integrated lec 20

Question 1

Cycles in Predator and Prey Population

Answer 1

Predator-prey interactions often exhibit population cycles, where predator and prey populations rise and fall in a coupled, lagged manner.
-Lotka Volterra model shows coupled oscillations where prey population peaks first, followed by predators.

Question 2

examples of cycles in predator and prey pop

Answer 2

Hudson’s Bay Company Data:

Lynx and hare pelts (1845–1935) showed population cycles.
Factors influencing these cycles:
Over-browsing by hares depleting food plants.
Social stress in overcrowded hare populations.
Indicates cycles are not purely Lotka-Volterra based but are influenced by additional ecological factors.

Huffaker’s Mites Experiment (1958):

Used prey and predator mites on trays of oranges.
Demonstrated how habitat complexity (e.g., barriers) helped sustain cycles.
Without sufficient complexity, predator-prey interaction led to unstable dynamics, often driving one species extinct.

Question 3

How do ecological factors such as habitat complexity influence predator-prey cycles in nature?

Answer 3

Habitat complexity influences predator-prey cycles by modifying predation rates, encounter frequencies, and population stability. Greater complexity tends to stabilize cycles by providing refuges, spatial variation, and dispersal opportunities for prey, while simpler habitats often lead to more volatile cycles with higher risks of local extinctions.

Ecological factors like habitat complexity play a significant role in influencing predator-prey cycles in nature by affecting interactions between predators and their prey. Here’s how habitat complexity specifically impacts these dynamics:

1. Refuges for Prey
   How it works: Habitat complexity often provides prey with refuges, such as dense vegetation, burrows, or physical structures where they can hide from predators.
   Impact on predator-prey cycles:
   By reducing the predation rate, refuges can stabilize predator-prey cycles and prevent extreme fluctuations.
   Prey populations are less likely to crash entirely, providing a more stable food source for predators.
   This can delay or dampen the amplitude of cycles.
2. Heterogeneous Resource Availability
   How it works: Complex habitats often have varying microenvironments that support diverse resources for prey and predators.
   Impact on predator-prey cycles:
   Prey populations can grow in resource-rich areas, creating “hotspots” of predator-prey interactions.
   Predators may exploit these areas while leaving other areas untouched, leading to spatially asynchronous cycles.
   This spatial variation can smooth out population fluctuations at the larger scale.
3. Movement and Encounter Rates
   How it works: Complex habitats reduce the efficiency of predator movements, lowering the encounter rates with prey.
   Impact on predator-prey cycles:
   Reduced encounter rates decrease the predation pressure, allowing prey populations to recover more quickly.
   This can lead to longer, less dramatic predator-prey cycles as opposed to rapid booms and crashes.
4. Diverse Predation Strategies
   How it works: In complex habitats, predators may rely on different hunting strategies, such as ambush or active pursuit, depending on the environment.
   Impact on predator-prey cycles:
   The diversity of predation strategies can lead to more complex, multi-species predator-prey dynamics.
   Some prey species may thrive in one part of the habitat while others are suppressed, introducing more nuanced cycles.
5. Prey Dispersal and Meta-Populations
   How it works: In a complex habitat, prey populations can disperse to new areas when predation pressure is high.
   Impact on predator-prey cycles:
   This dispersal reduces local prey extinctions and prevents predators from driving prey populations to critically low levels.
   It allows for a more dynamic predator-prey interaction, where local extinctions are compensated by recolonization, creating a spatially patchy but overall stable cycle.
6. Predator Competition and Specialization
   How it works: Complex habitats often support multiple predator species, which can compete or specialize in different prey types.
   Impact on predator-prey cycles:
   Competition among predators can reduce the pressure on a single prey species, stabilizing that prey population.
   Predator specialization may lead to more independent cycles for different predator-prey pairs, reducing the risk of cascading extinctions.
7. Temporal Variation in Habitat Complexity
   How it works: Seasonal changes, such as leaf fall, snow cover, or water levels, alter habitat complexity over time.
   Impact on predator-prey cycles:
   This temporal variation adds another layer of dynamics, where predator-prey interactions fluctuate seasonally.
   For example, prey may have better refuge during certain times of the year, allowing populations to recover before the next predation peak.

