Ecology - Lecture 15 - Effects Of Predation And Competition On Community Structure

Front 1

What are 3 main factors that organize communities?

Back 1

1) Competition

2) Predation

3) Mutualism

Front 2

The 2 general models for Community Structure are:

Back 2

1) The Equilibrium Model

2) The Non-Equilibrium Model

Front 3

The Equilibrium Model:

What are 5 general characteristics of this model?

(This is not Figure [20.2])

Back 3

The Equilibrium Model is the *classical* view - the end of a contiuum.

1) Communities display stability
- Time to recover from disturbance
- Variability
- Persistence over time

2) Biotic interaction determine structure

3) Density-dependent regulation

4) Species saturation

5) Tightly coupled - "the web of life"

Front 4

The Non-Equilibrium/Equilibrium continuum:

Figure [20.2] (pg. 404)

What are 8 characteristics for species at the extreme of Non-Equilibrium?

Back 4

1) Biotic decoupling
2) Species independence
3) Unsaturated
4) Abiotic limitation
5) Density independence
6) Opportunism
7) Large stochastic effects
8) Loose patterns

Front 5

The Non-Equilibrium/Equilibrium continuum:

Figure [20.2] (pg. 404)

What are 8 characteristics for species at the extreme of Equilibrium?

Back 5

1) Biotic coupling
2) Competition
3) Saturated
4) Resource limitation
5) Density dependence
6) Optimality
7) Few stochastic effects
8) Tight patterns

Front 6

Communities require _____ _____ to maintain a functional, highly ordered state.

Back 6

...energy input...

Front 7

What are the 3 steps (very generally) for how energy moves through a community?

Back 7

1) The *sun* is the ultimate source of energy for most communities.

2) Photosynthetic organisms convert sunlight energy into chemical energy.

3) Energy is then transferred to other components of the community.

Front 8

What is the ultimate source of energy for most communities?

Back 8

☼ ☼ ☼ The sun ☼ ☼ ☼

Front 9

Define:

Food Chain

Back 9

How energy moves through a community.

Front 10

What are the first 4 trophic levels for a food chain in a community?

Back 10

1) Primary producers (green plants)

2) Herbivores (primary consumers)

3) Carnivores (secondary consumers)

4) Higher level carnivores (tertiary, quartenary, quinary, senary, septenary...)

Front 11

The Ecological Pyramid:

What are the 3 ways trophic levels are quantified in the ecological pyramid?

Back 11

1) Energy content

2) Biomass

3) Number of individuals

Front 12

The Ecological Pyramid:

Starting at the bottom, name the trophic levels for an ecological pyramid with 4 layers.

Describe the shape of the pyramid for each trophic level.

Back 12

Primary producers (green plants) are at the bottom:
They are the most abundant, have the largest biomass and the highest energy content, thus they are the biggest layer.

Herbivores:
They are not as abundant as primary producers and have less energy content, thus their layer is smaller.

First carnivores:
Not as abundant as herbivores, and lower energy content, thus their layer is smaller.

Secondary carnivores:
Not as abundant as first carnivores and lower energy content, thus their layer is smaller.

Front 13

The Ecological Pyramid:

In terms of energy transfer, why does the ecological pyramid take the shape that it does?

What does this explain about organisms near the top of the pyramid?

Back 13

Energy transfer is *very* inefficient.
~10% of energy is transferred from one trophic level to the next.
~90% of energy is lost as heat.

This explains why:
- Big fierce "apex predators" are rare (because there is not enough energy to support them)
- Why apex predators have such large ranges.

Front 14

Define:

Food webs

Back 14

Conversion of food-chain into "who-eats-who" diagram.

Front 15

In general, if you (increase/decrease) biodiversity, this will (increase/decrease) the complexity of a food web.

Back 15

...increase...

...increase...

Front 16

Figure [20.3] (pg. 405)

What are 3 important things to note about this figure?

Back 16

1) Man replaced whales as the apex predator.

2) Each species has multiple linkages.

3) Some species occupy multiple trophic levels

Front 17

Food webs:

What is the link between species richness and the complexity of food webs?

Back 17

Increased species richness means an increase in *possible* linkages.

Increased species richness seems to increase *actual* linkages.

Front 18

Food webs:

As a general pattern for food webs, as species diversity increases this will (increase/decrease) the number of linkages between individuals.

Back 18

...increase...

Front 19

Food webs:

In general food chains are (short/long) in length.

Back 19

...SHORT...

Front 20

Define:

Food Chain Length

Back 20

The number of linkages from apex predator to basal species.

Front 21

Food webs:

In general, few species exceed _____ number of links.

Why is this?

Back 21

...8 or 9...

This is because of the Energetic Hypothesis.

Front 22

Define:

Energetic Hypothesis

Back 22

The length of food chains is limited by the inefficiency of the energy transfer along the chain.

Front 23

Factors Determining Community Structure:

List 3 characteristics of Keystone species

Back 23

1) They're generally not abundant

2) Identified by removal experiments

3) May reverse competitive interactions.

Front 24

Factors Determining Community Structure:

What are the 2 organisms used as examples of Keystone species?

Back 24

1) The starfish Pisaster Ochraceous (pg. 412)

2) Sea Otters (pg. 412-13)

Front 25

What are the 2 types of species we spoke about that are factors in determining community structure?

Back 25

1) Keystone species

2) Dominant species

Front 26

Factors Determining Community Structure:

List 3 characteristics of Dominant species

Back 26

1) They're numerically abundant

2) They dominate through competitive superiority

3) May influence physical conditions.

Front 27

Define:

Stability
(in terms of community structure)

Back 27

Ability of the community to recover from disturbance

Front 28

Community Stability:

The major tenet of Ecology is:

Back 28

"Biodiversity promotes stability"

Front 29

Community Stability:

What example was cited as evidence that "Biodiversity promotes stability"?

Back 29

FIG [20.20] (pg 419)

Tilman et al (2006)

Grassland plots were seeded with (1 --> 16) different species of grass.

Each plot's biomass yield was measured over a 10 year period.

Stability was defined as having less fluctuation in average yield over that time period.

Plots with more species diversity (16 species of grass) showed more stability.