Download Population Ecology

Population Ecology
CP Biology
What is Ecology?
´Ecology is the branch of biology that deals with
how organisms interact with one another and
their environment.
Populations
´Population – a group of interbreeding individuals
of the same species in a particular area
´Members of a population breed with one
another
´Researchers study populations’ geographic
range, density and distribution, growth rate
and age structure
Geographic Range
´ The area inhabited by a population
´ Can vary enormously in size w/different species
´ Ex: Bacteria in a rotting pumpkin – small range
Cod in the Atlantic – Greenland to N. Carolina
Density and Distribution
´Population density – The # of individuals per unit
area
´Density is based on availability of resources
´Clumped – patchy distribution of resourced
´Near-uniform – limited resources, intense
competition
´Random – uniformly distributed resources
Age structure
´Number of females & males of each age a
population contains
´Important to know reproductive potential of a
population
´ Only females produce offspring (animals)
´ Important to know age at which organisms reproduce
Population Growth
´Determined by the # of organisms that are
added to or subtracted from the population
´ Populations increase with births and immigration (in)
´ Populations decrease with deaths and emigration (exit)
´How the population changes determines the
type of growth you see in the population over
time
´Exponential vs. Logistic Growth
Exponential Growth
´When the size of each generation will be larger
that the generation before it
´The larger a population gets, the faster it grow
´Happens under ideal conditions
´Examples: Bacterial growth, elephants over a long
time, organisms in a new environment
´Produces a J-shaped curve
Population Sampling
´ Two basic methods of sampling a population:
´ Plot sampling
´Gives an estimate of the # of individuals in a larger area
based on actual #s in a smaller area
´Great for marine environments
´ Mark & recapture
´A group of animals are marked & captured, then turned
loose
´Second capture (recapture) done
´Proportion of marked animals in recapture represent
proportion of entire population
´Great for mobile populations
Exponential Growth Example:
Mice in a field
´ Imagine 2000 mice in a field
´ If 1000 mice are born each month…
´ And if 200 mice die each month…
´ The population will increase over time
´ But by how much? How fast?
Exponential Growth Example:
Mice in a field
Logistic Growth
´ Happens when a population’s size grows then stops after
exponential growth
´ Four stages:
´1. Exponential growth – resources are unlimited, population
grows quickly, few individuals die
´2. Growth slows down – In reality, population growth slows down,
can’t be sustained at an exponential rate
´3. Growth stops – Size of the population levels off, no more
growth, will remain at this size indefinitely
´ Produces an S-Shaped curve
´ Growth levels off when the population reaches carrying
capacity
´ Carrying capacity – the maximum # of individuals of a
particular species that a particular environment can support
Logistic Growth Curve
**Carrying capacity is species specific, environment-specific, and can change over time
Limiting Factors
´ Any factor that controls the growth of a population
´ Determine the carrying capacity of an environment for
a species
´ Two kinds:
´ Density-independent
´ Density-dependent
Density-Dependent Limiting Factors
´ Based on crowding of the population
´ Examples:
´Competition for limited resources, i.e. nesting sites, food,
water, hiding places, sunlight, etc.
´Predation, herbivory, human predators
´Parasitism, disease
´ Density-dependent limiting factors produce competition
between members of the same species
´More competition = organisms that don’t survive to
reproduce
´ The result is logistic growth
Density-Independent Factors
´ Factors that impact the size of a population that are unrelated to
crowding in a population
´ Ex: Natural disasters & weather related events such as hurricanes,
earthquakes, volcanic eruptions, floods, etc.
´ In nature, density-dependent and density-independent factors
often interact to determine a population’s size
´ Ex: Reindeer in Alaska