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20 reactivos de la materia de nominas de la especialidad de contabilidad
Quiz by Edgard Flores
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Elabora un cuestionario de 20 reactivos de opción múltiple a cerca de la Voz Pasiva y el uso de la preposicion By , cada planteamiento deberá tener 4 opciones distintas. Desarrolla un examen de 20 reactivos de opción múltiple referente al tema Introducción a las funciones linealesElabora un examen de opción múltiple de 20 reactivos con tres respuestas modelado y resolución de problemas utilizando funciones lineales y cuadraticasMeasuring the Effectiveness of police strategies and operations Clearance rates Def: The proportion of incidents known to the police that result in teh identification of a suspect Crime Displacement Def: relocation-due to the effective crime prevention, crime response initiates criminal activity from one local to another Professional Model of Policing Model of police work, reactive, incident driven and centred on random patrol Three Rs: random patrol, rapid response and reactive investigation Community policing Def: policing centred on police-community partnership and problem-solving The three ps: prevention, problem solving and partnership with the proactive role Community-based strategic policing Def: The model incorporates community policing with prevention, crime response and crime attack approaches Community engagement, police services strategic in their policies and operations Crime Analytics Sophisticated programs, and crime maps, provide intelligence to police officers in patrol and investigative units Intelligence-led policing: guided by collection, and analysis of information informs police decision-making Compstat: Increase effectiveness, and efficiency of police service while holding police personnel accountable for crime reduction Predictive policing: statistical analysis, identify time and location likely to occur Limited analytical capacity and not able to provide their officers with real-time information Biased policing certain areas, or persons, being identified as important for police attention in predictive policing How Predictive Policing Software Works The Police and the community Public Attitudes toward and Confidence in the police Community-based strategic policing: Recruitment, and deployment of volunteers in community police stations, storefronts Foot and bike patrols Team policing Restorative Justice Approaches Alternative for addressing, and resolving crime, needs of victims, offenders and the community Victim offender meditation Circle sentencing Community holistic healing programss Family group conferences Crime Prevention and Response Strategies Crime Prevention progemas Aimed at reducing crime, generating community involvement and heightening citizens; perceptions of safety Primary crime prevention programs opportunities for criminal offences and alter those conditions Secondary crime prevention programs focus on areas that produce crime and disorder Tertiary crime prevention programs are designed to prevent youth and adults from reoffending The Broken Windows Approach If minor crimes are left unaddressed in an environment, more serious crimes will emerge (originated in New York City in the 1980’s) “The exictsnce of unchecked and uncontrolled mirror incivilites in a neighbourhood- for example, panhandling, public drunkenness, vandalism and graffiti-produces an atmosphere conducive to more serious crime.” R.H. Burke Zero tolerance policing Zero tolerance policing: Strict order maintenance approach- specific area, coupled with high police visibility and presence Quality of life policing: Increased police visibility improves conditions in an area by targeting disruptive and annoying behaviour Problem Oritented policing (POP) Strategy, the idea that police should address teh cause of recurrent crime and disorder Root causes of recurring problems Solutions to problems Collabortaion with community SARA (scanning, analysis, response and assessment) problem-solving model helps officers identify, and respond to problems with the assistance of agencies, organizations, community groups The Police and Vulnerable/ At risk groups Persons with Mental Illness Patrol officers encountering more and more persons with mental illness (PwMi) Number of these end trragically Number of incidents increased significantly following deinstitutionalization of the mentally ill - in 1960 and 1970 De facto (in fact) mental health workers, first responders Crisis intervention training (CIT) Assertive outreach teams Assertive community treatment (ACT) teams Indigenouse, Vulnerable, and Marginalized women Sexual assault one of most underreported crimed. 