Transcript Document
Population Growth How Populations Grow Populations Growth Population Growth Three factors can affect population size: number of births (Birth Rate) the number of deaths (Death Rate) the number of individuals that enter or leave the population. * Simply put, a population will increase or decrease in size depending on how many individuals are added to it or removed from it Immigration & Emmigration Immigration the movement of individuals into an area, is another factor that can cause a population to grow. Emigration the movement of individuals out of an area, can cause a population to decrease in size. The rise and fall of populations….. Populations Increase: A higher birthrate in comparison to death rate Immigration Populations Decrease: A higher death rate in comparison to birth rate Emigration What if…… A population is provided with food, space, shelter, protection from predators and disease? The population will grow……because? Exponetial Growth Exponential Growth (J-shaped curve) If a population has abundant space and food, and is protected from predators and disease, then organisms in that population will multiply and the population size will increase. **unlimited resources Exponential Growth Exponential growth occurs when: the individuals in a population reproduce slowly Example: bacteria A change in a new environment (for a time) Example: invasive speciese Organisms reproduce slowly Example: Elephants produce offspring 2-4 years Checkpoint Which of the following is NOT a condition for a population to reach exponential growth? A.) presence of unlimited resources B.) Absence of predation and disease C.) movement of individuals out of the population Logistic Growth Logistic growth occurs when a population's growth slows or stops following a period of exponential growth; levels off at Carrying Capacity As resources become less available, the growth of a population slows or stops. The general, S-shaped curve of this growth pattern, called logistic growth Carrying Capacity Carrying Capacity The number or the largest number of individuals that a given environment can support. Phases of a Logistic Growth: I: Exponential Growth: unlimited resources II: Growth Slows Down: Population still grows, BUT rate of the growth is slowing down III: Growth stops: Population is stabilizing @ its carrying capacity Closure Question: What shape population growth curve would you expect to see in a small town made up of Senior citizens? Why? What shape population growth curve would you expect to see in a small town made up of newly married couples in their twenties? Why? Using Graphic Organizers Draw a concept map that shows how populations grow. Include the following terms: exponential growth, logistic growth, birthrate, death rate, immigration, emigration. Add any other terms that you think are useful to complete the map Population Density Population density is the number of individuals per unit area. The population of saguaro cactus in the desert plant community has a low density, whereas other plants in that community have a relatively high density. What factors determine carrying capacity? Limiting Factors! A factor that controls the growth of a population – Examples: Competition Predation Disease Unusual Weather Disasters Limited nutrients (productivity) Limiting Factors determine the CARRYING CAPACITY of an environment for a species!!!! Density-Dependent Factors Limiting factor is DEPENDENT on the population density Competition Predation Herbivory Disease Stress from overcrowding Real Life Examples Competition Predator/Prey Density-Independent Factors Limiting Factors that affect ALL populations in similar ways, REGARDLESS of population size and density Hurricanes Droughts Floods Natural disasters (wildfires) Real life examples Hurricane Sandy Drought Now…….. YOU COME UP WITH REAL LIFE EXAMPLES OF DENSITY-DEPENDENT AND DENSITY-INDEPENDENT FACTORS