Among-individual behavioral responses to predation risk are invariant within two species of freshwater snails [post-print]

Prey behavioral response to predation risk drives a range of ecological and evolutionary processes. Key to these effects is the degree to which conspecifics exhibit consistent individual differences in their response to risk or instead follow a mean population-level pattern. Here, we employed the behavioral reaction norm framework to quantify among-individual variation in average predator avoidance behavior (i.e., behavioral types) and the behavioral response to risk (i.e., individual plasticity) in two snail species (Helisoma trivolvis and Physa acuta) that differ in their vulnerability to predators. While both snail species exhibited substantial variation in behavioral types, individual plasticity in response to risk was remarkably invariant—both snail species increased avoidance behavior with increasing risk, but all conspecific individuals followed the population-level pattern (i.e., parallel reaction norms). Instead, individual snails differed in how they adjusted their behavior over the course of repeated behavioral assays (n = 12 per individual), with some exhibiting increased sensitization to risk cues and others habituation. We further show that among-individual behavioral variation, both in behavioral types and in individual responses to repeated assays, was sometimes correlated with physiological traits, providing potential mechanisms for the maintenance of this variation. In total, our results indicate that behavioral types and individual plasticity vary at different hierarchical scales (individual- vs. population-level, respectively) in freshwater snails, which has implications for species interactions and the evolution of predator avoidance behavior

Application of Screening in Rangeland Monitoring: Quantifying Early-Warning Signals of State Transitions in Nebraska

Woody encroachment, desertification, and exotic annual grass invasion are regime shifts (i.e., state-transitions) with detrimental effects on ecosystem health and services in grasslands of the North American Great Plains. Traditional approaches to rangeland monitoring are capable of detecting regime shifts after they have already occurred (i.e., diagnosing them); however, proactive management requires earlier warning. Regime shift screening is a new approach to rangeland monitoring capable of providing earlier warning of regime shifts. Regime shift screening proposes assessing the presence, persistence, and non-stationarity of regime shift signals; however, no studies have systematically evaluated these characteristics in real-world landscapes. In this thesis, I screened 30 allotments within Halsey National Forest (Chapter 1) and the 23 Natural Resource Districts (NRDs) of the State of Nebraska (Chapter 2) for three notorious rangeland regime shifts—woody encroachment, desertification, and exotic annual grass invasion—from 1984 to 2020, using spatial covariance between rangeland functional group combinations as a screening metric. Halsey allotments and Nebraska NRDs were screened at three scales (i.e., moving window sizes) to determine the number of scales at which different regime shifts occurred in space and time and to assess the efficacy of differentiating between stationary and non-stationary regime shift signals. For Halsey allotments, screening results were compared to time series tests of changes in functional group percent cover estimates (i.e., regime shift diagnosis). Results varied across space, time, scale, and transition types; however, woody encroachment regime shifts occurred over the strong majority of sites and scales, while desertification and exotic annual grass invasion signals occurred less frequently and at smaller scales. Collectively, my results support the use of regime shift screening for early warning of regime shifts in rangeland monitoring. Adviser: Daniel R. Ude

L'étendue des prés / Geneviève Bauloye ; avant-dire de Henri Falaise

Collection : Collection Caractères ; 685Collection : Collection Caractères ; 685Contient une table des matièresAvec mode text

Particulate matter and NO2 air pollution trigger ST-elevation myocardial infarction: Results from the Belgian STEMI registry 2009-2013

info:eu-repo/semantics/nonPublishe