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Chapter 8
Biogeographic Processes
Biogeography explores the distribution of plants and animals on the Earth. This chapter
examines how organisms live in ecosystems and the cycling of energy and matter through
ecosystems.
This chapter also explores ecological biogeography by examining factors that determine
the spatial distributions of organisms in time and space. We look at processes such as
evolution, dispersal, and extinction of species through time.

Ecology studies the interaction between life forms and their environments.
 An ecosystem is defined as a group of organisms and the environment with which
they interact. These systems import and export matter and energy.
 The food web, or food chain, refers to the flow of energy from one level to another in
an ecosystem.
 Primary producers are plants and animals that are able to create carbohydrates from
carbon dioxide and water and light energy through the process of photosynthesis.
 In the food web, consumers feed on the primary producers or on other consumers and
transfer energy through different levels in this manner.
 Decomposers (microorganisms and bacteria) feed on decaying organic matter at all
levels in the food web.
 Solar energy is absorbed initially by the primary producers and stored as chemical
energy which is digested by consumers. Only ten to fifty percent of the energy at any
level is passed on to the next level; consequently, the amount of organic matter and
consumers must decrease with each level.
 Photosynthesis is a biochemical reaction which results in the production of
carbohydrates and oxygen using water, carbon dioxide, and light energy. A simplified
chemical reaction is:
H2O + CO2 + light energy = —CHOH— + O2
 In the respiration process carbohydrate is broken down and combined with oxygen to
create carbon dioxide, water, and chemical energy. A simplified chemical reaction is
—CHOH— + O2 = CO2 + H2O + chemical energy
 Photosynthesis is dependent on light and heat. Photosynthesis only occurs when light
is available, so longer days produce more plant growth. Photosynthesis also increases
with temperature to about 20°C and then levels off.
 Net photosythesis is measured as the carbohydrate remaining after respiration takes
up carbohydrate to feed the plant. Net photosynthesis increases with temperature until
approximately 18° C, after which it declines as the rate of respiration increases faster
than the rate of photosynthesis.
 Net primary production is the annual amount of useful energy produced by an
ecosystem. It is controlled by light intensity and duration, temperature, and water
availability. Net primary production is measured as biomass, the dry weight of
organic matter per unit area within an ecosystem.
 Biomass is an important source of renewable energy. Using biomass involves
releasing solar energy that has been stored in plant tissue through photosynthesis.
Energy can be obtained by burning firewood, or through intermediate products such as
charcoal, methane gas, and alcohol.
 Biochemical cycles are the pathways of particular nutrients or materials through the
Earth's ecosystem.
 The macronutrients hydrogen, carbon, and oxygen account for 99.5% of all living
matter.
 The Carbon Cycle
 most carbon lies in storage pools as carbonate sediments
 only 0.2% is available as CO2 or as decaying biomass in active pools.
 carbon exists as carbon dioxide in the atmosphere and oceans, carbohydrate in
organic matter, hydrocarbon compounds in rock, and as mineral carbonate
compounds.
 CO2 is added to the Earth system by volcanic eruptions and by industry: it is taken
out of the Earth system by plants in photosynthesis and by phytoplankton in the
oceans.
 The Oxygen Cycle: oxygen is added to the Earth system by volcanic activity and is
lost to the system through organic respiration, mineral oxidation, industrial and natural
combustion, and dissolved in ocean water.
 The Nitrogen Cycle
 the atmosphere is a large storage pool of nitrogen.
 nitrogen can only be utilized through nitrogen fixation and is lost to the biosphere
through denitrification.
 human influence has increased the amount of nitrogen in the biosphere through the
use of nitrogen fertilizers and fuel combustion.
 Sedimentary cycles involve many macronutrients such as calcium, magnesium, iron,
potassium, sodium, and phosphorus which move from the land surface to the ocean
and subsequently return to land surfaces by tectonic uplift. Storage pools include sea
water, sediments, and sedimentary rocks. Eventually these macronutrients are
released into the Earth system through weathering.
 Ecosystems are strongly influenced by landforms and soils.
 Habitat refers to the preferences of a species for a particular location including such
factors as conditions of slope, water drainage, and soil type.
 Ecological niche refers to the functional role played by an organism, as well as the
physical space it inhabits. Many species may occupy the same habitat, but only a few
will ever share the same ecological niche.
 A community is an assemblage of organisms that live in a particular habitat and
interact with each other.
 The most important environmental factors influencing the location of species are
moisture and temperature.
 Species have a variety of adaptations to help them cope with the abundance or scarcity
of water. Xerophytes are plants adapted to dry conditions.
 Temperature affects physiological processes in plants. Plants have a temperature
range within which they can survive as well as optimum temperatures for each of their
functions.
 Climatic factors of moisture, temperature, light, and wind are important in determining
plant distributions. Bioclimatic frontiers are boundaries that mark the limits of the
potential distribution of a species.
 Geomorphic factors influencing ecosystems include slope steepness and slope aspect.
Edaphic or soil factors are also important in differentiating habitat.
 Species interactions also determine the distribution patterns of plants and animals.
Interactions may be positive or negative. These include:
 Competition between species occurs when two species require the same resource
that is in short supply.
 Negative interactions include predation, parasitism, herbivory, and allelopathy.
 Symbiosis includes three types of positive interaction between species:
commensalism, protocooperation, and mutualism.
 Ecological succession is a development sequence in which plant communities, or
seres, succeed one another as they progress to a stable climax, the most complex
community of organisms possible in an area.
 Succession starts with pioneer species that can survive in harsh conditions. These
pioneers moderate the harsh conditions and gradually other species move in.
Disturbances that can interrupt the sequence include fires, insects, disease, and
human activities such as cutting and clearing.
 Four key historical biogeography processes that affect the distribution of species are
evolution, speciation, extinction, and dispersal.
 Patterns of distributions include endemic species, which are found in one region and
no where else, cosmopolitan species which are found widely, and disjunction, in
which closely related species are found in widely separated regions.
 Biodiversity is determined by the variety of the Earth’s environments, as well as the
processes of evolution, dispersal, and extinction through geologic time. Human
activity on Earth is rapidly decreasing biodiversity by contributing to extinctions
through dispersing competing organisms, hunting, fire, habitat alteration, and
fragmentation.