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

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

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

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 as a trophic currency in dryland food webs

Water is essential for life on Earth, yet little is known about how water acts as a trophic currency, a unit of value in determining species interactions in terrestrial food webs. We tested the relative importance of groundwater and surface water in riparian food webs by manipulating their availability in dryland floodplains. Primary consumers (crickets) increased in abundance in response to added surface water and groundwater (contained in moist leaves), and predators (spiders and lizards) increased in abundance in response to added surface water, in spite of the presence of a river, an abundant water source. Moreover, the relative magnitude of organism responses to added water was greatest at the most arid site and lowest at the least arid site, mirroring cricket recruitment, which was greatest at the least arid site and lowest at the most arid site. These results suggest that water may be a key currency in terrestrial dryland food webs, which has important implications for predicting ecosystem responses to human‐ and climate‐related changes in hydrology and precipitation

Greenfall Links Groundwater to Aboveground Food Webs in Desert River Floodplains

Groundwater makes up nearly 99% of unfrozen freshwater worldwide and sustains riparian trees rooted in shallow aquifers, especially in arid and semiarid climates. The goal of this paper is to root animals in the regional water cycle by quantifying the significance of groundwater to riparian animals. We focused our efforts on the cricket, Gryllus alogus: a common primary consumer found in floodplain forests along the San Pedro River, in southeast Arizona, USA. Cottonwood trees make groundwater available to G. alogus as dislodged, groundwater-laden leaves (greenfall). We hypothesized that groundwater fluxes mediated by greenfall sustain G. allogus through the prolonged dry season and link these aboveground consumers to belowground aquifers. To test this hypothesis, we first characterized gradients in absolute humidity (air) and water stress in field-collected G. alogus. Absolute humidity declined with distance from river across wide stands of floodplain cottonwood forest during the dry season, but not during the rainy season. Similarly, G. alogus body water content declined along this gradient. Second, we measured evaporative water loss (EWL) by field-captured G. alogus in the laboratory at temperatures bracketing field conditions. EWL ranged from 0.05 ± 0.009 g·individual-1·d-1 0.13 ± 0.03 g·individual-1·d-1 (mean ± SD, at 30° and 40°C, respectively). These daily losses are high, but still less than the water content of a single cottonwood leaf (0.296 ± 0.124 g H2O/leaf). Third, we designed field experiments to quantify the relative dependence of G. alogus on greenfall. G. alogus more frequently consumed greenfall than various controls consisting of dried leaves. This preference occurred in distal habitats and during the dry season, but not proximal to the river or in the rainy season. Finally, we compared estimated daily water fluxes via greenfall to (1) estimates of water demand of the entire G. alogus population at our field site, and (2) reports of cottonwood transpiration and San Pedro River base flow from other authors. By our estimates, groundwater fluxes via greenfall sustain G. alogus populations despite their trivial magnitude compared to stream discharge and cottonwood transpiration. Primary consumers in turn provide dietary water to higher trophic levels (e.g., abundant and speciose birds in the region) through trophic pathways, thereby fueling secondary production from the bottom up. Thus, riparian trees root animals in the regional water cycle

Predator water balance alters intraguild predation in a streamsidefood web

Previous work suggests that animal water balance can influence trophic interactions, with predators increasing their consumption of water-laden prey to meet water demands.But it is unclear how the need for water interacts with the need for energy to drive trophic interactions under shifting conditions. Using manipulative field experiments, we show that water balance influences the effects of top predators on prey with contrasting ratios of water and energy, altering the frequency of intraguild predation. Water-stressed top predators (large spiders) negatively affect water-laden basal prey (crickets), especially male prey with higher water content, whereas alleviation of water limitation causes top predators to switch to negatively affecting energy-rich midlevel predators (small spiders). Thus, the relative water and energy content of multiple prey, combined with the water demand of the top predator, influences trophic interactions in ways that can alter the strength of intraguild predation. These findings underscore the need for integration of multi resource approaches for understanding implications of global change for food webs

Supporting Practices to Adopt Registry-Based Care (SPARC): protocol for a randomized controlled trial

