic interactions for a small plant population with fluctuating demography in a dynamic landscape. The user of this computer application can adjust the value of several input variables: mean census population size and density, range and shape of the seed and pollen dispersal distributions, the proportion of favourable habitat, the degree of spatial aggregation and temporal change of the landscape, the number of neutral loci, the number of alleles/loci and the mutation rate. Output parameters include the effective dispersal rate (measuring how effectively genes spread in space across generations), the effective population density (measuring the inequality in reproductive performance among individual plants), and the spatial coordinates and genotypes of all individuals in the population at any generation. Performing extensive simulations with this program, we found that spatial heterogeneities in local density may substantially restrict the effective dispersal of genes, increasing local inbreeding. Moreover, we found that anthropogenic habitat fragmentation and land usage could not only affect genetic processes of continuously distributed plants through a reduction of global density and an increase in local density variance, but also through a reduction in the movement of individuals across the landscape from generation to generation, which can enhance local relatedness and inbreeding. Our simulation study also showed that a common method to estimate effective population parameters from spatial genetic structure data is unbiased, even with important departures from the ideal demographic conditions assumed to develop that method. Finally, our simulation platform will allow further developments to investigate the process of local adaptation, and the accumulation of deleterious mutations, in a plant population subject to demographic perturbations.

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