Real-World Examples:

Lynx-Hare Cycles:

In the boreal forests of Canada, snowshoe hares rely on dense vegetation for cover. When habitat complexity is reduced (e.g., after overbrowsing), hares become more vulnerable to lynx predation, exacerbating the population crash phase of the cycle.

Coral Reef Ecosystems:

In coral reefs, the complexity of coral structures provides hiding spaces for smaller fish, which are prey for larger predators. The loss of coral complexity due to bleaching or destruction can lead to dramatic prey population declines and destabilized predator-prey interactions.

Question 4

Antagonistic Coevolution

Answer 4

Definition: Reciprocal evolutionary adaptations between predators and prey (or hosts and parasites), often described as an “arms race.”

Key Features:
Prey evolve defenses to avoid predation, while predators develop counter-adaptations to overcome these defenses.

Central to the Red Queen Hypothesis:
In evolutionary terms, “it takes all the running you can do to stay in the same place” (constant adaptation to maintain fitness relative to evolving adversaries).

Question 5

Examples of Antagonistic Coevolution:

Answer 5

1. Garter Snakes vs. Rough-Skinned Newts:

Newts (genus Taricha) produce tetrodotoxin (TTX), a potent neurotoxin.
Garter snakes (Thamnophis) have evolved resistance to TTX.
In areas where newts are more toxic, snakes exhibit higher TTX resistance, demonstrating local adaptation.

2. Life-Dinner Principle:

Unequal Selection Pressure: Predators and prey face different evolutionary stakes:
Prey face life-or-death consequences.
Predators face reproductive consequences (missing a meal but surviving).
Result: Prey often evolve more elaborate and faster defenses than predators’ counter-adaptations.

Question 6

Prey Defenses and Predator Counter-Adaptations:

Answer 6

Defenses:
Morphological (e.g., spines, shells).
Chemical (e.g., plant secondary chemicals, animal toxins like TTX).
Behavioral (e.g., avoiding detection, fleeing, group behavior).
Inducible Defenses: Activated in response to predator presence (e.g., Daphnia develop protective helmets).

Counter-Adaptations:
Enhanced sensory abilities (e.g., echolocation).
Physiological tolerance to toxins.
Behavioral strategies for overcoming defenses.

Question 7

What is the Red Queen Hypothesis, and how does it relate to predator-prey interactions?

Answer 7

The Red Queen Hypothesis is an evolutionary theory that describes how organisms must continuously adapt and evolve not just for reproductive success, but also to survive against ever-evolving opponents, such as predators, prey, or parasites

Question 8

Why is prey adaptation often faster than predator counter-adaptation (refer to the life-dinner principle)?

Answer 8

The Life-Dinner Principle
The principle states:

For prey: Failure in the interaction (being caught by the predator) results in death, which is the ultimate evolutionary cost. This creates strong selective pressure for prey to evolve effective defenses quickly.

For predators: Failure in the interaction (failing to catch the prey) results in the loss of a meal, which is a less severe evolutionary cost than death. While catching prey is important for survival and reproduction, the stakes are lower compared to the prey.

