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