Balance of terror: an alternative mechanism for competitive trade-offs and its implications for invading species

Journal ArticleThis article uses models to propose an explanation for three observations in community ecology: the apparent overreaction of prey to attack by specialist predators, the existence of a common trade-off among components of competitive ability in communities of unrelated competitors, and the ability of invading species to break the native trade-off. Strategies that increase resource collection ability are assumed to increase vulnerability to attack by specialist consumers according to a vulnerability function

Migration alone can produce persistence of host-parasitoid models

Journal ArticleIt has long been recognized that the unstable equilibrium of a single-patch predator-prey model cannot be stabilized by diffusive coupling with identical patches, since the coupled system acts exactly like the single-patch system if the patches are synchronized (Maynard Smith 1974; Allen 1975; Reeve 1988). Persistence of coupled locally unstable systems depends on the maintenance of asynchrony among the populations sufficient to buffer crashes (den Boer 1968; Allen 1975; Crowley 1981; Reeve 1988, 1990; Taylor 1988)

Effects of intraspecific density-dependence on species richness and species abundance distributions

ManuscriptAbstract Species richness and patterns of abundance result from the interplay between niche differences, realized as intraspecific density-dependence (IDD), and so-called neutral processes that arise when species fitnesses are similar. This paper presents an extension of neutral models that incorporates delays in IDD that could result from resource-mediated competition or through a pathogen pool. These delays reduce standing species richness and qualitatively change the shape of species abundance distributions and render them consistent with the hollow curve shape even in the presence of strong IDD

Construction of multidimensional clustered patterns

Journal ArticleEcological processes often depend upon the patterning, as well as the absolute density, of resources. In this paper, we develop methods for describing pattern from the perspective of the organism encountering and exploiting the resources, and for reconstructing pattern from the description

Use of strain typing data to estimate bacterial transmission rates in healthcare settings

Journal ArticleOBJECTIVE: To create an affordable and accurate method for continuously monitoring bacterial transmission rates in healthcare settings. DESIGN: We present a discrete simulation model that relies on the relationship between in-hospital transmission rates and strain diversity. We also present a proof of concept application of this model to a prospective molecular epidemiology data set to estimate transmission rates for Pseudomonas aeruginosa and Staphylococcus aureus. SETTING: Inpatient units of an academic referral center. PATIENTS: All inpatients with nosocomial infections. INTERVENTION: Mathematical model to estimate transmission rates. RESULTS: Maximum likelihood estimates for transmission rates of these two species on different hospital units ranged from 0 to 0.36 transmission event per colonized patient per day. CONCLUSIONS: This approach is feasible, although estimates of transmission rates based solely on strain typed clinical cultures may be too imprecise for routine use in infection control. A modest level of surveillance sampling substantially improves the estimation accuracy (Infect Control Hosp Epidemiol 2005;26:638-645)

Optimal tempo and defence for consumers of multiple resources

Journal ArticleEcological models of behaviour are typically based on the assumption that decisions can be evaluated with a single resource currency. Here we present models that predict the tactics of consumers collecting two nutritionally distinct resources: fuel that is used for activity and food used for growth (F4G). Both models assume that foragers seek to maximize F4G gain subject to collecting enough fuel for activity

Defended fortresses or moving targets? Another model of inducible defenses inspired by military metaphors

Journal ArticleWe use a common framework to compare three models of plant strategies to confront herbivory: constitutive defense, optimal inducible defense, and the "moving target." Plants with constitutive defenses retain a fixed defensive phenotype. Plants with optimal inducible defenses respond to attack by increasing defenses. Plants following the moving target strategy respond to attack by altering phenotype

Stochasticity, complex spatial structure, and the feasibility of the shifting balance theory

Journal ArticleSewall Wright's shifting balance theory of evolution posits a mechanism by which a structured population may escape local fitness optima and find a global optimum. We examine a one-locus, two-allele model of underdominance in populations with differing spatial arrangements of demes, both analytically and with Monte Carlo simulations

A time since recovery model with varying rates of loss of immunity

pre-printFor many infectious diseases, immunity wanes over time. The majority of SIRS models assume that this loss of immunity takes place at a constant rate. We study temporary immunity within a SIRS model structure if the rate of loss of immunity can depend on the time since recovery from disease.We determine the conditions under which the endemic steady state becomes unstable and periodic oscillations set in, showing that a fairly rapid change between slow and rapid immunity loss is necessary to produce oscillations

Aggregation and stability in parasite-host models

Journal ArticleThis paper generalizes the two-dimensional approximation of models of macroparasites on homogeneous populations developed by Anderson & May (1978), focusing on how the dispersion (the variance to mean ratio) of the equilibrium distribution of parasites on hosts is related to the stability of the equilibrium. We show in the approximate system that the equilibrium is stabilized not by aggregation, but by dispersion which increases as a function of the mean. Computer simulations indicate, however, that this analysis fails to capture properly the dynamics of the full system, raising the question of whether any two-dimensional system could produce an adequate approximation. We discuss the relevance of our results to several empirical studies which have examined the relation of dispersion to the mean