Estación Biológica de Doñana, CSIC, Seville, Spain.
Ecology. 2010 Nov;91(11):3312-21. doi: 10.1890/09-1520.1.
Intraspecific competition is a pervasive phenomenon with important ecological and evolutionary consequences, yet its effect in natural populations remains controversial. Although numerous studies suggest that in many cases populations across all organisms are limited by density-dependent processes, this conclusion often relies on correlative data. Here, using an experimental approach, we examined the effect of intraspecific competition on population regulation of the ant Aphaenogaster senilis. In this species females are philopatric while males disperse by flying over relatively long distances. All colonies were removed from 15 experimental plots, except for one focal colony in each plot, while 15 other plots remained unmanipulated. After the first reproductive season, nest density in the experimental plots returned to a level nonsignificantly different from that in the control plots, which was not expected if the populations were indeed regulated by density-independent phenomena. In both the control plots and the experimental plots colonies remained overdispersed throughout the experiment, suggesting colony mutual exclusion. Nests outside the plots rapidly extended their foraging span, but we did not detect any significant inward migration into the experimental plots. Experimental reduction in density did not significantly affect the focal colonies' biomass, measured just before the first reproductive season. However, the ratio of males to workers-pupae biomasses was smaller in experimental plots, suggesting that colonies there had redirected part of the resources normally allocated to male production to the production instead of new workers. Microsatellite analysis indicated that, after the reproductive season, many colonies in the experimental plots were headed by a young queen that was the mother of the brood but not of the old workers, indicating that reduction in colony density stimulated fission of the remaining colonies. Finally, at the end of the experiment, 14 months after experimental reduction in density, colonies that derived from fission were smaller in the experimental than in the control plots, suggesting that the former had undergone fission at a smaller size than in control plots, which presumably allowed them to colonize the emptied areas. We conclude that colonies adjust resource allocation and colony fission to the degree of intraspecific competition.
种内竞争是一种普遍存在的现象，具有重要的生态和进化后果，但它在自然种群中的影响仍存在争议。尽管许多研究表明，在许多情况下，所有生物的种群都受到密度依赖过程的限制，但这一结论往往依赖于相关性数据。在这里，我们使用实验方法研究了种内竞争对蚂蚁 Aphaenogaster senilis 种群调节的影响。在这个物种中，雌性是亲代的，而雄性则通过飞行长距离来扩散。所有的殖民地都从 15 个实验区中移除，除了每个区中的一个焦点殖民地外，而 15 个其他的区仍然未受干扰。在第一个繁殖季节之后，实验区的巢密度回到了与对照区无显著差异的水平，如果种群确实受到与密度无关的现象调节，这是不应该的。在对照区和实验区，殖民地在整个实验过程中仍然表现出过度分散，这表明了殖民地之间的相互排斥。在实验区之外，巢迅速扩大了它们的觅食范围，但我们没有检测到任何明显的向内迁徙到实验区的情况。实验减少密度并没有显著影响焦点殖民地的生物量，就在第一个繁殖季节之前测量。然而，在实验区，雄性与工蚁-蛹生物量的比例较小，这表明那里的殖民地将原本用于雄虫生产的部分资源重新分配给了新的工蚁的生产。微卫星分析表明，在繁殖季节之后，实验区的许多殖民地由一个年轻的女王领导，她是幼虫的母亲，但不是老工蚁的母亲，这表明殖民地密度的降低刺激了剩余殖民地的分裂。最后，在实验结束时，即密度降低后的 14 个月，来自分裂的殖民地在实验区比在对照区更小，这表明前者在较小的规模上发生了分裂，这可能使它们能够占领空出的区域。我们的结论是，殖民地会根据种内竞争的程度来调整资源分配和殖民地分裂。
