Ecology exam - community dynamics

Community

populations of all species in a specific geographic area

Community structure

dynamic and analyzes the patterns of species abundance and relationships between members within a community

Disturbance

any relatively discrete event in time that disrupts ecosystem/community/population structure and changes resources, substrate availability, or physical environment

Succession

the repeatable change in community composition through time following a disturbance

The stages of succession

Early (pioneer species), Mid (intermediate species), and Late (climax community)

Pioneer species

(R SELECTED) come about in the earliest stages of succession. annual plants grow and are succeeded by grasses and perennials

Intermediate species

tend to be shrubs, pines, young oak, and hickory that follow the growth of pioneer species

Climax community (late)

(K SELECTED) come about in the late stages of succession. mature oak and hickory forests remain stable until the next disturbance

Primary succession

1. Autogenic succession

2. Species are stationary 

3. Initial colonist species are good dispersers with life history traits that help then reach new habitats quickly

4. Initial colonists change conditions where they live

Facilitation model

primary succession with three assumptions

1. barren ground is uninhabitable by all but colonist species with high stress tolerance

2. early colonists help make the environment more suitable for successive species (trail blazers)

3. sequence continues until most competitively dominant species no longer facilitate the invasion and growth for any other specie

Secondary succession

1. after a non-catastrophic event 

2. not always governed by facilitation

Inhibition model

secondary succession with three assumptions

1. initial community composition is simply a function of who gets there first

2. once a colonist is established, it inhibits growth of subsequent arrivals

3. only when space/resources are released through death or decay of dominant species, then new colonists can invade and grow

short lived early species die more frequently, succession slowly progresses from short lived to long lived species

Tolerance model

secondary succession with four assumptions

1. initial community composition is simply a function of who gets there first

2. species appear later simply arrived later or arrived early but grew slower

3. late arriving species tolerate the presence of good species

• they are good competitors

• over time, late successors exclude other species

4. early successor species have no effect on late successor species

Allogenic succession

when principle forces driving succession are from outside of the system and communities are almost never at equilibrium

1. immigration of new species

2. seasonal changes in weather and sunlight

3. disturbance

Disturbance regime

the idea that disturbance creates diversity and habitat diversity means there’s species diversity usually defined in terms of:

1. timing

2. magnitude

3. frequency

4. predictability

Intermediate disturbance hypothesis

The idea that too low and too high levels of disturbance lead to low diversity levels. moderate amounts of disturbance means the highest amount of diversity (needs a good balance/equilibrium in order to thrive)

Indirect interactions between species

1. Trophic cascades

2. Behavioral cascades

3. Ecosystem engineers

Trophic cascades

“Top down control” - The removal/reduction in tertiary consumers impacts the population size of species in lower trophic levels.

1. Tuna population is removed/over fished

2. Medium sized fish population rises as they have less predators

3. Small sized fish are now being hunted in larger numbers than before, their population shrinks

4. Zooplankton populations rise due to their predator population being reduced

5. Phytoplankton population reduces since their predators (the zooplankton) are in abundance

Behavioral cascade

Ecology of fear/fear of predation. The existence of predators will instill fear in foraging animals and prey which stimulates primary production or alters population size of lower trophic levels

Ecosystem engineers

Species that physically modify their habitat which alters the availability of environmental resources for other species. Can be allogenic or autogenic.