1. Agenda 9/7 Niche Partitioning Activity Community Ecology Lecture
Turn in: Video notes, population math
Homework
1. Chp 53 reading and notes (due 9/12)
2. ‘Ecological Succession’ Video and Notes
3. Classifying Symbiotic Relationships (doc on website, answer on separate sheet)

2. Community Ecology

3. Community Ecology
Populations are linked by interspecific interactions that impact the survival and reproduction of the species involved
Example of a positive interaction?
Example of a negative interaction?

4. Factors that Impact Communities
1. Disease
2. Interspecific interactions (competition, predation, mutualism, commensalism, parasitism)

5. Community Structure
Dominant Species- most abundant, highest biomass, powerful control over occurrence and distribution of other species
Ex: VA sugar maple tree
Keystone Species- NOT always most abundant, but exert a strong control due to the ecological niches they occupy
EX: Sea otters
Species Richness- number and abundance of species
What could cause one species to become dominant over another?

6. Biodiversity Communities with higher diversity are
More productive and more stable regarding their productivity
Better able to withstand and recover from environmental stresses
More resistant to invasive species, organisms that become established outside their native range
Identify human actions that affect ecosystems and predict and explain the consequences
LO 4.21 The student is able to predict consequences of human actions on both local and global ecosystems.
Ask students to first identify some “human actions” that affect ecosystems. Possible answers will most likely include pollution of all sorts or destruction of habitat such as deforestation or damage to coral reefs. Once students identify a “human action”, have them predict and explain the consequences of the human action.

7. Species Diversity
Species Richness (# of different species) Species Diversity = + Relative abundance
Ecologists often use different types of Indices to quantify species diversity. A diversity index mathematically measures the diversity of community. There are different indices such as: Shannon Diversity, Simpson Diversity Index, etc.
Species diversity of a community is the variety of organisms that make up the community
It has two components: species richness and relative abundance
Species richness is the number of different species in the community
Relative abundance is the proportion each species represents of all individuals in the community
(proportion each different species represents of all the individuals in the community)

8. Which community is richer?
Species Richness A
Which community is richer?
Community B clearly has an abundance of different organisms as well as more organisms than community A. B

9. Sample Data
The data below represents the abundance of macro-invertebrates taken from three different river communities in Georgia. A variety of diversity indices may be used to calculate species diversity. Based on the data below, which community has the greatest diversity? Explain!
LO 4.21 The student is able to predict consequences of human actions on both local and global ecosystems.
Species diversity is related to both species richness and relative abundance. Species richness is the number of different species in the community and relative abundance is the proportion each species represents of all individuals in the community.
Answer: Community A has more species than either communities B or C. Community B is more abundant in leeches, but has no water penny. Community C only has two species, thus is low with regard to species richness.

10. Observation Of Sea Otter Populations And Their Predation
Food chain before killer whale involve- ment in chain
(a) Sea otter abundance
(b) Sea urchin biomass
(c) Total kelp density
Number per 0.25 m2
1972
1985
1989
1993
1997 2 4 6 8 10
100
200
300
400
Grams per 0.25 m2
Otter number (% max. count) 40 20 60 80
Year
Food chain after killer whales started preying on otters
Observation Of Sea Otter Populations And Their Predation
The graphs presented illustrate the effect sea otters have on an ocean community when orcas are absent vs. present. Have students examine the graph and discuss the impact on the community when the number of sea otters is reduced.
Their discussion should identify the following points (the “what”), but make them explain “why the what” happens within the food chain:
No orcas present, otters are more plentiful, but urchins are not, thus vegetation is more plentiful.
Orcas present, otters are less plentiful, urchins are more plentiful, thus vegetation is less plentiful.

11. Interestingly, The Sea Otter Is Not Usually The Orca’s Food of Choice
Why the change?
Some fish populations have declined in recent decades
Shortage of certain fish caused substantial declines in harbor seals and sea lions
Shortage of seals and sea lions resulted in killer whales preying on smaller sea otters

12. Why Should We Care About Declining Numbers of Sea Otters?
Sea otters are an important part of the coastal community
The loss of sea otters affects the community directly and indirectly
Sea otters (Enhydra lutris) have had a long history of federal protection dating back to 1911 when they were hunted to near extinction—the International Fur Seal Treaty was one of the earliest forms of legislation protecting marine mammals. Despite subsequent federal protection under the Marine Mammal Protection Act and the Endangered Species Act, southern and northern sea otters continue to be a threatened species. Most recently, the northern population (Enhydra lutris kenyoni) located in southwest Alaska was listed as threatened in Since the 1990's northern sea otters have undergone one of the worst population declines of carnivorous mammals in recorded history—and the Alaska SeaLife Center (ASLC) is trying to find out why.

13. Indirect Effect on the Community
A keystone species is one that has a strong effect on the composition of the community
Removal of keystone species causes a decrease in species richness
Sea otters eat sea urchins which are fierce competitors having a diet of kelp
Sea otters and the kelp forest ecosystem have a strong relationship with one another. The strength or robustness of one, often influences the productivity of the other. Often then, are sea otters considered a keystone species, an important species vital to the overall health of ecosystems. ASLC collaborators are currently investigating the benthic invertebrate communities to better understand the overall ecosystem health and how it relates to otter populations in the Aleutian and Commander Island chains.

