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Population Growth  Interesting
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Population Growth Diagram
Did You Know?????
Is the World Like
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U.S. Map Showing the 2010 Census
Populations grow in an environment until some force, either
internal or external to the population, slows or stops growth. An internal
force would be stress from many encounters with other members of the
population. External forces can be physical, including a reduced essential
resource such as water, air, food, or shelter, or biological, as is the case
when populations compete for similar resources or one population preys on
another.
When a population is
introduced to a new environment where survival conditions are good, growth is
generally slow at first and then becomes rapid as the population gains a foothold.
This is called exponential growth. Exponential growth cannot continue
indefinitely. Generally, some combination of environmental forces causes a
population either to decrease rapidly when it reaches a certain size or to
achieve an approximate state of equilibrium with the environment.
The ability of a population to grow in an unrestricted
environment where no forces are acting to slow the growth rate is called the
biotic potential. It has been calculated that a single female housefly laying
120 eggs at a time, of which 60 develop into females, would produce close to 6
trillion flies after seven generations, and flies might have seven or more
generations per year. The biotic potential is not recorded for many
populations. The maximum growth rate of a population does not continue for long
because of carrying capacity limits.
Most animal populations exhibit a growth pattern wherein the
numbers fluctuate about some mean size. This mean size, called the carrying
capacity, is usually the number of individuals the habitat can support at a
given time.
Interactions
Many forms of interactions occur among
individuals and populations living in the same habitat. They can result in
positive forces that aid the growth and survival of one or both of the
populations, or negative forces that result in a decrease or extinction of one
or both. A population can grow in an environment with all the necessary
materials for survival until space, food, or other resources become scarce. As
members of a population seek to use resources in short supply, they compete
with each other or with other populations.
Competition between members of the same species, called interspecific
competition, occurs as each member tries to get the best of everything: the
best food supply, the best mate, the best nesting materials, and so on. For
example, during the breeding season most male birds defend a territory against
other males of the same species. Territories of red-winged blackbirds are easy
to spot in a marsh because the males perch on top of the grasses and fly at
intruders.
Symbiosis occurs when organisms or species live together. Some biologists
stress the mutual dependency between two species which benefits both species
in their definition of symbiosis. Tree roots and fungi have this form of
relationship. Specific species of fungi grow around the roots of the tree,
particularly the very small rootlets. The fungi provide protection and some
nutrients for the tree; the tree, in turn, provides nutrients for the fungi.
Neither the fungi nor the tree can grow properly without the other. When soils
are devoid of fungi spores, trees are unable to grow.
Predation is one means of maintaining the balance of nature in an ecosystem.
The word predation is used to describe the eating of one individual by another.
Carnivores eat herbivores, large carnivores eat smaller ones, cannibals eat
their own kind. Such interactions occur between different trophic levels and
within the same trophic level. Energy flow in an ecosystem is very dependent
on predator-prey interactions.
Parasitism is a special case of predation. The parasite
(a predator) is smaller than its host (the prey) and does not destroy the host.
In parasitism, the tissue or food supply of the host is used by a parasite for
survival. Such interactions are part of a balanced ecosystem. From an
evolutionary viewpoint, any parasite that destroys its prey also destroys
itself. A number of diseases caused by parasites, including malaria,
schistosomiasis, and dysentery, are responsible for a tremendous amount of
human suffering in the world today. In their manipulation of the environment,
people sometimes alter the natural balance of these organisms. Cattle, for example,
are a reservoir for the parasite causing sleeping sickness that is transmitted
by tsetse flies to people. Suffering can be reduced by managing environmental
factors upon which parasites are dependent.
Commensalism is a relationship that benefits one
population and has no effect on the other. For example, cattle egrets and cowbirds
follow large grazing animals around. As the herbivores pull up grass and cause
disturbances with their hooves, many insects are dislodged. Thus, an easy meal
is provided for the birds, but there is no benefit for the herbivores.
