UNIT 3 POPULATIONS PDF

UNIT 3 POPULATIONS Population: a group of individuals of the same species who live in the same area 1  Populations change over time in reaction to a variety of factors Species that can live in many Specialist...

UNIT 3 POPULATIONS Population: a group of individuals of the same species who live in the same area 1  Populations change over time in reaction to a variety of factors Species that can live in many Specialist species different types of environments, and tend to be advantaged have a varied diet are considered generalists. Raccoons in habitats that remain are the classic example of a constant more than generalist species. Their range extends throughout North and Generalist species. As Central America. They a result, many specialist are omnivores that can thrive on many different foods, Common foods species are include fruits, plants, nuts, berries, insects, rodents, frogs, eggs, and crayfish. including human becoming threatened, garbage. It is this ability to be endangered, successful in a variety of different and extinct. environments that has enabled the raccoon to maintain large 2 population sizes  Life Strategies (r versus K) At the other end of the In an unstable, changing spectrum are populations environment, it can be a that live close to the survival advantage to expend carrying capacity (K) of energy to reproduce rapidly their habitats. Species that while conditions are are larger, take a long favorable. Species that are time to mature, live a small, easily dispersed, long time in stable reproduce quickly, at an environments and have early age and produce relatively few offspring large numbers of offspring which are then cared for and have short lifespans by parents are K are r strategists. Most r strategists. Most k strategists are generalists. strategists are specialists. 3 4 5  Explain why invasive species, such as the spongy moths shown here are categorized as r-selected. K-selected species are typically more adversely affected by invasive species than r-selected species, which are minimally affected by invasive species. Most invasive species themselves are Spongy moth caterpillars feed on more than 300 species of deciduous and evergreen trees including apple, oak, maple r-selected species. and aspen. Adult spongy moths do not feed. The entire life cycle of the spongy moth lasts about 4 months. The adults live for about 2 weeks, for the sole purpose of reproducing. A female lays only 1 egg mass in her lifetime. Each egg mass contains 600-700 eggs. 6 Many species, like sea turtles, have reproductive strategies that not uniquely r-selected or K-selected or they change in different conditions at different times. Identify which characteristics turtles share with the r strategists and which make them more like the k strategists. 7  A survivorship curve displays relative survival rates of individuals in a population Survivorship curves differ for K selected and r selected species Type I have a high survival rate through most of their life (typical of K-strategists) Type II have relatively constant death throughout their life Type III have high death rate at the beginning of their life (typical of r strategists) 8  Measuring populations An ecologist measures the changing populations by COUNTING INDIVIDUALS (N) AT VARIOUS TIMES OR IN SAMPLE AREAS Similar to a census 9 The rate of population growth The change in the number of individuals (∆N) in a population over a specific time frame (∆t), such as annually, is known as the growth rate (gr): 10 4 processes change the size of a population 1. Births (b) 2. Immigration (I) 3. Death (d) 4. Emigration (e) Change in population = [b+I] - [d+e] Growth rates may also be expressed as a percentage of the original population11 Practice problem: growth rate as a percent of original If a city of population 10,000 experiences 100 births, 40 deaths, 10 immigrants and 30 emigrants in the course of a year, what is its net annual percentage growth rate? GR= [(100 + 10) - (40 + 30)]/10,000 x 100 = 0.4% 12  Practice problem 2: percentage growth rate The western snowy plover is a small bird that makes its nest in In an initial population the sand on ocean and river of 100 snowy plovers, shores. The snowy plover’s breeding season is from March to there were 30 births September. A plover typically lays and 20 deaths with no three eggs each year. If disturbed, it will often abandon its nest. A immigration or snowy plover and its nest are emigration. Calculate shown below. the percentage growth rate of the plover population. 13 Practice problem: crude growth rate (growth per thousand) In 2019 the birth rate of China was a) 0.38% 11.9 per thousand. b) 0.49% The death rate was c) 0.60% 8.1 per thousand. d) 0.68% What is the growth rate for China in 2019? 14  Percent change in population Use the equation to determine the change North America’s in population as a snowy goose percent population exploded [(final-initial)/initial] x from 2 million in the 100 1970s to about 15 million in 2015 due to an increased food supply. Calculate the percent increase in snowy geese. 15  Practice Problem: percent change in population Which of the following calculation a) (17.6-11.9) x 100 methods would b) (11.9-17.6)/17.6 X correctly determine 100 the percent c) (17.6 + 11.9)/17.6 change in the d) 11.9/17.6 x 100 crude birth rate of a country? 16 Calculate the percent change in crude birth rates for all races and origins in the US between 201917and 2020  The number of individuals in a definite area (A) or volume (V) is known as POPULATION DENSITY Dp = N/A or N/V When it is not practical to count every individual, several large sample areas are used to estimate the actual population size. For example, if among sheep the average density is 1.2 sheep/m2 then there are 200 sq m that means that 240 sheep are in the area 18  PRACTICE Problem: Population Density Suppose that a 200mL sample of stagnant water contains 54 mosquito larvae. Calculate the population density of the sample. Round your answer to the nearest hundredth. This information can be used to estimate the size of a mosquito population in an aquatic community at a given time. Since mosquitoes carry infectious diseases, large numbers pose a 19 health risk.  