Bellwork  Explain the changes in both numbers and rates of growth in the following population growth curves


Exponential growth
occurs when resources are not limiting.

Logistic growth
increases.
occurs when resources become more and more limiting as population size

• Population Biology • Human Population

In terms of dispersion, individuals of a population can be clumped*, uniform, or randomly distributed.

Population size is governed by births, deaths and migration

[Population Change] = [Births + Immigration] –[Deaths + Emigration]
Population Change = (B + I) – (D + E)  If the number of individuals added by births & immigration are balanced by those lost by deaths & emigration then there is
zero population growth
;

Population growth  Populations vary in their capacity for growth, also known as
biotic potential
 The intrinsic rate of increase (r) is the rate at which a population will grow if it had unlimited resources.

Population Growth    As long as there is a plentiful supply of resources populations grow If we put some bacteria cells in a culture – the bacteria reproduce exponentially As the population grows, so too does the rate of growth

Population Growth  This is an example of positive feedback  The curve produced is sometimes called a J curve  The J-curve assumes there is no limit on resources

Population Growth  Darwin calculate that if you started with 2 elephants and exponential growth, after 700 years the world population of elephants would be 19,000,000  This obviously has not happened

Population Growth  The size of a population is limited by available resources and competition for them  This results in a maximum size that an environment can sustain  The Carrying Capacity
(K)

Population Growth  The carrying capacity is around 120 bacterial cells/mL  Negative feedback operates keeping the population around the Carrying Capacity

Population Growth  This produces an S curve (logistic growth) 
Limiting factors
resulting from an increased population provide negative feedback which reduces the growth rate  Food, water, living space, sunlight, etc

Population Growth    Lag phase : population grows slowly (environmental adaptation) Exponential or Log phase : population grows rapidly exploiting a plentiful resource supply (maximal growth) Stationary phase : population growth reaches a plateau – the maximum population size under the environmental conditions

Population Regulation  Factors that regulate population size can be categorized as DENSITY-INDEPENDENT or DENSITY-DEPENDENT  Density-Independent – effect does not vary with population density  Weather, climate, fire, volcano  Density-Dependent – effect varies with population density   infectious disease, competition, predation, waste accumulation, stress from crowding Negative feedback that leads to stability of populations

Population Regulation  Factors that regulate population size can be categorized as INTERNAL or EXTERNAL  Internal factors  – arise from within the population itself fertility rates, breeding territory size, intraspecefic competition for food, genetic disease, competition for mates  External factors population  – affect populations from outside the predation pressure, parasitism, disease, climate change, interspecific competition

Reindeer introduced to a small island off of Alaska in the early 1900s exceeded the carrying capacity, with an "overshoot" followed by a "population crash" in which the population was totally decimated by the mid–1900s.


During the mid–1800s sheep populations exceeded the carrying capacity of the island of Tasmania. This "overshoot" was followed by a "population crash". Numbers then stabilized, with oscillation about the carrying capacity.

Population cycles for the snowshoe hare & Canadian lynx are believed to result because the hares periodically deplete their food, leading to first a crash of the hare population & then a crash of the lynx population.

Population Regulation  What regulates population?

Population Regulation      Until the 1940s, the British population of Peregrine falcons had remained fairly constant—about 820 breeding pairs Limited by available nest sites (same places each year) Average brood size was about 2.5 fledged young each summer Come the next breeding season, the population was back to about 820 pairs Equilibrium

Population regulation  Mosquitoes are plentiful in the summer months  When autumn sets in, the populations crash  Boom and bust

Population Regulation     Some species are very good at taking full advantage of any opportunity Locust populations can explode They swarm in the thousands, eat everything in their path, and eventually outstrip their food supply Boom and bust

Population Regulation  The species described previously demonstrated either an equilibrium or boom and bust population growth  From this, two types of life strategies can be identified:  Equilibrium or K strategy species  Opportunist or r strategy species

Population Regulation  What are K and r?
 The two variables that define a population curve  K = carrying capacity  r = growth rate (intrinsic rate of increase)
r

         Low reproductive rate Large investment in parental care Late maturity Slow growth Large organisms Late successional species Niche specialists Require stable environment S—shaped curve  NC Zoo   Bomassa born 8/4 and Apollo born 8/31 Juma born 7/6

