Download What factors affect population growth

What factors affect population growth?
What limits the distribution and abundance of organisms?
 Abiotic environment
 Thermal limitations
 Ability to respond to change
 Interactions (intraspecific and interspecific)
 Characteristics inherent within the individual
 Not how an individual responds, but how an individual lives
 Life-history
Importance of density
 Some factors that regulate population sizes are directly related to density
 In other words, as density changes, the factor will change with density
 Density dependent factors
 Some factors that regulate populations are not related to density at all
 In other words, as density changes, the factor does not change
 Density independent factors
Density-dependent factors
 Higher proportion of population is affected as population density increases
 Tend to reduce population size by decreasing natality or increasing mortality
 Interspecific interactions
 Predator-Prey oscillations
 Intraspecific interactions
 Territoriality
 Stress and crowding
 Stress-related diseases
Crowding
 Annual plant Erophila verna
 Varied planting density
 Found shift in survivorship curves
 Intraspecific competition
 Density can affect all BIDE factors
Allee effect
Density-independent factors
 Factors unaffected by population density
 Examples include drought, hurricanes and floods
Density-independent factor
 Decline in the population of one of Darwin's finches (Geospiza fortis) on
Galapagos Islands due to drought
Community interactions
 Hare fluctuations due to both
 Food plants abundance
 Predator abundance
Why don’t all populations maximize their growth? i.e., why don’t all organisms
reproduce like rabbits?
Cost of reproduction
 Due to limited resources, increased reproduction may decrease survival and
chances of future production
 Therefore, there is a cost of reproduction
 Remember that natural selection will favor the life history that maximizes
lifetime reproductive success
Life history
 A life history is the complete life cycle of an organism
 “Choices” in life history
 How much to invest in each child
 How often to reproduce
 When to reproduce
 All “choices” involve significant trade-offs!
 So, organisms must make choices that maximize their reproductive
success overall given ecological conditions
Cost of reproduction
 Investment per offspring
 Key reproductive tradeoff concerns the amount of resources to invest in
producing any single offspring.
 number of offspring versus size of each offspring
– In many species, offspring size critically affects chances of survival
Parental investment
 Tradeoff between number of offspring and size of offspring
Number of reproductive events
 Trade off between current and future reproductive success
Cost of reproduction
 Reproductive events per lifetime
 Semelparity - organisms focus all reproductive efforts on a single, large
event
 Iteroparity - organisms produce offspring several times over many seasons
Cost of reproduction
 Age at first reproduction
 Longer-lived animals tend to reproduce later, and provide more parental
care than shorter-lived animals
Life-history strategies
 All of these trade-offs – and more -occur simultaneously
 Can not maximize one trait without losing in another
 Results in some common strategies for dealing with life
 r vs K
Life history strategies
 K-selected species tend to produce relatively few, large offspring
 large investment in parental care
 r-selected species tend to produce many, small offspring
 small investment in parental care
r/K species
 Species at near exponential phase of life = r
 Rapid growth
 “r-selecting” habitats
 Species at more constant density = K
 Growth more limited by resources
 “K-selecting” habitats
r-selection vs. K-selection