APBIO 8.1

Animal Behaviors

• The ways animals interact with other organisms and their physical environment

• A behavior is a change in activity in response to a stimulus

  • Stimulus can be internal, external, or both

Nature vs Nurture

• Some behaviors are inherited (genetic)

• Some behaviors are learned

• Many behaviors are a combination of both

Example

• Male songbirds have species-specific songs

• They must learn the song during a limited developmental (critical) period

Things to consider when evaluating behaviors

• Causation (Mechanism)

  • What triggers the behavior?

  • Includes internal and external stimuli (hormones, environment, signals)

• Development (Ontogeny)

  • How does the behavior develop over an organism’s lifetime?

  • Role of learning and genetic factors

• Function (Fitness)

  • How does the behavior contribute to survival or reproduction?

• Evolution (Phylogeny)

  • How did the behavior evolve over time?

  • What is its evolutionary history?

Hormones and. behavior

• Hormones influence behavior by affecting development and physiological state

• They can:

  • Change brain structure during development

  • Modify brain function in the short term

  • Alter neural activity

• Hormones also:

  • Alter gene expression

  • Change internal conditions of the body

  • Influence responses to internal and external stimuli

🔑 Key idea:
Hormones regulate behavior by modifying development, brain function, and physiological state, which changes how an organism responds to stimuli.

Innate behaviors

• Innate behaviors are behaviors that are inherited (genetically determined)

• They are:

  • Automatic and involuntary

  • “Wired in” (genetically programmed)

  • Do not require prior experience or learning

Learned behaviors

• Learned behaviors are changes in behavior based on experience

• They:

  • Change with experience

  • Can be modified over time

  • Allow organisms to adapt to their environment

Kinesis

• Kinesis is a simple change in activity or turning rate in response to a stimulus

• It is random (non-directional)

  • Does not move toward or away from the stimulus

• Helps organisms respond to environmental conditions

Example:

• Speeding up movement in an unfavorable environment

Taxis

• Taxis is an oriented movement toward or away from a stimulus

• It is directional (non-random)

  • An organism moves either toward (positive taxis) or away (negative taxis)

Examples:

• Phototaxis – response to light

• Chemotaxis – response to chemicals

Proximate causes

• Proximate causes explain the immediate mechanisms of behavior

• Focus on how behavior occurs (stimuli, learning, physiology)

Behaviorism

• Study of behavior based on learning and experience

• Classical Conditioning

  • Learning by association between two stimuli

  • Example: associating a sound with food

• Operant Conditioning

  • Learning through rewards and punishments

  • Behavior is strengthened or weakened based on consequences

Ethology

• Study of innate (genetically programmed) behavior

Instinct (Fixed Action Pattern)

• Innate, stereotyped behavior

• Triggered by a specific stimulus

• Once started, it is usually completed

Ethology

Ethology

• Study of instinctive (innate) behaviors

• Focuses on genetically determined behaviors

Fixed Action Pattern (Instinct)

• Innate, stereotyped behavior

• Not learned and resists modification

• Triggered by a specific stimulus

• Once started, it is carried to completion, even if conditions change

How to Identify

• Behavior is performed correctly without prior experience

Imprinting

• A type of learning that occurs during a critical period

• Leads to long-lasting behavioral responses

Male stickleback fish attacks

• Male stickleback fish show an innate aggressive behavior

• Triggered by a sign stimulus:

  • The red underside of another male

• This initiates a fixed action pattern:

  • The fish attacks anything with a red belly

  • Even unrealistic objects (like models) can trigger the attack

Behaviors and natural selection

• To the extent that behaviors have a genetic basis, they are subject to natural selection

• Behaviors that increase survival and reproductive success (fitness) are more likely to be passed on

• Over time, these behaviors become more common in the population

Animal communication

• Animals communicate using signals:

  • Visual

  • Auditory

  • Chemical

  • Tactile

• The type of signal is closely related to the organism’s lifestyle and environment

Functions:

• Mating, Establishing territory, Conveying information about food, Alarm calls (danger), Dominance and submission, Care for young

Response to external cues

Animal behavior can be triggered by internal cues (hormones, biological rhythms) and external cues (environmental stimuli)

Examples of Responses:

• Hibernation

  • Long-term state of inactivity

  • Reduced metabolic rate

  • Occurs in response to cold temperatures and limited resources

• Estivation

  • Reduced metabolic activity during hot or dry conditions

  • Helps conserve water and energy

• Migration

  • Seasonal movement from one region to another

  • Triggered by changes in temperature, day length, and resource availability

Response to internal cues

animal behaviors in response to internal cues

• Circadium rhythm

Mating is a combination of internal and external cues

Migration

• Migration is the seasonal movement of populations over large distances

• Triggered by environmental cues such as:

