chapter 8.3: Ecosystem Roles, Succession & Human Population Ecology

Pioneer species

Certain plant species that can tolerate environments with a low supply of soil nutrients.

Ecosystem engineers

Species that change the environment in a way that provides a new or improved habitat for other species.

Examples of ecosystem engineers

Beavers, alligators, earthworms, corals, woodpeckers, termites, and prairie dogs.

Beavers

Beavers build dams, which change water flow, water temperature, and provide habitat.

Alligators

Alligators play an important role by building mounds of soil and plant matter for their nests.

Earthworms

Earthworms are detritivores, meaning they consume detritus or leftover bits of organic matter. As they move through soil, they digest organic matter and leave behind ammonium that plants can absorb.

Corals

Corals build structures that provide habitat and safe, calm waters for many kinds of fish and plant species living in shallow oceans.

Role of corals as ecosystem engineers

Corals calm rough waves coming in from the open ocean and grow upward toward the surface of the water, offering plants and animals access to sunlight.

Other ecosystem engineers

Woodpeckers, termites, and prairie dogs provide important habitat or nutrient access to other species in their communities.

Abundance

The total number of organisms in a community.

Richness

The number of different species that make up a community.

Difference between abundance and richness

An anthill has high abundance because it has many individuals but low richness because it contains only one species. A tropical fish tank may have low abundance but high richness because it contains many different species.

Ecological structure

Describes where organisms are physically located across their environment and in relation to one another.

Succession

The process where communities shift and change over time.

Types of plant succession

1. Primary succession 2. Secondary succession.

Primary succession

A type of succession that begins in an area where no soil exists, such as exposed rock.

Secondary succession

A type of succession that occurs in an area where a community existed before but was disturbed.

Stages of succession in plant communities

1. Exposed rock 2. Pioneer community 3. Climax community.

Climax community

The end point of succession for plant communities, whether it is primary or secondary succession.

Disturbances

Events that disrupt the community.

Effects of disturbances

Disturbances can change the structure of plant communities by knocking down trees or removing plants and animals from large parts of an environment.

Disturbance-adapted species

Species that have adapted and evolved to depend on occasional community disturbances.

Example of disturbance-adapted species

Lodgepole pine trees need fire in order to open their pine cones and release seeds.

Resilience

The ability to respond quickly or bounce back from a disturbance.

Demography

The study of human populations.

Demographers

Scientists who study human populations.

Industrial age

The period that allowed the total population to grow exponentially for the first time in human history.

Crude birth rate

The number of babies born in a year per 1,000 people.

Crude death rate

The number of deaths per 1,000 people in a year; sometimes called the crude mortality rate.

Total fertility rate

The estimated number of children born to an average woman in that population over her entire lifetime.

Doubling time

An estimate of the number of years a population needs to double its current size.

Natural increase of a population formula

Subtracting the crude death rate from the crude birth rate.

Emigration

Moving out of a country.

Immigration

Moving into a country.

Total growth rate formula

(Crude births + Immigration) - (Crude deaths + Emigration).

Zero population growth

The number of births and immigrants equals the number of deaths and emigrants.

Replacement level fertility

The fertility level needed to maintain a stable population, usually about two children per childbearing woman, enough to replace parents when they die.

Reasons humans migrate

Humans migrate to follow resources like herds of animals, escape warfare and famine, and seek new resources.

Theory of demographic transition

The theory states that as the economy of a country moves from mostly subsistence-based activities to industrial development, the population will increase and stabilize.

Four stages of demographic transition

1. Stage 1 (Pre-modern) 2. Stage 2 (Industrializing) 3. Stage 3 (Industrial) 4. Stage 4 (Post-industrial).

Stage 1 (Pre-modern)

Population growth is slow or steady with a high birth rate and a high death rate. Total population size is relatively small and life expectancy is short.

Stage 2 (Industrializing)

Population increases exponentially as the birth rate stays high and the death rate declines.

Stage 3 (Industrial)

Population growth slows down as the birth rate drops closer to the death rate. Population growth becomes more stable though at higher total numbers than Stage 1.

Stage 4 (Post-industrial)

The final stage of demographic transition with low birth and death rates.

Demographic trap

A situation where many developing nations are caught in the early stages of the demographic transition model.

IPAT formula

A formula used to calculate the effect of an entire population on its environment.

IPAT formula equation

Impact (I) = Population Size (P) + Affluence (A) + Technology (T).

Population size

The easiest component of the IPAT formula to quantify.

Affluence

Refers to the consumption of goods and services.

Technology

Represents how many resources humans use to create the affluence of their society and how much they damage or degrade the environment in the process.