Cycles
in Populations (Click on Picture to left)
The cyclic nature of population growth
often involves predator-prey interaction. The lemmings of the arctic region are
prey for the snowy owl. The lemming populations follow a three-to-five-year
cycle, with the owls lagging a year behind. When the lemming population
increases in size to the extent that it destroys its own food and shelter, the
population declines rapidly during a cold winter. The snowy owl population,
which increases in response to a large lemming population, is then left without
a source of food, causing many owls to starve or fly south in search of food.
Predator-prey interactions are but one component of the study
of population cycles; regulation of population density is another interesting
aspect. Some ecologists believe that populations regulate themselves by
density dependent factors. In effect, they say that more deaths occur at
higher population densities because predation, disease, and food shortage can
act more severely when numbers are high. Food shortage appears to be the chief
natural factor limiting any animal, such as the snowy owl. Another group of
ecologists believes that the effect of any mortality factor depends on its
severity and the population’s susceptibility to it. This group accepts the idea
that populations are regulated by density independent factors, so regardless of
the population size 100 or 10,000 given perturbation will result in killing
the same percentage of the population.
Population
Distribution
Age
by Country
A population must have all of its essential needs met in order
to survive in any location. The habitat is the area where all the needs of a
population are satisfied and where we would find a member of that population.
Because species arrive at their respective niches through long
periods of evolution, no two species in the same community have the same niche.
Furthermore, quite unrelated species can occupy similar niches. For example,
kangaroos, bison, and cows are all grass eaters. They occupy similar, but not
identical, niches in different ecosystems. When a population is forced to leave
a particular habitat, its niche is taken over by another. The loss of large
grazing animals might result in more insects that feed on herbaceous material.
To maintain natural communities, it is critical for us to combine
comprehension of the biology of natural populations with effective planning of
changes in natural systems. We now understand that species in natural communities
evolve over millions of years in response to environmental conditions and that
community succession occurs over hundreds of years. Rapid alteration of these
conditions reduces the time available for the populations to respond, causing
many to become extinct.
Genetics
 Genetics
Human-Genetics
Genetics is the study of the biological
transmission of characteristics from one generation to the next. Not all the
characteristics a particular individual exhibits, however, result from transmission
of biological information from the parents. Some characteristics are the
result of the individual’s interaction with the environment. Because
characteristics are generally influenced by both genetic inheritance and the environment,
it is appropriate to discuss genetics in an environmental science book.
An individual’s genetic makeup is the genotype, which includes
all the genetic information passed down from both parents. Individual
appearance is referred to as phenotype. The genetic makeup or genotype sets the
limit to which an individual can respond. This limit can be thought of as a
scale. Within that scale, different responses or appearances, the phenotype,
are possible depending on different environmental characteristics. Thus, in
humans, a difference in diet can result in different phenotypical expressions.
Skin color is also partially determined by the environment. Exposure to the sun
generally darkens human skin, but a limit based on the individual’s genotype
determines the degree to which the skin can darken. Pigment beneath the skin
may be quite limited in some fair-skinned individuals and they may not darken
at all, but may burn quickly. On the other hand, eye color is influenced
entirely by genetics.
Genetic material is passed from parent to offspring in each
generation via chemical structures in the body. This revolutionary approach in
biology is one of the major discoveries of the 20th century and is the
foundation for major changes in our ability to develop new sources of food, to
respond to diseases, and to control the environment.
An individual’s chemical units of inheritance are genes. All of
the individual’s genes constitute its genotype. Genes combine in most plant
and animal cells on long rod like structures called chromosomes, long molecules
of deoxyribonucleic acid (DNA) associated with a number of proteins. The DNA
and proteins are organized in a specific way, consisting of a double helix
which continuously coils around and is connected by other chemical elements.
At least one complete set of chromosomes is found in all cells
of most plants and animals. The number of chromosomes varies from one species
to another. Some plants have only four chromosomes, and there are animals with
as many as 500. The number of chromosomes is usually, but not always,
consistent within a species and is not correlated with either the size of the
individual, the size of cell, or the evolutionary advancement of the species.
