Species concept

Mass

Len

gth

Different species usually form clusters of phenotypes

Chronospecies Evolutionary species

Species concepts

What is a species?

What are the criteria for defining a species?

Species consist of interbreeding populations that evolve independently of other populations

Species concepts

Biological species concept

Phylogenetic species concept

Morphospecies concept

Species concepts

Biological species concept - BSC

species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups

Species concepts

Biological species concept - BSC

species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups

Problems with BSC

-asexual organisms-hybridization

Species concepts

Phylogenetic species concept - PSC

a species is a monophyletic group composed of the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent

Species concepts

Phylogenetic species concept - PSC

a species is a monophyletic group composed of the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent

Problems with PSC

-quantifying synapomorphies

Species concepts

Morphospecies concept - MSC

species are statistically distinguishable from others based upon an analysis of their morphological characteristics

Species concepts

Morphospecies concept - MSC

species are statistically distinguishable from others based upon an analysis of their morphological characteristics

Problems with MSC

-arbitrary-leads to cryptic species

Species concepts

Biological species concept

Phylogenetic species concept

Morphospecies concept

Beware the Procrustes fallacy!

Reliable criteria for identifying species are essential for preserving biodiversity

Indian elephant African elephant

Indian elephant African elephantAfrican forest elephant

The speciation process begins when gene flow is disrupted and populations become genetically isolated

Prezygotic barriers1 potential mates do not meet

temporal isolation, habitat isolation2 behavioral isolation3 mechanical isolation4 gametic incompatibility

Barriers to gene flow

Prezygotic barriers1 potential mates do not meet

temporal isolation, habitat isolation2 behavioral isolation3 mechanical isolation4 gametic incompatibility

Postzygotic barriers1 zygotic mortality2 hybrid inviability3 hybrid sterility4 F2 hybrid breakdown

Barriers to gene flow

Hybridization occurs when offspring are produced by interbreeding between genetically different populations

In intermediate or transitional habitats, hybrid populations may be more fit than either parental population

Hybrid Zones

Hybrid fitness Hybrid zone Outcome

< parents narrow, short lived reinforcement

= parents wide, long lived coalescence

> parents depends stable zone or

speciation