Biology subjects

Ruhi, A.

Publications and source records attributed to Ruhi, A..

4 recordsLinked to original sources

bioRxiv2026

Comparing morphological and molecular methods for stream macroinvertebrate biodiversity assessment across seven watersheds in the southern United States

Freshwater biodiversity is declining at alarming rates globally, yet our capacity to monitor it depends heavily on the methods used for biodiversity assessment. Stream benthic macroinvertebrates are widely used as bioindicators, but traditional morphological identification is labor-intensive and limited by taxonomic expertise, while DNA metabarcoding offers a promising but incompletely evaluated alternative. Here, we compared biodiversity patterns detected by four macroinvertebrate sampling and identification methods (morphological identification of benthic samples, morphological identification of combined benthic and stream-edge samples, eDNA metabarcoding of bulk benthic samples, and eDNA metabarcoding of streamwater) across 62 sites in seven watersheds spanning the southern continental United States. We compared methods across three facets of biodiversity (gamma diversity, alpha diversity, and taxonomic composition) and three taxonomic levels (family, genus, and species). We found that which method detected more taxa shifted with taxonomic resolution: morphological methods detected more families and genera, while metabarcoding methods detected more species. Bulk benthic metabarcoding detected more families and genera than water eDNA metabarcoding, consistent with the "watered-down biodiversity" effect of DNA dilution in water samples, but the two metabarcoding methods did not differ significantly in species richness. All four methods detected largely distinct suites of taxa, with metabarcoding methods yielding more unique taxa than morphological methods. Notably, taxa uniquely detected by water eDNA were dominated by soft-bodied organisms (oligochaetes, leeches, earthworms) and water-column-associated taxa, while benthic eDNA uniquely detected hard-bodied EPT insects. We attribute this pattern to fundamental differences in eDNA shedding, transport, and deposition dynamics across organism types. These results demonstrate that no single method captures a complete picture of stream macroinvertebrate biodiversity, and that method choice should be guided by the taxonomic resolution and community components most relevant to the goals of the bioassessment program.

ecology↗

bioRxiv2026

Drought degrades riparian subsidy quality and constrains aquatic ecosystem functioning

The exchange of energy and organisms across habitat boundaries links aquatic and terrestrial ecosystems and sustains ecosystem functioning. Although disturbance may disrupt these linkages, the mechanisms at play remain poorly understood. Here, we investigated the extent to which flow intermittency may disrupt riparian-aquatic ecosystem linkages by altering consumer communities in the recipient ecosystem or by altering resource quality in the donor ecosystem. We ran an experiment in an intermittent river network in California, focusing on a critical forest-to-river subsidy (organic matter in the form of leaf litter), its transformation, and its reciprocal benefit (aquatic insect production). Using three riparian species (willow, cottonwood, and oak) at sites spanning a gradient of flow permanence, we quantified intraspecific plasticity in leaf traits (specific leaf area, nitrogen and phosphorus concentrations, and {delta}13C), measured decomposition rates, and estimated the secondary production of aquatic shredders (Plecoptera). Across all leaf species, decomposition rates were 16-36% lower at intermittent than perennial sites, an effect largely driven by intraspecific leaf trait plasticity rather than changes in consumer abundance. At high flow intermittency, willow experienced water stress (enriched {delta}13C) and reduced specific leaf area, while cottonwood showed primarily stoichiometric responses (reduced leaf nitrogen and phosphorus). Despite these divergent strategies, all species produced lower-quality litter at intermittent sites. Variance partitioning confirmed that initial litter quality uniquely explained 51.5% of variation in decomposition rates, more than double the contribution of invertebrate community metrics; and structural equation modeling revealed that both leaf traits and stonefly (Plecoptera) secondary production significantly predicted decomposition rates, with leaf traits exerting the stronger effect. Notably, stonefly secondary production was 37-98% lower at intermittent sites across leaf species. Because these insects later emerge as terrestrial adults, they provide a significant energy flux to riparian predators, and, thus, impoverished litter quality suppresses the reciprocal transfer of energy back to terrestrial food webs. As drought intensifies globally, the decoupling of terrestrial-aquatic linkages may begin in the riparian canopy.

ecology↗

bioRxiv2025

Groundwater and phenology data reveal vulnerability of riparian trees to drought

The increasing frequency and magnitude of climatic extremes are altering water availability in dryland ecosystems globally. However, riparian vulnerability to hydroclimate whiplash remains poorly understood. Here, we examined how riparian trees respond to groundwater fluctuations and drought through their water use patterns and phenology. To this end, we combined time-series analysis of long-term, high-frequency groundwater monitoring and satellite imagery from a drought-prone and relatively pristine watershed in California (Chalone Creek, Pinnacles National Park). We found that trees by intermittent river reaches displayed consistent but depth-limited groundwater reliance, while those at perennial reaches primarily relied on groundwater during the dry season. Machine-learning models revealed that at intermittent sites groundwater depth predominantly controlled vegetation greenness, represented by Normalized Difference Vegetation Index (NDVI). In contrast, variation in photoperiod length dominated at perennial sites where water was more reliably available. During the severe 2020-2022 drought, all species experienced reduced greenness, but phenological responses differed by flow regime. While the start of season was delayed across all sites, trees at intermittent reaches exhibited substantially earlier end of season during drought, resulting in growing seasons shortened by as much as 28 days. These phenological shifts vastly exceed those documented across aridity classifications in global datasets from satellite observations, ground-based monitoring networks, and experimental precipitation manipulations. Although riparian trees in drylands have been shaped by exposure to drought over evolutionary timescales, our findings challenge the prevailing assumption that ecosystems regularly exposed to hydrological are more resilient to drought. Instead, we show that trees in intermittent systems may be operating close to critical groundwater thresholds, rendering them particularly vulnerable to increasingly long and severe droughts.

ecology↗

bioRxiv2024

Prolonged low flows and non-native fish operate additively to alter insect emergence in mountain streams

Climate-induced flow alteration is subjecting mountain streams to more frequent and severe low-flow periods due to lower snowpack and earlier snowmelt. Yet, anticipating how stream ecosystems respond to prolonged low flows remains challenging because trophic levels can respond differently, and non-native predators could dampen or amplify responses. Here, we conducted a large-scale experiment to examine how early, prolonged low flows projected by the end of the century in Californias Sierra Nevada will alter mountain stream food webs and emerging insect flux--a critical stream-to-land cross-ecosystem linkage. Additionally, we tested whether Brown trout (Salmo trutta), a widespread non-native top predator, would change food-web responses to low-flow conditions. We found that early low flows and non-native fish effects were additive rather than synergistic or antagonistic. Early low flows did not alter the overall rate of emerging insects but they did shift community structure and reduce the prevalence of small-sized individuals--possibly reflecting larger size at emergence and faster growth rates due to warming. In contrast, non-native fish presence increased seasonally-aggregated abundance of stream insects up to 12%, mainly by increasing abundance of Chironomidae and small-sized Ephemeroptera and Trichoptera. In channels with fish, benthic algal biomass doubled and scraper-grazer and collector-gatherer insects emerged 60% and 55% more than channels without fish, likely benefiting from trout keeping mesopredators at bay. This experiment illustrates that prolonged low flows and invasions can profoundly alter mountain river food webs even when operating additively; and shows how mesocosm-based research may help understand global-change driven disruption of cross-ecosystem linkages.

ecology↗