REVISION: POPULATION ECOLOGY 18 SEPTEMBER 2013 Lesson Description In this lesson we: Revise population ecology by working through some exam questions. Key Concepts Definition of Population A population is the total number of individuals of the same species that occupy a specific area and that are able to interbreed (are able to breed with one another) at a specific time. Characteristics of a Population Density: The number of individuals per unit area or per unit volume. Sex ratios: The ratio of male and female individuals within the population. Pattern of distribution: The way in which individuals of a population are distributed over the area that they occupy. The distribution may be random, clumped or uniform. (Life Sciences for All, Macmillan 2012, p272) Parameters of a Population Population parameters are factors that characterise a population. A population parameter is a factor that determines the size of a population and the changes that occur to the size of the population over time. Parameters that affect population size are: o natality the rate at which new individuals are added to a population through reproduction o mortality the rate at which new individuals are lost to a population through death o immigration the rate at which new individuals join a population from somewhere else o emigration the rate at which individuals from a population leave it to go somewhere else.
(Life Sciences for All, Macmillan 2012, p273) Predator-Prey Relationships A community is a group of species living in a particular area. An animal that hunts, catches and kills another animal is called a predator. The animal that it catches and kills is called its prey. The feeding relationship between the predator and the prey determines the size of the two populations. The two populations regulate each other in a negative feedback mechanism. We call this a predator prey relationship. (Life Sciences for All, Macmillan 2012, p285)
(Life Sciences for All, Macmillan 2012, p286) Types of Competition Intraspecific competition: the type of competition that occurs between individuals of the same species. Intraspecific competition is very intense. E.g kittens competing for their mother s milk or male lions competing for territory or for a mate. Territoriality is how many animals compete for space and for food. A certain area may be able to support only a certain number of animals of a particular species. One of these animals will decide what territory it wants for itself and will then mark the borders of that territory in some way. Interspecific competition is the type of competition that occurs between individuals of different species. It is similar to intraspecific competition but is not as intense as competition between individuals of the same species. When two species with the same or similar ecological niches occupy the same habitat, their ecological niches will overlap to a greater or lesser extent. The competition that arises will lead to one of two possible outcomes: competitive exclusion or competitive coexistence. Specialisation Competitive exclusion occurs when one of two competing species is much more successful than the other. The successful species survives and the other species disappears. This has resulted in the extinction of most of the organisms that have ever existed on Earth and has had a significant part to play in the process of evolution. Competitive coexistence occurs when two competing species coexist in the same ecosystem. The organisms have overlapping niches and compete for the same resources but they coexist because they use the resources slightly differently. This is called resource partitioning. Temporal partitioning: is when two species use the same resource but at different times.
Questions Question 1 Seagulls use the coastal dunes as a breeding area. Over a 20-year period the size of the seagull population has been monitored on a coastal dune where vehicles drive. The data shown in the table was collected. Look at the table carefully and answer the questions that follow. a.) Write a hypothesis for this study. (2) b.) Identify the: i. dependent variable ii. independent variable. (3) c.) Discuss the result observed over the 20-year period. (2) d.) List possible reasons, other than the vehicles, for the decrease in the seagull population in the period 1994 1995. (2) e.) Calculate the percentage decrease in the seagull population over the 20 year period. Show all calculations. (5) f.) Consider the experimental design and suggest ways in which the technique used could be improved to make the investigation valid. (2) g.) What can you conclude from this study? (2) h.) Name two other examples of how the dune ecosystem is affected by the use of vehicles on the dunes. (2) (20)
Question 2 The table shows the results of a yearlong investigation into the air pollution from a factory near a town in South Africa. a.) According to the table, when was the smoke concentration the highest? (1) b.) Describe the relationship between: i. The average smoke concentration and the average sulphur dioxide concentration. (1) ii. The average sulphur dioxide concentration and the number of reported respiratory diseases. (1) c.) Name TWO respiratory diseases that can be caused by air pollution. (2) d.) Explain how sulphur dioxide in polluted air can lead to acid rain. (2) e.) Name THREE other negative effects of acid rain besides the effects on human health. (3) f.) South Africa, with its dependence on coal-fired power stations is at risk for increasing acid rain. Name THREE ways that South Africa could reduce its acid-forming emissions. (3) g.) An example of biodiversity loss caused by humans is deforestation. i. Explain what is meant by the term deforestation. (1) ii. List TWO possible effects of deforestation. (2) iii. Suggest ONE possible solution to the problem of deforestation. (1) (30)