AP BIO COMBINED PT 2

life history

• pattern of survival and reproduction events typical for a mmeber of the species

• evovle by natural selection, and they rperesnt an opitmization fo tradeoffs between growth, surivval, and reproduction

• A life history is the pattern of survival and reproduction events for a species

• Includes traits like:

  • Age at first reproduction

  • Number of offspring

  • Lifespan

• Life histories evolve through natural selection

• Represent trade-offs between:

  • Growth

  • Survival

  • Reproduction

Strategies in life history

• Organisms have limited resources due to competition and environmental constraints

• Resources must be divided among:

  • Growth

  • Maintenance

  • Reproduction

• Allocation of resources is shaped by natural selection

  • Strategies that maximize fitness are passed to offspring

• Life history strategies are collections of traits such as:

  • Number of offspring

  • Timing of reproduction

  • Level of parental care

• These depend on both genetic traits and environmental conditions

Fecundity

• Fecundity is the reproductive capacity of an organism

  • Number of offspring produced

• Fecundity is inversely related to energy per offspring

• High fecundity:

  • Many offspring

  • Low energy investment per offspring

  • Little or no parental care

  • Offspring must survive on their own

• Low fecundity:

  • Few offspring

  • High energy investment per offspring

  • More parental care

  • Higher survival rate per offspring

Reproduction times

Early Reproduction

• Lower risk of leaving no offspring

• Reproduce sooner before death

• Trade-offs:

  • Less energy for growth and maintenance

  • Often lower fecundity or lower offspring quality

Late Reproduction

• More time for growth and development

• Can lead to:

  • Higher fecundity

  • Better parental care

• Trade-off:

  • Risk of not surviving to reproductive age

Semelparity

• life history strategy where an organism reproduces once and then dies

• All resources are devoted to one reproductive event

• Trade-offs:

  • Maximizes reproductive output at once

  • Sacrifices future survival and reproduction

Iteroparity

• Iteroparity is a life history strategy where organisms reproduce multiple times over their lifespan

• Resources are not all used in one reproductive event

• Energy is divided among:

  • Growth

  • Maintenance

  • Multiple reproductive events

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

How might this graph change under current conditions of climate change?

Disruption of the Nitrogen Cycle

• Human activities (fertilizer runoff, fossil fuels, livestock) dump excess nitrates (NO₃⁻) into waterways, disrupting the nitrogen cycle

• Denitrifying bacteria can't remove it fast enough → nitrates accumulate and leach into aquatic ecosystems

• Nitrates are a limiting nutrient → trigger rapid phytoplankton blooms (eutrophication = increased primary productivity)

• Phytoplankton die → decomposers break them down via cellular respiration → dissolved O₂ depleted (hypoxia)

• Hypoxia kills aerobic organisms → dead zones form, especially offshore in summer (warm water holds less O₂)

Natural Events May Lead to Changes in Ecosystems

• El Niño (“Little Boy”) is a climate pattern where:

  • Surface waters in the equatorial Pacific become warmer than average

  • Trade winds weaken

• La Niña is the opposite condition:

  • Cooler-than-average surface waters

  • Stronger trade winds

• These climate shifts alter: temperature patterns, precipitation (rainfall/drought), Ocean productivity and food webs

• Human & Ecosystem Effects

• El Niño can cause:

  • Drought → food insecurity and reduced agricultural output

  • Flooding and heavy rains → habitat disruption

  • Temperature increases → heat stress

  • Disease outbreaks and respiratory illnesses

Continental drift

• Continental drift = movement of Earth’s tectonic plates over long time scales, shifting continents

Effects on Ecosystems

• Causes geographic isolation of populations

• Leads to changes in climate and habitat conditions

• Disrupts existing ecosystems by:

  • Separating species → allopatric speciation

  • Altering species distributions and migration pathways

  • Changing environmental conditions (temperature, rainfall, ocean currents)

Meteor impact

• mass extinction

Invasive species

• Invasive species are organisms introduced into an area outside their native range, often accidentally or intentionally

• They can spread rapidly and disrupt ecosystems because they often:

  • Outcompete native species for resources (food, space, nutrients)

