Bevers M, Flather C H
Rocky Mountain Research Station, USDA Forest Service, 240 West Prospect Road, Fort Collins, Colorado, 80526, USA.
Theor Popul Biol. 1999 Feb;55(1):61-76. doi: 10.1006/tpbi.1998.1392.
We examine habitat size, shape, and arrangement effects on populations using a discrete reaction-diffusion model. Diffusion is modeled passively and applied to a cellular grid of territories forming a coupled map lattice. Dispersal mortality is proportional to the amount of nonhabitat and fully occupied habitat surrounding a given cell, with distance decay. After verifying that our model produces the results expected for single patches of uniform habitat, we investigate heterogeneous and fragmented model landscapes. In heterogeneous single-patch systems near critical patch size, populations approach Gaussian spatial distributions with total population constrained by the capacity of the most limiting cell. In fragmented habitat landscapes, threshold effects are more complex and parametrically sensitive. The results from our experiments suggest the following: the ability to achieve persistence in hyperdispersed patchy habitats by adding similarly fragmented patches requires meeting threshold reproduction rates; persistent metapopulations in which no local population is individually persistent appear when dispersal distances and reproduction rates are both high, but only within narrow parameter ranges that are close to extinction thresholds; successful use of stepping-stone patches to support metapopulation systems appears unlikely for passively diffusing species; elongated patches offer early colonization advantages, but blocky patches offer greater population resilience near extinction thresholds. A common theme running through our findings is that population viability estimates may depend on our ability to determine when population and habitat systems are approaching extinction threshold conditions.
我们使用离散反应扩散模型研究栖息地大小、形状和布局对种群的影响。扩散被被动建模并应用于形成耦合映射格的领地细胞网格。扩散死亡率与给定细胞周围的非栖息地和完全被占据的栖息地数量成正比，并存在距离衰减。在验证我们的模型产生了均匀栖息地单一斑块预期的结果后，我们研究了异质和破碎的模型景观。在接近临界斑块大小的异质单斑块系统中，种群接近高斯空间分布，总种群受最具限制性细胞容量的限制。在破碎的栖息地景观中，阈值效应更复杂且对参数敏感。我们实验的结果表明：通过添加类似破碎的斑块在超分散斑块状栖息地中实现持久性的能力需要达到阈值繁殖率；当扩散距离和繁殖率都很高，但仅在接近灭绝阈值的狭窄参数范围内时，会出现没有局部种群单独持久的持久集合种群；对于被动扩散的物种，似乎不太可能成功使用踏脚石斑块来支持集合种群系统；细长斑块提供早期定殖优势，但块状斑块在接近灭绝阈值时提供更大的种群恢复力。贯穿我们研究结果的一个共同主题是，种群生存力估计可能取决于我们确定种群和栖息地系统何时接近灭绝阈值条件的能力。
