Biomedical subjects

J Bascompte

Publications and source records attributed to J Bascompte.

5 recordsLinked to original sources

PubMed2001

Aggregate statistical measures and metapopulation dynamics.

There are two main types of metapopulation models. Spatially implicit models are analytically tractable but neglect spatial heterogeneities. Spatially explicit models are more realistic but too complex. In this paper, I build a bridge between both approximations. I derive a new metapopulation model using a well-known technique in population genetics. Spatial heterogeneities are captured by an aggregate statistical measure of spatial correlation. When this correlation is zero, i.e., space is homogeneous, the model becomes the well-known Levins' model. As spatial correlation increases, equilibrium patch occupancy decreases from what would be expected under the spatially homogeneous assumption. I proceed by testing how well spatial complexities from a spatially explicit simulation can be encapsulated by such an aggregate statistical measure.

Animals↗

PubMed2000

Self-disturbance as a source of spatiotemporal heterogeneity: the case of the tallgrass prairie.

Tallgrass prairies are characterized by high levels of litter production, which has a profound effect on live biomass. Litter introduces a delayed inhibition of biomass growth, generating nonlinear dynamics and chaos. In this paper, we study a model of biomass-litter interaction, and focus on the litter persistence rate. The observed dynamics depends largely on this rate of year-to-year persistence. Different scenarios are explored and discussed. A spatially extended counterpart of such a model is later on introduced to account for the effects of space. Temporal chaos introduces spatial heterogeneity in terms of gaps where the current year biomass is almost zero. Such gaps can be colonized by fugitive species. The inhibitory effect of litter on biomass is thus an important source of intrinsic, small-scale heterogeneities that may promote diversity. On the other hand, the huge amounts of litter produced by the competitive dominants in tallgrass prairies enhance the probability of fires. Fires benefit, rather than depress, the superior competitive species. This fact explains why the intermediate disturbance hypothesis (IDH) stating that the highest diversity levels should be observed at intermediate disturbance frequencies, does not work in these communities. We define self-disturbances as small-scale disturbances affecting the growth and survival of the individuals that have generated them (e.g. due to the effects of the litter mass they produce). In the absence of other disturbances, self-disturbances can induce high heterogeneity and diversity levels in tallgrass prairies. We discuss the general implications of self-generated disturbances for landscape heterogeneity and diversity of communities in which the main external perturbations benefit the dominant species.

Biomass↗

PubMed1998

Effects of habitat destruction in a prey-predator metapopulation model

A mean field, metapopulation model of a predator-prey interaction is developed in order to understand the consequences of habitate destruction at different trophic levels. Such a model allows is to explore different ecological scenarios (donor control vs. top-down control) by changing a single parameter. The response to habitat destruction is qualitatively the same for both predator and prey, although there are interesting differences linked to the trophic position. A similar decrease in the colonization rates affects the two species quite differently. Predators diminish faster than prey, and furthermore, the fraction of occupied sites decreases more sharply as colonization rates are lowered, i.e. there is a nonlinear relationship between regional abundance and colonization rate. There is a well-defined threshold in the colonization rate below which the predator becomes extinct. Thus, dispersal rate is critical for predicting the consequences of habitat destruction. Finally, these results are compared with the behavior of a spatially explicit simulation. The only difference between the analytical model and the simulation is that colonization is no longer a global phenomenon in the latter, but it is a local process, constrained to the nearest patches. The bulk of the results are similar to the mean field behavior, and we comment on some differences related with non-homogeneity and real space. Some general implications for conservation biology and biological control are outlined. Copyright 1998 Academic Press

Journal Article↗

PubMed1998

Eradication thresholds in epidemiology, conservation biology and genetics.

A simple model has been used to describe metapopulation dynamics, the spread of an infectious disease, and the dynamics of transposable elements (TEs). This suggests underlying common dynamics despite the different nature of the systems. Eradication thresholds are derived from the common model and they are interpreted for each system. TEs have been viewed as intragenomic parasites. Thus, some ideas derived from epidemiology, and in particular the existence of such eradication thresholds, can be used to explain some evolutionary puzzles such as the strange distribution of TE families within the phylogeny of host species.

Animals↗

PubMed1996

Are critical phenomena relevant to large-scale evolution?

Recent theoretical studies, based on the theory of self-organized critical systems, seem to suggest that the dynamical patterns of macroevolution could belong to such class of critical phenomena. Two basic approaches have been proposed: the Kauffman-Johnsen model (based on the use of coupled fitness landscapes) and the Bak-Sneppen model. Both are reviewed here. These models are oversimplified pictures of biological evolution, but the (possible) validity of them is based on the concept of universality, i.e. that apparently very different systems sharing some few common properties should also behave in a very similar way. In this paper we explore the current evidence from the fossil record, showing that some properties that are suggestive of critical dynamics would also be the result of random phenomema. Some general properties of the large-scale pattern of evolution, which should be reproduced by these models, are discussed.

Biological Evolution↗