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Amphipod Predation on Northern Red-Legged Frog EmbryosMelissa Harbert & Brian Hudgens
Institute for Wildlife Studies
• Predation on early anuran life stages has potential to
• influence population dynamics1,6
• act as an important evolutionary force5
• link anurans to breeding pond food webs2
• Amphipods can be found in freshwater ponds but are usually
considered detrivores.7
• Amphipods have been documented to consume a variety of small
organisms under certain conditions,3,4,7 but amphipod predation on
amphibian embryos or larvae has never been documented.
• Here, we report on predation of Northern Red-legged Frog (Rana
aurora) embryos by the amphipod Crangonyx spp.
Study Sites:
Χ
Results:
Predation rates of Rana aurora embryos at different levels of predator exposure at 2
breeding ponds in Humboldt County, California. A+ and A- represent amphipod addition
to and exclusion from chambers, respectively. Error bars indicate ±1 standard error.
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Open Screened A+ A- Open Screened
Pre
da
tio
n R
ate
HBNWR BL
Conclusions:• Amphipods act as a major embryo predator at HBNWR. There, predation by
amphipods was about as significant as predation at BL by larger organisms such as
salamanders.
• Growing amphipods may have become trapped in screened chambers, inflating the
screened predation rate or conditions within the enclosed amphipod-addition
chambers may not have been optimal for amphipod survival, reducing the amphipod-
addition predation rate.
• The significance of predation by amphipods for whole egg masses in the open pond
at HBNWR is likely affected by amphipod density and food availability and the size
and cohesiveness of egg masses.
• Differences in biotic communities and environmental conditions likely explain why
embryo predation by amphipods was observed at HBNWR but not BL.
• This is the first published account of amphipods acting as predators on amphibians.
• Amphipods can be predators and their role in the food web may vary considerably
depending on the specific system studied. As with any ecological interaction, the
influence of amphipod predation on amphibian population growth or evolution is likely
to be highly context dependent.
Acknowledgements:We would like to thank the Humboldt Bay National Wildlife Refuge
and Green Diamond Resource Company for their cooperation. We
are grateful to W Gerth for providing the amphipod identification. This
work benefitted from comments by J Abbott, D Garcelon, K McHarry,
M House, E Nelson, D Page, and L Gordon. We thank SERDP
RC2512 for funding the work.
Literature Cited:1=BIEK R, FUNK WC, MAXELL BA, MILLS LS. 2002. What is missing in amphibian decline research: insights from ecological sensitivity analysis. Conservation Biology 16:728–734.
2=DAVENPORT JM, CHALCRAFT DR. 2012. Evaluating the effects of trophic complexity on a keystone predator by disassembling a partial intraguild predation food web. Journal of Animal Ecology 81:242–250.
3=HYNES HBN. 1954. The ecology of Gammarus duebeni Lilljeborg and its occurrence in fresh water in western Britain. Journal of Animal Ecology 23:38–84.
4=MACNEIL C, DICK JTA, ELWOOD RW. 1997. The trophic ecology of freshwater Gammarus spp. (Crustacea:Amphipoda): Problems and perspectives concerning the functional feeding group concept. Biological Reviews 72:349–364.
5=MAGNUSSON WE, HERO JM. 1991. Predation and the evolution of complex oviposition behaviour in Amazon rainforest frogs. Oecologia 86:310–318.
6=MCHARRY K. 2017. Influence of canopy cover and climate on early life-stage vital rates for Northern Red-legged Frogs (Rana aurora), and the implications for population growth rates [thesis]. Arcata, CA: Humboldt State University.
7=SCHWARTZ SS. 1992. Benthic predators and zooplanktonic prey: Predation by Crangonyx shoemaker (Crustacea; Amphipoda) on Daphnia obtuse (Crustacea; Cladocera). Hydrobiologia 237:25–30.
• Open canopy• Abundant emergent vegetation
• Warm, shallow water
• Common potential egg predators=diving
beetles, giant water bugs, mosquito
larvae, caddisfly larvae, dragonfly larvae,
rough-skinned newts
• Abundant amphipods (Crangonyx spp)
• Closed canopy• Sparse emergent vegetation
• Cold, deep water
• Common potential egg predators=
caddisfly larvae, northwestern salamanders
• No amphipods
Humboldt Bay National Wildlife Refuge,
CA (HBNWR)
Big Lagoon, CA (BL)
Methods:
n=15
n=10
AT HBNWR Site
n=11
At BL Site
Open treatment: all predators
can access eggs
Screened treatment: only
predators<1.5 mm diameter can
access eggs
Amphipod-addition
treatment: amphipods added
to enclosed chambers at
approximately 2X ambient
pond density
Amphipod-exclusion
treatment: no visible
predators can access eggs
• To determine predation rates of R. aurora embryos, we performed experiments
with a paired design by enclosing pieces of egg masses in chambers that
excluded predators of various sizes
AND
• We calculated predation rates as the ratio of viable embryos that disappeared
prior to the week before hatching (because tadpoles could easily swim out of
open chambers once hatching began) to the number of viable embryos originally
put in the container.
Introduction
Open treatment: all predators
can access eggs
Screened treatment: only
predators<1.5 mm diameter can
access eggs. Amphipods were
able to fit through screen.
Wildlife Studies
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