In western floodplains, species adapt to bullfrog and sunfish invaders – ScienceDaily
Non-native bullfrogs and sunfish species, introduced for consumption and sport, are known to alter ecosystems and interfere with native amphibians and fish in the Pacific Northwest highlands. But little research exists on how these introductions affect native species in lowland floodplains.
A new study of a southwestern Washington state floodplain reveals that most native species are adapting well to invaders by changing their food sources and feeding strategies.
The results may be true for other lowland water bodies and other native species in response to invading bullfrogs and sunfish. The results could also help wildlife managers develop appropriate action plans where these non-natives are established.
“The study shows that native species, at least in this floodplain, can tolerate non-native bullfrogs and sunfish,” said Meredith Holgerson, assistant professor of ecology and evolutionary biology in the College of Agriculture and Science. of life and first author of the study. , “Freshwater Floodplain Habitats Buffer Native Food Webs from Negative Effects of Non-native Centrarchids and Bullfrogs,” published online March 28 in the journal Freshwater science.
Diverse habitats — which create places to hide — and plenty of alternative food sources are two main factors that allow native species to co-exist with non-native invaders, Holgerson said.
“The good news is that we don’t have to worry about removing these non-native species from the floodplains like we do in high elevation systems where bullfrogs and sunfish have detrimental effects,” Holgerson said. “If we want to manage something, we have to manage for the habitat.”
This could include promoting available food resources and maintaining emergent vegetation along the edges of water bodies where fish or amphibian larvae can hide, she said.
Bullfrogs and sunfish have been introduced by man into
bodies of water on a global scale. Bullfrogs, native to the northeastern United States, were brought to the West Coast to farm frog legs. Sunfish, also known as centrarchid fish, including bass, crappie, bluegill, and pumpkinseed, were introduced to the West for recreational fishing.
In the study, researchers investigated the coexistence of native and non-native species by analyzing what different species ate and whether they competed for the same resources. Ideally, a perfect study design would have compared water bodies that only had bullfrogs and natives; only bluegills and natives; both invaders and natives; and bodies of water without any invaders.
“Unfortunately, in an overgrown landscape, you often get both bullfrogs and sunfish,” Holgerson said.
In bodies of water with and without non-natives, scientists took tissue samples from a range of predators and prey, and measured their stable isotopes of carbon and nitrogen, which occur naturally in the countryside. Carbon isotope signatures (ratios of carbon 12 and carbon 13) in a consumer’s tissues can be attributed to different food sources to understand what they are eating.
Similarly, nitrogen isotope signatures (ratios of nitrogen-14 and nitrogen-15) reveal an organism’s place in the food chain. Organisms that are higher up the food chain retain more heavier nitrogen-15 than nitrogen-14, Holgerson said.
Overall, ecologists found that two species of native salamander larvae and native threespine stickleback were feeding slightly lower on the food web and displacing food resources in the presence of bullfrogs and sunfish. The data suggest that stickleback – known to have flexible diets – ate more open-water zooplankton and fewer bottom-dwelling invertebrates (crustaceans, worms, and aquatic insects) when competing with sunfish for food. food.
Isotope data suggest that salamander larvae shifted from open water to hiding more at the edge of ponds, where they ate more benthic invertebrates.
Frogs have been less affected by non-native introductions. As frog larvae are herbivorous, the data suggests that the algae they ate were abundant enough to limit competition between non-native frog larvae and native frog larvae.
“By changing their feeding strategies, native species may be able to co-exist with these non-natives, instead of experiencing population declines,” Holgerson said.