Review the “Conservation Genetics” section in the instructional materials for this learning plan. Make sure you review the web links and case study. In your discussion post, explain genetic diversity and why is it important. Also, describe two factors which impact genetic diversity.

Learning Plan 5 Instructional Materials
Conservation Genetics
It’s important to understand what reduced population size, near-extinction and reduced habitat
space can mean to a given species. When the habitat for a given species is reduced and
numbers of that species’ population die back, the overall genetic pool is also reduced. Genetic
diversity is one of the means by which species avoid extinction because of disease and other
problems. Studies on populations that have been reduced to small numbers before conservation
allowed them to repopulate have shown serious threats to the long-term survival of those
species due to the reduced genetic diversity.
For example, when people get sick, some may be really sick, while others seem almost
immune. Because humans have somewhat different genetic construction, some people are
more or less susceptible to certain diseases based on their genes, while others are less affected
or even immune. What might affect one person greatly may not do the same for a second. Now
imagine that you were cloned 10 times and that you and your 10 clones became ill. If one died,
you all would most likely die, because you all have the same susceptibility to the same diseases
and hardships because you have the same genetic makeup. Genetic diversity is how
populations can survive and evolve through natural processes and catastrophes.
Cheetahs are an example of this point. Genetic studies have shown that the genetic makeup of
the male cheetah is so identical that skin grafts can be transferred from one to another without
an immune response against it. Genetic studies suggest that at one point there was just one
cheetah alive that gave rise to the current population of genetically near-identical male
cheetahs. Cheetahs have low fertility rates, deformed sperm and low infant survival, and
scientists say that lack of genetic diversity is one of the factors attributing to these issues. Thus,
reduced genetic diversity from a population reduction can contribute to future survival rates and
chances for the entire species.
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Case Study: In the days of Lewis and Clark, there were more than 50,000 grizzly bears
in North America. Because of loss of habitat and hunting, the grizzly bear population in
the area of Yellowstone National Park, were reduced to a population of just over 150
bears and were consequently put on the U.S. endangered species list in 1975. At that
point, they could be located in just 1 to 2 percent of their original roaming ranges.
Because of a serious threat of extinction, several conservation plans were put into place
to help save and protect them. Extensive recovery plans and research were
implemented that spanned private, public, and governmental sectors. Now, the bears’
population numbers have increased to over 500, and the U.S. government is considering
taking them off the endangered species list. You can read more about this topic at the
U.S. Fish and Wildlife Web site on grizzly bear conservation programs:
http://mountainprairie.fws.gov/species/mammals/grizzly/factsheettalkingpoints111405.pdf
Question: If the Yellowstone populations of grizzly bear were reduced to between 100200, their genetic diversity would also be reduced, along with and their ability to survive
natural disasters and hardship. How do you feel that could affect the current recovery
population of grizzlies? In what ways do you think density-dependent and density-

independent factors will have more or fewer effects on the reduced gene-pool grizzlies?
Is 500 enough to take them off the endangered list? How would it be different than the
effects on populations of bears with greater genetic diversity? What are some options for
dealing with these issues?

