Visualizing Environmental Science

Summary 155

with mild, moist winters and hot, dry summers; vegetation

is typically small-leafed evergreen shrubs and small trees.

Desert is a biome in which the lack of precipitation limits

plant growth; deserts are found in both temperate and

tropical regions. Savanna is tropical grassland with widely

scattered trees or clumps of trees. Tropical rain forest is a

lush, s pecies-rich forest biome that occurs where the climate

is warm and moist throughout the year.

2

Aquatic Ecosystems 142

1. In aquatic ecosystems, important environmental factors
   include salinity, amount of dissolved oxygen, and availability
   of light for photosynthesis.


2. Freshwater ecosystems include standing-water, flowing-
   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.

3

Population Responses to Changing

Conditions over Time: Evolution 147

1. Evolution is the cumulative genetic changes in populations
   that occur during successive generations.


2. Natural selection is the tendency of better-adapted
   individuals—those with a combination of genetic traits
   best suited to environmental conditions—to survive and
   reproduce, increasing their proportion in the population.
   Natural selection is based on four observations established
   by Charles Darwin: (1) Each species produces more offspring
   than will survive to maturity. (2) Organisms compete with
   one another for the resources needed to survive. (3) The
   individuals in a population exhibit inheritable variation in their
   traits. (4) Individuals with the most favorable combination of
   traits are most likely to survive and reproduce, passing their
   genetic traits to the next generation.

Summary

1

Earth’s Major Biomes 128

1. A biome is a large, relatively distinct terrestrial region with
   characteristic climate, soil, plants, and animals, regardless
   of where it occurs; a biome encompasses many interacting
   ecosystems. Near the poles, temperature is generally the
   overriding climate factor in determining biome distribution,
   whereas in temperate and tropical regions, precipitation is
   more significant.


2. 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. Boreal forest is a region of coniferous
   forest in the Northern Hemisphere, located just south of the
   tundra. Temperate rain forest is a coniferous biome with
   cool weather, dense fog, and high precipitation. Temperate
   deciduous forest is a forest biome that occurs in temperate
   areas where annual precipitation ranges from about 75 cm
   to 126 cm (30–50 in). 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

Average monthly temperature in

°C

Average monthly precipitation in cm

14

12

10

8

6

4

2

0

28

24

20

16

12

8

4

0

–4

Months

JMMJJASONDFA

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