1 in 20 incidents report to police. Many Women Do not want to deal with police Believe police would not take allegation seriously Language, cultural barriers Distrust the police Fear repercussions Missing and Murdered Indigenous women Canada, unknown number of missing and murdered indigenous women 2016, federal government announced National inquiry into Missing and Murdered Indigennouse women and girls Three goals of MMIWG 1. Finding the truth 2. Honouring the truth 3. Giving life to the truth as a path of healing Filmic Techniques Based on the work of Brad Smilanich Mis-en-Scene: originally a French theatrical term arrangements of all the visual elements of the stage area in film – “the contents of the frame and the way those contents are organized” include: lighting, costume, décor, props, camera movement or distance . . . all photographic decisions etc. Proxemics: Spatial relationship among characters within the mis-en-scene Rule of Thirds: a compositional rule of thumb in painting, design, photography etc. suggests image divided into 9 equal parts with two vertical and two horizontal lines important elements of the mis-en-scene should be placed along these lines and their intersections some suggest aligning with intersections makes for more interesting pictures than just centreing the subject Proxemics Camera Distance: Quite literally, how far the camera is from the subject being filmed The Hand Camera Camera Distance: Quite literally, how far the camera is from the subject being filmed Extreme Close Up: Singles out one small portion of the body or object Used to intensify emotion, or show reaction Camera Distance: Close up Shot: Shows head of character or small significant object Used to show emotions Camera Distance: Medium Shot: shows figures from the waist up allows character to be seen within background Camera Distance: Long Shot: shows figures from feet up similar to the “stage” in live theatre orients audience to figures within a location or surrounding Camera Distance: Extreme Long Shot: Sometimes called an ‘establishing shot’ Panoramic view of an exterior location orients audience to a location Camera Distance: Camera Angle: Camera’s angle of view relative to the subject being photographed High Angle Shot: looks down on the subject often used to make the subject look small and insignificant (in combination with camera distance) puts the camera (audience) in ‘power’ position Camera Angle: Low Angle Shot: looks up at the subject often used to make the subject look large and powerful puts the camera (audience) in a ‘submissive’ position Camera Angle: Flat Angle Shot: camera on same plane as the subject feels most ‘normal’ to an audience Camera Angle: Canted Shot: frame is unbalanced in relation to the subject may indicate a symbolic unbalance in the character Camera Angle: Camera Movement literally the camera moving with or around or to follow the subjects in the mis-en-scene or frame Camera Movement: Tilting Movement camera moves up or down on a horizontal axis similar to head nodding movement may be used to show subjects relation to surroundings Camera Movement: Panning Movement camera moves side to side on a vertical axis similar to head shaking movement may be used to establish setting Camera Movement: Dolly Movement camera mounted on a vehicle that moves along with the subject (camera moves, not pivots) follows the subject to signify something important Camera Movement: Crane Shot camera mounted on a crane or boom permits camera to move in & out, up & down, backward & forward often used for high aerial establishing shots Misc. Shots: Hand Held: camera carried to seem jerky, giving ‘realistic feel’ Push In: camera moves up to a character’s face to indicate an epiphany (realization) Spiral: camera circles subject for effect End for ELA 20-2 and 10-1 Shot Transitions/Editing: artificial editing done to string together multiple shots to create a narrative scene or sequence a cut is the change from one shot to another usually separated in to ‘soft’ and ‘hard’ cuts Jump Cut: an instantaneous change from one shot to another this can be very natural or may disorient the audience, depending on how it is used Transitions/Editing Swish Pan: A pan where the speed of the camera is so fast that images are blurry used often to connect events in different settings that are connected by time Transitions/Editing Dissolve: transition where one shot gradually dissapears while another shot gradually appears often used to suggest change of setting or long time passage i.e. flashbacks Transitions/Editing Fade In/Out: transition where the shot gradually overexposes to white or underexposes to black often used to suggest a lengthy passage of time or change in location Transitions/Editing Wipe: transition where one shot is gradually eliminated as another shot moves onto the screen can be vertically or horizontally often suggests movement of the camera to another location Transitions/Editing Iris In/Out: transition where one shot gradually appears as an expanding circle in the middle of an old image suggests . . .??? Transitions/Editing Shot-Reverse Shot: one character is shown looking (often off-screen) at another character, and then the other character is shown looking "back" at the first character. Since the characters are shown facing in opposite directions, the viewer unconciously assumes that they are looking at each other. Transitions/Editing Two-Shot: Face-up shot of two people. Often used in interviews, or when two presenters are hosting a show. A "One-Shot" could