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 a non-dimensional species concept Backyard bird feeder Species identified by unique differences.

Species level lineages Biparental organisms Organisms are united to form species-level lineages by the process of reproduction Uniparental organisms Constant divergence because lineages are not linked together by 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: Geographic variation Southwest AZ South-central AZ

Problem 3: How much hybridization is permitted? Discordant hybridization

The red wolf problem Is there presently such a thing as a Red wolf? Readily hybridizes How much $ should be allocated to its survival?

3. One species or two? Fertile hybrids

The hybridization zone: SW New Mexico Sites 22, 26, 28, 30

Three concordant step-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. F 1 diploid parthenogenetic  x A. inornata  Aspidoscelis uniparens (3n, parthenogenetic) 1. A. inornata  x A. stictogramma  2. F 1 diploid parthenogenetic  x A. inornata  Problem 4: Cryptic species velox uniparens