14. Sea Urchin Population vs. Kelp Density examine and interpret the graph!
Ask students to examine and interpret the data shown.
When the otters are removed from the community, their main prey, the sea urchin is able to expand their population. Sea urchins are predators of Kelp. The graph above shows the impact on the community when otters are removed. The kelp population is essentially depleted since the sea urchins are unchecked in the community.

15. Ecological Niches
An organism’s niche is the specific role it plays in its environment…its job!
All of its uses of biotic and abiotic resources in its environment
Ex: oak tree in a deciduous forest
Provides oxygen to plants, animals
Provides a home for squirrels
Provides a nesting ground for blue jays
Removes water from the soil
Ecological niche is a term describing the way of life of a species. Each species is thought to have a separate, unique niche. The ecological niche describes how an organism or population responds to the distribution of resources and competitors (e.g., by growing when resources are abundant, and when predators, parasites and pathogens are scarce) and how it in turn alters those same factors (e.g., limiting access to resources by other organisms, acting as a food source for predators and a consumer of prey).

16. The Niche
Ecological niche is the total of an organism’s use of biotic and abiotic resources in its environment
Ex: Barnacle species on the coast of Scotland
Compare and contrast fundamental and realized niches?

17. Competitive Exclusion Principle
Sometimes referred to as Gause's law of competitive exclusion states that two species competing for the same resources cannot coexist if other ecological factors are constant.
The competing species that has even the slightest advantage will dominate in the long term and emerge the victor.
The loser will either relocate or become extinct.
The principle has been paraphrased as "complete competitors cannot coexist".
The competitive exclusion principle, sometimes referred to as Gause's law of competitive exclusion or just Gause's law, is a proposition which states that two species competing for the same resources cannot coexist if other ecological factors are constant. When one species has even the slightest advantage or edge over another, then the one with the advantage will dominate in the long term. One of the two competitors will always overcome the other, leading to either the extinction of this competitor or an evolutionary or behavioral shift towards a different ecological niche. The principle has been paraphrased into the maxim "complete competitors cannot coexist".

18. Competition Between Organisms Of Different Species- Examine and interpret the results
Ask students to examine the graphs and interpret the results.
As long as the two species of Paramecium exist in separate Petri dishes (cultures or niches), both thrive and achieve carrying capacity with the P. aurella being slightly more successful at using the resources as evidenced by its higher carrying capacity.
When the cultures are combined, competition for resources ensues and P. aurella outcompetes P. caudatum ultimately causing its extinction in the Petri dish!
Also note the consequences of the competition: 1) it takes longer to achieve the carrying capacity (Day 10 vs. Day 14) 2) the carrying capacity of the population is lower.

19. Solutions to Competitive Exclusion
Resource partitioning− Species living in the same placeconsume slightly different foods or use resources in different ways
Ask students to define sympatric. Sympatric: Occupying the same or overlapping geographic areas without interbreeding.
This process allows two species to partition certain resources so that one species does not out-compete the other as dictated by the competitive exclusion principle; thus, coexistence is obtained through the differentiation of their realized ecological niches. Niche partitioning may not occur if there is sufficient geographic and ecological space for organisms to expand into.
Ex: Anolis lizard sp. perching sites in the Dominican Republic

20. Solutions to Competitive Exclusion
Character displacement− sympatric species tend to diverge in the characteristics that overlap
Ask students to define allopatric. Allopatric: occurring in separate nonoverlapping geographical areas.
Ask students to examine and interpret the data. The beak depth changed quite a bit for both species once they became sympatric species. The beak depth for G. fuliginosa decreased while that of G. fortis increased. The change is greater for G. fortis.
Character displacement refers to the phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur but are minimized or lost where the species’ distributions do not overlap. This pattern results from evolutionary change driven by competition among species for a limited resource (e.g. food). The rationale for character displacement stems from the competitive exclusion principle, also called Gause's Law, which contends that to coexist in a stable environment two competing species must differ in their respective ecological niche; without differentiation, one species will eliminate or exclude the other through competition.
Ex: Darwin’s finch beak size on the Galapagos Islands

21. Succession
Ecological succession− transition in species composition over ecological time
Pioneer organisms = bacteria, lichen, algae
Climax community = stable
Primary− begun in lifeless area; no soil, perhaps volcanic activity or retreating glacier.
Secondary an existing community has been cleared by some disturbance that leaves the soil intact
The pictures are of Yellowstone Park – on the left after the fires of 1988 and on the right the exact same area after recovering through the process of secondary succession a year later.
Common Misconception- “fire is bad” (it is a natural phenomena in nature). As a matter of fact when this fire started in 1988, the rangers told visitors that it was their policy not to put out fires in the park. The fire expanded through Yellowstone more than they anticipated and by the end of the summer, they began working to put the fire out.
Suggestion: The Succession Game