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Biology 30 Unit 4 – Population Genetics General Outcome D1: Students will describe a community as a composite of populations in which individuals contribute to a gene pool that can change over time. Bananas and Biodiversity Read the following news story, and then answer the questions. On Sunday May 21, 2006, Robin McKie, the science editor of the Observer, a weekly on-line publication of the Manchester Guardian, filed a report speculating on a possible crisis in the world food supply. Convenient for handling and eating, with a tab for wrapper-removal, a pleasing taste, an obvious sell-by-date mechanism (its skin turns black), and perfectly biodegradable, the banana is considered by many to be the perfect food. Sales of the fruit have recently reached all-time highs and more than 95 percent of UK households buy bananas every week. Only lottery tickets and gasoline sales outstrip them. There is trouble on the horizon, however. According to reports by biologists, the banana could be on the way to extinction. Or, to be more specific, the Cavendish—the variety sold in stores throughout Britain and around the world—may be in danger. According to Ann Vezina, of the International Network for the Improvement of Banana and Plantain, virtually all bananas traded internationally are this variety, and biologists have discovered that several predators—such as the black Sigatoka fungus—are attacking the Cavendish. Fungi such as the black Sigatoka are extremely dangerous. However, the situation is compounded by the biological heritage of the Cavendish. It is sexless, seedless, and sterile and can only be bred by growing plants from identical cuttings. All Cavendish bananas are clones, which means they are genetically identical. The fungi are not hampered by the same lack of genetic diversity. They are constantly developing new combinations to attack the Cavendish’s natural defences. Once a fungus develops a variation that is successful in its attack on one stand of bananas, that fungus population will spread like wildfire through the rest in the plantation. “One thing we can be sure of is that the Sigatoka won’t lose this battle,” said Dr Emile Frison, of the Consultative Group on International Agricultural Research. This story of the supermarket banana once again highlights the workings of natural selection. In fact, this looming crisis is a repeat of the fate of the Cavendish’s predecessor. In the 1950s, the banana of choice was the Gros Michel, until it was wiped out by Panama disease. And that fact has triggered alarm among biologists—small plantation managers have discovered that the Panama fungus—which the Cavendish was formerly immune to—has begun to attack and kill Cavendish plants. Scientists are looking for new varieties of wild banana plants that could be grown instead of the Cavendish or whose genes could be introduced to strengthen the Cavendish’s defences in its battle against the Panama, Sigatoka, and other diseases. But these attempts may be doomed to failure, as the UN Food and Agriculture Organization (FAO) warned this month. Wild banana plants species are being wiped out at an alarming rate as natural forests are destroyed across the sub-continent. “Due to eco-system destruction, it is probable that many valuable gene sources have now been lost,” said FAO Agricultural Officer NeBambi Lutaladio. Many of the genes that could have saved the Cavendish are likely already gone. For example, India’s lost bananas include a variety that might be able to confer genetic resistance to Sigatoka. Today that species exists as a single plant, found in the Indian Botanic Gardens in Calcutta. 1. How are small, isolated populations such as the sage grouse, wood bison, or peregrine falcon like the Cavendish banana? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 2. Why have the suppliers of foods such as bananas so carefully bred the biodiversity out of their plants? Name some examples of foods that have been managed the same way as bananas. Name at least one food you have seen in greater varieties. _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 3. When you return from a trip out of the country, you are usually asked if you visited any farms and reminded of regulations that forbid bringing foreign soil or plants into the country. Do you think this is an effective way to protect Canada’s crops and wildlife from biological threats? Why or why not? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ A. Genetic Variation • Main source of variation in a population lies in the differences in the genes carried by chromosomes (Modern theory of evolution ) • All the genes found in a population are called its gene pool. • A larger population will have a more diverse gene pool (more different alleles). • A stable population will have a fairly constant, unchanging gene pool. •Within this gene pool, the frequencies of different alleles remains the same. • This can be shown mathematically using the Hardy-Weinberg principle. B. Hardy-Weinberg Principle • Developed independently by an Englishman (Hardy) and a German (Weinberg). • States “in the absence of any outside forces, the frequency of each allele in a population will not change as generations pass” – genetic equilibrium. • This is useful for predicting allele frequencies in a population that are not evolving over time. So Why Use it? no change = no evolution • If this is true then the following 5 conditions must hold: 1. no mutations 2. no migration 3. large population size 4. random mating 5. no selection (artificial or natural) Symbols • p = frequency of the dominant gene • q = frequency of the recessive gene • p2 = frequency of the homozygous dominant trait • q2 = frequency of the recessive trait • 2pq = frequency of the heterozygous dominant trait Formula’s p+q=1 p2 + 2pq +q2 = 1 Summary Allele frequencies in a population will remain the same from one generation to the next, as long as five conditions are met: 1. The population is large enough that chance events will not alter allele frequencies. 