Takada Mayura, Baba Yuki G, Yanagi Yosuke, Terada Saeko, Miyashita Tadashi
Laboratory of Biodiversity Science, School of Agriculture and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
Environ Entomol. 2008 Aug;37(4):938-46. doi: 10.1603/0046-225x(2008)37[938:crowst]2.0.co;2.
We examined web-building spider species richness and abundance in forests across a deer density gradient to determine the effects of sika deer browsing on spiders among habitats and feeding guilds. Deer decreased the abundance of web-building spiders in understory vegetation but increased their abundance in the litter layer. Deer seemed to affect web-building spiders in the understory vegetation by reducing the number of sites for webs because vegetation complexity was positively correlated with spider density and negatively correlated with deer density. In contrast, the presence of vegetation just above the litter layer decreased the spider density, and deer exerted a negative effect on this vegetation, possibly resulting in an indirect positive effect on spider density. The vegetation just above the litter layer may be unsuitable as a scaffold for building webs if it is too flexible to serve as a reliable web support, and may even hinder spiders from building webs on litter. Alternatively, the negative effect of this vegetation on spiders in the litter may be as a result of reduced local prey availability under the leaves because of the reduced accessibility of aerial insects. The response to deer browsing on web-building spiders that inhabit the understory vegetation varied with feeding guild. Deer tended to affect web-invading spiders, which inhabit the webs of other spiders and steal prey, more heavily than other web-building spiders, probably because of the accumulated effects of habitat fragmentation through the trophic levels. Thus, the treatment of a particular higher-order taxon as a homogeneous group could result in misleading conclusions about the effects of mammalian herbivores.
我们研究了在鹿密度梯度下森林中网蛛的物种丰富度和数量，以确定梅花鹿啃食对不同栖息地和取食类群蜘蛛的影响。鹿减少了林下植被中网蛛的数量，但增加了枯枝落叶层中网蛛的数量。鹿似乎通过减少结网地点的数量来影响林下植被中的网蛛，因为植被复杂性与蜘蛛密度呈正相关，与鹿密度呈负相关。相比之下，枯枝落叶层上方植被的存在降低了蜘蛛密度，而鹿对这种植被产生了负面影响，这可能对蜘蛛密度产生间接的正面影响。如果枯枝落叶层上方的植被过于柔软而无法作为可靠的蛛网支撑，那么它可能不适合作为结网的支架，甚至可能阻碍蜘蛛在枯枝落叶上结网。或者，这种植被对枯枝落叶层中蜘蛛的负面影响可能是由于树叶下当地猎物可利用性降低，原因是空中昆虫的可接近性降低。林下植被中结网蜘蛛对鹿啃食的反应因取食类群而异。鹿对侵入其他蜘蛛蛛网并窃取猎物的侵入蛛网蜘蛛的影响往往比对其他结网蜘蛛的影响更大，这可能是由于营养级联导致的栖息地破碎化的累积效应。因此，将特定的高阶分类群视为一个同质群体来进行研究，可能会得出关于哺乳动物食草动物影响的误导性结论。
