局域种群的Allee效应和集合种群的同步性

Abstract

从包含Allee效应的局域种群出发,建立了耦合映像格子模型,即集合种群模型。通过分析和计算机模拟表明:(1)当局域种群受到Allee效应强度较大时,集合种群同步灭绝;(2)而当Allee效应强度相对较弱时,通过稳定局域种群动态(减少混沌)使得集合种群发生同步波动,而这种同步波动能够增加集合种群的灭绝风险;(3)斑块间的连接程度对集合种群同步波动的发生有很大的影响,适当的破碎化有利于集合种群的续存。全局迁移和Allee效应结合起来增加了集合种群同步波动的可能,从而增加集合种群的灭绝风险。这些结果对理解同步性的机理、利用同步机理来制定物种保护策略和害虫防治都有重要的意义。;A metapopulation describes a system of many small and extinction-prone fragmented local populations that are connected via migration. Spatial synchrony of oscillating populations has been observed in many ecological systems, and identifying its causes has attracted the interest of ecologists. Theory has shown that spatially autocorrelated environmental noise, dispersal, and trophic interactions are capable of producing spatial synchrony. Synchrony of a metapopulation has been shown to be detrimental to its persistence because all local populations may go extinct simultaneously.<br> Allee effects at the local population level and Allee-like effects at the metapopulation level are important topics in ecology and conservation. Allee effects result in the existence of a threshold density below which the population goes extinct. At low density, fecundity may decrease while mortality may increase because of a range of factors including difficulties in finding mates, social dysfunction and inbreeding depression. These demographic changes lead to negative population growth rates and ultimately extinction. Many studies have demonstrated the potential importance of Allee effects for the dynamics of small populations, range expansion, community composition and biological invasion. It is widely accepted that Allee effects may increase the extinction risk of low density populations. However, insufficient attention has been paid to the relationship between metapopulation synchrony and Allee effects within local populations. By incorporating detailed information on dispersal strategy in a heterogeneous landscape, we were able to address the following questions: (1) how do Allee effects affect the synchrony of metapopulations? (2) Does the impact of the Allee effect depend on the dispersal strategy? In this paper, we begin by assuming that local populations experience Allee effects and construct a coupled map lattice model of connected local populations, i.e. a metapopulation model. A stability criterion for synchrony involving the Lyapunov number of the local population system, the frequency of dispersal and the network configuration matrix was obtained by Earn et al. We extend these ideas to the situation of a metapopulation comprising local populations subject to Allee effects. Using analysis and simulations, the results suggest that when the intensity of the Allee effect on local populations is strong, the metapopulation goes extinct; (2) when the intensity of the Allee effect on local populations is relatively weak, the local populations fluctuate in synchrony. In this latter case, the metapopulation persists, but the synchronous fluctuations of the local populations cause it to be more susceptible to environmental and demographic stochasticity, which increases metapopulation extinction risk; (3) the connectivity of the network has an important effect on metapopulation synchrony, and fragmented habitat is beneficial for metapopulation survival. Global migration combined with Allee effects increases the possibility of synchronous oscillation, and therefore enhances extinction risk of the metapopulation. As a result, when local populations are subject to Allee effects, the metapopulation quickly goes extinct or has a relatively high extinction risk. Allee effects have a deleterious effect on metapopulation persistence. These results may play an important role in understanding the mechanism underlying population synchrony as well as in developing conservation management plans and controlling the abundance of pest species.