Chromosomes generally appear in homologous pairs that align together during
cell division. Each chromosome within the pair has identical loci with genes
that control the same characteristics. The chromosomes are duplicated as the
cell divides and an identical set goes to each new cell. Cell division
resulting in the reproductive cells, egg and sperm, varies from cell division
in nonreproductive cells. The reproductive cell contains only one member from
each homologous pair of chromosomes in a body cell. During sexual reproduction,
the reproductive cells unite to form the basic cell of a new individual, a
zygote. A zygote therefore contains one set of chromosomes from each parent.
These chromosomes then unite or pair up in the zygote, and cell division begins
as the new individual develops with a complete set of chromosomes in each of
its cells. This resulting process means that not all a parent’s individual
characteristics are passed on to their offspring—half are. Different forms of
reproduction occur in some organisms.
Specific sites on chromosomes are occupied by genes. A site is
generally called a locus. Geneticists have been able to determine the location
of some individual genes on chromosomes. Some genes are known to control specific
characteristics or expressions of an organism. As geneticists continue to
investigate the location of different genes and their controlling factors in
humans and animals and plants, they develop some ability to control the destiny
of populations.
Gene
Pool
Members of a species are often distributed
over a wide geographic area, but because they can interbreed, they are
considered members of the same species. As a result the species can be composed
of many local populations. An individual’s genetic make-up is often different
from another’s in the population. A local population can have a different
combination of genetic material than another population, but both populations
are the same species. Within a population, the total genetic information carried
by all interbreeding members is the gene pool. The gene pool is a population,
not an individual, characteristic. Where a population’s genetic makeup is
diverse, an individual may have only a small representation of the total gene
pool.
An individual gene can have a number of chemical forms that
cause different expressions of the characteristics the gene influences. Each
state of a gene is an allele. There may be one, two, or a number of alleles for
each gene in the population’s gene pool. Obviously, if there is only one
allele, the expression controlled by that gene should be the same in each
individual in the population unless some factor from other genes or the
environment overrides the expression of the characteristic.
Population genetics focuses on the total group or population
rather than on an individual. We will examine different genes present and genotypic frequency from one generation
to the next in a population rather in individual’s. The idea is to determine
how gene frequency affects the way a population lives and evolves. Rapidly
growing populations are occupying many new areas or concentrating heavily in a
particular habitat. It is possible that these populations have a different gene
frequency than populations that decline because of major changes in the
habitat. Likewise, the environment may change in such a way that a population’s
genetic makeup allows only certain members to survive. When this occurs, gene
frequency can change considerably.
Dominant/Recessive
Genes
Even though two alleles of a gene might be
present, the phenotypical expression of each may not be the same. In some cases
one allele masks another; the gene that masks the other is dominant. As an
example, each parent in the human population passes on to a child one gene for
eye color. The child has two sets of genes. If one gene is the allele for brown
eyes (B) and the other is the allele for blue eyes (b), the child’s genotype is
Bb. The child’s eye color will be brown, because the brown allele is dominant
over the blue allele. Thus a child with a genotype BB will have brown eyes,
with Bb will have brown eyes, and one with bb will have blue eyes. This shows
us that brown-eyed individuals can produce blue-eyed offspring; however, when
both parents are blue-eyed, all their offspring will most likely be blue-eyed.
Individuals in whom
alleles of the same gene are identical are homozygous for that allele; those in
whom the alleles differ are heterozygous for the gene. Thus in the case of eye
color, BB and bb are homozygous and Bb is heterozygous; in the case of blood
type, MM and NN are homozygous and MN is heterozygous. We can see that
population characteristics may exist, but may be masked by a dominance
characteristic. Further complicating factors result in masking traits that may
exist when the multiple gene effect is considered. Many of an individual’s
characteristics including eye color are based on a number of genes, and it is
possible for one gene to mask the effect of another.
