Variation Within Species

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Variation Within Species
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Individual Variation

• This is more obvious in some species than is
  others.
• E.g. in humans it is obvious, we are all unique,
  with different fingerprints etc, but if we looked
  at a jar of flies, it is doubtful if we could
  tell the difference between them. (although the
  flies probably could.)

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Geographic Variation

• Generally this occurs on a larger scale than
  individual variation.
• The different races of humans are mostly due to
  the geographical area in which each race evolved.
• Dark skin is an advantage in regions of intense
  sunshine, e.g. the equatorial belt. (India,
  Africa, Northern Australia, Polynesia)

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Geographic Variation

• Dark skin in high (cold) lattitudes prevents the
  formation of vitamin D in the skin, so in those
  areas pale skin has evolved.
• Along with this is a loss of pigment in the hair
  and eyes, giving blonde hair and blue eyes.

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Geographic Variation

• Among other animals the geographical variation is
  not so obvious, but birds and mammals living in
  high altitudes are generally larger, and have
  shorter ears, tails and limbs to reduce heat
  loss.
• In hot areas, long extremities and small body
  size increase heat loss.

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Arctic Fox small pinna
European Fox medium pinna
African Fox Large pinna
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A Cline

• If we move in a particular direction through a
  range of a species, and find that there is a
  continuous increase or decrease in some
  characteristics between adjacent populations,
  this pattern is called a Cline.

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A Cline

• The NZ Tomtit shows a clinal variation in the
  length of the tail and wing.
• North Island tomtits have shorter tails and wings
  than their South Island counterparts, and this
  reaches all the way down to the Chathams, the
  Snares and the Aukland Islands.

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A Cline

• The Snares Island sub-species is actually an
  exception as it has a longer wing than the more
  southern Auckland Island sub-species.
• This is probably due to random variation in the
  gene frequencies in a small population on the
  Snares.

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A Ring Species

• When 2 apparently different species are joined by
  a series of geographical and structural
  intermediate types.
• This is called a Ring Species.
• E.g. in Britain and NW Europe the herring gull
  and the black-backed gull.
• These dont interbreed in the wild, so they act
  as 2 species.

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A Ring Species

• If you go east, there are initially only
  black-backed gulls the further east you go, the
  more herring gull traits start to appear.
• If you go west, there are only herring gulls to
  start with but as you continue west, the birds
  start to show some black-backed gull
  characteristics.

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A Ring Species

• So you can form a circle around the Arctic polar
  region with this ring of different birds,
  emerging into 2 distinct species.

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