Transcript Climax communities

Environmental Science
A Study of Interrelationships
Eleventh Edition
Enger & Smith
Chapter 6
Kinds of Ecosystems and Communities
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Kinds of Ecosystems and Communities
Outline
 Succession
 Biomes: Major Types of Terrestrial Climax
Communities
 Major Aquatic Ecosystems
Succession
 Ecosystems are dynamic, changing units, plants
grow & die, animals feed on plants, and
decomposers recycle dead materials & chemical
elements that make up the biotic portion of any
ecosystem.
 Abiotic factors also affect kind of community that
will be established.
 Because of interdependency between organisms in
ecosystem, any change in community affects many
organisms w/in it.
 Certain conditions are key elements to the kinds
of organisms in an ecosystem because each
organism need specific requirement to survive.
 Over time, we can see trends in the way
structure of community has changed
 Climate is one factor that affects kind of
community.
 Result of climate change is a relatively longlasting, stable combination of species that is
self-perpetuating.
Succession
 Communities proceed through Succession: 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.
• Process of succession is not predictable but to
understand this process it is helpful to look at
general models before looking at the exceptions.
• In traditional view, climate is the primary
influence on establishment of climax community.
• Whenever new species arrive, they compete w
original one which may be replaced or become
less in numbers.
• Several factors such as climate, seed available,
frequent disturbances and invasion of other
organisms, determine pace & direction of
succession.
Succession
 Ecologists have traditionally recognized two kinds of
succession.
 Primary Succession - Begins with total lack of
organisms on bare mineral surfaces or water.
 This can happen when volcanic activity cause lava to
flow, glaciers scrape away the organisms & soil
 Primary succession takes a long time to established
because of lack of soil & nutrients
 Secondary Succession - Begins with disturbance of
an existing ecosystem. ex: fire, flood, human activities,
can disturb/destroy a community, but since some soil,
seeds or roots are available for plants to grow and to
establish
• Much more commonly observed, and generally proceeds more
rapidly.
Primary Succession
 Primary succession can take place on rock, sand,
standing water
 Rate & kind of succession depends on:
• kind of substrate (rock, sand, clay; affects kind of soil will
develop),
• kinds of spores, seeds determine kinds of species
available,
• kind of climate determine specie that will survive,
• rate of growth determine rate of organic matter
accumulation in soil.
• All these affect amount of water available for growth.
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.
 Bare rock or sand: no soil, T change drastically, little
moisture, no shelter from wind, few nutrients, few places
for organism to attach.
 Still wind brings spores or other small organisms and PC
is established.
 Lichens first kind of organism to establish on bare rock.
They are mutualistic relationship between algae/bacteria
(photosynthesis) & fungi (attach to surface & retain
water)
Primary Succession
Pioneer organisms
Primary Succession
 Lichen community replaced by annual plants which are
taller.
 Annuals will be replaced by perennial community.
 Perennial community replaced by shrubs.
 Shrubs replaced by shade intolerant trees.
 Shade intolerant trees replaced by shade tolerant trees.
 Eventually Stable, long lasting, complex climax community
often reached.
• Each step in the process is known as a Successional (seral)
Stage. The entire sequence of stages is called 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
 The principal concepts of land succession can
be applied to aquatic ecosystem.
 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.
– Establishment of wet soil encourages growth of
grass & other plants
– This successional step is called: wet meadow,
which as became drier, sets stage for terrestrial
succession & establishing climax community
– In many northern ponds & lakes, sphagnum
moss forms thick, floating mats that allow
establishment of certain plants.
– The roots of those plants bind mat together and
establish a floating bog which may contain
small trees & shrubs and many smaller
flowering plants that can tolerate wet soil.
Secondary Succession
 Same processes & activities drive both primary & 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.
• Tends to be more rapid.
Secondary Succession
Secondary succession on land
Modern Concepts of Succession and Climax
 Discussion of nature of succession & climax communities
was oversimplification of true nature of process.
 Some historical perspective will help to clarify how
ecologists have changed their concept of successional
changes.
 When explorers arrived at new land, they saw huge land
dominated by specific types of communities: from
hardwood forests in east, evergreen forests in N,
grasslands in central N America, & deserts in southwest.
 These regional communities are consider steady
state/normal situation for those areas.
 Ecologists thought of those ecosystems as the end point
or climax of a long journey, beginning w/ formation of soil
and its colonization by variety of plants & other
organisms.
 As settlers changed “original” ecosystems to agriculture,
climax communities were destroyed.
• Many farms were abandoned, and land began to return to
its “original” condition. Often this secondary succession
resembled those that been destroyed,
• But in most cases they contained fewer species & in some
cases were totally different.
