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).

Ecological Opportunity  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 lineage into a variety of different adaptive forms.” Futuyma, Evolutionary Biology, 1998 Adaptive Radiation

Hawaiian Honeycreepers

AR Definitional Issues  Is 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 Issues  Is 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 Issues  Is 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-Adaptive Radiation Non-Adaptive Non-Radiation

What Prompts AR? Classic idea (Simpson, Major Features of Evolution, 1954)—AR requires:  Geographical Access colonization  Physical Access mass extinction, appearance of new resource  Evolutionary Access key innovation

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

“The evolution of a trait that allows a species to interact with the environment in an entirely new way” Key Innovation Note: 1. KI does not necessarily cause AR

“The evolution of a trait that allows a species to interact with the environment in an entirely new way” Key Innovation Note: 1. KI does not necessarily cause AR 2. KI refers to ecological diversity, not number of species

What Is the Evidence that Ecological Opportunity Prompts AR?  Biogeography: AR on islands  Paleontology: AR after mass extinction  Evolution: AR associated with KI  Phylogeny: 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 islands  Paleontology: AR after mass extinction  Evolution: AR associated with KI  Phylogeny: Decline in diversification as radiation progresses  Experimental evolution in lab

Ecological Opportunity  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 Diversification  Speciation

(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?

Speciation Adaptive Differentiation 2 Steps

Adaptive Differentiation Speciation + 1 Step

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

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

Adaptive Differentiation Speciation + 1 Step Strong Flavor: Speciation in presence of gene flow

Speciation in allopatry Adaptive Differentiation 2-Step Models: Does adaptive differentiation occur in allopatry or sympatry?

42 Why might NS favor different adaptations on different islands?

43 Nat Sel may be involved in speciation (weak ES); Competition not important Nat sel not part of speciation

44 Character Displacement Assumption: Body size correlates with resource use

45 Nat Sel part of speciation; Competition not important Nat sel not part of speciation

46 Nat Sel part of speciation; Competition not important Nat sel not 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 1  More Prey 1  more Predator 1  Predator 1 also opportunistically eats Prey 2  More Predator 1  fewer Prey 2  Hence, more Prey 1  fewer Prey 2  “Apparent” competition  Promotes 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 above  Mutualism/Coevolution

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

Alternatives to Ecological Opportunity  A Clade Outcompetes the Incumbent Clade and Replaces It

Alternatives to Ecological Opportunity  A Clade Outcompetes the Incumbent Clade and Replaces It  A Radiating Clade Creates Its own Diversity  The More Species in a Clade, the Greater the Resources to Exploit

Anolis Scale-eating cichlid Intra-clade predation

Alternatives to Ecological Opportunity  A Clade Outcompetes the Incumbent Clade and Replaces It  A Radiating Clade Creates Its own Diversity  The 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

Alternatives to Ecological Opportunity  A Clade Outcompetes the Incumbent Clade and Replaces It  A Radiating Clade Creates Its own Diversity  A Radiating Clade Creates New Niches: Ecosystem Engineers

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

Ecological Opportunity  Does it promote AR?  If so, how?  Is it required for AR?  Is it an operationally useful concept, or just a useful heuristic? How do we identify EO, much less quantify it?

How Do We Explain Clades That Experience Ecological Opportunity and Don’t Radiate? Galápagos mockingbird Hawaiian thrush

How Do We Explain Clades That Experience Ecological Opportunity and Don’t Radiate?  Mistake: No Opportunity  Inability to Utilize Resources—Lack of Evolvability  Inability 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?

Cocos Island Finch

Estimating Adaptive Landscape Based on Distribution of Resources (seeds) Schluter, D. and P. R. Grant Determinants of morphological patterns in communities of Darwin’s finches. American Naturalist 123:175–196.

Critiques:  Laborious  Highly ad hoc  Ignores Interspecific Interactions  Environmental Snapshot of Resource Availability

Body Size of Lesser Antillean Anolis 1-species Islands: Medium 2-species Islands: 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 ?