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Barbara J. King , Department of Anthropology, College of William and Mary "Apes, Elephants and the Relational Self: Thinking Through Animal Personhood” Tuesday, March 15, 4:00pm Knight 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 Biology 10 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 tigers Feb 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 (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 Reproduction Females 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 II Type III
Type I survivorship curve Survival is high until old age
Humans in developed countries
Type II survivorship curve Mortality is spread evenly among all age groups
Many species of birds
Type III survivorship curve Very high mortality among the young
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
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.
Environmental Resistance —Any factor (limiting factor) in the environment influencing carrying capacity. Four main factors:
Raw material availability
Waste accumulation and disposal
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 availability death rate determined by predators, food Lynx population: birth and death rate determined by food availability (hares)
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 Salmon African elephant 2 months House Mouse
Life history traits – characteristics of an individual that influence survival and reproduction Atlantic Salmon African elephant House 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 Salmon African elephant House Mouse Number of reproductive events ~3 - 10 1 ~6-12
Life history traits – characteristics of an individual that influence survival and reproduction Atlantic Salmon African elephant House Mouse Lifespan 60 - 70 years 3-6 years ~2 years
By the end of this lecture you should be able to:
Explain the three types of survivorship curves.
List the factors that influence population growth rates and population density.
Describe the difference between exponential and logistic growth and why populations don ’ t grow exponentially forever.
Tell the four main factors determining carrying capacity.