3. 6.1 Succession
Succession is a series of regular, predictable
changes in community structure over time.
• Activities of organisms change their surroundings
• Make the environment suitable for other kinds of
organisms.
4. 6.1 Succession
A climax community
• relatively stable, long-lasting community that is the
result of succession.
• Traditionally, kind of climax community determined by
climate.
5. 6.1 Succession
Primary succession begins with a total lack of
organisms and bare mineral surfaces or water.
6. 6.1 Succession
Secondary succession begins with the
disturbance of an existing ecosystem.
• It is much more commonly observed
• generally proceeds more rapidly than primary
succession.
8. Pioneer Stage
• 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.
9. Intermediate Stage
Lichen community replaced by annual plants.
Annuals replaced by perennial community
(grasses).
Perennial community replaced by shrubs.
Shrubs replaced by shade-intolerant trees.
Shade-intolerant trees replaced by shade-tolerant
trees.
10. Climax community
Stable, complex, climax community eventually
reached.
Process of succession can stop at any point
The general trend in succession is toward
increasing complexity and more efficient use of
matter and energy.
13. Secondary Succession
Secondary succession
• 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, grow quickly and
reestablish themselves.
14. Secondary Succession
• Nearby undamaged communities can serve as
sources of seeds and animals.
• The new climax community is likely to resemble the
destroyed community.
16. 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.
18. 6.2 Biomes Are Determined by Climate
Biomes are terrestrial climax communities with
wide geographic distributions.
• Determination of a biome
– climate
20. Biomes: Major Types of
Terrestrial Climax Communities
Primary non-biological factors that impact the
kinds of climax communities:
• Temperature
• Patterns of precipitation
– Total
– Form
– Seasonal distribution
21.
22. The Effect of Elevation
on Climate and Vegetation
• Temperature is warmest near the equator and cooler
toward the poles.
• As altitude increases, average temperature
decreases.
23. The Effect of Elevation
on Climate and Vegetation
Relationship between height above sea level, latitude, and vegetation.
24. 6.3 Major Biomes of the World:
Desert
Deserts
• less than 25 cm annual precipitation.
• Unevenly distributed throughout the year.
Windy
Large daily temperature fluctuations.
There are many species, but they are present in
low numbers.
Many species exhibit specialized adaptations to
climate
• ability to conserve water.
26. Temperate Grassland
Temperate grasslands, also known as prairies or
steppes
• 25-75 cm of annual precipitation.
• Fire is an important force in preventing the invasion of
trees
• releasing nutrients from dead plants to the soil
Grasses 60-90% of vegetation
The primary consumers are large herds of
migratory grazing mammals.
– Many insect species are also common.
27. 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
– sheep, cattle, and goats.
• Little undisturbed grassland is left
– fragments that remain need to be preserved as refuges
for the grassland species
29. Savanna
Savannas
• tropical parts of Africa, South America, and Australia.
Extensive grasslands spotted with occasional
patches of trees.
They receive 50-150 cm annual precipitation,
unevenly distributed throughout year.
Predominant Mammals
• Grazers
Fire is a common feature.
30. Savanna
Human impact:
• Savannas have been heavily impacted by agriculture.
– Farming
– Livestock in drier areas
• In Africa, there are extensive areas set aside as parks
and natural areas
– ecotourism is an important source of income.
32. Mediterranean Shrublands (Chaparral)
Mediterranean shrublands
• located near oceans and are dominated by shrubby
plants.
Their climate features wet, cool winters and hot,
dry summers.
• 40-100 cm annual precipitation.
• Fire common feature
Vegetation is dominated by woody shrubs
adapted to hot, dry summers.
Insects, birds, reptiles, mammals
33. 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.
35. Tropical Dry Forest
The tropical dry forest
• heavily influenced by seasonal rainfall.
• Annual precipitation ranges from 50-200 cm.
Many exhibit a monsoon climate with highly
seasonal rainfall.
Plants have developed special adaptations to
survive drought.
36. Tropical Dry Forest
Human impact:
• Many of these forests occur in areas of very high
human population. (India)
• 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.
38. Tropical Rainforest
Tropical rainforests
• located near the equator where temperature is relatively
warm and constant.
– 200+ cm annual rainfall, and some receive in excess of 500
cm.
Tropical rainforests have a multi-layered canopy.
They also host a very high diversity of species.
• More species in tropical rainforests than in the rest of the
world
39. 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.
41. Temperate Deciduous Forest
Temperate deciduous forests
• 75-100 cm annual precipitation, evenly distributed
throughout the year.
• Mild winters and a long growing season (6 months).
Trees typically lose their leaves during the winter
and replace them the following spring.
• Specific species: maples, birch, oaks
Insects, migrant birds, small mammals, and
foxes, coyotes
42. Temperate Deciduous Forest
Human impact:
• 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.
44. Temperate Rainforest
West winds bring moist air to the coast.
• air is forced over the mountains, cools, and rain or
snow is produced.
• at least 130 cm of rain a year, many receive 300 cm
The cool climate slows evaporation, things are
generally damp.
• All trees are covered with mosses, ferns
Lush growth of plants
• Sitka spruce, Douglas fir
• Old growth forests have trees 800 years old.
45. Temperate Rainforest
Insects, as well as insect and fruit eating birds
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.
46. Temperate Rainforest
Human Impact
• Because of the rich resource of trees, at least half of
the original temperate rainforest has been logged.
• Some patches have been protected because they are
home to endangered northern spotted owls and the
marbled murrelet, a seabird.
48. Northern Coniferous Forest,
or Boreal Forest
An evergreen coniferous forest known as the
northern coniferous forest, or boreal forest.
• 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
The trees are adapted to winter conditions:
• Needle-shaped leaves prevent water loss.
• Flexible branches
51. Tundra
North of the taiga is the tundra,
• an extremely cold region that lacks trees and has a
permanently frozen subsurface soil.
The tundra receives less than 25 cm annual
precipitation.
• short, wet summer.
Plants are usually less than 20 cm tall.
• Grasses and lichens
Insects, waterfowl, Caribou, artic foxes
52. Tundra
Human impact:
• 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.
54. Grassland vs Savanna
Similarities:
•
•
•
•
Fire
Predominant plant: grasses
Primary consumers: grazers
Both have been impacted by agriculture
Differences:
• Precipitation: 25-75 cm in grassland; 50-150 in
savanna
• Savanna: heavy rainfall followed by drought
55. Tundra vs Desert
Similarities:
• 25 cm annual precipitation
• Windy
• Few people occupy
Differences:
• Temperature
• Type of plants and animals
56. 6.4 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
– Marine ecosystems have a high dissolved salt content.
57. Marine Ecosystems
Estuaries consist of shallow, partially enclosed
areas where freshwater enters the ocean.
• “Where the rivers meet the sea”
Organisms are specially adapted to varying
levels of salinity from tides and river flow.
Extremely productive ecosystems because
areas are shallow, warm, and nutrient-rich.
• important nursery sites for fish and crustaceans.
60. Freshwater Ecosystems
Freshwater ecosystems may be divided into two
broad categories:
• Stationary water (lakes, ponds, and reservoirs)
• Running water (streams and rivers)
Human impacts
Agricultural runoff, sewage, sediment, and trash all find
their way into streams and lakes.
63. 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.
64. Summary
Major biomes are desert, temperate grassland,
savanna, Mediterranean shrublands, tropical dry
forest, tropical rainforest, temperate deciduous
forest, temperate rain 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.