Population Ecology

Definitions in population ecology Individuals of a species within a given area constitute a Population Population density: the number of individuals of a species per unit of area (or volume) Population dynamics: change in population density through time and space Demography: study of birth, death, and movement rates that give rise to population dynamics

Population Size Size can affect the populations ability to survive Too big?? – issues Too small?? - issues Q – What are some challenges that populations have to face in order to survive? Competition for food, shelter, mates, water!

Q – What is the advantage of a large population over a small population?

Growth rates Growth occurs when: Populations are steady when: births outnumber deaths Immigration (into an area) is greater than emigration (out of an area) Populations are steady when: births = deaths Immigration = emigration Decline in populations occur when: deaths outnumber births. emigration is greater than immigration

Exponential Growth Population size increases steadily Example: bacteria 1 cell can divide every 30 minutes = 1 million bacteria in just 10 hours

Growth is limited Q – Specifically, what do you think can limit a populations growth? What can cause growth to slow down? Predators Disease Availability of resources

Resources When resources (food, water, shelter) become limited, growth will slow down. Density-dependent factors- -the rate at which resources are gone, depends on the size/density of the population

Determine… Name 1 density-dependent factor that could affect the following populations: Deer - Coyotes - Rabbits - Butterflies -

Density-dependent factors stabilize the population Per capita birth and death rates fluctuate in response to population density - e.g., dense population may deplete food supply, reducing the amount of food each individual gets. Poor nutrition may increase death rates and decrease birth rates -e.g., diseases, which may increase death rates, spread more easily in dense populations than in sparse populations

Logistic Growth Because these factors affect the size of populations, they can be shown as a Logistic Growth Model “logical”

Carrying Capacity (K) The population size an environment can sustain NOTE: when below carrying capacity, growth occurs rapidly (exponentially). Once resources are limiting (due to the growth) rate slows down.

Q- Explain the relationship between density-dependant factors and competition? These factors are what organisms must compete for in order to survive – water, shelter, mates, etc.

Density-independent factors Factors that affect birth and death rates in a population independent of its density (aka no matter how many there are) i.e. - a severely cold winter may kill large numbers of a population regardless of its density. Any other larger natural disaster (fire, hurricane, etc)

Show me your fingers!! Hold up the appropriate number of fingers for the number answer you think is correct

Which number shows exponential growth? 1 3 4 2 Population Growth Over Time

Population Growth Over Time Which number would represent the death rate increasing and the birth rate decreasing? 1 2 3 4 Population Growth Over Time

Which number shows the growth, if resources were NOT limited? 1 4 2 3 Population Growth Over Time

Which number best represents about the same birth and death rates? 3 1 2 4 Population Growth Over Time

“Strategists” Remember, animals can not “plan” or “strategize” their life. We say “strategists” meaning their pattern of living TWO main types: - r-strategists - K-strategists

r-strategists- grow exponentially when the environment allows them to Examples: a. mosquitos – breed like crazy in the summer months, populations decrease in the winter

K- strategists Organisms that grow slowly and have small population sizes. Bears, whales, etc.

In summary 1) There are many ways for the size of populations to be affected (density-dependant and independent factors) 2) There are many things populations must compete for (food, shelter, water, mates) 3) There are TWO main ways to model population growth (exponentially and logistically) 4) Depending on strategy, can either be an r-strategist or K-strategist (breed a LOT and fast OR slow and steady)