  • Lack natural predators or controls, allowing unchecked population growth

  • Change community structure, species interactions, and food webs

• This can lead to reduced biodiversity and displacement or extinction of native species in the invaded area

Human activities

• The human population is rapidly increasing, raising demand for food, water, energy, and space

• Humans can exceed natural carrying capacity because technology (agriculture, medicine, industry) temporarily increases available resources

• Population growth leads to major ecological impacts:

  • Land-use change: deforestation, urbanization, habitat destruction and fragmentation reduce biodiversity

  • Pollution: air, water, and soil contamination disrupt ecosystems and organism health

  • Resource exploitation: overuse of renewable and nonrenewable resources (e.g., fossil fuels, minerals) depletes natural systems

  • Movement of exotic species: global travel/trade increases introduced species, some becoming invasive and disrupting native communities

  • Ecosystem pressure beyond carrying capacity: increased consumption and waste reduce long-term ecosystem stability and biodiversity

Climate change

• Climate change is driven mainly by increased greenhouse gas emissions, especially from burning fossil fuels and intensive animal agriculture

• Greenhouse gases (e.g., CO₂, N₂O) trap heat in the atmosphere:

  • Incoming solar radiation reaches Earth

  • Some heat is radiated back, but greenhouse gases absorb and re-radiate heat, increasing global temperatures

• Ecological impacts include:

  • Rising temperatures → species may be unable to adapt quickly enough, leading to local or global extinctions

  • Sea level rise and flooding → loss of low-lying coastal habitats

  • Habitat shifts → species distributions change as organisms move toward cooler regions or higher altitudes

  • Ecosystem disruption → altered species interactions, food webs, and community structure

Conservation

• Conservation focuses on protecting ecosystems and species to prevent extinction and maintain biodiversity

• Key goals include:

  • Preventing species extinction, especially endangered species

  • Maintaining species richness and ecosystem stability

  • Protecting biodiversity at genetic, species, and ecosystem levels

• Conservation strategies often address:

  • Habitat protection and restoration

  • Reducing human impacts (habitat loss, pollution, overexploitation)

  • Controlling invasive species

  • Supporting sustainable resource use

Population ecology

• Population

  • All individuals of a species that interact in a given area at a specific time

• Population density

  • Number of individuals per unit area or volume

• Population size

  • Total number of individuals in a population

  • Often estimated using methods like mark and recapture

Mark and recapture

• A method used to estimate population size

Steps:

1. Capture a sample of individuals

2. Mark them and release them back into the population

3. Later, capture a second sample

4. Count how many are marked vs unmarked

Calculation:

• Population size ≈
  (number in first sample × number in second sample) / number of marked recaptured

How does abundance vary?

• Abundance varies depending on spatial scale

Geographic Range

• The region where a species is found

• Within this range:

  • Species may only live in specific habitats

  • Distribution is not uniform

Habitat Patches

• Suitable habitats exist as patches (“islands”)

• Surrounded by unsuitable environments

Population density

• Population densities are dynamic

  • They change over time due to environmental and biological factors

• The density of one species can be related to other species

• Examples:

  • Predator population depends on prey population

  • Competition between species affects densities

What is the difference between multiplicative and additive population growth?

• Multiplicative growth

  • Population increases by a constant multiple (percentage)

  • Growth becomes faster over time

  • Leads to exponential growth

• Additive growth

  • Population increases by a constant number each time period

  • Growth rate stays the same

Why don’t populations grow exponentially forever?

• Populations cannot grow multiplicatively for long due to limiting factors

• Growth slows and reaches a stable size

Density-Dependent Effects:

• As population becomes more crowded:

  • Birth rates decrease

  • Death rates increase

• Growth rate (r) decreases as density increases

Carrying Capacity (K):

• When r = 0 → population size stops changing

• Population reaches carrying capacity (K)

  • Maximum population size the environment can support

Population regulation

Density-Dependent Factors

• Affect per capita growth rate depending on population density

• Stronger effects in larger, crowded populations

• Can lead to logistic growth

Examples (biotic):

• Competition for food, water, light, shelter

• Predation: more prey → easier for predators to find food

• Disease spreads more easily in dense populations

• Waste accumulation harms individuals in crowded environments

Density-Independent Factors

• Affect populations regardless of density

• Usually abiotic

Examples:

