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Lecture 5

ENV200H1 Lecture 5: Lecture5

School of Environment
Course Code
Karen Ing

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Lecture #5 Mar 6 Biodiversity I
• Reason: possibly due to the Earth has many different combinations of
• Biodiversity – richness of biological variation
o Genetic diversity – variety of genes
o Species diversity – numbers of different kinds in a community
o Ecological diversity – richness and complexity in a community
Genetic diversity
• Varieties of different versions of the same gene in different individuals
• High levels of genetic diversity is generally desirable
o More likely to be adaptable to changes in environmental conditions
• Small populations with low genetic diversity, low adaptability to environmental
Species diversity
• Number of different kinds of species within individual communities or ecosystems
• Species richness
o Number of different species in a community; varies greatly; depends on
available niches
o Inversely related to
§ Geographic isolation
§ Environmental stress
§ less stable environment à no evolutionary process
o Greater at edges of adjacent communities: why?
§ Ecotone: transitional zones, species from 2 ecosystems
§ Edge effect: some unique surrounding edges will promote some
species to evolve
o Geologic history is important: why species is abundant in the tropic zone?
§ Tropic zones is believed to be the place that did not get glaciated,
so its biodiversity has been well preserved.
o Reduced when one species is dominant
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