Related Experiment Video
Updated: Jul 2, 2026
04:10
Visually Sexing Loggerhead Shrike (Lanius Ludovicianus) Using Plumage Coloration and Pattern
Published on: March 8, 2020
Latitudinal variation in subspecific diversification of birds
Paul R Martin1, Joshua J Tewksbury
1Department of Biology, University of Washington, Box 351800, 24 Kincaid Hall, Seattle, Washington 98195, USA. pm45@queensu.ca
Evolution; International Journal of Organic Evolution
|August 30, 2008
Summary
Bird subspecies are more numerous at lower latitudes, suggesting greater evolutionary divergence in these regions. This pattern holds globally and is not explained by breeding range area, supporting higher tropical speciation rates.
Area of Science:
- Evolutionary biology
- Biogeography
- Ornithology
Background:
- Latitudinal gradients in biodiversity are well-documented, but patterns of intraspecific diversification remain less understood.
- Previous research suggests evolutionary processes may vary with latitude, yet empirical evidence is limited.
Purpose of the Study:
- To investigate latitudinal patterns of subspecific diversification within bird species.
- To determine if subspecies abundance correlates with latitude and if breeding range area explains this relationship.
- To assess the global geographic variation in latitudinal subspecies differences.
Main Methods:
- Analysis of species with five or more subspecies from 12 major bird families worldwide.
- Statistical examination of the relationship between subspecies number, latitude, and breeding range area.
- Global comparison of latitudinal subspecies distribution across continents and hemispheres.
Main Results:
- A consistent pattern of more subspecies at lower latitudes was observed across all examined bird families, hemispheres, and continents.
- Breeding range area positively influenced subspecies numbers but did not account for the lower-latitude excess.
- Global subspecies patterns indicate greater phenotypic differentiation in populations at lower latitudes.
Conclusions:
- Lower latitudes exhibit higher rates of subspecific diversification in birds.
- These findings support hypotheses linking higher tropical speciation rates to the latitudinal diversity gradient.
- Subspecies density may serve as an indicator for rates of incipient speciation.
Related Concept Videos
01:46Types of Selection
Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...
01:07Speciation 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.
01:31Formation of Species
Speciation describes the formation of one or more new species from one or sometimes multiple original species. The resulting species are discrete from the parent species, and barriers to reproduction will typically exist. There are two primary mechanisms, speciation with and without geographic isolation—allopatric and sympatric speciation, respectively.Allopatric SpeciationIn allopatric speciation, gene flow between two populations of the same species is prevented by a geographic barrier, like...
02:16Genetics of Speciation
Speciation is the evolutionary process resulting in the formation of new, distinct species—groups of reproductively isolated populations.The genetics of speciation involves the different traits or isolating mechanisms preventing gene exchange, leading to reproductive isolation. Reproductive isolation can be due to reproductive barriers that have effects either before or after the formation of a zygote. Pre-zygotic mechanisms prevent fertilization from occurring, and post-zygotic mechanisms...
01:21Testing a Claim about Mean: Unknown Population SD
A complete procedure of testing a hypothesis about a population mean when the population standard deviation is unknown is explained here.
Estimating a population mean requires the samples to be approximately normally distributed. The data should be collected from the randomly selected samples having no sampling bias. There is no specific requirement for sample size. But if the sample size is less than 30, and we don't know the population standard deviation, a different approach is used; instead...
Estimating a population mean requires the samples to be approximately normally distributed. The data should be collected from the randomly selected samples having no sampling bias. There is no specific requirement for sample size. But if the sample size is less than 30, and we don't know the population standard deviation, a different approach is used; instead...
02:55The 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.