Sex-Linked
Characteristics
Some genetic material passed from parents
to offspring is associated with one sex or the other. In some animals, one set
of chromosomes is referred to as the sex chromosomes. Women have two female
chromosomes in this pair, and males have one male and one female chromosome.
The passing of sex chromosomes to offspring is similar to the division of
genetic material. Each male has one male chromosome designated Y and one
female chromosome designated X, and each female has two X chromosomes. When the
egg and sperm cells form, chromosomes divide, and each egg cell contains one X
chromosome from the sex chromosome pair, while each sperm contains either an X
or Y chromosome. When the egg and sperm combine, a male or female is formed.
Some genes are associated with these sex chromosomes, and the characteristics
these genes control are sex-linked.
These characteristics cannot be determined based on normal
distribution. One sex-linked trait in the human population is a form of
colorblindness. The gene for this condition is carried on the X chromosome,
and the allele for colorblindness is recessive to an allele for normal vision.
If a male receives an X chromosome from his mother that has an allele for
color-blindness, he will be colorblind because the Y chromosome does not carry
an allele for normal vision. Because a female has two X chromosomes, she may be
heterozygous for the allele. That is she would have normal vision but be a carrier of
the allele for color-blindness. A female with two X chromosomes that contain
the allele for colorblindness would be colorblind.
Mutations
Because of the number of possible genetic
combinations, the members of a population at any given time represent only a
small fraction of all possible genotypes. Changes can occur as the gene pool is
reshuffled each generation to produce new combinations in the genotype of the
offspring. No new alleles are produced in this process, only recombinations.
The production of a new allele can occur, however, and is referred to as a
mutation. Mutations actually increase the genetic variation in the population.
Mutations occur as the result of a change in one of the chemicals at the gene
or large changes in the chromosome. Changes at the individual gene loci are
called point mutations. Spontaneous mutations can occur.
Some genes and chromosomes seem to be more susceptible to mutations
than others. Massive changes in the environment, on the other hand, have
accelerated the mutation rate in some species. Specific chemicals found in air,
water, and soil and radioactive materials has increased the mutation rate in
organisms. In a number of cases, mutations have proven deleterious or harmful
to the organism. Many people believe that mutations resulting from radiation
produce cancer or other diseases in humans.
Migration
Different mutation rates in different subpopulations or
populations of the species can create allelic frequencies in those populations.
As a result, environmental pressures may allow different characteristics to
appear in different populations. Migration of genetic material in the
population occurs as individuals move between the two populations and
intermix. Migration can thus be regarded as the flow of genes between two
populations that were once geographically isolated
Inbreeding
Isolation of populations can create another phenomenon is
referred to as inbreeding. When a small group of individuals isolate themselves
and mate with individuals locally rather than on a random basis, serious
inbreeding occurs. In other words, individuals in small populations may have
homozygous characteristics for certain forms. As these individuals continue to
mate, any form of heterozygousness may disappear. The potential for genetic
variability therefore decreases. Inbreeding results from isolation caused by
geographic barriers, religious barriers, and behavioral barriers. Inbreeding
is of great concern when we are dealing with endangered species.
Evolution
Introduction
to Charles Darwin's Theory of Evolution
The
Evidence for the Theory of Evolution
Genetic
Evolution
Selection
Mutations and
migration introduce new alleles into a population. Natural selection, on the
other hand, is the force that shifts gene frequency within a population and is
therefore a driving factor in creating change in a population.
When a
particular genotype/phenotype confers an advantage to an organism in
competition with others that have a different combination, selection occurs.
This means that a larger number of offspring of the organism with the advantage
will survive. The relative strength of the particular selection varies with the
degree of the advantage. The probability that a particular phenotype will
survive and leave offspring is a measure of its fitness, which refers to the
total reproductive potential or efficiency. Fitness is usually expressed in
relative terms by comparing a particular genotype/phenotype combination to one
regarded as optimal. Fitness is a relative concept because as environmental
changes occur, so do the advantages conferred by a particular phenotype. Any
gain in fitness by one unit of selection is generally balanced by losses in
fitness of others.