• Natural disasters (fires, floods, storms)

• Extreme temperatures

• Do not regulate population size around a stable level

Population flunctuations

• Population fluctuations are changes in population size over time

• Occur when limiting factors interact

• Can involve:

  • Density-dependent factors (e.g., predation, competition, disease)

  • Density-independent factors (e.g., weather, disasters)

• Can occur even without density-independent factors

  • Example: predator–prey cycles

Population cycles

• Population cycles are regular, repeating fluctuations in population size

• Characterized by:

  • Cyclical oscillations

  • Continuous rise and fall of population size

• Often caused by interactions between species

  • Example: predator–prey relationships

Why is human population growth unique?

• Human population has grown at an increasing per capita rate

• Doubling time has decreased over time

• Technological advances have increased carrying capacity (K)

Examples:

• Improved food production (agriculture, technology)

• Advances in medicine and sanitation

  • Lower death rates

  • Increased life expectancy

life table

• A life table shows ages at which individuals survive and reproduce

• Tracks how many individuals successfully pass through life stages

Key Information:

• Survivorship

  • Fraction of individuals that survive from birth to different ages

• Fecundity

  • Average number of offspring produced at each age or stage

How do resources and environmental conditions affect organisms?

• Organisms require:

  • Resources (materials and energy)

  • Physical conditions within a tolerable range

• Resource acquisition depends on availability

  • More resources → faster acquisition

• Ability to gather food depends on resource density

  • Higher density → easier and more efficient foraging

  • Lower density → more time and energy required

Principle of allocation

Principle of allocation—once an organism has acquired a unit of some resource, it can be used for only one function at a time: maintenance, foraging, growth, defense, or reproduction.

Community ecology

• An ecological community = all populations of different species living and interacting in an area

• Community boundaries can be:

  • Natural (pond, forest edge)

  • Arbitrary (chosen for study, e.g., bird community)

• Communities are defined by:

  • Species composition (which species are present)

  • Relative abundance (how common each species is)

• A species must be able to:

  • Colonize + survive + reproduce to be part of a community

Extinction

• Local extinction = species disappears from a specific area but exists elsewhere

• Causes include:

  • Inability to tolerate local abiotic conditions

  • Resource limitation

  • Competition, predation, or disease

  • Small population size → failure to reproduce (demographic collapse risk)

• AP idea: local extinction often results from biotic + abiotic pressures + small population vulnerability

Species Interactions, Per Capita Growth, and Succession

• A species’ per capita growth rate depends on interactions with other species

• These interactions can drive ecological succession

• Examples:

  • Competition (dung beetles): late species outcompete early colonizers for nutrients

  • Shading (plants): later plants reduce light, causing pioneer species to decline

• AP idea: species interactions change community composition over time

Species richness

• Species richness = number of species in a community

• Highest richness near the equator (tropics) due to:

  • High solar energy → high NPP

  • Warm, stable climate

  • High rainfall + low seasonality

• Lower richness near poles due to:

  • Low energy input

  • Harsh seasonal variation

  • Slower productivity and higher stress

Species evenness

• Species evenness = how evenly individuals are distributed among different species in a community

• Considers:

  • Number of species (richness)

  • Relative abundance of each species

• High evenness = species have similar population sizes

• Low evenness = one or few species dominate the community

• Higher biodiversity (richness + evenness) generally leads to:

  • Greater ecosystem stability

  • Increased resilience to disturbances (disease, climate change, etc.)

Species Diversity

• Higher biodiversity (richness + evenness) generally leads to:

  • Greater ecosystem stability

  • Higher resistance and resilience to disturbances (e.g., disease, climate change)

Simpson’s Diversity Index

• A species diversity index quantifies diversity using:

  • Species richness (number of species)

  • Species evenness (relative abundance of species)

• It combines richness + evenness to give a single value of community diversity

• Community function is affected by diversity:

  • Higher species diversity → greater and more stable NPP (Net Primary Productivity)

  • More diverse communities are often more resilient to environmental changes

• Within the same community type:

  • Higher diversity = more consistent energy production over time

  • Lower diversity = more fluctuation and instability in productivity

Factors shaping community structure

Community structure is shaped by:

