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Related Concept Videos

Limits to Natural Selection01:38

Limits to Natural Selection

Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.For one, natural selection can only act upon existing genetic variation. Hypothetically, redtusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for redtusks, natural selection cannot increase the prevalence of...
Speciation Rates01:07

Speciation Rates

Speciation can proceed at markedly different rates, and evolutionary biologists commonly describe these differences through the models of gradualism and punctuated equilibrium. Both patterns explain how new species arise, but they differ in the tempo and continuity of evolutionary change. In both cases, evolutionary change arises from heritable variation within populations, with natural selection often shaping traits that improve survival and reproduction under specific environmental conditions.
Phylogenetic Trees03:21

Phylogenetic Trees

Phylogenetic trees come in many forms. It matters in which sequence the organisms are arranged from the bottom to the top of the tree, but the branches can rotate at their nodes without altering the information. The lines connecting individual nodes can be straight, angled, or even curved.The length of the branches can depict time or the relative amount of change among organisms. For instance, the branch length might indicate the number of amino acid changes in the sequence that underlies the...
Phylogenetic Trees03:21

Phylogenetic Trees

Phylogenetic trees come in many forms. It matters in which sequence the organisms are arranged from the bottom to the top of the tree, but the branches can rotate at their nodes without altering the information. The lines connecting individual nodes can be straight, angled, or even curved.The length of the branches can depict time or the relative amount of change among organisms. For instance, the branch length might indicate the number of amino acid changes in the sequence that underlies the...
The Evidence for Evolution02:55

The Evidence for Evolution

Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of novel varieties and entire new species. These changes are responsible for the diverse forms of life inhabiting the planet. The evidence for evolution suggests that all living organisms descended from common ancestors.The collection of fossils within sedimentary rocks give a record of common ancestry and often depicts the history of evolution.
Phylogeny01:23

Phylogeny

Phylogeny is concerned with the evolutionary diversification of organisms or groups of organisms. A group of organisms with a name is called a taxon (singular). Taxa (plural) can span different levels of the evolutionary hierarchy. For instance, the group containing all birds is a taxon (comprising the class Aves), and the group of all species of daisies (the genus Bellis) is a taxon. Phylogenies can likewise include just one genus (i.e., depict species relationships) or span an entire...

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Related Experiment Video

Updated: Jun 24, 2026

A Concoction Pipeline for Generating Molecular Operational Taxonomic Units (MOTUs) Among Riparian and Aquatic Beetles
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Ecological limits on clade diversification in higher taxa.

Daniel L Rabosky1

  • 1Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853-2701, USA. dlr32@cornell.edu

The American Naturalist
|March 24, 2009
PubMed
Summary

Species richness is largely independent of clade age, contrary to expectations. Ecological limits, not age or diversification rates, appear to regulate species accumulation in major taxa.

Area of Science:

  • Evolutionary biology
  • Ecology
  • Biodiversity science

Background:

  • Species richness varies significantly across different groups of organisms.
  • The drivers of this variation, particularly the roles of clade age and diversification rates, are debated.
  • Previous studies have yielded conflicting conclusions regarding the age-diversity relationship.

Purpose of the Study:

  • To investigate the relationship between clade age and species richness using a model-based approach.
  • To determine if clade age or diversification rates are primary drivers of species richness variation.
  • To explore alternative explanations for observed patterns in species richness.

Main Methods:

  • Employed a model-based statistical approach to analyze species richness data.

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  • Controlled for variations in diversification rates among different clades.
  • Examined five distinct data sets to assess the generality of findings.

    • Main Results:

    • Species richness was found to be largely independent of clade age across four out of five data sets.
    • Even substantial variation in diversification rates did not explain the lack of a positive age-diversity relationship in key taxa (angiosperms, birds, teleost fishes).
    • A clade volatility model did not account for these patterns.

    Conclusions:

    • Clade age is not a reliable predictor of species richness.
    • Ecological limitations, such as geographic area, likely mediate diversification rates over time.
    • These factors provide a more plausible explanation for the observed patterns in species richness than clade age or diversification dynamics alone.