Summary Oxford University Biology revision notes: Group-Level Behaviour
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Course
Animal Behaviour
Institution
Oxford University (OX)
My Oxford University notes for the Biology FHS exam in Animal Behaviour. Useful for Biology and Human Sciences. I achieved a first and multiple academic prizes. Includes descriptions of concepts and key examples/references.
Discuss how the principle of self-organisation can be used to explain various group-level behavioural
phenomena in both humans and non-humans. // How can studies of collective behaviour in animals help
us understand human crowd behaviour? // What is the role of leadership in collective behaviour? // How
do animal collectives coordinate behaviour? To what extent can ecology explain primate social systems? //
How is group living affected by ecology? // What are the costs and benefits of living in groups? // Do
animals understand each other’s intentions? // What evidence is there that group living benefits
individuals?
Frame answer as a cost-benefit analysis.
We are trying to explain group behaviour from the perspective of individual benefit.
Principle of self-organisation: a process where some form of overall order arises from local interactions
between parts of an initially disordered system
Spontaneous
Not needing control by any external agent
Often triggered by random fluctuations, amplified by positive feedback
Decentralized
The evolution of sociality
Four selective processes are putatively at work in the evolution of sociality, and they are: kin selection,
reciprocity, by-product mutualism and group selection.
Selective pressures for group living
Anti-predator
DILUTION
DAVIES et al. (2012): dilution of prey is a simple matter of probability; if a group of x individuals suffer less
than x times as many attacks as an individual, individuals will be safer in a group (where the risk of being
the victim is 1/ x )
In these cases, living in groups reduces the probability that any particular individual is the victim of
predation
The factors outlined below ensure that groups are attacked less than x times as many attacks as an
individual suffers
PREDATOR CONFUSION
DAVIES et al. (2012): when attacking a group, predators have difficulty in focusing on one target.
NEILL AND CULLEN (1974): tested the hunting success of four aquatic predators in laboratory experiments
which varied prey shoal size
Squid, cuttlefish and pike are ambush predators; they have a slow, stalking approach and then
make a rapid strike after a short chase. The perch is a chasing predator; it dashes after prey, often
with a long pursuit
Results: the success of an attack declined with increasing prey shoal size, which NEILL AND CULLEN
(1974) attributed mainly to increasing predator confusion
, Predator confusion can be enhanced by the synchronised movements of prey, maximising the confusion
effect and swamping the capacity of predators to capture prey.
Example: the synchronous emergence of mayflies (Dolania americana) in North America over a two-week
period in late May to early June creates a swamping effect, meaning that individual mayflies are safest
from predation during days when more adults emerge (DAVIES et al. 2012). The larvae transform into
winged adults at the water surface, just before sunrise each day, and are preyed upon at the water surface
by beetles, and after emergence by dragonflies, bats and birds.
Example: fish shoals (IOANNOU et al. 2017)
In more cohesive shoals of guppies, predator attack success was lower
Predator confusion demonstrated in an experiment finding that a differently coloured pigeon is more likely
to be picked off from the group.
PREY VIGLIANCE
For many predators, success depends on surprise, which can be compromised by prey vigilance.
Increased group size can reduce the work individuals are required to invest in order to maintain a given
level of vigilance overall. It should be noted that larger groups are more likely to be spotted by a predator
in the first place, creating a trade-off that may limit group size in certain contexts.
Example: meerkat (Suricata suricatta) sentinel systems (CLUTTON-BROCK et al. 1999).
Members of the group watch for predators from a prominent look-out perch while the rest of the
group forages on the ground below
Meerkats forage for 5 to 8 hours per day in the open, digging up to 20cm below ground to reach
invertebrates and small vertebrates
While digging, individuals are unable to detect predators and rely on the alarm calls of sentinels
Explanations of the evolution of sentinel behaviour have frequently relied on kin selection or
reciprocal altruism, but recent models suggest that guarding may be an individual's optimal activity
once its stomach is full if no other animal is on guard
Based on research in the Kalahari Gemsbok Park, South Africa, CLUTTON-BROCK et al. (1999) found
that although individuals seldom take successive guarding bouts, there is no regular rota, and the
provision of food increases contributions to guarding and reduces the latency between bouts by
the same individual. Furthermore, sentinel behaviour was found to provide a safety advantage to
the individual on guard, as these individuals were the first to detect predators and usually the first
below ground when a predator approached. As a result, acting as sentinel when satiated seems to
be the optimal selfish behaviour
One should note that giving guard calls to the rest of the group is unlikely to incur immediate direct
benefits (though the cost is probably low), making this aspect of sentinel behaviour difficult to
explain without invoking either deferred direct benefits of some kind or kin selection
^how would you test these hypotheses
The paradox of alarm calls: what is the advantage to the caller?
Need to look at potentially selfish explanations
E.g. does causing the rest of the group to panic/run reduce the chance that the caller is caught?
Group vigilance does NOT require altruism
Many eyes hypothesis (based on the simple premise that as group size increases, there are
progressively more eyes scanning the environment for predators. Thus, an individual forager can
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