PubMed Health⌕ Search

Biomedical subjects

John Vandermeer

Publications and source records attributed to John Vandermeer.

6 recordsLinked to original sources
PubMed2006

A keystone mutualism drives pattern in a power function.

Data that can be described by a power function are ubiquitous in nature. Although there is consensus that such data frequently emerge generally from nonlinear complex systems, a variety of specific mechanisms may be responsible for creating the pattern in particular cases. Here, we report on the distribution of a scale insect (Coccus viridis) that is a common agricultural pest. Its distribution in an organic coffee farm in southern Mexico generally follows a power function, but there are subtle deviations from that function. We offer a biological explanation for both adherence to the power functions and associated deviations, along with supporting evidence.

Animals↗
PubMed2006

Effects of predation pressure on species packing on a resource gradient: insights from nonlinear dynamics.

The classical case of three competitors arranged on a resource gradient such that the central competitor will be excluded due to competition from the other two is studied from the point of view of the effects of added predators. The basic formulation is motivated by a desire to understand the effects of asymmetries in multidimensional Lotka-Volterra systems. We first study the effects of perfectly specialist predators and find a rich collection of possible behaviors of the system including (1) extinction of all predators and subsequent extinction of the subordinate competitor, (2) dominant competitors and their predators coexist but the subdominant competitor goes extinct, (3) all species except the predator of the subordinate competitor coexist in coordinated phase-reversed chaos, (4) exclusion of one or more species occurs through an expanding heteroclinic cycle, and (5) all species coexist in an uncoordinated chaos. We then study the effects of five qualitatively distinct forms of polyphagy. In one case, corresponding to the well-known vulnerability to predation versus competitive ability trade-off, it is possible to have the subordinate competitor be the only survivor in the system. The other three cases of polyphagy lead to distortions in the basic pattern seen in the previously analyzed specialist case. Studying this case of ecologically motivated asymmetries in the basic Lotka-Volterra formulation is a step in the direction of fully understanding interacting populations.

Animals↗
PubMed2005

Omnivory and the stability of food webs.

The ecological concept of omnivory, feeding at more than a single trophic level, is formulated as an intermediate stage between any two of three classical three-dimensional species interaction systems-tritrophic chain, competition, and polyphagy. It is shown that omnivory may be either stabilizing or destabilizing, depending, in part, on the conditions of the parent systems from which it derives. It is further conjectured that the tritrophic to competition gradient cannot be entirely stable, that there must be an instability at some level of intermediate omnivory.

Animals↗
PubMed2004

Coupled oscillations in food webs: balancing competition and mutualism in simple ecological models.

As in other oscillating systems, oscillations of consumer resource pairs in ecological systems may be coupled such that complex behavior results. The form of that coupling may determine the nature and extent of this behavior. Two biologically significant forms of coupling are here investigated: first, where consumers consume each other's resources (CR coupling, representing competition between the two consumers), and second, where the resources are in competition with one another (RR coupling, potentially representing indirect mutualism between the two consumers). Interestingly, CR coupling leads to in-phase synchrony of the oscillations, whereas RR coupling leads to antiphase synchrony. With either form of coupling, if the coupling remains weak, synchronous behavior is generated in the two systems. At strong levels of coupling, when the two forms act simultaneously, a balance between competition and mutualism is generated, which is manifest differently at different levels of resource coupling.

Animals↗
PubMed2004

Enigmatic biodiversity correlations: ant diversity responds to diverse resources.

A pattern noted in ecology is that diversity at one level begets diversity at other levels. In the case of consumers competing for similar resources, the diversity of those resources is thought to provide some degree of niche diversification in which a diverse set of consumer species can coexist. If, however, the diverse resources are not sufficiently distinct from one another, from the standpoint of the consumer species, such niche diversification will not exist. We experimentally show that a diverse array of twigs attracted 80% more species of twig-nesting ants than a monospecific collection of twigs. The specific tree species from which the twigs were derived did not explain the pattern. It appears that diversity per se at one level (twigs) creates conditions that promote diversity at another level (nesting ants).

Animals↗