Data from: Various competitive interactions explain niche separation in crop-dwelling web spiders

Competition for resources is a major organizing principle in communities of organisms that share similar ecological niches. Niche separation by means of exploitation or interference competition was investigated in two taxa of crop-inhabiting spiders that overlap in microhabitat use and have similar web design. Competition for prey and web sites was tested in microcosm experiments with the most common species that build sheet-webs: Enoplognatha gemina (Theridiidae) and Alioranus pastoralis (Linyphiidae). A field survey over the crop season provided data on spatial and temporal dispersion of Enoplognatha spp. (Theridiidae) and linyphiid spiders (Linyphiidae) and on availability of prey over the season. In the microcosm experiments, both taxa took springtails as prey, but only Enoplognatha fed on aphids. Differences in diet, however, could not be attributed to either exploitative or interference competition. Spatial separation of websites was attained by vertical displacement of webs in the vegetation (Enoplognatha) and by avoidance of patches occupied by conspecific or heterospecific individuals (linyphiids). In the field, densities of linyphiids and Enoplognatha were correlated negatively and webs were over-dispersed relative to a random distribution. Both taxa colonized the field at the start of the season; linyphiids colonized as adults, quickly reproduced, and had a second adult peak; Enoplognatha matured in the middle of the season and their numbers remained fairly constant over the season. The combined experimental manipulations and field data suggest that niche separation occurs at different scales. The hypothesis of competition for websites was partially supported, while prey preference (or tolerance) and temporal differences in life history stages also may explain the negative correlations between densities of the two taxa.资源竞争是共享相似生态位的生物群落的主要组织原则之一。本研究针对两种微生境利用重叠、结网模式相似的农田栖息蜘蛛类群，探讨了通过利用性竞争或干扰性竞争实现的生态位分化。研究以两种最常见的片状网（sheet-webs）蜘蛛为对象开展微宇宙实验，对其猎物与结网位点的竞争情况进行了测试：分别为球蛛科（Theridiidae）的双突齿蛛（Enoplognatha gemina）以及Alioranus pastoralis（皿蛛科Linyphiidae）。本研究在整个作物季开展野外调查，获取了齿蛛属物种（Enoplognatha spp.，球蛛科Theridiidae）与皿蛛科（Linyphiidae）蜘蛛的时空分布格局数据，以及整个作物季的猎物可获得性数据。微宇宙实验结果显示，两类蜘蛛均以弹尾虫（springtails）为猎物，但仅齿蛛属蜘蛛可取食蚜虫（aphids）。然而，食性差异无法归因于利用性竞争或干扰性竞争。结网位点的空间分化通过两种途径实现：齿蛛属蜘蛛通过在植被中调整结网的垂直位置实现，而皿蛛科蜘蛛则通过避开同种或异种个体占据的斑块实现。野外调查结果表明，皿蛛科蜘蛛与齿蛛属蜘蛛的种群密度呈负相关，且其结网位点的分布相较于随机分布呈现过度离散格局。两类蜘蛛均在作物季初期定植农田：皿蛛科蜘蛛以成虫形态定植，快速繁殖后出现第二个成虫种群高峰；齿蛛属蜘蛛则在作物季中期成熟，其种群数量在整个作物季保持相对稳定。结合实验操控与野外调查数据的结果表明，生态位分化发生在不同尺度上。结网位点竞争的假说得到了部分支持，而猎物偏好（或耐受性）以及生活史阶段的时序差异，也可以解释两类蜘蛛种群密度间的负相关关系。