7.2 Populations and Sustainability UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.2 7.2 Populations and Sustainability A population is a group of organisms of one species that lives in the same place, at the same time, and can successfully reproduce. Populations increase when individuals within the population reproduce at rates that are greater than what is needed to replace individuals that have left the population or died. When will a population increase?

Exponential Growth UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.2 Exponential Growth Exponential growth is accelerating growth that produces a J-shaped curve when the population is graphed against time. Exponential growth only occurs under certain conditions for a short time. What are some conditions in which a population grows exponentially? Exponential population growth can occur when an organism comes to a new habitat and resources are plentiful or when pressures on the population are removed. The graph shows the population growth of elephants in a national park after the elephants were declared protected, ending elephant hunting in the area. Continued…

Exponential Growth UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.2 Exponential Growth A limiting factor is a factor that limits the growth, distribution, or amount of a population in an ecosystem. A density-independent factor is a limiting factor in the environment that does not depend on the number of members in a population per unit area. A density-dependent factor is a limiting factor in the environment that depends on the number of members in a population per unit area. What are examples of density-independent factors and density-dependent factors? Density-independent factors are usually abiotic and include weather events, natural disasters (floods, fires, avalanches) and pollution. Density-dependent factors are usually biotic factors such as disease, parasites, predation, and competition.

Carrying Capacity UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.2 Carrying Capacity Carrying capacity is the size of a population that can be supported indefinitely by the resources of a given ecosystem. When a necessary resource is used at a rate that exceeds the carrying capacity, the population will be reduced until the population size is in balance with the available resources. Estimation of carrying capacity begins with an estimation of the population. In the case of the white-tailed deer population, the number of deer pellet piles was counted and used to estimate the deer population. The population is tracked over time; the maximum population reached is the carrying capacity of the ecosystem at that time.

Carrying Capacity UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.2 Carrying Capacity The fur seal population was relatively constant before 1915; in 1915 the population began to grow exponentially. In about 1935, the seal population reached the carrying capacity of the ecosystem and the population size leveled off. Explain how the fur seal population changed over time, as represented by the graph above.

Activity 7-2A

Interactions Among Species UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.2 Interactions Among Species Ecological niche is the way an organism occupies a position in an ecosystem, including all the necessary biotic and abiotic factors. No two species can occupy the exact same ecological niche or provide the exact same services to their ecosystem because no two species live in exactly the same way. The biotic factors include the insects they eat, their competitors, and their predators. The abiotic niche factors include the places they use for roosting and hibernation, the time of night that they hunt for food, the airspace that they fly through when hunting, and the temperature range that they can tolerate.

Human Niches and Population UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.2 Human Niches and Population Sustainable use is use that does not lead to long-term depletion of a resource or affect the diversity of the ecosystem from which the resource is obtained. The exact carrying capacity of Earth for humans is unknown. In your own words, explain these graphs showing human population growth. Human population growth was steady, but not explosive, until about 1400 when the bubonic plague killed large numbers of people. After the plague, the population began to grow steadily until the 1800s. Around 1800, the population began to grow explosively.

Ecological Footprints and Carrying Capacity UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.2 Ecological Footprints and Carrying Capacity An ecological footprint is a measure of the impact of a human individual or population on the environment. The world has finite (limited) resources, and consuming large quantities of resources is unsustainable. Sustainability is the use of Earth’s resources, including land and water, at levels that can continue forever. What data is used to measure an ecological footprint? Unsustainability is a pattern of activity that leads to a decline in the function of an ecosystem. Data used to measure an ecological footprint include energy consumption, land use, water use, and waste production.

UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.2 Section 7.2 Review Populations tend to increase exponentially when there are abundant available resources. When resources that are needed by populations become limited, the carrying capacity of an ecosystem has been reached. Each species occupies an ecological niche, which has biotic and abiotic components. The ecological niche of humans has been broadened by our intellectual abilities and the development of technology. Humans have altered the ecosystems that support us, so our carrying capacity is high. However, modern human societies are still subject to the ecological principle of carrying capacity. An ecological footprint is used to describe the impact a person’s or population’s consumption habits have on the supporting ecosystems.

7.3 How Human Activities Can Affect Sustainability UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.3 7.3 How Human Activities Can Affect Sustainability Matter and energy are recycled through all four of Earth’s systems—the lithosphere, the hydrosphere, the atmosphere, and the biosphere. Essential matter, such as carbon, nitrogen, phosphorus, sulfur, oxygen, water, and other nutrients, are used and reused in repeating cycles. Human activities such as the production of materials that cannot be broken down into essential matter easily.

