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Chapter 6
Ecosystems and Communities
• Succession– Series of regular
predictable changes in community structure over time
– Result in climax community
Chapter 6
Primary Succession– Total lack of organisms and bare rock or water
• Terrestrial– Pioneer Community
• First to colonize bare rocks--lichens
– Successional or Seral Stage• Multiple sequence of stages/communities
– Climax Community• Relatively stable, long lasting, complex community
– Entire sequence of stages called a sere.
Chapter 6
Characteristics of Climax Communities:
• 1. able to maintain mix of species for a long period of time
• 2. in energy balance• 3. larger number and more kinds of organisms
and interactions between organisms complexity and energy efficiency
Chapter 6
• Secondary Succession• Succession in area after destruction or major
disturbance, flood, fire, agriculture • More common and rapid than primary
succession• Usually some soil, seeds or root mass that can
re-establish• Adjacent area can be source of seed, etc
Chapter 6
• Aquatic • Except for oceans, most aquatic ecosystems are considered
temporary.
• Ever increasing entrapment of soil particles and organic matter.
• Less depth means establishment of submerged plants
terrestrial succession
Chapter 6
Types of Climax Communities
• Biomes – terrestrial climax communities with a wide
geographic distribution. – Variation of species exist within biomes but
exhibit similar pattern and processes• Same general structure of ecosystem
• Same kinds of niches present
Chapter 6
2 primary factors which determine biome type:• Precipitation:
– total amount– form (rain, snow)– seasonal distribution—concentrated at particular time
• Temperature:– temperature swings– length of seasons
• Other factors: fires, winds, organisms
• Altitude and latitude can mimic these effects
Chapter 6
Desert: • Lack of water is primary factor• Less than 25 centimeters (10 inches) precipitation
per year. • Lack of clouds means no insulation
– Can be quite cold/hot
• Many types of plants and animals, most are quite adapted to conditions. – Large space between plants, dispersed animals too
Chapter 6
Grassland (aka: prairies or steppes):• Between 25 and 75 centimeters precipitation per year
(10-30 inches).• Windy, hot summers: cold or mild winters. • Fire is important in maintaining biome
– Prevent invasion of trees– Cycles nutrients
• Large herds of grazing mammals, many insects, many birds.
• Most converted to agriculture– 0.004% of Texas Blackland Prairie remains
Chapter 6
Savanna: • Similar in appearance to grassland, but has more
trees.• Precipitation is between 50 and 150 centimeters
per year (20 - 65 inches), but it comes in a few heavy events, with drought in between.
• Plants and animals behave accordingly.• Wildlife quite similar to grasslands. • Fire still important so trees fire resistant
– Texas Post Oak Savanna
Chapter 6
Tropical Rain Forest:• Near equator
– Africa, C&S America, SE Asia, some islands
• More than 200 centimeters precipitation per year (80 inches).– Some over 500 centimeters (200 inches).
• Warm temperatures/relatively constant.• Many species.• Soils are poor since nutrients are stored in biomass of
vegetation or washed out.– Highly weathered so clayey—sun and heat make?
Chapter 6
Temperate Deciduous Forest:• Distinct summer/winter seasons.
– Trees loose leaves in winter
• 100 centimeters (or more) of precipitation (40 inches).– Mild winters, 6 month growing season
• Relatively few species of trees.– Two or three major producers
• Many flowers, insects, birds and mammals. – Texas—Eastern and Western Crosstimbers
Chapter 6
Taiga (aka: Northern Coniferous Forest or Boreal Forest):
• Short cool summer, long hard winter.– Up to 6 months, soil freezes
• Precipitation between 25 and 100 centimeters per year (10 to 40 inches), with constant high humidity.
• Trees see winters as dry due to precipitation in form of snow.– Needle shaped leaves.– Flexible branches
Chapter 6
Tundra:• No trees, permanently frozen soil (permafrost)—
north of Coniferous forests• Low precipitation (less than 25 centimeters), but
comes in summer when snow melts.• Permafrost does not allow water to soak
in....many small pools.• Damage to systems takes long time to fix. • Same conditions on high mountains (alpine
tundra) but different species
Chapter 6
Aquatic Ecosystems:• Factors:
– - sun light penetrability– - nature of bottom substrate– - water temperature– - amount of dissolved material
• Marine—high dissolved salts• Freshwater—low dissolved salts
Chapter 6
Marine systems• Pelagic Ecosystems• Open ocean system, with free swimming organisms.
– Fish, whales, crustaceans,etc not attached to anything
• phytoplankton (producer) in euphotic zone.• zooplankton• other consumers• nutrients are in short supply, except in few
concentrated areas.
Chapter 6
Benthic Ecosystems• Systems at bottom of ocean.
– Critters attached or not
• If light can penetrate, plants exist.• Substrate determines types of organisms which can
occur.• No light: abyssal zone.• Warm waters coral reefsMangrove swamps• Near shore region
– Can lead to terrestrial ecosystem development
Chapter 6
Estuaries• Shallow partially enclosed area where freshwater enters
marines systems.• Relatively few organisms capable of tolerating salt
fluctuations seen in this system.• Large amount of nutrient inflow.• Typically, entire area has sunlight penetrating to
bottom.• Many organisms use as nursery.• Trap sediment—salt marsh—terrestrial ecosystem
Chapter 6
• Freshwater Systems • Lakes and Ponds:
– littoral zone (has rooted plants)– limnetic zone (no rooted plants)
• Productivity:– Temperature– Depth– Nutrients in water
• oligotrophic lakes—longer life• eutrophic lakes—shorter life
Chapter 6
• Dissolved oxygen (DO) determines what type of organisms will occur.– Free oxygen O2
• Biochemical oxygen demand (BOD)– A measure of how much decomposable
organic matter is in the water.– Enter through critter waste in lake, inflows of
organic wastes, critter death, etc
Chapter 6
Streams and Rivers:• periphyton - organisms attached to rocks and bottom
material.• Not much chance for plants, so most energy comes
from material that falls in stream rather than from photosynthesis.
• Many insects, fungi and bacteria use this organic matter.
• Dissolved oxygen: less in slow, muddy rivers• Wetlands: transition areas