Objectives: To define and understand: –Population biology –Characteristics of populationspopulations grow To estimate how pop’ns grow – initially w/ unlimited resources (exponential growth) –then as resources become limited (logistic growth) What limits growth? –What are patterns in survivorship? –Trade-offs between growth, reproduction and parental care –Human population growth

Definition of Pop’ns = What are characteristics of the pop’n?

How is growth rate determined? Measuring pop’n size (N). Census/count individuals Δ N = (Δ B - D) + (Δ I - E) survival and reproduction are key factors that determine change in N Growth of pop’n = change in # of individuals over time; G –Must calculate birth and death rates (b & d) –Find the rate of increase = r –Use r to estimate pop’n growth (G) for one time period = r N

The biotic potential of pop’n Depends on:

Age structure

Exponential growth implies unlimited resources But, limits on pop’n growth exist –Carrying capacity (= K) –Environmental resistance Logistic growth; G= r N [(K-N)/K] –What happens when N > K, N = K, N < K?

Density-dependent and density independent limiting factors: Pop’n may temporarily increase above carrying capacity Overshoot usually followed by a dramatic crash

Trade-off between births and density - as density increases births decrease

Size of pop’ns may fluctuate with regularity. Usually caused by multiple factors Snowshoe hare-lynx example:

Three types of survivorship curves Type I – Type III - Type II –

Trade-offs between: 1) frequency of reproduction, 2) # of offspring, and 3) parental care. Big-bang reproduction Repeated reproduction

Human pop’n growing exponentially Humans alter rate of increase; how? Humans alter environmental resistance; how?

Largest countries: China, India, U.S. Worldwide >6 b. today (r = 0.013) –In 2050 ~10 b? Rapid growth in U.S. (1.8 % annually) –b and I –U.S. 300 m (~265 m 2003); now? –2050, ~392 m