Palmer T M, Young T P, Stanton M L, Wenk E
Department of Environmental Horticulture and Graduate Group in Ecology, University of California, Davis, CA 95616, USA e-mail:
Department of Evolution and Ecology and Center for Population Biology, University of California, Davis, CA 95616, USA, , , , , , US.
Oecologia. 2000 May;123(3):425-435. doi: 10.1007/s004420051030.
In monospecific stands of Acacia drepanolobium in Laikipia, Kenya, virtually all but the smallest trees are occupied by one of four species of ants. Although trees are a limiting resource, all four ant species are maintained in this system. Three separate lines of evidence confirm a linear dominance hierarchy among these four ants: (1) experimentally staged conflicts, (2) natural transitions among 1773 tagged trees over a 6-month period, and (3) the average sizes of trees occupied by ants of different species. Short-term dynamics during a drying period reveal that many smaller trees (<1 m) occupied by dominant ants were subsequently abandoned, and that abandoned trees had grown more slowly than those that were not abandoned. Height growth increments over 6 months were generally independent of ant occupant, but increased with tree height. Among taller trees (>1 m), changes in ant occupation congruent with the dominance hierarchy (i.e., transitions from more subordinate ant species to more dominant ant species) occurred on trees that grew faster than average. In contrast, the (less frequent) changes in ant occupation "against" the direction of the dominance hierarchy occurred on trees that grew more slowly than average. Observed correlations between tree vigor and takeover direction suggest that colony growth of dominant ant species is either favored in more productive microhabitats, or that such colonies differentially seek out healthier trees for conquest. Colonies of dominant species may differentially abandon more slowly growing trees during (dry) periods of retrenchment, or suffer higher mortality on these trees. Subordinate ant species appear to move onto these abandoned trees and, to a lesser extent, colonize new recruits in the sapling class. These data reveal that within a simple linear dominance hierarchy, short-term variations exist that may reveal underlying mechanisms associated with coexistence.
在肯尼亚莱基皮亚的阿拉伯胶相思单物种林分中，几乎所有除最小的树之外的树木都被四种蚂蚁中的一种占据。尽管树木是一种有限的资源，但这四种蚂蚁物种都在这个系统中得以维持。三条独立的证据线证实了这四种蚂蚁之间存在线性优势等级制度：（1）实验性安排的冲突，（2）在6个月期间对1773棵标记树木的自然转变情况，以及（3）不同物种蚂蚁所占据树木的平均大小。干旱期的短期动态表明，许多被优势蚂蚁占据的较小树木（<1米）随后被遗弃，并且被遗弃的树木生长速度比未被遗弃的树木慢。6个月期间的树高生长增量通常与蚂蚁占据者无关，但随树高增加。在较高的树木（>1米）中，与优势等级制度一致的蚂蚁占据变化（即从从属程度较高的蚂蚁物种向优势程度较高的蚂蚁物种转变）发生在生长速度高于平均水平的树木上。相比之下，与优势等级制度方向“相反”的（较不频繁的）蚂蚁占据变化发生在生长速度低于平均水平的树木上。观察到的树木活力与接管方向之间的相关性表明，优势蚂蚁物种的蚁群生长要么在生产力更高的微生境中受到青睐，要么是这样的蚁群有差异地寻找更健康的树木进行占领。优势物种的蚁群在（干旱）收缩期可能有差异地遗弃生长较慢的树木，或者在这些树木上遭受更高的死亡率。从属蚂蚁物种似乎会迁移到这些被遗弃的树木上，并且在较小程度上在幼树类别中殖民新的树木。这些数据表明，在一个简单的线性优势等级制度中，存在短期变化，这些变化可能揭示与共存相关的潜在机制。
