ECOLOGY

Study Guide: Predation (BIOL 2250 - Chapter 12)

1. What is Predation?

Predation is a type of species interaction where one organism (the predator) feeds on another (the prey). It is a trophic interaction, meaning it involves feeding and energy transfer.

2. Predator-Prey Interactions

General Concepts

• Populations of predators and prey cycle together over time.

• Example: In Canada, snowshoe hare populations peak every 10 years, followed by a peak in lynx populations.

• Hare reproduction and survival are highest before the population peak and lowest after the peak.

Predation Types (Consumption/Exploitation)

• Carnivores eat animals.

• Herbivores eat plants (often specialized on certain species).

• Omnivores eat both plants and animals.

3. Foraging Strategies (How Predators Find Food)

Optimal Foraging Theory

• Describes how predators choose prey based on two factors:

1. Encounter Rate – If prey are rare, predators become generalists (eat a variety).

2. Handling Time – If prey take a long time to eat, predators become specialists (focus on a few species).

Generalist vs. Specialist Predators

• Generalists: Eat many different prey species (e.g., bears eat fish, berries, and small mammals).

• Specialists: Focus on a few specific prey (e.g., koalas eat only eucalyptus leaves).

Predator Hunting Strategies

1. Active Searching (Move to Hunt)

• Example: Wolves tracking a herd of elk.

2. Sit-and-Wait (Ambush Predators)

• Example: Spiders weaving webs to catch insects.

4. How Prey Avoid Being Eaten

Physical Defenses

• Large Size (e.g., elephants)

• Fast Speed/Agility (e.g., gazelles)

• Armor & Shells (e.g., turtles, armadillos)

Coloration and Camouflage

• Aposematic (Warning) Coloration: Bright colors signal toxins (e.g., poison dart frogs).

• Crypsis (Camouflage): Blends into the environment (e.g., chameleons, stick insects).

• Mimicry: Looks like a dangerous or toxic species (e.g., harmless king snakes mimic venomous coral snakes).

Behavioral Defenses

• Herding or Schooling: Animals move in groups (e.g., fish schools, zebra herds).

• Playing Dead: Some prey “fake” death to avoid attack (e.g., opossums).

• Alarm Calls: Warn others of predators (e.g., prairie dogs).

5. How Plants Defend Against Herbivores

Structural Defenses

• Spines, Thorns, Tough Leaves (e.g., cacti, roses).

• Tiny Hairs that make eating difficult.

Chemical Defenses

• Toxins that make plants taste bad or poisonous (e.g., nicotine in tobacco).

• Compounds that attract predators of the herbivore (e.g., plants release chemicals to attract wasps that kill caterpillars).

Induced Defenses

• Some plants increase defenses only after being attacked (e.g., cacti grow more spines after grazing)

6. Predator-Prey Population Cycles

Lotka-Volterra Model (Mathematical Model for Predator-Prey Cycles)

This model explains how predator and prey populations rise and fall in cycles.

• If prey numbers increase, predators have more food → predator numbers grow.

• If predators increase too much, they eat too many prey → prey numbers drop.

• With fewer prey, predator numbers then drop, allowing prey to recover → cycle repeats.

Example: Mites in Lab Experiment

• When predators could easily find prey, prey went extinct.

• When prey could hide and move, both populations persisted and cycled over time.

Final Summary

✔ Predation is a major force shaping ecosystems, influencing prey adaptations and population cycles.

✔ Predators use different foraging strategies (active hunting vs. ambush).

✔ Prey have evolved defenses (speed, armor, camouflage, toxins).

✔ Plants use structural and chemical defenses against herbivores.

✔ Predator-prey populations cycle together, following the Lotka-Volterra model.

Study Guide: Parasitism (BIOL 2250 - Chapter 13)

1. What is Parasitism?

Parasitism is a relationship where one organism (the parasite) benefits, while the other (the host) is harmed.

• Unlike predators, parasites do not immediately kill their host but depend on them for survival.

• Many parasites evolve alongside their hosts in a process called coevolution.

2. Key Definitions

Symbionts

• Organisms that live closely together with another species.

