Geoscience Reference
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Figure 7-12. Adult American bullfrog ( Rana
catesbeiana ) sits in a patch of mosquito fern ( Azolla
sp.) in a prairie marsh (see Color Plate 7-12). This frog
is a game species; the largest native frog in North
America, its body may reach 20 cm in length and weigh
nearly 1 kg (Elliot, Gerhardt and Davidson 2009). Photo
by J.S. Aber; central Kansas, United States.
Figure 7-11. Ferruginous hawk ( Buteo regalis ), the
largest hawk in North America, sits on a post beside Dry
Lake, a salina in western Kansas, United States. It prefers
open prairie habitats of the Great Plains region from
Canada to northern Mexico. It eats a wide variety of prey
from both wetland and upland settings; small mammals
comprise the majority of its diet. Photo by J.S. Aber.
nervous system, backbone, skin, eyes, ears, etc.
However, in contrast, most lay eggs for repro-
duction, and they lack hair or feathers. They
have lower rates of metabolism and require less
food than do birds or mammals; body tempera-
ture is regulated by behavior, such as basking
in the sun or seeking shade (Sievert and Sievert
2006). Amphibians depend on water; their soft,
jellylike eggs must be laid in water. Most have
two life stages, an aquatic larval (tadpole) phase
followed by a semi-aquatic or terrestrial adult
phase. This is true of all frogs, toads, and most
salamanders, but some salamander species
hatch from eggs directly into miniature versions
of adults. Frogs and salamanders must maintain
moist skin to avoid rapid dehydration, so they
remain in wet environments as adults (Fig. 7-
12); toads have dry skin, however.
Most amphibians have mucus glands in their
skin that produce toxic or unpleasant-tasting
secretions that presumably are a defense against
predators. Human eyes and mouth are sensitive
to these compounds, so it is important to wash
after handling amphibians (Sievert and Sievert
2006). Further defenses include leaping into
water, camoul age that changes to match the
surroundings, retreating in crevices or burrows,
sounding loud distress calls, and inl ating to a
Figure 7-13. Plains gartersnake ( Thamnophis radix )
has caught a small American bullfrog ( Rana
catesbeiana ) at the edge of a prairie marsh (see Color
Plate 7-13). The snake has already swallowed the entire
right hind leg of the frog, which has ceased to struggle.
Photo by J.S. Aber and S.W. Aber; central Kansas,
United States.
size too large for the predator to swallow (Elliot,
Gerhardt and Davidson 2009). Adult salaman-
ders, frogs and toads are carnivores eating
mainly insects, spiders, worms, slugs, and other
small invertebrates. Most tadpoles eat algae, and
some may prey on other tadpoles. Amphibians
are, in turn, prey for larger carnivores - i sh,
turtles, snakes (Fig. 7-13), birds and mammals
(Briggler and Johnson 2008).
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