Bio Lessons 19-21

Lesson 19

Levels of Analysis in Animal Behavior

1. Proximate Causation (focuses on mechanisms within the animal)

Explains how a behavior occurs internally (brain, hormones, nerves).

Breaks down into two sub-levels:

A. Physiological Analysis:

Looks at current/internal states (e.g., hormone levels, neural activity).

Example: How does brain activity differ between the schooling and non-schooling fish?

B. Ontogeny (Development):

Investigates how behavior develops in the individual.

Example: Do sticklebacks learn to school from others or is it innate?

2. Ultimate Causation (focuses on evolutionary/adaptive reasons)

Looks at why a behavior is advantageous in certain environments and inherited.

Breaks down into two sub-levels:

A. Phylogeny (Evolutionary History):

Studies how the behavior evolved in related species.

Example: Did the common ancestor of both fish types school?

B. Adaptive Significance:

Asks how the behavior helps with survival and reproduction.

Example: Why is schooling beneficial in one environment and harmful in another?

Fields of Behavioral Study

Ethology:

General study of animal behavior.

Often focuses on proximate causation.

Includes neuroethology, which looks at how the nervous system directs behavior.

Behavioral Ecology:

Focuses on how behavior contributes to survival and reproduction.

Concerned with ultimate causation and adaptive significance.

Types of Animal Behavior Studied

Associative Learning

Animal learns to associate stimuli or a stimulus with a response.

Two major types:

1. Classical (Pavlovian) Conditioning:

Associates two unrelated stimuli.

Example: Pavlov’s dogs salivated at the sound of a bell after learning to associate it with meat powder.

2. Operant Conditioning:

Associates a behavior with a consequence (reward or punishment).

Example: Skinner box—rat presses lever, gets food.

Animal Communication

Definition: Process where actors use signals/displays to modify the behavior of reactors.

Communication Modalities:

Acoustic (vocal)

Visual

Chemical

Electrical

Vibrational

Tactile (touch)

Animals often use multiple modalities together.

Functions of Communication

Courtship and Mating:

Species-specific courtship displays prevent cross-species mating (reproductive isolation).

Examples: Firefly flash patterns, frog calls.

Social Interaction (Within Species):

Signals presence of food, predators, territorial boundaries, or status.

Inter-Species Communication:

Prey alert others (even across species) of predators.

Can help reduce attacks by showing the predator they’ve been spotted.

Some animals form mixed-species groups for shared vigilance.

Communication and Natural Selection

Communication is shaped by natural selection on both sides:

Actor (sender): Signal evolves to be effective in influencing others in a way that benefits the sender.

Reactor (receiver): Reacts only if beneficial for itself, not the actor.

This leads to:

Repetitive signals

Ritualized behaviors

Honest signals

Deceptive signals (e.g., blue jay imitates hawk to scare others off food)

Example of deception & resistance:

Blue jay makes hawk call → competitors might ignore it if they’ve learned it’s fake.

Parental Investment & Reproductive Strategies

Reproduction requires significant energy and time, but it's necessary to pass on genes.

Parental investment: Uneven between sexes; typically higher for females.

Females invest more per offspring → fewer, higher-quality offspring.

Males invest less per offspring → goal is to have as many offspring as possible.

Example: African elephants

Females:

Gestation: ~2 years.

Lactation: 5–6 years.

Must defend and care for calves.

Alter behavior to support calves.

Only ~7 offspring in 60–70 years.

Males:

No post-mating involvement.

Contribute sperm and minimal courtship effort.

Can sire 12–25 offspring with less energy/time investment.

Sexual Selection

Sexual selection: A form of natural selection focused on the struggle to obtain mates.

A heritable trait increases or decreases based on mate acquisition success.

Historically separate from natural selection; now seen as a subtype.

Two types of sexual selection:

Intrasexual selection: Competition within one sex (usually males) for mates.

Leads to traits that help win competitions (e.g. large antlers in deer).

Physical fights are rare due to energy cost and danger; visual traits often enough.

Escalation occurs only between evenly matched individuals.

Intersexual selection: Mate choice by the opposite sex (usually females).

Leads to exaggerated traits (e.g. peacock tails).

These traits may help mating success but hurt survival.