• These new stable communities were also called climax
community but were not same as original ones.
• Additionally introduction of new species from Europe &
other parts changed the mix of organisms that might
colonize an area.
• Some became well established
• Today some communities r dominated by those introduced
species
 Diseases also changed the nature of climax community:
Chestnut blight & Dutch elm disease destroyed many of
tree species that were dominant at one point in certain
plant communities.
 Ecologists began to recognize there was not a fixed, predetermined community for each part of the world.
• The only thing differentiating a climax community from any other
successional community is its time scale.
• Today C.C is still used to talk about a stable stage following a
period of change but ecologists no longer believe land will
eventually return to a preordained climax condition.
 Ecologists have recognized many factors other than
climate affect type of CC that develop; ex availability of
seeds to colonize area can cause development of two
different communities in 2 areas w similar climate and
soil
• Human activities (farming) have changed
nature of succession process.
• Frequent logging, suppression of fire,
changing amount of water present, draining
area, irrigation and flooding all have changed
type of communities in an area.
 We should recognize that there is an
identifiable, predictable pattern of change
during succession and that later stages in
succession are more stable and longer
lasting than earlier ones.
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: tropical areas: warm,
unchanging T, while poles: long winter, short
summers, others evenly cold and warm
– Precipitation: total amt/yr, form of
precipitation, seasonal distribution
– Also other factors such as periodic fire, wind,
soil type & current organisms
Biomes: Major Types of
Terrestrial Climax Communities
Biomes are named after major typed of vegetation, but each includes a
specialized group of animals adapted to plant & climate
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.
Desert
 Deserts are areas that average less than 25 cm annual
precipitation.
• Unevenly distributed throughout the year, when and how
precipitation arrive is very different.
 Some get moisture as snow/rain in winter, others as
thunderstorm in frequent intervals (not sink)
 High evaporation rate: growth when water available
 Not always hot & dry (places that rain is low but T not high):
NW USA can be extremely cold in winter & relatively cool
summers
 Large daily temperature fluctuations.
 Low moisture, no cloud to block out sun & soil surface & air
above it very hot in day, after sun set, no insulating layer of
clouds to allow heat E be reradiated from earth so area
cools off rapidly
 Likely to be windy.
 Infrequent cloud cover.
 Many species, but low numbers. (great distance
plants)
 Most species exhibit specialized adaptations to
climate.
• Water Conservation (very small leaves, storing water
in spongy body or roots, having parts or seeds that r
dormant until rains & then grow rapidly, reproduce
and die. Many r spiny)
• Ex plants cacti, small bushes, short grass
• Animals r small, inactive, live w small amt of water,
skin resist water lost, efficient kidney
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.
 Has windy, hot summers, cold to mild winters
 Grass makes up 60-90% of vegetation, are close to each
other & their roots form a network that binds the soil
together
• Rainfall sporadic enough to cause droughts.
 Historically evolved with large herds of migratory
grazing mammals such as bison, wild horses,
sheep, cattle
• They Supply fertilizer and discourage invasion by woody
species.
• Also various kinds of insects such as grass hoper, flies,
birds, reptiles,
• Most land has been converted to agriculture, and drier
parts used for domesticated grazers
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. Plants & animals
reproductive activates coincide w/ rain.
 Fire is a common feature. Grass, drought resistant
trees & trees that resist fire are common
 Many trees involved in nitrogen fixation & provide
shade & nesting site
 Grazers predominant, wallabies (Australia), zebras,
elephants (Africa)
 Many kinds of rodents, birds, insects, & reptiles are
associated w/ this biome
 Mound-building termites common
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.
 Plants are dormant in summer
 Fire is a common feature. Shrubs are adapted to withstand
occasional fire
 Kinds of animals vary in different parts of world, many kinds of
insects, reptiles, birds, mammals
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. several months of heavy rain
followed by extreme dry period
 Plants have developed special adaptations to
survive drought.
– Drought resistant plants. Loose leaf in dry season
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.
 Trees form extensive root network associated w/
fungi to capture nutrients
 Multi-layered canopy (forms a solid wall of leaves bet
sun & forest floor) & vertical stratification.
• There are many kinds of Epiphytic plants (live on surface
of others) bec of rain bringing new nutrients
 Very high species diversity.
 Many understory species r veins attached
to tree & grow toward sun
 Trees also serve as a surface for the
growth of ferns, mosses, & orchids
 Has greatest diversity, Large variety of
plants & animals & many communicate by
making noise bec of low light
 Lots of insects, ants, termites, moths,
butterflies, beetles, climbing mammals,
tree frogs, nectar and fruit feeding birds &
mammals
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.
Forest floor
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.
