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Chapter 4: Community Distribution
Objectives:

Explain how limiting factors and ranges of tolerance affect
distribution of organisms

Sequence the stages of succession in different communities

Compare and contrast the euphotic and aphotic zones of ocean
biomes

Identify the major limiting factors affecting distribution of terrestrial
biomes

Distinguish among the terrestrial biomes
4:1 Homeostasis in Communities
1.
2.
3.
4.
5.
6.
Changing conditions within an ecosystem affect the communities of
organisms that live there.
Limiting factors are any biotic or abiotic factors that restrict the existence,
numbers, reproduction, or distribution of organisms.
a.
food availability
b.
temperature
Factors the limit one population in a community may also have an indirect
effect on another population.
Tolerance is the ability to withstand fluctuations in biotic and abiotic
environmental factors
a.
some species can tolerate conditions that another may not
b.
limits of tolerance are reached when an organism receives too much
or too little of some environmental factor.
c.
Organisms become fewer and fewer as conditions move from optimal
toward either extreme of the range of tolerance
Succession is the orderly, natural changes that take place in the
communities of an ecosystem.
a.
difficult to observe
b.
can take decade or even centuries for one type of community to
completely succeed another
Primary succession is the colonization of new sites by communities of
organisms.
a.
as primary succession slows down, the community becomes fairly
stable.
b.
Climax community is a stable, mature community that undergoes
little or no succession
7.
Secondary succession is the sequence of community changes that takes
place when a community is disrupted by natural disasters or human
actions.
a.
the community of organisms inhabiting an area gradually changes
but the species involved are different and takes less time to reach a
climax community
4:2 Biomes
1.
2.
3.
4.
5.
6.
A biome is a large group of ecosystems that share the same type of climax
community
a.
terrestrial biomes
b.
marine biomes
c.
freshwater biomes
Marine biomes contain the largest amount of biomass of any biome on
Earth, but most is made up of extremely small, microscopic organisms.
a.
The photic zone is the portion of the marine biome shallow enough
for sunlight to penetrate
(1) exist along coastlines of all land masses
(2) include rocky shores, sandy beaches and mud flats
b.
The aphotic zone is the portion of the marine biome with deeper
water that never receives sunlight
An estuary is a coastal body of water, partially surrounded by land, in
which fresh water and salt water mix.
a.
salinity ranges between that of seawater and freshwater and
depends on how much fresh water the river brings into the estuary.
b.
Salinity also changes with the tide
c.
Contain salt marsh ecosystems (dominated by grasses) that serve as
habitat for small organisms.
d.
Louisiana coastline is primarily estuary. Excellent habitat for
migrating fowl.
The Intertidal Zone is the portion of the shoreline that lies between high
and low tide lines.
a.
gravitational pull of the sun and moon twice a day causes the rise
and fall of ocean tides.
Many organisms live in the shallow water region that surrounds most
continents and islands feeding on nutrients washed from the land by
rainfall.
Plankton are microscopic organisms that float in the waters of the photic
zone comprising most of the marine biome biomass.
a.
7.
8.
9.
10.
11.
composed of both consumers (jellyfishes, worms, and juvenile stages
of animals such as crabs, snails, etc) and producers (unicellular algae
and diatoms)
Almost 90% of the ocean is more than a mile deep, extending miles below
the sunlit surface in some places.
a.
fish living in these depths depend on plankton either directly or
indirectly by feeding on other fish who feed on plankton.
b.
Fish are adapted to living in darkness with a scarcity of food
Freshwater biomes include lakes, rivers, and streams.
The shallow waters are highly productive and contain fish, algae, protists,
mosquito larvae, tadpoles, crayfish and a variety of plant life.
Abiotic factors that limit the kinds of organisms that can survive in deep
lakes include temperature variations and light penetration.
a.
as you go deeper in the water, the temperatures drop.
b.
Not enough sunlight penetrates to the bottom to support
photosynthesis so few aquatic plants or algae grow on or near the
bottom thus the density of populations is lower in deeper waters.
