07 pop bio

Barbara J. King, Department of Anthropology, College of William and Mary

"Apes, Elephants and the Relational Self: Thinking Through Animal Personhood”

Tuesday, March 15, 4:00pmKnight Auditorium, Spurlock Museum, 600 S. Gregory,

Urbana.

Barbara J. King is the author of Being With Animals: Why We Are Obsessed with the Furry, Scaly, Feathered

Creatures Who Populate Our World

Announcements: Feb 14, 2011

Do all species matter? Is there redundancy in communities?

Paul Ehrlich made an analogy between species in communities and rivets on the wing of an airplane. Removing a few rivets from an airplane is undoubtedly safe. How many are you willing to remove?

On average, there are only 2 degrees of separation between any two species in a food web.

Percentage of threatened or endangered species in the U.S. imperiled by:

Why are species declining?

Disease - 3%

Overexploitation - 17%

Pollution - 24%

Invasive species - 49%

Habitat degradation and loss - 85%

Dave Wilcove et al. 1998 BioScience

Population Biology10 February 2010

Lecture Objectives:

1. Learn the population characteristics that determine population growth rate

3. Understand the different types of population growth curves and life history traits

2. Understand why the number of individuals in a population may change over time

World Wildlife Fund launches campaign to save tigersFeb 10, 2010

* Number of tigers in the wild has dropped to 3,200 from 100,000 in 1900, group says

* Poaching, habitat loss, development, illegal trafficking

threaten tigers, WWF says

* There are now more tigers in captivity in the United States, about 5,000, than there are in the wild worldwide, the group said.

CNN

Population Characteristics

Population – All organisms of the same species found within a specific geographic region

Different populations can differ in:*Birthrate

*Death rate

*Sex ratio

*Age distribution

*Density

*Population growth rate

Birthrate (Natality)

Birthrate (b)—Number of individuals added through reproduction over a particular time period.

In many species, birthrate is influenced by the amount of food available

Sexually reproducing species must also find mates

In humans, expressed as # of babies/1000 individuals/year

Asexual ReproductionFemales that reproduce asexually do not need to find a mate

New Mexico Whiptail Daphnia

Death rate (Mortality)

Mortality (d) — Number of individuals removed via death

For many species, predation is a major contributor to death rate

In human populations, talk about # of people who die/1000 individuals/year

Mortality

Survivorship curve – a graph showing the proportion of individuals likely to survive to each age

Three main types:Type I

Type IIType III

Type I survivorship curve

Survival is high until old age

Examples:•Dall sheep•Humans in developed countries

Type II survivorship curve

Mortality is spread evenly among all age groups

Example:•Many species of birds

Type III survivorship curve

Very high mortality among the young

Examples:• Plants• Animals

that produce many offspring

Survivorship curves (continued)

One major factor determining the shape of the survivorship curve is the degree of parental care

How long do parents care for the offspring after they are born?

Population growth rate

Population growth rate (r) – the rate at which the size of the population changes

r = b - d

Assumes no immigration or emigration—when this happens population growth rate is then more generally, (birth + immigration) – (death + emigration)

Exponential Growth

Note: This equation is provided only to help. You do not need to memorize it. You will not be asked about the equation on a

test.

Change in number over time

Population growth rate

Number of individuals

The number of individuals in each generation is a multiple of the previous generation

Example of exponential growth

Populations do not grow exponentially forever

r

r

r

Example for a population of algae

r >0

r=0

r<0


r

r

r


In the red region, what might cause N to decline? What information do you need to answer this question fully?

Sex Ratio

In many sexually reproducing species, with separate sexes, sex ratio is 1:1

Other factors influencing population growth rate

In other species (e.g., asexuals, social insects) can have far more females than males

Sex Ratio—Relative number of males and females in a population.

Age Distribution (Age Structure)

Age Distribution—Number of individuals of each age in the population.

Greatly influences reproductive rate of a population.


How does the age distribution differ among these populations?

Why does age distribution influence reproductive rate of a population?

Dispersal: Movement of individuals

Emigration: leaving a population, often from crowded areas or in response to environmental change

Immigration: emigrating individuals become immigrants in a new population (joining a population)


Summary of factors influencing population growth rate

Birthrate Death rate

Sex Ratio Age distribution

Immigration Emigration

How many individuals are in a population at any given time?

Population Density (N)—Number of individuals per unit area.

High population density may lead to increased competition for resources.

Population Density

Population 1

N = 4 flowers/m2 N = 12 flowers/m2

Population 2

Population Growth Curve Biotic Potential—Inherent reproductive

capacity. Generally, biotic potential is much above

replacement level. Natural tendency for increase.

How to combine number of individuals (N) and population growth rate (r)?

When not limited, populations tend to grow exponentially

Population Growth Curve

Typical Growth Curve Lag Phase—First portion of the curve; slow

population growth. Exponential Growth Phase—More

organisms reproducing causing accelerated growth; continues as long as birth rate exceeds death rate.

Stable Equilibrium Phase—Death rate and birth rate equilibrate; population stops growing.

If death rate exceeds birth rate, population crashes

Carrying Capacity (K) Carrying Capacity—Number of individuals of a

species that can be indefinitely sustained in a given area.

Carrying Capacity

Environmental Resistance

Environmental Resistance—Any factor (limiting factor) in the environment influencing carrying capacity. Four main factors: Raw material availability Energy availability Waste accumulation and disposal Organism interaction

Logistic Equation

Note: This equation is provided only to help. You do not need to memorize it. You will not be asked about the

equation on a test.

Logistic growth describes this “S” shaped growth curve.

Population cycling due to organism interactions

Hare population:birth rate limited by food availabilitydeath rate determined by predators, food

Lynx population:birth and death rate determined by food availability (hares)

Population Cycles

Remember: Several factors influence population growth rate:

Birthrate Death rate

Sex Ratio Age Distribution

Immigration Emigration

But, there are also additional things about the individuals that influence how the population grows

Life history traits – characteristics of an individual that influence survival and reproduction

Age at maturity

11 - 20 years 3-6 years

Atlantic SalmonAfrican elephant

2 months

House Mouse


Atlantic SalmonAfrican elephantHouse Mouse

1 calf every 3-8 years

1,500 to 8,000 eggs once

5-8 young every month

Number of offspring produced



Number of reproductive events

~3 - 10 1~6-12



Lifespan

60 - 70 years 3-6 years~2 years

By the end of this lecture you should be able to:

1. Explain the three types of survivorship curves.2. List the factors that influence population

growth rates and population density.3. Describe the difference between exponential

and logistic growth and why populations don’t grow exponentially forever.

4. Tell the four main factors determining carrying capacity.

5. Explain why populations cycle.6. Know the key life history traits.

Technology

07 pop bio