MacNeil Calum, Dick J T A, Elwood Robert W
School of Biology and Biochemistry, M.B.C., The Queen's University of Belfast, Belfast BT9 7BL, N. Ireland, UK e-mail:
Oecologia. 2000 Jul;124(1):1-7. doi: 10.1007/PL00008864.
Physico-chemical regimes of river systems are major determinants of the distributions and relative abundances of macroinvertebrate taxa. Other factors, however, such as biotic interactions, may co-vary with changes in physico-chemistry and concomitant changes in community composition. Thus, direct cause and effect relationships may not always be established from field surveys. Equally, however, laboratory studies may suffer from lack of realism in extrapolation to the field. Here, we use balanced field transplantation experiments to elucidate the role of physico-chemical regime in determining the generally mutually exclusive distributions of two amphipod taxa, Gammarus (two species) and Crangonyx pseudogracilis. Within two river systems in Ireland, the former species dominate stretches of well oxygenated, high-quality water, whereas the latter dominates stretches of poorly oxygenated, low-quality water. G. pulex and G. duebeni celticus did not survive in bioassay tubes in areas dominated by C. pseudogracilis, which itself survived in tubes in such areas. However, both C. pseudogracilis and Gammarus spp. survived equally well in tubes in areas dominated by Gammarus spp. Physico-chemical regime thus limits the movement of Gammarus spp. into C. pseudogracilis areas, but some other factor excludes C. pseudogracilis from Gammarus spp. areas. Since previous laboratory experiments showed high predation rates of Gammarus spp. on C. pseudogracilis, we propose that predation by the former causes exclusion of the latter. Hence, presumed effects of physico-chemical regime on macroinvertebrate presence/abundance may often require experimental field testing and appreciation of alternative explanations.
河流系统的物理化学状况是大型无脊椎动物类群分布和相对丰度的主要决定因素。然而，其他因素，如生物相互作用，可能会随着物理化学变化以及群落组成的相应变化而共同变化。因此，实地调查不一定总能确定直接的因果关系。同样，实验室研究在推断到实地时可能缺乏现实性。在这里，我们使用平衡的实地移植实验来阐明物理化学状况在决定两种端足类动物（两种钩虾属物种和伪细钩虾）通常相互排斥的分布中所起的作用。在爱尔兰的两个河流系统中，前一种物种在含氧充足的优质水域占主导，而后一种物种在含氧不足的劣质水域占主导。在以伪细钩虾为主的区域，蚤状钩虾和凯尔特钩虾在生物测定管中无法存活，而伪细钩虾本身在这些区域的管中能够存活。然而，在以钩虾属物种为主的区域，伪细钩虾和钩虾属物种在管中存活情况相同。因此，物理化学状况限制了钩虾属物种向伪细钩虾区域的移动，但其他一些因素将伪细钩虾排除在钩虾属物种区域之外。由于先前的实验室实验表明钩虾属物种对伪细钩虾的捕食率很高，我们认为前者的捕食导致了后者的排除。因此，物理化学状况对大型无脊椎动物存在/丰度的假定影响通常需要进行实地实验测试，并考虑其他解释。
