Transcript Population and it`s importance to Ecology

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 spaced
1. Penguins – aggressively territorial
3. Clumped – form small groups
1. Families or herds (most common)
Demographers use
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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 for
very 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?