Summary ✓ THE PLANNER

1 Factors That Shape Biomes 128

1. A biome is a large, relatively distinct terrestrial region with

amount of precipitation. Temperate grassland is grassland
with hot summers, cold winters, and less rainfall than is found
in the temperate deciduous forest biome. Chaparral is a biome
with mild, moist winters and hot, dry summers; vegetation is
characteristic climate, soil, plants, and animals, regardless of where
it occurs; a biome encompasses many interacting ecosystems. typically small-leafed evergreen shrubs and small trees. Desert
Near the poles, temperature is generally the overriding climate is a biome in which the lack of precipitation limits plant growth;
factor in determining biome distribution, whereas in temperate deserts are found in both temperate and tropical regions.
and tropical regions, precipitation is more significant. Savanna is tropical grassland with widely scattered trees or
clumps of trees. Tropical rain forest is a lush, species-rich
forest biome that occurs where the climate is warm and moist
throughout the year.

2 Describing Earth’s Major Biomes 132

1. Tundra is the treeless biome in the far north that consists of

boggy plains covered by lichens and small plants such as mosses;
it has harsh, very cold winters and extremely short summers.
3 Aquatic Ecosystems 142

1. In aquatic ecosystems, important environmental factors include

Boreal forest is a region of coniferous forest in the Northern salinity, amount of dissolved oxygen, and availability of light for
Hemisphere, located just south of the tundra. Temperate rain photosynthesis.
forest is a coniferous biome with cool weather, dense fog,
and high precipitation. Temperate deciduous forest is a 2. Freshwater ecosystems include standing-water, flowing-
forest biome that occurs in temperate areas with a moderate water, and freshwater wetlands. A standing-water ecosystem is
a body of fresh water surrounded by land
and whose water does not flow, such as a lake or pond. A
flowing-water ecosystem is a freshwater ecosystem such as a
river or stream in which the water flows in a current. Freshwater
wetlands are marshes and swamps—lands that are covered by
shallow fresh water at least part of the year; wetlands have a
characteristic soil and water-tolerant vegetation. An estuary is
a coastal body of water, partly surrounded by land, with access
to the open ocean and a large supply of fresh water from a river.
Water in an estuary is brackish rather than truly fresh. Temperate
estuaries usually contain salt marshes, whereas tropical estuaries
are lined with mangrove forests.

4 Population Responses to Changing

Average monthly temperature in °C

28 Conditions over Time: Evolution 147

24
20
Average monthly precipitation in cm

16 1. Evolution is the cumulative genetic changes in populations that

12 occur during successive generations.
8
4 2. Natural selection is the tendency of better-adapted
0 individuals—those with a combination of genetic traits best
–4
14 suited to environmental conditions—to survive and reproduce,
12 increasing their proportion in the population. Natural selection
10 is based on four observations established by Charles Darwin:
8 (1) Each species produces more offspring than will survive
6
4 to maturity. (2) Organisms compete with one another for the
2 resources needed to survive. (3) The individuals in a population
0 exhibit heritable variation in their traits. (4) Individuals with the
J FMA MJ J A SOND
most favorable combination of traits are most likely to survive
Months
and reproduce, passing their genetic traits to the next generation.

Summary 155

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