Huntsman Brock M, Petty J Todd
Division of Forestry and Natural Resources, West Virginia University, Morgantown, West Virginia, United States of America.
PLoS One. 2014 Mar 11;9(3):e91673. doi: 10.1371/journal.pone.0091673. eCollection 2014.
Spatial population models predict strong density-dependence and relatively stable population dynamics near the core of a species' distribution with increasing variance and importance of density-independent processes operating towards the population periphery. Using a 10-year data set and an information-theoretic approach, we tested a series of candidate models considering density-dependent and density-independent controls on brook trout population dynamics across a core-periphery distribution gradient within a central Appalachian watershed. We sampled seven sub-populations with study sites ranging in drainage area from 1.3-60 km(2) and long-term average densities ranging from 0.335-0.006 trout/m. Modeled response variables included per capita population growth rate of young-of-the-year, adult, and total brook trout. We also quantified a stock-recruitment relationship for the headwater population and coefficients of variability in mean trout density for all sub-populations over time. Density-dependent regulation was prevalent throughout the study area regardless of stream size. However, density-independent temperature models carried substantial weight and likely reflect the effect of year-to-year variability in water temperature on trout dispersal between cold tributaries and warm main stems. Estimated adult carrying capacities decreased exponentially with increasing stream size from 0.24 trout/m in headwaters to 0.005 trout/m in the main stem. Finally, temporal variance in brook trout population size was lowest in the high-density headwater population, tended to peak in mid-sized streams and declined slightly in the largest streams with the lowest densities. Our results provide support for the hypothesis that local density-dependent processes have a strong control on brook trout dynamics across the entire distribution gradient. However, the mechanisms of regulation likely shift from competition for limited food and space in headwater streams to competition for thermal refugia in larger main stems. It also is likely that source-sink dynamics and dispersal from small headwater habitats may partially influence brook trout population dynamics in the main stem.
空间种群模型预测，在物种分布核心区域附近存在强烈的密度依赖性以及相对稳定的种群动态，而随着向种群边缘发展，密度独立过程的方差和重要性会增加。利用一个为期10年的数据集和信息论方法，我们测试了一系列候选模型，这些模型考虑了在阿巴拉契亚中部流域内核心 - 边缘分布梯度上溪红点鲑种群动态的密度依赖性和密度独立性控制。我们对七个亚种群进行了采样，研究地点的流域面积从1.3 - 60平方千米不等，长期平均密度从0.335 - 0.006条鲑鱼/平方米。建模的响应变量包括当年幼鱼、成鱼和溪红点鲑总数的人均种群增长率。我们还量化了源头种群的补充量与亲体数量关系，以及所有亚种群随时间的平均鲑鱼密度变化系数。无论溪流大小，密度依赖性调节在整个研究区域都很普遍。然而，密度独立的温度模型具有相当的权重，这可能反映了水温逐年变化对鲑鱼在寒冷支流和温暖干流之间扩散的影响。估计的成年鲑鱼承载能力随着溪流大小的增加呈指数下降，从源头的0.24条鲑鱼/平方米降至干流的0.005条鲑鱼/平方米。最后，溪红点鲑种群数量的时间方差在高密度的源头种群中最低，在中型溪流中趋于峰值，而在密度最低的最大溪流中略有下降。我们的结果支持了这样一个假设，即局部密度依赖性过程对整个分布梯度上的溪红点鲑动态有很强的控制作用。然而，调节机制可能从源头溪流中对有限食物和空间的竞争转变为较大干流中对热避难所的竞争。小源头栖息地的源 - 汇动态和扩散也可能部分影响干流中的溪红点鲑种群动态。
