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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