Chapter 6

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Enger & Smith

Environmental ScienceA Study of Interrelationships

Twelfth Edition

Chapter 6

Kinds of Ecosystems and Communities

Kinds of Ecosystems and Communities

Outline

Succession Biomes Are Determined by Climate Major Aquatic Ecosystems

Succession

Succession is a series of regular, predictable changes in community structure over time.

Activities of organisms change their surroundings and make the environment suitable for other kinds of organisms.

A climax community is a relatively stable, long-lasting community that is the result of succession. The kind of climax community that develops is primarily determined by climate.

Succession

Primary succession begins with a total lack of organisms and bare mineral surfaces or water.

Secondary succession begins with the disturbance of an existing ecosystem.• It is much more commonly observed, and generally

proceeds more rapidly than primary succession.

Primary Succession

Terrestrial primary succession• A pioneer community is a collection of organisms able

to colonize bare rock (e.g., lichens).– Lichens help break down rock and accumulate debris,

helping to form a thin soil layer.– The soil layer begins to support small forms of life.

Primary Succession

Pioneer organisms

Primary Succession

Lichen community replaced by annual plants. Annuals replaced by perennial community. Perennial community replaced by shrubs. Shrubs replaced by shade-intolerant trees. Shade-intolerant trees replaced by shade-tolerant

trees. Stable, complex, climax community eventually

reached.• Each step in the process is known as a successional

(seral) stage, and the sequence of stages is called a sere.

Primary Succession

Primary succession on land

Primary Succession Climax communities show certain characteristics

when compared with successional communities.• Climax communities maintain species diversity for an

extended period.• They contain multiple specialized ecological niches.• They maintain high levels of organism interactions.• Climax communities recycle nutrients while maintaining a

relatively constant biomass. The general trend in succession is toward increasing

complexity and more efficient use of matter and energy.

Primary Succession

Aquatic primary succession• Except for oceans, most aquatic systems are

considered temporary.• All aquatic systems receive inputs of soil particles and

organic matter from surrounding land. • This results in the gradual filling of shallow bodies of

water. – Roots and stems below water accumulate more material.– Establishment of wet soil.

Primary Succession

Primary succession from a pond to a wet meadow.

Secondary Succession Secondary succession occurs when an existing

community is disturbed or destroyed but much of the soil and some of the organisms remain.• Because the soil and nutrients remain, this process can

advance more rapidly than primary succession.• Plants and organisms that survive the disturbance can

grow quickly and reestablish themselves.• Nearby undamaged communities can serve as sources

of seeds and animals.• The new climax community is likely to resemble the

destroyed community.

Secondary Succession

Secondary succession on land

Modern Concepts of Succession and Climax

As settlers changed “original” ecosystems to agriculture, climax communities were destroyed.• Many farms were abandoned, and land began to

return to its “original” condition.

Ecologists began to recognize there was not a fixed, pre-determined community for each part of the world.• The only thing differentiating a climax community from

any other successional community is its time scale.

Biomes Are Determined By Climate

Biomes are terrestrial climax communities with wide geographic distributions. • When different communities within a biome are

examined, they will show differences in the exact species present, but the general structure of the ecosystem and the kinds of niches and habitats present are similar throughout.

Biomes: Major Types of Terrestrial Climax Communities

Two primary non-biological factors have major impacts on the kinds of climax communities that develop in any part of the world. • Temperature• Patterns of precipitation

Biomes: Major Types of Terrestrial Climax Communities

Biomes of the world

The Effect of Elevation on Climate and Vegetation

The distribution of terrestrial ecosystems is primarily related to precipitation and temperature.• Temperature is warmest near the equator and cooler

toward the poles.• As altitude increases, average temperature

decreases.• Moving from sea level to mountain tops, it is possible

to pass through a series of biomes similar to what would be encountered moving from the equator to the North Pole.

The Effect of Elevation on Climate and Vegetation

Relationship between height above sea level, latitude, and vegetation.

Desert Deserts are areas that average less than 25 cm

annual precipitation.• Unevenly distributed throughout the year.

They are likely to be windy. They experience large daily temperature

fluctuations. There is infrequent cloud cover. There are many species, but they are present in

low numbers. Many species exhibit specialized adaptations to

climate, such as the ability to conserve water.

