Population Ecology PDF

© Amy Brown Science Population Ecology © Amy Brown Science Characteristics of Populations A group of individuals that belong to the same species that live in the same area at the same time. These are the important characteristics of a population. 1. 2. 3. 4. 5. 6. Population Size Geographic distribu...

© Amy Brown Science Population Ecology © Amy Brown Science Characteristics of Populations A group of individuals that belong to the same species that live in the same area at the same time. These are the important characteristics of a population. 1. 2. 3. 4. 5. 6. Population Size Geographic distribution Density Dispersion Growth rate Age structure Population Size A population’s size is… … the number of individuals in the population. Size is a very important property of a population but can be very difficult to measure. A population of daisies that live in a field is easy to measure. The plants are _________ immobile and are confined _________ to a relatively small area. A scientist would simply _______ count the individual plants in the field. More often, the individuals in a population are very hard to count because they are … … too widespread, too abundant, or too mobile to be easily counted. For example: How big is the population of bullfrogs in Everglades National Park? (Park size is 1.5 million acres or 6,110 km2.) To determine the size of this population, scientists would have to use various methods of estimation, which have the potential for error. Geographic distribution is the range of the population. This term describes: the area that is inhabited by the population. size The range can vary in ______. It may be just a few centimeters, such as the mold on a piece of bread. Or the range may be huge, such as the migration area of whales. Population density is: the number of individuals per unit area. Density is one of the main characteristics that describes a population. There is tremendous variation in density depending on the _________ and the _____________. species ecosystem low Some populations have _____ densities, while other high populations have ______ densities. Dispersion is…. …. the spatial distribution of individuals within the population. The three types of dispersion are: Clumped Dispersion Random Dispersion Uniform or Even Dispersion Clumped Dispersion a) In clumped dispersion the individuals are clustered together. b) Clumped distributions often occur when: resources such as food, water, or living spaces are clumped together. c) Clumped distributions may also occur because a species has: a certain social behavior, such as herding animals, flocks of birds, schools of fish or hives of bees. Uniform or Even Dispersion These penguins exhibit even dispersion because of aggressive interactions that occur between neighbors. b) Even distributions are usually the social interactions but result of _________________, the interaction results in the individuals trying to: get as far away from each other as possible. a) In an even dispersion, individuals are: separated by a fairly even distance. Random Dispersion a) In random dispersion, the location of one individual is independent of the location of the other individuals. b) Random dispersal may result from seed dispersal: by the wind or animals. c) A forest or a field of wildflowers results from the random dispersal of seeds. Population Dynamics All populations are dynamic, meaning that they: change in size and composition over time. To understand the changes that are taking place in a population, the following must be considered: 1. Birth rate: the number of births occurring in a given period of time. 2. Death rate or mortality rate: the number of deaths in a given period of time. 3. Life expectancy: the length of time an individual is expected to live. Age Structure Age Structure: The distribution of individuals among different ages in a population. The future growth of a population is predicted using “age-structure diagrams.” For example, a population with a large number of very young individuals is predicted to have a higher growth rate in the future when these individuals reach reproductive age. Age structures are often presented in graphs. The mortality rate of the individuals in the population generally follows one of the following patterns. These are called __________________________ survivorship curves because they survival at different ages show the likelihood of ___________ _____ throughout the lifetime of the organism. Type I Survivorship Curve: c) An example is large mammals that produce very _____ few offspring but provide them with good care _______________. a) This curve is: flat at the start, indicating a low death rate in the early and middle stages of life. b) It drops steeply near the end indicating: a high death rate as the organisms become older. Type III Survivorship Curve: a) This curve drops sharply at the start, indicating: a high death rate among the young. b) It flattens out as death rates: decline for the few that do survive the early die-off. c) This would include organisms that produce: large numbers of offspring but provide them with little or no care. d) Examples include: fishes, many plants, and most marine invertebrates. Type II Survivorship Curve: c) The probability of dying does not change throughout life. d) This may occur in rodents and lizards. a) This curve is: intermediate to the above 2 curves. b) There is a constant death rate over the organism’s life span. The life history of an traits organism is the _______ that affect an organism’s schedule of: reproduction and survival. The reproduction of most organisms can be described as: 1. Big-bang reproduction 2. Repeated reproduction This is reproduction in which: an organism produces all of its offspring in a single event. Big-bang Reproduction Example: Pacific salmon spend several years growing and maturing __________________________. Near the end of their life spawn producing they _________, millions and millions of death eggs, followed by ________. Repeated Reproduction In this type of reproduction, the organism: produces a few offspring each year for several years. What determines which type of reproduction an organism will have? If the survival rate of the offspring is ____, low it is more likely to have ______________________. big-bang reproduction If the adults are more likely to survive and reproduce again, repeated reproduction will be favored. ______________________ “There are trade offs in reproduction and survival.” What does this mean? Reproduction requires time, energy and resources _______________________________. If all the resources are used up during reproduction, the __________ survival is in jeopardy. If all the resources are needed for survival, then reproduction _______________ cannot occur. A population may remain very stable over time, or there can be fluctuations in population size. At any given time, a population may experience tremendous growth or ______________. rapid decline ____________________, There are three factors that can greatly increase or decrease the size of a population. 