Biology Reference
In-Depth Information
Cane toads (
Bufo marinus
) introduced to Australia have been documented to
inflict population-level effects on the ground-nesting rainbow bee-eater (
Merops
ornatus
). In the absence of toads, these birds produce an average of 1.2 fledglings/
nest. But toads prey upon eggs and nestlings and usurp nest burrows, thereby
destroying one-third of all nests and reducing nest success rate to an average of 0.8
fledglings/nest (Boland, 2004a, b). Displaced adult birds suffer reduced average
nest productivity with subsequent nesting attempts, making the effects of the toads
even broader than that measurable by direct predation and nest destruction (Boland,
2004a, b). Susceptibility to nest predation by toads appears to result at least partly
from lack of proper defensive behaviors in the nesting birds, which can successfully
fend off attacks by much larger native predators (Boland, 2004a, b). Cane toads
have been reported to prey on an array of other native vertebrates (e.g., Rabor,
1952; Pippet, 1975; Stammer, 1981; Freeland and Kerin, 1988; Caudell et al.,
2000), but effects on populations have not been systematically researched. One
study reported a correlation between presence of toads and reduction in beetle
populations (Catling et al., 1999); another reported a similar correlation with a
reduction in gecko populations (Watson and Woinarski, 2003, cited in McRae et al.,
2005). Others have noted toads to have greater volumes of prey in their stomachs
where recently established compared to areas where they have been longer estab-
lished (Anonymous, 1968), suggesting suppressive effects on invertebrate commu-
nities by a prolonged history of predation, although temporal changes in invertebrate
populations have not been measured directly. Anecdotal reports of pest and native
invertebrate declines following introduction of toads (e.g., Wolcott, 1937, 1948,
1950a, b; Simmonds, 1957) suggest the same suppressive effects, but studies on
most native invertebrate communities are lacking (but see Greenlees et al., 2006 for
an exception).
A variety of studies has implicated alien bullfrogs (
Rana catesbeiana
) in
declines of native herpetofauna across the western United States. Evidence includes
anecdotal (Lardie, 1963; Dumas, 1966; Hammerson, 1982) and statistical (Moyle,
1973; Schwalbe and Rosen, 1988; Fisher and Shaffer, 1996; Kupferberg, 1997a;
Rosen and Schwalbe, 2002) analyses of distributional or historical trends, partial
recovery of affected populations with experimental reduction or exclosure of bull-
frogs (Schwalbe and Rosen, 1988; Rosen and Schwalbe, 1996a, b), skewed size-
class distributions in populations syntopic with bullfrogs (Holland, 1991, cited in
Hayes et al., 1999), and experimental demonstration of increased mortality or
decreased growth in laboratory or field experiments (Kieseker and Blaustein, 1997,
1998; Kupferberg, 1997a; Lawler et al., 1999; Adams, 2000; Pearl et al., 2004;
Maret et al., 2006). Natives argued to be affected by bullfrogs include the frogs
Bufo boreas
(Lardie, 1963),
Pseudacris regilla
(Jameson, 1956),
Rana aurora
(Lardie, 1963; Pearl et al., 2004),
R. blairi
(Hammerson, 1982),
R. boylii
(Moyle,
1973; Kupferberg, 1997a),
R. chiricahuensis
(Schwalbe and Rosen, 1988; Rosen
and Schwalbe, 1995, 2002; Rosen et al., 1995),
R. draytonii
(Moyle, 1973);
R. pipiens
(Hammerson, 1982),
R. pretiosa
(Lardie, 1963; Dumas, 1966; Pearl et al., 2004),
R. yavapaiensis
(Schwalbe and Rosen, 1988; Rosen and Schwalbe, 1995, 2002),
the entire suite of central Californian amphibians (Fisher and Shaffer, 1996), the