be a mid-shot of either of these subjects. A "Three-Shot", unsurprisingly, contains three people. Transitions/Editing Shot Transitions/Editing: Sound: used to reflect or enhance what is shown visually on the screen can include dialogue, music, sound effects, voiceover etc. Diegetic Sound: sound that has a source in the world of the story dialogue spoken by characters, sound made by objects, or music coming from a source grounded in the story of the film Non-diegetic Sound: sound that has a source outside the world of the story usually part of the score or the soundtrack Parallel Sound: sound that complements the image shown i.e. romantic music during a love scene Counterpoint Sound: sound that contradicts the ‘feeling’ of the image a happy song played while images of graphic violence are portrayed Voiceover: voice of a non-visible narrator laid over the scene often provides some comment about the narrative of the film Sound Bridge: used to ‘soften’ the transition between one scene and another takes sound from the next shot and overlays it on the current shot 2-3 seconds earlier than we see the image Examples of Diegetic/Non-Diegetic: In the first clip, the non-diegetic music changes to diegetic music when the main character moves inside of the convenience store. In the second clip, the “duhn duhn duuuuh” which often is non-diegetic becomes diegetic because it is the band in the passing bus playing that music! End for ELA 20-1 Lighting: Can be used by a director to: Control the mood of a scene guide a viewer’s eye to a specific place in mis-en-scene Emphasize and de-emphasize elements in frame Add texture and color Make people look beautiful, ugly, sinister, or angelic Standard 3-Point Lighting: uses three lights called the key light, fill light and back light forms the basis of most lighting. once you understand three point lighting you are well on the way to understanding all lighting. Key Light: main light usually the strongest and has the most influence on the look of the scene. it is placed to one side of the camera/subject so that side is well lit and other side has shadow. Fill Light: secondary light is placed on the opposite side of the key light used to fill the shadows created by key softer and less bright than key Back Light: placed behind the subject ; lights it from the rear. provides definition and subtle highlights around the subject's outlines. Separates subject from background provides a three-dimensional look. Standard 3-Point Lighting: http://www.zvork.fr/vls/ Try using this simulator to play with lighting with those 3 points.Blood Grouping: Injury or surgery can lead to a blood transfusion. Transfusion reactions/Agglutination: clumping of blood cells (bad). Antigens: molecules on surface of erythrocytes. Antibodies: proteins in plasma that bind to specific antigens. Blood groups: named according to antigen (ABO). ABO Blood Groups • In the ABO blood group system, there are two types of antigens that may appear on the surface of the red blood cells, type A antigen and type B antigen. • Type A blood has type A antigens, type B blood has type B antigens, and type AB blood has both types of antigens. • Type O blood has neither A nor B antigens. • The types of antigens found on the surface of the red blood cells are genetically determined. • Antibodies against the antigens are usually present in the plasma of blood. • Plasma from type A blood contains anti-B antibodies, which act against type B antigens; plasma from type B blood contains anti-A antibodies, which act against type A antigens. • Type AB blood plasma has neither type of antibody, and type O blood plasma has both anti-A and anti-B antibodies. • In Caucasians in the United States, the distribution is type O, 47%; type A, 41%; type B, 9%; and type AB, 3%. • Among African-Americans, the distribution is type O, 46%; type A, 27%; type B, 20%; and type AB, 7%.Make a multiple choice quiz for my year 8 science students based on the science in this transcript from a video: 3°C 0:04 It can be the difference between snow and sleet 0:08 Wearing a jacket or not 0:11 In your day-to-day life, it may not seem significant 0:15 But 3°C of global warming would be catastrophic 0:20 Heatwaves, droughts, extreme precipitation, even fire 0:25 3°C of warming is really disastrous 0:28 The scary thing is, the world is well on its way there 0:32 Since the industrial revolution, the Earth has warmed between 1.1°C and 1.3°C 0:40 This is a problem that babies you pass in the street will have to live with 0:46 Children born today... 0:47 ...are up to seven times more likely to face extreme weather than their grandparents 0:52 If global temperatures do rise by 3°C... 0:55 ...what would their world look like? Climate change is already having devastating effects 1:03 Rising sea levels 1:05 Desertification 1:07 Hollywood has always enjoyed imagining the end of the world 1:11 While blockbusters like this are clearly fiction... 