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Chapter 27 Ecosystems and Biomes
CHAPTER OUTLINE
27.1 An ecosystem is the functional ecological unit.
Ecosystems are composed of interacting populations and their abiotic habitat.
27.2 Energy moves through ecosystems and chemicals cycle within ecosystems.
The natural processes found within ecosystems allow for the flow of energy through an
ecosystem and the cycling of nutrients.
Energy is lost at each link in a food chain.
Photosynthesizers capture the sun's energy with subsequent passage to herbivores and
carnivores with loss of energy occurring at each step governed by the rule of 10%.
Pyramids of energy and pyramids of numbers represent how energy moves and is lost
within an ecosystem.
Natural processes recycle the chemical elements that are necessary for life.
Biogeochemical cycles provide for the cycling of elements within ecosystems.
Physical and chemical processes recycle water.
Most of the earth's water is found in the oceans; however, many organisms need
freshwater in order to survive. Through evaporation, condensation and precipitation,
water is cycled. Some freshwater is stored in aquifers, underground layers of porous rock
containing water.
Photosynthesis and respiration cycle carbon.
Carbon cycles within living organisms via photosynthesis and respiration, as well as, via
the decomposition of organic matter by bacteria and fungi. The atmosphere and ocean
are important reservoirs of carbon dioxide. Limestone, peat, coal, oil and natural gas are
also reservoirs of carbon.
Prokaryotes are key players in the nitrogen cycle.
Soil bacteria convert atmospheric nitrogen to a form usable by plants during nitrogen
fixation as well as converting nitrogen compounds back to atmospheric nitrogen during
denitrification.
The phosphorus cycle has no atmospheric component.
Rocks are an important source of phosphorus within this cycle which includes living
organisms.
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27.3 Ocean life is influenced by food, light, currents and pressure.
There is diversity of life within the ocean adapted to the characteristics found there.
Phytoplankton are the basis of ocean food chains.
Phytoplankton are photosynthetic organisms which form the base of the marine food
chain. Zooplankton are also a part of the plankton community.
Oceans contain a variety of habitats and ecosystems.
Nutrients, temperature and currents define ocean habitats. Zones include littoral, neritic,
pelagic, photic, oceanic, hadal, and abyssal. Some organisms can migrate vertically,
moving nutrients as they go. Estuaries are ecosystems in which freshwater and salt water
combine. The littoral zone is found between high and low tide lines, and subjects
organisms to periods of dryness and heat, and periods of rough water. The brackish
water of estuaries and mangrove swamps allow for growth of plants providing habitats
for some marine life to develop. Coral reefs are diverse ecosystems found near
coastlines. The ocean floor contains creatures not often seen including those inhabiting
hydrothermal vent communities.
27.4 Freshwater ecosystems link marine and terrestrial ecosystems.
Although freshwater is less prevalent than saltwater, most organisms are adapted to
freshwater habitats.
Lakes and ponds can become oxygen depleted.
Water within lakes and ponds can form layers which may not mix, although overturn can
occur with wind action. Accumulation of nutrients can result in eutrophication. Littoral
zones can occur in these freshwater habitats, defined in part by the emergent vegetation.
Also occurring are the limnetic zone and profundal zone.
Creeks, streams and rivers contain life adapted to moving water.
Pools and riffles are two types of habitats in moving waters. Each has characteristics to
which organisms adapt.
27.5 Biomes are characterized by typical vegetation.
Regions of the biosphere can be categorized as biomes with characteristic availability of
water, temperature and dominant vegetation.
Arctic tundra has short summers and permanently frozen subsoil.
Arctic tundra is characterized by permafrost. The tundra is threatened by global
warming, development of oil fields and bioaccumulation of toxins within the organisms.
Taiga is northern coniferous forest.
The uniformly tall trees of the taiga are characteristic of this northern biome. Habitat loss
and fragmentation threaten the taiga.
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Trees of temperate deciduous forests drop their leaves in the fall.
Having more moderate temperatures and water availability, trees in this biome typically
have broad, flat leaves which are shed before winter. The plant species create layers of
canopy, understory, shrub layer, and herbs, grasses and mosses. This biome is also
threatened by habitat fragmentation as well as development by humans.
Grasslands include savannas, pampas, prairies, veldt, and the outback.
Grasslands have limited rainfall and frequent fires which limit tree growth. Grasslands
suffer from habitat fragmentation.
Deserts can be hot or cold, but they are always dry.
Characterized by limited water availability, temperatures can fluctuate greatly in a desert.
In the U.S., deserts are threatened by development.
Tropical rainforests have the greatest biodiversity of any biome.
Having warm temperatures and plenty of freshwater, rainforests have the greatest
diversity. Vines and epiphytes are commonly found. Clear-cutting for agriculture is a
severe threat to rainforests.
27.6 The biosphere encompasses all of Earth's biomes.
Characteristics of the earth's surface and atmosphere along with energy from the sun
allow for living organisms to survive.
27.7 An added dimension explained: Has Lake Erie recovered?
Pollution seriously threatens many ecosystems. Due to unchecked pollution, much of the
life in Lake Erie was destroyed.
What polluted Lake Erie?
Phosphorus was a major pollutant of Lake Erie which caused numerous problems.
Mercury and invasive species also affected this lake.
Lake Erie is rehabilitated, if not recovered.
Legislation changed what substances could be released into the lake, forcing companies
to treat their effluent before release. Changes also occurred in sewage treatment plants
and detergents. Lake Erie is much healthier today because of these changes.
Now you can understand.
As all life is interconnected, any action has more than one effect.
What do you think?
Many ecologists feel it is critical to conserve wetlands. Issues are presented to stimulate
critical thinking.
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