Birds of Paradise: Males perform elaborate mating displays; females choose.

Example: Carola’s Parotia clears a dance floor and performs rituals.

Mate Choice Based on Resources

Females may choose mates based on resources, not just physical traits.

Example: Males with high-quality territories can attract mates.

Secondary Sexual Characteristics & Sexual Dimorphism

Secondary sexual characteristics: Develop only in one sex at maturity; aid in mating.

Examples: long tail feathers, antlers.

Sexual dimorphism: Visible differences between sexes (color, size, structures).

More pronounced when male parental investment is low.

Less dimorphism when males invest heavily in offspring.

Mating Systems

Monogamy:

One male + one female per reproductive event.

Common when offspring need extensive care (e.g. African paradise flycatcher).

Social monogamy doesn’t exclude extra-pair copulations (EPCs).

Polygyny:

One male mates with multiple females.

Occurs when males don't or can't care for young (e.g. Ruby-throated hummingbird).

Polyandry:

One female mates with multiple males.

Rare; often in resource-rich environments.

Example: African Jacana — females lay eggs in multiple male nests, males raise chicks.

Female is larger, more aggressive, defends territory and mates.

Promiscuity:

Both sexes mate with multiple partners.

Females often raise offspring alone or communally (e.g. vervet monkeys, banded mongooses).

In banded mongooses, adults care for all pups without distinguishing their own.

Altruism & Helping Behavior

Altruism (in behavioral biology): Increases another’s reproduction at a cost to own survival or reproduction.

Must reduce fitness of the actor to count as altruism.

Four Hypotheses for Helping Behavior:

Mutualism:

Both parties benefit immediately.

Not altruism.

Example: Male lion coalitions for territory/female access.

Manipulation:

Recipient tricks the donor into helping.

Example: Cuckoo birds (brood parasites) — lay eggs in other birds’ nests.

Reciprocity:

Help is paid back later.

Requires repeated interactions and individual recognition.

Common in primates.

Time delay separates this from mutualism.

Kin Selection:

Helping relatives increases inclusive fitness.

Helps reproduction of shared genes.

Seemingly altruistic, but genotypically selfish.

Fitness Types:

Direct fitness: From own reproduction.

Indirect fitness: From helping relatives reproduce.

Inclusive fitness = direct + indirect.

Hamilton’s Rule:

Benefit to recipient × Relatedness > Cost to donor

Example: Helping a sibling (r = 0.5) raise 3 extra offspring at cost of 1 of your own is favored: 0.5×3=1.5>1

Group Living in Animals

Types of groups:

Aggregations: No structure; random gathering (e.g. herds at a watering hole).

Social groups: Stable relationships (e.g. baboon troops, whale pods).

Colonies: Social + physical structure (e.g. prairie dog towns).

Benefits of Group Living:

Safety: More eyes for predators, dilution effect, collective defense.

Food access: Shared info or group hunting (e.g. wolves).

Mate access: Easier to find mates in a group.

Costs of Group Living:

Attracts predators.

Increased competition for resources (food, mates, space).

Optimal group size: Exists when benefits outweigh costs.

Cooperation in Group Living

Cooperation among group members often leads to better survival and reproductive success.

Can involve:

Alloparenting: Individuals other than the parents help raise the offspring.

Common in species like meerkats, elephants, and some birds.

Division of labor: Seen in highly social animals like ants, bees, and naked mole rats.

Social Hierarchies & Dominance

Dominance hierarchies help reduce conflict and stabilize group interactions.

Usually linear: alpha > beta > gamma, etc.

Dominance affects access to:

Mates

Food

Safe resting areas

Alpha individuals often reproduce the most.

Subordinates may:

Wait for an opportunity to rise in rank.

Help relatives to increase inclusive fitness.

Example: Wolves

Dominant breeding pair (alpha male and female) usually do all the reproducing.

Subordinates assist in hunting and pup care.

Communication in Social Animals

Vital for coordination and maintaining social bonds.

Methods include:

Vocalizations: Warning calls, mating calls (e.g., vervet monkeys have different alarm calls for different predators).

Visual cues: Body posture, facial expressions.

Chemical signals: Scents or pheromones (used by ants, dogs, etc.).

Tactile communication: Grooming, touching.

