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Conservation Ecology – Why is Biodiversity Important?
Timothy Bonebrake – February 4 2013
I. Genetics -> Populations -> Species -> Ecosystems
Species depend upon genetic diversity and ecosystems depend upon
species diversity (although this latter point is still the subject of some
debate).
II. Genetic Diversity -> Population/ Species Persistence
Evolutionary Potential – For species to adapt they must rely upon genetic
diversity to supply variation. Example: Moor frogs are locally adapted to
different habitats (also, moths of the industrial revolution).
Fitness – Similar idea (to evolutionary potential) but specifically genetic
diversity losses can lead to specific losses in fitness (often reproduction).
Example: Heterozygosity in a (vulnerable) plant population correlates
with greater seed production.
Heterosis – Heterozygote individuals are more “fit” than homozygotes.
Causes of genetic diversity losses:
Inbreeding depression – Reduced fitness and genetic diversity in a
population due to mating between closely related individuals. Example: In
butterfly populations it has been found that inbreeding increases
population extinction probability.
Outbreeding depression – “A reduction in reproduction and/or survival
in the first or later generations upon crossing populations” (Frankham
2010). Example: When distant populations are crossed sometimes the
fitness decreases, this could happen if, for example, the benefits of genetic
diversity are undercut by loss of local adaptation.
Genetic bottleneck – A population collapse which leads to a reduction in
genetic diversity (e.g. loss of alleles) for future generations. Example:
Based on genetic diversity scientists have inferred an orangutan
population collapse in recent decades.
Reduction of gene flow – If gene flow is restricted to any particular
subpopulation then genetic diversity will be diminished. Example: Habitat
fragmentation could reduce genetic diversity within populations.
Adaptation (maladaptation) – Loss of relevant genetic diversity through
adaptation to conditions not relevant to the habitat/ niche of interest.
Example: A population becomes adapted to conditions in captivity but
when released to the wild that population experiences reduced fitness.
II. Species Diversity -> Ecosystem Function
Are more diverse ecosystems (i.e. more species) more productive/ stable?
Some studies have shown that experimental plots tend to have greater
productivity. However, this could be due to a variety of mechanisms
including complementarity (niche differentiation), facilitation (one
species helps another/ mutualism) and the sampling effect (with more
species there is a greater chance of having a species with a significant
contribution to productivity/ function).
Keystone species – A species which exhibits a disproportionate impact on
its ecosystem relative to its abundance (e.g. the gray wolf).
Thus, while it is often true that species richness is positively correlated
with productivity it is also often the case that we don’t know why.
Ecosystems could also benefit from species richness by being more stable
due to redundancies (additional species) in the system. For example, no
one individual rivet of a plane wing is absolutely necessary (they are
redundant)… but you don’t want to lose too many!
So genetic diversity -> ecosystem services? Is all biodiversity good or
important? Does it matter?