Water-seeking behavior among terrestrial arthropods and mollusks in a cool mesic region: spatial and temporal patterns

Dehydration can have negative effects on animal physiological performance, growth, reproduction, and survival, and most animals seek to minimize these effects by reducing water losses or seeking water sources. Much—but not all—of the research on animal water balance comes from dryland ecosystems. However, animals inhabiting mesic regions may also experience desiccating conditions, for example within urban heat islands or during heatwaves and droughts. Here we examined how spatial variation in impervious surface and spatial and temporal variation in microclimate impact water demand behavior of terrestrial arthropods and mollusks in three areas of mesic Northwest Ohio, with analysis of taxa that exhibited the greatest water demand behavior. Water demand behavior was measured as the frequency that individuals were observed at an artificial water source (a moistened pouch), relative to the frequency at a control (a dry pouch). Overall, terrestrial arthropods and mollusks were found about twice as often at the water source than at the control (equivalent to 86 more observations on the wet pouch than on dry at each site, on average), with ants accounting for over 50% of the overall response in urban areas. Daily fluctuations in vapor pressure deficit (VPD) best predicted daily variation in water demand behavior, with increased demand at higher VPD. Mean VPD was generally highest near urbanized areas, but effects of VPD on water demand behavior were generally lower in urbanized areas (possibly related to reductions in overall abundance reducing the potential response). On certain days, VPD was high in natural areas and greenspaces, and this coincided with the highest arthropod water demand behavior observed. Our results suggest that terrestrial arthropod communities do experience periods of water demand within mesic regions, including in greenspaces outside cities, where they appear to respond strongly to short periods of dry conditions—an observation with potential relevance for understanding the effects of climate change.

脱水会对动物的生理机能、生长、繁殖与存活产生负面影响，多数动物会通过减少水分流失或寻觅水源来降低此类影响。动物水平衡的相关研究大多（但并非全部）源自旱地生态系统。然而栖息于中生区域（mesic region）的动物同样可能面临干燥胁迫环境，例如城市热岛（urban heat islands）内部或是热浪（heatwaves）与干旱（droughts）时段。本研究以俄亥俄州西北部中生区域的三处样地为研究对象，分析不透水面（impervious surface）的空间变异以及微气候的时空变化如何影响陆生节肢动物（terrestrial arthropods）与软体动物（mollusks）的需水行为，并对表现出显著需水行为的分类群（taxa）开展针对性分析。需水行为以个体在人工水源（artificial water source，即湿润棉袋）处的观测频次与对照（干燥棉袋）处的观测频次之比进行量化。整体而言，陆生节肢动物与软体动物在水源处的观测频次约为对照处的两倍（平均每个样地湿润棉袋的观测次数较干燥棉袋多86次）；在城市区域，蚂蚁贡献了整体响应的50%以上。水汽压亏缺（Vapor Pressure Deficit, VPD）的日波动最能预测需水行为的日变化，VPD越高，动物的需水需求越强。平均VPD通常在城市化区域附近最高，但VPD对需水行为的影响在城市化区域普遍较弱，这可能与种群整体丰度下降导致潜在响应减弱有关。部分日期中，自然区域与绿地的VPD较高，此时观测到的节肢动物需水行为也达到峰值。本研究结果表明，陆生节肢动物群落确实会在中生区域面临阶段性需水状况，包括城市外围的绿地中，且它们对短期干燥环境表现出强烈响应——这一发现对于理解气候变化的影响具有潜在参考价值。