Population Ecology I: Demography and Growth PDF

Population Ecology I: Demography and Growth Ecology in the news The “assassin bug” Salyavata variagata  Scales of Ecological Organization Biosphere Ecosystem Community Population Organism Why do we care about populatio...

Population Ecology I: Demography and Growth Ecology in the news The “assassin bug” Salyavata variagata  Scales of Ecological Organization Biosphere Ecosystem Community Population Organism Why do we care about population biology? Need to know Define a population and population ecology Understand concepts of density and dispersion Be able to estimate population size using mark-recapture formula Understand relationship between the environment, “life histories”, and population survival, growth and reproduction (incl. anadromous fish) Be able to identify and describe the three different types of survivorship Be able to describe the processes and basic mathematics underlying exponential population growth  Introduction A population is a group of interbreeding individuals of a single species living in the same general area Population ecology is the study of births, deaths, and the dynamics forces which regulate a population 2 ways of describing populations 1. Spatial: Density: the number of individuals per unit area or volume Dispersion: the pattern of spacing among individuals within the boundaries of the population 2 ways of describing populations 2. Temporal: Rates of birth, death Population growth and dynamics 1. Spatial: a. can measure total numbers b. or can measure density HOW DO WE DO THIS? 1. Spatial: How do we measure density? Can count individuals – used to be MUCH harder 1. Spatial: How do we measure density? Can count individuals Estimating density with “subsamples” 1. Spatial: How do we measure density? Can count individuals Count signs of individuals* *can only provide estimates of relative density What about when animals are highly mobile? 1. Spatial: How do we measure density? Can count individuals Count signs of individuals Mark-recapture methods Mark-recapture technique: 1. Capture critters 2. Mark ‘em 3. Re-capture 4. Do math Mark-recapture technique: 1. Capture critters 2. Mark ‘em 3. Re-capture 4. Do math (# marked * total of 2nd capture) __________________ = population estimate # marked found in 2nd capture So if you first catch 5 piglets And you mark them all… And then your second capture is 10 piglets, and there is ONE marked piglet… (5*10) divided by?  (5*10)/1 x = 50 piglets!!! Let’s LearningCatalytics for America You go out and trap desert gerbils. On your first trapping night, you capture 10 gerbils. On your second trapping night, you capture 1000 gerbils, and 5 are marked. How many gerbils do you estimate are in the population? A. 4000 B. 2000 C. 1000 D. Only the gerbils know  1. Spatial: Population Dispersion How are individuals distributed in space? Spatial: Population Dispersion spatial patterns aka “over-dispersed” What are some environmental or social factors that might lead to the formation of these spatial patterns?  Spatial: Population Dispersion spatial patterns Spaced – competition, territoriality Clumped -- may indicate social patterns or resource distribution Random--?? Learning Catalytics Satellite image of termite mounds in Kenya. What type of dispersion pattern is this? A. Clumped B. Random C. Spaced Learning Catalytics Satellite image of termite mounds in Kenya. What process can you infer might be causing this spatial distribution? A. Competition B. Predation C. Random factors such as wind or water flow D. No inference is possible 2. Describing population change over time (temporal) Patterns in birth rates Patterns in death rates 2. Temporal patterns in populations Unpredictable env. Stable environment Low competition High competition How are populations of frogs and elephants different? 2. Temporal: Patterns in Birth Rates Life history: the traits that make up an organism’s schedule of reproduction and survival Age at first reproduction Frequency and duration of reproduction Total number of offspring produced Life expectancy Life History Traits are Products of Natural Selection! Life History Diversity  Life History Diversity Why are Pacific salmon semelparous? Pacific salmon have an “anadromous” life style – born in freshwater streams, mature in the ocean, and then return to the stream to spawn – getting back upstream is hugely ENERGETICALLY COSTLY! 2. Temporal: Patterns in Death Rates 2. Temporal: Patterns in Death Rates a x is a le t h is sc te g1 0 N o n a lo Is o “Survivorship curves” Basic Population Growth Models How can we predict how many elephants will be in the Serengeti in 50 years? current population = approx 7000  Basic Population Growth Model* *note: ignores migration B (birth) M (death) Eq. 1. Change in Pop. Size =∆ N/ ∆T = B-M  Per Capita Population Growth Expressed on a per individual basis (i.e., per capita): per capita birth rate b = B/N where N = # of individuals in population So if there are 50 births in population of 1000 elephants, then b = 50/1000 = 0.05 Per Capita Population Growth per capita death rate m =M/N N = # of individuals  Per Capita Population Growth The population growth equation (Eq. 1) on a per capita basis is: Eq. 2. ∆ N/∆T = bN-mN Per capita rate of increase = r = b-m, therefore: Eq. 3. ∆ N/∆T = rN if r > 0, population is growing, if r