The Ecology of Adaptive Radiation. QUICK Think of the First Adaptive Radiation That Comes to Mind.

The Ecology of Adaptive Radiation

QUICK Think of the First Adaptive

Radiation That Comes to Mind

Hawaiian Silverswords

Malagasy Vangids

Andean Espeletia

Ecological Opportunity

“loosely defined as a wealth of evolutionarily accessible resources little used by competing taxa” (Schluter 2000, p.69).

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use of "ecological opportunity" according to Google Scholar


Does it promote AR?If so, how?Is it required for AR?Is it an operationally useful concept, or just a useful heuristic?

“Evolutionary divergence of members of a single phylogenetic lineageinto a variety of different adaptive forms.” Futuyma, Evolutionary Biology, 1998

Adaptive Radiation

Hawaiian Honeycreepers

AR Definitional IssuesIs pace of diversification part of the definition? In particular, does it have to be explosive?How are ARs distinguished from non-ARs?

AR

AR Definitional IssuesIs pace of diversification part of the definition? In particular, does it have to be explosive?How are ARs distinguished from non-ARs?Does it make sense to categorize a continuously distributed characteristic?

AR

AR Definitional IssuesIs pace of diversification part of the definition? In particular, does it have to be explosive?How are ARs distinguished from non-ARs?Does it make sense to categorize a continuously distributed characteristic?Is the number of species the appropriate metric?

AR

Non-AdaptiveRadiation

Non-AdaptiveNon-Radiation

What Prompts AR?

Classic idea (Simpson, Major Features of Evolution, 1954)—AR requires:Geographical Access colonizationPhysical Access

mass extinction, appearance of new resource

Evolutionary Accesskey innovation

“The evolution of a trait that allows a species to interact with the environment in an entirely new way”

Key Innovation


Key Innovation

Note:1. KI does not necessarily cause AR


Key Innovation

Note:1. KI does not necessarily cause AR2. KI refers to ecological diversity, not

number of species

What Is the Evidence that Ecological Opportunity Prompts

AR?Biogeography: AR on islandsPaleontology: AR after mass extinctionEvolution: AR associated with KIPhylogeny: Decline in diversification

as radiation progresses

Mahler et al., Evolution, 2010 Rabosky and Glor, PNAS, 2010

What is the Evidence that Ecological Opportunity Prompts

AR?Biogeography: AR on islandsPaleontology: AR after mass extinctionEvolution: AR associated with KIPhylogeny: Decline in diversification

as radiation progressesExperimental evolution in lab


Does it promote AR?If so, how?Is it required for AR?Is it an operational useful concept, or just a useful heuristic?

Adaptive Radiation Requires:

Adaptive DiversificationSpeciation

Resourceavailability

Resource Spectrum

1. A species finds itself in a resource-rich environment

(seed size)


Resource Spectrum

2. Speciation occurs

(seed size)


Resource Spectrum

3. Resources become scarce

(seed size)


Resource Spectrum

4. Species partition resources to minimize interactions

(seed size)


Resource Spectrum

5. Species adapt to new "niches"

(seed size)

Two Questions:

Is interspecific competition the only ecological interaction that can lead to AR?Is speciation+diversification a one-step process or a two-step process?

Two Questions:

Is interspecific competition the only ecological interaction that can lead to AR?Is speciation+diversification a one-step process or a two-step process?


Resource Spectrum

2. Speciation occursResourceavailability

Resource Spectrum



Resource Spectrum


Speciation

AdaptiveDifferentiation

2 Steps


Resource Spectrum



Resource Spectrum



Speciation +

1 StepResourceavailability

Resource Spectrum


Ecological Speciation

Andrew P. Hendry. 2009. Ecological speciation! Or the lack thereof? Canadian Journal of Fisheries and Aquatic Sciences 66: 1383-1398.

