Department of Biology, University of Nevada, Reno, Nevada, USA.
Oecologia. 2013 Jan;171(1):153-62. doi: 10.1007/s00442-012-2402-0. Epub 2012 Jul 10.
Population dynamics are typically affected by a combination of density-independent and density-dependent factors, the latter of which have been conceptually and theoretically linked with how variable population sizes are over time-which in turn has been tied to how prone populations are to extinction. To address evidence for the occurrence of density dependence and its relationship with population size variability (pv), we quantified each of these for 126 populations of 8 species of Salmoniformes. Using random-effects models, we partitioned variation in the strength of density dependence and the magnitude of pv between and within species and estimated the correlation of density dependence and population size variability at both the between- and within-species levels. We found that variation in the strength of density dependence was predominately within species (I(2) = 0.12 [corrected] variation in population size variability was distributed both between and within species (I(2) = 0.40). Contrary to theoretical and conceptual expectations, the strength of density dependence and the magnitude of population size variability were positively correlated at the between species level (r = 0.90), although this estimate had 95 % credibility intervals (Bayesian analogues to confidence intervals) that overlapped zero. The within-species correlation between density dependence and population size variability was not distinguishable from zero. Given that density dependence for Salmoniformes was highly variable within species, we next determined the joint effects of intrinsic (density-dependent) and extrinsic (density-independent) factors on the population dynamics of a threatened salmonid, the Lahontan cutthroat trout (Oncorhynchus clarkii henshawi). We found that density-dependent and -independent factors additively contributed to population dynamics. This finding suggests that the observed within-species variability in density dependence might be attributable to local differences in the strength of density-independent factors.
种群动态通常受到密度独立因素和密度依赖因素的共同影响，后者在概念上和理论上与种群大小随时间的变化有关——这反过来又与种群灭绝的倾向有关。为了证明密度依赖性的发生及其与种群大小变异性（pv）的关系，我们对 8 种鲑形目物种的 126 个种群进行了量化。使用随机效应模型，我们在物种间和物种内分别划分了密度依赖性的强度和 pv 的幅度的变化，并估计了物种间和物种内水平上密度依赖性和种群大小变异性的相关性。我们发现，密度依赖性的强度变化主要是在物种内（I² = 0.12），而 pv 的幅度则分布在物种间和物种内（I² = 0.40）。与理论和概念预期相反，物种间水平上的密度依赖性强度和 pv 的幅度呈正相关（r = 0.90），尽管这一估计值的 95%可信度区间（置信区间的贝叶斯类似物）与零重叠。物种内密度依赖性和 pv 之间的相关性与零没有区别。鉴于鲑形目动物的密度依赖性在物种内高度可变，我们接下来确定了内在（密度依赖）和外在（密度独立）因素对受威胁的鲑鱼——拉洪坦截尾鳟（Oncorhynchus clarkii henshawi）种群动态的联合影响。我们发现，密度依赖和非密度依赖因素对种群动态有累加效应。这一发现表明，观察到的物种内密度依赖性的变异性可能归因于密度非依赖性因素的强度在局部的差异。
