Disease Transmission: Chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis, is an emerging disease of amphibians responsible for population declines and even extinctions globally (Hanselmann et al., 2004). Introduced populations of Lithobates catesbeianus can harbour reservoirs of the fungal agent without showing significant clinical disease symptoms themselves (Hanselmann et al., 2004).
Native North American amphibians which may be affected by bullfrogs include: the Pacific chorus frog (Pseudacris regilla); the Northern red-legged frog (Rana aurora); the plains leopard frog (Lithobates blairi); the northern leopard frog (Lithobates pipiens); the lowland leopard frog (Lithobates yavapaiensis); and the entire suite of central Californian amphibians (Kraus, 2009).
Similar declines in native species concurrent with the introduction of bullfrogs have been noted in Europe, in Germany (C.R. Boettger, 1941; Thiesmeier et al., 1994 in Kraus 2009), Florence (Italy) (native Rana; Touratier. 1992b in Kraus 2009) and in the Aquitaine of southwestern France (native fish; Touratier, 1992a in Kraus, 2009).
Threat to Endangered Wildlife: In the USA the bullfrog is known to prey on the following endangered amphibians: Amargosa Toad (Anaxyrus nelsoni) (Jones et al., 2003 in Kraus, 2009); California tiger salamander (Ambystoma californiense); Chiricahua leopard frog (Lithobates chiricahuensis); the California red-legged frog (Rana draytonii); and the Oregon spotted frog (Rana pretiosa)
Ecosystem change: Several field studies portray tadpoles as ‘‘ecosystem engineers’’ that alter the biomass, structure and composition of algal communities (Dickman, 1968; Seale, 1980; Osborne & McLachlan, 1985; Kupferberg, 1997a; Flecker et al., 1999; Peterson & Boulton, 1999 in Pryor, 2003).
Modification of Nutrient Regime: High food intake (Wassersug, 1984 in Pryor, 2003) and high population densities (up to thousands of individuals per m²; Alford, 1986, in Pryor, 2003) suggest that tadpoles have considerable impact on nutrient cycling and primary production in freshwater ecosystems.
Predation: Tadpoles of L. catesbeianus feed upon eggs and larvae of the endangered Razorback Sucker (Xyrauchen texanus) in laboratory conditions (Mueller et al., 2006 in Kraus, 2009), and their densities in artificial habitats can depress fish larvae recruitment (Kraus, 2009).
Competition: Introduced bullfrogs compete with endemic species (Kupferberg, 1997; Kiesecker & Blaustein, 1997 in Hanselmann et al., 2004). Unlike many other frogs, bullfrogs can coexist with predatory fish (Hecnar, 1997 in Casper & Hendricks, 2005), giving bullfrogs a competitive advantage.
Interaction With Other Invasive Species: In Oregon, the invasion of bullfrogs appears to have been facilitated by the presence of the non-native sunfish (Adams et al., 2003).
For a detailed account of the environmental impacts of L. catesbeianus please read: Lithobates catesbeianus Impacts Information.
Location Specific Impacts:
Reduction in native biodiversity: It has been claimed that L. catesbeianus has led to decline of native Rana in the region around Florence, Italy (Touratier 1992b, in Kraus 2009) and of native fish in the Aquitaine of southwestern France (Touratier 1992a, in Kraus 2009). Concern has been expressed about their potential effects elsewhere in Europe (Albertini & Lanza 1987, Stumpel 1992, in Kraus 2009). They have also been implicated in numerous species declines, including the common midwife toad (Alytes obstetricans), the common toad (Bufo bufo) and the common fire salamander Salamandra salamandra in Europe (Etienne et al. 2007).
Disease transmission: A study by Garner and colleagues (2006) adds France to the list of European countries with amphibians that are known to be infected with Batrachochytrium dendrobatidis . For more information on disease transmission in relation to the American bullfrog please see Lithobates catesbeianus (American Bullfrog) Impacts Information.
Reduction in native biodiversity: It has been claimed that L. catesbeianus has led to decline of native fish in the Aquitaine of southwestern France (Touratier 1992a, in Kraus 2009).
Predation: Gut contents analysis of L. catesbeianus in Germany revealed the frog preys on the edible frog Rana esculenta, which represents a high percentage of the prey items found (CABI Bioscience 2005).
Reduction in native biodiversity: Declines in native herpetofauna concurrent with introduction of American bullfrogs have been noted in Germany (C.R. Boettger, 1941, Thiesmeier et al. 1994, in Kraus 2009).
Disease transmission: Italian amphibians have tested positive for the chytrid fungus Batrachochytrium dendrobatidis . For more information on disease transmission in relation to the American bullfrog please see Lithobates catesbeianus (American Bullfrog) Impacts Information.
Reduction in native biodiversity: It has been claimed that L. catesbeianus has led to decline of native Rana in the region around Florence (Italy) (Touratier 1992b, in Kraus 2009).
Threat to endangered species: Concerns have been expressed about the potential threat of bullfrogs to the IUCN Red List Endangered Kikuzato's Brook Snake (Opisthotropis kikuzatoi), endemic to Kumejima Island, Ryukyu Islands, Japan. The threat comes both from the frog’s potential to directly prey upon these small snakes but also because it is known to eat the endangered freshwater crab, (Candidiopotamon kumejimense), the only known food source for the snake (Ota et al. 2004a, in Kraus 2009).