         High reproductive rate Low investment in parental care Early maturity Rapid growth Small organisms Pioneer species Generalists Rapidly adapt to environmental variation J—shaped curve

K and r strategists  The reality is more of a continuum  Most organisms are located between the two extremes of this continuum and many show characteristics of both strategies

Survivorship  If survivorship is plotted for different species, three generalized types of life curve form  Type 1 (late loss) – Survivorship is high, most mortality later in life span  Type 2 (constant loss)– Constant mortality throughout life span  Type 3 (early loss)– High mortality early in life, low survivorship into late life span

Family Population  Gather the following information:  Make a list of your living family members starting with your grandparents  Find out the year they were born and indicate if they are male or female  Include all of the brothers and sisters of your parents and everyone in your generation (brothers, sisters, cousins)

Bellwork  Tally your table’s totals for males and females at each age group  We will then combine the whole class data

Age Structure Diagrams  Show the proportion of the population at each age level  Three main age categories:  Prereproductive (ages 0-14)  Reproductive (15-44)  Postreproductive (45+)

Age Structure Diagrams

Edwards A1 -60 -50 -40 -30 -20 -10 96-100 91-95 86-90 81-85 76-80 71-75 66-70 61-65 56-60 51-55 46-50 41-45 36-40 31-35 26-30 21-25 16-20 11-15 6-10 1-5 0-1 0 10 20 30 40 50 Male Female

How can Age Structure Diagrams be used to make population and economic projections?  Baby-Boom Generations  Creates social and economic changes that ripple through a society for decades  Competition for jobs; political clout; retirement benefits and needs

 Rapid pop. decline can lead to severe economic and social problems  A sharp rise in proportion of elderly will lead to a large share of medical care, social security and other costly social services  Labor shortages

World Population (7 min)

Human Population History

Human Numbers Through Time  Click for interactive

 Population change = [births + immigrations] – [deaths + emigration]  Zero Population Growth (ZPG) – when births plus immigration equal deaths plus emigration  Crude Birth or Death Rate - # births or deaths /1,000 people  U.S. CBR – 13.83
 U.S. CDR – 8.38

World Population  Rate of World's Population Change (%)  (Birth Rate – Death Rate)/1000 people x 100  Average Annual population growth rate   1.2% (global) .963 (U.S.)  World Population = 7 billion (video)   China and India - 37% of world's population U.S. – 4.5% of world's population  Population Clocks

World Population

Global Fertility Rates (2 types)
1. Replacement Level Fertility
 number of children a couple must bear to replace themselves (2.1 in developed countries and 2.5 in developing countries)  greater than 2 because some female children die before reaching their reproductive years  Population Momentum – The continued growth of a population after reaching replacement level resulting from a large number of people entering their childbearing years

Global Fertility Rates (2 types)
2. Total Fertility Rate (TFR)
 most useful for projecting future population change  the average number of children a woman will have during her childbearing years  2000  World – 2.9 (1.3 developed, 3.2 developing)  U.S. – 2.1
 2011  World – 2.46
 U.S. – 2.06

Global Fertility Rates

U.S. Growth  US - highest fertility rate and highest immigration rate of any industrialized country – Why?
 1.66 million more births than deaths; 800,000 legal immigrants; 300,000 illegal immigrants ***Because of the high per capita rate of resource use in the US, each addition to the US pop. has an enormous environmental impact!!

U.S. Growth   392 million by 2050 -- more than a 50 percent increase from the 1990 population size
Reasons for Projected Growth:
1.
2.
3.
4.
5.
Large number of baby-boom women still in child-bearing years Increase in number of unmarried mothers (incl. teenagers) Continued higher fertility rates for women in some racial and ethnic groups than for Caucasian women High levels of legal and illegal immigrants (43% of US pop. growth) Inadequate family-planning services

7.
8.
9.
10.
11.
1.
2.
3.
4.
5.
6.
Average level of education and affluence Importance of children as part of the labor force Urbanization Cost of raising and educating children Educational and employment opportunities for women Infant mortality rate Average age at marriage Availability of private and public pension systems Availability of legal abortions Availability of reliable methods of birth control Religious beliefs, traditions and cultural norms

What factors affect death rates?
 Decline in the CDR (crude death rate) has led to the rapid incr. in world's pop. People started living longer!  “It's not that people stopped breeding like rabbits; it's just that they stopped dying like flies” (UN)

2 Indicators of Overall Health
1.
   
Life expectancy (the avg. number of years a newborn infant can expect to live)
75 years (developed countries) 64 years (developing countries) U.S. - 78.37 years (2011) Angola – 38.76
 What is your life expectancy ?