2. Mates are chosen on a random basis. 3. There are no net mutations. 4. There is no migration. 5. There is no natural selection against any of the phenotypes. For a trait with two alleles, the sum of the allele frequencies must be 1.00, or 100%. The Hardy-Weinberg equation can be used to determine the frequencies of different genotypes in a population: Example 1 Four percent of the members of a population of pea plants are short. What is the genotypic frequency of the recessive allele and the dominant allele? What are the genotype frequencies in this population? First what is q2? Then calculate q. • q2 = 4% = 0.04 • q = 0.2 • therefore p = 0.8, (p + q = 1) • homozygous dominant = p2 =(0.8)2 = 0.64 • heterozygous dominant = 2pq = 2(.8)(.2) = 0.32 • homozygous recessive = q2 = (0.2)2 = 0.04 total 1.00 Example 2 An island population of monkeys with striped fur has a recessive characteristic of fur with no stripes. Out of a population of 14 000 monkeys, 1 260 of them do not have stripes. Calculate the frequencies of each allele and each genotype. First what is q2 ? Then find q. • q2 = 1260/14000 = 0.09 • q = 0.3 (p + q = 1 or 1 - 0.3 = 0.7) • p = 0.7 • homozygous dominant p2 = 0.49 • heterozygous dominant 2pq = 0.42 • homozygous recessive q2 = 0.09 total 1.00 Hardy-Weinberg Worksheet 1. Suppose that within a population of 325 ghosts, 58 exhibit the recessive trait, which makes them visible to humans. What is the frequency of the homozygous recessive genotype of the ghosts> 2. In the land of Krynn, a fire breath weapon is dominant to an acid breath weapon in dragons. If 90 out of 400 dragons display the acid breath what is the frequency of the dominant allele? 3. In cats, yellow eyes are controlled by a dominant allele and green eyes are recessive. If 90 out of 250 cats have green eyes, how many cats have at least one recessive allele? 4. Suppose that within the community of Sexsmith, 25 out of 101 children exhibit a homozygous recessive trait for lactose intolerance. Determine the frequency of the homozygous dominant individuals within this community. 5. In a hypothetical population of parrots, the dominant feather color is green. The recessive trait for multicolored feathers occurs in a frequency of 0.3. What is the genotypic frequency of the homozygous dominant trait? 6. In a pumpkin patch there are 400 pumpkins, 32% of the pumpkins have a recessive trait of purple spots. Assuming pumpkins reproduce sexually, how many pumpkins could have offspring with purple spots? 7. Out of 589 dolphins, 30 were found to give birth to human babies. The ability to give birth to human babies is a recessive trait. What is the genotypic frequency of the homozygous trait? 8. In a population of 4000 fairies, there is a dominant allele that produces green wing color. The recessive allele produces blue wing color. If 35% of the population expresses the homozygous dominant trait, calculate the number of fairies with the heterozygous trait. 9. A population of birds is in Hardy-Weinberg (genetic) equilibrium. 20 percent of the birds have short tail feathers, which is a recessive trait. Determine the genotype and allele frequencies of the population. 10. In a population of ferns, a biologist has determined that 60 percent of leaf-shape genes in the population carry the dominant allele for curly leaves (C). The remaining 40 percent of the genes carry the recessive allele for straight leaves (c). Determine the genotype and allele frequencies of the next generation of ferns. Use a Punnett square to show your work. 11. Allele Z is dominant, and is present in a population at a frequency of 37 per 100 individuals. Assuming the population is in Hardy-Weinberg equilibrium, what proportion of individuals in the population would be expected to be (a) homozygous dominant, (b) heterozygous, and (c) homozygous recessive? Show your work. 12. In a large, random-mating population, 85 in every 1000 humans carry the recessive allele for red hair. a) What percentage of the population carries this allele but does not exhibit red hair? ______________________________________________________ b) Would you expect to see a change in allele frequencies if members of this population preferentially mated with individuals with red hair? Explain your answer. 13. If a small, random-mating population has 18 percent of individuals exhibiting a recessive trait, could you calculate the genotype and allele frequencies of the next generation? Explain your answer. 14. 