Silver P, Cooper J K, Palmer M A, Davis E J
School of Science and Penn State Behrend Center for Mathematical Biology, Penn State Erie, The Behrend College, Erie, PA 16563, USA e-mail:
Zoology Department, University of Maryland, College Park, MD 20742, USA, , , , , , US.
Oecologia. 2000 Aug;124(2):216-224. doi: 10.1007/s004420050009.
The spatial arrangement of resources in patchy habitats influences the distribution of individuals and their ability to acquire resources. We used Chironomus riparius, a ubiquitous aquatic insect that uses leaf particles as an important resource, to ask how the dispersion of resource patches influences the distribution and resource acquisition of mobile individuals in patchy landscapes. Two experiments were conducted in replicated laboratory landscapes (38×38 cm) created by arranging sand and leaf patches in a 5×5 grid so that the leaf patches were either aggregated or uniformly dispersed in the grid. One-day-old C. riparius larvae were introduced into the landscapes in one of three densities (low, medium, high). In experiment 1, we sampled larvae and pupae by coring each patch in each landscape 3, 6, 12, or 24 days after adding larvae. In experiment 2, emerging adults were collected daily for 42 days from each patch in each landscape. In aggregated landscapes, individuals were aggregated in one patch type or the other during a particular developmental stage, but the "preferred" type changed depending on developmental stage and initial density. Adult emergence was lower by about 30% in all aggregated landscapes. In dispersed landscapes, individuals used both types of patch throughout their life cycles at all initial densities. Thus, patch arrangement influences the distribution of mobile individuals in landscapes, and it influences resource acquisition even when average resource abundance is identical among landscapes. Regardless of patch arrangement, high initial density caused accumulation of early instars in edge patches, 75% mortality of early instars, a 25% increase in development time, and a 60% reduction in adult emergence. Because mortality was extremely high among early-instar larvae in high-density treatments, we do not have direct evidence that the mechanism by which patch arrangement operates is density dependent. However, the results of our experiments strongly suggest that dispersion of resource patches across a landscape reduces local densities by making non-resource patches available for use, thereby reducing intraspecific competition.
斑块状栖息地中资源的空间布局会影响个体的分布及其获取资源的能力。我们利用摇蚊（Chironomus riparius），一种常见的水生昆虫，它将叶片颗粒作为重要资源，来探究资源斑块的分散如何影响斑块状景观中移动个体的分布和资源获取。在通过将沙子和叶片斑块以5×5网格形式排列而创建的重复实验室景观（38×38厘米）中进行了两项实验，使得叶片斑块在网格中要么聚集要么均匀分散。将一日龄的摇蚊幼虫以三种密度（低、中、高）之一引入景观中。在实验1中，在添加幼虫后的3、6、12或24天，通过对每个景观中的每个斑块进行取芯来对幼虫和蛹进行采样。在实验2中，在42天内每天从每个景观中的每个斑块收集羽化的成虫。在聚集景观中，个体在特定发育阶段聚集在一种或另一种斑块类型中，但“偏好”的类型会根据发育阶段和初始密度而变化。在所有聚集景观中，成虫羽化率降低了约30%。在分散景观中，个体在所有初始密度下的整个生命周期中都使用两种类型的斑块。因此，斑块布局会影响景观中移动个体的分布，并且即使景观之间的平均资源丰度相同，它也会影响资源获取。无论斑块布局如何，高初始密度都会导致早期龄期个体在边缘斑块中积累、早期龄期个体75%的死亡率、发育时间增加25%以及成虫羽化率降低60%。由于在高密度处理中早期龄期幼虫的死亡率极高，我们没有直接证据表明斑块布局起作用的机制是密度依赖性的。然而，我们的实验结果强烈表明，资源斑块在景观中的分散通过使非资源斑块可供使用来降低局部密度，从而减少种内竞争。
