Danielle Pitt
dpitt003@ucr.edu
3372 Spieth Hall
900 University Ave.
Riverside, CA 92521
Co-PI: Dr. Kurt Anderson
kurt.anderson@ucr.edu
Growth rates of three competitor minnow species (Gambusia affinis, Notemigonus crysoleucas, and
Pimephales promelas) at varying productivity levels and implications for coexistence
Gambusia affinis (western mosquitofish) is a globally invasive species that tends to displace
ecologically similar species when introduced. Effective control strategies for this species are non-existent
(Walton et al., 2012). I wish to investigate how addition of an invasive species that competes with G.
affinis will alter impacts on native competitors, particularly those that may be utilized for mosquito
control. The impact of multiple predator interactions on a prey species may be more or less than their
additive effects (Sih et al., 1998) and are not known relating to G. affinis. I hypothesize that two
intraguild predators will, through interference competition, show a less than additive effect on an
intraguild prey species assuming that both predators are size-structured, engage in both intraguild
predation and cannibalism (Mylius et al., 2001; Rudolf, 2007; Crumrine, 2010) and that neither adapts to
fill a niche occupied by the intraguild prey.
To do this, I need to establish the comparative effectiveness at resource exploitation at different
productivity levels. This will be useful to identify the conditions most likely to foster coexistence to a)
identify the ideal conditions under which this hypothesis should be tested, and b) identify habitats where
productivity levels may be ideal for field experiments.
In this preliminary study, Notemigonus crysoleucas (golden shiner) will serve as a model for an
intraguild predator and Pimephales promelas (fathead minnow) will be used as a model for an intraguild
prey species. The proposed study, based on Laha & Mattingly (2006), will be performed in aquaria (2
gal, 25.4 x 20.3 x 15.2 cm. glass aquaria) in a laboratory with artificial refugia. Five juvenile fish of the
same age and species will be paired with one of four productivity levels (0.25, 0.5, 1, and 2 mg of food
per day (corresponding to 0.05. 0.1, 0.5 and 1 mg per fish per day). This will be repeated for each species
(G. affinis, N. crysoleucas, and P. promelas) and replicated three times for a total of 36 aquaria. Fish will
be given a 5 day acclimation period during which any fish that die will be replaced. Every three days for
1 month, fish will be removed from aquaria with repeated hand netting for all individuals, placed in a
container with just enough water for fish to remain upright. Fish will then be photographed to determine
length and the container massed to estimate wet mass of all fish.
Potential for coexistence will be evaluated based on variation in specific growth rate. We assume
that the species with the higher specific growth rate at a given productivity level will be the superior
resource exploiter. We predict that as an intraguild prey species, P. promelas will be a superior resource
exploiter to the two intraguild predator species at some productivity levels. This research will increase
our understanding of the food web interactions of this important invasive species.
To test the hypothesis that intraguild prey densities will be higher if predation among
invasive species is greater than predation on the native competitor, I propose a laboratory study
to test the comparative effects of fish assemblages of one to three species in a guild. Information
gathered on these interactions can be used to model the complex short-term interactions within
these assemblages. Once these short-term interactions are determined in aquaria, we can 1)
repeat the study in enclosures in natural water bodies to test the real-world functioning of the
assemblage, and 2) establish how evolutionary pressures acting on the assemblage may influence
its long-term stability. Regardless of the results, these data and the resulting models can be used
to understand the factors involved in coexistence in IGP systems and predict the effects of
invasive intraguild predators. The goal will be to apply this work in the Shipley-Skinner Reserve
to see how intraguild interactions involving a single or multiple intraguild predators will
influence potential for coexistence in this system.
The competition study will be performed in aquaria with artificial refugia and one or two
prey types (daphnia as planktonic prey and chironomids as benthic prey) at a density
corresponding to low productivity for 8 months from May to December. Treatments will all
include 5 juveniles of G. affinis, N. crysoleucas, and P. promelas a) as a control with no adults,
or with b) 6 adults of each of these species, c) 12 adults of each species, d) 6 adults of each pair
of species, and e) 4 adults of G. affinis, P. promelas, and either N. crysoleucas or L. parva. Fish
are to be separated by species and size-class to acclimate for 5 days. Those that die will be
replaced. Behavior will be measured based on Altmann (1974) where 10 individuals are
observed for 3 minutes each once per week and their position relative to other fish are mapped
and aggressive encounters and foraging attempts are recorded. Fish will be sampled with
repeated hand netting for all individuals and measuring their weight and length to calculate
growth rate.
If my hypothesis is correct, this research may lead to novel control strategies to benefit native
species and habitat. Several species displaced by G. affinis have been proposed as mosquito control
agents, so recovery of these species may be valuable for mosquito control (Saba, 2012). Arroyo chub
(Gila orcutti), a southern California endemic displaced by G. affinis is a likely candidate for future
applied studies using this basic research.
REFERENCES
Crumrine, P.W. (2010). Size-structured cannibalism between top predators promotes the survival of
intermediate predators in an intraguild predation system. Journal of the North American
Benthological Society, 29(2): 636-646.
Laha, M. & Mattingly, H.T. (2006). Identifying environmental conditions to promote species coexistence:
An example with the native Barrens topminnow and invasive western mosquitofish. Biological
Invasions, 8: 719-725.
Mylius, S.D., Klumpers, K., de Roos, A.M., & Persson, L. (2001). Impact of intraguild predation and
stage structure on simple communities along a productivity gradient. The American Naturalist,
158(3): 259-276.
Rudolf, V.H.W. (2007) The interaction of cannibalism and omnivory: consequences for community
dynamics. Ecology, 88, 2697–2705.
Saba, M.V. (2012, May 10). Proposal to Use Native Fishes as Mosquito Control Agents by the Orange
County Vector Control District. Retrieved from: http://www.sawpa.org/wpcontent/uploads/2012/05/native-fish-proposal_OCVCD_April2012_final.pdf
Sih, A., Englund, G. & Wooster, D. (1998). Emergent impacts of multiple predators on prey. Trends in
Ecology & Evolution, 13(9): 350-355.
Walton, W.E., Henke, J.A., & Why, A.M. (2012). Gambusia affinis (Baird & Girard) and Gambusia
holbrooki Girard (mosquitofish). In R.A. Francis (Ed.), A handbook of global freshwater invasive
species (pp. 261-273). London: Earthscan.
BUDGET
Supplies: 100 fathead minnows
$20
100 golden shiners
20
66 qt plastic bins
18
Gravel
20
2 water filters
32
Air pump
22
9 packs of air stones
27
8 control valves
40
Tubing
18
Fish food
10
MS-222 (anesthesia)
33
Total estimated tax
20
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Total requested:
$ 280