Unit 8: Behavioural Ecology and Population Dynamics

Responses to the Environment

• Behavioral Ecology: Study of behaviors arising from ecology and evolution.

  • Behavior: Response to stimuli (internal or external), influenced by nature vs. nurture, allowing survival/reproduction, subject to natural selection.

Types of Behavior

• Innate vs. Learned:

  • Innate: Developmentally fixed, hereditary, no learning needed.

  • Learned: Depend on environmental influence, experiences affect behaviors.

Innate Behaviors

• Fixed Action Patterns (FAPs): Unlearned acts linked to a stimulus, unchangeable, carried to completion, triggered by a sign stimulus (e.g., stickleback fish aggression).

Understanding Behavior

• Proximate Cause: How a behavior occurs/is modified (stimulus, nurture).

• Ultimate Cause: Why a behavior occurs (survival/reproduction, nature).

Other Innate Behaviors

• Migration: Regular, long-distance change in location, triggered by cues (sun, magnetic field, celestial cues).

• Signal: Stimulus from one animal to another (visual, auditory, etc.).

  • Pheromones: Chemicals affecting same species members.

  • Stimulus Response Chains: Response to stimulus serves as next stimulus (courtships).

  • Directed Movements: Towards/away from stimuli.

    • Kinesis: Random movement.

    • Taxis: Directional movement (phototaxis, chemotaxis, geotaxis).

Learned Behaviors

• Learning: Behavior modification based on experience.

Imprinting

• Imprinting: Long-lasting response to an individual during a sensitive period (e.g., ducks following mother).

Spatial Learning

• Spatial Learning: Memories based on surroundings (cognitive map, landmarks).

Associative and Social Learning

• Associative Learning: Linking environmental features (e.g., monarch butterflies & taste).

• Social Learning: Learning through observation/imitation.

Natural Selection and Behavior

• Favors behaviors increasing survival/reproduction.

  • Foraging: Food obtaining behavior.

  • Mating Behaviors: Monogamous or polygamous, sexual dimorphism.

Cooperative Behaviors and Altruism

• Cooperative Behaviors: Increase fitness (warnings, kin selection, pack behavior).

• Altruism: Selfless behavior increasing population fitness (e.g., naked mole rats).

Territoriality

• Decreases competition, favored by natural selection.

Plant Responses

• Phototropism: Grows towards/away from light.

• Photoperiodism: Development based on day length.

Plant Defenses

• Physical: Thorns, trichomes.

• Chemical: Toxic compounds (e.g., lima beans releasing chemicals).

Soil Composition and Plant Responses

• Soil pH affects flower color (hydrangeas).

Plant Communication

• Plants communicate via roots (e.g., drought response).

Energy Flow Through Ecosystems

• Endotherms/ectotherms regulate body temperature.

• Reproductive strategies vary with energy availability.

• Metabolic rate inversely related to organism size.

• Energy gain = storage/growth; energy loss = mass loss/death.

• Energy availability affects population size.

• Autotrophs capture energy from physical/chemical sources.

• Heterotrophs capture energy from other organisms.

Ecosystems and Energy

• Endotherms: Use metabolism for temperature regulation.

• Ectotherms: Use external sources for temperature regulation.

• Ecosystem: Organisms and abiotic factors.

  • Biotic: Living components.

  • Abiotic: Nonliving components.

Laws of Thermodynamics

• 1st law: Energy conserved, elements recycled.

• 2nd law: Energy exchange increases entropy.

Energy Balance

• Net gain = storage; net loss = death.

Metabolic Rate

• Energy use per time unit (calories, heat loss, O2 consumption).

  • Smaller organisms: higher rate.

  • Larger organisms: lower rate.

Trophic Levels

• Species grouped by nutrition/energy source.

• Unlike mass, energy is not recycled; sun supplies energy.

• Primary Producers (Autotrophs): Synthesize organic compounds (plants, algae).

  • Chemosynthetic: Produce food via chemical reactions.

Heterotrophs and Trophic Levels

• Primary Consumers: Herbivores.

• Secondary Consumers: Carnivores (eat herbivores).

• Tertiary Consumers: Carnivores (eat carnivores).

• Decomposers: From detritus (fungi, prokaryotes), recycle elements.

Trophic Structure

• Feeding relationships in a community.