 Winters are very harsh and can last as long as 6 months
 Soil freezes in winter
 (Conifers such as spruces, firs, & larches) Trees adapted
to winter conditions: (winters r dry)
• Needle-shaped leaves prevent water loss.
• Flexible branches bent under load of snow
• Most inhabitant r temporarily active in summer
• Mostly migratory birds
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
 Found in regions just below ice caps of Arctic,
extending to N America, Europe, Siberia in Asia,
much of Alaska & ½ Canada: lacks trees
 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.
 Because permafrost does not let the water sink
into the soil, Waterlogged soils and shallow
ponds and pools are present in spring and
summer.
 Plants are usually less than 20 cm tall and grow
after snow melts.
 Tundralike communities known as alpine tundra
are found on mountaintops throughout the world.
Tundra*
 Many birds migrate here in spring, where
they mate, raise their young in summer
before migrate south in fall.
 No reptiles/amphibians
 Because very short growing season, any
damage to ecosystem take long time to heal
 Vegetation mostly mosses, sedges, lichens,
& few trees
 Permanent resident birds r ptarmigan and
snowy owl
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
 Terrestrial biomes r determined by the amt and
kind of precipitation & by T, soil type, & wind.
 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
 In open ocean, many organisms float or swim actively
 Organisms that r not attached to the bottom r called
pelagic organisms & the ecosystem they r a part of is
Pelagic ecosystem.
 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, located at greater depth but
migrate upward at night and feed on large popn of
phytoplankton.
 Zooplankton r eaten by larger animals such
fish & shrimps which r eaten by larger fish.
 Kind & amnt of dissolved material especially
inorganic matter such as P, N, C in water
major factor affecting marine community
• Productive aquatic ecosystems contain a plentiful
supply of essential nutrients.
Marine Ecosystems
All photosynthetic activity occurs in shallow water (euphoric zone) by attached algae or
phytoplankton in upper level, consumers r pelagic organisms or benthic organisms living at
the bottom
• Freshwater ecosystems include
streams, rivers, lakes, ponds, and
wetlands.
• Saltwater ecosystems include
estuaries, seashores, coral reefs, a
few inland lakes, and the deep ocean.
wetland
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
 T also important factor in establishment of kind of
community
 Some communities such as coral reefs or mangrove
swaps r found only in areas with warm water
 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.
–Skeletons of the corals provide a
surface for many other animals to
live, some feed directly on corals
while other feed on small plankton
and bits of algae, many fish,
crustaceans, sponges, clams and
snails members of coral reef
ecosystem
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.
 Develop terrestrial ecosystems in what was once shallow
ocean
Marine Ecosystems
Mangrove swamp
Marine Ecosystems
 Estuaries (a special category of aquatic
ecosystem) 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
where light can penetrate.
 These areas are important nursery sites for fish and
crustaceans.
– Also trap sediment & prevent many pollutants reaching
ocean, results in gradual filling of estuary that eventually
become a salt marsh and part of a terrestrial ecosystem
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 has much
less salt, T change greatly, short
supply of oxygen w different kinds of
organisms which may be divided into
two broad categories:
• Stationary water (lakes, ponds, and
reservoirs)
• Running water (streams and rivers)
Freshwater Ecosystems
 Large lakes have many of same characteristic as
ocean, can have euphotic zoon at top (if deep),
species different but have same role
 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 such as cattails & water lilies.
– Submerged plants stay submerged below the water’s
surface such as Elodea and Chara.
• 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.
• Temperature: Cold temperature reduces rate of
photosynthesis.
• Water depth: Shallow water with warmer T allows
more photosynthesis.
• Nutrient: 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 Pounds
 Lakes and Ponds
• Oligotrophic lakes are deep, cold, nutrient-poor, with low
productivity.
• 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.
– Organic matter enter aquatic system in several ways:
– Organisms living in water produce metabolic waste or
– Dead body of organism near shore,
– human use of fertilizers,
– organic waste from industry, agriculture, & municipal source
• Amnt of organic matter determine how much oxygen available
• Amt of oxygen determine # of organism in water
Freshwater Ecosystems
 Since water is moving, planktonic
organisms are less important than
attached organisms
 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.
 Most algae grow attached to rocks & other objects
at bottom.
 Periphyton is- Collection of algae, animals and
fungi attached to rocks and other objects on the
bottom.
 w/in streams is a community of organisms
specifically adapted to use debris as a source of
food.
 Bacteria and fungi colonize the organic matter and
many kinds of insects shred and eat this organic
matter along w/ fungi and bacteria
 Larger rivers are warmer, slower, w/ less oxygen,
they have different species of plants & animals
Freshwater Ecosystems
 Streams and Rivers
 Transition between aquatic & terrestrial
ecosystem are swamps & marshes
• 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.