Ecology Exam 3: Community Dynamics

3 conceptual models of succession

1. facilitation (primary succession)

2. inhibition (secondary succession)

3. tolerance (secondary succession)

Facilitation

1. Barren ground uninhabitable by all but most stress tolerant colonists

2. Early colonists make environment more suitable for successive species

3. Sequence continues until most competitively dominant species no longer facilitate invasion and growth of other species

inhibition

1. Initial community composition is who gets there first

2. Once colonist becomes established, it inhibits growth of following arrivals

3. Only when space and/or resources released through decay or decay of dominant residents can new colonists invade and grow

Tolerance

1. initial community composition is who gets there first

2. specis that appear later arrived later, or arrived early but grew more slowly

3. late arriving species tolerate presence of early species

- good competitors

- over time, late successional species exclude others

4. early successional species have no effect on late successional species (can live together)

Allogenic succession

When primary forces driving succession are from outside the system.

- immigration of new species

- seasonal changes in weather/sunlight

- disturbance

Autogenic succession

A type of succession where the plant community changes the environment; changes that occur within a community caused by the actions of the community members

- biotic

-has to occur within a forest

Primary succession

Starts on surface with no soil and usually no prior life.

ex. bare rock, lava rock

Secondary succession

Succession after non-catastrophic event, disturbance but soil still there.

Ex. after forest fire, flood

Intermediate disturbance hypothesis

Species diversity is highest at intermediate levels of disturbance because both early and late-successional species can coexist.

Behavioral cascade

Predator alters foraging behavior of its prey which stimulates primary production or alters population size lower trophic levels.

Ecosystem engineer

Species that physically modifies habitat and changes resource availability for other species.

Allogenic engineer

Changes environment by transforming materials from one state to another (e.g., beavers building dams).

Autogenic engineer

Changes environment through own physical structure (e.g., corals).

Trophic cascade

Top down control where higher trophic levels regulate abundance of lower trophic levels, control of primary production is biotic (consumers)

Bottom-up control

Resource availability at base of food web controls abundance of higher trophic levels, control of primary production is environmental abiotic

Trophic energy transfer

Only about 10% energy transferred from one trophic level to the next, so 90% is lost.

Headwater streams/ lakes

Fueled by allochthonous inputs (outside) and useful for testing bottom up effects bc boundaries and nutrient imputs easier to measure

Productivity hypothesis

argues that more productive ecosystems should have longer food chains/bottom up contorl determines food chain length

Ecosystem size hypothesis

Food chain length increases with ecosystem size

Productive-space hypothesis

Food chain length increases with ecosystem productivity and size

Exploitation ecosystem hypothesis

food chain length is controlled by bottom up forces, with top down control becoming increasingly important as more trophic levels are added

ex. herbivory, parasitism, predation

3 R's of Community stability

Resistance, return time, resilience (persistence).

Resistance

How much the community changes due to specific disturbance.

-more resistance=more stable

-How big a change did the disturbance cause?

Return time

Time it takes a community to return to equilibrium state.

- how quickly did the community recover from disturbance

Resilience (persistence)

How closely the post-recovery community resembles the pre-disturbance community.

Diversity vs. stability

More habitat and species diversity generally increase stability and persistence after disturbance.

Food web theory

Communities with higher connectance (with many species interactions) should be more stable.

How does biodiversity loss affect community stability?

More omnivores you have, more stable the environment/food web

Connectance

Number of realized interactions among species in the food web.

Keystone species

Effect on community structure is much larger than expected from its abundance or biomass.

Invasive species

Non-native species that spreads and causes ecological, economic, or human health harm; alter community structure

Succession

The series of predictable changes that occur in a community over time

r-selected species

-many offspring

-shorter life

-early reproduction

-pioneer species

K-selected

-density dependant

-fewer offspring

-longer life

-climax community

Climax community

stable, mature ecological community with little change in the composition of species

Disturbance Regime

timing, magnitude (small or large), frequency, predictability

Alternative state

occur when more than one type of community can exist in a particular environment