Species Diversity

What is a Species?

  • Biological Species Concept

    • Group of interbreeding natural populations that is reproductively isolated from other groups

  • Cohesion Species Concept

    • Genetic and/or demographic exchangeability

  • Phenetic Species Concept

    • Group of organisms that are phenotypically similar & look different from other groups

  • Phylogenetic Species Concept

    • Species is a ‘tip’ on a phylogeny

    • Smallest set of organisms that share an ancestor & can be distinguished from other sets

    • Genetic data often used

  • Ecological Species Concept

    • Set of organisms using the same resources & experiencing similar limiting factors


Speciation is a Process

  • Subspecies

    • Subdivisions of a species whose members are similar in some ways, but different in some recognizable way

    • Likely headed toward being different species

      • Ex. tigers have 9 subspecies


Mechanisms of Speciation

  • Allopatric speciation

    • Populations are spatially separated

    • Genetically diverge so they can no longer interbreed

  • Sympatric speciation

    • Populations are not spatially separated

    • Isolating mechanisms evolve that prevent interbreeding

      • Ex. cichlids in Lake Tanganyika 


Measuring Species Diversity

  • Alpha diversity

    • Number of species in a particular area

  • Gamma diversity

    • Number of species in a large region or continent

  • Beta diversity

    • Rate of change in species composition across a region

  • Species richness

    • The number of species present in a community


Measures of Diversity

  • Aim is to quantify how diverse or not diverse something is

    • Species richness- how many species?

    • Shannon-Weiner Diversity Index- considers richness AND evenness

    • Simpson’s Diversity Index- Probability based, how likely is it that if you randomly select an individual, it comes from one of the species?

    • Species Evenness- how close in numbers species are in an area (how close are their proportions)

      • ‘High count’ of each family


Green salamander, Ocoee salamander, Pigmy salamander, Three-lined salamander

Alpha Diversity mnt. 1: 5

Alpha Diversity mnt. 2: 4

Average Alpha Diversity: 4.5

Beta Diversity: 1.1