Summary of the
Biogeography can be simply defined as
the academic study of the factors that control the
spatial distribution of organisms. Scientist believe
that life first appeared on the Earth about 3.5 billion
years ago. At first, life was biologically simple and
consisted of one celled organ's that are similar to
bacteria. However, as time went on life become more
complex and diversified because of evolution. Species
are being continually modified genetically as spontaneous
mutations create new adaptations to the environment.
Some of these new adaptations replace old adaptations
through natural selection. Scientists estimate that
about 10 to 40 million different organisms inhabit
the Earth's surface, sky, and waters. Scientists classify
organisms using a hierarchical system first developed
several centuries ago by the biologist Linnaeus.
Biologists recognize four general types
of life: Archaea; Bacteria; Eukaryota; and Viruses.
Scientists have developed a hierarchical system for
the classification of these organisms into groups of
similar individuals. It is based on the taxonomic (classification
based on physiology) and phylogenic (classification
based on genetics) characteristics of the organism.
At the finest scale, organisms that share similar characteristics
are called a species. At the second level of the classification
similar organisms belong to a particular Genus. For
example, trees that are red maples are classified as
Evolution is the process
by which organisms come to possess genetic adaptations
to their environment by way of natural selection.
Adaptations are the various biological characteristics
of a species. Adaptations are always changing in
a population of organisms because of mutations. Mutations
result in an alteration of an organisms genetic
code and therefore can create new traits. However,
most mutations are fatal. The few that are not fatal
may provide an individual with an adaptation that
gives them a competitive advantage in terms of survival.
Over time reproduction can spread this adaptation
to numerous offspring resulting in evolution.
Scientists have recognized that organisms
can be organized according to several different functional
levels. The functional level known as species refers
to a group of organisms that are similar in morphology
and physiology and have the ability to interbreed.
All of the different organisms of a single species
occupying a specific area on the Earth represents a
population. A community is defined as all of the populations
of different species inhabiting a particular region
of the Earth. The most complex functional level of
organization is the ecosystem. An ecosystem consists
of the community and its relationship to abiotic factors
found in the environment.
Most organisms have the ability to move.
Through movement species have the ability to colonize
new habitats and expand their geographic range. Evolutionary
adaptations that allow a species to expand their geographic
range may also make a species more resilient to environmental
change. Once dispersed, a species can colonize a habitat
if a vacant site for colonization is available and
on if the abiotic conditions are right. Finally, colonization
leads to establishment. The establishment phase can
end for species because of temporal changes in the
site's abiotic or biotic characteristics.
A geographic range describes the distribution
of a species across space. Geographic ranges are never
fixed over time. Instead we find that the geographic
range of a species can shift, expand and contact because
of changes in a abiotic and biotic factors that influence
fitness. Many species are limited in some part of their
range by abiotic factors. For each of these abiotic
factors, species exhibits variations in its ability
tolerate the variable when its quantity in the environment
changes. When the abiotic variable is too available
or too scarce the species may not be able to survive.
In this situation, the species is said to have met
its limits of tolerance to this variable. In most situations,
the individuals of a species in a particular area are
limited by a single abiotic factor that controls the
fitness and growth of species.
Species can interact with
other species in a variety of different ways. Interactions
where neither species directly influences the fitness
of the other are called neutralism. Competition occurs
when both interacting species are negatively effected
in terms of fitness. Competition usually occurs when
two or more species are using the same common limiting
resource for survival. In an amensalism, one species
suffers while the other is not influenced in a positive
or negative fashion. Mutualism is an interspecific
association where the fitness of the interacting species
is positively effected. In many cases mutualisms are
necessary for the survival of both interacting species.
The final common interaction in nature is one where
one species gains while the species suffers. Ecologists
call these interactions either parasitism, predation
or pathogenic disease.
The ecological niche concept extends
the tolerance idea described above. The ecological
niche models the effect of all abiotic variables and
biotic interactions on the distribution of species.
Ecologists often refer to two types of niche: the realized
and fundamental niche.
Scientists estimate that between 2 to
100 million species currently inhabit the Earth. Most
of these species are found in the tropics. All species
will eventually go extinct. In most cases, the extinction
of a species is caused by a change in the environment
or by the presence of new evolved species. Over the
Earth's long history, there have been about 5 or 6
period of time where more than 35% of the species
existing become extinct over a relatively short period
of time. We call these events mass extinctions. Because
of the actions of humans, a large number of this species
may become extinct in the immediate future. Since the
beginning of the Industrial Revolution, about 700 biologically
classified species have gone extinct.
