Ryti Randall T, Case Ted J
Department of Biology, C-016, University of California, San Diego, 92093, La Jolla, CA, USA.
Oecologia. 1986 Jun;69(3):446-453. doi: 10.1007/BF00377067.
The nest locations of two ant species in the Colorado Desert are intraspecifically overdispersed. Intraspecific overdispersion has been thought to represent strong intraspecific competition. Here we consider this hypothesis along with three competing hypotheses: microhabitat selection by foundress queens, predation on foundress queens, and predation on established colonies. To test these hypotheses five types of data were collected: (1) the forager population sizes of Veromessor pergandei and Pogonomyrmex californicus, (2) the response of the territory use of V. pergandei to varying levels of food, (3) the encounter rates of conspecifics and other ant species to foundress queens artificially placed near and far from conspecific colonies, (4) predation on colonies as a function of colony spacing, and (5) the relationship between the plant microhabitat at the nest and colony spacing. The results show that established colonies have no apparent selectivity for a particular type of plant microhabitat nor do foundress queens show avoidance or attraction toward conspecifics. V. pergandei workers show only a slight ability to find V. pergandei queens that are artificially placed near their entrances. Certain spiders are the most common ant predators on our study area. Direct observations on spiders indicate that colonies with closer neighbors are not prone to a higher risk of predation. In addition, the estimates of the death rate of workers from a mark-recapture technique indicate that colonies with closer neighbors lose similar numbers of workers as compared to colonies with further neighbors. In favor of the competition hypothesis, the summed size of intraspecific nearest neighbor pairs are larger for colonies that are spaced further apart than those colonies that are spaced closer together. We also develop an index of foraging directionality for the column foraging species V. pergandei. Using this measure, we find that nearest neighbors tend to avoid foraging toward each other. The response of territory use to food levels was tested with experiments involving patches of cracked wheat. These experiments showed that patches away from nearest neighbors were found significantly sooner than patches toward nearest neighbors. The above five sets of data together suggest that resource competition and perhaps queen predation by established colonies account for the intraspecific spatial patterns of these species.
科罗拉多沙漠中两种蚂蚁的巢穴位置在种内呈过度分散分布。种内过度分散被认为代表着强烈的种内竞争。在此，我们探讨这一假设以及其他三种相互竞争的假设：蚁后对微生境的选择、对蚁后的捕食以及对已建立蚁群的捕食。为了检验这些假设，我们收集了五类数据：（1）佩氏纹蚁和加州收获蚁的觅食蚁群规模；（2）佩氏纹蚁的领地利用对不同食物水平的反应；（3）同种个体及其他蚁种与人工放置在同种蚁群附近和远处的蚁后的相遇率；（4）蚁群被捕食情况与蚁群间距的函数关系；（5）巢穴处植物微生境与蚁群间距之间的关系。结果表明，已建立的蚁群对特定类型的植物微生境没有明显的选择性，蚁后对同种个体也没有表现出回避或吸引。佩氏纹蚁的工蚁找到人工放置在其巢穴入口附近的佩氏纹蚁蚁后的能力很弱。某些蜘蛛是我们研究区域内最常见的蚂蚁捕食者。对蜘蛛的直接观察表明，邻居更近的蚁群并不更容易遭受更高的被捕食风险。此外，通过标记重捕技术对工蚁死亡率的估计表明，邻居更近的蚁群与邻居更远的蚁群损失的工蚁数量相近。支持竞争假设的是，种内最近邻对的总规模在间距更远的蚁群中比间距更近的蚁群更大。我们还为行纵队觅食的佩氏纹蚁开发了一种觅食方向性指数。通过这个指标，我们发现最近邻倾向于避免相互朝着对方觅食。利用涉及碎小麦片的实验测试了领地利用对食物水平的反应。这些实验表明，远离最近邻的碎片比朝着最近邻的碎片被发现的时间要早得多。上述五组数据共同表明，资源竞争以及可能已建立蚁群对蚁后的捕食导致了这些物种的种内空间模式。
