ECOLOGY

Populations and Limiting Factors

Characteristics of Populations

What is a Population?– A group of individuals of a species that occupy the same area

• Two parts:– 1) need to be same species (can interbreed)– 2) spatial delineation

(Where located? How are they dispersed?)

1. Aggregated (clumped) dispersion- individuals concentrated in specific portions of the habitat; most common scenario, resulting from patchy distribution of resources in habitat.

Population Dispersions

1. Aggregated (clumped) dispersion- individuals concentrated in specific portions of the habitat; most common scenario, resulting from patchy distribution of resources in habitat.

2. Uniform dispersion - all individuals are more evenly spaced than one might expect by chance.

Population Dispersions

1. Aggregated (clumped) dispersion- individuals concentrated in specific portions of the habitat; most common scenario, resulting from patchy distribution of resources in habitat.

2. Uniform dispersion - all individuals are more evenly spaced than one might expect by chance.

3. Random dispersion - individuals in a population are spaced in an unpredictable and random fashion that is unrelated to the presence of others.

Population Dispersions

Aggregated? Uniform?Random?

Aggregated? Uniform?Random?

Aggregated? Uniform?Random?

What makes a Population grow?

• Birth rate• Longevity of individuals’ lives• Immigration

• If this kept on, what would a population growth curve look like on a graph?

Exponential Growth Rate

Human population…

Sustainability

• Populations cannot keep on getting that large, that fast. What works against that?

• LIMITING FACTORS– Two types

• Density-dependent• Density-independent

Density-Dependent

• The growing size of the population eventually affects:– birthrate, death rate – emigration (leaving), competition– abundance/scarcity of food, – disease, parasitism, predation– physical space

Consider the predator/prey relationship:

Eventually…

• In any given ecosystem, a Carrying Capacity (K) is reached:– The maximum average number of organisms

of a given species that can survive in good condition in a particular ecosystem on a long-term basis.

Logistic (restricted) growth

(K)

In reality, the population density line may look like this:

So, what is the carrying capacity in this environment for the hare? The lynx?

Density-Independent

• Some things occur that affect populations, no matter how dense or sparse they may be:– unusual weather, – natural disasters, – seasonal cycles, – human activities

• damming, • clear-cutting

Tsunami…

Tsunami…

Eruptions…Mount St. Helens on May 17, 1980, the day before…

September 10, 1980

For more than nine hours a vigorous plume of ash erupted, eventually reaching 12 to 15 miles (20-25 km) above sea level. The plume moved eastward at an average speed of 60 mph (95 km/hr), with ash reaching Idaho by noon.

The eruption of May 18, 1980 sent volcanic ash, steam, water, and debris to a height of 60,000 feet. The mountain lost 1,300 feet of altitude and about 2/3 of a cubic mile of material stream downward from the center of the plume and the formation and movement of pyroclastic flows down the left flank of the volcano.

Forest Fire…

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”