Types of variation species

Organism

Any biological system that functions as an individual life form

Population

A group of organisms of the same species in the same area

Community

The populations of 2 or more species occupying the same geographical area

Variation

• physiological, structural or behavioural differences between individuals

Discontinuous variation (aka discrete)

• Traits that fall into distinct categories that have no immediate values between them

• Traits are typically controlled by a single gene; for example: ABO blood types, tongue rolling ability, and eye color

Continuous variation: 

• type of phenotypic variation where traits exhibit a smooth spectrum of measurable, quantitative differences between two extremes within a population. Controlled by multiple genes (polygenic) and strongly influenced by environmental factors, these traits follow a normal distribution (bell-shaped curve). Common examples include human height, skin color, and crop yield.

Intraspecific variation

• Variation within a specific species

These are inheritable and result from:

• Meiosis

• Sexual reproduction

• Mutation

• Gene flow*

• Intraspecific variations enables some individuals to survive/reproduce better than others*

Interspecific variation: 

• Variation between the individuals or two or more species

• More closely related species have more similar variations

• The higher order the taxonomic difference (eg. domain vs phylum), the larger the variation

Speciation: 

•  the formation of new and distinct species as the result of evolution

• Usually happens gradually

• traits within a population become increasingly different

• Becomes difficult/arbitrary when to then consider organisms new species

• Example: The California salamander, Ensatina eschscholtzii, originating 21.5 mya, has evolved into separate populations whose appearance and behaviour have changed to the point that they no longer recognize each other as potential mates

Species

• a group of organisms consisting of similar individuals capable of exchanging genes or interbreeding

Morphological species concept:

• Members are determined by qualitatively or quantitatively definable features

• Method used by Carl Linnaeus

• Has obvious limits…

Morphological species concept

Weakness: Sometimes DIFFERENT species look the SAME

2. Biological species concept

(‘the fertile offspring one’)

Members must be able to successfully breed with each other AND produce fertile offspring

Weakness (can’t account for…):

…for asexual reproduction

…horizontal gene transfer (eg. bacterial conjugation)

…extinct or fossilized organisms

…organisms whose reproductive patterns are hard to observe naturally

Evolutionary (or Phylogenetic) species concept

• Species members must share ancestry/a pattern descent and form a single branch on the tree of life

• Largely based on molecular* similarities

• (eg. genome, proteome, ribosomes, etc.)