07 pop bio
DESCRIPTION
TRANSCRIPT
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
Example for a population of algae
r
r
r
Example for a population of algae
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.
Other factors influencing population growth rate
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)
Other factors influencing population growth rate
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
Life history traits – characteristics of an individual that influence survival and reproduction
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
Life history traits – characteristics of an individual that influence survival and reproduction
Atlantic SalmonAfrican elephantHouse Mouse
Number of reproductive events
~3 - 10 1~6-12
Life history traits – characteristics of an individual that influence survival and reproduction
Atlantic SalmonAfrican elephantHouse Mouse
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.