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找水源来缓解此类影响。当前有关动物水平衡的研究大多（但并非全部）源自旱地生态系统。然而，栖息于湿润生境的动物同样可能面临干燥胁迫环境，例如城市热岛内部或是热浪与干旱时段。本研究以俄亥俄州西北部三处湿润生境区域为研究对象，探讨不透水面（impervious surface）的空间差异以及微气候的时空变化如何影响陆生节肢动物与软体动物的需水行为，并对表现出显著需水行为的类群展开分析。需水行为以个体在人工水源（湿润袋）处的观测频率相较于对照（干燥袋）处的观测频率进行量化。整体而言，陆生节肢动物与软体动物在人工水源处的观测频率约为对照处的两倍（平均每个样点的湿润袋观测量较干燥袋多出86次）；其中城市区域内的蚁类贡献了整体响应结果的50%以上。每日水汽压亏缺（vapor pressure deficit, VPD）的波动可最佳预测需水行为的日变化规律，且VPD越高，动物的需水需求越强。城市化区域附近的平均VPD通常最高，但VPD对需水行为的影响在城市化区域内普遍较弱，这可能与总个体丰度下降导致潜在响应能力降低有关。在部分时段，自然区域与绿地内的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湿润生境区域内出现需水时段，包括城市外围的绿地中，且此类群体会对短期干燥环境产生强烈响应——这一发现对理解气候变化的影响具有潜在参考价值。