Mutualists

• Symbionts that benefit both organisms (e.g., bees and flowers).

Parasites

• Organisms that live on or inside a host, harming it to gain resources.

Pathogens

• Disease-causing parasites (e.g., viruses, bacteria, fungi).

Macroparasites vs. Microparasites

• Macroparasites: Large parasites like ticks, fleas, or tapeworms.

• Microparasites: Small parasites like bacteria and viruses that multiply inside the host.

Parasitoids

• Insects that lay eggs inside a host; the larvae consume and kill the host (e.g., wasps).

Ectoparasites vs. Endoparasites

• Ectoparasites: Live outside the host (e.g., lice, ticks).

• Endoparasites: Live inside the host’s body (e.g., tapeworms).

3. Parasite-Host Interactions & Adaptations

Parasites Adapt to Survive

• Parasites evolve ways to attach to hosts, avoid detection, and spread to new hosts.

• Some parasites manipulate host behavior to increase transmission.

Example: “Zombie Crabs”

• The parasitic barnacle Sacculina spp. infects crabs.

• It grows inside the crab, replacing its reproductive organs.

• Infected male crabs become feminized, caring for the parasite’s eggs.

Multi-Host Parasites: Trematode Life Cycle

• Snail host: Parasite reproduces asexually, castrating the snail.

• Fish host: Parasite enters fish muscles and becomes dormant.

• Bird host: Bird eats infected fish, and the parasite reproduces in the bird’s gut.

• Bird feces spread eggs, starting the cycle again.

4. Parasite-Host Population Dynamics

How Diseases Spread

• S = Susceptible individuals (people who can get infected).

• I = Infected individuals (people who have the disease).

• β = Transmission rate (how easily the disease spreads).

• m = Death and recovery rate (how quickly infected individuals die or recover).

Equation for Disease Spread:

If S × β > m, the disease will spread.

If S < m/β, the disease will die out.

Threshold Density (ST)

• The minimum number of susceptible hosts needed for a disease to spread.

• ST = m/β (higher ST = harder for disease to spread).

5. Controlling Disease Spread

To prevent disease outbreaks, reduce the number of susceptible individuals below the threshold (S < ST) by:

1. Reducing Susceptible Individuals (S)

• Mass vaccination programs (e.g., measles vaccines).

• Slaughter infected livestock (e.g., to stop mad cow disease).

2. Increasing Recovery/Death Rate (m)

• Better medical treatment to speed up recovery.

• Early detection of infections to prevent spread.

3. Lowering Transmission Rate (β)

• Quarantining infected individuals (e.g., COVID-19 isolation).

• Wearing condoms to prevent STDs.

• Controlling mosquito populations (e.g., malaria prevention).

• Handwashing and sanitation to reduce disease spread.

6. Parasites as Biodiversity Indicators

• Some parasites are specific to certain ecosystems.

• A high diversity of parasites can indicate a healthy and complex ecosystem.

Final Summary

✔ Parasites live in or on a host and cause harm, unlike mutualists.

✔ Ectoparasites live outside; endoparasites live inside.

✔ Parasites evolve strategies to manipulate host behavior and reproduction.

✔ Diseases spread based on host susceptibility, transmission rates, and recovery rates.

✔ Vaccination, quarantine, and hygiene can control disease outbreaks.

✔ Some parasites indicate ecosystem health and biodiversity.

Study Guide: Ecology - Competition (Chapter 14)

Key Concepts

1. Types of Competition (-/-)

• Intraspecific Competition: Occurs within the same species.

• Interspecific Competition: Occurs between different species.

2. Mechanisms of Competition

• Exploitation Competition: Organisms compete indirectly by consuming shared resources (e.g., food, water, space).

• Interference Competition: Direct interactions between individuals, such as territoriality or aggressive behaviors.

3. Competition and Niches

• Niche: The role an organism plays in its environment, including resource use and interactions.

• Competition is often asymmetrical: One species is often more dominant, leading to competitive exclusion.

4. Competitive Exclusion vs. Coexistence

• Competitive Exclusion Principle: Two species using the same limiting resource in the same way cannot coexist indefinitely.

