1950’s – fish farmer introduced hydrilla into a canal in Florida. Out of control growth! The area inhabited by a population is called its geographic range. Population density refers to the number of individuals per unit area. Distribution refers to how individuals in a population are spaced out across the range of the population— randomly, uniformly, or mostly concentrated in clumps. Purple lupines grow randomly in a field among other wildflowers. The dots in the illustration represent individual members of a population with random distribution. An example of a population that shows uniform distribution is the king penguin. An example of a population that shows clumped distribution is the striped catfish. These fish organize into tight groups. A population’s growth rate determines whether the population size increases, decreases, or stays the same. A population will increase or decrease in size depending on how many individuals are added to it or removed from it. A population can grow when its birthrate is higher than its death rate. If the birthrate equals the death rate, the population may stay the same size. If the death rate is greater than the birthrate, the population is likely to shrink. Which of the following is NOT one of the factors that play a role in population growth rate? a. b. c. d. immigration death rate emigration demography The movement of organisms into a range is called a. b. c. d. immigration. emigration. population shift. carrying capacity. Which of the following could describe a population that is decreasing in size? A) The birthrate and the death rate remain the same. B) The death rate is becoming lower than the birthrate. C) The death rate is constant and the birthrate is increasing D) The death rate is becoming higher than the birthrate. Under ideal conditions with unlimited resources, a population will grow exponentially. In exponential growth, the larger a population gets, the faster it grows. If you plot the size of this population on a graph over time, you get a J-shaped curve that rises slowly at first, and then rises faster and faster. Logistic growth occurs when a population’s growth slows and then stops (most populations experience this type of growth) follows a period of exponential growth. Carrying capacity is the maximum number of individuals of a particular species that a particular environment can support. A) The birthrate and the death rate remain the same. B) The death rate is becoming lower than the birthrate. C) The death rate is constant and the birthrate is increasing. D) The death rate is becoming higher than the birthrate. A) logistic B) limiting C) demographic D) exponential Suppose that a species of toads is introduced into a new environment in an attempt to reduce the population of insects. The toad has no natural predators in the new environment. The toad population would most likely A) B) C) D) increase exponentially. increase logistically. decrease rapidly and die out. remain the same. If a population grows larger than the carrying capacity of the environment, which of these is most likely to happen? A) B) C) D) The death rate may rise. The birthrate may rise. The death rate must fall. The birthrate must fall. A limiting factor is a factor that controls the growth of a population. Some depend on population density and others do not. Density-dependent limiting factors include competition, predation, herbivory, parasitism, disease, and stress from overcrowding. When populations become crowded, individuals compete for food, water, space, sunlight, and other essentials. Competition is a density-dependent limiting factor. The more individuals living in an area, the sooner they use up the available resources. The effects of predators on prey and the effects of herbivores on plants are two very important densitydependent population controls. This graph shows the fluctuations in wolf and moose populations on Isle Royale over the years. Herbivory can also contribute to changes in population numbers. From a plant’s perspective, herbivores are predators. In some situations, human activity limits populations. Fishing fleets have raised cod death rates so high that birthrates cannot keep up. As a result, cod populations have been dropping. Parasitism and disease are density-dependent effects, because the denser the host population, the more easily parasites can spread from one host to another. This graph shows a sudden and dramatic drop in the wolf population of Isle Royale around 1980. At this time, a viral disease of wolves, canine parvovirus (CPV), was accidentally introduced to the island. Overcrowding causes stress in populations Lowers ability to fight disease Causes some females to neglect or even eat their young 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. A) competition. B) temperature. C) crowding. D) disease. A) a small, scattered population B) a population with a high birthrate C) a large, dense population D) a population with a high immigration rate A) earthquake B) disease C) emigration D) parasitism Hydrilla in its natural environment has natural predators, but in Florida they don’t exist. Efforts have been made to control their population. The best means of control so far seems to be an imported fish called grass carp, which views hydrilla as an especially tasty treat. Grass carp are not native to the United States. Only sterilized grass carp can be used to control hydrilla.