Download Populations

Populations
Rates That Affect Population Size
• Natality- the birth rate; the number of births
over time
• Mortality- the death rate; the number of
deaths over time
Rates That Affect Population Size
• Immigration- the rate of individuals entering
the population from a different population;
the number of individuals entering over time
• Emigration- the rate of individuals leaving a
populations to go to a different population;
the number of individuals leaving a population
Population Growth
• Two Types of Growth:
– Exponential
– Logistic
Exponential Growth
• Occurs when the individuals in a population
reproduce at a constant rate
• Under ideal conditions with unlimited
resources, a population will grow
exponentially
Exponential Growth
J-Curve
Logistic Growth
• Occurs when a population's growth slows or
stops following a period of exponential growth
Logistic Growth
S-Curve
• Carrying Capacity- the maximum
population size that environment can sustain.
– Usually determined by a limiting factor
• As resources become less available the growth
of a population slows or stops.
• New or early populations show exponential
growth
• Old, stable populations show no growth, but
stay near the carrying capacity of the
environment
• What happens if a population exceeds its
carrying capacity?
• If a population exceeds the carrying capacity
of its environment, the carrying capacity
decreases
Human Population
• Is the human population growing
exponentially or logistically?
Niches and Communities
• Niche - range of physical and biological
conditions in which a species lives and the
way the species obtains what it needs to
survive and reproduce.
• Different Factors:
– Tolerance – ability to survive and reproduce under
a range on environmental circumstances.
Tolerance Graph
Niche cont.
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Resources – food, water, nutrients, etc
Physical – abiotic factors
Biological – biotic factors
Competition – exactly what you would think
Competitive Exclusion Principle – no two
species can occupy exactly the same niche in
exactly the same habitat at exactly the same
time.
Predator-Prey Relationships
• Predation – interaction in which one animal
(predator) eats another animal (prey)
– Predators affect the size of prey populations
within a community and determine the places
where the prey can live.
• Herbivory – Same concept at predation just
with plants
Predator-Prey Graph
Symbioses
• Two creatures living in harmony and helping
each other survive.
• Mutualism – both benefit (Clown fish –
Anemone)
• Parasitism – one organisms lives inside or on
another organisms and harms it (Tapeworms)
• Commensalism – one organism benefits and
the other is neither harmed nor helped.
(Barnacles and Whales)