Department of Biology, University of the South 735 University Ave, Sewanee, Tennessee, 37383.
School of Natural Resources and the Environment, University of Michigan 440 Church St., Ann Arbor, Michigan, 48109.
Ecol Evol. 2014 Aug;4(16):3201-9. doi: 10.1002/ece3.1161. Epub 2014 Jul 23.
Interactions among members of biological communities can create spatial patterns that effectively generate habitat heterogeneity for other members in the community, and this heterogeneity might be crucial for their persistence. For example, stage-dependent vulnerability of a predatory lady beetle to aggression of the ant, Azteca instabilis, creates two habitat types that are utilized differently by the immature and adult life stages of the beetle. Due to a mutualistic association between A. instabilis and the hemipteran Coccus viridis - which is A. orbigera main prey in the area - only plants around ant nests have high C. viridis populations. Here, we report on a series of surveys at three different scales aimed at detecting how the presence and clustered distribution of ant nests affect the distribution of the different life stages of this predatory lady beetle in a coffee farm in Chiapas, Mexico. Both beetle adults and larvae were more abundant in areas with ant nests, but adults were restricted to the peripheries of highest ant activity and outside the reach of coffee bushes containing the highest densities of lady beetle larvae. The abundance of adult beetles located around trees with ants increased with the size of the ant nest clusters but the relationship is not significant for larvae. Thus, we suggest that A. orbigera undergoes an ontogenetic niche shift, not through shifting prey species, but through stage-specific vulnerability differences against a competitor that renders areas of abundant prey populations inaccessible for adults but not for larvae. Together with evidence presented elsewhere, this study shows how an important predator is not only dependent on the existence of two qualitatively distinct habitat types, but also on the spatial distribution of these habitats. We suggest that this dependency arises due to the different responses that the predator's life stages have to this emergent spatial pattern.
生物群落成员之间的相互作用可以创造出有效的栖息地异质性，为群落中的其他成员提供生存环境，这种异质性对于它们的生存可能至关重要。例如，捕食性瓢虫对蚂蚁 Azteca instabilis 的攻击的阶段依赖性脆弱性，创造了两种生境类型，这些生境类型被瓢虫的幼虫和成虫阶段不同地利用。由于 A. instabilis 和半翅目昆虫 Coccus viridis 之间的互利关系——这是该地区 A. orbigera 的主要猎物——只有在蚂蚁巢周围的植物上才有高浓度的 C. viridis。在这里，我们报告了一系列在三个不同尺度上的调查，旨在检测蚂蚁巢的存在和聚集分布如何影响这种捕食性瓢虫在墨西哥恰帕斯州一个咖啡农场的不同生命阶段的分布。成虫和幼虫在有蚂蚁的地方都更为丰富，但成虫仅限于蚂蚁活动最活跃的外围，以及咖啡丛中幼虫密度最高的地方。有蚂蚁的树木周围成年甲虫的数量随着蚁巢集群的大小而增加，但对于幼虫来说，这种关系并不显著。因此，我们认为 A. orbigera 经历了一个个体发育生态位的转变，不是通过改变猎物物种，而是通过对一种竞争物种的特定脆弱性差异，使丰富的猎物种群区域对成虫不可达，但对幼虫可达。结合其他地方提出的证据，本研究表明，一种重要的捕食者不仅依赖于两种性质上截然不同的生境类型的存在，还依赖于这些生境的空间分布。我们认为，这种依赖性是由于捕食者的不同生命阶段对这种新兴的空间模式的不同反应引起的。