Human Populations
Basically, then, there are only two kinds of solutions to the population problem. One is a "birth
rate solution," in which we find ways to lower the birth rate. The other is a "death rate solution,"
in which ways to raise the death rate - war, famine, pestilence - find us. Paul Ehrlich: The
Population Bomb, p. 17.
Until the Middle Ages, human populations were held in control by diseases, famines and war. It
took all of human history to reach 1 billion, and just 150 years to reach 3 billion, and just 12
years to go from 5 to 6 billion. The human population tripled during the 20th century alone.
Thomas Malthus (1798) argued that human populations tend to increase exponentially when
there are plenty of resources and available food but that humans will eventually use up their
food supplies and experience a population crash. He noted that while world populations can
increase geometrically (exponentially) that food supplies instead increase arithmetically, or at a
much slower rate. Malthus believed that human populations were, in general, just too lazy and
immoral to reduce birth rates by choice alone and thus an inevitable die-back was the eventual
outcome.
Karl Marx believed that population growth was a symptom rather than a basic cause of poverty
and other social issues. He felt that the real causes of these problems were exploitation and
oppression and that the real way to slow population growth and alleviate many social problems
was through improved social justice and opportunities for all, including better distribution of
wealth and resources.
The main difference between the theory of Malthus and Marx is that the former believes that
overpopulation is the root cause of the problems that result because of humanity’s inability or
lack of desire to control its population, while the latter, Marx, believes it’s the living conditions
and inequality that cause overpopulation and resulting issues that stem from that.
Today, there are those that still take aspects of one argument or the other when debating about
current population bursts or reductions in the world. Neo-Malthusians tend to believe we are
approaching or have already surpassed the Earth’s carrying capacity and that we should make
overpopulation issues the top priority by instituting family-planning programs. Neo-Marxists, on
the other hand, believe eliminating exploitation and poverty through social justice and
technological advances is the only solution to the population problem and that more equitable
wealth and resource distribution needs to be improved.
Others feel that the answer is somewhere between the two extremes. The United Nations’
Decade of Education for Sustainability program believes that sustainable growth and reduced
poverty, war, famine and suffering can only be achieved through balanced programs that offer
family planning, economic assistance and increased social justice and opportunities for all. They
believe that population growth, environmental degradation, overuse of resources, poverty and
economic instability are all tightly interconnected and that only by working to improve all aspects
at the same time can a sustainable method of living on Earth be achieved.
Question: What do you think? Would you consider your ideals concerning poverty and
overpopulation more in line with neo-Malthusian or neo-Marxism? Or a mix of the two? Explain.

"Most demographers predict that by 2100 global population will level off at about 10 billion. The
urgent question is whether current standards of living can be sustained while improving the
plight of those in need." (Stokstad, 2005, p 102)
Can more people be beneficial? Our government might say so when we look at Social Security
issues. More people mean larger populations of consumers who will buy more items on the
market and gives the markets more workers. Greater numbers also provide more intelligence
and ingenuity for dealing with world issues. Human demography statistics are recorded both by
governments and intergovernmental organizations, and they include data about people
concerning births, deaths and distribution and population size. In 1999, the U.N. officially
declared that human population had reached 6 billion people. That is only an estimate and has
increased since then. The Population Reference Bureau says that around the world, more than
15,000 people are born every hour. If we liken people to water lilies in a pond growing
exponentially, on what day do you think the world is half-full, and when do we overshoot our
carrying capacity and cover the pond completely? Questions like this are the subjects of heated
debates.
There are two main demographic groups. The first is the poor, young and rapidly increasing
populations found in underdeveloped nations such as Africa, Asia and Latin America. These
areas contain more than 75 percent of the world’s population and will account for more than 85
percent of projected growth. The second major group is the wealthy, old and mostly decreasing
populations in countries such as North America, Western Europe, Australia and Japan. In these
areas, the average age is in the mid-40s, and the populations are expected to continue to
decline except for immigration. Here is a chart that shows an estimation of the world’s
population up to the year 2100. We can see that it will be the less-developed regions of the
world that will contribute to this most.
•

Question: While the populations are growing dramatically in many underdeveloped
nations, the reality is that the majority of the garbage, pollution and the world’s resources
are used by most of the northern developed nations that have smaller populations. It is
estimated that the U.S. alone produces the highest levels of global warming gases and
the most garbage, and uses about 75 percent of the world’s resources. Currently, entire
groups of people in Africa or India will use fewer resources and produce less waste than
just one American, but that is starting to change. What will we do when countries such
as China and India, which contain over half the world’s population, begin to live like
Americans? Do you think it’s possible? What are some potential solutions? Can the
environment and world sustain continued population growth?