• Competitive Coexistence: Species can coexist if they use resources differently.

5. Resource Partitioning

• Definition: The process where species adapt to use different resources or the same resource in different ways, allowing coexistence.

6. Character Displacement

• Definition: Evolutionary changes in species traits that reduce competition by differentiating resource use.

Mathematical Models of Competition

Lotka-Volterra Competition Model

Mathematical equations used to describe interspecific competition:

• K = Carrying Capacity

• N = Population Size

• r = Intrinsic rate of increase

• α (alpha) = Effect of species 2 on species 1

• β (beta) = Effect of species 1 on species 2

Understanding α and β

• If α = 3, three individuals of species 1 have the same competitive effect as one individual of species 2.

• If β = 3, three individuals of species 2 have the same effect as one individual of species 1.

Species Coexistence Condition

• If both species are equally strong competitors (α ≈ β ≈ 1) and have similar carrying capacities, they may coexist.

Competition and Species Distribution

• Competitive interactions shape species distributions in ecosystems.

• Example: Rocky Intertidal Zonation—species are distributed along environmental gradients based on competition intensity.

Key Takeaways

1. Competition can limit population growth and species distributions.

2. Competitive exclusion occurs when one species outcompetes another for a resource.

3. Resource partitioning allows species to coexist by reducing direct competition.

4. The Lotka-Volterra model helps predict competition outcomes mathematically.

5. Species with similar competition strength and resource use can coexist under certain

GStudy Guide: Ecology - Mutualism (Chapter 15)

Key Concepts

1. Definitions of Positive Interactions

• Mutualism (+/+) – Both species benefit from the interaction.

• Commensalism (+/0) – One species benefits, while the other is unaffected.

• Facilitation – One species helps another, often in stressful environments.

• Symbiosis – A close and long-term interaction between species (can be mutualistic or not).

2. Types of Mutualism

• Obligate Mutualism – Essential for survival (e.g., coral and zooxanthellae).

• Facultative Mutualism – Optional; species can survive without it.

• Symbiotic Mutualism – Partners live together (e.g., gut bacteria).

• Free-living Mutualism – Partners interact but do not live together.

• Specialist Mutualism – One species depends on a specific partner.

• Generalist Mutualism – Species can interact with multiple partners.

3. Coral Mutualisms (Coral & Zooxanthellae)

• Zooxanthellae provide corals:

• Enhanced growth and calcification.

• Energy and oxygen through photosynthesis.

• Corals provide zooxanthellae:

• Nutrients (e.g., nitrogen waste).

• Protection through their hard skeletons.

• A stable habitat.

4. Other Examples of Mutualism

• Three-way Mutualism:

• Sea anemone, anemone fish, and zooxanthellae.

• Direct and indirect benefits between all three.

• Mutualisms in Coral Reefs:

• Many reef species form cooperative relationships for survival.

5. Evolutionary Conditions for Mutualism

• More common in stable, benign environments (e.g., tropical ecosystems).

• Evolves when benefits outweigh costs (cost-benefit models).

• Leads to co-evolution, where species develop traits specifically for their mutualistic partners.

• A major driver of biodiversity, especially in plants

6. When Mutualisms Change

• Facultative Interactions: Some mutualisms can cease if conditions change.

• Mutualisms Can Become Competitive: If costs begin to outweigh benefits, partners may become competitors.

7. Facilitation and Habitat Mutualisms

• Facilitation: One species helps another by modifying the environment.

• More common in stressful environments (e.g., high-altitude plants helping each other).

• Relative Neighbor Effect (RNE): Measures the growth of a species with and without neighbors.

• Foundation Species: Large or dominant species that facilitate others in their ecosystem.

8. Preventing Overexploitation in Mutualisms

• Mechanisms exist to prevent one partner from overexploiting the other.

• Ensures long-term benefits for both species.

9. Consequences of Mutualism on Community Diversity

• Increases species diversity by fostering interdependence.

• Helps maintain ecosystem stability.

Key Takeaways

• Mutualisms provide survival benefits and can drive evolution and biodiversity.

• Coral reefs are a prime example of obligate mutualisms.