Population distribution patterns are based on resource availability When resources such as water and food are scarce, populations tend to clump around them. When resources needed for growth are abundant, populations tend to spread out randomly 20  FLUCTUATIONS IN POPULATION GROWTH 1. When an organism is placed in a new habitat that is favorable, the population size will INCREASE slowly at first (lag phase) because there are so few individuals in the population to mate 2. As reproduction continues the number of individuals will MULTIPLY RAPIDLY (exponential phase) because more of them are giving birth at any given time and 21 competition is low Biotic Potential, r Biotic potential is the maximum reproductive rate for a population in ideal conditions. The higher the biotic potential, the faster the growth rate. It is exponential This is the intrinsic rate of growth that is possible given unlimited resources and ideal living conditions (no competition needed). 22  Growth is never exponential indefinitely Competition for resources and other limiting factors will slow the rate of growth. Most populations show logistic (S shape) growth. The initial J shape is followed by a levelling off of the curve over time. The levelling off is the habitat’s carrying capacity (K), the max population size the environment can sustain 23  GROWTH WITH RESTRICTIONS The rate of population increase will eventually either level off or bust since ideal conditions of food, water, oxygen, space and so on, cannot be maintained forever. The leveling off is the CARRYING CAPACITY (K) of the area and represents the maximum number of individuals the area can support 24  For example, if the birth rate of trout in a certain lake were higher than the death rate, the population will increase (the overshoot) This increases competition for food, oxygen, space and so on Many trout may then die of starvation or disease and parasites spread more rapidly between them The death (dieback) of some trout would bring the population density back down towards carrying capacity 25  REACHING CARRYING CAPACITY The carrying capacity is shown at the top of the population growth curve. It creates an S shaped curve when best-fitted, as it appears here in blue 26  DENSITY DEPENDENT FACTORS Any factor whose effect increases when the population size increases is a density dependent limiting factor Factors such as starvation (competition for food), parasitism, disease transmission and predation increase as the population gets larger. More organisms die only when the size of the population increases. Density 27 dependent factors do not affect small populations  BOOM THEN BUST For r strategists, once the population density reaches its peak, the individuals begin to die very rapidly This causes a huge crash in the population density (BUST) 28  Factors that limit a habitat’s carrying capacity can be either density-dependent or density-independent 29  Per capita rates Example: The US GDP in To compare populations 2022 was $25.463 that are different sizes the trillion US , the largest per capita rate is used of any nation, according to the World Bank. PER CAPITA is the rate of change per person However, the GDP per capita was only to calculate the per capita $76,398.60 US in 2022 rate you must divide by all when the GDP is divided the people in the population by all the people in the US. 30  How long will it take human populations to double in size? The RULE OF 70 states that dividing the number 70 by the percentage population growth rate approximates the population’s doubling time. 31  Practice questions 1. The United States has a population growth rate of 1%. In how many years will the population double if that growth rate remains constant? 2. Compare the doubling time of the US to that of Belize, which has a growth rate of about 2%? 3. Country X has a population of 50 million and an annual growth rate of 3.5%. If the growth rate remains constant, what will be the population of country X in 40 years? 60 years? 32  Answers 1. dt= 70/r 2. Dt (Brazil) = 70/2 dt= 70/1 = 35 years; dt= 70 years to much shorter than the double US time since It has a faster growth rate 3. dt=70/3.5= 20 years for country X to double in population. Starting population of 50 million will become 100 million in 20 years and 200 million in 40 years. In another 20 years it will double again, so there will be 400 million people after 60 years. 33 REVIEW: types of variables in an experiment 34 HUMAN POPULATION GROWTH 1. The rate of global population increase is determined by the number of daily births and deaths. 2. The global population growth rate is about 1.05% 3. Human population has not yet reached carrying capacity. Current world population is around 8.1 billion 35  Three most populous countries in the world China: 1.4 billion people; growth rate of 0.18% *memorize India: 1.4 billion people; growth rate of 0.7% United States: 340 million people; growth rate of 0.68% Propose an explanation for the prediction that the population of India will soon surpass that 36 of China even though there are equal populations in both countries (est 2023) Earth’s human carrying capacity? The English priest/economist Thomas Malthus said too many mouths to feed but not enough food would result in famine, war(technological advances, qualities are one sided limit deaths) and disease which would limit human population growth. Human populations may be limited by space, available food and fresh water or 37 perhaps technology will Growth rate and technological advances The industrial revolution and the subsequent agricultural and medical advances led to a population boom. Vaccines, cures for diseases, increased sanitation and increased production of food lowered the death rates. Recently, people with the greatest access to technology are choosing to have fewer children, resulting in decreasing rates of population growth in developed countries. sending kids to school causes them to delay pregnancy bceuase they will be spending time gaining an education rather then starting a family Growth rates of non-industrialized 38 countries continue to increase. Africa and South American Managing Human Population growth Africa and Asian Although 80% of the countries are Earth’s population lives in less developed countries, expected to have they consume only about the greatest future 20% of the resources. The growth (China is the impact of an society exception because depends on its of its long one-child population size, affluence and use of policy, even as it is technology (IPAT) now lifted) 39  Africa’s birth rate is high One reason for the high birth rates is the need to have more children to replace those lost due to high infant mortality. Other reasons are cultural or religious or the belief that many children will work to assist the family through child labor 40  Infant mortality rates Death rates in Mother’s will have children are higher many children since in LEDC since they expect several mothers do not to die so the birth have access to rates increase even good health care as infant death and nutrition. increases in poorer countries. 