45 percent of individuals in a population of raccoons have a recessive trait. If the population is in Hardy-Weinberg equilibrium, calculate the frequency of the dominant allele in the population. Thought Lab – The Spirit Bear Purpose: Assessing the role of the Hardy-Weinberg principle in explaining natural phenomena. The Kermode bear (Ursus americanus kermodei) is a white variety of black bear that is found only in small island populations and in populations on the coastal mainland of British Columbia. Known to local Aboriginal peoples as the spirit bear, the Kermode is rare and people are unclear about how best to ensure its survival. Scientists know that its white coat colour is due to a recessive allele. They rely on bear counts and DNA testing of hair samples to estimate the frequency and distribution of this allele. Estimated Frequency of White Kermode Bears on Two British Columbia Islands Location Frequency of white bears Gribbell Island Princess Royal Island 0.3 0.1 Procedure Use the information and table above to answer the following Analysis questions. Analysis 1. Predict the frequency of the white coat allele in the Kermode bear population of a) Gribbell Island b) Princess Royal Island 2. Predict the frequency of the heterozygous genotype for coat colour in the Kermode bear population of a) Gribbell Island b) Princess Royal Island 3. Suggest why the frequency of the white coat allele is different on Gribbell Island and Princess Royal Island. 4. Suggest why some conservationists are concerned about inland black bears having access to the coastal bears’ territories. 5. Scientists are unsure if Kermode bears select mates based on coat colour. Suggest how this form of non-random mating might affect coastal black bear populations. C. Evolution • Evolution may be defined as: changes of allele frequencies within a population over time. • Hardy-Weinberg has the 5 conditions which must be met. •It provides a theoretical standard to compare real populations with. • The process of evolution is constantly taking place in our populations. • There are several agents of evolution: 1. genetic drift 2. founder effect 3. bottleneck effect 4. gene flow 5. mutation 6. non-random mating 1. Genetic Drift • A change in genetic makeup of a population resulting from chance. • Usually in small populations. • Decrease or alters the frequency of alleles in a population. 2. Founder Effect Genetic drift that results when a small number of individuals separate from their original population and find a new population. Allele frequencies of the new population may deviate as the new population expands. Worksheet – Founder Communities Read the following news story and then answer the questions. The total population of Iceland is less than 300,000 people, and genealogy (family history) is a national interest. Most Icelanders can trace their families back around 1200 years. In December of 1998, after much heated debate, the parliament of Iceland passed a bill that mandated the creation of a centralized database of all the Icelandic peoples’ genealogical, genetic, and personal medical information. The original bill did not include genetic information; this provision was added when the bill was amended during parliamentary review. The Icelandic parliament then granted an exclusive contract to deCODE genetics, a biomedical company, giving deCODE access to Iceland’s national health records. About a year before the bill was passed, deCODE signed an agreement with Hoffman-LaRoche, a Swiss pharmaceutical corporation, on the understanding that deCODE would get the contract from the government of Iceland. deCODE requested the contract because it was searching for genes associated with over 30 diseases (for example, heart disease, emphysema, and Alzheimer’s); 12 of these searches would be financed by Hoffman-LaRoche. To research these diseases, deCODE initially worked with the voluntarily donated DNA of small groups of Icelanders. Later, the company launched a media campaign to attract DNA donors on a larger scale. deCODE has been able to combine genetic information with the genealogical and health records of each Icelander in order to create a comprehensive database. On January 1, 2000, deCODE announced that it had almost completed “The Book of Icelanders,” an extensive family history database of all Icelandic citizens, past and present, and was planning to publish it on the Internet. According to deCODE, an individual’s information is encrypted. Most experts who reviewed the project’s privacy measures consider the information in the database to be personally identifiable. Icelanders can refuse to continue to participate in the database but cannot petition to have any information already in the database removed. Furthermore, the law does not require that Icelanders be told what kind of research will be done with their personal data. 1. With respect to the “founder effect,” explain why the Icelandic population would be ideal for this type of study. 2. Why would scientists want to study a population rather than an individual? 3. Do you think there might be opposition to the project? If you lived in Iceland, would you want your family data to be part of the project? Why or Why not? 3. Bottleneck Effect • A dramatic population reduction in size. • Often temporary. • Significant genetic drift. • Allele frequency in survivors differ from the original population. • Caused by severe environmental event. 4. Gene Flow • Movement of large numbers of a population either in (immigration) or out (emigration). • Many alleles may be lost or gained which affects the frequencies. • Few populations are so isolated that they escape this gene flow. 5. Mutations • Changes one allele into a different allele. • They are neither ‘good’ nor ‘bad’ - it all depends upon the environment. • Chromosome mutations cause many problems (chromosomal number change i.e. Down Syndrome). • Gene mutations may be passed on via gametes and are the main reason for the process of natural selection (Darwin). 