Rand Tatyana A
Department of Ecology and Evolutionary Biology, Brown University, Providence, RI, 02912, USA.
Oecologia. 2002 Aug;132(4):549-558. doi: 10.1007/s00442-002-0989-2. Epub 2002 Aug 1.
Herbivore damage and impact on plants often varies spatially across environmental gradients. Although such variation has been hypothesized to influence plant distribution, few quantitative evaluations exist. In this study I evaluated patterns of insect herbivory on an annual forb, Atriplex patula var. hastata, across a salt marsh tidal gradient, and performed experiments to examine potential causes and consequences of variation in herbivory. Damage to plants was generally twice as great at mid-tidal elevations, which are more frequently inundated, than at higher, less stressful, elevations at five of six surveyed sites. Field herbivore assays and herbivore preference experiments eliminated the hypothesis that plant damage was mediated by herbivore response to differences in host plants across the gradient. Alternately, greater herbivore densities in the mid-marsh, where densities of an alternate host plant (Salicornia europaea) were high, were associated with greater levels of herbivory on Atriplex, suggesting spillover effects. The effect of insect herbivores on host plant performance varied between the two sites studied more intensively. Where overall herbivore damage to plants was low, herbivory had no detectable effect on plant survival or seed production, and plant performance did not significantly differ between zones. However, where herbivore damage was high, herbivores dramatically reduced both plant survival (>50%) and fruit production (40-70%), and their effects were stronger in the harsher mid-marsh than the high marsh. Thus herbivores likely play a role in maintaining lower Atriplex densities in mid-marsh. Overall, these results suggest that variation in herbivore pressure can be an important determinant of patterns of plant abundance across environmental gradients.
食草动物对植物的损害及其影响在空间上往往会随着环境梯度而变化。尽管有假设认为这种变化会影响植物分布，但定量评估却很少。在本研究中，我评估了一年生草本植物戟叶滨藜（Atriplex patula var. hastata）在盐沼潮汐梯度上的昆虫食草模式，并进行了实验以探究食草作用变化的潜在原因和后果。在六个被调查地点中的五个，植物受到的损害在潮汐中等高度处（此处更频繁被淹没）通常是较高、压力较小高度处的两倍。田间食草动物测定和食草动物偏好实验排除了植物损害是由食草动物对梯度上寄主植物差异的反应介导的这一假设。相反，在中潮带，替代寄主植物欧洲海蓬子（Salicornia europaea）密度较高，食草动物密度也更大，这与戟叶滨藜上更高水平的食草作用相关，表明存在溢出效应。在所更深入研究的两个地点，昆虫食草动物对寄主植物表现的影响有所不同。在植物总体受到的食草动物损害较低的地方，食草作用对植物存活或种子产量没有可检测到的影响，不同区域的植物表现也没有显著差异。然而，在食草动物损害较高的地方，食草动物显著降低了植物存活率（超过50%）和果实产量（40 - 70%），并且它们在更恶劣的中潮带比高潮带的影响更强。因此，食草动物可能在维持中潮带较低的戟叶滨藜密度方面发挥作用。总体而言，这些结果表明食草动物压力的变化可能是环境梯度上植物丰度模式的一个重要决定因素。
