Species concepts

• Problem with fossil material– How many species are represented?

• Coexisting populations– How many species were represented?– Homo sapiens– Homo neanderthalensis– or Homo sapiens sapiens and– Homo sapiens neanderthalensis?

• What is a species?

Species defined by a species concept

Most individuals use anon-dimensional species concept

Backyard bird feederSpecies identified by uniquedifferences.

Species levellineages

Biparental organismsOrganisms are unitedto form species-levellineages by the process of reproduction

Uniparental organismsConstant divergencebecause lineages arenot linked togetherby reproduction

• The Biological Species Concept• Species are groups of actually or potentially interbreeding

natural populations that are reproductively isolated from other such groups.

• Species criterion = absence of interbreeding.• The species concept• Used in field of anthropology • Used to make decisions re the Endangered Species Act

• Biological species concept = no interbreeding • Barriers to interspecific hybridization• Reproductive isolating mechanisms• A. Pre-reproductive (favored by natural selection)

– 1. Ecological• Timing of reproduction• Habitat segregation

– 2. Behavioral (courtship, etc.)– 3. Mechanical

• B. Post-reproductive (not favored by natural selection)– Waste of gametes in doomed fertilizations

• Other species concepts

• Criterion of reproductive isolation presents problems:

• 1. Populations that are geographically separated.• 2. Asexual and parthenogenetic populations.• 3. Morphological differences and similarities may not

be effective in distinguishing species under this concept. – A. Individual variation (e.g., ontological variation) – B. Geographic variation– C. How much hybridization is permitted?– D. Cryptic species

How many species? Problem 1: Ontological variation

Problem 2:Geographicvariation

Southwest AZ South-centralAZ

Problem 3: How much hybridization is permitted?

Discordant hybridization

The red wolf problem

Is there presently such a thing as a Red wolf?

Readily hybridizesHow much $ should be allocated to its survival?

3. One species or two?

Fertilehybrids

The hybridization zone: SW New Mexico

Sites 22, 26, 28, 30

Three concordantstep-clines

• The Evolutionary Species Concept• • A species is an entity composed of organisms

– maintaining its identity from other such entities through time and space

– and having its own independent evolutionary fate and historical tendencies.

• Operationalism absent• Use fixed diagnostic differences

Aspidoscelis velox (3n, parthenogenetic)

1. A. stictogramma x A. inornata 2. F1 diploid parthenogenetic x A. inornata

Aspidoscelis uniparens (3n, parthenogenetic)

1. A. inornata x A. stictogramma 2. F1 diploid parthenogenetic x A. inornata

Problem 4: Cryptic species

velox

uniparens