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Ecology 3: Community Interactions

3 of 4 of Ecology Unit

Sarah Blechacz

on 3 April 2014

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Transcript of Ecology 3: Community Interactions


Where Are We?
Ecology is the study of organism interactions with each other and the environment.

Ecological processes occur at multiple levels of organization on Earth.

Each level of organization emerges from the processes of the level below it
Behavior is an Organism-Level phenomenon.
Big Questions:
Make Sure You Can
How are communities structured?

How do the interactions of species in a community lead to emergent properties?
Describe and compare all of the community interactions discussed in this presentation and provide multiple examples of each.

Explain the relationship between community diversity and stability.

Quantitatively demonstrate the diversity of a community.

Explain the interactions in a community that contribute to its trophic structure.

Explain why community diversity is maximized when disturbance is present at an intermediate level.

Explain the processes of primary and secondary seccession.

Explain the effects of all of the biogeographical factors discussed in this presentation on community structure.
Characterizing Communities
Trophic Structure
Effects on Diversity
Biogeographic Factors
A contest between individuals for shared resources.

A -/- interaction
One species (the
) kills and eats the other species (the


A +/- interaction.

Predation drives many adaptations.
All of the populations in a contiguous area.

Properties emerge from interactions in the community.
One species (the
) eats part of a
(plant or algae)

A +/- interaction

Producers have evolved many adaptions to control herbivory.
Two or more species live in close contact with each other.

Three major types of symbiotic interactions...
Species have positive effects on other species in the community without being in a symbiotic relationship.

A +/+ or 0/+ interaction.
Between species (
) or within a species (
All of an organism's interactions in its environment
Competition limits an organism's niche.

Fundamental niche
: maximum possible niche.
Realized niche
: actual niche.
Removal of Balanus barnacles demonstrates the difference between the fundamental and realized niche of Chthamalus barnacle
Effects of Competition
Competitive Exclusion
Resource Partitioning
When two species have overlapping niches, one will outcompete the other.
Competitive exclusion of Asterionella by Synedra (2 diatom species) for silica in a laboratory culture.
Competition drives species with overlapping niches to adapt to non-overlapping resource pools.
Resource partitioning among Anole lizards in the Carribean tropics.
Character Displacement
Competing populations are more divergent in adaptive characteristics than non-competing populations of the same species.
Character Displacement of beak depth in 2 species of Galapagos Finch
Effects of Predation
Camouflage or other coloration that confuses predators
Warning coloration, advertising a threat to predators
Two or more harmful species with common predators mimic each other.
A harmless species mimics a harmful species.
Effect of "pod hairiness" on herbivory in pea plants.
a +/+ interaction
a +/- interaction
a +/0 interaction
Sea urchin/crab
Wasp/blowfly larva
Brood parasitism
African buffalo/Egret
Nesting bird/tree
Everybody wins!
The most common symbiosis
Is commensalism a myth?
Easily the grossest thing I show you all year
Lichens are classic facilitators.
Juncus is a facilitator in North American salt marsh ecosystems
Beavers are "
ecosystem engineers
", who create entire novel communities through their actions in an ecosystem.
The variety of different organisms that comprise the community.

Correlates to the stability of the community (more diverse = more tolerant of disturbances).

Can be understood in terms of:
Species richness
: the number of different species.
Relative abundance
: the proportion of each species to the total in the community
Two hypothetical communities. Which one is more diverse, and why?
The relationship between soild pH and microbial diversity in North American communities.

Diversity is frequently measured in terms of
Shannon Diversity
H' = Shannon Diversity
s = species richness
p = relative abundance of each species (i)
The feeding relationships present in a community. What eats what?
Food Chain
Food Web
One sequential series of trophic relationships in a community.
Many, interconnected trophic relationships in a community.
Keystone Species
Species that have a large effect on the structure of the community.
Evidence supporting the hypothesis that the Pisaster seastar is a keystone species.
Evidence supporting the hypothesis that sea otters are a keystone species.
Trophic Limits
Why are food chains limited in length?
Energetic Hypothesis
Only enough energy to support a certain number of links.
Dynamic Stability Hypothesis
The longer a food chain, the less stable it is.
As energy input decreases, trophic links decrease.
How are food chains controlled?
"Bottom-Up" Model
Factors that control producers have ultimate influence on higher trophic levels
"Top-Down" Model
Actions of predators control lower trophic levels.
The restoration of a community in Finland was accomplished through mostly top-down controls (adding a fourth trophic layer, and removing members of the third layer)
Any event that alters community structure by removing organisms or changing resource availability.
The "
Intermediate Disturbance Hypothesis
Diversity will be highest in ecosystems that experience intermediate levels of disturbance
Invertebrate taxonomic diversity is highest in Australain wetland ecosystems that experience intermediate amounts of flooding.
Human activities increase disturbance in most communities.

Community in Gulf of Mexico before fishing (top)

Post-fishing community (bottom)
The sequential changes that occur in a community following a disturbance.
Succession on previously uninhabited land
Primary succession in Glacier Bay, Alaska
Secondary succession following fire.
Succession on previously inhabited land
Pioneer Organisms Climax Community
Island Effects
Area Effects
The larger the ecosystem, the more species tend to be present.

The greater the rate of evaporation and transpiration, the more species tend to be present.

An "island" is any isolated ecosystem
(including actual islands).

Several factors contribute to the number of species in an island ecosystem.
Data demonstrating the relationship between island size and plant species diversity in the Galapagos Islands.
Immigration/Extinction rate, Island Size, and the distance of the "island" from the "mainland" all factor in determining the equilibrium number of species found in an island ecosystem.
An aphid extruding sap
Though really, we have nothing on nature...
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