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53
Introduction
• Ecology is the science that deals with all kinds of
biological interactions.
• The term environment includes both abiotic
(physical and chemical) and biotic factors (all
other organisms living in an area).
• Behavioral ecology is the study of how animals
make “decisions” that influence their survival and
reproductive success.
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Responding to Environmental Variation
• Organisms may evolve life cycles that anticipate
cyclical environmental change.
• Animals may migrate during winter.
 So do humans!!
• Other animals hibernate until environmental
conditions have improved.
• Animals may store food for winter months.
Figure 53.2 Migration Is a Response to Predictable Seasonal Changes
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Responding to Environmental Variation
• The environment in which an organism normally
lives is called its habitat.
• For choosing a habitat, an animal seeks food,
resting places, nest sites, and escape routes from
predators.
• Numerous factors influence how animals choose
environments.
 Availability of shelter, food, water, and others.
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Responding to Environmental Variation
• Many animals use the presence and success of
already settled individuals as an indication that
the habitat may be good ground.
• Collared flycatchers
 Settled preferentially in those areas with larger
birds.
• Do we do this?
 Major cities settled where previous
colonizations were.
 Resources: water, food, etc.
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Responding to Environmental Variation
• An animal may leave an area temporarily or
permanently if the population has grown too large
to be supported there.
• The most common way for an animal to improve
its survival and reproductive success is to
establish an exclusive territory.
Fewer competators for resources.
 Organims has more for themselves.
 This has costs: ex. Defending teritory.

53
Responding to Environmental Variation
• To understand the evolution of these types of
behavior, ecologists use a method called cost–
benefit analysis, based on two assumptions:
 An animal has a limited amount of time and
energy to devote to any particular activity.
 Animals generally do not perform behaviors
whose total costs are greater than the sum of
their benefits.
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Responding to Environmental Variation
• The cost of behavior has three components:
 The energetic cost is the difference between
the energy the animal would have expended
had it rested and the energy expended in
performing the behavior.
 The risk cost is the increased chance of being
injured or killed.
 The opportunity cost: Benfits lost due to time
spent doing the behavior.
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Responding to Environmental Variation
• Foraging theory is used to predict how animals
will behave when searching for food.
• A scientist first specifies the objective of the
behavior and then attempts to determine the
behavioral choices that would best achieve that
objective.
• This approach is known as optimality modeling.
• The underlying assumption is that natural
selection has molded the behavior of animals to
make the best choices.
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Responding to Environmental Variation
• For example the energy maximizing
hypothesis:
 If the most valuable prey type is abundant, a
predator gains the most energy per unit of time
spent foraging by taking only that prey type.
 As the abundance of the most valuable prey
type decreases, the predator adds less
valuable prey to its diet.
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Responding to Environmental Variation
• The energy maximizing hypothesis has been
tested using bluegill sunfish and Daphnia.
• If all three sizes of Daphnia were present in low
numbers, the fish ate every one encountered.
• If large Daphnia were abundant, the fish ignored
the smaller ones.
53
Responding to Environmental Variation
• The most basic mating decision is the choice of a
partner of the correct species.
• Decisions are made based on the qualities of a
potential mate, the resources it controls, and nest
sites.
• The reproductive behaviors of males and females
are often very different.
 Females are more selective about mates.
 More expensive to make eggs than sperm.
53
The Evolution of Animal Societies
• Three important concepts in understanding animal
social systems:
 Social systems are best explained by how they
benefit the individuals who join together.
 They are dynamic, as individuals constantly
communicate and adjust relationships.
 The costs and benefits to specific individuals
differ according to their age, sex, physiological
condition, and status.
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The Evolution of Animal Societies
• Group living may improve hunting success or
expand the range of prey that can be captured.
 Drive of buffalo off cliffs.
• Small birds forage in flocks; Fish in schools.
 Flocking and Schooling has been shown to
provide protection against predation.
53
The Evolution of Animal Societies
• Social behavior has costs as well as benefits.
• Individuals in a group may compete for food,
interfere with one another’s foraging, injure one
another’s offspring, inhibit one another’s
reproduction, or transmit diseases to their
associates.
53
The Evolution of Animal Societies
• The most widespread social system is the family.
 Parents and offspring.
• Parental care is altruistic—it involves
tremendous costs for parents and helpers. How
has it been possible, therefore, for altruism to
evolve?
53
The Evolution of Animal Societies
• An individual contributes to its own individual
fitness by producing offspring and may also help
relatives in ways that increase their fitness.
• By helping its relatives, an individual can increase
the representation of some of its own genes in the
population. This process is known as kin
selection.
• Together, individual fitness and kin selection
determine the inclusive fitness of an individual.
53
The Evolution of Animal Societies
• Species such as ants, bees, and wasps, whose
social groups include sterile individuals, are said
to be eusocial.
• In these species, worker females defend the
group against predators or bring food to the
colony, but they do not reproduce; only a few
females, known as queens, reproduce.
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The Evolution of Animal Societies
• Among the Hymenoptera, a diploid egg hatches
into a female and a haploid egg hatches into a
male.
• Therefore, if a female mates with only one male,
her daughters share all of their father’s genes but
only half of their mother’s.
• Because workers are more genetically similar to
their sisters than they would be to their own
offspring, they increase their own fitness by caring
for their sisters rather than by reproducing
themselves.
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Behavioral Ecology,
Population Dynamics, and Community Structure
• Social living also enables organisms to use
temporally and spatially patchy foods. An example
is the wildebeest, which travels in large herds and
is the most abundant wild mammal in Africa.
• Social organization allows humans to live in high
densities and to specialize in different activities.
 The butcher, the baker and candlestick
maker.
Figure 53.14 Social Organization Allows Humans to Live at High Densities