Two Flavors of Ecological Speciation

Strong—in the presence of gene flow (sympatric/parapatric speciation)Weak—divergence driven by natural selection regardless of geographic context


Resource Spectrum



Resource Spectrum



Speciation +

1 StepResourceavailability

Resource Spectrum


Strong Flavor:Speciation in presence of gene flow


Resource Spectrum



Resource Spectrum

3. Resources become scarce


Resource Spectrum


Speciation in allopatry

AdaptiveDifferentiation2-Step Models:

Does adaptive differentiation occur in allopatry or sympatry?

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Why might NS favor different adaptations on different islands?

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Nat Sel may be involved in speciation (weak ES);

Competition not important

Nat sel not part of speciation

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Character Displacement

Assumption: Body size correlates with resource use

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Nat Sel part of speciation;



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Nat Sel part of speciation;



Two Questions?

Is interspecific competition the only ecological interaction that can lead to AR?Is speciation-diversification a one-step process or a two-step process?

Other Processes That Could Promote AR

Apparent competition/Competition for predator-free space (predation)

Apparent Competition

In Habitat A, Predator 1 preys on Prey 1More Prey 1 more Predator 1Predator 1 also opportunistically eats Prey 2More Predator 1 fewer Prey 2Hence, more Prey 1 fewer Prey 2“Apparent” competitionPromotes habitat divergence by Prey 2 to escape Prey 1’s predators

Other Processes That Could Promote AR

Apparent competition/Competition for predator-free space (predation)Parasitism/Herbivory ecologically the same as aboveMutualism/Coevolution



Alternatives to Ecological Opportunity

A Clade Outcompetes the Incumbent Clade and Replaces It


A Clade Outcompetes the Incumbent Clade and Replaces ItA Radiating Clade Creates Its own DiversityThe More Species in a Clade, the Greater the Resources to Exploit

AnolisScale-eating cichlid

Intra-clade predation


A Clade Outcompetes the Incumbent Clade and Replaces ItA Radiating Clade Creates Its own DiversityThe More Species in a Clade, the Greater the Resources to Exploit

Coevolution: More Species on one Side of a Coevolutionary Relationship May Spur More on the Other


A Clade Outcompetes the Incumbent Clade and Replaces ItA Radiating Clade Creates Its own DiversityA Radiating Clade Creates New Niches: Ecosystem Engineers

R. Levins and R. Lewontin. 1987. The Dialectical Biologist. Harvard University Press.



How do we identify EO, much less quantify it?

How Do We Explain Clades That Experience Ecological Opportunity

and Don’t Radiate?

Galápagosmockingbird

Hawaiianthrush

How Do We Explain Clades That Experience Ecological Opportunity

and Don’t Radiate?

Mistake: No OpportunityInability to Utilize Resources—Lack of

EvolvabilityInability to Speciate

How Do We Identify Ecological Opportunity Other Than Retrospectively To Explain An Adaptive Radiation That

Has Occurred?

Can We Actually Quantify Opportunity Other Than Recognizing It After The Fact

When A Clade Has Radiated?

How Do We Identify Ecological Opportunity Other Than Retrospectively To Explain An Adaptive Radiation That

Has Occurred?

Can We Actually Quantify Opportunity Other Than Recognizing It After The Fact

When A Clade Has Radiated?

Cocos Island Finch

Estimating Adaptive Landscape Based on Distribution of Resources (seeds)

Schluter, D. and P. R. Grant. 1984. Determinants of morphological patterns in communitiesof Darwin’s finches. American Naturalist 123:175–196.

Critiques:LaboriousHighly ad hocIgnores Interspecific InteractionsEnvironmental Snapshot of Resource Availability

Body Size of Lesser Antillean Anolis

1-speciesIslands: Medium

2-speciesIslands:Large and Small

Schoener, Amer. Nat., 1970

Adaptive Peak for One Species

Resource (Insect) Availability

Adaptive Peaks for Two Species

Resource (Insect) Availability

Cocos Island Finch

How Would You Test Whether Ecological Opportunity Exists on Cocos Island?

The Ecology of Adaptive Radiation. QUICK Think of the First Adaptive Radiation That Comes to Mind.

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