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Environmental Science
A Study of Interrelationships
Eleventh Edition
Enger & Smith
Chapter 6
Kinds of Ecosystems and Communities
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Kinds of Ecosystems and Communities
Outline
 Succession
 Biomes: Major Types of Terrestrial Climax
Communities
 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, longlasting 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
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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: Major Types of
Terrestrial Climax Communities
 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 nonbiological 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
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.
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.
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 50-200cm.
 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.
Temperate Deciduous Forest
 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.
Temperate Deciduous Forest
 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 populations centers of eastern North America
and Europe are in areas that were originally
temperate deciduous forest.
Temperate Deciduous Forest
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.
Taiga, Northern Coniferous Forest,
or Boreal Forest
 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
Taiga, Northern Coniferous Forest,
or Boreal Forest
 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.
Taiga, Northern Coniferous Forest,
or Boreal Forest
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.
 Tundralike 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:
•
•
•
•
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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.
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 nutrientrich.
 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)
Freshwater Ecosystems
 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.
Freshwater Ecosystems
Lake ecosystem
Freshwater Ecosystems
 The productivity of a lake is determined by many
factors.
•
•
•
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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.
Freshwater Ecosystems
 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.
Freshwater Ecosystems
 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.
Freshwater Ecosystems
 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.
Freshwater Ecosystems
 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.