Background: Diabetes is predicted to increase in incidence by 42% from 1995 to 2025. Although most adults with diabetes seek care from primary care practices, adherence to treatment guidelines in these settings is not optimal. Many practices lack the infrastructure to monitor patient adherence to recommended treatment and are slow to implement changes critical for effective management of patients with chronic conditions. Supporting Practices to Adopt Registry-Based Care (SPARC) will evaluate effectiveness and sustainability of a low-cost intervention designed to support work process change in primary care practices and enhance focus on population-based care through implementation of a diabetes registry. Methods: SPARC is a two-armed randomized controlled trial (RCT) of 30 primary care practices in the Virginia Ambulatory Care Outcomes Research Network (ACORN). Participating practices (including control groups) will be introduced to population health concepts and tools for work process redesign and registry adoption at a meeting of practice-level implementation champions. Practices randomized to the intervention will be assigned study peer mentors, receive a list of specific milestones, and have access to a physician informaticist. Peer mentors are clinicians who successfully implemented registries in their practices and will help champions in the intervention practices throughout the implementation process. During the first year, peer mentors will contact intervention practices monthly and visit them quarterly. Control group practices will not receive support or guidance for registry implementation. We will use a mixed-methods explanatory sequential design to guide collection of medical record, participant observation, and semistructured interview data in control and intervention practices at baseline, 12 months, and 24 months. We will use grounded theory and a template-guided approach using the Consolidated Framework for Implementation Research to analyze qualitative data on contextual factors related to registry adoption. We will assess intervention effectiveness by comparing changes in patient-level hemoglobin A1c scores from baseline to year 1 between intervention and control practices. Discussion: Findings will enhance our understanding of how to leverage existing practice resources to improve diabetes care in primary care practices by implementing and using a registry. SPARC has the potential to validate the effectiveness of low-cost implementation strategies that target practice change in primary care

Supporting Practices to Adopt Registry-Based Care (SPARC): protocol for a randomized controlled trial

Background: Diabetes is predicted to increase in incidence by 42% from 1995 to 2025. Although most adults with diabetes seek care from primary care practices, adherence to treatment guidelines in these settings is not optimal. Many practices lack the infrastructure to monitor patient adherence to recommended treatment and are slow to implement changes critical for effective management of patients with chronic conditions. Supporting Practices to Adopt Registry-Based Care (SPARC) will evaluate effectiveness and sustainability of a low-cost intervention designed to support work process change in primary care practices and enhance focus on population-based care through implementation of a diabetes registry. Methods: SPARC is a two-armed randomized controlled trial (RCT) of 30 primary care practices in the Virginia Ambulatory Care Outcomes Research Network (ACORN). Participating practices (including control groups) will be introduced to population health concepts and tools for work process redesign and registry adoption at a meeting of practice-level implementation champions. Practices randomized to the intervention will be assigned study peer mentors, receive a list of specific milestones, and have access to a physician informaticist. Peer mentors are clinicians who successfully implemented registries in their practices and will help champions in the intervention practices throughout the implementation process. During the first year, peer mentors will contact intervention practices monthly and visit them quarterly. Control group practices will not receive support or guidance for registry implementation. We will use a mixed-methods explanatory sequential design to guide collection of medical record, participant observation, and semistructured interview data in control and intervention practices at baseline, 12 months, and 24 months. We will use grounded theory and a template-guided approach using the Consolidated Framework for Implementation Research to analyze qualitative data on contextual factors related to registry adoption. We will assess intervention effectiveness by comparing changes in patient-level hemoglobin A1c scores from baseline to year 1 between intervention and control practices. Discussion: Findings will enhance our understanding of how to leverage existing practice resources to improve diabetes care in primary care practices by implementing and using a registry. SPARC has the potential to validate the effectiveness of low-cost implementation strategies that target practice change in primary care

Nucleosome-mediated cooperativity between transcription factors

Cooperative binding of transcription factors (TFs) to cis-regulatory regions (CRRs) is essential for precision of gene expression in development and other processes. The classical model of cooperativity requires direct interactions between TFs, thus constraining the arrangement of TFs sites in a CRR. On the contrary, genomic and functional studies demonstrate a great deal of flexibility in such arrangements with variable distances, numbers of sites, and identities of the involved TFs. Such flexibility is inconsistent with the cooperativity by direct interactions between TFs. Here we demonstrate that strong cooperativity among non-interacting TFs can be achieved by their competition with nucleosomes. We find that the mechanism of nucleosome-mediated cooperativity is mathematically identical to the Monod-Wyman-Changeux (MWC) model of cooperativity in hemoglobin. This surprising parallel provides deep insights, with parallels between heterotropic regulation of hemoglobin (e.g. Bohr effect) and roles of nucleosome-positioning sequences and chromatin modifications in gene regulation. Characterized mechanism is consistent with numerous experimental results, allows substantial flexibility in and modularity of CRRs, and provides a rationale for a broad range of genomic and evolutionary observations. Striking parallels between cooperativity in hemoglobin and in transcription regulation point at a new design principle that may be used in range of biological systems