1:14 ...this film will show the scenario we all face... 1:17 ...unless more drastic measures are taken to stop burning fossil fuels 1:30 In some parts of the world the effects of inaction are already clear 1:35 The slums of Bangladesh’s capital are filling up with climate migrants 1:41 Minara comes from Bhola District, an area in southern Bangladesh 1:46 There, like many other parts of the country... 1:49 ...rivers swollen by heavier rain and melting Himalayan glaciers... 1:53 ...are washing away people’s homes 1:56 Many, like her, have lost everything 2:00 Our home in Bhola had endless amounts of land 2:03 There was lots of space for farming, we had a spacious house 2:08 There were different types of fruits, vegetation and trees growing at home 2:12 We used to eat the fruit from our own trees 2:18 I can’t eat them now because they don't exist anymore 2:21 Since the river flooded for the third time, I had to flee to Dhaka 2:26 Life was much better back home 2:29 It was unbearable to live through, truly intolerable 2:33 We didn’t have the time to save anything at all 2:38 1.1°C to 1.3°C of global warming has already transformed Minara’s life 2:45 It’s one of the reasons why so many migrants like her... 2:47 ...are moving to the city each year... 2:50 ...nearly 400,000 according to the last estimate 2:53 And climate models show there could be much worse to come How climate modelling works 3:02 Climate scientist Joeri Rogelj... 3:04 ...has spent the last ten years modelling future climate scenarios... 3:08 ...for the United Nations 3:10 The models we use to carry out this exercise... 3:13 ...really represent the state of the art... 3:15 ...of our current knowledge of climate change and where we are heading 3:19 Joeri’s projections use data collected by hundreds of scientists around the world 3:26 Here this is the 3°C level... 3:28 ...and so there is at least a one-in-four chance that under current policies... 3:32 ...we would hit 3°C by the end of the century 3:36 This is just one of the scenarios Joeri looks at 3:40 Another one imagines that all policy promises are kept 3:44 The most optimistic assumes that all promises have been kept... 3:47 ...and net-zero targets are met 3:50 Where our best estimate ends up around 2°C at the end of the century... 3:54 ...there is still a one-in-20 chance that we end up with 3°C instead 3:59 One would not be entering a plane if there is a one-in-20 chance... 4:03 ...that the plane will crash Nowhere is safe from global warming 4:07 A rise of 3°C would affect everyone 4:10 Even wealthy cities in rich countries wouldn’t be immune to the consequences 4:15 European capitals like Paris and Berlin... 4:18 ...would bake under more extreme heatwaves 4:22 Frequent storm-surges in New York could turn parts of the city desolate 4:27 In many ways, cities magnify, intensify climate events 4:33 Cities are hotter than the places around them... 4:36 ...they tend to be more vulnerable to flooding 4:39 And you can get a really bad event in a city in a way that you can’t in the countryside 4:46 And because of their denser populations... 4:49 ...disasters in a city affect far more people 4:52 Some cities might be badly prepared for the changes coming 4:56 But they have the means to adapt 4:59 Cities tend to be wealthier than surrounding places 5:03 They have a lot of amenities 5:05 A city that has taken seriously the risks of a 3°C world... 5:08 …wouldn’t necessarily be a worse place to be in a 3°C world 5:12 But a city that hasn’t prepared for these sort of eventualities... 5:16 ...that might be a really nasty place The impact of prolonged droughts 5:20 So far, many developed cities have got off lightly... 5:24 ...but some rural parts of the world are suffering disproportionately 5:29 Smallholders—small-scale farmers—are particularly vulnerable to climate change 5:35 And there are over 600 million around the world 5:38 Smallholders with farms under two hectares... 5:40 ...produce around a third of the global food supply 5:46 Central America’s “Dry Corridor”... 5:48 ...supports a mix of smallholdings and medium-sized farms 5:53 Sandwiched between the Pacific Ocean and the Caribbean Sea... 5:56 ...the area is prone to droughts 6:08 Israel Ramírez Rivera is a smallholder in Guatemala 6:12 Here, climate change is making the dry seasons longer, and more severe 6:18 This is the biggest ear of maize that this plot could deliver 6:23 He depends on his crops of corn and beans 6:26 But they’re getting harder to grow 6:30 The surrounding mountains... 6:32 ...used to provide us with native food... 6:38 ...and now that isn’t an option anymore... 6:41 ...due to climate change and its effects 6:46 Nearly two-thirds of the smallholders in the Dry Corridor now live in poverty 6:52 The impact of all of this for us... 6:59 ...malnutrition among children 7:03 We’ve lost a few 7:07 For my crops especially, the midsummer heat is harder than before 7:16 The plant dries up and can’t provide us... 7:19 ...with the necessary food provision 7:24 Severe droughts in Central America... 7:26 ...are now four times more likely than they were last century 7:30 Many families from here have gone to the States 7:37 The economic despair and debts... 