Jacobson Bailey, Grant James W A, Peres-Neto Pedro R
Département des Sciences Biologiques, Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville, Montréal, QC, H3C3P8, Canada.
Department of Biology, Concordia University, 1455 de Maisonneuve Blvd. West, Montréal, QC, H3G1M8, Canada.
J Anim Ecol. 2015 Jul;84(4):934-42. doi: 10.1111/1365-2656.12365. Epub 2015 Apr 6.
How individuals within a population distribute themselves across resource patches of varying quality has been an important focus of ecological theory. The ideal free distribution predicts equal fitness amongst individuals in a 1 : 1 ratio with resources, whereas resource defence theory predicts different degrees of monopolization (fitness variance) as a function of temporal and spatial resource clumping and population density. One overlooked landscape characteristic is the spatial distribution of resource patches, altering the equitability of resource accessibility and thereby the effective number of competitors. While much work has investigated the influence of morphology on competitive ability for different resource types, less is known regarding the phenotypic characteristics conferring relative ability for a single resource type, particularly when exploitative competition predominates. Here we used young-of-the-year rainbow trout (Oncorhynchus mykiss) to test whether and how the spatial distribution of resource patches and population density interact to influence the level and variance of individual growth, as well as if functional morphology relates to competitive ability. Feeding trials were conducted within stream channels under three spatial distributions of nine resource patches (distributed, semi-clumped and clumped) at two density levels (9 and 27 individuals). Average trial growth was greater in high-density treatments with no effect of resource distribution. Within-trial growth variance had opposite patterns across resource distributions. Here, variance decreased at low-population, but increased at high-population densities as patches became increasingly clumped as the result of changes in the levels of interference vs. exploitative competition. Within-trial growth was related to both pre- and post-trial morphology where competitive individuals were those with traits associated with swimming capacity and efficiency: larger heads/bodies/caudal fins and less angled pectoral fins. The different degrees of within-population growth variance at the same density level found here, as a function of spatial resource distribution, provide an explanation for the inconsistencies in within-site growth variance and population regulation often noted with regard to density dependence in natural landscapes.
种群中的个体如何在不同质量的资源斑块间分布，一直是生态理论的重要关注点。理想自由分布预测个体间的适合度与资源呈1:1的比例相等，而资源防御理论则预测，作为时间和空间资源聚集以及种群密度的函数，会出现不同程度的垄断（适合度差异）。一个被忽视的景观特征是资源斑块的空间分布，它会改变资源可获取性的公平性，进而影响有效竞争者的数量。虽然有很多研究探讨了形态对不同资源类型竞争能力的影响，但对于赋予单一资源类型相对能力的表型特征，尤其是在剥削性竞争占主导时，我们了解得较少。在这里，我们使用当年幼体虹鳟（Oncorhynchus mykiss）来测试资源斑块的空间分布和种群密度如何相互作用，以影响个体生长的水平和差异，以及功能形态是否与竞争能力相关。在溪流河道内进行摄食试验，设置了九个资源斑块的三种空间分布（分散、半聚集和聚集）以及两个密度水平（9只和27只个体）。高密度处理下的平均试验生长更大，且不受资源分布的影响。试验内生长差异在不同资源分布中有相反的模式。在这里，在低种群密度时差异减小，但在高种群密度时随着斑块因干扰与剥削性竞争水平的变化而变得越来越聚集，差异增加。试验内生长与试验前和试验后的形态都有关，具有竞争能力的个体具有与游泳能力和效率相关的特征：头部/身体/尾鳍更大，胸鳍角度更小。这里在相同密度水平下发现的种群内生长差异程度不同，作为空间资源分布的函数，为自然景观中常提到的密度依赖性下的位点内生长差异和种群调节的不一致性提供了解释。
