POPULATION GROWTH DYNAMICS

Population growth (r) is controlled by variety of factors depending on scale examined:

Global Scale -- no. of births v. no. of deaths.

r = b - d

"r" is expressed as a proportion

(e.g., 0.1 , -0.05 ; equiv. to 10% increase and 5% decrease).

Example --

Given: Population of 10,000

400 births/yr (40 per 1,000 people)
200 deaths/yr (20 per 1,000 people)

Calcs: r = b - d

b = 400/10000 = 0.04
d = 200/10000 = 0.02

Therefore: r = 0.04 - 0.02 = 0.02

(The population is growing at an annual percentage rate of 2%.)

Local Scale -- (b-d) + migrations in and out

Migrate in = immigration (i)
Migrate out = emigration (E)

So, on local scale, population growth rate (r) is calculated taking into account births, deaths, immigrants and emigrants:

r = (b - d) + (i - E)

Example--

Given: Population of 10,000

400 births/yr (40 per 1,000 people)
200 deaths/yr (20 per 1,000 people)
20 immigrants/yr
50 emigrants/yr

Calcs: r = (b - d) + (i - E)

b = 400/10000 = 0.04
d = 20010000 = 0.02
i = 20/10000 = 0.002
E = 50/10000 = 0.005

Therefore: r = (0.04 - 0.02) + (.002 - .005) = 0.017

(The population is growing at an annual percentage rate of 1.7%.)

Strategies of Population Growth

• r-adapted species (adapted for high rates of growth)
  • Insects, rodents, marine invertebrates, parasites, and annual plants
• K-adapted species (adapted for living at or near carrying capacity)
  • Wolves, elephants, whales, and primates

Characteristics of contrasting reproductive strategies
r-adapted species	K-adapted species
Short life Rapid growth Early maturity Many small offspring Little parental care or protection Little investment in individual offspring Adapted to unstable environment Pioneers, colonizers Niche generalists Prey Regulated mainly by extrinsic factors Low trophic level	Long life Slower growth Late maturity Fewer large offspring High parental care and protection High investment in individual offspring Adapted to stable environment Later stages of succession Niche specialists Predators Regulated mainly by intrinsic factors High trophic level