Biodiversity is a term used to describe
the diversity of life. This term has a much broader
definition than the species concept. Biodiversity describes
the diversity of life at the genetic, species, and
ecosystem levels. Many scientists like to use the biodiversity
concept to describe the abundance of forms of life
found on the our planet because of definitional problems
that exist with the species concept.
Plant succession is a repeatable, directional
change in the types of plant species that occupy a
habitat through time after a disturbance. Scientists
have classified many different types of succession.
In the majority of these successions types, the initial
plant community is dominated by small, short lived
weed species that have the ability to produce many
seeds. The species found the late stages of succession
tend to huge, long lived species that produce only
a few large well developed seeds. A number of mechanisms
have been identified as the causal mechanisms responsible
for succession. The mechanisms involved in succession
include: facilitation, abiotic modification and resource
competition; differential competition of resources
by the plant species; and differential competition
of space by the plant species.
Ecosystems are dynamic entities composed
of a mosaic of biotic and abiotic components that interact
in some fashion. Some of the more important components
include soil, atmosphere, solar radiation, water, and
living organisms. Soil provides the living organisms
found in an ecosystem with nutrients, water, a home,
and a structural medium for the roots of many types
of plants. The atmosphere is an important sink for
oxygen, carbon dioxide, and water. These substance
cycle from the atmosphere to life and back to the atmosphere
mainly through the processes of photosynthesis, respiration,
evapotranspiration, and precipitation. The Sun provides
ecosystems with energy in the form of radiation which
is used to generate heat and power photosynthesis.
Water also plays and important role in the functioning
of an ecosystem. Water is incorporated into the bodies
of organisms, is a medium fro nutrient exchange between
soil and life, and is used in photosynthesis.
Ecosystem can also be modeled in terms
of energy and matter flow. Plants are the only organisms
found in ecosystems that can chemically fix energy.
Using the Sun's light and nutrients and water from
the environment, plants can create a variety of organic
materials. Organic matter is then passed on to heterotrophic
forms of life through consumption. A special group
of heterotrophs, know as the decomposers, play an important
ecosystem function by converting organic matter back
into its inorganic constituents. This process also
provides the decomposers with energy to run their metabolism.
Energy and matter can also move from one ecosystem
to another. This movement is done through processes
like seed dispersal, animal migration, leaching, and
A biome is a major ecosystem type that
can be found in different regions of the planet where
similar environmental conditions exist. The types of
species found in a single biome type are often genetically
distinct from each other from region to region. However,
these species are similar in terms of the morphological
and physiological adaptations that they possess indicating
similar natural selection processes. The major biomes
found on the Earth's surface are: tundra, boreal forest,
temperate deciduous forest, grassland, chaparral, desert,
tropical savanna, and tropical rainforest. Each of
these biomes is described generally in terms of environmental
characteristics and the types of plants and animals
that dominate these ecosystems.
A portion of the solar energy that enters
ecosystems is used by plants to create organic chemical
energy. Through photosynthesis, carbon dioxide, water
and sunlight are converted into glucose (form of organic
chemical energy) and oxygen. Glucose can then be altered,
through the addition of other chemicals, into pigments,
lipids, sugars, proteins and nucleic acids. This organic
energy can then be passed on to other organisms, the
heterotrophs, through consumption and assimilation.
Energy is freed for use by life through respiration
which operates both in plants and animals. The amount
of energy fixed by organisms in ecosystems is usually
less than 3% of energy received as sunlight. Some
ecosystems that are photosynthetically limited because
of scarce water or cold temperatures fix less than
1% of the energy available for photosynthesis.
The grazing food chain models the movement
of energy in producers and consumers at the trophic
level. It begins with the photosynthetic fixing of
energy by plants. These plants are then consumed by
the herbivores, and the herbivores are consumer by
carnivores. Note that you can have several levels of
carnivores. The number of levels in the grazing food
chain is determined by the productivity of the habitat.
More productive habitats have more trophic levels.
The detritus food chain models the consumption of waste
or dead organisms by the decomposers. The organisms
found in this food chain gain their energy either through
respiration or fermentation. Consumption of organic
matter by decomposers also converts this material into
its original inorganic components.
Trophic pyramids are used by scientists
to model the flow of energy and organic matter through
ecosystems. In most ecosystems, the amount of energy
and matter found in each successive trophic level decreases
in quantity. This observation is related to assimilation
efficiencies and the fact that many organisms have
defense mechanisms to reduce the chance of being consumed.
