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

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)

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

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

Use of lung transplantation survival models to refine patient selection in cystic fibrosis

Journal ArticleLung transplantation in cystic fibrosis may improve survival for patients with low 5-year predicted survival. Identifying characteristics that affect post-transplantation survival may improve patient selection and survival benefit. Using Cystic Fibrosis Foundation Patient Registry and United Network for Organ Sharing data, we identified 845 lung transplant recipients from 1991-2001, and 12,826 control patients from 1997. We used Cox proportional hazards models to identify variables that influence post-transplantation survival

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

Departure time versus departure rate: how to forage optimally when you are stupid

Journal ArticleForagers unable to leave a patch at the optimal moment must act as constrained foragers. Extending the results of Houston and McNamara (1985), we compare a blundering forager that leaves patches at a constant rate with an unconstrained optimal forager that leaves patches at the optimal time

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