Geology topics

Justin F. Pomeranz

Publications and source records attributed to Justin F. Pomeranz.

3 recordsLinked to original sources

USGS2026

Effects of temperature on ectothermic predators are modulated by warming-induced changes to prey

Global temperature increases can fundamentally alter ecosystems through myriad pathways including by impacting top predators, whose movement, behavior, and trophic interactions often shape the structure of food webs and associated ecosystem processes. Forecasting how ectothermic predators will respond to climate change currently relies heavily on quantifying the direct impacts of temperature on their physiology and performance. However, prey resources are also likely to shift with warming, but less is known about how changes in ecosystem productivity may interact with rising temperatures to influence ectothermic predators. Understanding such interactions can thus help refine predictions for how these consumers will respond to a dynamic future and may clarify recent findings that some cold-water species are buffered and even benefit from warming temperatures despite elevated metabolic costs. Here, we capitalize on a growing body of literature linking temperature increases to changes in invertebrate prey assemblages to describe how these drivers interact to influence the performance (e.g., body size and growth rate) of a globally distributed ectothermic predator in freshwater ecosystems. We disentangled these drivers with a novel approach that blends conceptual synthesis and a mechanistic drift foraging-bioenergetics model developed for Oncorhynchus mykiss (rainbow trout). Overall, we found that warming-induced changes to invertebrate prey assemblage size structure, production, or both, can strongly reshape thermal performance curves describing how rainbow trout respond to temperature. Notably, we found that shifts towards larger-bodied prey or higher prey production increased trout performance across a gradient of temperatures. Additionally, our results show that these shifts in prey also increased the temperature that optimizes fish growth. Our findings underscore the critical role that prey resources may play in either buffering or amplifying future risks of warming and can help improve future conservation and management of ectothermic animals, including cold-water fish, in a warmer and rapidly changing world.

Food Webs↗

USGS2020

Cross-ecosystem linkages and trace metals at the land-water interface

At low concentrations, trace metals are critical for sustaining life on Earth. However, at high concentrations, they become a global contaminant with particularly strong effects on freshwater communities. These effects can propagate to terrestrial ecosystems in part by altering production and community structure of adult aquatic insect emergence and aquatic insect-mediated metal fluxes to terrestrial insectivores. Here we highlight mechanisms driving effects of trace metals on aquatic organisms in general, aquatic insects specifically, and insectivorous consumers at the land-water interface. Specifically, we focus on how trace metals impact and bioaccumulate in aquatic organisms and communities and how these changes propagate through aquatic food web interactions and insect metamorphosis to alter fluxes of aquatically derived prey and trace metals to terrestrial consumers. Ultimately, trace metals impact food webs at the land-water interface by altering aquatic insect prey composition and availability for aquatic insectivores and by reducing aquatic insect subsidies to terrestrial consumers, and not by increasing exposure to trace metals in prey. Exposure of terrestrial insectivores to trace metals in prey is decoupled from aqueous concentrations due to high rates of metal excretion during insect metamorphosis from aquatic larvae to terrestrial adult. These effects increase reliance of aquatic insectivores on terrestrial insect prey subsidies and/or lead to declines and behavioral changes in terrestrial insectivore populations.

Book chapter↗

USGS2015

Aquatic pollution increases use of terrestrial prey subsidies by stream fish

Stream food webs are connected with their riparian zones through cross-ecosystem movements of energy and nutrients. The use and impact of terrestrial subsidies on aquatic consumers is determined in part by in situ biomass of aquatic prey. Thus, stressors such as aquatic pollutants that greatly reduce aquatic secondary production could increase the need for and reliance of stream consumers on terrestrial resource subsidies. To test this hypothesis, we surveyed stream fish, their diets and resource availability in 16 subalpine streams over a regional gradient of trace metals known to strongly impact aquatic insect communities (i.e. fish prey) in the Colorado Rocky Mountains, USA. Fish increased their reliance on terrestrial insect prey as stream metals increased. Relative biomass of terrestrial insects in stomach contents of Brook and Brown Trout increased with respect to aquatic insect biomass and total stomach contents. Drifting insect biomass showed a declining trend for aquatic, but not terrestrial insects, over the metal gradient. Trout densities were unrelated to metal concentrations in streams where we found fish. Synthesis and applications . Our results indicate that diets of aquatic consumers can become more terrestrial as aquatic stressors that limit in situ food production increase and that these subsidies may compensate for loss of aquatic resources. This work implies an important connection between preserving aquatic–terrestrial linkages and management of fish populations in stressed watersheds. Specifically, intact riparian zones and aquatic–terrestrial linkages are likely to be important for maintaining trout production in streams with moderate metal contamination.

Colorado↗