• Facilitation is more common in stressful environments and helps species persist.

• Mutualistic relationships can shift depending on environmental conditions and costs.

• Preventing overexploitation ensures mutualisms remain stable over time.

To-Do List

• Review key mutualism examples (coral, anemone fish, facilitation).

• Understand cost-benefit models of mutualism evolution.

• Study how mutualisms influence community diversity and species interactions.

Study Guide: Community Ecology (BIOL 2250 - Chapter 16)

1. What is a Community?

• A community consists of interacting species that occur together in the same place and time.

• Community structure refers to the characteristics that shape communities.

2. Factors Controlling Community Composition & Structure (Coastal Ecosystems)

A. Dispersal & Recruitment

• Dispersal: Emigration (species leaving an area)

• Recruitment: Immigration (species arriving in an area)

B. Abiotic Factors

• Temperature

• Salinity

• Wave energy

• Dissolved oxygen

C. Biotic Factors (Species Interactions)

• Competition: Species compete for limited resources.

• Predation: One species preys on another.

• Facilitation: One species benefits another, sometimes indirectly.

3. Defining & Subdividing Communities

Ways to Classify Communities

• Physical Characteristics: Habitat features (e.g., intertidal zones).

• Biological Characteristics: Species composition and function.

Ways to Subdivide a Community

• Resource use: Species that use the same resources.

• Functionality: Species that perform similar roles.

• Evolutionary Lineage: Species with shared ancestry.

4. Community Structure

Key Components

• Species richness: Number of species in a community.

• Species evenness: Relative abundance of different species.

• Species diversity: A combination of richness and evenness.

• Biodiversity: Includes genetic, species, and ecosystem diversity.

Measuring Species Diversity

• Shannon Index (H): A mathematical measure where a higher value indicates higher diversity.

5. Species Interactions

Types of Interactions

• Direct: Occur when species interact physically or behaviorally.

• Indirect: Influence occurs through a third species (e.g., trophic cascades).

Trophic Interactions

• Trophic cascade (Top-down effect): Predators at higher levels influence lower levels.

• Trophic facilitation: One species indirectly benefits another by modifying the environment.

Competition

• Competition Network: No single species dominates; balance maintained.

• Competition Hierarchy: One species consistently outcompetes others.

Keystone & Foundation Species

• Keystone Species: Have a disproportionate effect on community structure (e.g., sea otters controlling urchin populations).

• Foundation Species: Habitat-forming species (e.g., corals, trees).

• Ecosystem Engineers: Modify environments in ways that benefit other organisms (e.g., beavers building dams).

Environmental Context

• The importance of keystone and foundation species can change depending on environmental conditions.

6. Invasion & Community Structure

• Example: Seagrass (Posidonia oceanica) vs. invasive algae (Caulerpa taxifolia)

• Invasive species can alter native community composition and ecosystem functioning.

Key Takeaways

1. Community structure is shaped by species interactions, dispersal, and environmental factors.

2. Species richness, evenness, and diversity are key measures of community composition.

3. Keystone species, foundation species, and ecosystem engineers play critical roles.

4. Species interactions can be direct or indirect and may change depending on environmental conditions.

5. Invasive species can disrupt native community structure.

Study Guide: Changes in Communities (BIOL 2250 - Chapter 17)

1. Agents of Change in Communities

• Agents of change can be subtle (e.g., gradual climate shifts) or catastrophic (e.g., hurricanes, wildfires).

• They can be classified as abiotic (non-living) or biotic (living factors).

A. Abiotic Factors

• Physical disturbances: Waves, currents, storms, floods, tsunamis, volcanic eruptions.

• Climate-related factors: Droughts, excessive heat, freezing, snow, ice, fire, sea-level rise or fall.

• Chemical changes: Pollution, acid rain, fluctuations in salinity or nutrient availability.

B. Biotic Factors

• Negative interactions: Competition, predation, herbivory, parasitism, disease.

• Organism-induced changes: Trampling, digging, boring, or modifying habitats (e.g., beavers building dams).

2. Stress vs. Disturbance

• Both factors vary in intensity and frequency, influencing how communities evolve.

