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Ch.50 Ecology Review
Key Concepts:
Dispersal and Distribution, Biotic
Factors, and Abiotic Factors
By Christopher Choe, Paul Bergin, Mario Gagliardo, Michael Goglia
Dispersal and Distribution
 Dispersal is the movement of individuals away from
centers of high population density, and results in
broad patterns of geographic distribution.
 Natural range expansions of organisms
demonstrates the influence of dispersal on
distribution Organisms move into areas where they did not
previously exist.
 Dispersal-a key factor in limiting distribution (depends
on whether or not species transplants are
successful or not)
Effects of DDT and other pesticides
 Dispersal and distribution are greatly affected by herbicides,
pesticides and other chemical products.
 Dispersal and distribution normally depend upon the climate and
ecosystem; the usual limiting factors are prey and predators.
 Poisonous pesticides, if not immediately devastating an
ecosystem, will generally pass through it by cycling.
 One of their many effects include destroying food sources. This
prevents the distribution of new offspring in polluted areas and
causes species to move elsewhere. In addition, the areas that
would ideally be used for relocation could be poisoned as well,
preventing dispersal of organisms.
The Greenhouse Effect and Distribution of
Species
The greenhouse effect is the impact of heat being retained by
gases in the atmosphere on the Earth’s climate.
Climate change alters distribution in several ways:
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Higher air temperatures increase fire risks for vegetation, and lower soil
moisture.
Rising sea levels increase the amount of sea water into freshwater or wetland
areas, also known as saline intrusion, which occurs mainly in estuaries.
They can also increase the frequency and size of storm surges, a type of
disturbance in communities. *Only moderate disturbances can contribute
positively to species.
Higher sea surface temperatures can change nutrient cycling within
ecosystems.
Biotic Factors
 Biotic factors are the living components or all the organisms
that are part of an individuals environment.
 Such factors may be responsible for the distribution of several
species.
 Species transplants, for example, can result in the species’
inability to complete a life cycle.This can be a direct result of
negative interactions with other species through the form of
predation, parasitism, disease, or competition, all biotic
factors.
 More often, predators and herbivores are the biotic factors
involved in limiting distribution.
Effects of DDT and other Pesticides
The threat that DDT poses to living organisms involves biomagnification, and it
begins with microorganisms.
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While microorganisms are affected by DDT, many tend to keep it inside of them
rather than dying. This causes a chain reaction, as they make up the bottom of
the food chain.
Likewise, many small creatures on land (ex. Earthworms) can accumulate DDT
in their systems, which is harmful to predators that eat them.
In birds, DDT causes the thinning of eggshells.
Humans can also accumulate DDT in their bodies, where it is stored in fatty
organs and can be extremely harmful to bodily functions
Pesticides are used to kill unwanted living things, and their effects are not limited
to what they are applied.
They can affect many processes of living organisms, including growth,
reproduction, neurological development, and the immune system.
Global Warming and Biotic
Factors
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Global warming is causing polar ice caps to melt, resulting in
increased water levels.
Due to the lack of thermal and light energy because of the increasing
depth of water in aquatic environments, marine organism populations
may decrease.
Because mountain snow packs will melt earlier, probably in the
spring, conditions will actually be drier when crops are most in need of
the water, in midsummer.
Global warming is entailed by high rates of climate change. Many
organisms, primarily plants, won’t be able to survive the changing
conditions. This is because of the rapidity of the changing climate,
giving populations little time to move into areas with more suitable
conditions.
Abiotic Factors
Abiotic factors are essentially non-living components that effect the living
organisms of the freshwater community.
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Four abiotic factors are temperature; water, sunlight, and wind. They are the major
components of climate, the prevailing weather conditions in an area.
Environmental temperature is an important factor in the distribution of organisms because
of its effect on biological processes. An organismʼs internal temperature is affected by heat
exchange with its environment, and most organisms cannot maintain tissue temperatures
more than a few degrees above or below the ambient temperature.
The dramatic variation in water availability among habitats is another important factor in
species distribution.
Sunlight provides the energy that drives nearly all ecosystems, although only plants and
other photosynthetic organisms use this energy source directly.
Wind amplifies the effects of environmental temperature on organisms by increasing heat
loss due to evaporation and convection.
Also, the physical structure, pH, and mineral composition of rocks and soil limit the
distribution of plants.
Effects of DDT and other Pesticides
 The effect of DDT and generally all pesticides
on abiotic factors in a habitat are similar to
those of acid rain.
 Once DDT enters a lake, stream, or river it
pollutes it, as it is a poisonous substance.
Therefore, it effects water availability.
 DDT is also highly persistant in soil, having
the ability to last up to 15 years.
Acid Rain and Abiotic Factors
Acid rain is precipitation containing amounts of nitric
and sulfuric acid above normal levels.
 Acid rain effects abiotic factors in several different ways:
 Because of certain components in acid rain, toxins are
mobilized, which take away several vital nutrients and minerals
in soil.
 The resulting decline in plants dependant on the soil will in turn
affect the chain of herbivores dependant on the plants.
 Acid rain can directly affect the water availability of habitats,
such as lakes.
 Water in lakes that becomes acidified is not available for use; it
cannot support he variety of life as healthy bodies of water can.