41 Less Developed Countries (LDC) are the fastest growing 42 Challenges to decreasing birth rates are often cultural Africa’s Population In order to make the Surge - The New York transition to an MEDC a country has to lower its Times birth rates. This means – offering family planning (contraceptives); – educational opportunities for women (to delay childbearing), Or this video – encouraging later marriages to delay child bearing/starting a family 43  Memorize these… TFR (total fertility rate) is the number of children a woman will have in her lifetime The earlier a woman starts having children, the higher the TFR. Education of women lowers TFR since it puts off childbearing. REPLACEMENT fertility is the number of children a couple must have in order to replace themselves and keep the population stable. Replacement fertility is 2.1 due to infant mortality- not all babies born will survive If the fertility rate is at replacement levels, a population is considered 44 relatively stable  With demographic transition from LEDC to MEDC, more women want fewer children Government policies that encourage the education of women result in lower TFR and therefore lower birth rates and lower population growth Total fertility is the number of children a woman will have in her lifetime. The more time spent in school, the longer the delay of pregnancies, and 45 fewer children are born  AGE STRUCTURE DIAGRAMS population growth rates can be interpreted from the shape of the age structure diagram It shows the relative number of individuals (males and females) of each age in the population 46 47  a rapidly growing population will have a higher proportion of younger people compared to stable populations Pyramids show rapid future growth because all those kids will one day have kids of their own (high population momentum) Diagrams that are broader on top predict declining growth rates with more future deaths than births as the old 48 people die  DEMOGRAPHIC TRANSITION Results in In a stable Two possible ways for human population, birth rate equals death rate a population to (b=d) become stable: a) High birth rate= high Assuming no immigration death rate or emigration takes place b) Low birth rate= low death rate Lower br and dr take place as a country moves toward The movement toward a state of greater economic development and stability from high to low birth as it moves from a and death rates is pre-industrial to an called DEMOGRAPHIC industrial economy. TRANSITION 49 Demographic transition occurs in 4 stages. MEMORIZE THEM 50  TWO EXAMPLES GERMANY (MEDC) KENYA (LEDC) – Low Birth rates and death – High Birth rates and rates because… falling death rates – Industrialized country – Developing country – Increased quality of – Decreased use of healthcare, sanitation contraceptives – Increased education of – Lower quality of women which delays healthcare, sanitation pregnancies – Families have more – Higher availability of children as kind of “social contraceptives security” or may need – Families invest in the them to work to support education of a few the farm/family children rather than have many 51  Demographic transition in age structure pyramids Stage 1: PRE-TRANSITION-high birth rate and high death rate, high infant mortality Stage 2: TRANSITION-Country becomes more economically developed, death rates fall. Life expectancy increases due to better medical care and food.The birth rate is still high. Growth rate is high Stage 3: INDUSTRIAL-More economic opportunities, birth control and education for women leads to falling birth rates. But high life expectancy causes continued population growth even as birth rates decrease. Growth is slowing Stage 4: POST-INDUSTRIAL-the birth rate and death rates are low; population continues to have an older mean age. Eventually reaches zero population growth (ZPG) or may begin to see negative growth rates 52 Practice questions 53 Urbanization (the redistribution of people from rural to urban areas) occurs as countries industrialize 54  China’s One Child policy In the late 1970s, China So even with two children experienced population per couple, the numbers were beyond what could be momentum, meaning managed. In 1979, China that there was already a instituted a mandatory large population, most of policy that there could which was under age 30. only be 1 child per family without loss of government High population growth benefits (such as rates deplete a country’s subsidized housing, access resources and increase to better jobs, food, pensions and schooling) problems with sanitation, and a very high fine for supply of goods, food, non-compliance energy, education etc 55  China’s one child policy- pros and cons Cons (disadvantages) Pros (advantages) – Encouraged a preference for male – Total Fertility Rates, children, perhaps encouraging TFR, in China was abortion of female fetuses. Society becomes unbalanced in the number reduced from 5.9 to of males and females 1.7 – Increased economic burden on the child to care for aging parents and grandparents (4-2-1 conundrum). China does not have an extensive pension or social security program so each child must care for 2 parents and 4 grandparents. – Smaller population will mean fewer taxpayers and workers, lowering the GDP 56 Turn and talk to a partner about the age structure of any TWO of the countries shown below 57