analysis of diversity and disparity - indiana university …indiana.edu/~g404/lectures/lecture 19 -...

Department of Geological Sciences | Indiana University (c) 2011, P. David Polly

G404 Geobiology

Hunter, 1998

Adaptative radiation and key innovations

Analysis of diversity and disparity


G404 Geobiology

Allison Bormet: Artiodactyls and ecomorphology

Blaire Hensley-Marschand: Hominins and mammals

“Take home” lab, no meeting


G404 Geobiology

Discussion on Thursday


G404 Geobiology

Schulter, 1996. American Naturalist, 148: S40-S64.

Adaptive radiation“A proliferation of species within a single clade accompanied by significant interspecific divergence in the kinds of resources exploited and in the morphological and physiological traits used to exploit those resources.” (Schluter, 1996)

Five components:

1. Monophyletic group2. increase in diversity (number of species

or lineages)3. increase in ecological differentiation

(resources such as food, substrate, etc.)4. increase in disparity (morphological

differences)5. by implication, relatively rapid increases

in these properties


G404 Geobiology

Examples of adaptive radiations

• Early metazoan life in the Proterozoic✴ Timescale: Ediacaran (635-542 mya, 90 million years)✴ Diversity: relatively small number of species✴ Disparity: large, with organisms from fronds to actriarchs✴ Monophyletic: maybe

• Amniota in the late Carboniferous and early Permian✴ Timescale: late Carboniferous to Early Permian (307-294 mya, 13 million years)✴ Diversity: large number of species and subclades✴ Disparity: large for tetrapods, ecological diversity great✴ Monophyletic: yes

• Eutheria in the early Cenozoic✴ Timescale: Paleocene to early Eocene (65-50 mya, 15 million years)✴ Diversity: extremely large number of species, many subclades✴ Disparity: large, bats to whales; ecological diversity great✴ Monophyletic: yes

• East African Lake Cichlids✴ Timescale: Miocene to Modern (10-0 mya, 10 million years)✴ Diversity: very large, 200+ species per lake✴ Disparity: largish, ecological diversity great✴ Monophyletic: yes (with subtleties)


G404 Geobiology

Key innovation

Key innovations are new features that facilitate adaptive radiations.

“Aspects of organismal phenotype important to the origin or subsequent success of a group.” (Hunter, 1998)

✴ May contribute to adaptive radiation✴ Differs from adaptive radiation in that key feature may evolve homoplastically and result

in diversification of more than one clade in parallel✴ Linked to diversity but not necessarily disparity✴ Trait must be a true adaptation, not an exaptation


G404 Geobiology

Hunter, 1998

Key innovation 1: hypocone in mammal teethEvolutionary addition of hypocone to the ancestral tribosphenic molar pattern transforms shearing dentition to crushing dentition

Key innovation in evolution of herbivory and omnivory

Occurs in parallel in many independent mammal groups, all of which diversify


G404 Geobiology

Hunter, 1998

Association between hypocone and mammalian diversityTribosphenic and partial hypocone taxa maintain constant diversity

Hypocone taxa radiate with large diversity


G404 Geobiology

Hunter, 1998

Key innovation : locomotor changes in birdsTransformation of one locomotor system in basal theropods to three in aves allows diversification into many types of forms

Hindlimbs + tail in theropods (coordinated)

Hindlimbs versus forelimbs versus tails in birds (semi-independent)


G404 Geobiology

A B C

Character change(exaptation)

Character change(adaptation)

Function change

Testing a hypothesis of adaptation

• Phylogenetic change in trait and function must be shown to coincide

• Link between trait and function must be demonstrated

• Improved “performance” because of change in trait must be demonstrated

Adaptation - a trait that evolves by natural selection for a specific function

Exaptation - a character, previously shaped by natural selection for a particular function (an adaptation), is co-opted for a new use (Gould and Vrba, 1982)

Example: Feathers are an exaptation for flight because they evolved before flying.


G404 Geobiology

Diversity and disparity

DiversityDiversity is the number of taxa living at one time, and changes to that number. Extinction lowers diversity, radiation raises diversity.

DisparityDisparity is the difference among taxa, roughly equal to the degree to which contemporary taxa are specialized for different things or specialized for the same thing.

The two are not necessarily correlated. Many species (high diversity) could have only a few specializations (low disparity); few species (low diversity) could have remarkably different specializations (high disparity).


G404 Geobiology

Diversity curvesEstimated from fossil record by dividing time into bins (either equal length bins or named geological periods)

Diversity curve

Num

ber o

f lin

eage

s


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Studying patterns of diversity

Standing diversity is the number of taxa (usually species, but sometimes genera or families) during a given time period

Standing diversity is a function of number of lineages existing at the beginning of a time period, the number of originations during the time period and number of extinctions

Basic data are first appearances (FADs) and last appearances (LADs) of taxa


G404 Geobiology

Disparity in Osteostracan morphospaceMorphospace is a mathematical space based on morphological measurements. Objects that are close together are similar to one another. The sum of the distances of objects is a measure of how different they are from one another. Disparity is often measured this way.


G404 Geobiology

Measuring disparity

Disparity is the average spread of taxa in morphospace

Can be measured from meristic characters or continuous characters

Distance between taxa is calculated and a morphospace produced using principal coordinates analysis (PCO) or principal components analysis (PCA)

PCO for meristic characters: distance = number of different character states

Taxon 1 0011001Taxon 2 0010110

Distance = 4 (four characters differ in state)

PCA for continuous characters: distance = Euclidean distance summed across traits

Taxon 1 0.5 1.0Taxon 2 0.7 1.2

Distance = sqrt( (0.5-0.7)2 + (1.0-1.2)2 ) = 0.4


G404 Geobiology

Photo credit

Disparity through timeCrinoid morphospace from Cambrian (CM) to Upper Devonian (UD) showing changing disparity through time

Maximum disparity reached by Ordovician (LO, O2)

Later changes merely fill in the morphospace


G404 Geobiology

(Tom Holtz, based on original by Matt Wedel, UC Museum of Paleontology website)


G404 Geobiology

Scientific papers for further readingAdams, D. C., C. M. Berns, K. H. Kozak, and J. J. Wiens. 2009. Are rates of species diversification correlated with rates of morphological evolution? Proceedings of the Royal Society B, 276: 2729-2738.

Gould, S. J. and R. C. Lewontin, 1979. The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme. Proceedings of the Royal Society B, 205: 581-598.

Hunter, J. P. 1998. Key innovations and the ecology of macroevolution. Trends in Evolution and Ecology, 13: 31-36.

Schluter, D. 1996. Ecological causes of adaptive radiation. American Naturalist, 148: S40-S64.

analysis of diversity and disparity - indiana university …indiana.edu/~g404/lectures/lecture 19 -...

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