Population Growth Chapter

What you need to know!  The differences between exponential and logistic models of population growth  How density-dependent and density-independent factors can control population growth

Population Growth  The rate at which a population increases or decreases  G = growth rate of a population (# of individuals added per unit time)  N = population size (at a given time)  r = intrinsic rate of increase (maximum capacity of members of that population to reproduce)  The average contribution of each individual to population growth  r = (births – deaths)/N in a time period  K = carrying capacity (maximum population size an environment can support)

Practice  A pod of dolphins has 100 members. In a single reproductive cycle there are 50 births and 30 deaths. What is the net increase per individual (r) in one reproductive cycle?

Exponential Growth Model  Rate of population growth under ideal conditions  The whole population is reproducing in each time interval  G = rN

Logistic Growth Model  Populations cannot increase indefinitely  Limiting factors will restrict population growth  Carrying capacity is the maximum population size an environment can support  G = rN[(K-N)/K]

Practice  If a pod of dolphins has 150 members (N) and an intrinsic rate of increase of.2 (r), then what is the growth rate (G) in ideal conditions (G = rN) in a single reproductive cycle?  If that same pod of dolphins is in an environment that can only support 200 dolphins (K), then what is G in a single reproductive cycle?

Limiting Factors  Anything that reduces population growth  Density-dependent factors apply as populations increase in size:  Competition: food, water, territory, etc.  Health (disease, waste)  Physiological factors: stress triggered transformations  Density-independent (abiotic) factors apply to all populations, regardless of size  Weather  Climate change  Natural disasters

Boom-and-Bust  Some species have very specific patterns of growth followed by rapid decline  Lemmings and Snowshoe hare both exhibit this pattern  Several hypothesis exist for why the populations bust, but no one knows for certain  Lynx hunt Snowshoe hare almost exclusively and show the same boom-and-bust pattern  Predator prey interdependence