Competition (DONE)

Question 1

Define coevolution

Answer 1

The reciprocal evolutionary changes that occur between interacting species - driven by their mutual effects on one another’s evolution

Question 2

What are the two levels of coevolution?

Answer 2

1. Diffuse coevolution:
2. Specific coevolution:

Question 3

How does competition relate to coevolution?

Answer 3

In coevolution, species evolve in response to competition for resources. This can drive evolutionary changes in resource use and adaptations that reduce competition, like character displacement.

Question 4

What is competitive exclusion?

Answer 4

Competitive exclusion occurs when a superior competitor drives an inferior competitor out of a habitat or ecological niche, due to stronger competitive abilities.

Question 5

What is character displacement?

Answer 5

Character displacement refers to evolutionary changes in species’ traits that reduce competition. This usually results from exploitation competition, where species evolve to use resources in slightly different ways to minimize overlap.

Question 6

What is exploitative competition?

Answer 6

Exploitative competition occurs when species compete indirectly for shared resources (e.g., food, space), as opposed to interference competition, which involves direct aggression or interference between species.

Question 7

How can competition lead to evolutionary changes?

Answer 7

Competition can lead to character displacement, where species evolve differently in traits like resource use, reducing overlap and the intensity of competition, thereby allowing species to coexist in the same habitat.

Question 8

What is the basic model of character displacement + example?

Answer 8

Character displacement occurs when species evolve traits that help them use different resources, reducing competition and allowing them to coexist.

For example, species of finches with different beak sizes specialize in different seed sizes to reduce overlap in resource use.

Question 9

How do organisms evolve traits to match the resource gradient?

Answer 9

Organisms evolve traits, like beak size in finches, that allow them to access the most available resources. This leads to a population distribution of traits, matching the resource gradient, creating an optimal trait size for resource use.

Question 10

Define diffuse coevolution:

Answer 10

Interactions among multiple species in a community

e.g. shared predators or pollinators (bee and moth pollinating same plant for example)

Question 11

Define specific coevolution:

Answer 11

Focussed interaction between 2 species

e.g. predator-prey, host-parasite, mutualistic relationships

Question 12

What are the 3 graphs in the basic model of character displacement?

Answer 12

1 - Resource gradient

2 - Trait utilisation curve

3 - Carrying capacity curve (K curve)

Question 13

How does the “resource gradient” relate to character displacement?

(The resource gradient curve)

Answer 13

Available resources are distributed along a gradient –> e.g. variation in seed size, prey size

The model assumes normal distribution

Question 14

What is the “utilization function” in the context of character displacement?

(AKA the trait utilisation curve)

Answer 14

Organisms possess traits that enable them to exploit resources

These traits depend of how efficiently the organism can exploit the resource (utilisation function)

Question 15

What does the carrying capacity curve (K curve) represent in relation to character displacement?

Answer 15

It reflects the population density of individuals possessing specific traits that are optimised for resource exploitation

This curve is often associated w polymorphic traits (this means a no. diff genes affect a singular trait)

Question 16

What is the K curve shaped by?

(Carrying capacity curve)

Answer 16

K curves are shaped by selection over generations

Question 17

What are the assumptions of character displacement?

Answer 17

• There is a 1:1 relationship between trait size & resource use
• A positive response to resources between generations

Question 18

What does the 1:1 relationship assumption of character displacement mean?

Answer 18

It assumes a direct, proportional relationship between an organism’s trait size and its resource use

e.g., larger beaks correlate with consuming larger seeds (Galapagos finches)

Question 19

What does the positive response to resources (between generations) assumption of character displacement mean?

Answer 19

It assumes that traits evolve to optimize resource use –> successive generations will adapt to exploit the most available or accessible resources for maximum fitness.

Question 20

What are the 3 evolutionary outcomes of competition?

Answer 20

1 = Divergence

2= Convergence

3 = Phenotypic plasticity

Question 21

Explain Divergence:

(An evolutionary outcome of competition)

Answer 21

When 2 species compete for a SHARED RESOURCE, their traits may diverge to minimise overlap in resource use

e.g. 2 bird species w overlapping beak sizes may evolve distinct beak sizes in sympatry

Question 22

What is trait divergence a classic example of?

Answer 22

Character displacement!

