Population Growth in an Ecosystem

1. Population Growth in an Ecosystem Pre AP Biology

2. Populations and Communities • If an organism is given the right conditions for growth and reproduction, there will be a rapid increase in is population.

4. Exponential Growth • If nothing stops a population from growing it will show a growth pattern called exponential growth.

5. Exponential growth curves do not continue in populations for long. Populations that start growing exponentially and then come crashing down are called boom-and-bust populations. Insects quite often exhibit boom-and-bust population growth.

6. Populations exhibiting boom-and-bust population growth patterns are usually regulated by density independent factors such as rainstorms, drought, heat , cold, and fires. The population starts to grow exponentially , then a fire or something else will cause the population to crash. When these environmental conditions occur, they effect the population the same way no matter the size of the population. Boom-and-bust organisms are called r-strategists.

7. This slide goes with your notesWrite this down!! • Exponential growth is uncontrolled growth in a ecosystem with plenty of resources (food, space etc.) Exponential growth cannot continue forever. Some populations grow exponentially and then come crashing down due to density independent factors such as rain, drought, fire etc. Size of the population as no effect on result. Example-Insects are regulated by density independent factors. Insects are called r-strategists.

8. Write this down!! • The population growth rate is equal to the birth rate minus the death rate r=(b-d). r is called the intrinsic rate of increase. The population growth rate is also dependent on the number of individuals present in the population N. The total population growth rate is equal to G=rN • The total population growth rate is equal to G=rN. • r = (b-d) or (birth rate – death rate) intrinsic rate of increase . • N is the number of individuals present in the population

9. Write this down!! • Other populations go through a number of growth phases which can be shown on a logistic growth curve. At first the population starts to grow slow (lag phase). It is followed by rapid growth (exponential growth). Then the population growth rate slows down until it reaches the steady state. The carrying capacity of an ecosystem is the maximum number of organisms that ecosystem can carry without damaging the ecosystem.

10. Write this down!! • Steady state is when the birth rate equals the death rate. Usually this happens at the carrying capacity . There are some fluctuations at the steady state. As the population becomes more dense, other factors regulate the population. These include competition for factors like food, water, space. If the competition is within the same species it is called intraspecific competition and if it is between two different species is called interspecific competition. Other density dependent limiting factors include predator-prey interactions and simbiotic relationships.

11. For about the last 500 years the human population has grown exponentially. • Populations in most of the world are still growing very rapidly. • Some scientists estimate there are • close to 6 billion people on Earth.

12. Organisms that show logistic growth curves are called K strategists. • r-strategist K-strategist • Produce many young Fewer young • No parental raising young Parents invest time in raising young • Boom-and-bust growth Logistic growth curve • Live unstable environments Lives in stable environments • Density independent factors Density dependent regulate population factors regulate population

13. Predator-prey relationships can regulate populations • Just about every species serves as food(prey) for another species(predator). • Many predator-prey relationships must coexist over a long period of time. • The two populations will go in cycles. If one population gets too large or small it affects the other population.

14. Write this down!! • Predator-prey relationships can regulate populations • Prey is what is eaten and predator is what does the eating. The predator population mirrors what happens to the prey population. • Many predator-prey relationships must coexist over a long period of time. • The two populations will go in cycles. If one population gets too large or small it affects the other population.

15. In this Predator-prey Relationship which population must always be greater?

16. Symbiotic relationships • Some organisms interact in relationships called symbiosis. • There are three types of symbiosis • 1. Mutualism-Both organisms benefits. This black rhinoceros is being cleaned of parasites by yellow-billed ox-peckers.

17. 2. Commensalism (symbiosis)- one species benefits while the second species is not helped or harmed in any way • The example is the fish and sea anemone The clown fish is is protected by the sea anemone and is not harmed by the poinson found in the tentacles of the anemone. In this case the clown fish benefits and the anemone is not harmed or benefits in anyway.

18. 3. Parasitism (symbiosis)- one species harms its host and the other species benefits. This is Schistosoma mansoni, or a blood fluke. It has 2 host, humans and snails. It causes schistosomiasis which include dysentery and anemia. Victims become weak and succumb to other diseases due to their weakened condition.

19. Write this down!! • Symbiosis-Organisms living together. • Types of symbiosis • 1. Mutualism-Both organisms benefits. • 2. Commensalism (symbiosis)- one species benefits while the second species is not helped or harmed in any way • 3. Parasitism (symbiosis)- one species harms its host and the other species benefits.

20. Niche-is the role of an organism in the environment. It includes the habit, food, predator-prey relationships. The more two species niches overlap the greater the competition. • Example: two different niches

21. Population Ecology Review • 1. What is a population? • 2. Compare exponential and logistic growth curves. • 3. What limits an area's carrying capacity? • 4. Identify density dependent and independent limiting factors. • 5. How do predators and prey affect each other? • 6. What is a community? • 7. Compare parasitism, mutualism and commensalism. • 8. Describe how ecosystems interact with each other.