7:44 ...have pushed many people from this community to do this journey 7:53 Migration from Guatemala to the United States has quadrupled since 1990 7:59 Not all of this has been due to climate change 8:02 But longer droughts would force even more to move 8:05 In a 3°C world, annual rainfall in this region... 8:09 ...could drop by up to 14% 8:12 At 3°C, over a quarter of the world’s population... 8:16 ...could endure extreme droughts for at least a month of the year 8:19 Northern Africa could see droughts that last for years at a time Rising sea levels, storm surges and flooding 8:24 But for some, too much water will be the problem 8:29 10% of the world’s population lives on a coastline... 8:32 ...that’s less than 10 metres above sea level 8:35 For these coastal inhabitants, a 3°C world would spell disaster 8:40 By 2100, global sea levels could have climbed by half a metre from 2005 levels 8:46 Low-lying cities like Lagos would be especially vulnerable... 8:49 ...with up to up to a third of the population displaced 8:54 And in Fiji, rising waters are already upending lives 9:04 You can see the graveyard there, it’s all under water now... 9:08 ...due to this rising sea level and climate change 9:15 The village of Togoru in Fiji is being swallowed by the sea 9:19 Barney Dunn, the village headman, has seen over half the village disappear 9:24 Relatives’ houses have been abandoned, and family graves are now under water 9:29 We have been asked by the government to relocate... 9:32 ...but no one wants to relocate... 9:34 ...because we have our great-great-grandparents down there in the sea 9:39 This is the place we’ve been brought up in 9:41 ...it’s not easy to leave 9:44 Past attempts to build a seawall haven’t worked 9:48 But Barney sees building a new one as the village’s only hope 9:52 If they do that, maybe we can save whatever is left 9:56 But if we don’t have the seawall, then it will be keep eroding and time will come... 10:01 ...maybe in ten,15 years, Togoru will be all eroded 10:05 Rising seas also mean storms cause more floods 10:11 And many more countries could suffer 10:14 The Philippines and Myanmar are just two countries... 10:17 ...that will also see an increase in storm surges in a 3°C world 10:21 To escape, many will move… 10:24 …often, to urban areas Extreme heat and wet-bulb temperatures 10:27 Half the world’s population already lives in cities... 10:31 ...almost a third in slums 10:36 For them, a 3°C world could be deadly 10:40 Minara has moved to Dhaka to escape the impact of climate change 10:44 But life could get even worse for her 10:47 I’m struggling a lot nowadays 10:49 The heat during the day is unbearable 10:52 Even late at night it doesn’t cool down 10:57 The heat is getting more intense every day 10:59 I mean, it’s going to get much worse 11:03 I can barely survive it now, how will I live through it in the future? 11:08 Dhaka is getting hotter 11:11 In the last 20 years the average daytime temperature... 11:13 ...has crept up by nearly half a degree 11:17 Days that approach 40°C are now being reported 11:20 And high so-called wet-bulb temperatures are on the rise 11:26 A wet-bulb temperature is a measure of heat and humidity 11:30 Humans cool themselves by sweating… 11:32 But in these conditions, when relative humidity is near 100%... 11:36 ...sweat doesn’t evaporate well 11:38 So people can’t cool down… 11:41 ...even if given unlimited shade and water 11:45 At a high wet-bulb temperature, the body can’t lose heat... 11:49 ...and so it gets hotter and hotter... 11:51 ...and the body is designed to work at a given temperature 11:53 And if it gets too hot inside, you will die 11:58 The human limit for wet-bulb temperatures is 35°C... 12:02 ...around skin temperature 12:04 Dhaka will have a much higher chance... 12:05 ...of reaching dangerous wet-bulb temperatures... 12:07 ...if global warming reaches 3°C 12:12 You can’t really adapt to that 12:14 You have to get out. If the temperature is so high that you can’t work... 12:20 ...can’t do hard manual labour outside for significant parts of the year... 12:25 ...then many places will become functionally no longer part of the economy 12:33 Jacobabad in Pakistan, and Ras al Khaimah, in the United Arab Emirates... 12:37 ...have already recorded deadly wet-bulb temperatures 12:40 More of the tropics and the Persian Gulf... 12:43 ...as well as parts of Mexico and the south-eastern United States... 12:47 ...could all get to this threshold by the end of the century 12:50 Climate modelling might show us the weather Increased migration and conflict 12:52 But it doesn’t show us its other effects on society 12:56 Established migration patterns could change 12:59 Climate disasters may exacerbate reasons people cross borders 13:03 Within countries, more people will move to cities 13:07 In a 3°C world, tens of millions of people a year... 13:10 ...could be displaced by disasters made worse by climate change 13:15 When people are displaced by climate... 13:18 …they may well go to cities... 13:19 ...because cities are the places that attract people from the countryside already 13:25 A lot of people who can get to the developed world... 13:28 ...not least because the developed world tends to be less hot, will give that a go 13:35 As migration around the world increases... 