• What is the difference between proximate and ultimate explanation?
Casual and developmental factors are referred to as proximate because they
explain how a given individual comes to behave in a particular way during its
lifetime. Factors influencing adaptive advantage and evolution are called ultimate
because they explain why and how the individual has evolved the behavior.
• Reproductive behavior in lions.
Three and twelve adult females, onesix males and several cubs.
At age 3, young related males leave their natal pride. They live as nomads; they attempt
to take over pride from old and weak males. A male’s reproductive life is therefore short.
Female lions show synchronous estrus:
Lions breed throughout the year, females tend to come into estrus at about the same time.
One adaptive advantage of estrus synchrony is that different litters in the pride are born at
the same time and cubs born synchronously survive better. There is communal suckling,
with females lactating together; a cub may suckle from another female if the mother is
out hunting. In addition, synchronous
Hypothesis Testing in Behavioral Ecology
What are the three methods of hypothesis testing?
1) Comparison between individuals and species.
3) Comparison among species.
What is the comparative approach?
The comparative study of different species. We ask questions like: Why does species A
live in groups compared with species B that is solitary?
Breeding behavior of gulls Gulls nest on the ground, with eggs and chicks are vulnerable to predation. The black
headed gull seems to make adaptations to decrease this predation risk. For example:
1.) Adults take flight when a predator comes and it gives off an alarm and attacks
2.) They also camouflage their nests by refraining from defecation nearby
3.) They also remove empty eggshells, which have white interiors that attract
4.) The chicks are cryptically colored, and hide in vegetation after hatching.
5.) Parents give off food calls so that they can direct parental care to chicks.
Esther Cullen, Tinbergen’s student, showed comparison between breeding traits
of cliffnesting gull, the kittiwake.
Kittiwake nests are safer from mammalian predators; can’t climb through steep hills,
and avian predators, wind is too much around cliffs to make attacks. So kittiwake
does not have to do any of the things the blackheaded gulls have to do. The kids
remain in the nest until they can fly and also become mixed with other chicks (parents
don’t need to recognize young). There is no need for parental food calls because
young were not hidden. So this shows strong support that various suites of behavior
have evolved as adaptations in response to predation differences between two sites.
The gull comparison only had two species but a larger number of species will
obviously improve the power of the analysis. John Crook did the first systematic
study. Small sparrowlike birds from Africa and Asia build cryptic nests in large
defended territories while others cluster their nests together. Some are monogamous,
others are polygamous.
Crook wanted to search correlations between aspects of social organization and the
species ecology. The variables he considered were food, distribution and
abundance, predators and nest sites.
According to him, the birds fall under two categories:
1) Species living in the forest tends to be more insectivorous, solitary feeders, defend
large territories and build cryptic solitary nests. Monogamous. And both birds
2) Species living in savannah eat seeds, feed in flocks and nest colonially. They are
polygamous and there is sexual dimorphism in plumage.
Why is the behavior and morphology of the weaverbirds linked to their
ecology in such a striking way?
Crook invoked predation and food as the main selective pressures that
influenced evolution of social organization.
1) In the forest, insect food is dispersed. So birds feed solitary and defend their
territory. Since the food is hard to find, parents have to feed the young, therefore
both parents stay together as a pair during breeding season and they’re not
brightly colored to avoid predation. 2) In the savannah, seeds are patchy. It is more efficient to find patches of seeds by
being in a group, since groups can cover larger areas. Birds cannot hide their nests
and s the seek safety in protected sites such as acacia trees. Nests are bulky to
provide thermal insulation. Males compete for nest sites and try to attract more
females. Since food is not scarce, males spend more time trying to attract females
and females spent more time in parental care. That’s why men are brightly colored
(sexual selection) and polygamy exists.
These results suggest that food and predation are important in determining social
organization. Also shows how several traits such as nests, feeding behavior, color and
mating systems can be considered together as a result of the same ecological
Jarman looked at 74 species of AU, all that eat plant material but differences in the
precise type of food eaten are correlated with differences in movements, mating
systems and antipredator behavior.
The correlate of diet and social organization is body size.
Small species=higher metabolic requirement=high quality food such as berries or
shoots. These foods are dispersed so smaller animals are solitary feeders. Since
females are dispersed, males are dispersing and commonest mating system is for a
pair to defend territory. And they just hid when predators were around.
Large species eat poor quality food in bulk and graze less on plains. It doesn’t make
sense to defend food supplies and these species wander in herds. In herds, strongest
male monopolize many females. When predators were around, it was harder to flee
because of the group size.
Limitation of early comparative studies
1) Alternative hypothesis: How can we be sure that predation is the key selective
pressure, rather than one of these other variables?
2) Quantification of ecological variables: Weaver birds: are insects ‘dispersed’
and are seeds ‘patchy?’ How exactly will these differences influence the
economics of exploitation by individuals?
3) Cause and effect: We thought weaverbirds: seed eating selects for flocking
because this is the best way to find a patchy food supply. However, we could
equally suggested that predation selects for locking, so birds are forced t o select
locally abundant foods so all flocks can eat it.
4) Alternative adaptive peaks or nonadaptive differences: Some differences
between species may reflect different solutions to the same problem. Example:
sheep use horns, deer’s use antlers. 5) Statistical analysis and independent data: What are the independent data? Can we
consider all these as the outcomes of independent ‘ evolutionary experiments’?
Comparative approach to primate ecology and behavior? – TIM CLUTTON
BROCK AND PAUL HARVEY
Three improvements in comparative studies:
1.) They measured the various aspects of behavior and morphology on a
continuous scale (didn’t categorize primates into groups with different traits).
2.) They considered alternative hypothesis, and used multivariate statistics to
tease out effects of ecological variables.
3.) They used different genera as independent data points for analysis, rather than
species, to reduce problem of similarity through common ancestry.
Home Range size
We expect: larger animals= large