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Life Science: Session 8


What is an ecosystem?

An ecosystem is defined as a self-sustaining community of organisms living in a physical environment. Part of what sustains an ecosystem is the constant interchange of matter between its living and physical components. This is the focus of Session 8: Material Cycles in Ecosystems.

Coniferous forest, a North American

Ecosystems can be vast, like the tropical rainforests that occur along the equator. They can also be very small, like the ecosystem inside the leaves of pitcher plants discussed by Dr. Aaron Ellison in the video.

An ecosystem is shaped by physical factors such as rainfall, temperature, humidity, sunlight, and soil type. The interaction of these factors determines the types of organisms that live there. Scientists classify larger terrestrial ecosystems into several major types that occur over wide geographical areas. They are recognized by their distinctive climates and are given their names from the dominant plant life.

The ecosystems listed below are found in North America, including Hawaii. Which ecosystem do you live in?

Ecosystem type Average Precipitation Average Temperature Dominant Plant Life
Tropical rain forests 250+ cm
(100+ in.)
20 - 28°C
(68 - 82°F)
Broad-leaved trees; dense undergrowth; more species than any other ecosystem
Deserts 2 - 20 cm
(1 – 8 in.)
10 - 32°C
(50 - 90°F)
Cactus; shrubs with thick leaves that store water
Temperate grasslands 10 – 60 cm
(4 – 24 in.)
8 - 20°C
(46 - 68°F)
Tall, dense grasses in rich soil; few trees
Deciduous forests 75 – 250 cm
(30 – 100 in.)
5 - 20°C
(41 - 68°F)
Broad-leaved trees that drop their leaves in winter
Coniferous forests 20 – 60 cm
(8 – 24 in.)
-5 - 5°C
(23 - 41°F)
Trees with needles and cones
Tundra 25 – 50 cm
(10 – 20 in.)
-15 - -5°C
(5 - 23°F)
Mosses and lichens; some dwarfed trees; permanently frozen ground
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