I. Community structure refers to the physical appearance, species diversity and abundance, and ecological relationships in an ecosystem (p.
144)
A. biodiversity varies across different ecosystems
1. types of biodiversity: ecological, species, genetic,
functional (Miller p. 62)
2. in general, diversity increases as you move toward the
equator
3. diversity also varies with depth in water
4. pollution has a significant effect on diversity in aquatic systems (such as streams
and the Chesapeake)
B. island biodiversity varies with island size and distance to the mainland
1. number of species on an island depends on rates of immigration and extinction
2. larger islands have more species
3. nearer island have more species
4. research supports these theoretical projections
C. types of species – ecological roles
1. species can be described by their mode of obtaining energy
(predator, decomposer, etc) – see chap 3
2. non-native species cause problems (more on this later)
3. indicator species are particularly sensitive to environmental problems (amphibians are a good example; also certain stream insects)
4. umbrella species:
A recent article in National Parks calls the Greater Prairie
Chicken an umbrella species , because each type of habitat
required by this bird also serves as important habitat for many
other species, including deer and other prairie birds
5. are all species vitally important? Compare the rivet and redundancy models
6. keystone species have a disproportionate effect on the rest of the ecosystem
a. top predators such as wolves,
cougars, or grizzly bears
b. ecosystem engineers such as elephants, beavers, buffalo, prairie dogs, and even ants
c. providers of important services, such as pollinators
| more here -
match pollinators with their flowers |
Another pollinators page
D. competition
1. intraspecific competition (within the same species) leads to natural selection, but does not affect community structure
2. interspecific competition refers to competition between different species for resources such as food and habitat
3. interference competition – individuals chase each other away or otherwise physically exclude them
4. exploitation competition – individual vary in how efficiently they use a resource
5. the competitive exclusion principle states that two
species cannot occupy the same niche (classic experiment with
mussels - described in class)
6. species reduce competition through resource partitioning - fig.
7-6 and 7-7 and also 4-7: they use different parts of the same habitat or forage at different times
E. predator-prey relationships – fig. 7-8
F. non-predatory ecological relationships
1. interactions between species can be positive, negative, or neutral
2. parasitism is a relationship in which one species benefits and the other is harmed
3. mutualism is a relationship in which both species benefit (fig.
7-9)
a. symbiosis – organisms living on or in each other
i. lichens
ii. myccorhizal fungi
iii. termites
b. non-symbiotic
i. herbivores and grasses
ii. dispersal of fruits by birds and small mammals
iii. pollination
iv. cleaner fish
v.
animals that are normally enemies will sometimes form
mutual relationships
4. commensalism - one organism benefits and the other is not harmed.
(fig 7-10)
a. ephiphytes (distinguish from parasitic plants)
b. barnacles
c. remora and shark
II. Ecological succession
A. Primary succession
1. Occurs in an area previously unoccupied by organisms
2. Examples – volcanic islands, places exposed by retreating glaciers, etc.
3. example of typical progression shown for Isle Royale
in fig. 7-11
B. Secondary Succession
1. Occurs in areas that have been disturbed by some natural phenomenon
2. examples of disturbances: fire, storms, floods,
agriculture
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C. Examples:
1. field to forest (fig. 7-12)
2. pond to bog to meadow
3. fire-disturbed areas
4. sand dunes
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D. Climax communities
1. type of climax community is determined by local climate, soil, rainfall, etc.
2. Succession is not necessarily a predictable event, and
some ecologists prefer the term “mature” to “climax” – see
discussion p. 157-158