Lecture 07

Environmental Science

Population

   
 Seminar Song

 

  This lecture may be listened to by clicking the word lecture. It will take several seconds to begin.
You may also download this lecture by right clicking, the word lecture, and ďSaving Target asĒ to your computer.
 
 

Population Growth    Interesting Clock   

            Population Growth Diagram        Did You Know?????         Is the World Like Me?            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 foot≠hold. 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 environ≠ment, 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 inter≠esting aspect. Some ecologists believe that populations regulate themselves by density dependent factors. In effect, they say that more deaths occur at higher population densities be≠cause 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 populationís 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 individualís 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 individualís 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 individualís 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 individualís chemical units of inheritance are genes. All of the individualís 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 parentís individual characteristics are passed on to their offspringóhalf are. Different forms of reproduction occur in some organ≠isms.

††††† 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 individualís genetic make-up is often different from anotherís 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 populationís 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 populationís 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 presentand genotypic frequency from one generation to the next in a population rather in individualís. 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 populationís 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 childís genotype is Bb. The childís 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 heterozy≠gous. 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 individualís 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 chromo≠somes 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 hetero≠zygousness may disappear. The potential for genetic variability therefore decreases. Inbreeding results from isolation caused by geographic barriers, religious barriers, and behavioral bar≠riers. 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 victimís blood≠stream 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 situ≠ations 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 in≠teract 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 populationís 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 speciesí 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 an≠imal 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 notoccurred 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 1996urban 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 in2025 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 whichhelps 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, andcities 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. Farmlandsare able to resist urban sprawl.

††††† Cities have water and flooding problemsWater 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.

 

Pollutions Affect on Population    Human Activities

††††† 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 causeextensive 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 manyfactors:

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 populationís needs are called habitats. The populationís role in that habitat is its niche. Lack of habitat limits a populationís distribution.