Adaptations
Some members of a population develop characteristics,
or adaptations, that make them better suited to their environment. Human
ancestors adapted to the extensive forests which stretched over the earth about
70 million years ago. Anthropologists speculate that long periods of drought
reduced the types of forests over millions of years, giving advantages to
those individuals who could adapt to the more open savanna.
Adaptations that made early humans better able to live on the
savanna included upright posture, rapid movement on two legs, use of hands for
grasping material, loss of hair through increased activity, and a dark skin pigment
to prevent harmful effects from the sun.
A more recent example of human adaptation is found in certain
areas of central Africa. There the inhabitants have been exposed to years of
malaria. The malaria parasite in the victim’s bloodstream deformed some red
cells into the shape of a sickle. Apparently, those individuals are more
resistant to the malaria parasite. Over the years they have become dominant in
the area, so this trait was passed on to their descendants. While this special
trait served the people well who were exposed to malaria, the same sickle cell
does not function well in carrying oxygen throughout the body. Thus, under
stress situations which require more oxygen, those with this adaptation are
vulnerable and in danger of dying from the sickle cell trait as well as from
anemia and complications.
Each adaptation making individuals in a population better
suited to their environment allows them to leave more offspring and so
contribute more genetic material to future generations. Random genetic forms
appear regularly, but the survival of the new individual depends on how well
it can adapt to its environment. The dominance of a new genetic form as a
result of environmental change is called natural selection. A change in the
genetic makeup of a population over time through natural selection results in
evolution.
Speciation
In an environment that is changing, new genotype/phenotype
frequencies may become dominant. Changes such as habitat alterations,
earthquakes, and volcanic eruptions isolate some individuals in population from
others. Currently, parks, reserves, and refuge populations are becoming
increasingly isolated from other populations by habitat modification. Population
isolation can occur both geographically and behaviorally.
Speciation has resulted in a diverse array of genetic material,
so that the living components of ecosystems can better interact and withstand
stress factors. Actually, isolation rarely produces new species; it may make a
population susceptible to predators, diseases, or forms of competition that
impede population growth.
Hybrids
Behavioral differences in individuals can also create
isolation. The courtship pattern of some waterfowl species isolates them from
other species. When the courtship pattern is broken down, these populations can
interbreed. When two populations that were considered a species interbreed, the
resulting offspring is hybrid. In waterfowl species, mallards can form hybrids
in the wild with eight species of ducks. Many of the ducks in parks began as
hybrids between mallards and other species. Hybrids can sometimes breed back
with members of either of the original populations, or they sometimes cannot
breed at all. If hybrids can breed back to members of the original population,
the flow of genetic material can occur between two populations.
Extinction
A population that no longer exists is
extinct. Many animals have become extinct over the last hundred years,
including the dodo birds, passenger pigeons, and the Carolina parakeet. Extinction
can occur in the species or in a population. Often, environment changes in such
a way that a particular population’s genetic pool can no longer adapt and
therefore produce offspring. This form of extinction has probably occurred many
times historically. While climate, habitat change, and other factors can cause
local extinctions, a chronic presence of low-level pesticides or major environmental
changes can cause declines throughout a species’ range.
Conservation
efforts throughout the world are now directed at preventing extinction of many
species, and habitat management seems to play a key role. Habitats have changed
so that they no longer support the species, or the species can no longer
survive in relation to changing conditions, such as the influx of human
populations. Zoos and other reserves are often used to preserve species. Nearly
one-third of all bird species and one-sixth of all animal species have been
bred in zoos in recent years. Zoos often maintain species under artificial
conditions, but many feel that by maintaining the gene pool of individuals in
these isolated conditions may enable us to develop breeding programs and eventually
release individuals back into the wild.