Desert

Human impact on deserts:• Humans have historically had little impact on deserts.• Modern technology allows for the transport of water to

the desert.• This has resulted in the development of cities in some

desert areas and some limited agriculture as a result of irrigation.

Desert

Temperate Grassland Temperate grasslands, also known as prairies or

steppes, are widely distributed over temperate parts of the world.

They typically receive 25-75 cm of annual precipitation.

Fire is an important force in preventing the invasion of trees and releasing nutrients from dead plants to the soil.

The primary consumers are large herds of migratory grazing mammals. Many insect species are also common.

Temperate Grassland

Human impact on grassland:• Most of the moist grasslands of the world have been

converted to agriculture.• Most of the drier grasslands have been converted to

the raising of domesticated grazers like sheep, cattle, and goats.

• Little undisturbed grassland is left, and those fragments that remain need to be preserved as refuges for the grassland species that once occupied huge portions of the globe.

Temperate Grassland

Savanna

Savannas are found in tropical parts of Africa, South America, and Australia.

They are characterized by extensive grasslands spotted with occasional patches of trees.

They receive 50-150 cm annual precipitation, unevenly distributed throughout year.

Rainfall patterns produce a seasonally structured ecosystem.

Fire is a common feature. Many trees are involved in nitrogen fixation.

Savanna

Human impact:• Savannas have been heavily impacted by agriculture.• Because of long periods of drought, raising crops is

difficult without irrigation.• Some areas support nomadic herding.• In Africa, there are extensive areas set aside as parks

and natural areas and ecotourism is an important source of income.

Savanna

Mediterranean Shrublands (Chaparral)

Mediterranean shrublands are located near oceans and are dominated by shrubby plants.

Their climate features wet, cool winters and hot, dry summers.

They receive 40-100 cm annual precipitation. This biome is typical of the Mediterranean coast,

coastal southern California, as well as parts of Africa, Chile, and Australia.

Vegetation is dominated by woody shrubs adapted to hot, dry summers.

Fire is a common feature.

Mediterranean Shrublands (Chaparral)

Human impact:• Very little undisturbed Mediterranean shrubland still

exists.• Agriculture is common, often with the aid of irrigation.• Major cities are located in this biome.

Mediterranean Shrubland (Chaparral)

Tropical Dry Forest

The tropical dry forest is another biome heavily influenced by seasonal rainfall. These biomes are found in Central and South America, Australia, Africa, and Asia.

Annual precipitation ranges from 50-200 cm. Many exhibit a monsoon climate with highly

seasonal rainfall. Plants have developed special adaptations to

survive drought.

Tropical Dry Forest

Human impact:• Many of these forests occur in areas of very high

human population.• Harvesting of wood for fuel and building materials has

heavily affected these forests.• Many of the forests have been converted to farming

or the grazing of animals.

Tropical Dry Forest

Tropical Rainforest

Tropical rainforests are located near the equator where temperature is relatively warm and constant.

Most areas receive 200+ cm annual rainfall, and some receive in excess of 500 cm.

The soil allows high levels of leaching, thus most nutrients are tied up in biomass.

Tropical rainforests have a multi-layered canopy.• Epiphytic plants

They also host a very high diversity of species.

Tropical Rainforest

Human impact• Tropical rainforests are under intense pressure from

logging and agriculture.• Many of the countries where tropical rainforests occur

are poor and seek to obtain jobs and money by exploiting this resource.

• Forestry can be a sustainable activity, but in many cases it is not.

Tropical Rainforest

Temperate Deciduous Forest

Temperate deciduous forests are typical of the eastern half of the United States, south-central and southeastern Canada, southern Africa, and many parts of Europe and Asia.

These areas receive 75-100 cm annual precipitation, evenly distributed throughout the year.

Trees typically lose their leaves during the winter and replace them the following spring.


This biome features mild winters and a long growing season (6 months).

In contrast to tropical rainforests, where individuals of a tree species are scattered throughout the forest, temperate deciduous forests have many fewer species; some may have two or three dominant tree species.


