Biology 12

434 MHR • Unit 5 Population Dynamics

example, the tree in Figure 13.8 could be

considered an entire ecosystem. It contains a

community of living things and abiotic components

such as air, water, and nutrients. This ecosystem

interacts with, and is part of, a larger ecosystem

containing the community of organisms living in

the small wooded area. Both of these ecosystems

are part of a larger ecosystem, which extends

beyond the boundaries of the photograph.

Figure 13.8The ecosystem in this tree is part of the larger

ecosystem that comprises ZooWoods, located outside the

Ramsay Wright Zoological Laboratories in downtown

Toronto. Many of the plants in ZooWoods were salvaged

from ecosystems that were destroyed as a result of

development in Toronto’s suburban communities.

All of these ecosystems and their interactions

make up the biosphere(as shown in Figure 13.1 on

page 430). The biosphere can be thought of as the

largest possible ecosystem. It includes all portions

of Earth inhabitable by some type of life (that is,

all the land surfaces and bodies of water on the

planet) and extends several kilometres into the

atmosphere and into the soil under Earth’s crust.

All living things that inhabit these environments

are part of the biosphere.

A Species’ Place in the Biosphere

The various types of organisms that live on Earth

are not scattered randomly — each has its own

“place” in the biosphere. The large-scale patterns

we see in the distribution of species are ultimately

the result of unequal heating of Earth’s atmosphere,

land masses, and oceans (see Figure 13.9).

This unequal heating gives rise to Earth’s major

climate zones, from the tropics near the equator

through the temperate zones to the cold regions

near the north and south poles. In addition, unequal

heating sets up conditions that produce global air

and water movements (trade winds and ocean

currents) that interact with physical features

(mountains, islands, and lakes) to produce the

various patterns of rainfall we experience. The

result is that some areas of the world are quite

dry, while others are very wet.

Figure 13.9Earth is roughly spherical, so the solar energy

that arrives near the poles is spread out over a greater area

(and is therefore less intense at any given point) than the

solar energy that arrives near the equator. The spreading

out of solar energy results in the differential heating of the

equator and the poles.

The pattern of rainfall influences the climate

and the type of soils found in the different regions.

These factors together determine the type and

abundance of plants and other photosynthetic

organisms that can survive. This, in turn,

determines the size of the populations and the

variety of species that will inhabit the area. It is

possible to identify some very general types of

large ecosystems, called biomes, or groups of

ecosystems found in specific regions on Earth.

These large regions (shown in Figure 13.10) are

characterized by a particular combination of

physical conditions and communities of organisms.

Habitat and Range

The division of the world into large biomes is

somewhat arbitrary. Each type of biome blends into

the adjacent one gradually, making it difficult to

identify exactly where the boundaries of the major

biomes are located.

http://www.mcgrawhill.ca/links/biology12

Biosphere 2 provides a variety of interesting experiences for

students of all ages. University students can enroll in Earth

Semester, a four-month course during which they participate

in Biosphere 2 research projects, take field trips to other

environments in the surrounding area, and learn about the

interactions between Earth and its inhabitants. If you want to

learn more about these courses or the research going on at

Biosphere 2, go to the web site above, and click on Web Links.

WEB LINK

equator

North

Pole

South

Pole

equator