Population and its importance to Ecology

Demographers• These are scientists who study populations

• Talk about populations in terms of DENSITY

• Density- # of individuals of a species per unit area 46/50 SD - 10.86 inhabitants

per square mile

50/50 –AK - 1.264 inhabitants per square mile

1/50 – NJ - 1,189 inhabitants per square mile

Distribution of density• How spread out the population is

1. Random – no pattern (least common)1. Dandelions blown by wind (chance)

2. Uniform – fairly evenly spaced1. Penguins – aggressively territorial

3. Clumped – form small groups1. Families or herds (most common)

Demographers use• Growth rate = birth rate - death rate

• Per capita (1000)

• Positive growth rate (+) - increasing (reds)

• Negative growth rate (-)- decreasing (blues)

Deer population in SD from 2000 – 2009

Population Growth Rate

• Amount / Time

• Depends on:– Birth rate and Death rate– Immigration (move into)– Emigration (move out)

Is the world population still growing, even though the line graph is going down?

• Density-dependent Factor-a factor that limits a population more as population density increases Examples: food, space

• Density-independent Factors- factors that limit the population but are unrelated to population density Examples: Extreme weather

Exponential Growth• Larger it gets, the faster it grows• “J” Curve• No limiting factors (Something that

restrains the population)• Doesn’t occur in real

world populations forvery long

• EXAMPLES:

Bacterial Growth• If one bacterium divides to produce 2 cells every

20 min, how many bacteria would you have after just 1 day?

• 0 min – 1• 20 min – 2 • 40 min – 22 = 4• 60 min – 23 = 8• 1 day = 272 = 4,720,000,000,000,000,000,000

In a few days, bacteria would cover the planet

Logistic Growth• Accounts for influences of limiting factors

• Birth rates and Death rates are not constant

• Carrying Capacity- the maximum number of individuals an environment can support

• “S” curve

1. Phase 1 – Exponential Growth

- unlimited resources, many offspring, few deaths

2. Phase 2 – Growth slows down

- resources become limited, less offspring, growth rate starts to decrease

3. Phase 3 – Growth stops

- rate of growth stops, pop. maintains size

- # births = # deaths

- Carrying capacity is reached

Populations Fluctuate in Nature

• Small populations (Endangered species)• Siberian tigers, black footed ferret, California

condor• Very vulnerable

• Inbreeding-reduces genetic variation

Age structure - # of males and females of each age in a population

- Shows how the population will grow over next few generations

Consider what the population of the world might be like in 20 years, 50 years, 100 years…

What will be the limiting factors that cause us to reach our carrying capacity?