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Community Ecology 2


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Around the world, where are more species found in contrast to were least are found? (6)
1. low latitude vs. high
2. lg areas vs. small
3. shallow water vs. deep
4. low elevation vs. high
5. mainland vs. island (both of similiar area)
6. mainland vs. peninsula
What are the two issues concerning low latitude versus high latitude?
1. Evolutionary: why hv so many sps evolved in tropics?
2. Ecological: how can so many sps coexist in tropics?
What are the proposed explanations/hypotheses for the species richness patterns around the world?
1. Time Hypothesis
2. Habitat Diversity H.
3. Competition H.
4. Predation H. (top-down control)
5. Productivity H. (bottom-up control)
6. Stability-Time H.
7. Intermediate Disturbance H
8. Mid Domain Effect (MDE)
What are the key points of the Time Hypothesis?
Key points
1. Sps richness depends on time allowed for evolution
2. More time since distrubance in tropics (ie: glaciers in N & S, but not tropics)
What are some problems with the Time Hypothesis?
1. Tr hv been over 10,000yrs for sps to migrate N&S
2. Post disturbances hv occured in tropics: climate changes causing terrain to change from tropics to Savannah
3. Poor fossil record in tropics due to heat: makes it hard to evaluate ts hyp.
What is the explanation given by the Habitat Diversity Hypothesis for Sp. Richness pattern?
The more complex the environment, the more sps it has. (tropics, coral reef)

**an area tt's not tropical, tt has a comparable complexity still hs less sps, indicates other reasons for sp. richness pattern
What does the Competition Hypothesis propose?

Sps. richness depends on resources available
What does the Predation Hypothesis (top-down control) propose?
The predators on the top of food chain control those below them (and their prey)
Give an example of the top-down control hypothesis: use Sea Stars.
Sea star is keystone sps and top predator. Specializes on mussels. Wn s.s. is removed, muscles outcompete the other sps (algae, barnicles, ect)
What does the Stability-Time Hypothesiss propose?
Environments w/low physiological stress factors will have more species
Gradient of physiological stress:
------->high sp richness
*Coral reef & Deep sea have more stable conditions and thus more S than rocky intertidal and estuaryies
What does the Intermediate Disturbance Hypothesis propose?
A system with intermediate level of disturbances will have a higher sp. richness because the old species are "cleared" out and new ones are allowed to populate
What is another name for the Intermediate Disturbance Hypothesis?
Non-Equilibrium Hypothesis
Give an example of the Intermediate Disturbance Hypothesis: use Connell's experiment on the Great Barrier Reef
-Found many different types of corals that coexistent
-Competed by overshadowing, sending out tenticles to kill other coral, ect
-Found that after a hurrican, new sps colonized
-Yrs since last hurrican: peak at 50yrs, few S at 100yrs and 1-3 yrs: strong colonizers early, strong competitors late, mix of both at peak
What does the Mid-Domain Effect (MDE) Hypothesis assume?
1. Sps occurances are continuous w/in the domain (geographic space we're looking at)
2. Place ranges randomly w/in domain (ie: Sps occurance has no correlation to geography/environmental conditions
The Mid-Domain Effect (MDE) has been very controversial, why?
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It suggests that all other/previous hypotheses can be thrown out
In the long ass S. American study on species richness, what was the sp. richness of the birds correlated to?
Temperature, Precipitation, and not primary productivity
What percentage of species reflected correlations of species w/the largest geographic ranges?
What percentage of species reflected contemporary climate is uncorrelated w/species richness?
What is the importance of the S American results?
Results implicate importance of historical evolutionary forces in shaping species richness
What are the two general assumptions for Log-Series, Log-normal, Broken Stick, and Geometric models?
1. Assemblage is at equilibrium
2. Equilibrium pop size is proportional to resources used by a species
What are the two assumptions for the Geometric Series Model?
1. Species colonize sequentially & one at a time
2. Each species consumes a constant fraction of remaining resources
What does the Broken Stick model assume? What’s unique about this graph and what can it be thought of as? Draw model.
Assumes: Sps enter Simultaneously and use a random fraction of resources
*produces the most "even" of the distribution
*can be thought of as a null model for resource partitioning
Describe the log normal model
Hierarchal niche partitioning
Why is log normal called log normal?
many multiplicative factors interacting randomly give a normal distribution; it may not always be biological stuff behind it. Ex: how long before a glass is broken in a restraunt
What is the Neutral Model?
Assumes random speciciation, pop growth, & extinction. Anagalous to neutral theory of pop. genetics
Sara's lecture: Fire affects the species richness how?
Fire affects sp. richness differently depending on habitat type
Sara's lecture: Which did the ants prefer, tuna or honey?
The N in tuna, not the honey
Sara's lecture: Did competition structure co-occurance?
How are the ants activness related to one another? Why?
Active at different times of day, prolly due to regular spacing of temp.
Sara's lecture: What do individual species show?
Show idiosyncratic response to fire, habitate type and time

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