Ecological opportunity

Question 1

Define adaptive radiation

Answer 1

• Groups of distinctive yet closely related species that have evolved from a common ancestor in a relatively short time
• Includes variation in morphological traits = exploitation of range of environs

Question 2

Most theories of adaptive radiation suggest that the process begins with ________ ___________

Answer 2

ecological opportunity

Question 3

What are the 3 sources of ecological opportunity

Answer 3

New habitat
Key innovation
Antagonist extinction

Question 4

Sources of ecological opportunity

Give some examples of new habitats & novel environments

Answer 4

• E.g island colonisation - Darwin’s finches, Anolis
• E.g Hawaiian honeycreepers
  → but, doesn’t necessarily mean adaptive radiation will occur (Order of colonisation and resources available matter)

Question 5

How does release from antagonists drive adaptive radiations, and why is it controversial?

Answer 5

Removal of antagonists (e.g., predators, competitors) creates ecological opportunities for diversification. E.g: End-Cretaceous extinction thought to enable mammal diversification.

Controversy:
Recent phylogenetic evidence shows little immediate diversification of mammals after the extinction.
Major diversification occurred millions of years later, suggesting other factors (e.g., climate change) were key

Question 6

Describe how Simpson’s Key innovation drives adaptive radiations

Answer 6

Acquisition of prospective adaptation may lead to occupation of a new niche without physical movement or ecological change

Question 7

Give an example of Simpson’s key innovation

Answer 7

Nectar spurs in Columbines Aquilegia

• Huge variation in nectar spur length, colour orientation
• Key trait in pollination and repro
• Specialized Pollination: Nectar spurs attract specific pollinators e.g hummingbird and hawkmoth
• New Ecological Niches: Allows the plant to reduce competition and specialize in attracting particular pollinators.
• Evolutionary Diversification: Varying spurs = reproductive isolation and speciation = diversification

Question 8

What is ecological release?

Answer 8

• Niche expansions and shifts when a constraining interspecific interaction (e.g competition & predation) is reduced or removed
• Relaxation of stabilising selection should increase trait variation (rare forms become common)

Question 9

What is density compensation, and what evidence supports it?

Answer 9

Population density increases in the absence of competitors or predators.
- Example: Buckley & Jetz (2007) studied lizard populations on islands.
- Finding: Lizards on islands had elevated population densities.
- Finding: Controlled for factors like energy use and primary productivity.
- Conclusion: Reduced competition and predation on islands drive density compensation.

Question 10

Density compensation

What would happen to the frequency and strength of interactions within species as pop. density increases?

Answer 10

Intraspecific interactions become more frequent

Intraspecific competition becomes stronger

Question 11

How might niches and phenotypic diversity change in response to shifting selection pressures (stronger intraspecific competition)?

Answer 11

• Absence of interspecific competition and increase intra competition favours niche expansion
• Increased phenotypic diversity of the population

Question 12

Describe how Svanbäck & Bolnick’s 2007 findings relate to density compensation

(Sticklebacks)

Answer 12

• Method: Manipulated population densities of three-spine sticklebacks in natural lake enclosures.
• Increases pop density = decreased prey availability
• Caused individuals to add alternative prey types to their diet
• Diet variation increased relative to low-density control enclosures

Take home: Artifically manipulated density compensation resulted in increased niche breadth

Question 13

Describe the study into whether niches evolve in response to intraspecific competition

Answer 13

• Study on niche width expansion in Drosophila: Introduced cadmium-intolerant populations to environments containing both cadmium-free and cadmium-laced resources.
• Implies that where theres high competition, you can more rapidly evolve a response to feed under diff resources
• Competition can drive niche expansion onto new resources for which competition is less severe

Question 14

What were the findings of Rainey & Travisano (1998) on niche filling in Pseudomonas fluorescens?

Answer 14

• Investigated morphological divergence in Pseudomonas fluorescens under different environmental conditions.
• Morphs: Smooth spreader, wrinkly spreader, and fuzzy spreader.
• Method: Propagated smooth morph in test tubes, monitored diversity in homogeneous (shaken) vs. heterogeneous vials.
• Findings:
  In heterogeneous environments, morphological divergence occurred after 3 days and persisted for 10 days.
  No morphological divergence was observed in homogeneous environments.
• Conclusion: Ecological opportunity in heterogeneous environments promotes niche filling and diversification.
• Further study shows divserity is stable, so long as the environ conditions persist

Question 15

Describe a study into whether niche occupation limits adaptive radiations.

Answer 15

• Used Pseudomonas microcosms to assess the effect of niche occupation on morphological divergence.
• Method: Varied the number of occupied niches (0–3) and measured the number of evolved morphotypes.
• Findings:
  As the number of occupied niches increased, the number of evolved morphotypes decreased.
  Suggests that lack of ecological opportunity (niche space) limits divergence.
• Conclusion: Niche occupation constrains adaptive radiations by reducing ecological opportunity

Question 16

Define ecological opportunity

Answer 16

The availability of underutilized resources, new habitats, or reduced competition that allows species to diversify and adapt into new ecological roles

often happens due to: mass extinctions, colonisations, new innocations
= new niches

Question 17

What are the main factors that drive adaptive radiation?

Answer 17

• Ecological Opportunity – Vacant niches, reduced competition, or predator absence allow species to expand and diversify
• Geographic Isolation – Isolation (e.g., islands, lakes) reduces gene flow and promotes divergence (e.g., Hawaiian honeycreepers).
• Key Innovations
• Resource Availability – Abundant, diverse resources support niche differentiation and speciation (e.g., cichlid fish in African lakes).
• Disruptive Selection & ECD – Competition drives species to evolve distinct traits to minimize overlap (e.g., anole lizards in the Caribbean).