Predation: L. catesbeianus has been observed preying on native species in Puerto Rico, including Leptodactylus albilabris (Santos-Barrera et al. 2009).
Humacao Nature Reserve (Puerto Rico)
Predation: There have been reports of bullfrogs preying on several bird species, including a duckling of the threatened white-cheeked pintail (Anas bahamensis)
Competition: Tadpoles compete with native tadpoles and, as shown in the western USA, significantly decrease survivorship of the latter; in general, the tadpoles are not eaten by fish, which gives them a competitive edge over the native frogs (CABI Bioscience 2005).
Ecosystem change: Tadpoles can have a significant impact on algae, which can affects the aquatic community structure (CABI Bioscience 2005).
Predation: The potential environmental impacts of the American bullfrog are substantial. The main concerns are that the American bullfrog will devour native frog and reptile species; the adults devour all prey items they can swallow (CABI Bioscience 2005).
United Kingdom (UK)
Disease transmission: In Great Britain Garner and colleagues (2005) found chytrid fungus (Batrachochytrium dendrobatidis) in two of 14 introduced North American bullfrogs caught in 2004 but did not find it in wild-captured native British species. The ability of the North American bullfrog to act as a vector for chytrid range expansion has been hypothesised (Hanselmann et al. 2004; Daszak et al. 2004, in Garner et al. 2005). Data from Garner and colleagues (2005) may indicate that bullfrogs can fulfill this role in Great Britain and other areas; they have found the molecular signal of chytrid infection from introduced North American bullfrogs collected on three separate continents (T.W.J. Gamer et al. Unpub. Data, in Garner et al. 2005). For more information on disease transmission in relation to the American bullfrog please see Lithobates catesbeianus (American Bullfrog) Impacts Information.
Arizona (United States (USA))
Disease transmission: Pathogens reported from L. catesbeianus, include Batrachochytrium dendrobatidis, a chytrid fungus found to be responsible for an outbreak of disease which occurred in Arizona (Sredl et al. 2000, in Casper & Hendricks 2005) and which has been implicated as the cause of amphibian declines in Australia and Panama (Berger et al. 1998, Casper & Hendricks 2005).
California (United States (USA))
Predation: The bullfrog has long been implicated as a competitor of and predator on native western ranid frogs (Kiesecker & Blaustein 1997, Kupferberg 1997, Licht 1974, Moyle 1973, Nussbaum et al. 1983, in Cook & Jennings 2007). Bullfrogs have also been documented consuming red-legged frogs (Rana draytonii) at the tadpole, metamorph, and adult life stages (Doubledee et al. 2003; Lawler et al. 1999; Cook, 2002; Cook and Jennings 2001, D. G. Cook Unpub. Data, in Cook and Jennings 2007). According to Cook and Jennings (2007) the effect of bullfrog predation on the red-legged frog depends on the sizes of the individuals involved in the interaction. The much larger body size of the bullfrog suggests it could have a significant impact, especially if it were to become numerically superior (Pearl et al. 2004, in Cook & Jennings 2007).
Threat to endangered species: The bullfrog has displaced the endangered California red-legged frog (Rana aurora draytonii) in some locations (Scalera 2007). Model simulations created by Doubledee Muller and Nisbet (2003) indicate that winter floods, which strongly increase mortality of bullfrogs but not California red-legged frogs (Rana aurora draytonii), facilitate coexistence in south Californian streams if they occur more than once every 5 years. In other words, in areas where flooding occurs once every five years or more introduced bullfrogs may be able to live in harmony with red-legged frogs in California. This would of course not apply to all environments and streams with little flooding would still be at risk of invasion by L. catesbeianus.
Iowa (United States (USA))
Predation: Bullfrogs negatively impact smaller frog species in Iowa (Christiansen, 2001).
Oregon (United States (USA))
Competition: Bullfrogs compete with the native northern red-legged frog (see Rana aurora in IUCN Red List Of Threatened Species) and Oregon spotted frog (see Rana pretiosa in IUCN Red List of Threatened Species) (Pearl et al., 2004). Competition between bullfrogs and the northern red-legged frog appears to be context-dependent, with competition only having negative effects on red-legged frog larvae when resources are clumped as opposed to scattered (Kiesecker et al., 2001).
Modification of nutrient regime
Predation: Bullfrogs prey on juveniles of the native northern red-legged frog and Oregon spotted frog Rana pretiosa (Pearl et al., 2004).
Washington (United States (USA))
Modification of nutrient regime
Disease transmission: In 1999 a bullfrog farm in Uruguay experienced a mass die-off due to an outbreak of chytridiomycosis.
Disease transmission: In one study, conducted on a population of introduced American bullfrogs (N=48) in the Venezuelan Andes B. dendrobatidis was present in 96% of the individuals examined. The majority of frogs had few small lesions consistent with little clinical disease and no unusual mortality was observed. The high prevalence of Batrachochytrium but lack of clinical signs or chytridiomycosis-related mortality suggests that L. catesbeianus may be a good reservoir for this parasite in Venezuela (Hanselmann et al. 2004).
Threat to endangered species: The zone of Merida state, called Jaji, is near the habitat of some endemic frogs of the genus Atelopus, especially the IUCN Red List Critically Endangered Venezuelan yellow frog (A. carbonerensis), which may be extinct.