Why Prey Adaptation is Faster
The life-dinner principle explains why prey are under stronger and more immediate selective pressure than predators:

Higher Consequences for Prey:

If prey fail to escape, they are removed from the gene pool entirely. This creates intense selection for traits like speed, camouflage, or other defenses.
For predators, a missed meal is significant but not always life-threatening. They can still survive to hunt another day.
Asymmetry in Selection Pressure:

The selective pressure to avoid death is much stronger than the selective pressure to increase hunting success.
As a result, prey evolve adaptations like cryptic coloration, toxic defenses, or rapid escape behaviors more quickly than predators evolve countermeasures.
Population Dynamics:

Prey often reproduce more rapidly than predators (e.g., mice versus owls). This allows prey populations to adapt faster because genetic variations spread more quickly in faster-reproducing species.
Predators, which are typically larger and reproduce more slowly, take longer to evolve counter-adaptations.
Arms Race Costs:

Developing counter-adaptations (e.g., faster speed or toxin resistance) is often energetically costly for predators. If the costs of adapting outweigh the benefits, predators may not evolve countermeasures as quickly as prey evolve defenses

Question 9

How does local adaptation affect the coevolution of Thamnophis and Taricha?

Answer 9

Key Idea: Local adaptation drives a geographic mosaic of coevolution between Thamnophis garter snakes and Taricha newts, shaping their predator-prey dynamics.

-Newts (Taricha):
Produce tetrodotoxin (TTX) as a defense.
Higher TTX levels in regions with resistant predators (hotspots).
Lower TTX in regions without resistant predators (coldspots) to conserve energy.

-Snakes (Thamnophis):
Evolve TTX resistance in hotspots to prey on toxic newts.
Resistance has trade-offs (e.g., reduced speed and performance), so it’s absent in coldspots.

Arms Race:

Hotspots: High toxin levels in newts and strong resistance in snakes.
Coldspots: Minimal coevolutionary adaptation.

Outcome:

Reciprocal adaptation creates a geographic mosaic of coevolution.
Hotspots and coldspots drive biodiversity and ecological dynamics.

Question 10

Flowchart of antagonistic coevolution:

Answer 10

Prey evolves defense → Predator evolves counter-adaptation → New prey adaptation.

Question 11

What is the latitudinal gradient in species richness?

Answer 11

A: Biodiversity is highest at the equator and decreases toward the poles due to stable climates and resource abundance

Question 12

Provide examples of invasive species and their impacts.

Answer 12

A:
Asian carp: Disrupt freshwater ecosystems.
Purple loosestrife: Displace native wetland plants.
Emerald ash borer: Destroys ash trees

Question 13

What is the Enemy Release Hypothesis?

Answer 13

A: Invasive species succeed because they lack natural predators or pathogens in new environments

Question 14

Define ecosystem function and give examples.

Answer 14

A: Processes that regulate energy and nutrient flow, such as primary production, nutrient cycling, and decomposition.

Question 15

How do predators affect community structure?

Answer 15

A: Predators prevent competitive exclusion, promoting coexistence. For example, Pisaster sea stars maintain biodiversity in intertidal zones by preying on mussels​

Question 16

What are amplification and dilution effects in disease ecology?

Answer 16

Amplification: More host species increase pathogen abundance (e.g., mosquito diversity increases malaria prevalence).

Dilution: Diverse hosts reduce disease spread

Question 17

Summarize Robert Paine’s experiment with sea stars.

Answer 17

A: Removing sea stars led to mussel dominance and reduced biodiversity, demonstrating the role of predators in maintaining species diversity​

Question 18

What factors influence lynx and hare population cycles?

Answer 18

A: Factors include food availability (e.g., browsing impacts) and predator-prey dynamics, with cycles lagging between predator and prey

Question 19

Provide an example of antagonistic coevolution.

Answer 19

A: Garter snakes evolved resistance to tetrodotoxin (TTX) from toxic newts (Taricha), showcasing reciprocal adaptations

Question 20

How does biodiversity enhance ecosystem function?

Answer 20

A: Through:
Complementarity: Species use resources differently.

Facilitation: Some species improve others’ success.

Redundancy: Overlapping roles provide stability.

Question 21

How does host diversity affect disease risk?
A:

Answer 21

Dilution: Reduced disease risk with diverse hosts.