1. The number of births. 2. The number of deaths. 3. The number of individuals that enter or leave the population. Growth Rate: The amount by which a population’s size changes in a given time. If more individuals are being born than die in a given period of time, the increase population size will _________. If birthrate is equal to death rate, the population will stable in size. remain ________ If the death rate is greater than the birthrate, the decline population will ________. Migration is… …the movement of individuals into and out of a population. Immigration: The movement of individuals into an area. Emigration: The movement of individuals out of an area. increase the size of the population while Immigration would _________ emigration would cause the population to __________ decrease in size. Two processes increase the size of the population: birth rate and immigration. Two processes decrease the size of the population: death rate and emigration. When studying population density, some questions to be answered are: 1. Why is the birth rate unusually high (or low)? 2. Why are more individuals dying than normal? 3. Is there a reason for an unusually high immigration or emigration? Exponential Growth Under what conditions would rapid growth occur in a population? ² There would have to be plenty of space and an abundance of food. ² There could be no predators or disease. If all factors for reproduction and growth are ideal, the population might grow ____________. exponentially Exponential growth describes a population that is increasing _________. rapidly larger the The ________ population gets, the ________ faster it grows. For example: A single bacterium can reproduce by dividing into two cells every 20 minutes. At the end of the first 20 minutes, there would be two bacterial cells. At the end of 40 minutes, four cells will have been produced, and by the end of the first hour, there would be eight cells. This growth doesn’t seem too impressive at first. But, if the number of cells doubles every 20 minutes, then at the end of one day the colony would contain 4.72 x 1021 cells (4,720,000,000,000,000,000,000 cells!) Exponential Growth: This occurs when the members of the population are reproducing at a constant rate. At first, the population seems to be growing slowly but over time, the _______, power of exponential growth can produce a population of extremely ______ large size. Under ______ ideal conditions, with unlimited resources, a ___________ population will grow exponentially. When exponential growth is viewed on a graph, the pattern of growth is a ________ J-shaped curve. A J-shaped curve indicates the population is growing exponentially. In reality, populations _____ cannot continue to grow exponentially for very long. scarce and Resources will become _____ _____ will accumulate, ______ wastes limiting growth. Limiting Factor: In addition, competition for the limited resources will intensify as the population grows. Any factor that restrains the growth of a population. Limiting factors may be space to grow, food, water, etc. Carrying Capacity Exponential growth NOT continue does ________________ in natural populations for very long. At first a population may appear to be experiencing exponential growth, but as less available the growth of resources become ______________, the population will _____________. slow or stop f) There will be increased competition between _____________ the members of the group. g) The accumulation of: wastes could lead to an increase in diseases and poor health. a) Food will become: more and more scarce. b) There may be: water shortages. disease might be c) A ________ introduced into the population. d) The population will: run out of space. predators may e) Additional __________ be attracted to the rising prey population. ______ Eventually a growing population will reach the carrying capacity of the environment. The carrying capacity is: the number of individuals the environment can support over a long period of time. The ___________ overshoot in the graph to the right indicates that the population has exceeded the carrying capacity of _________________ the environment. Many members of the population will ______________, die or starve causing the population size to ____________ drop below the carrying capacity. The size of the population will fluctuate above and below the _________________ carrying capacity of the environment. Logistic Growth Logistic Growth: A graph of logistic growth looks like a stretched out __________. letter “S” A model of population growth in which growth slows or stops following a period of exponential growth. Logistic Growth When the population is at the carrying capacity: the birth rate equals the death rate, and growth stops. When the population size is ______, small birth rates are high and death rates ______ are _____, low causing the population to grow nearly ______________. exponentially As the population reaches the carrying capacity, the growth rate _______. slows Assumptions of the Exponential Model and the Logistic Mode One assumption made by both models is that: the carrying capacity is constant and does not fluctuate. In reality, the carrying capacity changes with the environment _____________. During a drought in a prairie, there would be less vegetation. Fewer prairie dogs would survive since there is less plant matter to eat. The carrying capacity is lower than normal. The exponential model and the logistic model are not accurate representations of real populations, but they are: useful tools that scientists can use to study populations. Limits to Growth Examples of limiting factors include: 1. Competition 2. Predation 3. Parasitism and disease 4. Drought and other climate extremes 5. Human disturbances No population can undergo exponential growth forever. There are… …limits to how fast and how big a population can grow. Limiting Factors: A limiting factor is a factor that causes population growth to decrease. 