Ch 14/15 - Exploitative Interactions + Mutualism

What is exploitation in ecology?

An interaction where one organism benefits and the other is harmed (+/-)

What are the three main types of exploitative interactions?

Predation, parasitism, and pathogens

What is predation?

An interaction where a predator kills and consumes prey

What is parasitism?

A relationship where a parasite lives on a host and reduces its fitness without usually killing it

What is a pathogen?

A disease-causing organism

How do predators affect prey populations?

They influence distribution, abundance, and population structure

What do predator-prey cycles show?

Population sizes fluctuate over time in response to each other

What is the Lotka-Volterra model?

A model predicting oscillations in predator and prey populations

What happens to predator populations after prey increases?

Predator populations increase after a lag

What happens to prey after predator populations rise?

Prey populations decrease

Why are predator-prey cycles not perfectly stable in real life?

Environmental factors and refuges affect them

What is a refuge?

A place or condition where prey avoid predators

Why are refuges important?

They allow prey populations to persist

What happens without refuges?

Both predator and prey may go extinct (from overexploitation)

What role does immigration play in predator-prey dynamics?

It can maintain oscillations in populations

What is a spatial refuge?

A physical location that protects prey (burrows, trees)

What is predator satiation?

When predators cannot consume all prey at high prey density

How does group living protect prey?

It reduces individual risk of predation

What happens at very high prey density?

Predator consumption rate levels off

What is the dilution effect?

Individual probability of being eaten decreases in large groups

How can predators influence prey behavior?

They can alter where and how prey feed or move

What is an example of predator-induced behavior change?

Elk avoiding riparian areas due to wolves

How can parasites manipulate host behavior?

They alter behavior to increase transmission

Example: what happens to infected amphipods?

They move toward light, increasing predation risk

Why is host manipulation beneficial to parasites?

It increases the likelihood of reaching the next host

How does the rust fungus manipulate plants?

It creates pseudoflowers to attract pollinators

What are pseudoflowers?

Fungal structures that mimic real flowers

Why do pseudoflowers attract pollinators?

They produce sugary secretions

What is mutualism?

An interaction where both species benefit (+/+)

When will mutualism evolve?

When benefits outweigh the costs

What must be true for mutualism to persist evolutionarily?

Combined fitness must exceed non-mutualists

What are common plant mutualisms?

Nitrogen fixation, pollination, seed dispersal, nutrient uptake

What is nitrogen fixation mutualism?

Bacteria convert nitrogen into usable forms for plants

What do mycorrhizal fungi provide plants?

Increased access to nutrients (N, P, K, etc.)

What do plants provide mycorrhizae?

Carbohydrates

What are arbuscular mycorrhizae?

Fungi that form exchange structures inside root cells

What are ectomycorrhizae?

Fungi that surround roots externally

How do mycorrhizae affect water balance?

They improve water uptake and leaf water potential

Why are mycorrhizae especially beneficial in poor soils?

They increase nutrient acquisition

What happens to mutualism in nutrient-rich environments?

It may become less beneficial or even parasitic

Why might fungi become more “selfish” in rich soils?

They take more carbon while providing fewer nutrients

What is the mutualism between ants and acacia trees?

Ants defend the plant; plant provides food and shelter

What do ants receive from acacia?

Nectar, protein (Beltian bodies), and housing

What do acacia trees gain from ants?

Protection from herbivores and competing plants

What happens to acacia fitness with ants?

It increases (growth and survival improve)

What is a potential conflict in mutualism?

One partner harming another mutualist

Example of conflict: ants vs pollinators

Ants may interfere with pollination

How do acacias prevent ant-pollinator conflict?

Flowers produce ant repellents

What is coral mutualism?

Corals depend on algae and animals for nutrients

Why are coral mutualisms critical?

Oceans are nutrient-poor environments

What do algae provide corals?

Photosynthetic products (energy)

What do corals provide algae?

Shelter and nutrients

What is a coral protection mutualism?

Crustaceans protect corals from predators

What happens to corals without crustaceans?

Higher predation rates

What is the overall ecological role of exploitation?

It regulates population size and structure

What is the overall ecological role of mutualism?

It enhances survival, growth, and ecosystem function

How do exploitation and mutualism together shape ecosystems?

They control population dynamics and species interactions