Amplification: Higher risk with more host species, as seen with mosquito diversity increasing malaria cases in Kenya

Question 22

Provide an example of the amplification effect in disease spread.

Answer 22

A: Malaria prevalence increases with mosquito species richness in Kenya​

Question 23

What explains higher species richness near the equator?

Answer 23

A: Stable climates and resource abundance favor biodiversity

Question 24

Inducible Defenses

Answer 24

Definition: Defenses that are only expressed in response to threats or attacks, rather than being constantly present. These defenses save energy while providing protection when needed.

Examples:

Morphological Defenses:
Daphnia lumholtzi (water fleas) grow protective helmets when predators are present.

Chemical Defenses:
Plants produce secondary chemicals (e.g., tannins, alkaloids) in response to herbivore attack.

Behavioral Defenses:
Animals may change activity patterns, such as becoming nocturnal to avoid predators.

Immune System Responses:
Humans and other animals upregulate immune defenses upon detecting pathogens.

Question 25

significance of inducible defenses

Answer 25

Adaptive Advantage: Allows organisms to allocate energy efficiently by avoiding the costs of maintaining constant defenses.

Trade-Offs: Inducible defenses are slower to deploy than constant defenses, potentially leaving organisms vulnerable in rapidly changing environments.

Question 26

What are the energy trade-offs associated with inducible defenses?

Answer 26

Definition: Inducible defenses are traits developed in response to environmental threats, but they come with significant energy trade-offs.

Key Trade-Offs:
1. Growth vs. Defense:
-Energy diverted to defenses slows growth.
-Example: Plants produce chemical defenses, reducing growth rates.

Reproduction vs. Defense:
-Reduced energy for reproduction.
-Example: Mussels thicken shells but produce fewer gametes.

Energy Reserves vs. Defense:
-Depletes stored energy, reducing survival under stress.
-Example: Toxins produced by prey deplete energy stores.

Developmental Costs:
-Defense changes delay growth or reduce adult fitness.
-Example: Tadpoles develop wider tails but grow slower.

Risk from Other Threats:
-Defenses for one threat increase vulnerability to others.
-Example: Spines in Daphnia attract other predators.

Behavioral Trade-Offs:
-Reduced activity to avoid predators limits food intake.
-Example: Prey hide instead of foraging.

Energetic Costs of Plasticity:
-Maintaining the ability to induce defenses consumes energy.
-Example: Pathway activation for chemical defenses.

Recovery Costs:
-Post-threat repair or maintenance of defenses incurs energy costs.
-Example: Plants regrow tissues after herbivory.

Long-Term Impacts:
-Reduced growth, reproduction, and fitness.
-Population-level effects, such as slower recovery from threats.

Takeaway: Inducible defenses enhance survival but impose significant energy costs that impact growth, reproduction, and overall fitness

Question 27

Paine’s Sea Star Experiment

Answer 27

-Predation and Biodiversity:
Predation can prevent competitive exclusion, maintaining species diversity in communities.
Keystone Species: Predators like sea stars play a disproportionate role in maintaining community structure.

-Experiment Details:
Conducted by Robert Paine in rocky intertidal zones.

Hypothesis: Predation by sea stars prevents dominant species (mussels) from outcompeting others.

Findings:
Removing sea stars (Pisaster ochraceus) allowed mussels to dominate, reducing species diversity.
Sea stars maintained biodiversity by preying on mussels, preventing them from monopolizing resources.

Significance:
Demonstrates how predators can increase community biodiversity by disrupting competitive hierarchies

Question 28

How does predation affect competitive exclusion?

Answer 28

Key Idea: Predation modifies competitive exclusion, often preventing one species from outcompeting another and promoting coexistence.

Effects of Predation:

1.Prevents Competitive Exclusion:
Predators target the dominant competitor, reducing its advantage and allowing inferior competitors to persist.
Example: Starfish preying on mussels in intertidal zones.