1. A limiting factor that depends on population size is called a densitydependent limiting factor. Density-Dependent Factors 2. This means that the limiting factor only limiting when: becomes “________” the population density reaches a certain level. Population density refers to the … … number of organisms per unit area. Density-dependent limiting factors include: ü competition ü predation ü parasitism and disease ü shortages of food ü shortage of nesting sites. As a population becomes more and more crowded, organisms will have to compete with one another for: food, water, sunlight, space to grow, and nesting sites. Competition is a density-dependent factor. Competition Competition may also occur between populations consisting of separate species. The more individuals that live in the population: the sooner they will use up the available resources. The greater the population size becomes, the more intense the competition for resources. Predation Predation: The interaction between two different organisms in which one captures and feeds on the other. Predation Predator: In a predator-prey relationship, the predator is: the organism that feeds upon the other. Prey: In a predatorprey relationship, the prey is: the organism that is the food source for the other. The predator-prey relationship is one of the best known methods of … … controlling the size of a population. Study the graph to the right. Notice that prey an increase in ______ population is followed by an increase in ___________ predator population. As the predator population increases, they kill more prey, and the prey population drops _______. As the prey population drops, the predators have less food to eat, so the predator population declines ___________. This relationship controls: the size of each population. Parasitism and Disease 1. Parasite: An organism that feeds upon another living organism. 2. Host: The organism that the parasite feeds upon. predator-prey relationship 3. This is very similar to a _______________ and can also control the size of the population. 4. The parasite takes nourishment and nutrition from the host. The host is weakened and may eventually die. TICK Territoriality A territory is a space that … … an animal defends against encroachment by other individuals, usually of its own species. The territory becomes a ________ resource for which individuals compete must ________. The benefit of a territory is that the “owner” of the territory has: unlimited use of the resources found there without competition from others. The densityindependent factors affect: all populations in similar ways, regardless of the size of the population. Density-Independent Factors Examples of density-independent factors include: a) Unusual weather or natural disasters such as floods and fires. b) Certain human activities, such as the damning of a river, or clear-cutting a forest. These factors (fires, floods, etc.) would affect …. ….. any population of any size. In response to densityindependent factors, populations may experience a crash where “_____” the population is nearly eliminated _________. If one population is nearly decimated, it may also affect another population if the second population depends on the first as a food source. Human Population Growth For most of human existence, the population grew very slowly. There were many limiting factors that kept the human population low: 1. Food was not always readily available. 2. Diseases were rampant. About 500 years ago, the human population began to grow at a staggering rate. Reasons for this include: 1. The beginning of agriculture and industry made life much easier and much safer. 2. Food is available on a regular basis. 3. Goods can be shipped around the world. 4. Improved sanitation and living conditions eliminated the high levels of diseases. 5. Death rate dropped while birth rate increased. As a result, the human population is experiencing exponential growth ____________________. The human population cannot continue to grow in ________ this manner. The resources on Earth are limited ________. The questions to be answered are: Ø When will we reach the limit of these resources? Ø How large will the population get? Ø Will the planet be able to support this huge human population? Demography is the scientific study: of human populations. Some countries today have a much higher growth rate than other countries. Birthrates, death rates, and the age structure of a population help predict why some countries have a higher growth rate than other countries. This is a map of the world's countries by total population, with darker shading indicating larger populations. In many countries, such as the United States, Japan, and much of Europe… ….the growth rate has slowed. These countries have completed the demographic transition: a term used to describe a dramatic change in birth and death rates. As a society becomes more modern, there is a higher educational level. As the standard of living increases, families have fewer children. The demographic transition is said to be complete when: the birthrate falls to meet the death rate, and the population stops growing. The demographic transition has occurred in only a few countries: the United States, Japan and much of Europe. However, most of the world population is still growing ______________. exponentially Most of the world population is contributed to about 10 countries, with India and China in the lead. Age-Structure Diagrams The future growth of a The growth of a population is predicted population depends on: using: how many people make up the given population. “age-structure diagrams.” An “age-structure diagram” shows: the population of a country broken down by gender and age group. Each bar in the diagram represents individuals within a 5year range. Males are shown to the left of the center line. Females are shown to the right of the center line. Look at the age structure of population B. There are: nearly equal numbers of individuals in each age group. In can reasonably be predicted that: population B will experience slow and steady growth in the future. Look at the age structure of population A. There are many more children than ______ older _________ groups. In each higher age group, there are fewer and fewer individuals. It can reasonably be predicted that population A will experience: rapid growth in the future as the large number of children reach adulthood. 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