Reproductive Suppression in Social Groups

In some species, only dominant individuals reproduce.

Others are reproductively suppressed through:

Behavioral control.

Hormonal suppression.

Seen in:

Naked mole rats: One queen and a few males breed; others are sterile workers.

Wolves and meerkats: Subordinates may be physically prevented from mating or rearing young.

Eusociality (Extreme Social Behavior)

Most extreme form of social living, defined by:

Cooperative brood care.

Overlapping generations.

Reproductive division of labor (some individuals never reproduce).

Found in:

Insects: Bees, ants, termites.

Mammals: Naked mole rats (the only known eusocial mammal).

Selfishness in Animal Behavior

Not all social behaviors are cooperative.

Animals often act in ways that benefit themselves, even in groups.

Example: Cheaters in reciprocal relationships (take help but don’t give back).

Dominant individuals may monopolize resources.

Animals may fake signals to deceive others (like bluffing about danger to steal food).

Behavioral Trade-Offs

Animals constantly make cost-benefit decisions.

Example: Foraging in a risky area may get better food but increases predation risk.

Optimal behavior is the one that maximizes net benefit.

Considerations: energy gained, time spent, predation risk, competition.

Lesson 20

Introduction to Ecology

Ecology: Study of how organisms interact with each other and their abiotic (non-living) environment.

Interactions occur on various scales:

Between individuals of the same species

Between different species

Between entire ecosystems

Ecology includes multiple subfields:

Behavioral ecology: Interaction of animal behavior with environment and other organisms (focuses on individual level)

Physiological ecology: How an organism’s physiology interacts with environmental conditions

Levels of ecological study:

Individual

Population

Community

Ecosystem

Ecology vs. Environmentalism

Ecology is a scientific discipline.

Environmentalism is the advocacy to reduce human impact on the environment.

Ecology can inform environmentalism, but they are not the same.

Adaptation

Often confusing because it has two meanings:

Phenotypic plasticity (individual level):

The ability of an organism to change its phenotype in response to environmental conditions.

Example: A wolf grows thicker fur in the winter.

Evolutionary adaptation (species level):

An inherited trait that increases survival and reproduction.

Example: A leopard’s spots help it camouflage.

Important note: Phenotypic plasticity itself is an evolutionary adaptation.

Population Ecology

Population: A group of individuals of the same species that is:

Demographically, genetically, or spatially separated from other groups

Or, individuals that can breed with one another but rarely breed with other groups

Populations have several key characteristics:

Size

Distribution

Density

Challenges in defining populations:

Populations may be very large or spread out

Not all individuals interact (e.g., tree species spread along Appalachian Mountains)

Sometimes, only a subset of a population is studied → called a sub-population

Metapopulation:

A collection of populations that have limited interaction

Example: Trees growing only on mountaintops, occasionally pollinating trees on nearby peaks

Distribution of Individuals

Distribution: Spacing pattern of individuals within a population

Three main types:

Uniform:

Individuals are evenly spaced

Caused by intraspecific competition for evenly spread resources

Random:

Rare in nature

Occurs when individuals have no strong interaction

Clumped:

Most common

Happens when resources are clumped (e.g., birds at a feeder)

Types of Competition

Intraspecific competition:

Within the same species

Relevant in population ecology

Interspecific competition:

Between different species

Discussed in community ecology

Population Density

Density = Number of individuals per unit area

Density often decreases as body size increases

Elephants → low density

Grass species → high density

Distributions and densities can vary:

Example: U.S. human population is clumped at large scale (cities)

But uniform at neighborhood scale (houses/apartments)

Different densities depending on factors like income

Demographics

Demography: The quantitative study of populations

Ecologists analyze features like:

Sex ratio

Age structure

Generation time

Cohort: Group of individuals of the same age

Fecundity:

Number of offspring produced in a standard time period

Mortality:

Number of individuals that die in a given time period

Fecundity and mortality for each cohort affect population growth

Generation time:

Time between the birth of an individual and the birth of its offspring

Can be constant or variable depending on population/location

Example: Australian women have children later than South American women

Group size can also be a demographic factor:

Only relevant for group-living species

Demography & Population Growth Basics

Demography: The study of factors that determine the size and structure of populations over time.

