Interspecific Competition II
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Transcript of Interspecific Competition II
Interspecific Competition II
Getting back to plants…
Although competition clearly appliesto plants, most of the theory iszoologically based
The Problem with Plants…
All plants have essentially same requirements:
LightWaterNutrients
These are not typically discrete packages
Shortage of one may affect ability tocompete for other needed resources
The Problem with Plants…
Cause and effect are very difficult to establish without experimentation
Coexistence explanations:
•Frequently focus on demonstratingthat spp are different in somecharacteristics
Not conclusive in terms of mechanisms~
SIX MECHANISMS OF COEXISTENCEIN PLANTS
1. Resource Partitioning
•Niche separation
•Intraspecific competition > Interspecific competition
2. Spatial Segregation
Example: Solidago
(Begon et al. 1996 p. 102)
Soil moisture andinterspecific comp.appear to determineeach realized niche
Six Mechanisms of Coexistence in Plants
3. Recruitment Limitation
•The dispersal/competitive abilitytrade-off
4. Pest Pressure
These four mechanisms all assume thatcoexistence is an equilibrium condition
Six Mechanisms of Coexistence in Plants
5. The Storage Effect
6. Density-Independent Mortality
•Overlapping generations
•Asynchronous recruitment
These two mechanisms are based onnonequilibrium as the condition
Mechanisms of Coexistence
Very difficult to demonstrate
Too much emphasis on adult plants?Maybe preemptive competition forregeneration niche the key?
Need to consider indirect abiotic effects?
Tilman et al. (1982) experimentalwork with planktonic algae
Two algae and abiotic Influences on competition
Asterionella formosa requires less SiO2
at lower temperatures
Synedra ulna requires less SiO2 at higher temperatures
Coexistence: temperature fluctuations, alternating competitive displacement
(Tilman et al. 1982)
Theory and Real Result
(Begon et al. 1996 p. 104)
Experimental Work Vital To Elucidate mechanisms of
coexistence
Particularly due to history of agriculturalresearch, standard experimentaldesigns developed
These include additive and substitutivedesigns
Experimental designs for plants
Simple Additive
Substitutive orReplacement Series
Full Additive
Some Experimental Results: Replacement series design
2 Species, 4densities
(Begon et al. 1996 p. 86)
Competitionuneven
A. fatua lessaffected thanA. barbata
Two Botanical Measures of Competition
Relative Yield Total (RYT):
Yield of X in mixtureYield of X in monoculture
Relative Resource Total (RRT):
Measure of performance in mixture
Both try to measure the extent to which 2 spp utilize different resources
Theoretical explorations of competitive exclusion and
coexistence
The logistic model of two-speciescompetition….
Outcomes of the model
(Begon et al. 1996 p. 108)
Competitiveexclusion
Unstable coexistence
Stablecoexistence