6. Non-Random Mating • Sexual selection: favours the selection of any trait that influences the mating success of the individual. • Sexual dimorphism: traits favoured in sexual selection (differences in the appearance of male and females in a population and behavioral differences) i.e. female mate choice and from maleversus-male competition. Thought Lab Maintaining Genetic Diversity in the Whooping Crane Population Purpose: Assessing the value of captive breeding programs in preserving the genetic diversity of an endangered species. The whooping crane (Grus americana) is the tallest bird in North America. Standing 1.5 m high, this graceful white bird has a wingspan of 2.5 m. The whooping crane— affectionately referred to as the whooper—lives and breeds in shallow wetlands surrounded by bulrushes (Scirpus sp.) and other sedges. Its diet includes plant roots, crustaceans, mollusks, and insects. At age 3 to 4, it reaches sexual maturity. The adult whooper is known for its magnificent mating behaviour, which involves displays of plumage, courtship dances, and synchronized honking to signal its choice of a life mate. The female lays two eggs a year, but the couple will raise only one, usually the first to hatch, and may push the other from the nest. The largest current population of whooping cranes migrates between Wood Buffalo National Park in northern Alberta and Aransas National Wildlife Refuge in southern Texas. Scientists estimate that there were 1400 migrating whooping cranes in the late 1800s. The total population fell to about 15 in the 1940s. Loss of habitat, excessive hunting, avian disease, and lead poisoning were some of the factors that contributed to their decline. The discovery and preservation of the whoopers’ nesting and over-wintering grounds has helped to reverse this trend. The introduction of hunting regulations and the establishment of captive breeding programs, one of which is at the Calgary Zoo, has also helped. The world population of whoopers has now increased to over 300. Procedure Use the preceding information to answer the following Analysis questions. You may also use library, Internet, or other resources to help you answer the questions. Analysis 1. All the whooping cranes that are alive today are descendants of the 15 or so that remained in the 1940s. Make a hypothesis about the degree of genetic diversity within current whooping crane populations, and justify your thinking. 2. Does the fact that pairs bond for life help or hinder captive breeding programs? Explain your answer. 3. DNA technologies, such as DNA sequencing, are being used to determine the relatedness of all the whooping cranes in the main migrating population. How could conservationists use this information to assess the vulnerability of the population to environmental change? 4. To re-establish another wild population of whooping cranes, conservationists placed whooping crane eggs in the nests of sandhill cranes (Grus canadensis). The whooping cranes reared by the sandhill cranes feed normally and migrate, but are not breeding. Suggest a reason why the breeding program has not been successful. D. Speciation A way of altering the gene pool. A species is a group of similar organisms that can interbreed and produce fertile offspring. Speciation id caused by either geographical or reproductive isolation. A population gets separated from the others and over time, mutations produce fertile offspring. Selective pressures will vary – geographical barriers include water, mountains and canyons. Species end up evolving in different directions based on varying habitat conditions and therefore, different adaptations evolve. Reproductive barriers may mean incompatibility of the chromosomes, different mating rituals, or different mating seasons. General Outcome D2: Students will explain the interaction of individuals in a population with one another and with members of other populations. E. Population Relationships • Populations affect each other in many complex ways. • There are symbiotic relationships, there are predator-prey relationships, and all species are in competition with each other over the available resources. These resources are usually: food, water and living space. Competition may be interspecific: where different populations are competing or intraspecific: where the competition is within the one population. • Gause’s principle (competitive exclusion principle) states that if two populations are competing for a limited resource then one will be eliminated. • Normally, populations can coexist within the same ecosystem. An organisms niche is its role or its place within an ecosystem. Most organisms competing for a resource have a different enough niche that they may coexist. Symbiotic Relationships • Close relationships between two different species. 1. Parasitism • One organism benefits and the other is harmed. • Every parasite requires a host organism, usually it is a very specific host. • There are three different types of parasites: • exoparasites - fleas, ticks, leeches • endoparasites - tapeworms, liver flukes, protozoans • social parasites – cuckoos 2. Commensalism • One species benefits but the other is neither harmed nor helped. Examples: fox and caribou shark and remora orchids and trees 3. Mutualism • Both species will benefit from the relationship. • This relationship may be obligatory mutualism - each depends upon the other exclusively or facultative mutualism - neither is wholly dependent upon the other. Examples: plants and pollinators bacteria and human intestines ants and aphids Complete the following concept map by: a) Defining the term symbiosis. b) Defining the terms mutualism, parasitism, and commensalism. c) Identify two examples of each. Symbiosis Definition: Mutualism Parasitism Commensalism Definition Definition Definition Example Example Example Example Example Example Predation • One organism feeding on another. Predators have many mechanisms for feeding, but prey also have many ways of avoiding predators. If prey have no way of hiding out, then eventually both populations would die. If prey had easy hideouts, then the predator population would die out, if prey can hide temporarily, then both populations will cycle. • There are two types of hiding: 1. camouflage - they blend in with their background. 