13:38 ...there could be more competition for fewer resources 13:42 Water—already a highly contested resource—will be a focal point 13:47 Turkey’s new Ilisu dam has reduced the flow of water into Iraq 13:53 China lays claim to rivers vital to India and Pakistan 13:57 The prospect of a water-conflict makes people very uneasy 14:03 How national tensions would exacerbate those sorts of reactions... 14:08 ...in a 3°C world... 14:09 ...is the sort of thing that no one should really want to find out 14:14 I think you’d have to be incredibly sanguine... 14:16 ...not to think that the sort of climate extremes that we talk about... 14:19 ...in a 3°C world wouldn’t lead some places... 14:22 ...to the brink of societal collapse 14:25 Those lucky enough to escape unrest... Adaptation and mitigation are crucial 14:28 ...would still have to adapt to a radically different world 14:32 People can adapt to climate change in all sorts of ways, one of the most obvious ones... 14:37 ...is air conditioning 14:39 But other ways to adapt at a local or regional level... 14:42 ...I mean, one of the most obvious is diversifying agriculture 14:47 There are physical things you can do, like seawalls 14:52 The fact that people can adapt and that adaptation will reduce suffering... 14:57 ...doesn’t mean that it will eliminate suffering 15:00 Suffering is built into this whole process of heating up the planet 15:06 Adaptation will only get the world so far 15:09 The best way to deal with a 3°C world... 15:12 ...is not to go to a 3°C world 15:14 And that’s why increasing efforts on mitigation are important 15:17 It’s why working towards negative emissions... 15:20 ...that could bring down the temperature after it peaks are important 15:25 Once you get to a 3°C world, you are in real bad global trouble 15:33 The scale of change needed... 15:35 ...and the slow progress of governments so far... 15:38 ...means 3°C of warming is uncomfortably likely unless more is done 15:44 Despite existing pledges, greenhouse-gas emissions... 15:48 ...are still set to rise by 16% from 2010 levels by 2030 15:54 The need to act has never been clearer 15:57 There’s still time to reduce emissions, so that a 3°C world remains fiction... 16:02 ...rather than becoming factFigure 18-11 represents the amount of energy stored as organic material in each trophic level in an ecosystem. The pyramid shape of the diagram indicates the low percentage of energy transfer from one level to the next. On average, 10 percent of the total energy consumed in one trophic level is incor- porated into the organisms in the next. Why is the percentage of energy transfer so low? One reason is that some of the organisms in a trophic level escape being eaten. They eventually die and become food for decomposers, but the energy contained in their bodies does not pass to a higher trophic level. Even when an organism is eaten, some of the molecules in its body will be in a form that the consumer cannot break down and use. For example, a cougar cannot extract energy from the antlers, hooves, and hair of a deer. Also, the energy used by prey for cellu- lar respiration cannot be used by predators to synthesize new bio- mass. Finally, no transformation or transfer of energy is 100 percent efficient. Every time energy is transformed, such as during the reactions of metabolism, some energy is lost as heat. Limitations of Trophic Levels The low rate of energy transfer between trophic levels explains why ecosystems rarely contain more than a few trophic levels. Because only about 10 percent of the energy available at one trophic level is transferred to the next trophic level, there is not enough energy in the top trophic level to support more levels. Organisms at the lowest trophic level are usually much more abundant than organisms at the highest level. In Africa, for exam- ple, you will see about 1,000 zebras, gazelles, and other herbivores for every lion or leopard you see, and there are far more grasses and shrubs than there are herbivores. Higher trophic levels con- tain less energy, so, they can support fewer individuals.A population is a group of organisms that belong to the same species and live in a particular place at the same time. All of the bass living in a pond during a certain period of time make up a pop- ulation because they are isolated in the pond and do not interact with bass living in other ponds. The boundaries of a population may be imposed by a feature of the environment, such as a lake shore, or they can be arbitrarily chosen to simplify a study of the population. The humans shown in Figure 19-1 are part of the pop- ulation of a city. The properties of populations differ from those of individuals. An individual may be born, it may reproduce, or it may die. A population study focuses on a population as a whole—how many individuals are born, how many die, and so on. Population Size A population’s size is the number of individuals that the population contains. Size is a fundamental and important population property but can be difficult to measure directly. If a population is small and composed of