Community composition in a given landscape is a complex product of the constituent species' niche requirements, geographic connectivity, environmental properties, species interactions and drift. In this study, we examined niche use of 16 cladoceran species in 81 zooplankton communities that inhabit environmentally variable sites along a strong urbanization gradient. We tested to what extent niche shifts occurred along the urbanization gradient. We also quantified to what extent niche overlap can explain co-occurrence patterns and tested whether alternative processes such as dispersal limitation or environmental heterogeneity impact co-occurrence patterns. Niche use in the study region was size-mediated, with larger species preferring nutrient-rich environments while smaller species were more specialized on distinct niche axes. Our analyses also revealed that mainly generalist species were able to establish in urban sites. While the average niche position for most species was conserved from rural to urban sites, the niches of those species occurring in both rural and urban areas remain partly unfilled in the urban populations. We observed that a relatively small proportion (13%) of species pairs co-occurred more or less often than expected by chance, but also that niche overlap was the only predictor that was strongly and significantly associated with co-occurrence scores in our study. While most of these species pairs showed evidence for a role of environmental filtering, a few common, generalist species pairs displayed segregated co-occurrence patterns and high niche overlap, suggesting a role of limiting similarity relationships as well. Our study highlights the damaging effects on biodiversity of urbanization through biotic homogenization benefitting generalist species, as well as the difficulty species may face in occupying available niche space in urbanized habitats.

中文翻译：

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沿强烈城市化梯度的浮游动物生态位利用和共现模式

给定景观中的群落组成是组成物种的生态位需求、地理连通性、环境特性、物种相互作用和漂移的复杂产物。在这项研究中，我们检查了 81 个浮游动物群落中 16 个枝角类物种的生态位利用，这些群落沿着强烈的城市化梯度栖息在环境可变的地点。我们测试了沿着城市化梯度发生的生态位变化的程度。我们还量化了生态位重叠在多大程度上可以解释共现模式，并测试了诸如分散限制或环境异质性等替代过程是否会影响共现模式。研究区域的生态位使用是大小介导的，较大的物种更喜欢营养丰富的环境，而较小的物种更专注于不同的生态位轴。我们的分析还表明，主要是通才物种能够在城市场所建立。虽然大多数物种的平均生态位位置从农村到城市都得到了保护，但在农村和城市地区出现的这些物种的生态位在城市人口中仍然部分未填补。我们观察到，相对较小比例（13%）的物种对共同发生的频率比偶然预期的多或少，但生态位重叠是唯一与我们研究中的共现分数强烈且显着相关的预测因子。虽然这些物种对中的大多数显示出环境过滤作用的证据，但一些常见的通才物种对显示出分离的共现模式和高生态位重叠，这表明也有限制相似性关系的作用。