Ecology-Chapter 5- 4.5, 5.1, 5.3: Populations- Terms and Key Questions

Photic Zone
The sunlit region near the surface in which photosynthesis can occur.

Aphotic Zone
Below the photic zone, dark, and photosynthesis cannot occur.

Benthos
Organisms that live on, or in, rocks and sediments on the bottoms of lakes, streams, and oceans.

Plankton
A general term that includes both phytoplankton and zooplankton.

Wetland
An ecosystem in which water either covers the soil or is present at or near the surface for at least part of the year.

Estuary
A special kind of wetland, formed where a river meets the sea. They contain a mixture of fresh water and salt water.

What factors affect life in aquatic ecosystems?
Aquatic organisms are affected primarily by the water’s depth, temperature, flow, and amount of dissolved nutrients.

What are the major categories of freshwater ecosystems?
Freshwater ecosystems can be divided into three main categories: rivers and streams, lakes and ponds, and freshwater wetlands.

Why are estuaries so important?
Estuaries serve as spawning and nursery grounds for many ecologically and commercially important fish and shellfish species.

How do ecologists usually classify marine ecosystems?
Ecologists typically divide the ocean into zones based on depth and distance from shore.

Population Density
The number of individuals per unit area.

Age Structure
The number of males and females of each age a population contains.

Immigration
Individuals move into its range from elsewhere.

Emigration
Individuals move out of a population’s range.

Exponential Growth
The larger a population gets, the faster it grows.

Carrying Capacity
The maximum number of individuals of a particular species that a particular environment can support.

How do ecologists study populations?
Researchers study populations’ geographic range, density and distribution, growth rate, and age structure.

What factors affect population growth?
The factors that can affect population size are the birthrate, death rate, and the rate at which individuals enter or leave the population.

What happens during exponential growth?
Under ideal conditions with unlimited resources, a population will grow exponentially.

What is logistic growth?
Logistic growth occurs when a population’s growth slows and then stops, following a period of exponential growth.

Demography
The scientific study of human populations.

Demographic transition
A dramatic change from high birth and death rates to low birth and death rates.

How has human population size changed over time?
The human population, like populations of other organisms, tends to increase. The rate of that increase has changed dramatically over time.

Why do population growth rates differ among countries?
Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly.