A1.1 05. A, E, O | Quizalize

Riferimenti normativi per il settore residenziale: Art 81: Accesso alla rete viaria—>> il cancello deve essere arretrato di almeno 4,5m dal filo esterno del marciapiede Art 82: Passo carrabile—>> larghezza non inferiore a 4,5m e non superiore a 6,5m Art 83:Pendenza Rampa —>> max 16% Art 97: Superficie minima degli ambienti - cucina —>> min 5mq - studio—>> min 7mq - soggiorno—>> min 14 mq - soggiorno spazi di cottura—>> 17 -camera (1posto letto)—>> 8mq - camera (2posti letto)—>> 12mq Superficie alloggio totale —>> non inferiore a 28 mq Art 95: Altezze minime- cucina, soggiorno, camera e studio—>> min 2,70m -locali accessori—>> min 2,40 m (bagno, lavanderie) - locali di servizio—>> min 2,10m (disimpegni, riposti.) - soppalchi—>> min 2,10m - parapetti—>> non inf. a 1,1m (10 cm cordolo) (92) Art 86: Distanze - negli edifici di nuova costruzione la distanza degli edifici dal confine con proprietà di terzi — nei NAF—>> non inf. a 3 m — altri ambiti —>> non inf. a 5m Art 89: Scale (R.E. ) —alzate—>> max 12 consecutive — a chiocciola—>> consentite solo all’interno di un’unità abit. — illuminazione—>> se collegano più di due piani devono . essere areati con lucernario. Dim: 0,3 mq . per ogni piano servito (R.I.: 0,4 mq x piano) — areazione —>> non ci può essere areazione verso i vani scala . ( Lo dice anche il regolamento d’igiene ) (R.I) —>> superficie non inferiore a 1mq per piano servi. — larghezza (R.I.) —>> deve garantire la possibilità di soccorso e . trasporto di persone Art 88: Locali sotterranei —>> non possono MAI essere adibiti ad abitazione Locali seminterrati—>> possono ma devono rispettare determinati . requisiti - l’altezza media deve essere > di 2,7m Art 91: Copertura—>> istallazione di apparati tecnici non deve essere visibile . dalle pubbliche vie Art 98: Bagni —>> ambiente contenente il vaso deve essere disimpegnato . dalla cucina (R.I: disimpegnato dai locali abitabili, esclusione Secondo bagno se è a servizio esclusivo di una camera) (R.I)—>> deve essere dotato di vaso, lavabo, bidet doccia o vasca —>> il lavabo può essere ubicato nell’antibagno Art 100: Areazione —>> riscontro d’aria deve essere garantito su aperture . perpendicolari o contrapposte.(non inf. a 1\10) —>> appartamenti inf. a 60mq possono essere . monoaffaccio ( ma non esposti a nord) Art 125: Raccolta rifiuti (R.E)—>> non meno di 0,18mq per ogni abitante . virtuale —>> non meno di 5 mq —>> altezza minima 2,4m (R.I: 2 m) —>> deve avere un punto di allacciamento d’acqua Regolamento d’igiene —>> dimensione tale da poter contenere 4,5l Di rifiuti per abitante.( in ogni caso > di 2mq) —>> scarichi sifonati dall’acqua di lavaggio —>> accorgimenti che assicurino un’adeguata Difesa antimurina e antinsetti Norma UNI 10750: superficie commerciale (ciò che compriamo) , cioè la somma delle superfici coperte—>> 100% delle superfici calpestatili —>>100% delle superfici su cui poggiano . Le pareti divisorie interne non portanti —>> 50% delle pareti portanti interne perimetrali —>> 25% delle aree non abitabili Superfici scoperte—>> 25% dei balconi e delle terrazze scoperte —>> 35% dei balconi e dei terrazzi coperti (3 lati) —>> 35% dei pati e dei porticati —>> 60% delle verande —>> 15% dei giardini di appartamento —>> 10% dei giardini di ville e villini (Se un muro è al confine con un altro appartamento lo considero dalla mezzeria, se confina con uno spazio comune idem, lo considero tutto invece se da sull’esterno ) Regolamento d’igiene (su esso prevale il Re) : norme che discipilinano degli aspetti della vita quotidiana al fine di tutelare la salute dei fruitori Si occupa di : Rumori , odori , fumi, vapori. Scarichi nel sottosuolo Pulizia e decoro Malattie infettive Igenicità degli ambienti Pareti trasparenti (tenendo conto di telai e infissi)—>> deve avere un area pari a 1\8 (nazionale), 1\10 (Milano ) della superficie di pavimento Profondità di pavimento—>> non deve superare i 2,5m dalla finestra Bagno cieco solo se la superficie lorda di pavimento è inferiore ai 70mq e se è presente una sola camera da letto , oppure se è un secondo bagno (altrimenti finestra > 0,5 apribile). Superficie illuminante—>> superficie totale dell’apertura meno - superficie finale non utile (C): 60 cm - superficie superiore non utile (A) A= va considerato per intero se non ci sono aggetti o se questi sono inferiori a 150 cm. Al contrario ne considero solo un terzo. Es: con aggetto, b+ 1\3a . Se il rapporto illuminante è rispettato la profondità del locale non può essere più di 2,5 volte l’altezza del voltino . Se non è rispettato (inferiore a 1\8) allora deve essere 3,5 volte Alloggi devono essere dotati— per 1\2 perone—>> 1 spazio cottura,1 servizio igienico , 1 ripostiglio — per 3\4 persone—>> 1 cucina indipendente, 1 servizio igienico , 1 ripostiglio — per 4\5 persone —>> 1 cucina indipendente, 2 servizi igienici, 1 ripostiglio (per il secondo servizio è richiesta una superficie minima di 2mq e un lato minimo di 1,2m) Dotazione dei servizi: Cucina—>> pavimenti e pareti con superficie Di materiale impermeabile, liscio, lavabile,resist. —>> soffitto materiale traspirante —>> cappa collegata a ogni punto di cottura (Vedi bagno su) Prevenzione incendi : definisce —dimensionamenti—accessi all’area (locali di intrattenimento e di pubblico Spettacolo —>> larghezza 3,5 —>> h libera 4m —>> raggio di svolta 13m —>> pendenza non sup al 10% —>> resist al carico almeno 20t —profondità locali —>> i locali al chiuso non possono Essere ubicati oltre il secondo piano Interrato (non oltre i 10m) . Questi se Sono tra i 7,5 e i 10 m devono essere Protetti da un’impianto sprinkler e Essere dotati di uscite sicure. — carichi d’incendio — comunicazione (locali di intrattenimento e di pubb. Spettacolo —>> locali possono comunicare con altre Attività purché dotate di filtri a prova di Fumo e di porte REI (ameno 30) (queste Non vanno cont nel comp. delle vie d’uscit) — compartimentazioni — autorimesse — comportamento al fuoco

Art 125: Raccolta rifiuti (R.E)—>> non meno di 0,18mq per ogni abitante . virtuale —>> non meno di 5 mq —>> altezza minima 2,4m (R.I: 2 m) —>> deve avere un punto di allacciamento d’acqua Regolamento d’igiene —>> dimensione tale da poter contenere 4,5l Di rifiuti per abitante.( in ogni caso > di 2mq) —>> scarichi sifonati dall’acqua di lavaggio —>> accorgimenti che assicurino un’adeguata Difesa antimurina e antinsetti Norma UNI 10750: superficie commerciale (ciò che compriamo) , cioè la somma delle superfici coperte—>> 100% delle superfici calpestatili —>>100% delle superfici su cui poggiano . Le pareti divisorie interne non portanti —>> 50% delle pareti portanti interne perimetrali —>> 25% delle aree non abitabili Superfici scoperte—>> 25% dei balconi e delle terrazze scoperte —>> 35% dei balconi e dei terrazzi coperti (3 lati) —>> 35% dei pati e dei porticati —>> 60% delle verande —>> 15% dei giardini di appartamento —>> 10% dei giardini di ville e villini (Se un muro è al confine con un altro appartamento lo considero dalla mezzeria, se confina con uno spazio comune idem, lo considero tutto invece se da sull’esterno ) Regolamento d’igiene (su esso prevale il Re) : norme che discipilinano degli aspetti della vita quotidiana al fine di tutelare la salute dei fruitori Si occupa di : Rumori , odori , fumi, vapori. Scarichi nel sottosuolo Pulizia e decoro Malattie infettive Igenicità degli ambienti Pareti trasparenti (tenendo conto di telai e infissi)—>> deve avere un area pari a 1\8 (nazionale), 1\10 (Milano ) della superficie di pavimento Profondità di pavimento—>> non deve superare i 2,5m dalla finestra Bagno cieco solo se la superficie lorda di pavimento è inferiore ai 70mq e se è presente una sola camera da letto , oppure se è un secondo bagno (altrimenti finestra > 0,5 apribile). Superficie illuminante—>> superficie totale dell’apertura meno - superficie finale non utile (C): 60 cm - superficie superiore non utile (A) A= va considerato per intero se non ci sono aggetti o se questi sono inferiori a 150 cm. Al contrario ne considero solo un terzo. Es: con aggetto, b+ 1\3a . Se il rapporto illuminante è rispettato la profondità del locale non può essere più di 2,5 volte l’altezza del voltino . Se non è rispettato (inferiore a 1\8) allora deve essere 3,5 volte

