Ecology Lecture | Competition

Importance of Competition

1. Major driving force for evolution via natural selection

What are the modes of competition

1. Intraspecific vs Interspecific

2. Interference vs Exploitation (difference is intensity and result)

What is Intraspecific competition

Intraspecific : competition with members of own species

What is Interspecific competition

1. Interspecific : competition between individuals of two species 

What is Interference in competition

1. Intense

2. Winning group competes for the resources with the other group

3. Most often seen in a population's absolute resource 

   1. Absolute resource : resources that you can be the only one to have e.g. plants 

What is Exploitation in competition

1. Less intense 

2. If the result is not super intense but the outcompeted group is competed out of resources

How does Intraspecific Competition Among Herbaceous Plants work

1. Plant growth rates and weights have been found to increase in low density populations → inverse is true 

   1. Competition for resources is more intense at higher population density

   2. Usually leads to mortality among competition plants

      1. Self-thinning

What is Yoda’s law

1. (Yoda’s Law) → predicts that plants will decrease in population density (self-thin) as the total biomass of the population increases 

How does Intraspecific Competition among planthoppers work

1. Denno and Roderick attributed prevalence of competition among Homoptera to their habit of aggregating (clustering), rapid growth, and the mobile nature of their food supply → strong intraspecific competition 

   1. Demonstrated intraspecific competition within populations of planthopper Prokelesisia marginata 

      1. Probably result of limited resources 

What are the Feeding Niches of Galapagos Finches

1. Grant found differences in beak size among ground finches translates directly into diet 

2. Size of seeds eaten can be estimated by measuring beak depths 

3. Individuals with deepest beaks fed on largest and hardest seeds 

4. After the 1977 drought, the remaining seeds were very hard. Thus mortality was most heavy in birds with smaller beaks 

   1. Larger beaks prevailed 

What is the Competitive Exclusion Principle

1. Two species with identical niches can not co-exist indefinitely (no 2 species can co-exist in the same niche indefinitely) 

   1. One will be a better competitor and thus have higher fitness and eventually exclude the other 

What are lab models

1. Abstractions and simplifications (note models aren't meant to be copy of something) , not facsimiles of nature 

2. Man-made construct; partly empirical and partly deductive 

3. Used to provide insights into natural phenomena

What does Lotka Volterra explain and predict

1. Effect of Interspecific Competition on population growth of each species 

2. Predicts coexistence of two species when, for both species, interspecific competition is weaker than intraspecific competition 

3. Predict population growth would stop when

   1. N₁ = K_1-a12 N₂ 

   2. N₂ = K_2-a21 N₁

What was found in Pharmacia (single cell protist) Lab experiments

1. Gause demonstrated resource limitation with Paramecium caudatum and Paramecium aurelia in presence of two different concentrations of Bacillus Pyocyaneous (common food)

   1. When grown alone, carrying capacity was determined by intraspecific competition 

   2. When grown together, P. caudatum quickly declined

   3. Reduced resource supplies increased competition

      1. Interspecific more intense than intraspecific 

What was found in Flour Beetle Experiments

1. Triboilium beetles infest stored grain products 

   1. Park studied interspecific competition between T confusum and T castaneum under varied environmental conditions

   2. Growing the two species together suggested interspecific competition restricts the realized niches of both species to fewe

What does competition do to niches

1. Competition can restrict species to their realized niches 

2. But if competition interactions are strong and pervasive enough, they may produce and evolutionary response (to the outcompeted) in the competitor population

   1. Changes fundamental niche 

What was observed in Niche Overlap and Competition between Barnacles 

1. Connell discovered interspecific competition in barnacles, Balanus plays a role in determining lower limit of Chthamalus within intertidal zone 

   1. Did not account for all observed patterns

What occured in Competition and niches of small rodents 

1. Brown studied competition among rodents in Chihuahuan Desert

2. Predicted if competition among rodents is mainly for food, then small granivorous rodent populations would increase in response to the removal of larger granivorous rodents 

3. Insectivorous rodents would show little or no response

4. Result supported hypothesis 

What is character displacement

1. Overtime competing species can diverge from one another and displace peacefully 

2. Because degree of competition is assumed to depend upon degree of niche overlap, interspecific competition has been predicted to lead to direction selection for reduced niche overlap 

Factors regarding sympatric and allopatric populations

1. Morphological differences between sympatric species are statistically greater than differences between allopatric populations

2. Difference between sympatric and allopatric populations have genetic basis → bc this is the only way directional selection occurs 

3. Differences between sympatric and allopatric populations evolved in place, and are not derived from different founder groups already differing in character

What must Variation in character show

1. Must be demonstrated competition for the resources and competition must be directly correlated with character similarity 

2. Must be demonstrated competition for the resource and competition must be directly correlated with character similarity

Can the difference in character be explained by resources in the population?

No | Difference in character cannot be explained by difference in resources available to each of the populations