2. mimicry - they look like a different organism. The resources that are available to the predators (A), so the predator population increases (B). This leads to a reduction in the prey population (C), followed by a reduction in the predator population (D). And the cycle continues. Population estimates of snowshoe hare and Canada lynx show a pattern of 10-year cycles in population size. The hare population usually peaks about a year before the lynx population peaks. F. Succession • The way in which populations and communities change over time. • Primary succession is when there was no previous life. • Secondary succession is after partial destruction (eg forest fire, road building). • Pioneer organisms take root first (moss, lichen, insects) and build up the soil layer. • Transition communities take over and continue the process. • Climax community is the stable end populations that develop. Primary succession starts with rock and ends with a stable ecosystem (shown below). The first organisms to grow on bare rock are lichens, likely carried there by wind or visiting birds. Organisms that live in inhospitable places, without soil or shelter, are called pioneer species. They slowly create conditions suitable for other organisms. Secondary succession occurs in developed communities that have been disturbed and is usually faster than primary succession. This is because a disturbance such as a forest fire does not remove the soil or completely destroy all of the organic matter in the area, and conditions are suitable for grasses and shrubs to become established quickly. Thought Lab – Succession On average, fires in the boreal forest of Alberta occur every 50 years. The life span of a lodgepole pine is 220 years. Many lodgepole pines do not have a chance to live to “old age” because of the frequency of these fires. The classical model of succession came out of an explorer’s observations of a glacial valley in the late 1800s. Because succession is such a long process, however, early ecologists had difficulty testing this model of succession. In fact, no studies have lasted the hundreds of years required to observe the entire life cycle of certain types of trees. Nevertheless, with the development of new technologies and long-term studies of model forests, ecologists are able to gather and assess new information. Suppose that you are studying the impact of a wild land fi re in an area of Alberta’s boreal forest. All the above-ground vegetation in the area was destroyed. Suppose that you visit the area 20 years after the fire and see a layer of small white spruce trees growing below a layer of tall lodgepole pines. You hypothesize that this community is following the classical model of succession. If your hypothesis is correct, then presumably the pine trees are being replaced by the spruce trees, which are characteristic of climax communities in this area. Procedure Use the information above to answer the following Analysis questions. Analysis 1. What type of succession—primary or secondary—is taking place in the area? Explain your answer. 2. You hypothesized that the community is following the classical model of succession, with one species replacing another. If your hypothesis is correct, what would you predict about the ages of the pine trees relative to the spruce trees? Explain your answer. 3. How could you determine the ages of the trees in the area? 4. Analysis of the trees in the area indicates that both populations are about 20 years old. How does this information affect your original hypothesis? 5. Scientists have studied the birth rate and death rate of each species of tree. They have used their data to create the following survivorship curves, which show the proportion of individuals in a population that survive over time. As shown in section A on the graphs, both populations have a great decline in numbers after the seeds started germinating. List three factors that might cause the young seedlings to die. 6. Compare the rate of death of lodgepole pine trees with the rate of death of spruce trees in section A of the graphs. 7. Section B of the graphs represents a natural process called density thinning. It occurs in dense populations, when resources are very limited. Some of the population dies, which leaves more resources for the remaining population. Suggest a reason why density thinning affects the lodgepole pine population more than the spruce population. 8. Lodgepole pines are shade intolerant. When their seeds germinate, the seedlings grow very tall very quickly. In contrast, spruce trees are shade tolerant and grow more slowly than lodgepole pines. Would you expect the taller or shorter lodgepole pines to die during density thinning? Explain your answer. 