1. Population Growth and Limiting Factors

2. Population Growth
Population Growth - An increase in the size of a population over time.
Populations of organisms do not experience linear growth. That is they do NOT grow at equal rates over equal time.
Instead, populations grow exponentially.
As the population gets larger, it also grows faster.
The graph looks like the letter …….. J
NOT

3. Exponential Population Growth
Exponential growth is shown by a J-shaped graph. This indicates as more individuals are added to a population, the faster the population will grow.
Number of
Individuals
Time

4. Exponential Population Growth
Populations will continue to grow exponentially if there are unlimited resources and NO limiting factors – plenty food, space, etc.
Limiting factor – ANYTHING in the environment which limits the growth of a population
Limiting factors include biotic and abiotic factors.
All regulate the size of populations & prevent further growth
Examples- food, space, disease, natural disaster, etc.

5. Environmental Limits
Density Dependent Limiting Factors- When a population increases & becomes more densely populated (more individuals per space) these factors will limit the population.
For these things to limit the size of a population, it DOES depend on how many organisms are in an area.
Examples – disease, competition, parasites, food, predation
When there are more individuals these factors have an increasing effect

6. Environmental Limits
Density Independent Limiting Factors - affect all populations regardless of their density.
The size of a population does not influence the affect of these factors. They limit population growth anytime they are present.
Most of these factors are abiotic - such as temperature, storms, floods, drought, and habitat disruption.
They can limit a population ANYTIME

7. Another way to classify factors:
Biotic
Biological influences on organisms within an ecosystem
how living things affect other living things
“density dependent factors”
Abiotic
Physical, non-living factors that influence organisms within an ecosystem
“density independent factors”

8. Limits to the Environment
The MAX number of organisms of one species that an environment can support is its carrying capacity.
Carrying capacity is often influenced by the limiting factors of an area – harsh winter, food availability, etc.

9. Carrying Capacity
If populations are UNDER the carrying capacity they will continue to grow exponentially, with the birth rate exceeding the death rate
If populations reach carrying capacity, the birth rate & death rate begin to equal out and the population begins to level off. This is called LOGISTICAL growth and is shown with an S-curve on a graph.
A population which exceeds the carrying capacity can no longer be supported by the environment in which it lives

10. Reaching Carrying Capacity
Number of
Individuals
S-shaped graph shows
LOGISTICAL growth
TIME

11. Interactive Limits A population can reach its growth “limit” due to:
Predation (read about Isle Royale)
Competition for resources (food, space, etc) – occurs in crowded populations and even among different species
Stress (manifests as disease, aggression, decrease in parental care)

12. Population Impacts on Other Populations
Predator-prey – populations cycle – more food for predator, more deaths of prey & vice versa
Prey
Number Of
Individuals
Predator
Time

13. Population Impact on the Environment
Large populations need more natural resources – shelter, food, water
Densely populated areas can be extremely devastating to the environment – placing demands on space & resources
Overuse of natural resources can also devastate other populations of species
Population control is needed to “protect” environmental resources in cases of wildlife. Humans need to be educated in wise practices concerning use of resources and land.