Urban Populations
The urban sprawl that has characterized
American growth patterns for the past 45 years has been held responsible for a
host of problems, including: profligate energy use; rising municipal
infrastructure costs; the loss of agricultural and wetlands; the loss of
community values; the erosion of current or potential tax bases in urban
centers; and the decline of urban environmental quality.
While many factors contribute to sprawl,
the suburbanization of America could not have occurred without the automobile.
If auto use remains cheap and easy, we can expect continued sprawl. Given the evidence that low density
development in turn leads to increased reliance on automobiles, the problem
appears to feed on itself. There are two main issues facing American
planners. The first derives from the fact that suburbanization is currently
the norm, both for work and residences. Less than 10% of the total population
work in the central business districts of traditional cities (Lowry,
1988). The first issue, then, is how
best to provide access to existing jobs and residential amenities not located
in the city center. The second issue is what shape future growth should take. Transportation
decisions will be critical to both of these issues.
The conventional view is also that
continued sprawl is inevitable and that planners must simply respond by building
more roads. Evidence for
this proposition is provided by pointing to the fact that transit used
primarily by those who work or live in central business districts, whereas the
majority of the population relies on their cars. To assert that this pattern
demonstrates an underlying preference for automobile use assumes that
transportation and land use decisions have evolved in the absence of public
planning. However, both travel behavior and land use patterns are at least in
part also functions of public policy. In particular, the current
decentralization of services and employment could have not occurred in the way it did without extensive
reliance on the highway.
Land use policies, or lack of thereof,
have also contributed to sprawl. While current practice is changing, American
land policies have traditionally had little focus on controlling growth
(Altshuler, 1981;Bay vision 2020). Indeed, low-density suburbanization has been
encouraged by federal tax deductions and mortgage guarantees for single family
residences (Heilbrun, 1987 and Pucher, 1988). Many of the direct costs of
servicing low-density developments are hidden and not passed directly on to the
homeowner (Frank, 1989). Similarly, local density limits and red lining
encourage sprawl. Even where growth is a concern, fragmented regional
governmental structures hinder efforts to address the issue (Heilbrun, 1987;Bay
Vision 2020, 1991). While some affluent neighborhoods have passed no-growth
ordinances, the net effect has simply been to push sprawl elsewhere. This
fragmented local government structure also lacks the capacity to engage in the
comprehensive planning required to integrate social, environmental, transit and
other transportation considerations into regional development.
Continued reliance on the automobile, as
the only solution to the transportation demands of the future is unlikely to be
successful. Continued emphasis on highway construction may be
counter-productive. As is noted above, added capacity will not solve the growing
problems of air pollution and congestion. Providing access to the
city center by mixed modes of road and transit can allow a city to grow beyond
that point while remaining attractive and livable (Newman and Kenworth,
1989).
Any policy directed at the problem of
sprawl must address Americans' high willingness to pay for the space and privacy
offered by suburban lifestyles. In addition, there is no question that
automobile use is at least in part determined by Americans' preference for the
privacy, convenience and speed of their cars. The evidence from Europe and
Canada is that by incorporating mixed modes, including transit, cycling and
pedestrian access into urban plans, future development could actually enhance
"access" while reducing the demand for and social costs of travel.
Currently more than 50% of the world's
population are urban dwellers. By 2025 about 65% of people will be living in
urban areas. Reshaping existing cities and designing new ones to be sustainable
becomes a priority. Urban areas have
populations of more than 2,500 people and some countries use 10,000 to 50,000
residents. Rural areas have fewer than 2,500 people. Between 1950 and 1996 urban population increase 13 folds. By 2925
urban population may reach 5.5 billion and 90% of urban growth is in developing
countries. Urban growth shows these
trends:
1. U.N.
projects by 2025- 60% of the world's population will be living in urban
population
2. Large
cities are rapidly increasing. By U.N. Projections in 1996 there were 290
cities of 1 million population and in
2025 there will be 400 cities of 1 million population. Currently there
are 21 megacities of 10 million plus population.
3. The urban population in developing countries
is growing at 3.5% per year and will be 5% by 2025.