• Climate (temperature, rainfall, seasonality)

• Geography (location, barriers, latitude)

• Environmental heterogeneity (habitat variety → more niches)

• Disturbance frequency (fires, storms, floods reset succession)

• Species interactions (competition, predation, mutualism, parasitism)

• Chance events (random colonization/extinction)

Geographic Patterns of Species Richness

• Patterns of species richness help identify factors that influence biodiversity across ecosystems

• Species richness follows predictable global patterns:

  • Highest in tropics (latitudinal gradient)

    • Due to high NPP, stable climate, long evolutionary time

  • Lower at higher latitudes

• Island biogeography:

  • Islands have fewer species than mainland

  • Smaller islands → higher extinction rates

  • More isolated islands → lower immigration rates

keystone species

• A keystone species is a species that has a disproportionately large effect on ecosystem structure and function relative to its abundance or biomass

• Its removal can cause major community shifts or ecosystem collapse

• Keystone species are:

  • Often not the most abundant species

  • Can occur at any trophic level, but are commonly top predators

  • Important because they regulate populations of other species and maintain community balance

• Unlike foundation species (which shape habitat through abundance/biomass, e.g., trees, coral), keystone species:

  • Influence communities through ecological interactions (predation, competition control, etc.)

  • Have effects that are out of proportion to their population size

Foundation species

• Foundation species are species that physically shape and structure an ecosystem by creating or modifying habitat

• They are typically abundant and have high biomass

• They increase ecosystem complexity by:

  • Providing physical structure and habitat

  • Creating niches for other species

  • Increasing biodiversity and community stability

• Example: Brown algae (kelp forests)

  • Forms dense underwater “forests”

  • Provides shelter, food, and breeding space for many marine organisms

  • Supports high species richness by increasing habitat availability

• Foundation species influence ecosystems through habitat formation and abundance

• Unlike keystone species, their impact comes from being structurally dominant, not necessarily rare or highly interactive

Trophic cascade

• A trophic cascade is a chain reaction across trophic levels caused by changes in a species’ population or behavior

• Occurs when a species is reduced, removed, or behaviorally suppressed due to predation risk, disrupting ecosystem balance

• Altering one species can trigger system-wide changes in community structure

• Effects:

  • Changes in one trophic level affect multiple other trophic levels

  • Leads to ecological imbalance across the food web

Interspecific interactions

• Interspecific interactions occur between individuals of different species

• They affect:

  • Population density

  • Species distribution

  • Can drive evolutionary change over time

Interspecific interactions

Interspecific Competition (-/-)

• Occurs when two species use the same limited resource

• Both species are negatively affected

• Often happens when niches overlap and a limiting resource is in short supply

• Variation in traits affects competition success (some individuals are better adapted)

• reduced by resource partitioning

Predation (+/-)

• One species (predator) benefits, the other (prey) is harmed

• Includes herbivory (plant consumption by animals)

• Leads to evolutionary adaptations in prey and predators

Symbiosis (long-term close interactions)

• Mutualism (+/+) → both species benefit

• Commensalism (+/0) → one benefits, other unaffected

• Parasitism (+/-) → parasite benefits, host is harmed

• Species live in long-term close association

Niches

A niche is a species’ ecological role, including:

• The resources it uses

• The abiotic conditions it requires

• Its interactions with other species (competition, predation, etc.)

• Two species with identical niches cannot coexist long-term

  • Leads to competitive exclusion (one outcompetes the other)

• Partial niche overlap can allow coexistence if:

  • Species partition resources (use different parts of the niche)

  • Competition is reduced through behavioral or evolutionary differentiation

Competitive Exclusion Principle

• two species cannot occupy the same niche indefinitely in the same environment

• When two species compete for the same limiting resource, one will outcompete and exclude the other locally

• This leads to:

  • Restricted habitat distribution

  • Niche separation or habitat partitioning

resource partitioning

Species can coexist if they use resources in different ways or different parts of a habitat

• This reduces direct competition and allows stable coexistence

• Example:

  • Paramecium caudatum can coexist with Paramecium bursaria because they partition resources, using different parts of the environment or food sources

Consumer predator interactions

• Organisms obtain energy by consuming other living organisms

• These are +/- interactions:

