Download Sustainable ecosystems Limiting factors

SUSTAINABLE
ECOSYSTEMS
LIMITING FACTORS
LIMITING FACTORS
Limiting factors are factors that can affect a population. They
can cause an increase or a decrease in the population.
These limiting factors can be divided into two groups: densitydependent and density independent.
Density: Organisms per unit area.
DENSIT Y INDEPENDENT FACTORS
These are factors that can affect a population regardless of what it’s
density is.
For example: Natural disasters, temperature, sunlight, behaviours, and
human activities.
Natural disasters include droughts, floods, hurricanes, fires, etc.
Temperature can determine which organisms can live in an area, such as a
lake. It can also influence the activity and growth of organisms. Warm
water holds less oxygen.
Sunlight is needed for plants to perform photosynthesis.
Behaviour can include migrating to a new area for food or for mating.
Human activities can include fishing, building of damns, hunting,
deforestation, etc.
DENSIT Y DEPENDENT FACTORS
These are factors that can only affect a population when it reaches a
certain density.
For example: Competition, predation, disease, parasitism, crowding, stress.
Competition can only occur between organisms of the same habitat.
Predation occurs when the population density of predators is high.
Disease increases with the density of the population.
Parasitism is a relationship in which one species benefits at the expense of
the other.
Crowding occurs at high densities.
Stress can make organisms weak and prone to more disease.
EXAMPLES
Each of the statements below involves a situation that will affect the growth of
a population. Classify each of the statements as DD (density dependent) or DI
(density independent) and give a reason for your choice.
1. Rainbow smelt and yellow perch attempt to occupy the same area. The
more aggressive smelt survive; the perch do not.
2. A severe flood brings a lot of sediment and silt into Lake Winnipeg. The
turbidity of the lake increases greatly.
3. A drought decreases the water level in Lake Winnipeg. The carrying capacity
of the lake decreases.
4. Due to the introduction of rainbow smelt, Lake Winnipeg becomes crowded
and some fish species do not survive.
EXAMPLES
5. Since northern pike prey on yellow perch, an increase in the perch
population causes an increase in the pike population.
6. Many fish die due to an increase in water temperature.
7. Due to over-fishing, the number of walleye in Lake Winnipeg decreases.
8. A population is growing quickly when parasites cause disease to spread
quickly.
9. Since lake sturgeon migrate long distances to spawn, many do not
survive the trip.