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21 Cards in this Set
- Front
- Back
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What conditions facilitate competition?
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01: Resources must be limited
02: Densities of the the organisms must be high (high population) 03: Environment is stable |
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Why must densities be high for competition to ensue?
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- High density and low resources = INCREASED chance to INTERACT over low resources.
- Only see this when ABIOTIC conditions are the controlling factors in a STABLE environment - In an unstable environment, densities decrease |
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Flashy streams vs. Stable streams (What are the controlling factors?)
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FLASHY: unstable, up and down.
- changes in discharge = controlling factor STABLE: homogenous flows - biological interactions = controlling factors |
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What are the four types of competition?
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01: INTRAspecific (within)
--> A vs. A 02: INTERspecific (between) --> A vs. B 03: Interference (Direct) --> A or B <--> A or B -- Direct PHYSICAL interaction with organism 04: Exploitative A or B <--> Resource <--> A or B - Interaction mediated through RESOURCE |
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What is the Competitive Exclusion Principle?
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- No 2 species can occupy the same niche simultaneously or one will be driven to extinction.
- Complete competition cannot co exist: one will go extinct. - Other factors tamper it. |
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What is the Ghost of Competition Past?
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- Past competition has led to niche diversification in the present
- Obtain direct results from the past |
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Ghost of Competition Past: Niche Overlaps
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- When a niche overlap is present, expect a shift overtime so that the overlap decreases.
---> Leads to more species diversification because opens up niche space (expands the niche) - If there is NO MOVEMENT (niche does not get any larger): species may be genetically or physiologically FIXED - species is specialized by morphology, physical characteristics, or behaviour ---> ex. seeds as bird food; all birds are competing for the same seed size |
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What is the problem with the theory of Ghost of Competition Past?
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- Presents a circular argument:
--- hard to measure --- presents multiple conclusions by same evidence |
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How do you measure resource partitioning?
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01: Large scale habitat use
----> If boundaries are tight, strong competition 02: Temporal (seasonality) ----> Different species engage in different behaviours at different times of the year 03: Microhabitat ----> Small scale measurement ----> If A is here but B is not, does this imply competition? 04: Food resources ---> Overlap or share? |
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Example of measuring resource partitioning:
(Winemiller: lack of diet overlap [D.O] in tropical fishes) |
01: When FOOD is ABUNDANT:
----> Competition DECR, D.O INCR -- Plenty of food, can share resources, thus no specialization. 02: When FOOD is SCARCE: ----> Competition INCR, D.O DECR -- When resources are limited, species specialization kicks in to reduce competition -- Suggests competition is currently operating -- Dietary overlap is based on a resource gradient |
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Distributional Comparisons: allopatry vs. sympatry (define)
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SYMpatric: living together
ALLOpatric: living alone |
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Is a niche wider where competitors are absent (competitor release)?
Expt: Hynes -- Great Britain vs. Isle of Mann |
- Testing if a breadth of a niche gets wider where competitor is not present.
- In Great Britain found Sp. A at headwaters and B at mouth - Isle of Mann, found A throughout, no B ---> Suggests competituve release for A when B is not present = niche shift |
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Problem in Hynes Great Britain vs. Isle of Mann experiment?
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01: Density relationships: neg. correlation suggests competition, but correlation does not insinuate causation.
