Unit 3: Populations Chapter 8: Understanding Populations

1. Unit 3: PopulationsChapter 8: Understanding Populations

2. Section 1: How Populations Change in Size Key Terms: Population Density Dispersion Growth rate Reproductive potential Exponential growth Carrying capacity

3. A. What Is a Population? • All the members of one species living in the same place at the same time.

4. B. Properties of Populations • Density is the number of individuals per unit area or volume. • Dispersion is the relative distribution of its individuals within a given space. it may be: - even - random - clumped

5. C. How Does a Population Grow? The change in population size = births – deaths. • Growth rates can be positive, negative or zero. • For a population to be stable each adult pair produces two fertile offspring.

6. D. How Fast Can a Population Grow? • Most species have a huge reproductive potential. • If all survived the species would grow exponentially. • Various factors keep populations in check.

7. 1. Reproductive Potential • Biotic potential = the fastest rate at which a species can reproduce. • Reproductive potential is limited by genetic factors. • Ex: 2 elephants can make 19 million descendents in 750 years, 2 bacteria can do that in a few days. • Generation time: time between birth and reproduction.

8. 2. Exponential Growth • A species grows in population faster and faster: • 2 parents  6 offspring  18 offspring  54 …

9. E. What Limits Population Growth? • Resources are used up. • The environment changes. • Only the best suited to the environment survive.

10. 1. Carrying Capacity • The maximum population that an ecosystem can support indefinitely. • A population can rise above the carrying capacity but cannot stay at that rate.

11. 2. Resource Limits • A species reaches its carrying capacity when it uses a resource at the same rate as the resource is being created. • Water, minerals, food…

12. 3. Competition Within a Population • Because all members of a species use the same resources, as they come closer to the carrying capacity, there will be competition. • There may be indirect competition through social status, i.e. territoriality.

13. F. Two Types of Population Regulation • Density dependent: deaths occur more frequently in a crowded location. • Density independent: organisms die regard less of population density (weather, natural disasters).

14. Review: • Compare two populations in terms of size, density and dispersion. 2. Describe exponential population growth. 3. Describe three methods by which the reproductive behavior of individuals can affect the growth rate of a population. 4. Explain how population sizes in nature are regulated. 5. Making Predictions: How accurately do you think the size of a population can be predicted? What information would you need to make a prediction?

15. Quick Lab: Population Growth Procedure: 1. Model the change in size of a population by applying the equation: population size = births – deaths. 2. Start with 100 g of dry beans. Count out five beans to represent the starting population of a species. 3. Assume that each year 20% of the beans each have two offspring. Also assume that 20% of the beans die each year. 4. Calculate the number of beans to add or subtract for 1 year. Round your calculations to whole numbers. Add to or remove beans from your population as appropriate. 5. Continue modeling your population changes over the course of 10 years. Record each change. Analysis: Make a graph of your data. Describe the changes in your population.

16. Section 2: How Species Interact with Each Other Key Terms: Niche Competition Parasitism Mutualism Commensalism Symbiosis

17. A. An Organism’s Niche • The unique role of a species in the environment. = physical home, interaction with other species, needs for survival. = functional role or job.  Different depending on habitats.

18. B. Ways in Which Species Interact • Relationships are determined by the benefit or harm to the other species. • Relationships can be indirect.

19. C. Competition • Individuals attempt to use the same limited resources. • Can occur in or between species = overlap niches.

20. 1. Indirect Competition • Species can compete even though they are not in direct contact. • Example: humans and insects

21. 2. Adaptations to Competition • Niche restriction = each species uses less of the environment that it is capable of using.

22. D. Predation • An organism that feeds on another organism – predator. • Some predators eat only certain types of prey = increase/decrease of populations occur in patterns.

23. E. Parasitism • One organism lives off of and feeds on another. • The parasite takes nourishment from its host.

24. F. Mutualism • Species work together for survival each provides a benefit to the other.

25. G. Commensalism • The relationship where one species benefits and the other is neither harmed nor helped.

26. H. Symbiosis and Coevolution • Symbiosis is the close relationship between organisms. • Coevolution is the change in species over time as they adapt, reducing the harm or increasing the benefit between those organisms.

27. Review: • List as many parts as you can of the niche of an organism. 2. Give examples of species that have the same habitat but not the same niche as the lion has. 3. Describe the fife types of species interactions. 4. Making Comparisons: How do predators compare to parasites? 5. Analyzing Relationships: Choose an example of mutualism and explain how the relationship could have developed.