Human impact:• Most of the temperate deciduous forests have been

heavily affected by human activity.• Much has been cleared for farming.• Much of the current forest is subjected to periodic

logging.• Major population centers of eastern North America

and Europe are in areas that were originally temperate deciduous forest.

Temperate Rainforest

Temperate rainforests exist in coastal areas of northern California, Oregon, Washington, British Columbia, southern Alaska, New Zealand, and the southwest coast of Chile.

West winds bring moist air to the coast. The air is forced over the mountains, cools, and rain or snow is produced.


These forests receive at least 130 cm of rain a year, many receive 300 cm or more.

The cool climate slows evaporation, things are generally damp.

Fertile soil, mild temperatures, and water result in a lush growth of plants.


Sitka spruce, Douglas fir, and western hemlock are typical evergreen coniferous trees.

Old growth forests have trees 800 years old. Deciduous alder, maple, and cotton wood occur

in open areas with enough light. All trees are covered with mosses, ferns, and

other plants that grow on the surface of trees. Dead trees fall to the ground and rot, providing a

site for new tree growth. Dead trees are called nurse trees.


Insects, as well as insect and fruit eating birds such as woodpeckers, chickadees, juncos, and warblers are common.

Slugs are common on the forest floor. Elk, black tail deer, bears, beavers, and owls are

common. Several species of salmon migrate seasonally

up the streams and rivers to spawn.


Human Impact• Because of the rich resource of trees, at least half of

the original temperate rainforest has been logged.• Many remaining forests are scheduled to be logged.• Some patches have been protected because they are

home to endangered northern spotted owls and the marbled murrelet, a seabird.

Taiga, Northern Coniferous Forest, or Boreal Forest

Throughout the southern half of Canada, parts of northern Europe, and much of Russia, there is an evergreen coniferous forest known as the taiga, northern coniferous forest, or boreal forest.

This biome receives 25-100 cm precipitation annually.


It features short, cool summers and long winters with abundant snowfall.

The climate is humid because of the great deal of spring snowmelt; low temperatures reduce evaporation.

The trees are adapted to winter conditions:• Needle-shaped leaves prevent water loss.• Flexible branches


Human impact:• Human impact is less severe than with many other

biomes because population density is low.• Logging is common.• Herding of reindeer occurs in northern Scandinavia.

Tundra

North of the taiga is the tundra, an extremely cold region that lacks trees and has a permanently frozen subsurface soil.

The permanently frozen soil layer is called permafrost.

The tundra receives less than 25 cm annual precipitation.

Tundra

This biome has a short, wet summer. Waterlogged soils and shallow ponds and pools

are present in spring and summer. Plants are usually less than 20 cm tall. Tundra like communities known as alpine

tundra are found on mountaintops throughout the world.

Tundra

Human impact:• Few people live in this region.• Local native people often rely on subsistence hunting

for food.• Because of the very short growing season, damage to

this kind of ecosystem is slow to heal, so the land must be handled with great care.

Tundra

Major Aquatic Ecosystems

Aquatic ecosystems are shaped by key environmental factors:• The ability of the sun’s rays to penetrate the water• Depth of the water• The nature of the bottom substrate• The water temperature• The amount of dissolved salts

Major Aquatic Ecosystems

Aquatic ecosystems with little dissolved salt are called freshwater ecosystems.

Marine ecosystems have a high dissolved salt content.

Marine Ecosystems

The pelagic region is the open sea above the sea floor.

The euphotic zone is the upper layer of ocean where the sun’s rays penetrate.

Phytoplankton are microscopic plants floating in the ocean (perform photosynthesis).

Zooplankton are microscopic animals of many kinds that feed on phytoplankton.

Productive aquatic ecosystems contain a plentiful supply of essential nutrients.

Marine Ecosystems

Marine Ecosystems

Benthic marine ecosystems• Benthic organisms, attached or non-attached, live

on the ocean bottom.• Substrate and temperature are very important

characteristics in determining benthic community development.

• An abyssal ecosystem is a benthic ecosystem that occurs at great depths in the ocean.

– There is no light to support photosynthesis.– Animals are scavengers; many are small and generate

light for finding or attracting food.

