Chapter 8
Biogeographic Processes
Biogeography explores the distribution of plants and animals on the Earth. This chapter
examines how organisms live in ecosystems and how energy and matter is cycled through
those ecosystems.
This chapter also explores ecological biogeography by examining factors that determine
the distributions of organisms in time and space. It examines processes such as
evolution, dispersal, and extinction of species through time.

Ecology is the study of the interactions between life forms and their environments.
 An ecosystem is defined as a group of organisms and the environment with which
they interact. Both matter and energy are imported into and exported from
ecosystems.
 The food web, or food chain, refers to the flow of food energy between different
organisms within an ecosystem.
 Primary producers are plants and animals that are able to synthesize carbohydrates
from carbon dioxide, water and light energy through a process known as
photosynthesis.
 The transfer of food energy to different levels of the food wed is accomplished by
consumers which feed on the primary producers or on other consumers.
 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 available for digestion by consumers. Since on average only ten to
fifty percent of the energy at any level is passed on to the next level, the amount of
organic matter and consumers must therefore 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
version of this biochemical reaction is:
H2O + CO2 + light energy = —CHOH— + O2
 During the respiration process carbohydrates are broken down and combined with
oxygen to create carbon dioxide, water, and chemical energy. A simplified version of
this chemical reaction is:
—CHOH— + O2 = CO2 + H2O + chemical energy
 Photosynthesis is dependent on light and heat. Photosynthesis only occurs when light
is available and therefore, longer days result in more plant growth. Photosynthesis
also increases steadily with temperature to about 20°C and then levels off.
 Net photosythesis is the amount of carbohydrate remaining after respiration has
broken down a sufficient amount of 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 as an energy
source 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.
 Biogeochemical cycles define 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’s atmosphere through volcanic eruptions and
anthropogenic consumption of fossil fuels. Carbon dioxide is removed from the
Earth’s atmosphere through the combined photosynthetic efforts of terrestrial
plants and marine phytoplankton.
 The Oxygen Cycle: oxygen is added to the Earth’s atmosphere by volcanic activity
and photosynthesis. Oxygen is removed from the atmosphere through organic
respiration, mineral oxidation, industrial and natural combustion, and ocean water
solution.
 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 and needs of an organism or group of organisms with
respect to such factors as conditions of slope, water drainage, and soil type.
 Ecological niche of a species describes how it obtains energy and how it influences
other species within its own environment. Many species may occupy the same habitat,
but only a few will ever share the same ecological niche.
 A community is an assemblage of interacting organisms that live in a particular
habitat.
 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 in addition to optimum temperatures for each of
their specific functions such as photosynthesis, flowering, fruiting, and seed
germination.
 Climatic factors such as moisture, temperature, light, and wind can limit the
distribution of plant and animal species. Boundaries marking the critical level of
climatic stress beyond which a plant or animal species cannot survive are called
Bioclimatic frontiers.
 Geomorphic factors influencing ecosystems include slope steepness, slope aspect
(the orientation of the sloping ground surface with respect to geographic north) and
relief. Since soil types are largely related to climate, 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. Examples of species interactions include:
 Competition between species occurs when two species require the same resource
that is in short supply.
 Negative interactions include predation (on species feeding on another),
parasitism (one species gaining nutrition from another), herbivory (animal
grazing reduces the plant population viability), and allelopathy (chemical toxins
emitted by one plant species inhibits the growth of another).
 Symbiosis includes three types of positive interactions between species:
commensalisms (one species benefits while the other is unaffected),
protocooperation (both species benefit from the relationship), and mutualism
(one or both species cannot survive without the other).
 Ecological succession is a development sequence in which plant communities, or
seres, succeed one another as they progress to a stable climax which represents the
most complex community of organisms possible in an area.
 Succession starts with pioneer species which are species that can survive in harsh
conditions. The pioneer species eventually moderate the harsh conditions allowing the
gradual invasion of other species (secondary succession). Disturbances such as
fires, insects, disease, and disruptive human activities such as clear cutting which
remove or alter existing communities results in secondary succession.
 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.