Population Ecology
Chapter 14
Population Ecology
• Population – group of one species
– Interact and interbreed with each other
• Based on density
– Number of individ. In a given area
– Can vary depending on dispersion
• Uniform – evenly spaced
• Random – position independent of others
• Clumped – end to aggregate in patches
Population Dispersion
Population Growth
• Changes in populations
– Based on how many organisms are added
and how many are taken away
– Growth rate- change in population size
• can be positive, negative or zero
Population Growth
• Under ideal conditions population will grow
– More organisms are born than die
– Exponential growth – the larger a population
is, the faster it grows
• Will not last forever- will slow down
– Zero growth – population stays the same
Limits to Population Growth
•
•
Eventually nutrients run out
Carry Capacity – average number of individuals
an area can support
– Based on density dependent factors
•
•
•
Limit large, dense populations
Energy, shelter, predators, soil nutrients, water,
competition, etc.
Density – Independent Factors
– Kill off organisms no matter how large the population
is
– Examples: weather, natural disasters, human
activities
Density Dependent Limiting
Factors
• Competition –
– When individuals compete for resources (ie
food, energy, etc)
– More individuals in an area limits the amount
of certain resources available
• Helps determine the carrying capacity of an
environment
Density Dependent Limiting
Factors
• Predation
– When one species eats another.
– Tend to live in balance with each other
• As one population goes up, so does the other and
vise versa
– Increase in prey, leads to an increase in predator
– Decrease in predator, leads to an increase in prey
Density Dependent Limiting
Factors
• Parasitism
– An organism that takes nourishment from its
host
• Live at the expense of the host
– Parasite populations grow only if host
population is dense
• Easier to spread
Density Dependent Limiting
Factors
• Crowding and Stress
– Most animals need a certain amount of space.
– Higher the population, the less space
available.
– Also weaken immune system
Demography
• Study of population growth
and other stats
• Life Tables – age specific summary of
birth and death rates
– Determines survivorship curve
• Types
– Type I – many live to adulthood, then rapid die
off
– Type II – equal chance of dying at any age
– Type III – lots of young, but not many make it to
reproductive age