CH 14 Lo's- Competition

Competition

Define and differentiate between the following pairs of terms: interspecific vs. intraspecific competition

• Interspecific competition→ between members of different species

  • ex: lions and cheetahs

• Intraspecific competition→ between individuals of a single species

fundamental vs. realized niche

• Fundamental niche: the full set of resources and other biotic and abiotic requirements of a species

• Realized niche: the restricted set of resources a species is limited to due to species interactions 

direct vs. indirect competition

• Direct→ species directly interferes with the ability of its competitor to use a limiting resource 

  • ex: fighting, bird defending its nest during breeding season preventing other birds from nesting in same place 

• Indirect→ indivs decrease the supply of a resource as they use it, decreases the amount available for other individuals 

  • ex: tree takes up water from soil, leaving less water for other trees 

symmetrical vs asymmetrical competition

• symmetrical→ Competitors have same abilities, both harmed equally

  • ex: two equally sized oak trees competing for light or water

• Asymmetrical→ 1 species is harmed more than the other, fitness is still negative for both but 1 suffers more, and population growth rates still negative but 1 is more impacted.

  • ex: taller plants can outcompete shorter plants,

Differentiate between competitive exclusion and competitive coexistence and describe the importance of resource partitioning for coexistence.

• Competitive exclusion→ states that complete competitors cannot coexist 

  • complete competitors are 2 distinct species, live in same place, and have exactly same ecological needs

  • ex: Gause’s experiment with paramecium, when grown together leads to elimination of one

• Competitive coexistence→ multiple species can live in same habitat despite them competing for same limited resources

  • can occur through resource partioning where species use a limited resource in different ways. For example, feed at diff times or use diffs parts of resource, which reduces comp between them

Competitive exclusion→ Gause's paramecium experiment

• 2 paraecium species showed logistic growth when grown alone 

• when paired some species drove others to extinction some coexsited

• they both shared a feeding strategy→ same ecological needs→ competitive exlcusion

Discuss co-evolutionary outcomes that are seen in two populations competing for a common resource. Explain the process of character displacement.

• Coevolutionary outcomes

  • =competitive exclusion→ one species outcompetes the other which may go extinct or move to diff habitat

  • Character displacement→ both species evolve differences that reduce competition → results in resource portioning

• For example, Galapagos finches 2 species. They evolved different beak sizes over time that decreased the overlap of resource use. Allows them to both coexist.

Define the components of the Lotka-Volterra population growth equations. Link them to logistic growth. Explain/interpret competition coefficient

• N1,N2→ pop sizes of species 1 and 2

• r1,r2→ intrinsic growth rates 

• K1,K2→ carrying capacity 

Competition coefficients 

• a 1,2→ per capita negative impacts of species 2 on species 1

  • if a=0.5 one individual of species 2 uses half as many resources as a single individual of species 1 

  • a=1 they compete equally 

• B 1,2→ per capita negative impacts of species 1 on species 2 

Linking to logistic growth 

• Lotka volterra is just logistic growth plus competition from another species 

Given competition coefficients and K values for two populations, sketch zero net growth isoclines, and interpret them to determine what the predicted outcome of competition would be under different starting population size

4 outcomes

K1 and K1/a always go together, and K2 and K2/B go together

Outcome 1

• Competitive exclusion of species 2 by species 1 → species 1 wins because it’s on top

• On x axis K2/B<K1 on y axis K2<K1/a

• Middle vector has —> then one up  (or just remeber that N1 growing to K1) 

Outcome 2 

• competitive exclusion of species 1 by species 2→ species 2 wins because now its on top 

• switch x and y axis, so on x axis K1<K2/B on y axis K1/a < K2

Outcome 3: coexistence 

• Species 1 and 2 coexsting 

  • No matter where you are driven to coexistence 

  • all vector arrows point to E (the intersection/stable equilibirum) 

  • x axis: k1< k2/B, y axis: k2<k1/a 

Outcome 4: instability 

• the 2 species cannot coexist, either ½ wins depending on starting pop sizes of both species 

• in quadrant 1, species 2 goes to K2 

• In quadrant 2 species 1 goes to K1 

• In middle intersection both species stable, but overall unstable bc if deviates then species 1 or 2 wins in Q1/Q2

Interpret examples showing how context, such as varying environmental conditions, can change the outcome of competition

• environmental changes can shift which species has the advantage

• The winner in 1 setting might lose in another

• ex: 2 species compete for water in wet years plant x grows faster and outcompetes Y, in dry years plant Y survives better. 

Describe K, a/B in reference to the type of competition. If they are high/low

• K→ (carrying capacity)

  • measure of intraspecific competition

  • K big→ intraspecific competition low

  • K small→ intraspecific competition high

• a/B→ if these are big then interspecific effect high