immobile organisms, such as plants, its size can be determined simply by counting individuals. Often, though, individ- uals are too abundant, too widespread, or too mobile to be counted easily, and scientists must estimate the number of individuals in the population. Suppose that a scientist wants to know how many oak trees live in a 10 km2 patch of forest. Instead of searching the entire patch of forest and counting all the oak trees, the scientist could count the trees in a smaller section of the forest, such as a 1 km2 area. The scientist could then use this value to estimate the population of the larger area. SECTION 1 OBJECTIVES ● Describe the main properties that scientists measure when they study populations. ● Compare the three general patterns of population dispersion. ● Identify the measurements used to describe changing populations. ● Compare the three general types of survivorship curves. VOCABULARY population population density dispersion birth rate death rate life expectancy age structure survivorship curve FIGURE 19-1 A population can be widely distributed, as Earth’s human population is, or confined to a small area, as species of fish in a lake are. Copyright © by Holt, Rinehart and Winston. All rights reserved. 382 CHAPTER 19 If the small patch contains 25 oaks, an area 10 times larger would likely contain 10 times as many oak trees. A similar kind of sampling technique might be used to estimate the size of the pop- ulation shown in Figure 19-2. To use this kind of estimate, the sci- entist must assume that the distribution of individuals in the entire population is the same as that in the sampled group. Estimates of population size are based on many such assumptions, so all esti- mates have the potential for error. Population Density Population density measures how crowded a population is. This measurement is always expressed as the number of individuals per unit of area or volume. For example, the population density of humans in the United States is about 30 people per square kilome- ter. Table 19-1 shows the population sizes and densities of humans in several countries in 2003. These estimates are calculated for the total land area. Some areas of a country may be sparsely popu- lated, while other areas are very densely populated. Dispersion A third population property is dispersion (di-SPUHR-zhuhn). Dispersion is the spatial distribution of individuals within the popu- lation. In a clumped distribution, individuals are clustered together. In a uniform distribution, individuals are separated by a fairly con- sistent distance. In a random distribution, each individual’s location is independent of the locations of other individuals in the popula- tion. Figure 19-3 illustrates the three possible patterns of dispersion. Clumped distributions often occur when resources such as food or living space are clumped. Clumped distributions may also occur because of a species’ social behavior, such as when animals gather into herds or flocks. Uniform distributions may result from social behavior in which individuals within the same habitat stay as far away from each other as possible. For example, a bird may locate its nest so as to maximize the distance from the nests of other birds. These migrating wildebeests in East Africa are too numerous and mobile to be counted. Scientists must use sampling methods at several locations to monitor changes in the population size of the animals. FIGURE 19-2 TABLE 19-1 Population Size and Density of Some Countries Population size Population density Country (in millions) (in individuals/km2) China 1,289 135 India 1,069 325 United States 292 30 Russia 146 8 Japan 128 337 Mexico 105 54 Kenya 32 54 Australia 20 3 dispersion from the Latin dis-, meaning “out,” and spargere, meaning “to scatter” Word Roots and Origins Copyright © by Holt, Rinehart and Winston. All rights reserved. POPULATIONS 383 The social interactions of birds called gannets, which are shown in Figure 19-3b, result in a uniform distribution. Each gannet chooses a small nesting area on the coast and defends it from other gannets. In this way, each gannet tries to maximize its distance from all of its neighbors, which causes a uniform distribution of individuals. Few populations are truly randomly dispersed. Rather, they show degrees of clumping or uniformity. The dispersion pattern of a population sometimes depends on the scale at which the popu- lation is observed. The gannets shown in Figure 19-3b are uni- formly distributed on a scale of a few meters. However, if the entire island on which the gannets live is observed, the distribution appears clumped because the birds live only near the shore. POPULATION DYNAMICS All populations are dynamic—they change in size and composition over time. To understand these changes, scientists must know more than the population’s size, density, and dispersion. One important measure is the birth rate, the number of births occur- ring in a period of time. In the United States, for example, there are about 4 million births per year. A second important measure is the death rate, or mortality rate, which is the number of deaths in a