Nutrient Cycles and the Sustainability of Aquatic Ecosystems UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.3 Nutrient Cycles and the Sustainability of Aquatic Ecosystems Human activities, such as fertilizing crops, interrupt the nitrogen cycle and the phosphorus cycle. Excess nitrogen and phosphorus run off into aquatic ecosystems. Eutrophication is a process in which nutrient levels in aquatic ecosystems increase, leading to an increase in the populations of primary producers such as algae. Why would fish die during eutrophication? Light is blocked, which kills many plants; the bacterial population increases exponentially because there is so much matter to feed on; bacteria consume oxygen during decomposition. Oxygen levels in the water fall so low that the fish cannot survive

Carbon Dioxide and Other Greenhouse Gases UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.3 Carbon Dioxide and Other Greenhouse Gases Greenhouse gases are atmospheric gases that prevent heat from leaving the atmosphere, thus increasing the temperature of the atmosphere. Many scientists hypothesize that the increased concentration of carbon dioxide in the atmosphere, along with an increase in other greenhouse gases, such as methane, contributes to global climate change. The natural insulating capacity of greenhouse gases is known as the greenhouse effect. Sample answer: Carbon dioxide levels started to rise at the time of the Industrial Revolution, when humans dramatically increased the use of fossil fuels as an energy source. When did carbon dioxide levels start to rise? Continued…

Carbon Dioxide and Other Greenhouse Gases UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.3 Carbon Dioxide and Other Greenhouse Gases There are many ways to reduce the amount of carbon dioxide being released into the atmosphere, including international initiatives by governments from around the world, initiatives by the federal, provincial, and local governments of Canada, and efforts by individuals. The Kyoto Protocol, which is an international agreement of over 180 countries to reduce emissions, was an international effort to reduce CO2 emissions. The preservation of boreal forests, which are natural carbon sinks, is an example of a national effort. Recycling, which helps reduce carbon emissions because less energy is required to recycle products than to create them from raw materials, is an example of efforts by individuals, corporations, and municipalities. Recycling also reduces the amount of materials going into landfill and waste dumps, which has other environmental benefits. Name three examples of efforts to reduce carbon dioxide emissions.

UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.3 Trophic Levels Matter and energy are transferred between trophic levels within the biosphere. Trophic efficiency is a measure of how much of the energy in organisms at one trophic level is transferred to the next higher trophic level. Describe in your own words how energy moves from one trophic level to the next trophic level. A trophic level is a category of organisms that is defined by how the organisms gain energy. Primary producers are organisms, such as plants, that can make their own food. Consumers are organisms that cannot make their own food. They consume producers at the primary consumer level. At higher trophic levels, they consume other consumers. At each level, only 10% of the available energy is passed on to the next trophic level. Biomass is the mass of living cells and tissues that has been assembled by organisms using energy from the Sun.

UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.3 Trophic Levels Bioaccumulation is a process in which materials, especially toxins, are ingested by an organism at a greater rate than they are eliminated from the organism’s body. Biomagnification is the increase in the concentration of a toxin as it moves from one trophic level to the next. DDT and PCBs are pollutants that have affected organisms. How might PCBs affect herring gulls? PCBs increase at each trophic level, and the greatest health problems are found at the highest trophic levels. PCBs usually affect the reproductive abilities of the organisms, leading to decreased populations. In the case of peregrine falcons, the populations were on the brink of extinction. Continued…

UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.3 Trophic Levels Terrestrial and aquatic ecosystems are connected. Beluga whales in the St. Lawrence River have a high rate of cancer, which scientists suspect is caused by exposure to pollutants from land and water. Scientists hypothesize that pollutants settle in the sediment of the river, which is where the whales feed on invertebrates, such as krill and worms. The chemicals bioaccumulate in the whales’ tissues, which leads to a weakened immune system.

UNIT 4 Chapter 7: Factors that Affect Sustainability Section 7.3 Section 7.3 Review Human activities that increase the influx of nutrients into a terrestrial or aquatic ecosystem can upset the nutrient balance in the ecosystem. Burning fossil fuels has dramatically increased the concentration of carbon dioxide, a greenhouse gas, in the atmosphere. Most of the stored energy in one tropic level does not move to the next trophic level. Bioaccumulation and biomagnification can result in unhealthy levels of pollutants in organisms.