9. Consider again your hypothesis that the community is following the classical model of succession and, therefore, the spruce trees are replacing the lodgepole pine trees. Based on your hypothesis, sketch a graph of the number of individual trees in each population versus time. Compare your graph to the survivorship curves. Formulate an alternative hypothesis about how succession is occurring in the community under study. 10. Which type of competition—interspecific or intraspecific—is more important to the pattern of succession in the study area? Explain your answer. Extensions 11. Explain how the trees came to grow in the study area in the first place. 12. Some plants need more light than others to survive. Knowing this, explain how the following factors might affect the type of plants that will start the process of secondary succession after an ecological disturbance. Then identify the factor that is probably the most important in determining which species will be the first to repopulate an area after an ecological disturbance. Explain your reasoning. a) the type of ecological disturbance (for example, a forest fire versus a fallen tree) b) the types of seeds left in the soil after the disturbance c) the availability of moisture in the soil d) the availability of nutrients in the soil General Outcome D3: Students will explain, in quantitative terms, the change in populations over time. G. Chaos Theory • States that ‘since randomness is a basic feature of many complex systems, long term predictions may well be difficult to impossible’. Small uncertainties in short term predictions of individual events may be magnified to such an extent over the long term that expected behaviors in complex systems become unpredictable. H. Dynamic Equilibrium or Steady State Theory • In mature ecosystems populations tend to remain relatively stable over long periods of time I. Populations Populations are characterized by three criteria: Population size Population Density Rate of Change a) Population size • Can be determined in two different ways - either a total count (okay in small area with small population), or representative sampling (sample a small area and multiply by total area). This assumes the population is distributed randomly Factors affecting population size: 1. natality 2. mortality 3. immigration 4. emigration • open populations - where all four factors are functioning. • closed populations - no immigration or emigration. b) Population Density • Populations are usually given in numbers per unit area. • Dp = N/A Dp = population density N = number of individuals in a population A = area (or V=volume) • Density will change depending upon the area (eg; Canada vs. Vancouver). • Population density may change over time: increase density means the population is increasing. • distribution may be: 1. clumped 2. random 3. uniform • Type of distribution depends upon the resource availability - most common is a clumped distribution Thought Lab – Distribution Patterns and Population Size Estimates Purpose: To see how transects (long, narrow areas of land used for ecological study) might be used to sample different moose populations. Procedure 1. Examine the three diagrams of hypothetical moose populations. What are the two different distribution patterns shown? 2. The shaded parts of the diagrams represent the transects that were used to sample each population. Calculate the area per transect. (In these diagrams, 1.0 cm represents 1.0 km.) 3. For each hypothetical population, count the moose within each transect. 4. For each hypothetical population, calculate the average number of moose per transect. 5. Calculate the average density of each hypothetical moose population. 6.Calculate the total study area that is inhabited by one moose population. Estimate the total number of moose in each hypothetical population. Analysis 1. The actual numbers of moose in the three populations are 60, 133, and 133, respectively. How close were your estimates to the actual sizes of the populations? 2. Explain the difference, if any, between your estimate and the actual size of the first population. 3. Explain any differences between your estimates and the actual sizes of the second and third populations. 4. How would you design a sampling experiment on a real population of wild moose? (Note: In real life, the time and expenses involved usually restricts the proportion sampled to between 10 and 20 percent of the total area of interest.) Extension 5. There is concern that an introduced population of moose may deplete the resources in its home range. Why would scientists want to know the density of this population? If you were given the size of this population, how would you calculate its population density? c) Rate of Change – Population Growth • Change in population size, ∆N= [natality + immigration] – [mortality + emigration] • Rate of change in a population refers to some factor such as density changing over time also referred to as growth rate(gr). rN = ∆N/∆t ∆N = change in population size ∆t = time interval Problem A collard pika (Ochotona collaris) population dropped from exactly 25 individuals in 1998 to 5 individuals in 2000. Calculate the growth rate of this population from 1998 to 2000. What Is Required? To determine the growth rate (gr) of the collard pika population from 1998 to 2000 What Is Given? The values needed to calculate the change in population size (ΔN): The original number of individuals is 25.0. The final number of individuals is 5.00. The values needed to calculate the change in time (Δt): The beginning of the time frame is 1998. The end of the time frame is 2000. Step 1 ΔN = final number of individuals – original number of individuals = 5.00 – 25.0 = –20.0 individuals Step 2 Δt = final