Competition Flashcards
Intraspecific vs Interspecific
INTRA: competition with members of own species
INTER: competition between individuals of two species
Interference vs Exploitation competiton
Interference: direct interference; organisms of the same species compete directly with each other over resources [think moose battling for a female]
Exploitation: indirect interference; organisms usage of a limited resource reduces the availability of the total resource for the other organisms; both intraspecific and interspecific
Intraspecific competition among herbaceous plants
How does plant growth and plant density interact with one another?
Plant growth rates and weights have been found to increase in low density populations
–> Competition for resources is more intense at higher population densities
–> Think of cacti that start of clustered but eventually become uniform/regular in distribution
Self-thinning
Progressive decline of a plant density of a growing population;
increasing biomass = decreasing population density
Intraspecific competition among Planthoppers
How does population density and intraspecific competition interact with one another?
Homoptera attributed prevalence of competition to their habit of aggregating, rapid growth, and mobile nature of their food supply
Greater population density = lower survivorship [competition for resources], increased development time [, reduced body size
These signs of intraspecific competition were probably the result of reduced food
quality at high leafhopper densities, since plants heavily populated by planthoppers show reduced concentrations of protein
chlorophyll, and moisture.
Lotka Volterra [IMPORTANT]
Effect of interspecific competition on population growth of each species;
predicts COEXISTENCE of two species when interspecific competition is WEAKER than intraspecific
Competitive Exclusion Principle
No two species can occupy the same niche; eventually one specie with greater competitiveness and fitness will force the other out of the niche
Feeding niches of Galapagos Finches
How do environmental conditions e.g. drought affect different niche of bird Finch populations?
3 species of Galapagos with different beak sizes: fuliginosa < fortis < magnirostris [increasing beak size]
After a drought, seeds were in limited supply.
- Smaller softer seeds eaten first –> Larger harder seeds increased in abundance
- Thus, fuliginosa increased in mortality
- Bird population was dominated by Finches with largest beaks
Lotka Volterra formula
dN1/dt = (rm1)(N1) ((K1-N1-alpha1&2(N2)) / K1)
where dN1/dt = population growth of species 1
rm1 = maximum intrinsic growth rate of species 1
N1 = population size specie 1
K1 = carrying capacity of species 1
alpha1&2 = effect of individual of species 2 on rate of population growth of species 1
In Lotka Volterra’s model, which variables represent interspecific and intraspecific competition?
INTRASPECIFIC: [-N1]
INTERSPECIFIC: [-alpha1&2]
What does alpha12 < 1 mean?
If alpha12 < 1, then the competitive effect of an individual of species 2 is LESS THAN the competitive effect of an individual from species 1
INTRAspecific competition influence > INTERspecific
When is population growth predicted to stop in Lotka Votlerra’s model?
N1 = K1 - (alpha12)(N2)
N2 = K2 - (alpha21)(N1)
What does alpha12 mean?
The competitive effect of an individual of species 2 on an individual of species 1 relative to the competitive effects of an individual from species 1.
Paramecia lab experiments [Laboratory Models of Competiton]
How does food supply affect competition?
Would Paramecium caudatum and Paramecium aurelia drive the other to extinction if food supply was limited?
P. aurelia > P. caudatum carrying capacity at BOTH half strength and full strength growth medium [refers to food concentration]
Thus, when grown together, P. aurelia survived while P. caudatum declined.
Conclusion: Reduced resource supplies increases competition. Competitive Exclusion results from food limitation/competition.
Flour Beetle Experiments [Laboratory Models of Competition]
How does competition influence niches?
Interspecific competition between T. confusum and T. castaneum.
Growing the two species together suggested that interspecific competitions restricts the REALIZED NICHES of BOTH SPECIES to fewer environmental conditions
Priority Effect
Species that establishes itself first in greater numbers usually wins the competition
How does competition, realized, and fundamental niches influence one another?
Competition can restrict species to their realized niches.
BUT if competitive interactions are STRONG ENOUGH, they may induce an EVOLUTIONARY RESPONSE which CHANGES FUNDAMENTAL NICHE
Competition and niches of small rodents [Competition]
What happens to small granivorous rodent populations and insectivorous rodent populations when large granivorous rodents are removed?
If competition among rodents is mainly for food, then after large GRANIVOROUS rodents are removed:
1. Increase in SMALL granivorous rodent populations
2. No change in insectivorous rodent populations
Thus competition in this case study is mainly driven by food
Character displacement
Two species differ more from each other in geographical areas where they overlap versus where their distributions DO NOT overlap.
Species coexisting together ARE MORE DIFFERENT from each other than if each individual specie was isolated.
DIRECTIONAL SELECTION for reduced niche overlap.
Allopatric
Occurring in separate non-overlapping geographical areasS
Sympatric
Occurring in overlapping geographical areas
Character Displacement Characteristics
- Morphological differences between sympatric species > allopatric species
- Differences between sympatric and allopatric populations have genetic basis
- Differences between sympatric and allopatric populations due to evolutions in their unique environmental context rather than differing founder groups
