Name Block Partner s Name POPULATION DYNAMICS

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1 Name Block Partner s Name POPULATION DYNAMICS Population dynamics is the area of Ecology devoted to how populations are spaced in the environment, and how they change over time. There are four characteristics of populations that are investigated: SIZE, DENSITY, DISPERSION, and GROWTH pattern. SIZE Population size is simply the number of interacting (and interbreeding) individuals in a given location. What is the most recent population size of caribou in Denali National Park in Alaska? What is the estimated population size of grizzly bears in Yellowstone National Park? DENSITY Density is a measure of how closely individuals are spaced. It is usually measured as the number of organisms per unit area. List the following in order of their density (number per square kilometer) from lowest to highest: Ants, panda bears, sea lions, mackerel DISPERSION Individuals are spread over their habitat in specific patterns. In ecology, these patterns are identified as dispersion. There are three types: Clumped; Uniform (regular); and Random. Clumped is the most common; random is the most rare. You will need to review each of these three patterns. Two things determine species dispersion: the interaction between individuals (positive or negative); and the spatial distribution of their resources. For example, you would expect to find sea birds showing a clumped dispersion pattern because their food source, small fish, are clumped (by schooling). Therefore, the birds that prey on them are also clumped. There are two species listed below. Your job is to identify what dispersion pattern they exhibit. In order to do this, you will need to learn some about these species. Once you have identified the pattern, you need to draw what this pattern looks like, and describe whether the pattern is due to intraspecific interactions, or resource distribution. In essence, you are to explain the cause of the observable pattern. 1) red-winged blackbirds Pattern pattern diagram 1

2 Name Block Partner s Name 2) Prairie dogs Pattern pattern diagram POPULATION GROWTH Many people believe that most beautiful bird in North America is the Resplendent Quetzal. The Aztecs considered these birds sacred, and only the royalty were permitted to wear their feathers. Unfortunately, these birds are now endangered. Read about this bird at: In one grove of trees in the southwestern slope of Costa Rica, there are 17 avocado trees. Wild avocado trees have very large seeds (about 2cm) that cannot be eaten by most birds. However, they are the dietary specialty of the Resplendent Quetzal. Use the information below to calculate the carrying capacity of quetzals in the grove. Number of fruits need per bird per day = 17 Number of seeds produced by the average tree over the fruiting season = 350 Percent of fruits that ripen on any given day = 3% Carrying capacity (include units!) = What other factors (besides number of avocado fruits) might affect the carrying capacity of quetzals in this grove? Edwin Ramirez, a Costa Rican farmer and tour guide, is working to rehabilitate his property by planting native tree species. He loves quetzals, and so ten years ago decided to plant a grove of avocado trees on his property in Central Costa Rica. He planted 52 trees, which are now mature and producing fruit. This past spring, one pair of quetzals migrated from a neighboring farm, and became established in Edwin s trees. A pair of quetzals can produce 1 offspring per year, and the population can grow at a rate of 7% per year. At this rate, the population will double every 10 years. 2

3 Name Block Partner s Name Small populations in an environment with adequate resources will grow exponentially. Provide a general graph of what exponential growth looks like, and describe the shape of the graph (what letter does it look like?) Species cannot grow exponentially forever. At some point the population will stabilize and stop growing. Why do you think this happens? This population of quetzals will begin growing exponentially, calculate the level at which the population will it stabilize? (What s the carrying capacity?) You should now have some idea about how the population will grow over time, and stabilize. Your job is to plot the growth of this population from 2 individuals to its stable population size. (Hint: You already know how long it will take the population to double, and you know the maximum size the population can grow to.) Pop.size Time (yrs) What is the specific name for this type of growth (rapid initial growth, followed by stabilization at a carrying capacity? What letter does this growth look like? 3

4 AGE Name Block Partner s Name Some of the factors below are responsible for stabilizing populations and preventing them from growing above their carrying capacity. These are factors that only become important when population density increases. In other words, large populations are more affected than are small populations. We say that they are densitydependent factors. Circle the density-dependent regulating factors below. Competition Drought Flood Disease Predation Parasitism Fire Earthquakes If you have done the about correctly, you will notice that density dependent factors are caused by negative interaction with other organisms. Therefore, the greater the number of organisms, the more the population growth rate is slowed (eventually hitting zero population growth (where births = deaths). We can tell how fast a population is going to grow by how many individuals are in the pre-reproductive, reproductive, and post-reproductive periods of their lives in a population. Use the three Age structure diagrams below to answer the following questions. POP A POP B POP C POP D In which population is the greatest percent of the population in the reproductive and pre-reproductive stages? the least percent?. Obviously, the greater number of people in the reproductive and pre-reproductive stages, the more people that are reproducing (and will soon in the future), and the faster the population will grow. Therefore, the population you expect to show the greatest growth is, and the least growth is. All individuals have a limited amount of energy that they will obtain in their lifetimes. There are two primary uses for that energy: reproduction; and maintenance. Therefore, an individual can put most of its energy toward maximizing reproduction (at the expense of its own body and life), or put that energy toward supporting its own body (resulting in a lower reproduction level). Every species through natural selection, demonstrates one of these two patterns that are called life-history strategies. Do some research about r-selected and K-selected species. 4

5 Name Block Partner s Name Below is a list of characteristics of r- and K- selected species. Identify the characteristics of each, and place them in the appropriate columns below. Population A (above) Population C (above) large body size many off spring short life good parental care stable population size pioneer species logistic growth small body size few offspring long life poor parental care fluctuating population size climax species exponential growth followed by crashes r-selected species K- selected species Human population growth is an area of great concern in Ecology and Environmental Science, because we cannot expect to make any real progress in rehabilitating and maintaining the health of the planet when our population continues to spiral upward, out of control. More people require more space, energy, and resources. Obtaining these necessities obviously impacts our natural environment. What is the current size of our human population? If people are added to the population each year for each person already present in the population, how many people are added to the world each year? An entire US population is added to the world every years. 5

6 Name Block Partner s Name Historically, death rates and birth rates have been high in human populations. As long as birth rate = death rate, then the population doesn t grow. However, the human population has grown immensely (exponentially) since the end of World War II. The graph below shows what happens to a country as it becomes industrialized, and can be used to explain why world population has grown so much recently. Using this graph, discuss the trends in birth rate and death rate during the preindustrial, transitional, industrial and postindustrial stages. At the same time, discuss what happens to the population size during the four time periods. Preindustrial- Transitional- Industrial- Postindustrial- 6

7 Name Block Partner s Name What can explain the changes in a) birth rate, and b) death rates as industrialization occurs? There are many things that we can do to improve population growth. Traditionally, people think of family planning. Although this is a critical element to any plan, there are many other ways that we can reduce birth rates. Suggest some below. (Hint: think about why people have kids in the first place, and then think of ways to reduce those needs/desires). 7