Implications of animal water balance for terrestrial food webs

Recent research has documented shifts in per capita trophic interactions and food webs in response to changes in environmental moisture, from the top-down (consumers to plants), rather than solely bottom-up (plants to consumers). These responses may be predictable from effects of physiological, behavioral, and ecological traits on animal water balance, although predictions could be modified by energy or nutrient requirements, the risk of predation, population-level responses, and bottom-up effects. Relatively little work has explicitly explored food web effects of changes in animal water balance, despite the likelihood of widespread relevance, including during periodic droughts in mesic locations, where taxa may lack adaptations for water conservation. More research is needed, particularly in light of climate change and hydrological alteration

The Influence of Beached Harmful Algal Blooms On Terrestrial Arthropods on the Shore of Lake Erie

Marine primary inputs, such as sea wrack and algae, offer a great niche for insects and other animals to exploit. The existence of a similar niche on the coast of lakes has received less attention. To complicate matters, many freshwater systems are seeing increases in proliferation of toxic and non-toxic cyanobacteria blooms. This study examined patterns in lake shore terrestrial arthropod abundance, diversity, and community composition across gradients of beached algae, with varying toxicity. We detected water microcystin effects on arthropod richness in survey three, beached material effects on Shannon’s Diversity in survey two, and water microcystin effects on the community structure on survey three. Our results suggest the beached aquatic inputs have diversifying effect and microcystin has a positive indirect relationship with certain orders of arthropods such as flies and spiders. We recommend further study into the mechanisms surrounding shore arthropod resource utilization and predator release from toxic blooms

Water Loss Rates and Desiccation Tolerances for Spiders and Crickets

Despite the importance of water to living organisms, access varies across the globe with high variability over space and time. Seventy-five percent of the world’s freshwater alone is ice while 99% of unfrozen freshwater is underground (Winter et al. 1998). Understanding how terrestrial species respond to water availability and compensate for water stress can provide insight to their behavior, ecology and physiology. The goal of this research was to examine the differences in the evaporative water loss rates and desiccation tolerances of Hogna carolinensis and Acheta domesticus. First, an experiment was conducted to quantify the rate of evaporative water loss of the species Hogna carolinensis and Acheta domesticus. This was done by desiccating twenty specimens of Hogna carolinensis and forty specimens of Acheta domesticus within an environmental chamber set at 30%RH and 30C and measuring their masses until death. Another experiment was conducted to explore how prey hydration influenced predation of Hogna carolinensis. Thirty-nine female specimens of Hogna carolinensis were housed within the environmental chamber under the same conditions, treated to a four day period of starvation and desiccation then fed eight specimens of Acheta domesticus from one of three hydration treatments. Initial observations concluded that there was little difference between how much mass was consumed by the predators across the three treatments

Differential sensitivity of bees to urbanization-driven changes in body temperature and water content

Predicting how species will respond to climate change and land use modification is essential for conserving organisms and maintaining ecosystem services. Thermal tolerances have been shown to have strong predictive power, but the potential importance of desiccation tolerances have been less explored in some species. Here, we report measurements of thermal and desiccation tolerances and safety margins across a gradient of urbanization, for three bee species: silky striped sweat bees (Agapostemon sericeus), western honeybees (Apis mellifera), and common eastern bumblebees (Bombus impatiens). We found significant differences in thermal tolerances, measured as critical thermal maximum (CTmax), amongst species. Bumblebees were the least sensitive to warming, with a higher CTmax (53.1 °C) than sweat bees (50.3 °C) and honeybees (49.1 °C). We also found significant differences in desiccation tolerances, measured as critical water content (CWC), between all species. Sweat bees were the least sensitive to desiccation, with the lowest CWC (51.7%), followed by bumblebees (63.7%) and honeybees (74.2%). Moreover, bumblebees and sweat bees were closer to their CTmax in more urbanized locations, while honeybees were closer to their CWC. These results suggest that bees have differential sensitivities to environmental change and managing for diverse bee communities in the face of global change may require mitigating both changes in temperature and water

Sensitivity and Tolerance of Riparian Arthropod Communities to Altered Water Resources along a Drying River

Rivers around the world are drying with increasing frequency, but little is known about effects on terrestrial animal communities. Previous research along the San Pedro River in southeastern AZ, USA, suggests that changes in the availability of water resources associated with river drying lead to changes in predator abundance, community composition, diversity, and abundance of particular taxa of arthropods, but these observations have not yet been tested manipulatively

Water availability directly determines per capita consumption at two trophic levels

Community ecology has long focused on energy and nutrients as currencies of species interactions. Evidence from physiological ecology and recent studies suggest that in terrestrial systems, water may influence animal behavior and global patterns of species richness. Despite these observations, water has received little attention as a currency directly influencing animal species interactions. Here, we show that the per capita interaction strength between predatory wolf spiders and their primary prey, field crickets, is strong (0.266) when predators and prey are maintained in ambient dry conditions, but is near zero (0.001) when water is provided ad libitum. Moreover, crickets consume 31-fold more moist leaf material in ambient dry conditions, switching from old litter to moist green leaves when free water is scarce. Under dry conditions, animals may make foraging decisions based first on water needs, not energy or nutrients, suggesting strong and predictable effects of alterations in aridity on species interactions

