Environmental Engineering Reference
In-Depth Information
5 a.m.
6
7
9
10
11
Noon
2
0
20
40
60
80
100
4 p. m.
5
6
7
8
10
Midnight
4 a.m.
7
0
20
40
60
80
100
FIGURE 19.5
Diel vertical migration of young
Daphnia longispina
in Lake Lucerne (data
from Worthington, 1931).
Predator avoidance in time and space is a crucial adaptation to preda-
tion in many species. It is clear that many species simply hide or run away
when they sense a predator in the vicinity. Timing of reproduction is an-
other approach to avoiding predation. This is the case for some species of
zooplankton that produce diapausing eggs in the presence of increased pre-
dation pressure (Hairston, 1987). Massive synchronous hatches of aquatic
insects not only increase the chance that adults will be able to find a mate
but also saturate predators, allowing some adults to survive and mate.
ADAPTATIONS OF PREDATORS
Predation can be characterized by a sequence of events (Brönmark and
Hansson, 1998). Prey must be encountered and detected, then attacked and
captured, and finally ingested. Adaptations are evident at all stages; this
section is organized by the natural sequence of events.
The behavioral strategy used by organisms to obtain prey can vary from
remaining immobile and allowing prey to approach to active foraging. The
specific strategy that has evolved presumably allows for the most efficient
harvesting of food given morphological, abiotic, and community constraints.
The simplest encounter strategy is to sit and wait for prey. For example,
pike
(Esox)
lie hidden, waiting for prey to come close. Pike have large tail
(caudal) fins and pull their bodies into “S” shapes from which they can ac-
celerate explosively to catch prey. Odonate dragonfly nymphs also wait for
prey. They have a hinged labial jaw that ejects very rapidly and snatches
prey.
Hydra
captures larval bluegill
(Lepomis macrochirus)
that contact its
stinging nematocysts, a form of sit-and-wait predation that can have con-
siderable impact on the populations of the larval fish (Elliot
et al.,
1997).
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