School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia.
Ecol Appl. 2012 Jan;22(1):311-21. doi: 10.1890/11-0952.1.
Two important processes determining the dynamics of spatially structured populations are dispersal and the spatial covariance of demographic fluctuations. Spatially explicit approaches to conservation, such as reserve networks, must consider the tension between these two processes and reach a balance between distances near enough to maintain connectivity, but far enough to benefit from risk spreading. Here, we model this trade-off. We show how two measures of metapopulation persistence depend on the shape of the dispersal kernel and the shape of the distance decay in demographic covariance, and we consider the implications of this trade-off for reserve spacing. The relative rates of distance decay in dispersal and demographic covariance determine whether the long-run metapopulation growth rate, and quasi-extinction risk, peak for adjacent patches or intermediately spaced patches; two local maxima in metapopulation persistence are also possible. When dispersal itself fluctuates over time, the trade-off changes. Temporal variation in mean distance that propagules are dispersed (i.e., propagule advection) decreases metapopulation persistence and decreases the likelihood that persistence will peak for adjacent patches. Conversely, variation in diffusion (the extent of random spread around mean dispersal) increases metapopulation persistence overall and causes it to peak at shorter inter-patch distances. Thus, failure to consider temporal variation in dispersal processes increases the risk that reserve spacings will fail to meet the objective of ensuring metapopulation persistence. This study identifies two phenomena that receive relatively little attention in empirical work on reserve spacing, but that can qualitatively change the effectiveness of reserve spacing strategies: (1) the functional form of the distance decay in covariance among patch-specific demographic rates and (2) temporal variation in the shape of the dispersal kernel. The sensitivity of metapopulation recovery and persistence to how covariance of vital rates decreases with distance suggests that estimating the shape of this function is likely to be as important for effective reserve design as estimating connectivity. Similarly, because temporal variation in dispersal dynamics influences the effect of reserve spacing, approaches to reserve design that ignore such variation, and rely instead on long-term average dispersal patterns, are likely to lead to lower metapopulation viability than is actually achievable.
两个决定空间结构种群动态的重要过程是扩散和人口统计波动的空间协方差。保护的空间明确方法，如保护区网络，必须考虑这两个过程之间的紧张关系，并在足够近以维持连通性的距离和足够远以受益于风险传播之间取得平衡。在这里，我们模拟这种权衡。我们展示了两种衡量复群持久性的方法如何取决于扩散核的形状和人口统计协方差中距离衰减的形状，并且我们考虑了这种权衡对保护区间距的影响。扩散和人口统计协方差中距离衰减的相对速率决定了长期复群增长率和准灭绝风险是否在相邻斑块或中等间隔斑块中达到峰值；复群持久性也可能存在两个局部最大值。当扩散本身随时间波动时，权衡会发生变化。传播体传播的平均距离的时间变化（即传播体平流）会降低复群的持久性，并降低相邻斑块达到峰值的可能性。相反，扩散的变化（围绕平均扩散的随机扩散程度）会增加整体复群的持久性，并使其在较短的斑块间距离处达到峰值。因此，如果不考虑扩散过程中的时间变化，就会增加保护区间距无法满足确保复群持久性的目标的风险。本研究确定了两个在保护区间距实证研究中相对较少受到关注的现象，但它们可能会定性地改变保护区间距策略的有效性：（1）斑块特定人口统计率协方差中距离衰减的功能形式，以及（2）扩散核形状的时间变化。关键率协方差随距离减小的功能形式对复群恢复和持久性的敏感性表明，估计该函数的形状对于有效的保护区设计可能与估计连通性一样重要。同样，由于扩散动态的时间变化会影响保护区间距的效果，因此忽略这种变化并依赖长期平均扩散模式的保护区设计方法可能会导致低于实际可行的复群生存能力。
