Chapter 8: Antipredator Behaviour
8.1 Animals Modify Their Behaviour To Reduce Predation Risk
1. Cryptic Coloration: morphological colouration that matches the colour of the
environment to reduce detection by predators.
PREY TAKE EVASIVE ACTION WHEN DETECTED
2. When a predator initiates an attack, prey often flee in an effort to escape. This
predatorprey interaction can be very dramatic, as when a Canadian lynx chases
a showshoe hare, or when a hawk chases a squirrel.
3. Other species cannot flee because they move slower than heir predators, and in
these cases, we see different kinds of antipredator behaviour.
1. For example, in the dark of an Arizona night, a fascinating behavioural
interaction occurs between big brown bat preators and their prey, tiger moths,
which fly much more slowly.
1. Bats hunt by sound. They emit sonic pulses and find flying insects such as
moths by hearing the sonic pulses that bounce of of their prey.
2. This sonar system is a highly effective way for bats to pinpoint the
location and size of potential prey in the dark night sky.
3. Moths’ ears can also detect the sonic pulses, so they know when bats are
hunting nearby. They then fly in a more erratic pattern in an attempt to
evade the fastmoving bat.
8.2 Many Behaviour Represent Adaptive TradeOffs Involving
4. A world without predators would allow animals to concentrate their behaviour on
activities that maximize their fitness, perhaps by increasing time searching for
mates. In that light, the existence of predators represents a cost to animals: they
modify their behaviour to reduce the probability that they will be killed.
5. Behavioural Trade Off: sacrificing one activity for another.
INCREASED VIGILANCE DECREASES FEEDING TIME
6. Vigilance Behaviour: a behaviour in which an animal scans the environment for
7. This headdown position usually results in a reduced visual scanning rage.
Vegetation, such as grasses or other plants, can also increase the obstruction of
an animal’s scanning range.
VIGLIANCE AND PREDATION RISK IN ELK
8. Another strategy is to move to a safe location before eating food. Lima and
colleagues hypothesized that food carrying might represent a tradeoff between
feeding in safety (in a tree) and obtaining highenergy intake rates.
9. Energy Intake Rate: the energy acquired while feeding divided by total feeding
1. The model assumes that a squirrel’s fitness increases as energy intake rate
increases and the probability of being killed decreases. 2. It also assumes that a squirrel is at risk od being killed while one the ground
but safe while in a tree.
10. Handling time: the amount of time to manipulate a food item so that it is ready
ENVIRONMENTAL CONDITIONS AND PREDATION RISK IN FORAGING
PREDATION RISK AND PATCH QUALITY IN ANTS
11. Nonacs has studied predation riskforaging tradeoffs in Lasius, a common ant in
western North America. Much as in the study on redshanks, Nonacs asked
whether ants will trade off higher predation risk for feeding in a richer food
12. In order to demonstrate that Lasius ants respond to the threat of predation by
Formica ants, Nonacs set up a simple experiment with Larry Dill.
13. The researchers offered a Lasius colony twofood patches that contained identical
food. This food was solution of sugar, proteins, vitamins, and nutrients and was a
preferred ant food. The two food patches were identical distances away from a colony, but Lasius workers had to ravel through a small arena that contained a
Formica predator in order to obtain food from one of the patches.
1. In the control patch, Lasius ants did not need to encounter a Formica
predator to obtain food. Thus, the patches contained identical food, but the
control patch was safe (no predators), while the other, the experimental
treatment, was risk.
2. They found that after some Lasius workers had been killed, the rest would
avoid the risky patch and obtain food only from the safe patch. From this
experiment they concluded that Lasius ants prefer to avoid predators.
14. Once they had demonstrated that Lasius ants prefer to avoid Formica predators,
Nonacs and Dill designed another experiment. They wished to see if these ants
would exhibit a behavioural tradeoff between predation risk and food rewards.
1. To examine this question, they offered the Lasius ants two food patches that
differed in both predation risk and food quality. One food patch was both
risky (predator present) and rich with food, and the other was safe (no
predator present) but poor in food quality.
1. Both food patches again contained a solution of sugar, protein, vitamins,
and nutrients and were placed equidistant in their concentration of food:
the rich food patch had a higher concentration of food than the poor food
2. In this experiment, the Lasius ants always ha to travel through an arena that
contained a Formica predator if they wanted to feed from the rich patch.
Thus, to feed from the richer patch, workers were subject to higher rates of
predations, making it the riskier food patch.
3. Nonacs and Dill varied the relative difference in quality between the two food
patches. Because the food patches offered a food solution, the researchers
could manipulate the quality of a food patch by altering the concentration of
1. The safe food patch always had the lowest concentration of food, while