4. Developed countries'
urban growth is less than 1% but will be 84% urbanized by 2025.
5. More poor people migrate to cities. Urban
poverty will increase. Globally, about 100 million people are homeless.
Half of all urban children under 15 years
live in extreme poverty with little or no family support. Urban populations increase by more births
than deaths (natural) and by immigration. Cities are centers for new jobs,
higher income, trade and better health care. Freedom from village customs as
well as poverty, drought, lack of land ownership, war and famine are factors.
Governments distribute more social services and income to urbanites. Mexico City is a classic example of
mega-city problems.
How urbanized is the United States? The U.S. has had three major population
shifts.
1. Migration to large
central cities. -50% population live in metro areas.
2. Migration from large central cities to
suburbs and smaller cities. 41% population in large central cities, 59% in
suburbs.
3. Migration from North and East to South and
West. Since 1980, 80% population increase has occurred in the South and West.
Many of the worst urban environmental
problems in the U.S. and developed countries have declined greatly. The major
problem facing U.S. cities are deteriorating services, aging streets, schools,
housing, sewers and lost tax revenues as people and businesses move out of
large central cities.
Poverty
Poverty rises as well as violence, drug
abuse, crime and blight. Environmental
problems in urban areas are due to poverty and/or economic growth that is in
resource use resulting in pollution and environmental degradation. Most cities
today import food, water, energy and other resources from near by lands and
watersheds. They produce waste and pollution that affects areas within and
outside their borders. There are environmental benefits to urbanization.
Recycling is economically practical, birthrates are lower than rural areas,
better opportunities are available for education about environmental issues,
more money is spent on environmental protection than in rural areas, and
concentrating people in urban areas reduces stress on wildlife habitats
which helps to preserve biodiversity.
Green Cities
Most cities have very few trees and food
producing gardens. Trees help to absorb air pollution, give off oxygen, cool
the air with leaf transpiration, muffle noise, provide wildlife habitats, and
increase beautification. Individuals
can grow their own food by planting community gardens such as farm-a-lot,
roof-top gardens, school gardens, and
cities can encourage farmer's markets which allow farmers to sell
directly to customers. This encourages local production and consumption, which
keeps resources in the area. Farmlands
are able to resist urban sprawl.
Cities have water and flooding
problems Water is transferred to urban
areas at the expense of rural and wild areas. Surface water and groundwater is
depleted faster that it can be replenished. Paving land and covering land with
buildings causes run-off to occur faster, overloading sewers and storm
drains which contributes to water
pollution. Cars contaminate runoffs with oil and toxic liquids. Road salts for
deicing is a major pollutant in the Clinton River Watershed. Large expanses of
concrete or asphalt can prevent recharging of groundwater. Development on flood
plains, areas subject to natural flooding, cause flood damage to the sites and
water pollution. Many of the world's cities are in coastal areas that will be
prone to flooding, especially with increased global warming and sea levels
rising. City dwellers generally are
subjected to more pollution than rural dwellers. People of developing countries
suffer from air pollution due to using coal, charcoal and wood for industry and
home cooking and heating.
The World Bank says developing countries
can not afford to treat their wastewater and to purify their drinking water. In
Latin America, 98% of urban sewage receives no treatment. City dwellers have
better access to education, social services, and medical care. The crowded
condition of urban living does increase industrial and traffic accidents,
increase infectious diseases from sewage and unclean drinking water. Health
problems are affected by exposure to pollution and noise.
Death Rate
Death Rate Due to Disease
Activities that Shorten Life Span
Urban Sprawl is
threatening the quality of life in areas near central cities. The developing countries travel mostly by
foot, bicycle or motor scooter. Only 1% of their population can afford to have
a car. Automobiles are convenient and
provide mobility, but they are the largest source of air pollution (22% of
global CO2). Auto emissions are strict in the U.S. but this is
offset by increase in number of cars and distances traveled by cars. Fifty
percent of the world's total oil consumption is devoted to transportation.
