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We combined approximately 28,000 raven point count surveys with data from more than 900 sage-grouse nests between 2009 and 2019 within the Great Basin, USA. We modeled variation in raven density using a Bayesian hierarchical distance sampling approach with environmental covariates on detection and abundance. Concurrently, we modeled sage-grouse nest survival using a hierarchical frailty model as a function of raven density as well as other environmental covariates that influence risk of failure. Raven density commonly exceeded more than 0.5 ravens per square kilometer and increased at low relative elevations with prevalent anthropogenic development and/or agriculture. Reduced sage-grouse nest survival was strongly...
This study demonstratest he correlationo f an arrayo f ecological characteristicsw ith foraging mode in sit-and-wait foraging Crotalus cerastes and widely foraging Masticophis flagellum. Crotalus cerastes are chiefly nocturnal and spend most of their time on the surface either coiled on or partially buried in the sand waiting to ambush prey. Masticophis flagellum are strictly diurnal predators and cruise through the habitat searching for active and sedentary prey. In this study, C. cerastes averaged 7.2 ? 0.7 (SE) h/day on the surface, almost twice the time of M. flagellum (3.9 ? 0.9 h/day). Body temperatures (Tb's) of active M. flagellum, determined from surgically implanted radio transmitters, were significantly...
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These data were compiled to evaluate the potential impact various environmental conditions may have on native fish populaitons through predation. Introduced warm-water sport fishes present a high predation risk for juvenile native fishes, but observations of juvenile native fish surviving and recruiting in some rare cases led us to question what environmental conditions might be responsible for these trends. These data were compiled to allow for a relative comparison of predation effectiveness between a suite of warm-water predators under a variety of environmental conditions. Mean numbers of prey fish surviving in replicated overnight laboratory predation trials were quantified.
Frog eggs of three different species were presented to giant apple snails (Pomacea maculata) to determine if the snails will eat the eggs. There were four treatments: control (eggs in water only); control with lettuce (eggs in water and lettuce which was used as snail food); snail (eggs in water with snail); and snail with lettuce (eggs in water with snails and lettuce as an alternative food for the snail). Eggs were counted at the start and end of the experiment, and if an egg hatched to a tadpole, the tadpoles were counted as un-eaten eggs.
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These rasters are the result of calculating the difference in Greater Sage-grouse nest survival after a simulated reduction of raven density to 0.1 ravens per square kilometer. The difference in nest survival represents spatial variation in potential to improve nest survival by reducing raven impacts. The extent of each individual raster is the extent of the field site at which sage-grouse nest observations were recorded.
The desert tortoise Gopherus agassizii is federally listed as Threatened because of documented declines in some populations, yet the proximate causes of these declines are not well understood. With use of radiotelemetry, I monitored a total of 55 individual tortoises at two Mojave Desert sites over three years. Both populations suffered high adult mortality during an extreme drought period, but the temporal pattern and inferred proximate causes of mortality differed between sites. At the eastern Mojave site, no telemetered tortoises died in 1988 or 1989, but 41% died in 1990. All nine carcasses were found and only one showed any evidence of predation or scavenging. Tortoises that died had symptoms of dehydration...
Understanding how communities respond to changes in temperature is a major challenge for community ecology. Temperature influences the relative degree to which top-down and bottom-up forces structure ecological communities. In greenhouse experiments using the aquatic community found in pitcher plants (Sarracenia purpurea), I tested how temperature affected the relative importance of top-down (mosquito predation) and bottom-up (ant carcasses) forces on protozoa and bacteria populations. While bottom-up effects did not vary consistently with temperature, the top-down effects of predators on protozoa increased at higher temperatures. These results suggest that temperature could change the relative importance of top-down...
map background search result map search result map Laboratory Predation Data (various nonnative warm-water sport fishes), Arizona Data to Support Hierarchical Models and Decision Support Maps to Guide Management of Subsidized Avian Predator Densities Estimates of Raven Impacts on Greater Sage-Grouse Nest Survival Delineated by Field Site in California, Nevada, and Idaho (2009 - 2019) Laboratory Predation Data (various nonnative warm-water sport fishes), Arizona Data to Support Hierarchical Models and Decision Support Maps to Guide Management of Subsidized Avian Predator Densities Estimates of Raven Impacts on Greater Sage-Grouse Nest Survival Delineated by Field Site in California, Nevada, and Idaho (2009 - 2019)