1. General Model Information

Name: Prey flux in predator-prey dynamics

Acronym: PREY_FLUX


Main medium: all
Main subject: population dynamics, agriculture
Organization level: Population, Ecosystem
Type of model: ordinary differential equations
Main application: research, decision support/expert system
Keywords: extinction threshold, functional response, Lotka-Volterra, open system

Contact:

Dr C. Patrick Doncaster
School of Biological Sciences,
University of Southampton,
Bassett Crescent East, Southampton SO16 7PX, UK

Phone: +44 (0)23 80594352
Fax: +44 (0)23 80594269
email: cpd@soton.ac.uk
Homepage: http://www.soton.ac.uk/~cpd/

Author(s):

Kent, A., Doncaster, C. P., Sluckin, T.

Abstract:

The size of a population can be augmented by enriching the carrying capacity of its limiting resource, or by subsidising the renewal of the resource. The well known paradox of enrichment models the first case, in which enrichment can force consumers and their limiting resource into destabilising limit cycles, whereas impoverishment stabilises the dynamics. We model the case of resource subsidy, where the resource is a limiting prey to predators. In contrast to enrichment, the system is stabilised by an influx of prey in the form of a rescue effect, and destabilised by an outflux of prey in the form of an Allee effect. Limit cycles are not sustained by the Allee effect; instead both populations collapse to zero over a large region of the predator-prey phase plane. The catastrophic extinction of prey requires the presence of both an Allee effect on prey and a predator with a type II functional response, though neither needs to contribute a large impact to prey dynamics. The novel implication is that consumers exaggerate the impact of Allee effects on a renewing resource. Conversely, an Allee effect in the form of a cull of resource, even of small value, can trigger local extinction of resource-dependent consumers.


II. Technical Information

II.1 Executables:

Operating System(s): Microsoft Windows

II.2 Source-code:

Programming Language(s): Mathcad 2000
cpd@soton.ac.uk

II.3 Manuals:

cpd@soton.ac.uk

II.4 Data:

This is a data-free model, but example values for constants are given figure legends of Kent, A., Doncaster, C. P., Sluckin, T. (In press).

III. Mathematical Information


III.1 Mathematics

Scaling of model and linear stability analysis are provided in appendices to Kent, A., Doncaster, C. P., Sluckin, T. (In press).


III.2 Quantities

s: non-dimensionalised prey abundance. n: non-dimensionalised predator abundance.


III.2.1 Input

D: intrinsic prey flux into (+ve) or out of (-ve) a prey population. C: ratio of intrinsic search to handling tim of each prey by each predator. sigma: predator's relative marginal subsistence demand for prey. v: conversion ratio of consumed prey into new predator biomass.

III.2.2 Output


IV. References

Rosenzweig, M.L., 1971. Paradox of enrichment: destabilization of exploitation ecosystems in ecological time. Science 171, 385-387.
Kent, A., Doncaster, C. P., Sluckin, T. (In press) Consequences for predators of rescue and Allee effects on prey. Ecological Modelling.


V. Further information in the World-Wide-Web


VI. Additional remarks

This develops Rosenzweig's (1971) 'paradox of enrichment'. It is intended as a conceptual aid to understanding how the presence of predators can exaggerate the effects of resource fluxes and Allee/rescue effects on the dynamic stability of prey.
Last review of this document by: Mon Sep 9 14:38:18 2002
Status of the document: Contributed by C. Patrick Doncastrer
last modified by Joachim Benz Wed Sep 18 15:03:02 CEST 2002

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