  • Consumer benefits

  • The consumed organism is harmed

Types of Consumer–Resource Interactions

• Predation (+/-)

  • One organism (predator) kills and eats another

  • Example: ladybug feeding on aphids

• Herbivory (+/-)

  • Animals consume plants or plant parts

  • Example: American bison grazing on grasses

• Parasitism (+/-)

  • Parasite lives in or on a host and feeds on it over time (usually not immediately killing it)

  • Example: parasitic wasp lays eggs on a caterpillar; larvae consume host

Biological Magnification (bioaccumulation) of Toxins/Pollutants

• Toxin concentration increases at each trophic level because:

  • Predators consume many contaminated prey organisms

  • Toxins are not easily broken down or excreted

  • They often bind to fat tissues or are chemically stable

• Why toxins remain in bodies:

  • Many pollutants are non-biodegradable or slowly metabolized (fat-soluble)

  • They are stored in fatty tissues (adipose tissue) rather than being excreted

  • Organisms cannot efficiently eliminate them, so they accumulate over time

  • Each consumer inherits the toxins stored in its prey, leading to higher concentrations up the food chain

Mutualism

• Mutualism is an interspecific interaction where both species benefit (+/+)

• Occurs when each species acts in its own self-interest, but the interaction benefits both

  • AP idea: not “cooperative intent,” but natural selection favors interactions that improve fitness

Commensalism

• Commensalism is an interspecific interaction where one species benefits and the other is unaffected (+/0)

• Occurs when one species gains food, transport, or shelter without significantly harming or helping the other

Ammensalism

• Amensalism is an interspecific interaction where one species is harmed and the other is unaffected (–/0)

• Often occurs as a non-intentional or indirect effect of another organism’s activity (not a direct evolutionary interaction like predation or mutualism)

Species Interactions & Evolution

• Species interactions affect individual fitness (survival and reproductive success)

  • Individuals with phenotypes that benefit most from positive interactions (e.g., mutualism) or are least harmed by negative interactions (e.g., competition, predation) have higher fitness

  • These individuals leave more offspring → their traits become more common over time

• Result:

  • Natural selection acts on interspecific interactions

  • Populations can evolve in response to other species (co-evolutionary effects)
    

Consumer resource interactions

• Consumer–resource interactions involve one organism consuming another (e.g., predation, herbivory, parasitism)

• These interactions create opposing selective pressures:

  • Consumers benefit from better ways to capture/eat hosts/prey

  • Resources benefit from better defenses

• Leads to continuous coevolution between species

  • Prey/hosts evolve defenses (camouflage, toxins, speed, armor, etc.)

  • Predators/consumers evolve counter-adaptations (better detection, speed, resistance, etc.)

• Each adaptation in one species selects for a response in the other

Prey predator cycle

• predator and prey population sizes fluctuate over time in linked cycles

• Core pattern:

  • Prey population increases → more food for predators → predator population increases

  • Predator population increases → more predation → prey population decreases

  • Prey population decreases → less food → predator population decreases

  • Cycle then repeats

Metabolic rate

• Metabolic rate is the sum total of biochemical reactions in an organism’s body

• It reflects how quickly fuels are broken down to keep cells running

• Can be measured using:

  • Energy units (joules, calories, kcal)

  • Oxygen consumption

• Higher activity → higher metabolic rate

Metabolic rate and size

• Larger organisms have a higher total metabolic rate

• Smaller organisms have a lower total metabolic rate

• However, per unit body mass:

  • Small organisms have higher metabolic rates

  • Large organisms have lower metabolic rates

• Smaller organisms:

  • Lose heat faster

  • Require more energy per gram

• Larger organisms:

  • Lose heat more slowly

  • Require less energy per gram

Endotherm

• Maintain body temperature internally

• Have higher metabolic rates and energy needs

• BMR (Basal Metabolic Rate):

  • Measured at rest

  • In a thermoneutral environment (no extra energy used for temperature regulation)

• Smaller animals have higher BMR per unit mass

Ectotherm

• Body temperature depends on external environment

• Have lower metabolic rates and energy needs

• SMR (Standard Metabolic Rate):

