Mutualism • Nature of Communities • Change in Communities • Species Diversity (Biogeography and Within Communities

What is mutualism?

A positive (+/+) interaction where both species benefit.

Difference between facultative and obligate mutualism?

Facultative: benefit but not dependent.
Obligate: benefit and are dependent for survival.

What is symbiosis?

A close ecological relationship where a smaller symbiont lives on or inside a host. Can be mutualistic or not.

Three types of mutualism?

• Trophic – exchange nutrients/energy

• Habitat – shelter or living space

• Service – ecological services (e.g., pollination, cleaning)

Example of a service mutualism?

Cleaner fish removing parasites → affects abundance and diversity of fish on reefs.

What is commensalism?

A (+/0) interaction where one species benefits and the other is unaffected, though this is often hard to prove clearly.

Why are many interactions context-dependent?

Abiotic and biotic conditions change across space/time, altering the nature of the interaction.

Define species richness.

Number of species in a community.

Define species composition.

Which species are present in a community.

What is abundance?

The number of individuals of each species.

What is a rank–abundance curve?

Plot of species rank (x-axis) vs relative abundance (y-axis). Used to visualize diversity.

What does Simpson’s Index measure?

The probability that two individuals drawn at random belong to the same species.
Formula: D = Σ(ni/N)²

What is a keystone species?

A species whose removal causes disproportionately large community-wide effects.

What is a foundation species?

A dominant species that defines community structure (e.g., kelp).

What is an ecosystem engineer?

A species that creates or modifies habitat (e.g., trees, beavers).

What is a trophic cascade?

When changes at one trophic level cause effects up or down the food web.

What is primary succession?

Succession on newly formed habitats with no soil (e.g., lava flows).

What is secondary succession?

What is secondary succession?

What is a climax community?

The stable end-point of succession.

Describe the facilitation model of succession.

Early species modify environment in ways that help later species; ends in climax community.

Describe the tolerance model of succession.

Early species do not help or hinder later species; later species tolerate conditions.

Describe the inhibition model of succession.

Early species inhibit later ones until removed or die.

Typical species richness pattern over time after disturbance?

Richness increases early, then decreases later due to competitive exclusion.

What is a cosmopolitan species?

Species that occur nearly worldwide.

What is an endemic species?

Species found in only one location.

What is a disjunct distribution?

Populations occur in separate, distant locations.

Define species–area effect.

Larger islands contain more species.

Define species–isolation effect.

More isolated islands have fewer species.

What is the MacArthur–Wilson Island Biogeography theory?

Species richness reaches equilibrium based on immigration vs extinction rates.

What is resource partitioning?

Species divide resources to reduce competition (e.g., MacArthur’s warblers).

What does the Intermediate Disturbance Hypothesis propose?

Highest diversity occurs at intermediate disturbance levels.

What does the Menge & Sutherland model evaluate?

How stress, predation, and competition interact to determine diversity.

What do neutral / lottery models assume?

All species have equal competitive ability; chance determines resource acquisition.

What is the Recruitment Limitation Hypothesis?

Poor dispersal prevents full mixing, allowing coexistence even among similar species.

What did Hubbell (1999) find about seed dispersal?

Species show patchy seed deposition; not all species appear in all traps.

What does dispersal limitation allow?

Poor competitors can persist by avoiding strong competitors spatially