Animals - Freshwater Ecology: Concepts and Environmental Applications - page 177

variable (Figs. 9.13 and 9.14). The streamlined bodies of rover predators
such as the salmon (Fig. 9.14E) allow them to pursue prey. The lie-and-
wait predator (Fig. 9.14B) with a pointed snout, torpedo-shaped body, and
large posterior fins is able to generate sudden thrust and acceleration. Fish
that live near the surface and obtain food from it generally have upturned
mouths, flattened heads, and large eyes (Fig. 9.13B). Bottom fish generally
have flattened bodies and often special adaptations, such as sensory bar-
bels or paddles, for sensing prey on the benthos (Figs. 9.13E and 9.14C).
Deep-bodied fish have narrow bodies and large fins (often spiny; Fig.
9.13D), and they are adapted to maneuvering in tight quarters such as
dense macrophyte beds. Eel-like fish (Fig. 9.13C) have reduced fins and
elongated bodies, and they are adapted to move through narrow spaces,
soft sediments, or holes.
Fishes also have extensive sensory adaptations. The ability for chemore-
ception is acute; chemical concentrations as low as 10 13 M can stimulate
behavioral responses (Moyle and Cech, 1996). Sounds and vibrations can
also be sensed by the inner ear and lateral line system. This includes the
ability to sense remote objects by their hydromechanical signals. Fishes also
have a series of pit organs that allow sensing of weak electrical currents
generated by prey. Many fishes have well-developed eyes that facilitate
sight feeding and sexual displays.
Freshwater fishes can be divided into three geographic types. A few
marine fishes can enter freshwaters for extended periods of time and may
be found in the lower regions of coastal streams. Obligatory freshwater
species must inhabit freshwaters for at least part of their life cycles and
many cannot tolerate marine waters for any significant length of time. Di-
adromous fishes spend part of their life cycles in marine systems. These
species include fishes that are catadromous and move from freshwater to
saltwater to spawn (e.g., some eels) and those that are anadromous and
move from saltwater to freshwater to spawn (e.g., salmon).
Tetrapods
Fishes gave rise to several groups of vertebrates that are prominent in-
habitants of some freshwater systems. These include the amphibians, rep-
tiles, birds, and mammals. The total diversity of these species is not high
relative to that of the fishes or the arthropods, but they draw public inter-
est. Several species such as beavers have extensive ecosystem effects.
Amphibians are divided into three groups: the salamanders (Urodela
or Caudata), the caecilians (Gymnophiona), and the frogs (Anura). The
frogs account for 4100 of the more than 4600 species of amphibians
(Pough et al., 1998). Many of these species spend part or all of their time
in freshwaters, particularly as eggs or larvae. Adult amphibians are preda-
tors but some larvae, such as some tadpoles, consume algae and detritus.
Amphibians can be associated with lentic and lotic habitats. Frog tadpoles
are very susceptible to predation by fish and other large predators, al-
though some are toxic or distasteful and avoid predation (Alford, 1999).
Adult amphibians are consumed by a wide variety of animals, including
fish, other amphibians, reptiles, birds, and mammals. Many amphibians
are sensitive to environmental change and are used as indicators of