Of the 7 billion people on Earth roughly 0:02 6 billion own a cell phone which is 0:05 pretty shocking given that only 4 and2 0:07 billion have access to a working toilet 0:09 so how are these popular gadgets 0:11 changing your body and brain If you're 0:13 looking down at your phone right now 0:15 your spine angle is equivalent to that 0:17 of an 8-year-old child sitting on your 0:19 neck which is fairly significant 0:21 considering people spend an average of 0:23 4.7 hours a day looking at their phone 0:26 this combined with the length of time 0:28 spent in front of computers has led to 0:30 an increase in the prevalence of myopia 0:32 or nearsightedness in North America in 0:34 the 1970s about one quar of the 0:36 population had myopia where today nearly 0:39 half do and in some parts of Asia 80 to 0:41 90% of the population is now nearsighted 0:44 and it can be hard to put your phone 0:46 down take for example the game Candy 0:48 Crush as you play the game you achieve 0:50 small goals causing your brain to be 0:52 rewarded with little bursts of dopamine 0:54 and eventually you're rewarded in the 0:56 game with new content this novelty also 0:58 gives little bursts of dopamine and 1:00 together create what is known as a 1:01 compulsion Loop which just happens to be 1:04 the same Loop responsible for the 1:05 behaviors associated with nicotine or 1:07 cocaine our brains are hardwired to make 1:10 us novelty seeking and this is why apps 1:12 on our phones are designed to constantly 1:14 provide us with new content making them 1:16 hard to put down as a result 93% of 1:19 young people aged 18 to 29 report using 1:21 their smartphone as a tool to avoid 1:23 boredom as opposed to other activities 1:26 like reading a book or engaging with 1:27 people around them this has created a 1:29 new term nomophobia the fear or anxiety 1:32 of being without your phone we also see 1:35 a change in brain patterns Alpha rhythms 1:37 are commonly associated with wakeful 1:39 relaxation like when your mind wanders 1:41 off whereas gamma waves are associated 1:44 with conscious attentiveness and 1:46 experiments have shown that when a cell 1:47 phone is transmitting say during a phone 1:49 call the power of these Alpha Waves is 1:52 significantly boosted meaning phone 1:54 Transmissions can literally change the 1:56 way your brain functions your smartphone 1:58 can also disrupt your sleep the screen 2:00 emits a blue light which has been shown 2:02 to alter our circadian rhythms 2:03 diminishing the time spent in deep Sleep 2:06 which is linked to the development of 2:07 diabetes cancer and obesity Studies have 2:10 shown that people who read on their 2:11 smartphone at night have a harder time 2:13 falling asleep and produce less 2:15 melatonin a hormone responsible for the 2:17 regulation of sleep wake Cycles Harvard 2:20 medical school advises the last 2 to 3 2:22 hours before bed be technology free so 2:24 pick up a book before bed instead of 2:26 course smartphones also completely 2:28 change our ability to access information 2:30 most notably in poor and minority 2:32 populations 7% of Americans are entirely 2:35 dependent on smartphones for their 2:37 access to the internet a 2014 study 2:40 found that the majority of smartphone 2:41 owners use their phone for online 2:43 banking to look up medical information 2:45 and searching for jobs so while phones 2:47 are in no way exclusively bad and have 2:50 been part of a positive change in the 2:51 world there's no denying that they are 2:53 changing us but many successful people 2:56 have now decided to take smartphone 2:58 vacations in order to increase 3:00 productivity in our new ASAP thought 3:01 video we break down the top six reasons 3:04 you should take a smartphone vacation 3:06 and how it could benefit your life right 3:08 now and subscribe for more weekly 3:09 science videos