Learn More About Energy Use
United Nations on energy use by country: http://unstats.un.org/unsd/energy/
Fertility and birth rates are looked at via several avenues. The first is by looking at the crude
birth rate, which is the number of births in a year per 1,000 people. The second is by looking at
the total fertility rate, which is the number of children born to an average woman in a
population during her life. Finally, the third is by looking at the zero population growth, which
occurs when births plus immigration in a population equal emigration plus deaths.
Mortality and death rates are looked at by noting the crude death rate, which is the number of
deaths per 1,000 people in a given year. Some rapidly growing countries have very low crude
death rates compared to slower-growing countries, because of a greater number of young
people in the population. The life expectancy is the average age a newborn can expect to attain
in any given society. Declining mortality is one of the major reasons for most population growth
in the last several hundred years. Around the world, the average life expectancy has risen to an
average of 67 years in the last 100 years, and the greatest progress has been in developing
countries. Rapidly growing and slowly growing countries can have a problem with dependency
ratio, which is the number of nonworking compared to working individuals in a population.
Age structures of males to females vary significantly in rapidly growing nations, stable nations,
and in declining nations. In the rapidly growing nation, there are more young people than old. In
a stable nation, the range is more equal throughout all ages. And in a declining nation, you have
a lot of middle-aged people and fewer young people.
Unlike plagues of the dark ages or contemporary diseases (which) we do not yet understand,
the modern plague of overpopulation is soluble by means we have discovered and with
resources we possess. What is lacking is not sufficient knowledge of the solution, but universal
consciousness of the gravity of the problem and the education of the billions who are its victims.
Dr. Martin Luther King Jr.
Emigration and immigration play a large role in human population dynamics as well. Developed
regions expect millions of immigrants a year for the next 40 to 50 years. Immigration is a
controversial issue. Immigrants often take on the least -anted and most dangerous jobs that
come with low wages and few or no benefits or worker rights and protections. Locals complain
that immigrants take away jobs and overload social services, but others point out that the jobs
taken by immigrants are jobs locals wouldn’t take. Immigration is a controversy that many
developed nations are struggling with. Who do you let in? Who do you keep out? How many?
How do you decide?
Pro-natalist pressures are factors that increase the desire for children. This can be for several
reasons, including that children are a means of pleasure and comfort, that they are a support
means for older parents, that they can bring in more family income, that they are a means of
social status and that they are meant to replace members in a nation as others die. It’s not
uncommon for boys to be more valued than girls, causing some major demographic and social
issues in some countries, such as China, where only one child per couple is allowed.
Higher education and personal freedom for women often result in decisions to limit childbearing.
When women have more opportunities to earn a salary, they are less likely to have children.

Education and socioeconomic status are usually inversely related to fertility in wealthier
counties.
In developing countries, higher income often means that families can afford more children, and
fertility therefore often increases. In less-developed countries, adding more children to the family
won’t cost much, while in developed countries raising an additional child can carry significant
costs such as college, medical and other costs.
Demographic transition is a model of falling death rates and birth rates due to improved living
conditions accompanying economic development. The following figure:
http://innovate.national.edu/naulor/resource.aspx?id=866 represents a demographic transition.
A pre-modern society’s poor conditions keep death rates high due to extensive untreated
disease, malnutrition and famine, and other factors. Birth rates are correspondingly high, too,
because of lack of family planning and other options for women. Economic development brings
improved conditions and standards of living, so death rates fall while birth rates tend to stay
constant or to sometimes even rise. Eventually, as this transition continues, the birth rates also
begin to fall along with the death rates. Populations grow rapidly between where the birth rates
start to fall alongside the death rates. In developed countries, demographic transition is
complete when both the death and birth rates are low and the population is in equilibrium and
growth is stabilized.
On one side, demographers believe that the demographic transition is already taking place in
many developing countries and that the world population should stabilize during the next
century. Others argue that many poorer countries are trapped in the middle phase of transition
where death rates have been reduced but birth rates are still high and that their population is
growing so rapidly that human demands exceed sustainable resource yields.
A third demographic view is based on the fact that currently there are enough resources for
everyone in the world and that it’s just allocation and distribution that cause the problem. This
view believes social justice across all countries must be improved. Poor nations sometimes view
the rich nations’ calls for population control as a type of genocide, and they point to the fact that
the rich nations use a disproportionately large share of the world’s resources. Social justice
demands that better and more equitable resource distribution occur so that all may have a
chance at improved living standards.
To learn more: •
•

The Worldwatch Institute
http://www.worldwatch.org/
United Nations Demographics and Social Statistics:
http://unstats.un.org/unsd/demographic/

Family planning allows couples to determine the timing, number and spacing of their children. It
also allows women to choose when and how to have a child. Birth control is any method used to
reduce births. Traditional methods were long breast-feeding, taboos against intercourse while
breast-feeding, celibacy, folk medicine, abortion and infanticide. Modern methods of birth control
offer safe and easier options than those of the past. These can include: avoidance of sex during
fertile periods, mechanical barriers preventing contact between sperm and egg, surgical
prevention of sperm and or egg release, chemical prevention of sperm and/or egg maturity,
physical barriers to implantation and abortion.