2.Mediates Resource Partitioning:
Weakens competition, enabling species to specialize or exploit different resources.
Example: Predators in grasslands reduce dominant herbivores, allowing others to thrive.

3.Keystone Predator Effect:
Keystone predators suppress dominant species, increasing community diversity.
Example: Sea otters controlling sea urchins in kelp forests.

4.Alters Competitive Hierarchies:
Predators may accelerate or hinder competitive exclusion depending on their prey preferences.
Example: Fish targeting smaller zooplankton allow larger zooplankton to dominate.

5.Density-Dependent Control:
Predators regulate population densities, preventing any one species from monopolizing resources.
Example: Lions controlling zebra populations in grasslands.

6.Context-Dependent Impact:
Habitat complexity (e.g., refuges) can reduce predation effects, allowing competitive exclusion to proceed.

Takeaway: Predation often prevents competitive exclusion by suppressing dominant competitors, promoting coexistence, and maintaining biodiversity.

Question 29

enemy release hypothesis

Answer 29

Definition: Invasive species often experience fewer natural enemies (predators, parasites, or pathogens) in their introduced ranges, allowing them to grow unchecked and outcompete native species.

Examples:
Asian Carp: Rapid population growth in North America due to lack of natural predators.
Purple Loosestrife: Prolific spread in wetlands with reduced herbivory.
Emerald Ash Borer: Devastating ash trees in areas with no natural predators to control its population.

Significance:
Explains the success of many invasive species and their negative impacts on native biodiversity.

Question 30

Amplification and dilution effects

Answer 30

Community Ecology of Disease: Examines how biodiversity affects disease dynamics in human, livestock, and wildlife populations.

-Dilution Effect: High host diversity reduces disease risk by diluting pathogen transmission.
-Amplification Effect: High host diversity increases disease risk by supporting larger pathogen populations.

Examples:
1. Amplification Effect (Malaria):
In Kenya, increased mosquito species richness was linked to higher malaria prevalence.
Parasite (Plasmodium falciparum) uses diverse Anopheles mosquitoes as vectors.

2. Dilution Effect:
   High diversity of small mammals reduces Lyme disease transmission by lowering the proportion of competent hosts for Borrelia burgdorferi.

Question 31

What are the key differences between the dilution and amplification effects?

Answer 31

Key Idea: Both concepts describe how biodiversity influences disease transmission, but they have opposite outcomes.

Dilution Effect:

Definition: Increased biodiversity reduces disease transmission.
Mechanism:
Non-host species “dilute” interactions between pathogens and primary hosts, decreasing pathogen spread.
Reduced abundance of competent hosts or increased presence of poor hosts interrupts disease cycles.
Example: Higher vertebrate diversity reduces Lyme disease by diluting interactions between ticks and effective hosts (e.g., mice).

Amplification Effect:

Definition: Increased biodiversity enhances disease transmission.
Mechanism:
Greater species diversity introduces more hosts or vectors, increasing opportunities for pathogen spread.
More ecological niches may sustain pathogen populations for longer.
Example: Higher mosquito diversity in wetlands increases malaria risk by adding efficient vectors.

Key Differences:
Outcome: Dilution reduces disease risk; amplification increases it.
Drivers: Dilution relies on non-hosts reducing pathogen spread, while amplification depends on diverse hosts/vectors boosting pathogen success.

Takeaway: The balance between dilution and amplification depends on host competence, vector behavior, and ecosystem dynamics.

Question 32

Latitudinal gradient in species richness

Answer 32

Biodiversity is higher in tropical regions compared to temperate zones, a robust biogeographical pattern observed across taxa.

Potential Causes:
Climate Stability: Tropics have historically stable climates, allowing for greater evolutionary diversification.
Higher Energy Input: More solar energy supports greater productivity and ecological specialization.
Niche Specialization: Greater resource availability allows species to specialize, reducing competition.
Evolutionary Time: Tropics have had fewer extinction events, leading to the accumulation of species.

