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Biomedical subjects

D J Earn

Publications and source records attributed to D J Earn.

6 recordsLinked to original sources
PubMed2000

Coherence and conservation.

A principal aim of current conservation policy is to reduce the impact of habitat fragmentation. Conservation corridors may achieve this goal by facilitating movement among isolated patches, but there is a risk that increased connectivity could synchronize local population fluctuations (causing coherent oscillations) and thereby increase the danger of global extinction. We identify general conditions under which populations can or cannot undergo coherent oscillations, and we relate these conditions to local and global extinction probabilities. We suggest a simple method to explore the potential success of conservation corridors and, more generally, any manipulations of dispersal patterns that aim to protect threatened species or control pests.

Animals↗
PubMed2000

A simple model for complex dynamical transitions in epidemics.

Dramatic changes in patterns of epidemics have been observed throughout this century. For childhood infectious diseases such as measles, the major transitions are between regular cycles and irregular, possibly chaotic epidemics, and from regionally synchronized oscillations to complex, spatially incoherent epidemics. A simple model can explain both kinds of transitions as the consequences of changes in birth and vaccination rates. Measles is a natural ecological system that exhibits different dynamical transitions at different times and places, yet all of these transitions can be predicted as bifurcations of a single nonlinear model.

Baltimore↗
PubMed1999

Opposite patterns of synchrony in sympatric disease metapopulations.

Measles epidemics in UK cities, which were regular and highly synchronous before vaccination, are known to have become irregular and spatially uncorrelated in the vaccine era. Whooping cough shows the reverse pattern, namely a shift from spatial incoherence and irregularity before vaccination to regular, synchronous epidemics afterward. Models show that these patterns can arise from disease-specific responses to dynamical noise. This analysis has implications for vaccination strategies and illustrates the power of comparative dynamical studies of sympatric metapopulations.

Bordetella pertussis↗
PubMed1998

Population dynamic interference among childhood diseases.

Epidemiologists usually study the interaction between a host population and one parasitic infection. However, different parasite species effectively compete, in an ecological sense, for the same finite group of susceptible hosts, so there may be an indirect effect on the population dynamics of one disease due to epidemics of another. In human populations, recovery from any serious infection is normally preceded by a period of convalescence, during which infected individuals stay at home and are effectively shielded from exposure to other infectious diseases. We present a model for the dynamics of two infectious diseases, incorporating a temporary removal of susceptibles. We use this model to explore population-level consequences of a temporary insusceptibility in childhood diseases, the dynamics of which are partly driven by differences in contact rates in and out of school terms. Significant population dynamic interference is predicted and cannot be dismissed in the limited case-study data available for measles and whooping cough in England before the vaccination era.

Child↗
PubMed1998

Persistence, chaos and synchrony in ecology and epidemiology.

The decline of species in natural habitats concerns ecologists, who view extinction as a danger and conservation of biological diversity as a goal. In contrast, the proliferation of 'undesirable' species is the principal concern of epidemiologists, who view persistence as a problem and eradication as an achievement. While ecologists and epidemiologists have essentially opposite goals, the mathematical structure of the population dynamics that they study is very similar. We briefly review the similarities and differences between these two fields, emphasizing recent work in both areas on the effects of spatial synchrony and dynamical chaos. We hope to stimulate further cross-fertilization of ideas between the disciplines.

Animals↗