time – initial time = 2000 – 1998 = 2 years Step 3 N t 20.0 individuals 2 years 10 individuals/year gr The growth rate of the collard pika population was –10 individuals per year. In other words, the population dropped at a rate of 10 individuals per year. Check Your Solution N t gr t N gr 10 individuals/ year 2 years 20 individuals 20 individuals 20 individuals • Growth rate is also referred to as a per capita growth rate (cpr), and represents the change in population size ∆N, relative to the initial population size, N. cgr= ∆N/N Problem A population of 26 caribou (Rangifer tarandus) was introduced onto a predator-free island in Alaska in 1910. For the next 25 years, the per capita growth rate of the population was 75.9. In about 1935, resources became limited and the population crashed. Calculate the number of caribou on the island just before the population crashed. What Is Required? To determine the size of the island caribou population after the given time interval What Is Given? The value of the original number of individuals in the population (N): 26 caribou The per capita growth rate (cgr) for the population over 25 years: 75.9 Step 1 N N N cgr N cgr Step 2 ΔN = (75.9)(26 caribou) = 1973.4 caribou Step 3 Final number of individuals in population = ΔN + N = 1973.4 caribou + 26 caribou = 1999.4 caribou Step 4 1999.4 caribou ≈ 2.0 × 103 caribou There were about 2000 caribou on the island just before the population crashed. Check Your Solution ΔN – N = 2000 caribou – 26 caribou = 1974 caribou N N 1974 caribou / 26 caribou cgr 75.9 Is effective when comparing populations of different sizes i.e. school population vs. community • Many factors affect the growth of populations. • The capacity for reproduction is the biotic potential. • The biotic potential is regulated by four factors: 1. maximum number of offspring per birth 2. chances that the offspring will reach reproductive age 3. number of times per year the organism reproduces 4. the age at which reproduction begins • The ability of an environment to support a population is called its carrying capacity (changes with availability of resources). • Some factors affecting the growth of populations are density - dependent, some are density – independent. • Density - dependent work by increasing death and limiting reproduction as a population increases: disease, food supply, predation. • Density - independent work regardless of the population number: floods, drought, temperature Thought Lab – What Limits the Growth of Grizzly Bear Populations? Procedure Using the data in the first table, draw a graph that shows the change in size of the Alberta grizzly bear population outside the National Parks over time. Then complete the following Analysis questions. Analysis 1. 2. 3. To manage the grizzly bear population better, the government of Alberta introduced a hunting lottery that awards a limited number of grizzly bear hunting licenses. Predict the year that this regulation was introduced. The number of grizzly bear deaths in Alberta from 1976 to 1988 was estimated to be 581. Only 281 deaths were recorded from 1988 to 2000. How does this information affect the prediction you made in question 1? Explain your answer. Determine the per capita growth rate (cgr) for each of the following time intervals: 1991 to 1992, 1997 to 1998, and 1998 to 1999. Suggest why the cgr has changed over time. Number of Grizzly Bears in Alberta, Outside the National Parks Year Population size 1988 575 1989 536 1990 547 1991 638 1992 669 1993 686 1994 700 1995 735 1996 765 1997 776 1998 807 1999 833 2000 841 4. Population counts were made in several bear management regions around the province. Some of the data are shown in following table. Grizzly Bear Population Sizes in Alberta Region Area (km2) Bear population A 14 128 31 B 6 089 44 C 22 840 168 Source: Alberta Wildlife Status Reports, Alberta Sustainable Resource Development, 2002 a) For each region, determine the number of grizzly bears per 1000 km2. b) Compare the densities for the three regions. Suggest three reasons for the differences, if any. Explain your thinking. 5. Very few grizzly bears die of old age. What are two other possible causes of death, not associated with human activities? 6. Studies have shown that male grizzly bears will cross roads and use underpasses to forage in a better environment. Females tend to remain in more restricted areas. a) How might the movement of male and female grizzly bears in their habitat affect genetic diversity in the population? b) How would this behaviour influence the per capita growth rate of the population? 7. Grizzly bears reach sexual maturity at five years of age. When food is abundant, females average two cubs per litter every other year. With inadequate nutrition, females produce fewer cubs. a) Compared with mosquitoes, how would you describe the life strategy of grizzly bears? b) Explain why the biotic potential of grizzly bears is relatively low. c) How might grizzly bears’ low biotic potential present challenges for people who are working to conserve the grizzly bear population? 8. Near Lake Louise, Alberta, there is a road sign that asks drivers on the highway to reduce their speed from 90 to 70 km/h along a 15 km stretch where grizzly bears are known to forage for food, especially at dusk and dawn. Do you think that lowering the speed limit along this stretch of highway is a reasonable action? Would the installation of underpasses along this stretch of highway be a better alternative? Compare the advantages and disadvantages of each option. What questions might you want answered before making a decision about this issue? 