Population Growth Rate:

Defined as: (Birth rate + Immigration rate) – (Death rate + Emigration rate)

Uses rates, not absolute numbers.

Positive growth: When births + immigration > deaths + emigration.

Negative growth: When deaths + emigration > births + immigration.

Simple Model of Population Growth: Exponential Growth

Assumptions of Exponential Growth (Geometric Model):

No net immigration or emigration.

Unlimited resources – all individuals reproduce at max capacity.

Exponential Growth Equation:

dN / dt = ri(N)

dN/dt: Change in population size over time.

rₐ or rᵢ: Intrinsic (maximum) rate of population increase.

N: Current population size.

Analogy to compound interest:

rᵢ = interest rate.

N = amount of money in a bank.

As N increases, the amount added to the population (or money to bank) also increases over time, even if rᵢ stays constant.

Realistic Growth: Logistic Growth Model

Logistic Growth Equation:

dN / dt = r(N)[(K−N) / K]

Adds a limiting factor: K = carrying capacity.

Carrying Capacity (K): Max number of individuals the environment can sustain.

As N approaches K, growth slows down due to limited resources.

Limitation vs. Regulation

Population Limitation:

Factors that directly limit the population (e.g., food, space).

Example: If bats need caves and insects, and only 100 caves are available despite food for 500, then cave availability limits the population to 100.

Carrying capacity can change over time (e.g., fewer insects after a harsh winter lowers carrying capacity).

Population Regulation:

Describes how populations tend to fluctuate around a stable size due to feedback from limiting factors.

Focuses on density dependence.

Density Dependence vs. Density Independence

Density-Independent Factors:

Affect population regardless of density.

Examples: Natural disasters (floods, droughts, fires).

Density-Dependent Factors:

Effect increases with population density.

Example: Food – competition increases as density rises.

Higher density → more competition → more deaths, fewer births.

Lower density → less competition → more births, fewer deaths.

Causes negative feedback on population growth.

Positive Feedback: Allee Effect

Allee Effect:

Positive feedback at very small population sizes.

Population density increases → easier to find mates → increased growth.

Example: Endangered species struggle to find mates if spread too thin.

Life History Strategies: r vs. K Selection

K-selected Species:

Live near carrying capacity.

Traits:

Long lifespan

Few offspring

High parental care

Competitive

Examples: Humans, elephants

r-selected Species:

Thrive in unstable environments.

Traits:

Short lifespan

Many offspring

Little/no parental care

Fast reproduction

Examples: Mice, cockroaches

Continuum: Most species fall between r and K, with mixed traits.

Human Population Growth

Historical Trends:

Population was <1 billion for most of human history.

Bubonic plague (1350): Major population drop (75–200 million deaths).

Afterward: Huge growth due to improvements in:

Agriculture

Medicine

Public health

Recent Growth:

Population now >7 billion.

Exponential growth pattern over past 200 years.

Growth Rate vs. Actual Increase:

1967:

Growth rate = 2.1%

Population ≈ 3.5 billion → ~73.5 million increase

1987:

Growth rate = 1.8%

Population ≈ 5 billion → ~90 million increase

Even with lower growth rate in 1987, total added population was higher because of larger base population.

Human Demographics: Age Structure & Sex Ratio

Age Structure Graphs:

Show percentage of population in each age group by sex.

Sweden:

Rectangular shape → stable population

Low birth rate, even distribution of ages

High survival across most age groups

Kenya:

Pyramid shape → rapidly growing population

High birth rate

High mortality at all ages

Few working-age adults supporting many children

If survival improves, future population will grow even more

Upside-down Pyramid (not shown):

Indicates aging/shrinking population

Seen in developed nations with low birth rates

Social/Economic Consequences:

Too few young workers → economic issues

Example: Denmark’s “Do It for Denmark” campaign to encourage reproduction

Lesson 21

Community Ecology Overview

Community Ecology: The study of how different species interact with one another in a given area.

Biological Community: All the organisms that live in one place.

Community ecologists may study a subset of species (e.g. tree community, predator-prey interactions).

Like populations, community boundaries can be hard to define.

Describing Communities

Communities can be described by:

Species richness: The number of different species in a community.

Species diversity: A measure that includes both richness and the relative abundance of each species.

