In western floodplains, species adapt to bullfrog, sunfish invaders


Date:
April 21, 2022
Source:
Cornell University
Summary:
A new study of a southwestern Washington floodplain finds that
most native species adapt well to the invaders by shifting their
food sources and feeding strategies.



FULL STORY ========================================================================== Non-native bullfrogs and sunfish species, introduced for consumer
and sport purposes, are known to alter ecosystems and hinder native
amphibians and fish in the Pacific Northwest highlands. But scant
research exists about how these introductions affect native species in
lowland floodplains.


==========================================================================
A new study of a southwestern Washington floodplain finds that most
native species adapt well to the invaders by shifting their food sources
and feeding strategies.

The results may hold true for other lowland waterbodies and other native species in response to bullfrogs and sunfish invaders. The findings 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 Life Sciences, 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 journalFreshwater Science.

Diverse habitats -- which create places to hide -- and plentiful alternate
food sources are two main factors that allow native species to coexist
with non- native invaders, Holgerson said.

"The good news is that we don't need to worry about removing these
non-native species from floodplains like we do in high elevation systems
where bullfrogs and sunfish have adverse effects," Holgerson said. "If we
want to manage something, we should manage for the habitat." This could include promoting available food resources and maintaining emergent
vegetation along waterbody edges where fish or amphibian larvae can hide,
she said.



==========================================================================
Both bullfrogs and sunfish have been introduced by people into fresh waterbodies globally. Bullfrogs, native to the northeastern U.S., were
brought to the West Coast for farming for frog legs. Sunfish, also known
as centrarchid fishes, including bass, crappie, bluegill and sunfish,
were introduced in the West for recreational fishing.

In the study, the researchers investigated how native and non-native
species coexist by analyzing what the different species ate and whether
they competed for the same resources. Ideally, a perfect study design
would have compared waterbodies that had only bullfrogs and natives;
only sunfish and natives; both invaders together and natives; and water
bodies without either invader.

"Unfortunately, in an invaded landscape, you often get both bullfrogs
and sunfish together," Holgerson said.

In water bodies with and without non-natives, the scientists took tissue samples from a range of predators and prey, and measured their carbon
and nitrogen stable isotopes, which occur naturally in the landscape. The isotopic signatures for carbon (ratios of carbon-12 and carbon-13) in a consumer's tissue can be traced to different food sources to understand
what it is eating.



========================================================================== Similarly, isotopic signatures for nitrogen (ratios of nitrogen-14 and nitrogen-15) reveal an organism's place within the food chain. Organisms
that are higher on the food chain retain more of the heavier nitrogen-15
than of nitrogen-14, Holgerson said.

Overall, the ecologists found that two species of native salamander
larvae and native three-spine stickleback fish fed a little lower on
the food web and shifted 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 less bottom-dwelling invertebrates (crustaceans, worms and aquatic insects) when competing with sunfish
for food.

The isotopic data suggest that salamander larvae shifted from open
water to hiding more at pond edges, where they ate more bottom-dwelling invertebrates.

Frogs were less affected by nonnative introductions. As frog larvae are herbivorous, the data suggest that the algae they ate was plentiful enough
to limit competition between nonnative bullfrog and native frog larvae.

"By shifting their feeding strategies, native species may be able to
coexist with these non-natives, as opposed to undergoing population
declines," Holgerson said.


========================================================================== Story Source: Materials provided by Cornell_University. Original written
by Krishna Ramanujan, courtesy of the Cornell Chronicle. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Meredith Holgerson, Martha Barnard, Byunghyun Ahn, Marc Hayes,
Angela
Strecker. Freshwater floodplain habitats buffer native food
webs from negative effects of non-native centrarchids and
bullfrogs. Freshwater Science, 2022; DOI: 10.1086/720137 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220421105502.htm

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