- Spurious correlations, suggested and not tested - Could be seasonal succession: temp differences, seasonal cues, food abundance, etc. 02: Spacial Scale - Complete for small scale but not large. |
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ex. of Problem with Hynes experiment (spatial scale)
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- Hydropsycid caddisflies and blackflies
- Caddisflies are scrapers, build nests - Both are filter feeders, found in riffles and fast flowing water - Blackflies are quick dispersers, and form big colonies on rocks - In a large spatial scale: no competition - On a small spatial scale, there is competition for space - These species interact on a scale of cm, not m |
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Experimental Tests Measuring Resource Partitioning: Interference Competition (Direct) within the Riffle Bug (intraspecific)
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- Expt tests usually performed in stable streams
- Observations: 01: Female adult riffle bugs are always at the best locations (top) -- High flow, high food 02: Male adults intermediate (middle) -- Intermed flow and food 03: Juveniles at the worst (tail) --Low flow, low food - How to maintain distribution?? ---> Pull females out: find that males replace and the juveniles move to the middlle - Distribution maintained by competition/agression - Ex. of predatory release in a niche shift Conclusion Size of bugs determine feeding sites (females largest) |
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Interference Competition (direct interaction)
ex. Brown trout and brook trout (interspecific) |
- Brown trout place themselves at the interface of fast flow and food exposure
- Hide behind rock, no E expenditure - River = conveyer belt of food - Brook trout are lower in the river with no shelter from force of water - Brook trout have higher E cost but also high amount of food vs. behind the rock where the brown trout have high food return for little E spent Expt: REMOVE BROWN TROUT Find: Brook trout change resting sites to vacated sites were brown were Conclusion: Demonstrates competitive release --> area to rest is the limited resource --> driven by physical, direct competition: brown are bigger and stronger, they fight |
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Exploitative Competition: Why are there so many species and how is diversity maintained?
(ex. Tropical Habitats) |
- Ghost of Competition Past: (evolutionary time scale)
- Diversity is maintained through speciation - Predictions: diversity is positively correlated to environmental stability - Ex. Tropical Habitats -- less seasonality --> more stability --- More heat delivered at constant rate --- No glaciation --- Fish tendency tends to increase towards the equator but no trend for insects. WHY? ----> Insects can fly ----> Glaciation can dessimate fish because fish cannot recolonize ----> Insects can colonize more easily an have rapid division rate ----> Thus insects are more flexibile and homogenize versatility |
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Consequences of Competition: Ongoing Competition (ecological time scale)
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- Competitive Exclusion: diversity is reduced by strong competition
- Comp INCR, Diversity DECR |
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What maintains diversity with current competition?
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01: Disturbance
- Remove organisms and frees space for inferior competitors - Removes superior competitor, which must specialize. - Tradeoff between competitive ability (in order to exist in high density with limited resources) and colonization ability (and reproduce quickly with fast growth rates) - Abiotic conditions (winter) can also reset species composition in terms of discharge -- ex. Temperate waters in spring to winter, goes from relatively stable to relatively unstable in terms of discharge --->Harsh waters (fall), results in nutrient depletion, dried out by winter --->Decrease D, increase C |
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Ex. of Disturbance: How does it maintain species diversity?
Sedentary Invertebrates (Interspecific Competition): Hydropsyche (net spinning caddisfly) & Simulum (blackfly) |
Observation: Successional replacement over the summer
- Winter, water is low, conditions too harsh - After, Simulum comes in first rapidly but tails off --> hardly any in lat summer - Hydropsyche comes slow, peaks late spring -----> WHY? -- Could be simulum is a faster colonizer, then tails off because of the algae on rocks (substrate competition) or some other type of competition |
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Does competition drive successional replacement?
(Expt: Hydropsyche and Simulum) |
Hypotheses:
01: Seasonality: abiotic factors change 02: Competition for space Treatments: 01: Remove hydropsyche -- Hydropsyche DECR, Simulum INCR --> Not abiotic conditions, must be biological 02: Remove Simulum -- Hydropsyche: NO change, Simulum DECR ---> No blackfly effect on caddisfly 03: Remove BOTH -- Hydropsyche DECR, Simulum INCR ---> Asymmetrical, competition unshared 04: Control -- No changes Results: hydropsyche out-competes Simulum for space -- Hypothesis 2 is confirmed...WHY? ---> If you remove hydropsyche, simulum stays all season long ---> Simulum has NO effect on hydropsyche, thus it is inferior in competitive interactions ---> Hydropsyche wants to get rid of simulum for location for feeding sources/ space for more food intake ---> Pops them off the rocks, simulum then lifts off and drifts Conclusion: Hydropysche oucompetes Simulum for space but the outcome is moderated by disturbance. -- If moderately disturbed: even distribution -- Tradeoffs in competitive vs. dispersal ability: moderate disturbance leads to coexistence and high species diversity -- Increase level of disturbance: get more spread, thus more S exclusively and eliminate H completely |
