Mécanismes d'extinction dans les petites populations – Extinction

The massive extinction of species and populations is a major concern today. To solve this crisis, we need conservation programs dedicated to the preservation of small populations that are particularly vulnerable. One method widely available to guide such conservation programs is Population Viability Analysis (PVA) – a tool relying on stochastic population theory to estimate the future size and risk of extinction for small populations. However, our understanding of the dynamics of small populations is quite limited and there is hardly any knowledge about the predictive ability of PVA. Here, we propose to challenge the predictive ability of PVA methods by linking population biological theory with experimental studies of extinction dynamics. Our overall aim is to gain better knowledge of the dynamics of small populations and the mechanisms leading to population extinction. We will investigate four key mechanisms of small populations' extinction, namely (1) population fluctuations caused by demographic stochasticity, (2) the Allee effect caused by sex ratio fluctuations, (2) genetic drift resulting from small population sizes and (4) habitat degradation. To do so, we will combine field experiments of extinction dynamics in small populations of the common lizard (Lacerta vivipara, a model non-endangered species) with stochastic population modelling. We will ask three main questions:· What are the critical determinants of population extinction? We will test the effects of demographic factors, genetic factors and habitat degradation on extinction dynamics. How much do individual traits contribute to the extinction risk? We will assess the degree of individual variation to portray the individual syndromes associated with extinction dynamics. We will also use this knowledge to implement stochastic population models that account for individual variation in life history, behavioural and genetic traits. What is the predictive ability of stochastic population models? We will test the predictive ability of standard PVA methods used by conservationists, as well as that of new models specifically designed for this project. Our field experiments will be conducted at the Research Centre for Experimental and Predictive Ecology (CEntre de Recherche en Ecologie Expérimentale et Prédictive, CEREP) where we will set up outdoor facilities for the manipulation of entire populations of the common lizard in the wild. To investigate the consequences of demographic stochasticity and the Allee effect, we will manipulate initial population size and the adult sex ratio. The influence of genetic drift will be tested with manipulative studies of migration in small populations. Finally, we will change habitat quality and investigate the interplay between genetic and environmental factors of population extinction. Our manipulative protocols will be combined with detailed assessments of individual behaviour (mate choice), physiology (hormonal stress and immunocompetence), life history traits (body growth, reproduction and survival) and genetic variation (heterozygosity, consanguinity and allelic diversity). In addition, we will conduct extensive PVA to quantify the extinction risks facing small populations of the common lizard. We will develop advanced models that aim at understanding how individual variation in life history, behavioural and genetic traits can affect the extinction risks of small populations. These models will be fitted with demographic parameters estimated from the field experiments.Our integrative approach will shed new lights on the dynamics of small populations and will also be critical to further advance theory in this field. Our results will provide timely tests of a central conservation and management tool, the Population Viability Analysis and thus contribute to bridge the gap between theory and practical conservation rules. We are confident that our collaborative effort will result in several significant contributions to the field of population dynamics and conservation biology, and will provide a step stone for a long-term collaborative work between the young researchers.