2 Indicators of Overall Health 2. Infant mortality rate - the number of babies out of every 1000 born each year that die within 1 year  The single most important measure of a society's quality of life –it reflects the general level of nutrition and health care

U.S. Infant Mortality Rate  2011 - 6.06 deaths/1,000 live births  These rates are high because:  inadequate health care (poor women)  drug addiction (among pregnant women)  high birth rate among teenage women  Babies born to teenage women are more likely to have low birth weights – the most important factor in infant deaths  US – highest teenage pregnancy of any industrialized country

Should we reduce births?
 Can we provide enough food, energy, water, sanitation, education, health care, and housing for twice as many people if the world pop. continues to grow?  Can we provide adequate standard of living for twice as many people without causing massive environmental damage?  Some say the Earth is already overpopulated  Others say the Earth could support 20-48 billion people if everyone existed at a minimal survival level (grain diet only, cultivate all arable land, mine the Earth's crust to a depth of 1 mile)


Demographic Transition (a hypothesis of
population change): As countries become more industrialized, first their death rates and then their birth rates decline  4 stages:

Demographic Transition
1.
Pre-industrial stage – harsh living conditions, high IMR, DR, BR - growth is small

Demographic Transition 2. Transitional stage – industrialization begins, rise in food production, improved health care, lower DR, high BR, pop. grows rapidly (2.5-3%/year) – Developing countries

Demographic Transition 3. Industrial stage – industrialization is widespread. BR drops and approaches the DR. Better access to birth control, reduced IMR, incr. job opportunities for women, high cost of raising children, HS and college educations. Pop. grows but at a slower rate.

Demographic Transition 4. Post-industrial stage – BR declines further, equals (ZPG)  37 countries (mostly western Europe, 12% of world's pop.) are in this stage.

Ways to Reduce Births   
Family Planning
 How many children and when to have them  Contraceptives (55% drop in TFR in developing countries)
Economic Rewards and Penalties
 higher taxes, other fees, elimination of tax deductions for a third child, lose health care benefits, food allotments and job options  Work best if they encourage rather than mandate
Empowering Women
 Education, jobs, rights

 Hans Rosling : On Global Population Growth (10 minutes)

Limits to Growth  How do we estimate carrying capacity for a species?
 Examine requirements of given species  Examine resources available to given species  For Humans….
 How deep is the barrel?

Limits to Growth  Why is this difficult to estimate for humans?
1.
Range of resources used is too great (MEDC vs LEDC)  Resource requirements vary according to lifestyles  Resource requirements differ from time to time and population to population 2.
When a resource becomes limiting, we show great ingenuity in substituting one resource for another  Technological developments give rise to continual changes in the resources required and available for consumption

Limits to Growth  Why is this difficult to estimate for humans?
3. Human populations regularly import resources from outside immediate environment  Enables them to grow beyond local boundaries  Increases their carrying capacity (but decreases it somewhere else!)

Limits to Growth  So what factors are used to determine human carrying capacity?
 Rate of energy and material consumption  Level of pollution  Extent of human interference in global life-support systems  Affect reuse and recycling have on reducing these impacts/increasing carrying capacity

Population Practice Problems  The United States has a population of 3.15 billion and a growth rate of 0.9 percent. How long will it take our population to double?

Population Practice Problems  The United States has a CBR of 14 per 1,000 and a CDR of 8 per 1,000. What is the natural annual percent increase of our population?
 Why is this different than the growth rate?

Population Practice Problems  Mexico has a population of 116,221 thousand. Last year, they experienced 2,163 thousand births, 574 thousand deaths, and -348 thousand net migrants. What was its net annual percentage growth rate?

Population Practice Problems  The current global human population is about 7 million and is growing at a rate of 1.2%. If the world population were to grow at this rate for the next year, approximately how many people would be added?