Chapter 5: Principles of Ecology: Biomes and Aquatic Life
Zones
5.1 Weather and Climate: An Introduction
Weather refers to daily conditions such as rainfall and temperature. Climate is the
average weather over a long period. Climate determines the plant and animal life of a
region.
Major Factors that Determine Weather and Climate
The Earth is unequally heated, which creates three major climatic zones: tropical,
temperate, and polar. Air tends to flow from the equator to the poles.
The Coriolis Effect and Topography
Weather within the major climatic zones is altered by wind flow patterns, which are
profoundly influenced by the spin of the Earth. Weather is also affected by topography,
especially mountain ranges.
Ocean Currents
Warm water from the equator flows toward the poles, warming landmasses near which it
passes. As it flows northward, it cools. Cool water eventually sinks, and flows back
toward the equator, creating a huge global circulation pattern.
5.2 The Biomes
The Earth’s surface can be divided into biologically distinct zones called biomes, each
with a distinct climate and unique assemblage of plants and animals. Nevertheless,
regional variations occur within each biome.
The Tundra
The Arctic tundra, the northernmost biome, is characterized by the harshest climate.
Because the growing season is so short, life on the Arctic tundra is extremely vulnerable
to human actions.
The Taiga
The taiga is a band of coniferous trees spreading across the northern continents just south
of the tundra. Its climate is milder and its life forms are more diverse than those of the
tundra. The taiga supports many large populations of wild animals, but the forests of this
region are under heavy pressure to meet rising demands for wood and wood products.
The Temperate Deciduous Forest Biome
The temperate deciduous forest biome occurs in regions with abundant rainfall and long
growing seasons. This biome has been heavily settled by humans and dramatically
altered.
The Grassland Biome
The grassland biome occurs in regions of intermediate precipitation – enough to support
grasses but not enough to support trees. On most continents, the rich soil of the biome has
been heavily exploited by humans for agriculture.
The Desert Biome
The desert biome is characterized by dry, hot conditions, but often abounds with plants
and animals adapted to the heat and lack of moisture. Unfortunately, deserts of the world
are expanding as a result of human activities such as overgrazing livestock and the
production of greenhouse gases.
The Tropical Rain Forest Biome
The tropical rain forest is the richest and most diverse biome on Earth because of its
abundant rainfall and warm climate. About half of the world’s rain forest has been
destroyed; huge tracts could be eliminated in the near future, with devastating effects on
climate and plants and wildlife if current trends continue.
Altitudinal Biomes
Because climate varies with altitude, the distribution and abundance of life also change.
5.3 Aquatic Life Zones
Aquatic systems are divided into distinct regions, known as aquatic life zones, which may
be freshwater or saltwater. The abundance of life is determined by energy and nutrient
levels. Phytoplankton form the base of aquatic food chains.
Freshwater Lakes
Lakes are divided into four regions – the littoral zone, the limnetic zone, the profundal
zone, and the benthic zone – with very different conditions and, consequently, very
different life forms.
Rivers and Streams
Rivers and streams are complex ecosystems that rely more on agitation for oxygenation
of their waters than lakes do. Many nutrients in streams that support aquatic life come
from neighboring terrestrial ecosystems. The quality of water in a stream is profoundly
influenced by activities in the watershed.
Protecting Freshwater Ecosystems
Like lakes and ponds, streams are self-purging, but are extremely vulnerable to pollution
if sources exceed the capacity to self-cleanse.
Saltwater Life Zones
The oceans cover 70% of the Earth’s surface. The most important factors in the ocean
ecosystems are energy and nutrients.
The Coastal Life Zones
The coastlines are highly productive waters characterized by abundant sunlight and a rich
supply of nutrients, both of which contribute to an abundance of life forms.
Estuaries are nutrient-rich zones at the mouths of rivers, often associated with coastal
wetlands, together forming the estuarine zone. The estuarine zone is highly productive
and of great value to humans and other species. Human activities severely threaten this
important biological asset.
The shorelines of the world are rocky or sandy regions that are home to a surprising
number of organisms adapted to the tides and the turbulence created by wave action.
Coral reefs are the aquatic equivalent of the tropical rain forests and are being rapidly
destroyed.
The Marine Ecosystem
The marine ecosystem consists of four ecologically distinct life zones, similar to those
found in lakes.