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John Vandermeer

Publications and source records attributed to John Vandermeer.

8 recordsLinked to original sources
arXiv2023

The ghost of ecology in chaos, combining intransitive and higher order effects

Historically, musings about the structure of ecological communities has revolved around the structure of pairwise interactions, competition, predation, mutualism, etc. . . Recently a growing literature acknowledges that the baseline assumption that the pair of species is not necessarily the metaphorical molecule of community ecology, and that certain structures containing three or more species may not be usefully divisible into pairwise components. Two examples are intransitive competition (species A dominates species B dominates species C dominates species A), and nonlinear higher-order effects. While these two processes have been discussed extensively, the explicit analysis of how the two of them behave when simultaneously part of the same dynamic system has not yet appeared in the literature. A concrete situation exists on coffee farms in Puerto Rico in which three ant species, at least on some farms, form an intransitive competitive triplet, and that triplet is strongly influenced, nonlinearly, by a fly parasitoid that modifies the competitive ability of one of the species in the triplet. Using this arrangement as a template we explore the dynamical consequences with a simple ODE model. Results are complicated and include include alternative periodic and chaotic attractors. The qualitative structures of those complications, however, may be retrieved easily from a reflection on the basic natural history of the system.

q-bio.PE↗
arXiv2021

The interplay of extinction and synchrony in the dynamics of metapopulation formation

The idea of a metapopulation has become canonical in ecology. Its original mean field form provides the important intuition that migration and extinction interact to determine the dynamics of a population composed of subpopulations. From its conception, it has been evident that the very essence of the metapopulation paradigm centers on the process of local extinction. We note that there are two qualitatively distinct types of extinction, gradual and catastrophic, and explore their impact on the dynamics of metapopulation formation using discrete iterative maps. First, by modifying the classic logistic map with the addition of the Allee effect, we show that catastrophic local extinctions in subpopulations are a pre-requisite of metapopulation formation. When subpopulations experience gradual extinction, increased migration rates force synchrony and drive the metapopulation below the Allee point resulting in migration induced destabilization of the system across parameter space. Second, a sawtooth map (an extension of the Bernoulli bit shift map) is employed to simultaneously explore the increasing and decreasing modes of population behavior. We conclude with four generalizations. 1. At low migration rates, a metapopulation may go extinct faster than completely unconnected subpopulations. 2. There exists a gradient between stable metapopulation formation and population synchrony, with critical transitions from no metapopulation to metapopulation to synchronization, the latter frequently inducing metapopulation extinction. 3. Synchronization patterns emerge through time, resulting in synchrony groups and chimeric populations existing simultaneously. 4. There are two distinct mechanisms of synchronization: i. extinction and rescue and, ii.) stretch reversals in a modification of the classic chaotic stretching and folding.

q-bio.PE↗
arXiv2020

New forms of structure in ecosystems revealed with the Kuramoto model

Ecological systems, as is often noted, are complex. Equally notable is the generalization that complex systems tend to be oscillatory, whether Huygens simple patterns of pendulum entrainment or the twisted chaotic orbits of Lorenz convection rolls. The analytics of oscillators may thus provide insight into the structure of ecological systems. One of the most popular analytical tools for such study is the Kuramoto model of coupled oscillators. Using a well-studied system of pests and their enemies in an agroecosystem, we apply this model as a stylized vision of the dynamics of that real system, to ask whether its actual natural history is reflected in the dynamics of the qualitatively instantiated Kuramoto model. Emerging from the model is a series of synchrony groups generally corresponding to subnetworks of the natural system, with an overlying chimeric structure, depending on the strength of the inter-oscillator coupling. We conclude that the Kuramoto model presents a novel window through which interesting questions about the structure of ecological systems may emerge.

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arXiv2018

Some elementary mechanisms for critical transitions and hysteresis in simple predator prey models

Trait-mediated indirect effects are increasingly acknowledged as important components in the dynamics of ecological systems. The hamiltonian form of the LV equations is traditionally modified by adding density dependence to the prey variable and functional response to the predator variable. Enriching these non-linear elements with a trait-mediation added to the carrying capacity of the prey creates the dynamics of critical transitions and hysteretic zones.

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arXiv2015

Local dynamics of the coffee rust disease and the potential effect of shade

In this paper we present a mode that incorporates two levels of dynamic structuring of the coffee rust disease (caused by the rust fungus, Hemileia vastatrix). First, two distinct spatial scales of transmission dynamics are interrogated with respect to the resultant structure of catastrophic transitions of epidemics. Second the effect of management style, especially the well-known issue of shade management, is added to the base-line model. The final structure includes a simple one-to-one functional structure of disease incidence as a function as well as a classical critical transition structure, and finally a hysteretic loop. These qualitative structures accord well with the recent history of the coffee rust disease.

q-bio.PE↗
arXiv2015

Some complications of the elementary forms of competition in a source/sink and metacommunity context: the role of intranstive loops

Dynamic interspecific interactions are thought to contribute to fundamental structures of ecological communities. Using the Yodzis framework of dominance control versus founder control versus niche control, the importance of intransitive loops in sub-communities in a source/sink or metacommunity competition context is examined. It is found that a three-species sub-community sampled from a species pool composed of nothing but dominance controlled species pairs can result in a stable three species coexistence. It is shown that if effect and response competition are balanced, the overall sub-community will be persistent, anchored by one or more intransitive loops. It is proposed that such an arrangement be referred to as an intransitive structure. It is concluded that persistence of a sub-community (when species pairs in the species pool are all dominance controlled) of more than three species is possible only if it has an intransitive structure.

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arXiv2014

The interaction of regional and local in the dynamics of the coffee rust disease

A simple mean field model is proposed that captures the two scales of dynamic processes involved in the spread of the coffee rust disease. At a local level the state variable is the fraction of coffee plants on an average farm that are infested with the disease and at the regional level the state variable is the fraction of farms that are infested with the disease. These two levels are interactive with one another in obvious ways, producing qualitatively interesting results. Specifically there are three distinct outcomes: disease disappears, disease is potentially persistent, and disease is inevitably persistent. The basic structure of the model generates the potential for tipping point behavior due to the presence of a blue sky bifurcation, suggesting that the emergence of epizootics of the disease may be unpredictable.

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