Holt Robert D, Barfield Michael, Gonzalez Andrew
Department of Zoology, 223 Bartram Hall, P.O. Box 118525, University of Florida, Gainesville, FL 32611-8525, USA.
Theor Popul Biol. 2003 Nov;64(3):315-30. doi: 10.1016/s0040-5809(03)00087-x.
Ecological communities are typically open to the immigration and emigration of individuals, and also variable through time. In this paper we argue that interesting and potentially important effects arise when one splices together spatial fluxes and temporal variability. The particular system we examine is a sink habitat, where a species faces deterministic extinction but is rescued by recurrent immigration. We have shown, using a simple extension of the canonical exponential growth model in a time-varying environment, that variation "inflates" the average abundance of sink populations. We can analytically quantify the magnitude of this effect in several special cases (square-wave temporal variation and Gaussian stochastic variation). The inflationary effect can be large in "intermittent" sinks (where there are periods with positive growth), and when temporal variation is strongly autocorrelated. The effect appears to be robust to incorporation of demographic stochasticity (due to discrete birth-death-immigration processes), and to direct density dependence. With discrete generations, however, one can observe a wide range of effects of temporal variation, including depression as well as inflation. We argue that the inflationary effect of temporal variation in sink habitats can have important implications for community structure, because it can increase the average abundance (and hence local impacts) of species that on average are being excluded from a local community. We illustrate the latter effect using a familiar model of exploitative competition for a single limiting resource. We demonstrate that temporal variation can reverse local competitive dominance, even to the extent of allowing an inferior competitor maintained by immigration to exclude a competing species that would be locally superior in a constant environment.
生态群落通常对个体的迁入和迁出开放，并且也随时间变化。在本文中，我们认为当将空间通量和时间变异性结合在一起时，会产生有趣且可能重要的影响。我们所研究的特定系统是一个汇生境，在其中一个物种面临确定性灭绝，但通过反复迁入得以拯救。我们已经表明，在时变环境中使用经典指数增长模型的简单扩展，变异性会“放大”汇种群的平均丰度。我们可以在几种特殊情况下（方波时间变化和高斯随机变化）分析量化这种效应的大小。在“间歇性”汇（存在正增长时期）以及时间变化具有强烈自相关性时，放大效应可能很大。该效应似乎对纳入人口统计学随机性（由于离散的出生 - 死亡 - 迁入过程）以及直接密度依赖性具有鲁棒性。然而，对于离散世代，人们可以观察到时间变化的广泛影响，包括抑制以及放大。我们认为汇生境中时间变化的放大效应可能对群落结构具有重要意义，因为它可以增加平均而言正被排除在当地群落之外的物种的平均丰度（从而增加局部影响）。我们使用一个熟悉的单一限制资源的剥削性竞争模型来说明后一种效应。我们证明时间变化可以逆转局部竞争优势，甚至达到允许通过迁入维持的劣势竞争者排除在恒定环境中在当地会占优势的竞争物种的程度。