A food web is a model that describes who eats who in
Within an ecosystem nutrients can cycle
between the biosphere, hydrosphere, lithosphere, and
atmosphere. For each element, the exact pattern of
cycling is quite unique and may involve a number of
abiotic and biotic processes. About 20 to 30 nutrients
are required for the metabolic processes in the various
types of life. The most frequently used nutrients are
referred to as macronutrients. Carbon, oxygen, hydrogen,
nitrogen and phosphorus are the most common macronutrients
and they ordinarily constitute more than 1% of the
dry weight of an organism. Elements required in very
small amounts are called micronutrients. Nutrients
can enter or leave the nutrient store of an ecosystem
through a variety of processes. In a stable ecosystem,
losses of nutrients are normally small in amount. Disturbance
can increase the quantity of nutrients removed from
an ecosystem substantially. The main processes that
add nutrients to ecosystems are weathering, atmospheric
input, and biological fixation. Losses of nutrients
to ecosystems can occur by way of erosion, leaching,
gaseous emission, and the emigration and harvesting
of biomass. The magnitude of nutrient loss to ecosystems
can often be greater than inputs.
The most active interface of nutrient
cycling within an ecosystem is the uppermost layers
of the soil. In the soil layer, numerous types of organisms
are found whose primary function in the ecosystem is
to decompose organic matter. Decomposition breaks down
complex organic molecules into much smaller inorganic
molecules and atoms. This inorganic matter can then
reenter the ecosystem when absorbed by plant roots
for metabolism and growth. The soil also receives inputs
of nutrients through biological fixation, atmospheric
input, and weathering.
The carbon cycle models the movement
and storage of carbon in the biosphere, lithosphere,
hydrosphere and atmosphere. Carbon is stored in the
biosphere as living organisms; in the atmosphere as
carbon dioxide gas; in the lithosphere as soil organic
matter, as fossil fuel deposits, and as sedimentary
rock deposits; and in the oceans as dissolved carbon
dioxide gas and as calcium carbonate shells in marine
organisms. Processes the move carbon from one store
to another include photosynthesis, respiration, oceanic
diffusion, biomass combustion, fossil fuel burning,
fossil fuel creation, and sedimentary rock formation.
Humans have altered the carbon cycle through fossil
fuel burning, deforestation, and land-use change. The
net result of these processes is an increasing concentration
of carbon dioxide in the atmosphere.
The nitrogen cycle is one of the most
important nutrient cycles in relation to terrestrial
ecosystems. Most plants are limited in their growth
by the availability of nitrogen despite the fact that
the atmosphere is 78% nitrogen gas. Only a few organisms
have the ability to use atmospheric nitrogen. Most
organisms prefer nitrogen in the solid nitrate form.
Besides the atmosphere, the other important stores
of nitrogen are the soil and the organic molecules
of life. Nitrogen is added to ecosystems in solid form
primarily through biochemical fixation by specialized
microorganisms like bacteria, actinomycetes, and cyanobacteria.
The conversion of organic nitrogen to inorganic nitrogen
within the soil is a complex process that involves
a number of organisms and chemical processes. Humans
have also severely altered the nature of this nutrient
cycle by generally making solid forms nitrogen more
List of Key Terms
Abiotic, Acidic, Actinomycetes, Adaptation, Algae, Alkaline, Allelopathy, Allogenic
Succession, Amensalism, Amino
Acid, Ammonia, Ammonium, Amphibian, Anaerobic, Angiosperm, Archaea, Archaebacteria, Asexual
Reproduction, Assimilation, Atmosphere, Autogenic
Cycling, Biomass, Biome, Biosphere, Biotic,
Explosion,Carbohydrate, Carbonate, Carbon
Dioxide, Carnivore, Cation
Exchange, Cell, Cellular, Cellulose, Chalk, Chaparral, Chemical
Weathering, Chlorophyll, Clay, Climax, Climax
Community, Coal, Colonization, Community, Community
Boundaries, Competition, Coniferous, Consumer, Cyanobacteria,
Deciduous, Decomposer, Decomposition, Denitrification, Dispersal, Dissociation, Distributional
Limit, Disturbance, Detritivore, Detritus, Detritus
Food Chain, Dispersal, Divergent
Evolution, Diversity, Dolomite, DNA,
Niche, Ecosystem, Ecotone, Electromagnetic
Energy, Element, Eluviation, Energy, Environmental
Gradient, Epiphytic, Erosion, Establishment, Eukaryota, Eukaryote, Evolution, Exploitation, Extinction, Evapotranspiration, Evaporation, Evolution,
Model of Succession, Fermentation, Fixation, Fixed
Diversity, Genus, Geographic
Range, Glucose, Grazing
Food Chain, Gravity, Gross
Primary Productivity, Gross