Question 23

Explain the mechnaism of trait divergence:

Answer 23

Individuals at the extremes of overlapping rage will have a higher fitness –> (this is bc there is a high density of organisms at the overlap, doubling the density of exploiters here)

This leads to selection for divergence

Question 24

Explain convergence:

(An evolutionary outcome of competition)

Answer 24

Occurs when resources are irreplaceable or critical –> leading to traits converging for efficient exploitation

Less common than divergence (in fact quite rare)

Question 25

Explain phenotypic plasticity:

(An evolutionary outcome of competition)

Answer 25

The ability of an organism to alter its phenotype in response to changes in the environment w/o changes to its underlying genetic makeup

e.g. body size influenced by diet

NOTE: this is an alternative explanation, not an evolutionary response

Question 26

What are the 6 criteria required for character displacement?

(Schulter & McPhail’s criteria)

Answer 26

1 - Rule out chance

2 - Genetic basis for differences

3 - Evolutionary shifts, NOT exclusion

4 - Trait differences linked to resource use

5 - Consistent environmental context

6 - Evidence of competition

Question 27

Elaborate on why (1) chance must be ruled out in the criteria for character displacement:

Answer 27

Observed patterns must not be due to random variation

Question 28

Elaborate on why (2) there should be a genetic basis for differences in the criteria for character displacement:

Answer 28

The phenotypic differences between populations in sympatry & allopatry should have a genetic basis

Question 29

Elaborate on why (3) it must be evolutionary shifts, NOT exclusion in the criteria for character displacement:

Answer 29

Enhanced differences in sympatric species should result from evolutionary changes (e.g. selection pressures)

Rather than mechanisms like competitive exclusion (one species driving another out)

Question 30

Elaborate on why (4) trait differences must be linked to resource use in the criteria for character displacement:

Answer 30

The morphological (or other phenotypic) difference should reflect differences in resource use

Question 31

Elaborate on why (5) consistent environmental context is in the criteria for character displacement:

Answer 31

The environmental conditions such as food availability & climate should be similar between sympatric & allopatric sites

Ensures difference is due to competition, not environmental availability

Question 32

Elaborate on why (6) evidence of competition is in the criteria for character displacement:

Answer 32

Must be independent evidence that similar phenotypes compete for resources

Question 33

Define sympatry:

Answer 33

When 2 or more species live in the same geographic are & have the potential to encounter each other

Question 34

Define allopatry:

Answer 34

When 2 or more species are geographically separated, preventing interaction or interbreeding

Question 35

When do trade offs in performance tend to occur?

Answer 35

In systems with strong competition, specialisation to specific niches may occur –> leading to trade offs

e.g. growth rate differences in limnetic & benthic sticklebacks reflect performance trade-offs in their respective habitats

Question 36

What are the 3 patters of trait evolution that occur?

Answer 36

1 - Divergence in sympatry

2 - Trait overdisposition

3 - Species-for-Species matching

Question 37

What is divergence in sympatry?

(Patterns of trait evolution)

Answer 37

Closely related species in overlapping geographic areas (sympatry) evolve distinct traits to reduce competition

e.g. divergence in gill raker length in limnetic & benthic sticklebacks

Question 38

What is trait over disposition?

(Patterns of trait evolution)

Answer 38

Traits of sympatric species become more evenly spaced to avoid overlap & competition

e.g. regular spacing of canine diameter in weasels across diff locations

Question 39

What is species-for-species matching?

(Patterns of trait evolution)

Answer 39

Competition across an entire community can structure traits among multiple species

e.g. morphological variation in Anolis lizards in the Caribbean, w distinct ecotypes (twig, truck-bound, trunk-crown) evolving independently on different islands

Question 40

What are 3 good examples of character displacement?

Answer 40

The 3 patterns of trait evolution:

• Divergence in sympatry (sticklebacks)
• Trait over dispertion (mustelid teeth)
• Species for species matching (Anolis)

Question 41

What are the 3 challenges in identifying character displacement?

Answer 41

1 - Distinguish between evolutionary responses & environmentally driven phenotypic plasticity

2 - Accounting for clinical variation (e.g. trait changes due to latitude or climate gradients)

3 - Verifying that competition, rather than other factors (e.g. predation or mating choice) drives trait differences

Question 42

Summary:

Answer 42

Character displacement and competition form a feedback loop where ecological interactions shape evolutionary outcomes. By identifying patterns of divergence or convergence and applying rigorous criteria, evolutionary ecologists can elucidate the mechanisms underlying trait evolution in competitive contexts. This theoretical framework is supported by models like Lotka-Volterra(?) and empirical evidence from systems such as sticklebacks, Anolis lizards, and Galápagos finches.