Terrestrial Biomes
a.
three factors determine which biome will be dominant in a terrestrial
location
(1) latitude
(2) altitude
(3) precipitation
b.
Biome distribution is determined by
(1) air currents
(2) Earth’s rotation
(3) Prevailing winds
(4) Proximity to the ocean
c.
Tundra
(1) a treeless land with long summer days and short periods of
winter sunlight
(2) temperatures never rise above freezing for long so only the
topmost soil layer thaws during summer
(3) permafrost is a layer of permanently frozen ground beneath the
topsoil
(4) shallow-rooted grasses and small plants
(5) nutrient recycling is slow due to slow decay
(6) short growing season is a limiting factor for life
(7) mosquitoes and other biting insects are most common tundra
animals during summer
(8) many small animals like lemmings, weasels, artic foxes,
snowshoe hares, snowy owls, and hawks
(9)
d.
e.
f.
musk-oxen, caribou, and reindeer are a few of the large
animals
Taiga or Northern Coniferous Forest
(1) land of mixed pine, fir, hemlock, and spruce trees
(2) usually somewhat warmer and wetter than tundra, but the
prevailing climatic conditions are still harsh, with long, severe
winters and short, mild summers
(3) permafrost is usually absent
(4) topsoil is acidic and poor in minerals
(5) the abundance of trees provides more food and shelter for
animals than the tundra
(6) more large species of animals are found here such as the
moose, elk, and lynx
Desert
(1) driest of the biomes
(2) arid region with sparse to almost nonexistent plant life
(3) usually get less than 25 cm of precipitation annually
(a) Atacama Desert in Chile gets 0 rainfall yearly
(4) vegetation varies greatly depending on precipitation levels
(a) more rainfall = shrub communities
(b) less rainfall = scattered plant life and large areas of bare
ground
(c) driest deserts = drifting sand dunes with virtually no life
(5) plants evolved adaptations for desert life
(6) most mammals are small herbivores that emerge at night to
forage on plants
(7) A few larger herbivores (pronghorn antelope) are found in
American desert
(8) Foxes, coyotes, hawks, owls, and roadrunners are carnivores
that feed on snakes, lizards and small mammals
Grasslands
(1) large communities covered with grasses and similar small
plants
(2) receive between 25 & 75 cm of precipitation annually
(3) principally occur in climates that experience a dry season (not
enough water to support forests)
(4) occupies more area than any other terrestrial biome
(5) higher biodiversity than deserts (100 species per acre) than
deserts
(6) soils have considerable humus content; grass roots survive
through the winter, enlarging every year to form a continuous
underground mat called sod.
(7)
g.
h.
Grasslands have become known as the “Breadbaskets of the
World”
(8) Populated by large herds of grazing animals such as bison
(9) Important prairie animals include wolves, coyotes, prairie dogs,
foxes, ferrets, and many species of insects, birds and reptiles
Temperate Forests
(1) dominated by broad-leaved hardwood trees that lose their
foliage annually
(2) precipitation ranges from 70 to 150 cm annually
(3) soil consists of a top layer rich in humus and a deeper layer of
clay
(4) animals include squirrels, mice, rabbits, deer, and bears
(5) many birds live here year round while others migrate south in
winter
Tropical Rain Forests
(1) most biologically diverse of the terrestrial biomes
(2) a region of uniformly warm, wet weather dominated by lush
plant growth
(3) occupy the equatorial regions of the world
(4) receives at least 200 cm of rain annually with some receiving as
much as 400 cm
(5) temperatures remain warm year round about 25 C
(6) form jungles of dense, tangled vegetation only near stream
banks or in areas that have been disturbed by fire, logging, or
agriculture
(7) undisturbed rain forest communities have leafy tops of tall trees
shading the forest floor so completely that few plants can grow
(canopy)
(8) tree roots are shallow, forming a thick mat on the surface of
the soil
(9) most of the nutrients are tied up in living material
(10) ants, termites, fungi, and other decomposers are plentiful
(11) many animals live in dense vegetation
(12) more species of reptiles, amphibians, and birds are found here
than in any other terrestrial biome
(13) large animals like gorillas and cougars are ground dwellers,
while most rain forest organisms live in the trees
(14) Butterflies and other insects are the most numerous animals in
the rain forest (about 3 million species)