Marine Ecosystems

The substrate is important in determining the kind of benthic community that develops.• Large plants and algae cannot become established in

shifting sand substrate.• Mud usually contains little oxygen but is a good

substrate for some kinds of rooted plants. • Rocky surfaces in the ocean provide a good substrate

for many kinds of algae.– A profuse growth of algae is associated with a large

variety of animals.

Marine Ecosystems

Coral reef ecosystems are composed primarily of coral animals that build cup-shaped external skeletons.

Corals contain single-celled algae and carry on photosynthesis.

They require warm water, thus are found only near the equator.

Most require clear, shallow water with ample sunlight penetration.

Marine Ecosystems

Coral reef.

Coral reef development

Marine Ecosystems

Mangrove swamp ecosystems are tropical forest ecosystems that occupy shallow water near the shore and adjacent land.

Their trees tolerate high salt content and excrete salt from their leaves.

They have extensively developed roots that can extend above water.

The trees trap sediment in shallow areas, which results in the development of terrestrial ecosystems.

Marine Ecosystems

Mangrove swamp

Marine Ecosystems

Estuaries consist of shallow, partially enclosed areas where freshwater enters the ocean.

Organisms are specially adapted to varying levels of salinity from tides and river flow.

Estuaries are extremely productive ecosystems because areas are shallow, warm, and nutrient-rich.

These areas are important nursery sites for fish and crustaceans.

Marine Ecosystems

Human impact:• Oceans cover about 70% of the Earth’s surface.• Overfishing has destroyed many of the traditional

fishing industries of the world.• Fish farming results in the addition of nutrients and

has caused diseases to spread from farmed fish to wild fish.

• Estuaries are affected by fertilizers, animal wastes, and pesticides that flow down rivers from farmland.

• Use of the oceans as transportation results in oil pollution and trash floating onto the shore.

Freshwater Ecosystems

Freshwater ecosystems may be divided into two broad categories:• Stationary water (lakes, ponds, and reservoirs)• Running water (streams and rivers)


Lakes and Ponds• The littoral zone of a lake is the region of a lake with

rooted vegetation.– Emergent plants have leaves that float on, or protrude

above, the water’s surface.– Submerged plants stay submerged below the water’s

surface.• The limnetic zone is the region of lake with no rooted

vegetation.


Lake ecosystem


The productivity of a lake is determined by many factors.• Cold temperature reduces rate of photosynthesis.• Shallow water allows more photosynthesis.• Erosion from land increases nutrient levels.• Dissolved oxygen, input via wave action and

photosynthesis from aquatic plants, determines the kinds of organisms that can inhabit the lake.


Lakes and Ponds• Oligotrophic lakes are deep, cold, nutrient-poor.• Eutrophic lakes are shallow, warm, nutrient-rich.• Biochemical oxygen demand (BOD) is the amount

of oxygen used by decomposers to break down a specific amount of organic matter.


Streams and Rivers• Even though most streams are shallow, it is difficult

for most photosynthetic organisms to accumulate nutrients necessary for growth.

Most clear streams are not very productive.– Most debris is input from terrestrial sources.

• Periphyton is the collection of algae, animals, and fungi attached to rocks and other objects on the bottom.


Streams and Rivers• Swamps are wetlands containing trees able to live in

environments that are permanently flooded, or flooded most of the year.

• Marshes are wetlands dominated by grasses and reeds.

• Many swamps and marshes are successional states that eventually become totally terrestrial communities.


Human impact:• Most freshwater ecosystems have been heavily

affected by human activity.• Any activity that takes place on land ultimately affects

freshwater because of runoff from the land.• Agricultural runoff, sewage, sediment, and trash all

find their way into streams and lakes.

Summary

Ecosystems change as one kind of organism replaces another in a process called succession.

The climax community is a relatively stable stage. Major regional terrestrial climax communities are

called biomes. Primary determiners of the kinds of biomes that

develop are temperature and yearly rainfall distribution.

Summary

Major biomes are desert, grassland, savanna, Mediterranean shrublands, tropical dry forest, tropical rainforest, temperate deciduous forest, taiga, and tundra.

Aquatic ecosystems can be divided into marine (saltwater) and freshwater ecosystems.

The shore substrate determines the mixture of organisms that can live there.

Lakes have a structure similar to that of the ocean, but with different species.

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