Day 19 November 20th Chapter 14

Dr Amy B Hollingsworth

The University of Akron

Fall 2014

14.7 Life histories are shaped by natural selection.

Do any animals mate themselves to death?

Why?

Why all the variation?

Is one strategy better than others, evolutionarily?

There are many possible responses to the challenge of:• when to reproduce • how often to reproduce• how much to reproduce

Life History

The vital statistics of the species

Includes: age at first reproduction, probabilities of survival and reproduction at each age, litter size and frequency, and longevity

Reproductive Investment

The material and energetic contribution that an individual will make to its offspring

Single episode of reproduction

Repeated episodes of reproduction

Which life history strategy is best?

1. What is the cost of reproductive investment during any reproductive episode?

2. What is an individual’s likelihood of surviving to have future reproductive episodes?

Natural selection favors lifetime reproductive success.

Why do humans put off mating so much longer than cats or mice?

14.8 Populations can be described quantitatively in life tables and survivorship curves.

Life Tables and Survivorship Curves

Life table

• Allow biologists to predict an individual’s likelihood of either dying within a particular age interval or surviving the interval.

Life Tables and Survivorship Curves

Survivorship curves

• graphs of the proportion of individuals of a particular age that are alive in a population

14.9 There are tradeoffs between reproduction and longevity.

Designing an Organism

To structure its life history for maximum fitness, create one that could:

produce many offspring,

beginning just after birth,

continuing every year,

while growing tremendously large, to reduce the predation risk

and living forever.

Evolutionary Constraints

These traits are not all possible because selection that changes one feature tends to adversely affect others.

Evolutionary tradeoffs

Three areas to which an organism can allocate its resources:

Growth

Reproduction

Survival

14.10–14.12

Ecology

influences the

evolution of

aging in a

population.

14.10 Things fall apart: What is aging and why does it occur?

Physiological Deterioration over Time

Aging: an increased risk of dying with increasing age.

Why do organisms age?

The force of natural selection lessens with advancing age.

Many genetic diseases kill old people, but almost none kill children.

Why not?

Mutations That Arise and Cause Their Carrier to Be More Likely to Die Later in Life

Such mutations include those that increase the risk from cancers or heart disease or other types of ailments.

Do not affect reproductive output.

Consequently, these mutants are never cleaned out of a population.

A cure for cancer may be discovered but not a cure for aging.

Why the difference?

14.11 What determines the longevity of different species?

Hazard Factors

High-risk worlds

• Death from external sources

• Reproduce early

Low-risk worlds

• Death from external sources low

Age at Time of Reproduction

A key factor determining longevity.

Early reproduction will also favor early aging.

Later reproduction will also favor later aging.

14.12 Can we slow down the process of aging?

Life extension is possible.

14.13–14.15

The human

population is

growing

rapidly.

What is the baby boom?

Why is it bad news for young people today?

14.13 Age pyramids reveal much about a population.

Describing Populations

In terms of the proportion of individuals from each age group

The population age distribution

Age groupings called cohorts

14.14 As less-developed countries become more developed, a demographic transition often occurs.

Population growth is alarmingly slow in Sweden and alarmingly fast in Mexico.

Why is there a difference?

14.15 Human population growth: How high can it go?

How high can it go?!

Very difficult to assess just how many resources each person needs.

Ecological footprints

• Evaluating how much land, how much food and water, and how much fuel, among other things, are necessary.