Download Biological Importance of Biodiversity I: Variation Below the

Biological Importance of Biodiversity I: Variation
Below the Species Level
(pp. 27 - 30, 375 - 387)
1. Case Study: The Alpine Ibex
2. What do we mean by
‘biodiversity’?
3. Variation within individuals
4. Variation within populations
5. Variation among populations
1. Case Study: The Alpine Ibex
Alpine ibex (Capra ibex) are
popular game animals in Europe.
The populations in the Czech and
Slovac republics have been
hunted to extinction, but healthy
populations remain in Austria and
Turkey. Can ibex be reintroduced
to Czechoslovakia from Turkey?
2. What do we mean by ‘biodiversity’?
Biodiversity maybe defined in many ways:
- “the sum total of all living things”
(Groom et al.)
Problems with this definition?
- "the variability among living organisms from all sources,
including terrestrial, marine and other aquatic
ecosystems and the part of the ecological complexes of
which they are part; this includes diversity within
species, between species and of ecosystems" (the
Convention on Biological Diversity)
Biodiversity exists at many levels:
Biomes
Landscapes
Ecosystems
Species
Among Populations
Within Populations
Within Individuals
The biological value of
biodiversity tends
to be manifest at
the next level of
organization
3. Variation within individuals
The main type of variation within individuals is genetic variation.
- typically indexed using
- “heterozygosity” (HE: the proportion of loci that are
heterozygous), or
- “inbreeding coefficient” (FIS: the probability that two alleles
are identical by descent).
- may be estimated using DNA sequences, protein
electrophoresis, karyographs, quantitative genetics...
In theory, an individual's fitness is directly related to its genetic
variation;
- low heterozygosity L low survival or reproductive success
Empirical evidence for this relationship
is extensive:
- ideas?
4. Variation Within Populations (Among Individuals)
Variation within a population may involve neutral
genes, physiology, morphology, behaviour, ecology...
- VP = VG + VE + VGxE
- typically indexed using
- heterozygosity (HE), or
- the “genetically effective population size” (Ne:
the size of an idealized population that contains
the observed amount of variation)
- almost always lower than the census (NC)
Furthermore, low variation may
lead to an “extinction vortex” -a
rapid decline to extinction:
L Minimum genetically viable
population sizes may exist.
Empirical support for these effects is accumulating, e.g.
- allelic diversity, hatching success and NC in greater
prairie chickens in Illinois (Bouzat et al. 1997;
Westermeier et al. 1998)
- supplementation with birds from
Tennessee increased all three
parameters
Fig. 14.4
- population survival in Glanville
fritillaries correlated with
heterozygosity (Saccheri et al. ‘98 )
But, all these studies
have short-comings
N.Z. black robin
And, many populations have
recovered from very small
elephant seal
numbers:
5. Variation Among Populations
Conspecific populations may differ in neutral genes,
morphology, physiology, behaviour...
- commonly indexed using “Wright’s FST”: the proportion
of variation representing differences among populations
Turkish ibex rut in the fall instead of the
summer, so kids were born in February
º population extinction.
...and "evolutionary significant units" (ESUs):
- populations that are genetically
distinct and represent a significant component of the
evolutionary legacy of a species
- may be 'cryptic'
- e.g. tuatara