Raccoon Activity Each of you is a raccoon foraging for resources You must leave your “cache” brown bag hidden When I say go, you must walk into the “forest” and gather 1 resource (1 paper square) at a time and bring it back to your cache. 1-Blind 1- mom with 2 pups 1-Broken leg

Raccoon Activity Count each color paper and solve for Percent. Ideally Brown= Nuts= 25% Diet Purple=Berries and Fruit= 25% Yellow= Insects= 15% Red=Meat=10% Green= Plants= 20% Blue= Water Did what you gather represent these ratios? Did you survive or die? Why? What was your experience like? (competing with other raccoons for resources) Do you think that the raccoon with the broken leg, the blind raccoon, and the raccoon with the two babies survive? Why? Why didn’t all of the raccoons survive? (explain in terms of carrying capacity)

Chapter 5: Populations Section 5.1: How Populations Grow Section 5.2: Limits To Growth Section 5.3: Human Population Growth Chapter 5: Populations

5.1: How Populations Grow Describing Populations How do ecologists study populations? Recall that a population is a group of organisms of a single species that lives in a given area. Researchers study populations’ geographic range, density and distribution, growth rate, and age structure. Why do you think that the birth and death rate of the human population fluctuates so much?

Describing Populations Populations can be described in four ways: Geographic Range Density and Distribution Growth Rate Age Structure

Geographic Range The area inhabited by a population is called its geographic range. A population’s range can vary enormously in size, depending on the species. Example: Bacterial culture vs. a school of cod in the Atlantic Ocean.

Density and Distribution Population density refers to the number of individuals per unit area. Populations of different species have different densities. Distribution refers to how individuals are spaced out across the range of the population. Random Uniform Clumped

Discussion What would happen to a population’s density if the population size stayed the same while its geographic range decreased? Which characteristic would most directly determines if a population increases or decreases over time? Its density would increase Growth rate; immigration and births> emigration and death

Growth Rate A population’s growth rate determines whether the size of the population increases, decreases, or stays the same. If a population’s growth rate is zero, then it remains the same.

Age Structure To fully understand certain populations, such as plants or animals, researchers need to know the population’s age structure. This is the number of males and females of each age that a population contains. This is due to the fact that most plants and animals cannot reproduce until they reach a certain age. p1

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Population Growth What factors do you think affect population growth? The factors that can affect population size are birth rate, death rate, and the rate at which individuals enter or leave the population.

Birth Rate and Death Rate How do you think a population can grow? Populations can grow if more individuals are born than die in any period of time. Birth Rate Death Rate = Overpopulation Birth Rate Death Rate = Constant (Same Size Population) Birth Rate Death Rate = Population Shrinks

Immigration and Emigration A population may grow if individuals move into its range from elsewhere. This is called immigration. A population may decrease in size if individuals move out of the populations range. This is called emigration. Let’s draw a diagram!

Exponential Growth What do you think happens during exponential growth? If a population has all of the resources available, essential space, and are free from predation or illness, the population will grow. The size of each generation of offspring will be larger than the generation before it. This is known as exponential growth. Under ideal conditions with unlimited resources, a population will grow exponentially. Organisms can reproduce quickly (bacteria) Organisms can reproduce slowly (elephants) Organisms in new, beneficial environments

Exponential Growth

Logistic Growth What is logistic growth? When populations grow exponentially for a period of time, it eventually, it plateaus. There are Phases of Growth that organisms go through: Phase 1: Exponential growth. Phase 2: Growth slows down. (Exponential growth does not continue for very long) Phase 3: Growth stops. (Size of population levels off)

Logistic Growth Phase II Phase I

Logistic Growth Logistic growth occurs when a population’s growth slows and then stops, following a period of exponential growth. Remember that a population grows when more organisms are born than die.

Carrying Capacity When birth and death rate are the same as well as immigration and emmigration, population growth stops. If a population keeps growing, eventually it will reach its carrying capacity. Carrying capacity is the maximum number of individuals of a particular species that a particular environment can support. Once a population reaches the carrying capacity of its environment, a variety of factors act to stabilize it at that size. What factors or events do you think could arise when a population goes over its carrying capacity?