Examples:
Terrestrial Vertebrates: Richness peaks near the equator.
Pathogen Diversity: Human pathogen species richness is higher in tropical regions, mirroring host diversity.

Question 33

How does climate stability contribute to the latitudinal gradient in species richness?

Answer 33

Climate stability in tropical regions contributes to higher species richness along the latitudinal gradient.

How Climate Stability Contributes:
Longer Evolutionary Time:

Stable climates in the tropics provide consistent conditions over evolutionary timescales, allowing more time for species diversification.

Lower Extinction Rates:

Fewer extreme climatic events (e.g., ice ages) reduce species extinction rates, leading to greater species persistence.
Specialization Opportunities:

Stable environments enable species to specialize in narrow niches, increasing biodiversity through reduced competition.

Faster Speciation:

Predictable climates allow populations to adapt locally, driving speciation through geographic or ecological isolation.

Higher Productivity:

Stability supports continuous resource availability, fostering larger and more diverse populations.

Takeaway: Tropical climate stability provides consistent conditions for speciation, persistence, and specialization, driving the latitudinal gradient in species richness.

Question 34

What does the Lotka-Volterra predator-prey model predict?

Answer 34

A: Coupled, lagged population cycles where prey peaks are followed by predator peaks

Question 35

What ecological factors complicate real-world predator-prey cycles?

Answer 35

A: Food availability, habitat complexity, and social stress in prey populations.

Question 36

What was the significance of Huffaker’s mites experiment?

Answer 36

A: Demonstrated that habitat complexity stabilizes predator-prey interactions.

Question 37

Provide an example of predator-prey cycles in nature.

Answer 37

A: Lynx and hare populations in Canada (Hudson’s Bay Company data).

Question 38

Define antagonistic coevolution.

Answer 38

A: Reciprocal evolutionary adaptations between predators and prey, often described as an “arms race.”

Question 39

What is the Red Queen Hypothesis?

Answer 39

A: The idea that species must continuously evolve to keep up with evolving adversaries.

Question 40

Explain the life-dinner principle.

Answer 40

A: Prey face life-or-death stakes, while predators face only reproductive stakes, creating unequal selection pressures.

Question 41

How do Thamnophis snakes counter newt TTX toxins?

Answer 41

A: They have evolved resistance to tetrodotoxin (TTX).

Question 42

What is a real-world example of local adaptation in coevolution?

Answer 42

A: Garter snakes in regions with highly toxic newts exhibit greater TTX resistance.

Question 43

What are inducible defenses?

Answer 43

A: Defenses expressed only in response to threats, saving energy compared to constant defenses

Question 44

Provide an example of a morphological inducible defense.

Answer 44

A: Daphnia lumholtzi develop helmets when predators are present

Question 45

Name a behavioral inducible defense.

Answer 45

A: Animals altering activity patterns to avoid predators.

Question 46

What is a keystone species?

Answer 46

A: A species that disproportionately affects community structure, like Pisaster sea stars.

Question 47

How did Pisaster predation affect biodiversity?

Answer 47

A: It prevented mussels from excluding other species, maintaining intertidal biodiversity.

Question 48

What was the main finding of Paine’s sea star experiment?

Answer 48

A: Predation can increase species diversity by preventing competitive exclusion.

Question 49

What is competitive exclusion?

Answer 49

A: The process where dominant species monopolize resources, driving others extinct.

Question 50

What is the enemy release hypothesis?

Answer 50

A: Invasive species succeed because they face fewer natural enemies in their new range.

Question 51

What role do natural predators play in regulating species invasions?

Answer 51

A: They limit population growth, preventing dominance by invasive species.

Question 52

What is the dilution effect in disease ecology?

Answer 52

A: High host diversity reduces disease risk by diluting pathogen transmission.

Question 53

Provide an example of the amplification effect.

Answer 53

A: Malaria prevalence increases with higher mosquito species richness.