Exam 6

Question 1

How to find optimal offspring size

Answer 1

Multiply number by survival probability for each size

Question 2

Pros/cons of one vs many bouts of reproduction

Answer 2

One is good because all resources can be put in at once

Many is good because more offspring are likely to survive

Question 3

Pros/cons of early vs late start of reproduction

Answer 3

Early can produce more offspring and individuals have a lower risk of dying before reproduction
Delaying allows time for individual to grow

Question 4

Take home messages on life history strategies

Answer 4

All strategies involve tradeoffs
We expect strategies to evolve that optimize AVERAGE lifetime fitness
Optimal strategies vary across species and even populations

Question 5

Population

Answer 5

A group of organisms of the same species living in a particular area

Question 6

Characteristics of populations

Answer 6

Abundance
Age structure
Survivorship curve

Question 7

Abundance

Answer 7

Population size

Can be estimated by mark and recapture studies

Question 8

Some sources of error for mark and recapture studies

Answer 8

Trap shyness
Tag affects survival
Assumes no changes in population size (no reproduction or death)
No migration

Question 9

Replacement level fertility

Answer 9

2.1 children/family

Question 10

Type 1/ Convex curve

Answer 10

Common in organisms that produce few offspring, but take good care of them
Humans, elephants, whales, etc.

Question 11

Type II/ Constant curve

Answer 11

Common in organisms with relative constant change of death throughout life
Rodents, songbirds, hydra

Question 12

Type III/ Concave curve

Answer 12

Many die early in life but those who survive usually live long
Lots of offspring but little care
Many plants, turtles, tadpoles

Question 13

What can be done to slow population growth?

Answer 13

Education to delay age of first reproduction

Question 14

How do scientists identify genes that are (or were recently) under selection?

Answer 14

As a favored version of a gene becomes more common in a population, genomes will look increasingly alike in and around the gene. Because variation is brushed away, the favored gene’s rise in popularity is called a sweep

Question 15

Why did the scientists find more evidence of recent selection on genes in populations in Europe and Asia than in Africa?

Answer 15

One could argue that we are adapted to the African environment and that most signals are seen when people adapt to new environments
The people who left Africa were then forced to adapt to different environments.

Question 16

Why is there greater genetic variation among people living in Africa than among people living in other parts of the world?

Answer 16

Diversity decreases steadily the further a population has migrated from the African homeland, since each group that moved onward carried away only some of the diversity of its parent population.

Question 17

According to the article, is light colored skin homologous or analogous between people of European and East Asian ancestry? Why?

Answer 17

Analogous- 2 different genes contribute to light skin color in each population
Presumably, different mutations were available in each population for natural selection to work on. The fact that the two populations took independent paths toward developing lighter skin suggests that there was not much gene flow between them.

Question 18

What is the difference between a hard sweep and a soft sweep? We talked in the past about selection on new mutations vs selection on standing genetic variation. Which scenario is associated with a hard sweep vs. a soft sweep?

Answer 18

Hard sweeps= substantial sweeps, with a new version of a gene being present in a large percentage of the population. These hard sweeps are often assumed to start from a new mutation. (Less common)

Soft sweeps= work on traits affected by many genes, like height. (more common) act on standing genetic variation

Question 19

The title of the article makes reference to ‘very recent evolution.’ Based on the examples in the article, what time-scale is considered ‘very recent’ in the context of human evolution - tens, hundreds, thousands, or millions of years?

Answer 19

3,000 years ago, if confirmed, would be the most recent known instance of human evolution. (monks evolving genes to better withstand low oxygen levels)

Question 20

People can be short either because they grow slowly or because they stop growing at an earlier age than others. Which explanation for short stature do the authors derive from the data on Pygmy populations?

Answer 20

The authors conclude that Pygmy populations stop growing at an earlier age.

Question 21

What is the life-history trade-off that the authors postulate has resulted in short stature in these populations?

Answer 21

There is a life history tradeoff between extended growth and early reproduction, with the balance pending toward the latter because of their exceptionally high mortality rates.

Question 22

The authors point out that selection isn’t favoring short stature per se. What life history trait does selection favor in these populations? Why is it favored?

Answer 22

Selection favors earlier onset of reproduction, because the earlier one starts reproducing, the more likely they are to pass on genes to subsequent generations because they have a greater opportunity to have more children.

Question 23

What are the characteristics of stages 1-4 of the model in terms of birth rates, death rates, and changes in population size? Make sure you understand how these characteristics are represented in the top figure, how they change over time, and how a population at the start of stage 1 differs from a population at the end of stage 4.

Answer 23

Stage 1: Pre-modern; balance between birth and death rates; very slow population growth (High Stationary Stage)

Stage 2: Urbanizing/Industrializing; Birth rate stays high with declining death rate; increasingly rapid rise in population growth, young age structure

Stage 3: Mature Industrial; decline in birth rate, population growth

Stage 4: Post Industrial; Stability; no population change; population age structure has become older, population decline may set in quickly

Question 24

Look at the third figure, illustrating survivorship curves for different countries at different times. Compare the survivorship curves of 17th century England with modern Great Britain. Are you surprised by the difference? What are the factors that have caused this change?

Answer 24

17th century England shows a Type III (Concave) curve while Modern GB shows a Type I (Convex) curve. In 17th century England, there were very high child mortality rates. So few females lived to reproduction, so only high fertility rates could sustain the population.

Question 25

Why do populations start growing in size during stage two?

Answer 25

There are declines in death rates. Due initially to 2 factors: 1) improvements in food supply from greater agricultural yield (crop rotation, selective breeding, seed drill technology) and 2) significant improvements in public health that greatly reduced childhood mortality (improvements in water supply, sewage, food handling, personal hygiene, etc.)

Question 26

What caused the decrease in deaths from scurvy in the 20th century?

Answer 26

General improvements in human well-being, an increase in public health awareness, and a decline in poverty.

Question 27

Why is there typically a time lag between the decline of the death rate and the decline in the birth rate as societies move through the demographic transition?

Answer 27

Continued decline in childhood death means that at some point parents realize they need not require so many children to be born to ensure a comfortable old age

Question 28

Why do populations continue to grow in size for a period of time after birth rates have fallen to replacement level fertility?

Answer 28

Population momentum- tendency for population growth to continue beyond the time that replacement-level fertility has been achieved because of a relatively high concentration of people in the childbearing years. Population momentum occurs towards the end of Stage Three

Question 29

According to the population clock, what is the current world population, rounded to two significant digits?

Answer 29

7,600,000,000

Question 30

What two countries have the highest population? Where does the US rank?

Answer 30

1. China
2. India
3. U.S.

Question 31

Look at the graph called World Population: Past, Present, and Future. What is striking about the history of population size?

Answer 31

A tremendous change occurred with the industrial revolution: whereas it had taken all of human history until around 1800 for world population to reach one billion, the second billion was achieved in only 130 years (1930), the third billion in 30 years (1960), the fourth billion in 15 years (1974), and the fifth billion in only 13 years (1987).

Question 32

What does it mean to say that the world has declining growth rates? Does this mean that population sizes are shrinking?

Answer 32

Population size is still growing, but the rate at which is grows is decreasing, meaning the population is not growing as quickly.

Question 33

Look at the table called ‘World Population by Country.’ Based on the information in the table, which one of the top 10 countries would you predict will exhibit an enormous surge in population size in the coming decades? What information in the table leads you to this conclusion?

Answer 33

Nigeria, because it has the highest growth rate at 2.63%