River drying lowers the diversity and alters the composition of an assemblage of desert riparian arthropods

Summary 1. Many studies have shown negative effects of river drying on in‐stream animals. However, the influence of river drying on riparian animals remains poorly studied. We examined ground‐dwelling riparian arthropod assemblages along a drying section of the semi‐arid San Pedro River in southeastern Arizona, U.S.A. 2. We found strong differences in assemblage composition, taxon diversity and the abundance of key taxa between dry and flowing sites, with higher diversity and abundance of most taxa at flowing sites. 3. Changes in assemblage composition, taxon diversity and abundance of representative taxa were associated with a combined measure of water availability that included distance to water and type of water. Other environmental variables showed a weaker association with changes in these arthropod assemblages. 4. Thus, we found evidence that desert riparian arthropods are sensitive to river drying and to reduction in water resources. Increases in drying along this river may reduce the diversity and the abundance of many groups of ground‐dwelling arthropods, leading to marked shifts in community composition

Animal water balance drives top-down effects in a riparian forest-implications for terrestrial trophic cascades

Despite the clear importance of water balance to the evolution of terrestrial life, much remains unknown about the effects of animal water balance on food webs. Based on recent research suggesting animal water imbalance can increase trophic interaction strengths in cages, we hypothesized that water availability could drive top-down effects in open environments, influencing the occurrence of trophic cascades. We manipulated large spider abundance and water availability in 20 × 20 m open-air plots in a streamside forest in Arizona, USA, and measured changes in cricket and small spider abundance and leaf damage. As expected, large spiders reduced both cricket abundance and herbivory under ambient, dry conditions, but not where free water was added. When water was added (free or within moist leaves), cricket abundance was unaffected by large spiders, but spiders still altered herbivory, suggesting behavioural effects. Moreover, we found threshold-type increases in herbivory at moderately low soil moisture (between 5.5% and 7% by volume), suggesting the possibility that water balance may commonly influence top-down effects. Overall, our results point towards animal water balance as an important driver of direct and indirect species interactions and food web dynamics in terrestrial ecosystems

Water availability influences arthropod water demand, hydration and community composition on urban trees

The drive for animals to regulate their water content can have significant consequences for food webs in xeric ecosystems. But the importance of animal water balance (gains vs losses) for mesic food webs has not been explored. Impervious surfaces in cities absorb and re-radiate solar radiation, raising local temperatures. Higher temperatures lead to greater rates of organismal water loss. Thus, urbanization of mesic regions may lead to greater likelihood of desiccation, with consequences for food webs. We tested the effects of animal water balance on a mesic urban food web by supplementing animal-available water (but not plant) within trees in a parking lot in Raleigh, NC, a mesic city with previously documented urban warming. We found that during dry periods, arthropods in control trees were desiccated (lower water content), with higher water demand behavior. This coincided with shifts in community composition during dry periods. Continuous experimental supplementation of animal-available water mostly reduced or erased these patterns. Thus, animal water balance may play a role in mediating food web dynamics in mesic cities

Urbanization alters communities of flying arthropods in parks and gardens of a medium-sized city

Urbanization transforms undeveloped landscapes into built environments, causing changes in communities and ecological processes. Flying arthropods play important roles in these processes as pollinators, decomposers, and predators, and can be important in structuring food webs. The goal of this study was to identify associations between urbanization and the composition of communities of flying (and floating) arthropods within gardens and parks in a medium-sized mesic city. We predicted that flying arthropod abundance and diversity would respond strongly to percent impervious surface and distance to city center, measurements of urbanization. Flying arthropods were sampled from 30 gardens and parks along an urbanization gradient in Toledo, Ohio, during July and August 2016, using elevated pan traps. A variety of potential predictor variables were also recorded at each site. We collected a total of 2,369 individuals representing nine orders. We found that flying arthropod community composition was associated with percent impervious surface and canopy cover. Overall flying arthropod abundance was negatively associated with percent impervious surface and positively associated with distance to city center. Hymenoptera (bees, wasps, ants), Lepidoptera (moths, butterflies), and Araneae (spiders) were positively associated with distance to city center. Hemiptera (true bugs), Diptera (flies), and Araneae were negatively associated with percent impervious surface. Both distance to city center and percent impervious surface are metrics of urbanization, and this study shows how these factors influence flying arthropod communities in urban gardens and city parks, including significant reductions in taxa that contain pollinators and predators important to urban agriculture and forestry. A variety of environmental factors also showed significant associations with responses (e.g. canopy cover and soil moisture), suggesting these factors may underlie or modulate the urbanization effects. More research is needed to determine mechanisms of change