  • Food Chain: Energy transfer up trophic levels.

  • Food Webs: Linked food chains.

• Energy changes disrupt ecosystems; producer-level changes affect remaining trophic levels.

• Primary Production: Light energy converted to chemical energy.

  • Gross Primary Production (GPP): Total.

  • Net Primary Production (NPP): GPP - respiration.

• Secondary Production: Chemical energy converted to biomass (10% efficiency).

Matter Cycling

• Matter cycles, unlike energy; limited amounts.

  • Biogeochemical Cycles: Nutrient cycles (water, carbon, nitrogen, phosphorus).

Nutrient Cycles

• Water, carbon, nitrogen, and phosphorus cycles are covered.

Population Ecology and the Effects of Density

• Population: Group of same species in an area.

• Population Ecology: Factors affecting population size.

• Density: Individuals per unit area (counting, sampling).

Population Distribution

• Dispersion: Spacing patterns.

  • Clumped: Patches.

  • Uniform: Even.

  • Random: Unpredictable.

Population Dynamics

• Influenced by births/deaths, immigration/emigration.

  • Demography: Population statistics over time.

  • Life Table: Survival pattern summary.

Survivorship Curves

• Type I: Low death rate early/middle, high later.

• Type II: Constant death rate.

• Type III: High death rate early, lower survival death rate.

Population Change

• Change calculated as:

  $Change\ in\ population\ size = Birth\ rate - Death\ rate$

$\frac{ΔN}{Δt}= B-D$

Growth Models

• Exponential: Ideal conditions, rapid growth ($\frac{ΔN}{Δt} = r_{max}N$ ).

• Logistic: Growth approaches zero near carrying capacity ($\frac{ΔN}{Δt} = r_{max}N \frac{(K - N)}{K}$)

  • K = carrying capacity, N= population size, r= growth rate.

Population Dynamics

• Influenced by selection/environment.

  • Life History: Reproduction and survival schedule; when reproduction starts, how often, offspring number.

K-Selection vs. R-Selection

• K-Selection: Sensitive to population density (high-density populations).

• R-Selection: Maximizes reproductive success (low-density populations).

Regulation Factors

• Density-Dependent: Slow/stop growth by changing birth/death rates (competition, predation).

• Density-Independent: Influence population size regardless of density (weather, climate).

Community Ecology, Biodiversity, and Disruptions

• Community: Group of interacting populations.

Niches

• Habitat: Place occupied by an organism.

• Ecological Niche: Species role in environment.

  • Fundamental Niche: Potentially occupied niche without limits.

  • Realized Niche: Actually occupied niche.

Interspecific Interactions

• Interactions between different species (competition, predation, herbivory, symbiosis, facilitation).

Competition

• (-/-) Competing for resources.

  • Competitive Exclusion Principle: Two species can't coexist permanently.

  • Niche Partitioning: Natural selection drives species to use different resources.

Predation

• (+/-) Predator eats prey.

  • Cryptic Coloration: Camouflage.

  • Batesian Mimicry: Harmless mimics harmful.

  • Mullerian Mimicry: Bad-tasting species resemble each other.

Herbivory

• (+/-) Organism eats plant/alga.

Symbiosis

• Species in direct contact.

  • Parasitism: (+/-) Parasite benefits from host.

  • Mutualism: (+/+) Both benefit.

  • Commensalism: (+/0) One benefits, the other is neutral.

Facilitation

• (+/+ or 0/+) One species helps another without symbiosis.

Species Diversity

• Variety of organisms.

  • Species Richness: Number of species.

  • Relative Abundance: Proportion of each species.

Simpson’s Diversity Index

• Calculates diversity based on richness/abundance
  

• $D = 1 - \frac{\Sigma n(n-1)}{N(N-1)}$ ($n$ is the total number of organisms of a particular species and

       $N$ is the Total number of organisms of all species)

• High index = high biodiversity.

Invasive Species

• Thrive outside native range.

Exploitation of New Niches By Invasive Species

• Exploit niches without predators/competitors.

Keystone Species

• Pivotal role in community (e.g., coral, bees).

Disturbances and Succession

• Disturbance: Alters community by removing organisms.

  • Ecological Succession: Community changes over time.

    • Primary Succession: New habitat colonization