Carrying Capacity

In your own words, come up with a definition for the following key words… Population Density Age Structure Immigration Emigration Exponential Growth Logistic Growth Carrying Capacity

5.2: Limits to Growth What factors determine carrying capacity? Acting separately or together, limiting factors determine the carrying capacity of an environment for a species. A limiting factor is a factor that controls the growth of a population. Limiting factors keep most natural populations somewhere between extinction and overrunning the planet.

Limiting Factors

Density –Dependent Limiting Factors What limiting factors depend on population density? Remind me again what population density was? Density-dependent limiting factors operate strongly only when population density reaches a certain level. Density-dependent limiting factors include competition, predation, herbivory, parasitism, disease, and stress from overcrowding.

Competition When populations become crowded, individuals compete for food, water, space, sunlight, and other essentials. Can lower birth rates, increase death rates, or both. Competition is a density-dependent limiting factor because the more individuals living in an area, the sooner they use up the available resources. Compete not only for food, but for territory, mating partners, etc. Can occur can also occur among members of different species that are attempting to use similar or overlapping resources. What are the 2 types of competition?

Predation and Herbivory In a predator-prey relationship, populations of predators and prey may cycle up and down over time. They fluctuate. Ex: If moose population grows, they become easy prey for wolves, causing the wolf population to grow. Wolf population grows, and begin to kill more moose than are born, causing moose and wolf population to fall.

Predation and Herbivory Herbivory can also contribute to changes in population numbers. From a plant’s perspective, herbivores are predators. Populations of herbivores and plants cycle up and down just like predator- prey relationships do. In some situations, human activity limits populations. Fishing Hunting

Parasitism and Disease Parasites and disease causing organisms feed at the expense of their hosts, weakening them and often causing disease or death. Parasitism and disease are density-dependent effects because the denser the host population, the more easily parasites can spread from one host to another.

Parasites and Diseases

Density-Independent Limiting Factors What limiting factors do not typically depend on population density? Density-Independent limiting factors affect all populations in similar ways, regardless of population size and density. Unusual weather such as hurricanes, droughts, or floods, and natural disasters such as wildfires, can act as density-independent limiting factors. This may cause a population to “crash”. The population can rebuild quickly after the crash or take a long time to re-establish.

True Density Independence? Sometimes, however, the effects of so-called density independent factors can actually vary with population density. Human activities can also place ecological communities under stress in ways that can hamper a populations ability to recover from a natural disaster.

5.3: Human Population Growth How has the human population size changed over time? The human population, like populations of other organisms, tends to increase. The rate of that increase has changed dramatically overtime. For most of human existence, the population grew slowly because life was harsh: Search/hunt for food Disease Predators

Historical Overview Those limiting factors kept the human death rate very high. Because death rates were so high, humans would have many children to ensure that a couple would survive. As civilization advanced, life became easier, and the human population began to grow more rapidly. Continued through the 1800’s during the Industrial Revolution. Improved nutrition, sanitation, medicine, healthcare all dramatically reduced death rates. The combination of lower death rates and higher birth rates led to exponential growth.

Human Population Growth

Predictions of Malthus Exponential growth cannot continue forever. Thomas Malthus, English economist, suggested that only war(competition), famine(limited resources), and disease (and parasitism) could limit the human population growth. Recall that those are density-dependent limiting factors.

World Population Growth Slows What is happening to human population growth today? The human population growth rate reached a peak around 1962-1963, and then began to drop. The size of the global population is still growing rapidly, but the rate of growth is slowing down. Why?

Patterns of Human Population Growth Why do population growth rates differ among countries? Scientists have identified several social and economic factors that affect human population growth. The scientific study of human population is called demography. Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly.

The Demographic Transition Human societies had equally high birthrates and death rates during most of history. In the past century, growth rates have slowed dramatically. Demographers have developed a hypothesis for this shift. The hypothesis explains that countries have completed the demographic transition. The demographic transition is a dramatic change from high birthrates and death rates to low birthrates and low death rates. It is divided into 3 stages.

Demographic Transition

Age Structure and Population Growth To understand population growth in different countries, we turn to age-structure diagrams. It compares age structures between males and females in populations.

Future Population Growth To predict how the world’s human population will grow, demographers consider many factors, including the age structure of each country and the effects of diseases on death rates. Current projections suggest that by 2050 the world population will reach 9 billion people. Current data also suggests that global human population will grow more slowly over the next 50 years than it grew over the last 50 years.