1. Community Ecology
APES Chapter 8

2. 8-1 Community Structure and Species Diversity
Ecologist use 3 characteristics to describe a biological community.
Physical appearance- sizes, stratification, and distribution of its population and species
Edge Effect
Species diversity- a combination of numbers of different species (richness) and abundance of individuals with each species (species evenness)
High richness usually means low evenness (few #’s per species)
Factors affecting diversity are latitude in terrestrial communities and pollution in aquatic communities.
Niche structure- the number of ecological niches, similarities/differences, and interaction of species with each other.

3. Species Equilibrium model (Theory of island biogeography)
The number of different species on an island (species richness) is determined by how fast a species arrives, how fast old species become extinct, island size and distance from mainland.
Important:
Balance between rate of immigration of species and rate of extinction of existing species.
Size of island (smaller has less diversity) and distance from mainland (closer to mainland, increases species richness)

4. General Types of species
Native: species that normally live and thrive in a particular ecosystem
Non-native species: species that migrate into an ecosystem or are deliberately or accidentally introduced into an ecosystem by humans.
Also known as: Exotic/ Alien
Problems caused by Non-native species:
the non-natives have no natural enemies so they can thrive in the new ecosystem and crowd out the native species: Examples: Melaleuca plants, Burmese pythons, iguanas

5. Indicator Species:
species that serve as early warnings that a community or ecosystem is being damaged or changed:
Birds are good indicators because:
Trout and macro-invertebrates are good indicators of:
Amphibians indicate:

6. Keystone species:
species that play a pivotal role in the structure, function, and integrity of an ecosystem because
Their strong interactions with other species affect the health and survival of these species
They process material out of proportion to their numbers and biomass
Keystone species:
Pollinate
Scatter seeds
Modify habitats
Predation to control prey populations
Help plants get nutrients
Recycle animal waste
Examples:

8. Foundation Species- shape communities by creating and enhancing habitat for other species
Elephant tearing down tree

9. 5 Types of Species Interactions

10. Competition: Two or more animals competing for the same resources.
Two Types:
Intraspecific: competition between members of the same species (mates)
Interspecific: competition between members of two different species (food, space, sunlight)
The more a species niche overlaps, then the more competition. This can lead to one species migrating, adapting new behaviors or dying out. Over a long time scale, adaptations lead to RESOURCE PARTITIONING (warblers) or NICHE SPECIALIZATION (owls/hawks)

11. Warblers and resource partitioning

12. Species Interactions (continued)
Predation: members of one species feed directly on all or part of a living organism or other species. They do not live on or in the other species. One species is clearly harmed and the other clearly benefits.
Benefits:
Predation can be a good thing for the population of prey species as predators often weed out the sick and dying animals, thereby reducing competition amongst the prey species and controlling population growth. Also, enhances the passing of successful genetic traits to the next generations. (Sharks)

13. Predators have characteristics that help them catch prey, such as:
Running fast, ex.
Good eyesight, Ex.
Hunting in packs, ex.
Camouflage for ambush, ex.

14. Prey have characteristics that help them escape predators, such as:
Run fast
Good sense of smell and eyesight to alert them to the presence of predators
Protective shell
Spines
Camouflage
Chemical warfare like poisonous skin
Foul smells
Bad tasting
Warning coloration
Mimicking a predator
Examples:

15. Symbiosis: a long lasting relationship in which species live together in an intimate association.

16. Parasitism: when one species feeds on part of another organism (host) by living on or in the host. In this relationship the host is harmed and the parasite benefits.
Examples:

17. 4) Mutualism: symbiotic relationship in which both species involved benefit from the relationship. Ways in which this happens are pollination, providing food, and providing shelter. Examples:

18. Commensalism: a symbiotic relationship in which one species benefits and the other species is neither helped nor harmed.
For example:

19. Review Species Interactions Quiz!

20. Ecological Succession: Communities in Transition
Ecological Succession: One characteristic of all ecosystems is that they change over time due to changes in environmental conditions.
There are 2 types of succession:
Primary and secondary

21. Primary Succession:
Succession that starts with an essentially lifeless area where there is no soil or bottom sediment in an area. Examples include new lava, an abandoned parking lot, land exposed from retreating glaciers, etc.
Succession happens in stages:
1) Pioneer species move in and make soil: Ex. Lichens and mosses
2) When enough soil is made and spread out, then plants that are small and close to the ground move in. These plants can live under harsh conditions and usually have short lives. They are called early successional species. Examples: small annuals
3) After hundreds of years ,there is enough soil for Mid-successional species. Examples: small herbs/shrubs
4) As the Mid-successional plants grow they create enough shelter for Late successional species such as: trees.

23. Secondary Succession:
Begins in an area where the natural community of organisms has been disturbed or destroyed, but the soil remains.
For example:
abandoned farms, burned or cut forests, and heavily polluted streams.
Secondary succession occurs in the same way as primary starting with pioneer species and ending with late successional species.
Climax community- stable, self-sustaining community at the ending stages of ecological succession.

25. Disturbances can Affect Succession
Some disturbances can be beneficial in the long run like fire, because they increase biodiversity, clear out excess brush, renew nutrients and encourage other species to grow.
Some catastrophic disturbances can convert the ecosystem back to a lower level of succession. It’s an ongoing struggle to always progress towards a climax community.

26. Ecological Stability and Sustainability
3 aspects that lead to stability of a living system
Inertia/persistence – ability of a living system to resist being disturbed or altered
Constancy- ability of a living system to keep its numbers within limits of available resources.
Resilience- ability of a living system to repair damage after an external disturbance that is not too drastic.
Complexity- Populations with more biodiversity are more stable. More biodiversity means greater primary productivity and more resilience.

27. Everything is Connected!
There is overwhelming evidence that human disturbances are disrupting important ecosystem services that support and sustain all life and economies. Taking action to prevent these disruptions even if they haven’t happened yet is the precautionary principle.
(“Better safe then sorry” approach)