Assessing the effect of habitat fragmentation on population dynamics: An implicit modelling approach

To better understand the impact of habitat fragmentation on population dynamics at the landscape scale, we develop a model combining a spatially implicit landscape model, a multisite Leslie-type model and an implicit model of habitat fragmentation. The studied species (Abax parallelepipedus, Coleoptera: Carabidae) is a corridor forest insect sensitive to wood fragmentation. The population of A. parallelepipedus was divided into three stages and move in the landscape between four classes of elements: wood, lane bordered by two hedgerows, hedgerow and agricultural matrix. The landscape representation was supposed to be implicit and the four classes of elements were randomly distributed in space. The originality of this approach is that we fit the movement frequency between elements according to woodland forest fragmentation. When wood fragmentation increases, the movement process can be very frequent and the method of aggregation of variables allows us to simplify the analysis of the model. Outputs of the model include the asymptotic population growth rate, stable stage structure and asymptotic spatial distribution that allow comparison of the influence of different spatial scenarios of wood fragmentation on population dynamics. Our results indicate that a single large patch of wood is better than several small patches of wood for population viability, that hedgerows have negative effects on population viability but lanes border by two hedgerows have positive effects even if they are randomly distributed at the landscape scale. When wood fragmentation is important, hedgerows create a population drain in woods and individuals pass and die more frequently in agricultural matrix.