Bullfrog (Rana Catesbeiana) Invasion of a California River: The Role of Larval Competition

Abstract

I studied the invasion of Rana catesbeiana (the bullfrog) into a northern California river system where bullfrogs are not native. Native yellow-legged frogs, Rana boylii, a species of special concern, were almost an order of magnitude less abundant in reaches where bullfrogs were well established. I assessed the potential role of larval competition in contributing to this displacement in a series of field manipulations of tadpole density and species composition. The impact of R. catesbeiana on native tadpoles in the natural community agreed with the outcome of more artificial experiments testing pairwise and three-way interactions. In 2-m 2 enclosures with ambient densities of tadpoles and natural river biota, bullfrog tadpoles caused a 48% reduction in survivorship of R. boylii, and a 24% decline in mass at metamorphosis. Bullfrog larvae had smaller impacts on Pacific treefrogs, Hyla regilla, causing 16% reduction in metamorph size, and no significant effect on survivorship. Bullfrog tadpoles significantly affected benthic algae, although effects varied across sites. Responses to bullfrogs in field settings were similar qualitatively to results seen in smaller-scale experiments designed to study size-structured competition among disparate age/size classes of species pairs and trios. Competition from large overwintering bullfrog larvae significantly decreased survivorship and growth of native tadpoles. Competition from recently hatched bullfrog larvae also decreased survivorship of R. boylii and H. regilla. Native species competed weakly, both interspecifically and intraspecifically. The only suggestion of a negative impact of a native species on bullfrogs was a weak effect of H. regilla on recent hatchlings. Competition appeared to be mediated by algal resources, and there was no evidence for behavioral or chemical interference. These results indicate that, through larval interactions, bullfrogs can exert differential effects on native frogs and perturb aquatic community structure.

Diets of tadpoles from a temporary pond in southeastern Brazil (Amphibia, Anura)

“…The tadpoles ingested items ranging in size from 10- (KUPFERBERG et al 1994, KUPFERBERG 1997a and that competition between tadpoles of Rana catesbeiana Shaw, 1802 and R. boylii Baird, 1854 (Ranidae) appeared to be mediated by algal resources (KUPFERBERG 1997b). The detection of Ciliophora and other soft-bodied animals, such as Tardigrada and Rotifera in the intestines, is an important finding because few studies have detected soft-bodied organisms or bacteria, and they could be the real source of nutrients for tadpoles (INGER 1986, HOFF et al 1999.…”

“…In choice experiments, KUPFERBERG (1997a) showed that tadpoles foraged selectively on the algal foods that promoted most rapid growth and development. DUELLMAN & TRUEB (1986) commented that food partitioning among anuran tadpoles is caused by differences in the ability of the various species to ingest particles of varying sizes and also to the position they occupy in the water column, a consequence of morphological adaptations for the exploitation of specific microhabitats.…”

The Presence of Micropterus Salmoides (Largemouth Bass) Influences the Populations of Rana Draytonii (California Red-Legged Frog) and Pseudacris Regilla (Pacific Treefrog) in Two Ponds in Santa Barbara County, California

“…Although both species evolved in the presence of native fish, the antipredator responses to the native species may not be sufficient to allow coexistence with this alien species (Gamrat and Kats 1996). It is possible that there was a combination of predation (Vredenburg 2004;Pope 2008;Knapp and Matthews 2000), competition (Adams 2000), behavioral modifications (Lawler et al, 1999;Kupferburg 1997), or trophic influences (Heyer et al, 1975;Smith 1982;Caldwell et al, 1980;Adams 2000) or synergisms between these factors that influenced my results.…”

“…In California and much of western North America, amphibian population declines are occurring, and several causal factors have been proposed including disease Kiesecker et al, 2001;Blaustein et al, 2005;, increased use of pesticides and air pollution (Davidson et al, 2001;Relyea and Mills 2001;Kiesecker 2002), habitat destruction (Davidson et al, 2002), over-exploitation (Jensen and Camp 2003;Jennings and Hayes 1985), climate change (Pounds et al, 1999), UV-B radiation Anzalone et al, 1998;Blaustein et al,1998), and alien predators and competitors (Kupferburg 1997;Knapp and Matthews 2000;Vredenburg 2004;Pope 2008). Recent studies have suggested that amphibian declines are potentially influenced by a number of contextspecific interactions of multiple stressors and synergisms between these causal factors (Blaustein and Kiesecker 2002;Kiesecker 2002;Pounds et al, 2006).…”

Reproductive phenology of the American Bullfrog in subtropical Brazil: photoperiod as a main determinant of seasonal activity

“…At North American introduction sites of bullfrogs, the decline of various amphibian species was recorded (Bury and Luckenbach 1976, Hayes and Jennings 1986, Hecnar and M'Closkey 1997, Pearl et al 2005. Experimental studies have shown that bullfrog tadpoles can reduce food resources for tadpoles of others species like Ranidae, Bufonidae, Hylidae and tiger salamander (Kupferberg 1997, Adams 2000, Boone et al 2004. Bullfrogs also have the potential to affect native species in the acoustic niche (Both and Grant 2012).…”