9. One report concluded that people must “find a way” to prevent the Trans-Canada highway from being a barrier to grizzly bear migration. List the stakeholders in this issue. Based on the point of view of one of these stakeholders, suggest what actions could be taken to overcome the fragmentation of the grizzly bear’s habitat. Share your ideas on this issue in a class discussion J. Growth Curves There is different shaped curves depending upon the type of population growth. Exponential growth gives a J-shaped curve, where the speed of growth is determined by maximum reproductive rate. However, organisms in nature cannot sustain unlimited growth. Therefore, most populations show an S-shaped curve, which is characteristic of sigmoidal or logistic growth. J-shaped Curve • Occurs in closed systems - aquarium containing paramecium or bacteria, yeast or other microorganisms which have short life span and are easy to handle and manipulate. • 4 definite phases 1. lag phase - adjustment to new environment. 2. growth phase - rapid increase in population. 3. stationary phase - lack of space, nutrients or accumulation of wastes population growth ceases - natality = mortality. 4. death phase - mortality > natality. nutrients run out and wastes accumulate. S-shaped Curve • This curve is typical when a limiting factor is introduced or increased or when an organism is placed in a new environment. • Reaches new equilibrium. • Carrying capacity is the maximum number of individuals the environment can support. The human population is at the top of the J right now. Population is almost due for a crash - 1/5 is malnourished - no housing - no water. Population Growth Curve Depicts Life Strategy • K-selected Reach sexual maturity later in life. Spend a lot of time with their offspring. Large animals. Have few offspring. S-shaped growth curve. Long life span. Live in stable communities. • r-selected Reach sexual maturity quickly. Spend no time with their offspring. Small organisms. Have many offspring. J-shaped growth curve. Short life span. Live in fluctuating, unstable environments. Histograms • Histograms are useful for depicting the percentages in age groups within a population. The shape of the histogram tells if a population is growing, stabilized or declining. Thought Lab – Population Growth Rates in Different Countries Procedure Use the table below to answer the following Analysis questions. Human Demographic Information for Selected Countries in 2001 Country Population size (millions) (N) Number of births (b) per 1000 individuals Number of deaths (d) per 1000 individuals Canada 32.2 10 7 Ethiopia 77.4 41 16 Finland 5.2 11 9 Germany 82.5 9 10 Greece 11.1 9 10 India 1103.6 25 8 Nigeria 131.5 43 19 Analysis 1. Use the following data table to record the results of your calculations, or create a computer spreadsheet with the following headings: Predicted Population Growth from 2001 to 2011 in Selected Countries 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 Population size (N) at one-year intervals 2001 Countr Annu y al per capita growt h rate (cgr) 2. The table of demographic information on the previous page shows the total population size and the number of births and deaths that occur annually per 1000 people in different populations. In other words, the table shows birth and death rates for each population. Subtract the deaths per 1000 individuals from the births per 1000 individuals each year to calculate the annual per capita growth rate (cgr) for each population: b d cgr 1000 1000 Note that this estimate of cgr does not take into account emigration or immigration. 3. Use Canada’s 2001 population size and annual cgr to calculate the predicted population size for 2002: N(Canada in 2002) = N(Canada in 2001) + (cgr)(N(Canada in 2001)) = (1 + cgr)(N(Canada in 2001)) = (1 + cgr)(32.2 × 106) Then use Canada’s 2002 population size and annual cgr to calculate the predicted population size for 2003. Repeat this step for the rest of the years listed in your data table. (Show one sample calculation.) 4. Repeat the calculations in step 3 for each country listed in your data table. 5. Using a full sheet of arithmetic graph paper (or a computer graphing program), graph the size of Canada’s population from 2001 through 2011. This graph is a hypothetical population growth curve for Canada for 2001 through 2011. Remember to label each axis and include a title for your graph. 6. Graph population growth curves for the six other countries listed in your data table. You can use the same piece of graph paper (or plot area) for all the growth curves, as long as you use a different symbol or colour for each growth curve and provide a legend. 7. Compare the steepness of the different growth curves. Describe how annual cgr affects the steepness of a growth curve. 8. Describe the effect of a population’s initial size on the steepness of its growth curve. 9. Why is the annual cgr negative for some populations? Describe the growth curve for a population with a negative cgr. 10. Based on your graph, which populations are currently undergoing exponential growth? 11. Based on your graph, for which populations is the growth rate (gr) slowing? (Recall N that gr .) t 12. Classify the countries in your data table into countries that you would consider to be more industrialized and countries that you would consider to be less industrialized. Compare the growth curves that are typical of each group. Explain the differences between the two types of curves.