  • Depends on environmental temperature

  • Measured at a specific temperature

• Higher temperature → higher metabolic rate

  • Increases molecular collisions → faster reactions

  • Too high temperature → protein denaturation

• Behaviorally regulate temperature:

  • Seek sun or shade

Temperature change between extotherms and endotherms

Ectotherms

• Body temperature depends on external environment

• Temperature increase → increase in metabolic processes

  • More molecular collisions → faster reactions

Endotherms

• Maintain body temperature within a narrow range

• Temperature increase → little to no change in metabolic rate

• Use metabolic heat production to keep body temperature constant

Heat Exchange Mechanisms

• Heat is gained or lost through:

  • Radiation

  • Conduction

  • Evaporation

Metabolism process

• Food contains energy stored in chemical bonds

• Metabolic reactions (cellular respiration):

  • Break down molecules to release energy

  • Some energy is captured as ATP to power cellular processes

• Nutrient use:

  • Proteins → broken into amino acids → used to build new proteins

  • Excess glucose → stored as glycogen

  • Excess energy → stored as triglycerides (fat)

• Energy transformations are not 100% efficient

• Some energy is always released as heat (nonusable energy)

How do resources and environmental conditions affect organisms?

• Organisms require:

  • Resources (materials and energy)

  • Physical conditions within a tolerable range

• The rate of resource acquisition depends on availability

  • More available resources → faster acquisition

• The ability to gather food (energy) depends on resource density

  • Higher density → easier and more efficient foraging

  • Lower density → more time and energy required

Principle of allocation

• The principle of allocation states that organisms have a limited amount of energy and resources

• A unit of energy can only be used for one function at a time

Possible Uses:

• Maintenance (basic survival)

• Foraging (obtaining food)

• Growth

• Defense

• Reproduction

Trade-offs occur because investing in one function reduces energy available for others

Torpor

• Torpor is a state of decreased activity and metabolism

• Helps organisms conserve energy during unfavorable conditions

Hibernation

• Long-term form of torpor during winter

• Triggered by low temperatures and limited resources

• Characterized by inactivity and reduced metabolism

Estivation

• Dormancy during summer

• Occurs in response to hot, dry conditions

• Characterized by inactivity and lowered metabolism

Diapause

• Diapause is a pause (arrest) in development

• Allows organisms to survive extreme environmental conditions

• Development resumes when conditions become favorable

• Helps time offspring's development or birth to optimal environmental conditions

Endotherm thermoregulation

Heat Production

• Shivering thermogenesis

  • Muscle contractions generate heat

• Non-shivering thermogenesis

  • Brown fat (rich in mitochondria) releases energy as heat

• Increased metabolic activity (e.g., influenced by hormones like insulin)

Heat Conservation

• Vasoconstriction

  • Blood vessels constrict → reduce heat loss

• Insulation

  • Fur and feathers trap air near the skin

  • Fat reduces heat loss

• Countercurrent heat exchange

  • Heat transfers from warm blood to cooler blood to conserve heat

Heat Loss

• Vasodilation

  • Blood vessels expand → increase heat loss to environment through the skin

• Evaporation

  • Sweat or panting removes heat from the body

Behavioral thermoregulation

• use of behavior to control body temperature

• Does not rely on internal physiological changes

• Involves changing location or activity

Examples:

• Moving into sun or shade

• Changing body orientation to the sun

• Burrowing or seeking shelter

• Huddling together

K-selected species

• Produce few offspring at a time

• Provide high parental care

• Tend to be:

  • Larger

  • Longer-lived

  • Mature more slowly

• Use a more energy-efficient strategy

• Invest more resources in each offspring

• More common in stable environments

• Populations tend to stay near carrying capacity (K)

R-selected species

• Produce many offspring at a time

• Provide little or no parental care

• Tend to be:

  • Smaller

  • Shorter-lived

  • Mature more quickly

• Use a less energy-efficient strategy

• Invest fewer resources in each offspring

• More common in unstable environments

• Populations often grow rapidly and fluctuate

Annual plants

• An annual is a plant that completes its life cycle in one growing season

• Life cycle includes:

  • Germination

  • Growth

  • Flowering

  • Seed production

• After reproduction, the plant dies

• The dormant seed is the only stage that survives to the next season