1. Chapter 14 Interactions in Ecosystems
UNIT 7: Ecology
Chapter 14
Interactions in Ecosystems

2. CH. 14.3 Population Density & Distribution
Each population has a density, dispersion, and a reproductive strategy.
Population density is a measurement of the number of individuals that live in a defined area.
Calculating population density can help scientists notice changes over time and help to determine if they were caused by environmental factors.
# of individuals
area (units2) =
population density

3. CH. 14.3 Population Density & Distribution
Dispersion patterns help us understand species interactions by showing how populations group together.
Population dispersion is the way in which individuals of a population are spread in an area or population.

4. CH. 14.3 Population Density & Distribution
Population Dispersion Patterns
Clumped: Individuals may live close together in groups to facilitate mating, gain protection, or access food resources.
Uniform: Territoriality and intra species competition for limited resources lead to individuals living at specific distances from one another.
Random: Individuals are spread randomly within an area or a volume.

5. CH. 14.3 Population Density & Distribution

6. CH. 14.3 Population Density & Distribution
Survivorship curves help to describe the reproductive strategy of a species.
A survivorship curve is a generalized diagram showing the number of surviving members over time from a measured set of births.
It gives information about the life history of a species.

7. CH. 14.3 Population Density & Distribution

8. CH. 14.3 Population Density & Distribution
Survivorship Curves
Type I: low level of infant mortality and and a population that will generally survive into old age (large mammals, humans).
Type II: equal chance of living and dying at all times, whether from disease or predation (birds, small mammals, some reptiles).
Type III: high birth rate and high infant mortality rate. Many offspring die from predation, but some survive to pass on genes (invertebrates, trees).

9. CH. 14.4 Population Growth Patterns
Populations grow in predictable patterns.
Changes in a population’s size are determined by:
Immigration: the movement of individuals into a population from another population.
Births: increase in the number of individuals in a population due to reproduction.
Emigration: the movement of individuals out of a population and into another population.
Deaths: decrease in the number of individuals in a population due to death.

10. CH. 14.4 Population Growth Patterns
Population growth is based on available resources.
When resources are abundant, a population has the opportunity to grow rapidly.
Exponential Growth: occurs when a population size increases dramatically over a period of time.
Represented graphically by a “J-shaped curve”.

11. CH. 14.4 Population Growth Patterns
Most populations face limited resources and thus show a logistic growth rate.
Logistic growth: when a population begins with a period of slow growth followed by a brief period of exponential growth before leveling off at a stable size.
Resources are abundant in the beginning, but over time begin to deplete and growth slows
Represented graphically by an “S-shaped curve”.

12. CH. 14.4 Population Growth Patterns
The environment determines how many individuals can be supported.
Carrying capacity of an environment is the maximum number of individuals of a particular species that the environment can normally and consistently support.
A population crash is a dramatic decline in the size of a population over a short period of time.

13. CH. 14.4 Population Growth Patterns
(K)
J-Shaped Curve
S-Shaped Curve

14. CH. 14.4 Population Growth Patterns
Ecological factors limit population growth.
The factor that has the greatest effect in keeping down the size of a population is called the limiting factor.
Density-dependent limiting factors are limiting factors that are affected by the number of species in an area (competition, predation, parasitism/disease).
Density-independent limiting factors are the aspects of the environment that limit a population’s growth regardless of the density of the population (severe weather, natural disasters, human activity).