Li Kevin, Vandermeer John H, Perfecto Ivette
School of Natural Resources and the Environment , University of Michigan , Dana Samuel Trask Building, 440 Church Street, Ann Arbor, MI 48109 , USA.
Department of Ecology and Evolutionary Biology , University of Michigan , Kraus Natural Science Building, 830 North University, Ann Arbor, MI 48109 , USA.
R Soc Open Sci. 2016 May 25;3(5):160073. doi: 10.1098/rsos.160073. eCollection 2016 May.
Spatial patterns in ecology can be described as reflective of environmental heterogeneity (exogenous), or emergent from dynamic relationships between interacting species (endogenous), but few empirical studies focus on the combination. The spatial distribution of the nests of Azteca sericeasur, a keystone tropical arboreal ant, is thought to form endogenous spatial patterns among the shade trees of a coffee plantation through self-regulating interactions with controlling agents (i.e. natural enemies). Using inhomogeneous point process models, we found evidence for both types of processes in the spatial distribution of A. sericeasur. Each year's nest distribution was determined mainly by a density-dependent relationship with the previous year's lagged nest density; but using a novel application of a Thomas cluster process to account for the effects of nest clustering, we found that nest distribution also correlated significantly with tree density in the later years of the study. This coincided with the initiation of agricultural intensification and tree felling on the coffee farm. The emergence of this significant exogenous effect, along with the changing character of the density-dependent effect of lagged nest density, provides clues to the mechanism behind a unique phenomenon observed in the plot, that of an increase in nest population despite resource limitation in nest sites. Our results have implications in coffee agroecological management, as this system provides important biocontrol ecosystem services. Further research is needed, however, to understand the effective scales at which these relationships occur.
生态学中的空间格局可以被描述为反映环境异质性（外源性），或者是由相互作用物种之间的动态关系产生的（内源性），但很少有实证研究关注这两者的结合。阿兹特卡丝光蚁是热带地区关键的树栖蚂蚁，其巢穴的空间分布被认为是通过与控制因素（即天敌）的自我调节相互作用，在咖啡种植园的遮荫树之间形成内源性空间格局。使用非齐次点过程模型，我们在阿兹特卡丝光蚁的空间分布中发现了这两种过程的证据。每年的巢穴分布主要由与上一年滞后巢穴密度的密度依赖关系决定；但通过对托马斯聚类过程的新颖应用来考虑巢穴聚类的影响，我们发现巢穴分布在研究后期也与树木密度显著相关。这与咖啡农场农业集约化和树木砍伐的开始相吻合。这种显著的外源性效应的出现，以及滞后巢穴密度的密度依赖效应特征的变化，为该地块观察到的一个独特现象背后的机制提供了线索，即尽管巢穴地点资源有限，但巢穴数量仍增加。我们的结果对咖啡农业生态管理具有启示意义，因为这个系统提供了重要的生物防治生态系统服务。然而，需要进一步研究以了解这些关系发生的有效尺度。