Most demographers believe the world population will stabilize sometime during the next century.
These projections vary between 8 billion on the low end up to 25 billion on the high end. Family
planning is one method used to offer more choices to poor countries in helping them combat
population explosions
"Most demographers predict that by 2100 global population will level off at about 10 billion. The
urgent question is whether current standards of living can be sustained while improving the
plight of those in need." (Stokstad, 2005, p 102)
To learn more:
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Population Connection (previously Zero Population Growth)
Home
Planned Parenthood http://www.plannedparenthood.org/pp2/portal/ BP Statistical Review of World Energy 2012
Source organization Web sites used: The United Nations Population Division http://www.un.org/esa/population/unpop.htm United Nations Demographics and Social Statistics: http://unstats.un.org/unsd/demographic/ The United States Census Bureau: http://www.census.gov/ Population Reference Bureau
PRB
U.S. Fish and Wildlife Service http://www.fws.gov/ Other Resources: Browne, Malcolm W. (1998, December 8) Will Humans Overwhelm the Earth? The Debate Continues. New York Times. p F-5. Campbell, Neil A and Reece, Jane B. (2004) Biology. 7th ed. San Francisco CA, USA : Benjamin/Cummings. Cunningham, William P, Cunningham Mary Ann, and Saigo Barbara (2005) Environmental Science: A Global Concern. 8th ed. New York NY, USA: McGraw Hill. De Souza, Roger-Mark, Williams, John S, and Meyerson, Frederick A.B. (2003, Sep) Critical Links: Population, health, and the environment. Population Bulletin. 58(3), 2. Michael, Parenti. (1998) The increasing relevance of Marxism. Socialism and Democracy. 12(12), 115. Motavalli, Jim (2004, Jan/Feb) The Numbers Game. Norwalk. 15(1), 26. Pimentel, David, et al. 1999. Will limits of the earth’s resources control human numbers?Environment, Development and Sustainability. 1, 19-39. Ross, Eric B. (1998) Malthusianism, counterrevolution, and the Green Revolution. Organization & Environment. 11(4), 446-451. Stiling Peter (2001) Ecology: Theories and Applications. 4th ed. Englewood Cliffs, NJ: Prentice Hall Stokstad, Erik. (2005) Will Malthus Continue to be Wrong? Science. 309(5731), 102. Wakabi, Wairagala. (2006, Feb 18-Feb 24) Population growth continues to drive up poverty in Uganda . The Lancet. 367(9510), 558. Population Principles After studying this section, you will understand some dynamics of population growth such as: exponential vs. arithmetic growth, Malthusian vs. logistic growth, population increases and decreases and factors that affect them, and regulations on population growth such as density dependent and independent factors. Finally, you’ll take a look at population dynamics and issues in conservation biology. Next, you’ll look at the history of human population growth, summarize Malthusian and Marxian theories on growth limits and social justice, explain the process of demographic transition, understand how different factors affect human population changes and evaluate pressures for and against family-planning methods. Dynamics of Population Growth Under the right factors and environmental conditions, such as plenty of food, shelter and nutrients, most populations can grow at exponential rates. Exponential growth (also called Geometric Growth) has a constant rate of change per a given unit of time. That is to say that a biological species that grows at an exponential rate will increase as a constant fraction (or exponent) that the existing population is multiplied by. For example, if the bacteria population increases by the constant multiplied fraction of 2, then on Day 1, there would be 2 bacteria, on Day 2 there would be 4 (2*2), and on Day 3 there would be 8 (2*4), and on Day 4 there would be 16 (2*8), etc. Arithmetic growth, on the other hand, instead increases a population size via constant amounts added per units of time. For example, if a population grows by the Arithmetic unit of 3 cows per year, then in Year 1, there is just 1 cow, and in Year 2 there are 4 cows (1+3), and in Year 3 there are 7 cows (4+3), etc. In exponential growth, there are only a few numbers added at the beginning, and the growth of population initially seen is slow. Then, numbers are added increasingly more rapidly as the growth continues, suddenly creating dramatic changes in the population size. So, we can find a population unpleasantly crowded because of exponential growth. When we study the populations of different species, from bacteria to flies to humans, we will take into account several factors that affect the growth of those populations. The biotic potential of any given group of organisms is the maximum rate of production that would occur if there were no limits on the growth. This is the idealized conditions, such as having plenty of clean water, ample food and great housing for all humans. If this occurred on an endless planet with resources and space for all, population growth would continue unhindered. The reality, though, is that any given organism doesn’t have conditions of unlimited growth or never-ending natural resources. Ecosystems only have so much food, nutrients and shelter to go around, and organisms must live within these constraints or even compete with each other for the same resources. The carrying capacity of a given species in a given environment is the maximum number of individuals that can be supported on a long-term basis in that environment. The carrying capacity can change from year to year and from ecosystem to ecosystem. Example: Imagine a prairie in a year that received a lot of rain. Because of the extensive rain, it would have more grass growing, which produces more seeds for small mammals and small birds and more pollen for the insects. More small mammals and insects mean more food for larger birds and larger carnivores. Because there is more food and resources produced that year, the carrying capacity of the ecosystem for the year is increased, while during a year of drought, there would be far fewer resources. Some natural populations exhibit explosive growth until they overshoot their carrying capacity. Then, the population experiences a die-back because of overuse and lack of resources. Later, the populations grow explosively again, die-back again and so forth. Some organisms that exhibit this kind of growth include insects, bacteria, rodents and annual plants (weeds). This kind of oscillating growth pattern of explosive growth followed by a population crash is called Malthusian growth. It’s named after 18th century economist Thomas Malthus who theorized that human growth occurs until all resources are used, at which time the population has a dieback from starvation, disease and war over remaining resources. Many other natural populations, though, tend to instead follow logistic growth, which is unlimited growth while needed resources are abundant until the carrying capacity is near, at which time the growth slows due to reduced resource supplies. In population ecology, the Jcurve represents the growth explosion of the unlimited biotic potential growth. The S-curve represents the population growth, increase and stabilization due to the factors that limit growth within the carrying capacity of a given area. A J-curve is the idealized world of unlimited growth due to the presence of unlimited resources; this represents the biotic potential of any given species. In the following graphic: http://innovate.national.edu/naulor/resource.aspx?id=867 you will see a representation of a J and S curve. Both of these curves start the same, with a lag time where growth is slow as the population begins to multiply. As we pointed out previously, exponential growth starts with small increases. That growth rapidly increases as it expands. Then, in the Jcurve of idealized unlimited growth, we see the up-shoot of growth that would occur were there unlimited resources and no limits on growth. This is in contrast to the S-curve growth that is based on limited environmental resources, which characterizes the carrying capacity of a given ecosystem. In between the idealized J-curve and the observed realistic S-curve is environmental resistance. Environmental resistance is composed of all the factors that can affect and limit growth. Some of these many factors will now be discussed. Natality is the rate of production of new individuals in a given population, while mortality is the rate of death. The rate at which a group of organisms is giving birth vs. dying will affect its total population growth. Life expectancy is the average age that individuals of a given population are likely to reach, and this changes from population to population, species to species, from country to country, and even between genders of the same species. The life expectancy in developed nations is longer than in undeveloped nations, for example, and on average women outlive men. Such factors can also affect population rates. Furthermore, growth rates in a given area are affected based on emigration and immigration, where emigration is members of a population that move out of a given area and immigration is members who move in. There are also biotic and abiotic factors that affect populations. Abiotic factors are usually density-independent factors and include things such as weather and climate. That is to say, factors such as really cold weather, an earthquake or a tornado affect large and small populations the same. They are factors that are independent of density. Biotic factors, though, such as disease, predation or competition are density-dependent because their effects often increase as the population size increases. This means that as the population size grows, the biotic factors increase and greater mortality occurs, eventually causing a decrease in population size. Density-dependent factors tend to lower natality and increase mortality. These kinds of factors usually include interactions between populations, such as competition and predation. Interspecies interactions are one kind of biotic density-dependent factor, which is competition and predation between members of different species. For example, if there are several bird species in the same ecosystem that are all looking for the same kind of nesting area, they will compete with each other for the available sites. As their population size grows, they compete more fiercely, until some lose and die, creating drops in the population size based on the biotic factor of interspecies interactions. Intraspecies interactions, or interactions between members of the same species, can create reduced population as well. Examples of this would be mating competition between members of the same species, such as two male deer fighting over the same female mate or stress and crowding when overpopulation occurs. Question: Categorize the following population regulating factors into either density-dependent or density-independent groups: • • • • • Mutualism between two species. A wolf eating a rabbit. A large fire burns down many of the trees in a forest. A disease kills all of the mice in a local radius, and the foxes have nothing to eat. A three-year drought.