Sixty percent of the oil used in the U.S. is used for transportation.
Car culture cities are locked in traffic
jams and road rage has increased. The major hidden cost of driving include
traffic injuries and deaths, air pollution, time wasted in traffic grids, and
cost of military intervention to guarantee Middle East oil supply avenues.
Paying for the true costs of automobile use can break this cycle. Drivers need
to pay gasoline taxes for transportation infrastructures such as roads. Today
these costs are covered only 60% to 70%
By taxes and the rest is subsidized by federal, state and local
governments. Heavy trucks cause
extensive damage to roads and they are subsidized by public funds. This
gives trucking an unfair advantage over more efficient and less damaging rail
freight. These hidden costs are not put on the cost of cars, trucks and gasoline
because it would be very unpopular politically. Developing countries should
promote modern efficient low polluting public transit systems and avoid the
private auto transportation's developed countries embraced. Bicycles, walking
and mass transit such as buses and light rail such as streetcars are much more
efficient.
Land Use Planning Based Upon
Population
Conventional land use
planning is based on increasing growth and environmental growth regardless of
uncontrolled urban sprawl. Most revenues for public services come from property
taxes so there is great pressure to develop the land. Usually, the cost of
development and services exceeds the tax revenue from property. If taxes get
too high, resident and businesses move away and the tax base worsens. Detroit's
population shift to the suburbs is an example of this.
Ecological land use planning
is a complex process that has to consider many
factors:
1. Areas need to be identified and protected
that are necessary for protecting water quality, supplying drinking water,
reduce erosion and flooding.
2. Goals need to be identified and prioritized.
Should economic development and
population growth be encouraged or discouraged? What lands should be
preserved from development?
3. Maps need to be developed showing
socio-economic, geological and ecological factors.
4. Form a master plan, considering how the
three factors interact.
5. Master plan
is renewed by experts, public officials and the general public and is written and approved.
6. The master plan needs to be implemented,
monitored, updated and revised.
Ecological land-use planning is not widely used because
politicians up for re-election focus only on short-term problems and are often
influenced by development forces.
Zoning laws that encourage homes, workplaces and shopping areas to be
mixed, reduces urban sprawl, energy waste and loss of community. High-density
residential development should be along public transit lines. America's older cities have enormous
maintenance and repair problems that are due to years of neglect. Sewage
backups into residential basements when it rains. Bridges are unsafe; Highways
are in poor condition and need repair.
Urban open spaces need to be preserved.
New cities can develop large to medium size parks while older cities can
turn abandoned buildings and lots into small to medium parks. The greening
(link) open space can provide recreation areas for urban residents.
Urban areas need to become self-reliant, sustainable and have a
high quality of living. Sustainable cities need to be in balance with its
surrounding countryside. Suburbs need to build houses and apartments in small
dense clusters which make more open space available, develop a town center for
civic life focus and community spirit, plant more trees than are out and
encourage walking and bicycling and less dependence on the automobile. Chattanooga, Tennessee has worked to become
more sustainable. They have projects that:
1. Entire zero-emission industries to locate locally.
2. Renovate low-income housing.
3. Build tourist attractions such as museums and aquariums to renew
the downtown.
4. Replace buses with non-polluting electric buses.
5. Develop a 5 mile long Riverfront Park.
6. Launching an innovated recycling program.
Urban areas that do not become more ecologically sustainable
over the next 20 years are encouraging economic depression, increased
unemployment, pollution and social tension.
Conclusion
Populations are composed of individuals of a species that
occupy a particular place at a particular time. Population demographic characteristics
differ from those of their individual members. Population characteristics
include birth rate, death rate, age distribution, and genetic composition or
gene pools. Habitat carrying capacity has a restrictive nature on population
growth. Populations can interact through competition, predation, parasitism,
and in other ways. Areas that satisfy a population’s needs are called habitats.
The population’s role in that habitat is its niche. Lack of habitat limits a
population’s distribution. |
