ENV 1101 Lecture Notes - Prentice Hall

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Class 7: Population Dynamics
Dramatic declines in amphibian populations since 1980s
o Mass localized extinctions
o Locations around the world
Possible causes (not well understood)
Habitat destruction and modification
Pesticide use
Introduced alien species
Increased UV radiation
Changes in Population
The number of organisms within an ecosystem from any given species is not stable
Tends to fluctuate along with environmental conditions
Under extremely favourable or extremely unfavourable conditions, the shifts may be dramatic
Biotic Potential
The capacity for a given species to increase its number given optimum conditions, through reproduction,
geographical expansion of habitat or both
Environmental resistance
The total sum of factors that limit the potential for a species to increase its numbers or its geographic range
Carrying capacity
Describes the upper limit of the number of organisms that an ecosystem can support over the long term
Critical Number
The lowest number of organisms required to ensure that a population may reproduce and continue
Without human intervention, a species below the critical number will likely become extinct (although it is often
human processes that drive the population below the critical number in the first place)
Trumpeter Swans (Cygnus Buccinator)
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