3. Succession: How Communities Change Over Time

Succession is the gradual, directional change in species composition within a community due to biotic and abiotic forces.

A. Two Types of Succession

1. Primary Succession

• Occurs in areas where no life previously existed.

• Examples: Volcanic rock after an eruption, newly formed sand dunes, retreating glaciers.

• Requires pioneer species (e.g., lichens, mosses) to colonize bare surfaces and initiate soil formation.

2. Secondary Succession

• Happens in areas where an ecosystem existed but was disturbed.

• Examples: Post-wildfire recovery, abandoned farmland, regrowth after hurricanes.

• Some soil and organisms usually remain, leading to faster recovery than primary succession.

B. Space-for-Time Substitution

• Henry Cowles (1899) used the sand dunes of Lake Michigan to study succession.

• Older plant assemblages were farther from the shore.

• Younger plant assemblages were closer to the water.

• This method allows scientists to infer past ecological changes based on current spatial patterns.

4. Theories of Succession

A. Early Views

1. Frederic Clements (1916)

• Proposed that plant communities function as superorganisms.

• Believed succession follows a predictable pattern toward a climax community (a stable, long-term endpoint).

• Assumed that once a climax community is reached, it remains unchanged unless disturbed.

2. Henry Gleason (1917)

• Challenged Clements’ idea.

• Argued that communities are random assemblages of species, shaped by environmental fluctuations.

• Believed no two successions are identical; outcomes depend on chance and species interactions.

3. Charles Elton (1927)

• Emphasized the context-dependent nature of succession.

• Suggested that both species interactions and environmental factors determine successional pathways.

B. Three Models of Succession (Connell & Slatyer, 1977)

1. Facilitation Model

• Early species modify the environment to benefit later species.

• Example: Lichens and mosses breaking down rock into soil, allowing larger plants to establish.

2. Inhibition Model

• Early species hinder the establishment of later species through competition.

• Example: Certain grasses prevent tree seedlings from growing by monopolizing water and nutrients.

3. Tolerance Model

• Species coexist initially, and later species gradually outcompete others based on environmental conditions.

• Example: Some trees grow slowly in the shade of others but eventually replace them as they mature.

5. Succession in Different Ecosystems

A. Primary Succession: Rocky Intertidal Communities

• Example: Barnacle species in intertidal zones.

• Balanus barnacles facilitate macroalgae growth by providing a stable surface.

• Why not Chthamalus barnacles?

• Chthamalus is smaller and does not create the same stability for macroalgae.

B. Secondary Succession: New England Salt Marsh

• Tidal disturbances create bare patches where succession occurs.

• Stages of succession:

1. Distichlis (spike grass) colonizes first due to high salinity tolerance.

2. Spartina (cordgrass) and Juncus outcompete Distichlis in their respective zones over time.

6. Alternative Stable States

• Richard Lewontin (1969) proposed that communities can develop into multiple stable states depending on environmental conditions and disturbances.

• Key concepts:

• Hysteresis: A disturbed community may not return to its original state, even if conditions revert.

• Stability: A community is stable if it can resist change or recover quickly after disturbances.

Example:

• Coral reefs vs. algae-dominated states

• Healthy reefs can shift to algae-dominated states due to pollution or overfishing.

• Even if pollution is reduced, reefs may not recover without additional interventions.

7. Key Takeaways

1. Communities change constantly due to abiotic and biotic forces.

2. Succession can follow different pathways, depending on disturbance type and environmental factors.

3. Different models of succession explain how species interactions shape community development.

4. No single succession model fits all ecosystems—each case is context-dependent.

5. Communities can shift to alternative stable states, and some disturbances may permanently alter ecosystems.

6. Experimental studies on succession show variability, demonstrating that community development is unpredictable and dynamic.

8. Review Questions

1. What is the difference between primary and secondary succession?

2. How do abiotic and biotic agents of change influence community structure?

3. Compare and contrast Clements’ and Gleason’s views on succession.

4. How do the facilitation, inhibition, and tolerance models of succession differ?

5. What is hysteresis, and how does it relate to alternative stable states?

6. Give an example of an ecosystem that follows each of the three models of succession.