Primary productivity: The rate at which plants and other photosynthetic organisms produce organic compounds.

Communities Change Over Space and Time

Example: Santa Catalina Mountains Tree Community

Different tree species respond uniquely to environmental factors (e.g., moisture gradients).

Species composition shifts across space due to different responses to environmental changes.

Ecological Niche

Niche: The total of all the ways an organism uses the resources in its environment.

Includes: food use, temperature range, moisture needs, etc.

N-dimensional hypervolume: A way to describe a niche using multiple factors (each factor = one axis on a graph).

Example: food size (1st axis), foraging height (2nd), light needed to hunt (3rd), etc.

Theoretically infinite dimensions → "n-dimensional."

Types of Niches:

Fundamental Niche: The full range of resources a species could theoretically use if there were no other species present.

Realized Niche: The actual portion of the fundamental niche a species uses when competition and other biotic factors are considered.

Example: Deer using both forest and grassland in absence of predators (fundamental), but only forest when predators are present (realized).

Competition

Interspecific competition: Competition between different species for the same resource.

Interference competition: Physical interaction or fighting over a resource.

Exploitative competition: One species uses a resource more efficiently, leaving less or none for the other.

Connell’s Barnacle Study

Species 1 (small barnacle): Lives above low tide mark.

Species 2 (large barnacle): Lives below low tide mark.

When large species removed → small species expanded downward.

Conclusion:

Small species’ realized niche is limited by competition.

Large species fills its entire fundamental niche.

Competitive Exclusion Principle

Competitive Exclusion: No two species can occupy the exact same niche forever if resources are limited.

Coined by G.F. Gause (1930s) using Paramecium species in lab.

Only one species survived when both competed in a test tube.

If one species uses a resource more efficiently, it will exclude the other.

Modifications to the Principle:

Competing species can coexist if:

Resources are not limiting.

Niches differ enough.

Environmental conditions change, giving each a turn at being favored.

Resource Partitioning

When two species avoid competitive exclusion by dividing a niche.

Example: Caribbean lizards

Different species live in different microhabitats (canopy, trunk, grass).

May specialize in different insects.

When alone, a species' niche expands—evidence of resource partitioning.

Character Displacement

Evolutionary changes that reduce niche overlap between species.

Example: Darwin’s Finches

Allopatric populations: Bill sizes overlap.

Sympatric populations: Bills evolve to different sizes → specialization on different seed sizes.

Occurs naturally, not through any kind of cooperation.

Criticism of Niche Theory

Some ecologists argue:

Niche theory is outdated.

It’s not falsifiable, so it may not qualify as a scientific theory.

Neutral theory: An alternative (not covered in detail).

Predation

Predation: One organism consumes another.

Includes carnivores (lion/antelope), insectivores (bird/insect), and herbivores (deer/grass).

Predators strongly impact prey population sizes.

Example: Lab Predators (Didinium & Paramecium)

Without refuge: Prey population crashes → predator extinction.

With refuge: Prey survives at low level → both persist.

Real World Impacts:

Removing predators can cause prey population explosions (e.g., sea urchin boom after sea otters nearly extinct).

Invasive predators can drive native prey to extinction.

Non-lethal Predator Effects

Even if not killed, prey may:

Avoid best foraging areas due to danger.

Experience chronic stress → lower immunity & reproduction.

Predator-Prey Coevolution

Coevolution: Reciprocal evolutionary change between predators and prey.

Prey evolve better defense (camouflage, speed, etc.).

Predators evolve better hunting skills in response.

Plant Adaptations Against Predation

Morphological Defenses:

Thorns and spikes: Defend against large herbivores.

Small hairs and sticky secretions: Defend against insect herbivores.

Silica deposits: Make tissues too tough to chew and digest.

Chemical Defenses:

Secondary chemical compounds / secondary metabolites: Chemicals not used in basic metabolism, but for defense (e.g., mustard oils).

Co-evolution: When predator and prey evolve in response to one another.

Example: Cabbage white butterfly evolved to tolerate mustard oils in cabbage.

Caterpillars of this species also use cryptic coloration to blend into the cabbage and avoid predation.

Animal Adaptations Against Predation

Toxin Storage:

Example: Monarch caterpillars eat milkweed, a toxic plant.