In this video we take a look at the 0:02 fetch to code 0:03 execute cycle including its effect on 0:06 the various registers we've previously 0:12 [Music] 0:14 discussed a computer is defined Definition 0:17 as an electronic device that takes an 0:20 input 0:22 processes data 0:25 and delivers output 0:29 in this simple example you can see we're 0:31 taking the input 5 0:35 we're multiplying it by 2 that's our 0:37 process 0:39 and we're outputting 10. 0:44 but this could be way more complex for 0:46 example of a game console 0:48 the input could be the buttons you press 0:50 on a controller 0:53 the processes would then be carried out 0:55 by the console itself 0:59 and the output would be some form of 1:01 update to a monitor 1:02 and sound out for a speaker possibly 1:04 vibration feedback through the 1:06 controller 1:10 to process data a computer follows a set 1:13 of instructions 1:14 known as a computer program 1:18 if we take the lid off a typical desktop 1:20 computer we can identify 1:22 two critical components the memory 1:26 that stores the program and the central 1:29 processing unit or processor 1:31 which is under this large fan and 1:33 carries out the instructions 1:37 a computer carries out its function by 1:40 fetching 1:41 instructions decoding them and then 1:43 executing them 1:44 in a continuous repetitive cycle 1:46 billions of times a second 1:48 let's look at each of these stages in a 1:50 little more detail Fetch 1:53 so let's start with the fetch stage the 1:55 very first thing that happens 1:57 is the program counter is checked as it 2:00 holds the address 2:01 of the next instruction to be executed 2:07 the address stored is then copied into 2:09 the memory address register 2:14 the address is then sent along the 2:16 address bus to main memory 2:18 where it waits to receive a signal from 2:21 the control 2:22 bus so it knows what to do 2:27 as we want to read the data that's 2:29 stored in memory address 2:30 0 0 0 0 the control unit sends 2:34 a read signal along the control bus to 2:36 main memory 2:41 now main memory knows the data needs to 2:44 be read 2:45 the content stored in memory address 000 2:49 can be sent along the data bus to the 2:51 memory data register 2:56 now as we're currently in the process of 2:58 fetching an instruction 3:00 the data received by the memory data 3:03 register gets copied 3:04 into the current instruction register 3:11 the instruction effectively has now been 3:14 fetched from memory 3:16 just before we proceed to the decode 3:18 phase we now 3:19 increment the program counter so that 3:22 the address it contains 3:24 points to the address of the next 3:26 instruction which will need to be 3:30 executed 3:32 the instruction now being held in the 3:33 current instruction register 3:35 is ready to be decoded 3:39 now as we mentioned in the previous 3:41 video the instruction is made up of two 3:43 parts 3:44 we have the op code that's what it is we 3:47 need to do 3:50 and we have the operand what are we 3:53 going to do it to 3:55 now the operand could contain the actual 3:57 data 3:58 or indeed it could contain an address of 4:01 where the data is to be found 4:06 by decoding this instruction we can see 4:08 the operation we need 4:10 is a load operation so we need to load 4:14 the contents of memory location0101 4:18 into the cpus accumulator 4:25 in the exam a simple model will be used 4:27 to describe the 4:29 structure of any given instruction 4:32 you're not going to be expected to 4:34 define how an opcode is made up 4:36 but simply to interpret opcodes in the 4:39 given context of an exam 4:40 question in the example here 4:44 you can see there's a total of 16 4:46 different opcodes available 4:48 and this is because we're using four 4:50 bits for our representation 4:56 so now we've fetched the instruction and 4:59 we've decoded it so we know what we need 5:00 to do 5:01 we're finally ready to execute it 5:05 so we now send address 0101 5:08 to the memory dress register 5:13 now we're in the memory address register 5:15 we can finally send the address 5:18 down the address bus to main memory 5:24 this time we want to read the data 5:26 that's stored in memory 5:28 and so the control unit again sends a 5:30 read signal along the control bus 5:36 so main memories now receive an address 5:38 and a read signal 5:40 so the content stored at memory location 5:43 0101 5:44 can now be sent along the data bus back 5:46 to the cpu 5:47 and into the memory data register 5:54 finally the contents of the memory data 5:56 register are copied to the accumulator 5:59 and this is one of a number of general 6:00 purpose registers found in the cpu 6:04 this first instruction is now complete Branching 6:11 so what does this program actually do 6:14 you should be able to work it through 6:16 carefully and figure it out 6:19 we're now pointing instructions zero 6:21 zero zero one in the program counter 6:23 and we're ready to fetch the second 6:25 instruction 6:27 at the end of this video we're gonna 6:29 provide you with the answer 6:34 so let's talk a second about programs 6:37 that branch 6:40 on the left here we have a very simple 6:42 piece