Blundell Arthur G, Peart David R
Department of Biology, Dartmouth College, Hanover, NH 03755, USA e-mail:
Oecologia. 1998 Nov;117(1-2):151-160. doi: 10.1007/s004420050643.
We assessed density- and distance-dependence in herbivore effects and juvenile condition for four species of Shorea, the most speciose genus in the dominant canopy family of southeast Asian rain forest trees (Dipterocarpaceae). Herbivore damage was quantified as partial leaf loss on young leaves, and whole plant foliar condition as the product of the fraction of leaf nodes containing leaves and the fraction of tissue remaining on extant leaves. Adults of the four species were centers of high total, as well as conspecific, density of juveniles (<1 m tall). For two species, S. hopeifolia and S. pinanga, herbivore damage declined significantly with distance, decreasing by 40% and 51% respectively, between 5 m and 35 m from the parent. For the same two species, foliar condition improved significantly between 5 m and 35 m, increasing by 45% for S. hopeifolia and 24% for S. pinanga. If foliar condition influences juvenile survival and growth, more widely dispersed seeds of these species are more likely to recruit to the canopy. In contrast, there was no significant distance-dependence for S. parvifolia or S. longisperma. Among species, herbivore damage was greatest in those species with greatest local juvenile abundances, i.e., those with highest densities, leaf size, juvenile foliar mass and/ or foliar mass/m ground area, but was unrelated to the toughness of mature leaves. However, distance was a better predictor of herbivore damage than was conspecific juvenile density, as evaluated by backward elimination regressions, for both S. hopeifolia and S. pinanga. For foliar condition, the best predictor was distance for S. pinanga, but conspecific density for S. hopeifolia, whose juveniles were smallest and occurred at the highest densities. Total juvenile density (all woody plants) was eliminated as a factor in all cases. The species-specificity of effects (i.e., their dependence on conspecific distance or density), together with the marked differences among congeneric species, caution against generalizations regarding distance-dependent effects in diverse forests.
我们评估了东南亚雨林树木优势冠层科（龙脑香科）中种类最多的属——娑罗双属四种植物的食草动物影响和幼树状况的密度依赖性和距离依赖性。食草动物造成的损害以幼叶上的部分叶片损失来量化，而整株植物的叶片状况则是含有叶片的叶节点比例与现存叶片上剩余组织比例的乘积。这四个物种的成年树是幼树（<1米高）总密度以及同种密度较高的中心。对于其中两个物种，即霍氏娑罗双和矮桫椤，食草动物造成的损害随距离显著下降，从距母树5米到35米之间分别下降了40%和51%。对于同样的两个物种，叶片状况在5米到35米之间显著改善，霍氏娑罗双增加了45%，矮桫椤增加了24%。如果叶片状况影响幼树的存活和生长，那么这些物种更广泛传播的种子更有可能进入冠层。相比之下，小叶娑罗双或长籽娑罗双没有显著的距离依赖性。在物种之间，食草动物造成的损害在当地幼树数量最多的物种中最大，即那些密度、叶片大小、幼树叶片质量和/或叶片质量/地面面积最高的物种，但与成熟叶片的韧性无关。然而，通过向后逐步回归分析评估，对于霍氏娑罗双和矮桫椤来说，距离比同种幼树密度是食草动物损害的更好预测指标。对于叶片状况，矮桫椤的最佳预测指标是距离，而霍氏娑罗双的是同种密度，其幼树最小且密度最高。在所有情况下，总幼树密度（所有木本植物）都被排除为一个因素。效应的物种特异性（即它们对同种距离或密度的依赖性），以及同属物种之间的显著差异，警示我们不要对不同森林中距离依赖性效应进行一概而论。