  • Temperature

  • Day length

  • Availability of resources

• Helps organisms:

  • Find food

  • Reproduce

  • Survive unfavorable conditions

Foraging

• Foraging is behavior related to finding and obtaining food

• Animals aim to get the highest energy gain with the lowest energy cost

Types:

• Solitary foraging

  • Individual searches for food alone

• Group foraging

  • Animals search for food together

  • Can increase efficiency or protection

Influences:

• Genetics (innate tendencies)

• Learning (experience improves success)

Piloting

• Piloting is navigation by using landmarks and remembering the structure of the environment

• Animals rely on familiar visual cues to find their way

Example:

• Gray whales migrate from Mexico to the Bering Sea by following the coastline

Homing

• Homing is the ability to return to a specific location from long distances

• Does not rely only on familiar landmarks

Example:

• Pigeons can return home from unfamiliar locations

• They can navigate without visual cues by:

  • Detecting the Earth’s magnetic field

Spatial learning

• Involves understanding the spatial structure of the environment

• Allows animals to:

  • Remember locations of resources (food, shelter)

  • Navigate efficiently

Habituation

• Habituation is a simple form of learning

• It involves a decrease (loss) of response to a repeated stimulus

• Occurs when the stimulus provides little or no important information

• Allows organisms to ignore irrelevant stimuli and conserve energy

Insight Behavior

• Insight learning is the sudden realization (“ah ha” moment) that leads to solving a problem

• Occurs when an individual in a novel situation displays a new behavior

• The solution appears without trial-and-error

Habitat selection

• Habitat selection is the process by which animals choose where to live

• It is one of the most important behavioral decisions

• A suitable habitat must provide:

  • Food

  • Shelter

  • Nesting sites

  • Escape routes

• Animals use environmental cues to choose habitats

• These cues are generally reliable indicators of good fitness outcomes

Cost-benefit approach

• The cost–benefit approach is used to analyze and evaluate behaviors

• Assumes animals have a limited amount of energy

• A behavior will only be favored if:

  • Benefits (fitness gains) outweigh

  • Costs (energy, risk, time)

• Animals cannot sustain behaviors that cost more than they provide

Potential cost regarding a behavior

Energetic cost is the difference between performing a behavior and not performing it

Risk cost is the increased chance of being injured or killed performing a behavior

Opportunity cost is the benefit the animal forfeits by not performing other behaviors during the same time

Territorial behavior

• Territorial behavior is aggressive behavior used to deny other animals access to a habitat or resource

Costs:

• Requires significant energy

• Increases risk of predation

• Reduces time available for:

  • Feeding

  • Parental care

Agonistic behavior

• Agonistic behavior includes threats, displays, and submissive behaviors during competition

• Occurs often in male–male competition

• Reduces risk by:

  • Avoiding serious injury

  • Using ritualized displays instead of fighting

  • Allowing one individual to retreat without harm

Lek

• A lek is a gathering where males display to attract females

• Males compete for prime locations within the lek

• Males in the best positions have higher mating success

• Females visit the lek and choose mates based on displays

Game theory

• Game theory evaluates alternative behavioral strategies

• The success of a strategy depends on:

  • The individual’s behavior

  • The behavior of other individuals

  • No single strategy is always best

  • Success depends on interactions with others

Example:

• Male side-blotched lizards show different mating strategies (polymorphism)

• Mating success depends on the frequency of each type of male in the population

How can altruistic behavior be explained in terms of fitness?

• Altruistic behavior benefits another individual at a cost to the performer

Inclusive Fitness

• Total fitness = own reproduction + helping relatives reproduce

Kin Selection

• Selection favors behaviors that increase the success of relatives

• Works because relatives share genes

Example:

• Scrub jays help at the nest

  • Helpers are previous offspring

  • Increases reproductive success of parents

Eusocial

• Eusocial societies are an extreme example of kin selection

• Characterized by:

  • Cooperative care of offspring

  • Overlapping generations

  • Division of labor (reproductive vs non-reproductive individuals)

Example:

• In honey bees:

  • Most females are non-reproductive workers

  • Some act as soldiers to defend the colony

  • Only the queen reproduces

  • Diploid individuals are female

  • Haploid individuals are male

Living in a group has both benefits and costs.

• Group living can increase foraging efficiency

  • Example: wild dogs hunting in packs

• Can reduce the risk of predation

  • Safety in numbers

  • Increased vigilance