of pseudo code 6:44 line zero says first execute this line 6:46 of code 6:47 line 1 now execute this line and then 6:50 line 2 says 6:52 if the age is greater than 18 then 6:56 we're going to execute lines 3 and 4 6:58 otherwise 6:59 we're going to execute lines six and 7:02 seven 7:03 so this program doesn't necessarily 7:05 follow strictly in sequence from line 7:07 zero through to seven there's a chance 7:10 here the program may branch and jump 7:14 around 7:16 so we're going to pretend that this 7:17 program has been loaded into memory 7:20 each line of code on the left here has 7:23 ended up 7:24 as a location in memory now this is not 7:27 strictly how this would happen in this 7:28 one-to-one way 7:29 but for the purpose of example it's 7:31 absolutely fine 7:35 so the program counter starts by 7:37 pointing to memory address zero 7:39 and we fetch the first instruction 7:41 decode it and execute it 7:44 it then updates and tells us the next 7:47 instruction 7:48 is zero zero zero one because remember 7:50 the program counter is being incremented 7:52 so we fetch it decode it and we execute 7:55 line one of our program 7:59 we then fetch line two which in binary 8:01 is one 8:02 zero 8:06 now at this point depending on what 8:10 happens during the execution 8:11 of line two the program may be required 8:15 to fetch line three from memory or 8:18 line five from memory 8:25 so let's look at how this actually works 8:27 because we've said the program counter 8:28 simply gets incremented 8:31 well in the current instruction register 8:33 we have an instruction with the op code 8:36 0 1 1 0. 8:41 now when we look this up in the decode 8:43 unit we discover that this 8:45 code means branch always 8:51 this replaces the value held in the 8:54 program counter 8:56 with the contents of the operand that's 8:58 the second part of the instruction 9:01 from the current instruction register so 9:03 this case 9:04 one zero zero one 9:09 now when the next fetch cycle begins the 9:12 program counter is obviously checked 9:14 and as its contents have been previously 9:16 updated to a new memory location 9:19 and not simply incremented the program 9:22 effectively is able to jump 9:24 around memory 9:28 so having watched this video you should 9:30 be able to answer the following key 9:32 question 9:33 how does a cpu work 9:39 okay so let's um answer the question we 9:41 posed 9:42 earlier what did that program actually 9:48 do 9:50 so this is the first fetch to code 9:53 execute cycle 9:55 and this is the one that we ran through 9:57 in detail earlier 9:58 it effectively loaded the contents of 10:01 the memory 10:02 stored at location location0101 10:05 into the accumulator in other words 10:08 the dna number 3 is moved 10:11 from memory into the cpu 10:18 we then proceed onto the second fetch 10:20 decode execute cycle 10:23 now this one adds the contents of memory 10:27 located at 0 1 1 0 10:30 to the current contents of the 10:32 accumulator 10:34 so in other words the dna number one 10:38 because that's what's stored at address 10:40 zero one one zero 10:43 is added to the number three that was in 10:45 the accumulator 10:46 the results are stored back over the 10:48 accumulator 10:49 so effectively we've done three plus one 10:53 equals four 10:58 the third fetch to code execute cycle 11:00 stores the contents which are in the 11:02 accumulator 11:03 into memory location zero one one one 11:07 and that's because the op code the first 11:09 part of this current instruction 11:10 zero zero one one is the command to 11:13 store when we look it up in the decoder 11:15 unit 11:16 so in other words the result of the 11:17 previous calculation three plus one 11:19 equals four 11:20 is now written back into main memory 11:28 the fourth fetch decode execute cycle 11:30 outputs the contents of the accumulator 11:33 remember they were copied into main 11:34 memory but they're still held in the 11:35 accumulator 11:37 so in this simple abstraction the number 11:40 four is now 11:41 output to the user so they can see the 11:43 result of the calculation 11:49 the fifth and final fetch code execute 11:51 cycle 11:52 brings a halt to the current program 11:58 so this very simple program which has 12:01 five 12:02 fetch decode execute cycles has 12:04 performed the calculation 12:06 three plus one is then stored the result 12:09 in main memory 12:10 and displayed the result four to the 12:12 user 12:13 and in a high-level language this may 12:15 look something very similar to the 12:17 following two lines of code 12:20 sum variable equals num1 plus num2 12:24 print sum to the user 12:27 so you can start to get an appreciation 12:29 here of how the high level code you 12:32 write actually ends up being fetched 12:34 decoded 12:35 and executed inside a processor 12:38 of course your processor is doing 12:40 billions and billions of these 12:42 operations a second 12:43 which when you think about it is really 12:45 very impressive 12:52 [Music] 13:03 you. make 10 questions for a standerd of a level

Figure 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

A1 (1)

A1.1 scegli il verbo

Related quizzes

Related quizzes