Haploid, Heterogeneity, Heterotroph, Homeostatic, Herbivore, Holistic, Host, Humus, Hurricane, Hydrosphere, Hyphae,
Model of Succession, Inorganic, Interaction, Interference, Interspecific
of the Minimum, Leaching, Lichen, Lightning, Limestone, Limiting
Factor, Lipid, Lithosphere, Litter, Litterfall, Litter
Macronutrient, Mammal, Metabolism, Micronutrient, Migration, Mineralization, Molecule, Mutation, Mutualism, Mycorrhizae,
Natural Gas, Natural
Selection, Negative Feedback, Neutralism, Net
Primary Productivity, Niche
Specialization, Nitrate, Nitrification, Nitrite, Nitrogen
Oil, Optimum, Organic, Organic
Parasite, Pathogen, Peat, Permafrost, Photosynthesis, Photosynthetic
Autotroph, Phylogenic, Phylum, Pigment, Pioneer Species, Plant, Population, Positive Feedback, Potential
Energy, Precipitation, Predator, Prey, Primary Carnivore, Primary
Succession, Producer, Productivity, Progressive
Succession, Prokaryote, Protein, Protoplasm, Pyramid
Niche, Reduction, Reptile, Respiration, Resource, Retrogressive
Succession, Sediment, Sedimentary
Reproduction, Shale, Sink, Soil, Solar
Isolation, Species, Species
Associations, Succession, Sugar, Symbiotic
Taiga, Taxonomic, Temperature, Tertiary
Consumer, Time, Tolerance
Model of Succession, Tolerance
Range, Transpiration, Trophic
Problems and Exercises
(1). Discuss the concept
that ecosystems are essentially energy systems.
(2). Compare and contrast
the function and structure of the grazing and detritus
(3). What is an ecosystem?
How does it differ from a community? What are some
of its important components?
(4). Evolution describes
the process by which species come to possess adaptations.
In an essay, describe how evolution works through natural
selection, spatial isolation, and gene mutation.
(5). Explain in detail how
energy moves through the grazing food chain and the
detritus food chain. Also, discuss how these food chains
are related to each other and are necessary for the
cycling of nutrients in an ecosystem.
(6). What seven conditions
are required to define something as living?
(7). How did life begin?
How did it change from its beginnings to the present?
(8). Outline the four recognized
different groups of biological entities.
(9). What are some of the
major components of ecosystems? How are these components
related to each other?
(10). Describe how energy
flows through ecosystems.
(11). Discuss the term dispersal.
Include in your answer an explanation of why organisms
want to disperse, and how organisms accomplish this
(12). Discuss Connell and
Slatyer's three mechanisms of succession. Start your
answer with a definition and an example of what is
succession, and describe how succession begins.
(13). With the aid of a
diagram explain the ecological niche concept. Also,
discuss in your essay the difference between the fundamental
and realized niche, and the relationship between niche
and tolerance range.
(14). Compare and contrast
the characteristics (climate, plant types, animal life,
soil types, etc.) of the following biomes: Tundra,
Temperate Deciduous Forest, Desert, and Tropical Rainforest.
(15). Discuss the different
types of species interactions. Be sure to include in
your essay information on how each type of interaction
between two species influences the fitness of each
(16).Species vary in abundance
both spatially and temporally. Further, we can generalize
that a species will occur only where and when:
(a). It is capable of
reaching a location;
(b). Appropriate conditions and resources exist for survival; and
(c). Interspecific interactions do not preclude it.
Discuss these statements
(17). Understanding biogeochemical cycling
in an ecosystem requires complete knowledge of the
inputs and outputs to that ecosystem. With the aid
of diagrams and examples, discuss the cycling of a
nutrient in a typical ecosystem focusing on the concept
of inputs and outputs to a system.
(18). How do the following attributes
control the population dynamics of a species: natality,
immigration, mortality and emigration.
(19). Organic matter is continually being
added to the surface of soils by way of wastes and
death. Why is the input of organic matter important
in community and ecosystem function?
(20).Discuss in detail the nitrogen or
carbon cycle. In your discussion be sure to explain
how humans have altered these systems.
(21). Why should we be careful of introducing
exotic animals and plants into habitats where they
never existed before?
(22). How does competition differ from
predation or parasitism?
(23). What is plant succession? What
are the differences between a primary and a secondary
succession? How does facilitated succession work?
(24). What is an ecological niche? How
do fundamental and a realized niches differ?
(25). Why does the nitrogen cycle require