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r and K
• r is the per capita rate of growth
– r is determined both by genetics and
environment
– r can be measured (observed) rate of growth
of an estimate of biotic potential (the
maximum growth rate under ideal conditions
• K is the carrying capacity
– K is a measure of how many individuals the
environment can support
– K is determined both by genetics and
environment
r-selected species
• Weedy species found in environments
where disturbances are common
• Disturbance lowers population denisty
• Between disturbances the populations
grow exponentially
K-Selected Species
• K-selected species live in stable
environments.
• Population sizes remain stable.
• Selection favors traits that improve
competiveness.
r - Selection and K-selection
StableUnstablePopulation Stability
LongShortLongevity
LongShortGeneration time
LotsLittleParental Care
HighLowInvestment per
offspring
SmallLargeLitter size
“K”“r”Trait