Instead of breaking it down, they store the toxins in fatty tissue.

Predators, like the blue jay, get sick (vomit) after eating them and learn to avoid them in the future.

Chemical Defenses in Animals:

Examples: Poison dart frogs, bees, puffer fish.

Poison dart frogs produce alkaloids toxic enough to kill humans.

Warning Coloration (Aposematic Coloration):

Bright, distinctive colors that warn predators of toxicity.

Example: Poison dart frogs.

Cryptic Coloration (Camouflage):

Allows prey to blend in with their surroundings.

Example: Inchworm caterpillars mimic twigs or stems.

Mimicry

Batesian Mimicry:

Harmless species mimics the appearance of a toxic or dangerous one.

Example: Two Swallowtail butterflies—one toxic, one not.

Müllerian Mimicry:

Two or more toxic species evolve to resemble each other.

Benefit: Predator learns to avoid one and avoids all.

Example: Multiple pairs of warningly colored species in Panel B.

Symbiosis

Definition: Two species living in close association over time.

Types of Symbiosis:

Mutualism: Both species benefit.

Examples:

Acacia trees + acacia ants

Mycorrhizal fungi + plants

Rhizobium bacteria + legumes

Parasitism: One benefits, the other is harmed.

Can affect individuals, populations, and communities.

Similar to predation, especially when the parasite kills the host.

Endoparasites: Live inside host.

Examples: Worms, malaria-causing protozoans.

Ectoparasites: Live on the outside of host.

Examples: Fleas, ticks.

Parasitoids: Insects that lay eggs in/on a host.

Larvae feed on host and eventually kill it.

Example: Many wasps.

Parasite-induced behavior:

Some parasites alter host behavior to increase their own transmission.

Example: Toxoplasma gondii (protozoan):

Found in rats → makes them bolder, increasing chances of being eaten by cats.

Can infect humans (via cat feces).

Linked to ADHD, OCD, schizophrenia, and suicidal behavior.

Commensalism: One benefits, the other is unaffected.

Example: Spanish moss living on trees.

Note: Can shift into parasitism or mutualism depending on the situation.

Interactions Between Species

Predation and Competition:

Predators can reduce competition among prey.

By eating the dominant competitor, predators keep populations balanced.

Prevents competitive exclusion.

Parasites and Competition:

Parasites can also reduce competition by harming one competitor more than another.

Indirect Effects

Occur when two species affect each other through another species.

Rodents vs. Ants example:

Rodents and seed-eating ants compete directly.

Removing rodents:

Initially: Ants increase.

Eventually: Ants decline again.

Indirect Effect:

Rodents eat large seeds → reduces competition for small-seed plants.

Small-seed plants support more ants.

Therefore, rodents indirectly help ants.

Other example: Wolves have an indirect positive effect on trees.

Wolves eat elk, which eat tree seedlings.

Fewer elk → more tree growth.

Keystone Species

Definition: Species whose impact is much greater than expected based on their abundance.

Examples:

Beavers:

Build dams, create ponds → transform ecosystems.

Top predators:

Control herbivore populations → indirectly influence plant communities.

Ecological Succession

Definition: Gradual change in species composition in a community over time.

Secondary Succession:

Occurs after a disturbance, but some organisms remain.

Example: Abandoned farm field turning back into forest.

Primary Succession:

Occurs on bare substrate (e.g., new volcanic rock).

No pre-existing organisms.

Causes of Succession:

Species modify the habitat, making it more favorable for others.

Examples: Changing soil pH, increasing soil nitrogen.

3 Processes in Succession:

Establishment:

Initial colonization by weedy, r-selected species.

Traits: tolerate harsh conditions, reproduce quickly.

Facilitation:

Early species change the environment to support k-selected species.

Inhibition:

K-selected species prevent r-selected species from reestablishing.

Example:

Alder trees increase soil nitrogen, allowing spruce trees to grow.

Spruce trees then shade out alders → kill them.

Species Richness and Disturbance

Species Richness = number of different species in a community.

During succession:

Richness increases, then declines as k-selected species dominate.

Disturbance:

Can be large (e.g., fire) or small (e.g., tree falling).

Can be natural or human-caused.

Affects species richness:

Frequent disturbances may prevent dominance of any one species.

Allows for more diversity.