Pitt BIOSC 0160 - Chapter 52 Population Ecology

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Chapter 52 Population EcologyPopulation – individuals of a species in a given area- Populations defined by two factorsDensity – number of individuals per unit of space (area or volume)Dispersion – pattern of spacing of individuals within the geographic boundaries of the populationCensus taking impractical alternate approach: mark-recaptureAssumption:% of marked/recaptured animals = % of marked individuals in the population% Tagged animals recaptured tells you the % of the total population that is marked. Also reveals population densityLimitations- Individual patterns of movement- Some way avoid traps via learningIndirect population measurements also possibleIs the sea otter decline really due to orcas?- Evidence for it being orcaso Increase in observed attack on sea otters concurrent with declineo No decline in areas inaccessible to orcasAlternate Hypothesis- Increase in shark populations concurrent with sea otter declines- High contaminant levels in sea otters  their role in health, vital rates, and population decline unknown- Disease has not been rules outTwo Orca Groups- Transient – mammal diet- Resident – fish diet (outnumber transients 4:1)o Who was harassing the otters?o Residents have never been observed consuming mammals, they do sometimes harass marine mammalsKuluk Bay (greater deline)- Has a lot of military activity- High concentrations of PCBs, petroleum products reported in mussels that otters occasionally eat- In 1989, 2 million liters jet fuel dumped into cove that drains into Kuluk bay- Effects of jet fuel on humans – intoxication, fatigue, cancer, sleep disturbance, poor coordination- Much lower levels of pollution present in adjacent Clam LagoonWhat about other predators?- Bald eagles prey on pups- Sharks – pacific sleeper sharks and salmon sharks are common in area; no one has checked their diets for otters- Otters and sleeper sharks overlap in same habitat during the nightPatterns of Dispersion- May be due to behavior, resources, or combo of the two1. Clumped2. Uniform3. RandomDemography – study of factors that affect population size (growth and decline)Affected by:- Deaths- Births (reproduction)- Movement in (immigration) ignored in Chapter 52- Movement out (emigration) ignored in Chapter 52Life Table – age-specific summary of survival pattern of populationCohort – defined group of individuals of same age followed from birth to deathSurvivorship – proportion of offspring that survive to a particular age- Survivorship Curve – life table data put into graphic form. Population size vs. ageo Type I – flat start, steep declineo Type II – intermediateo Type III – sharp drop at start, flattens as death rate stabilizes for survivors- Two class of death rates1. Density Dependent – strong correlation with the concentration of the population and the mortality rate2. Density Independent – population is separate from the mortality ratea. Ex. correspond to weather effectsSecond factor affecting population- Reproductive Rateso Tally is of females giving birth and number of females born. Males considered to be “gene distributors” only, for purposes of statisticso Fecundity – number of female offspring produced by each female in a population- Reproductive TableReproductive Strategies- Big-bang reproduction (AKA semelparity)o Copulate once at the end of your life- Repeated Reproduction (AKA iteroparity)o Continuous reproductionLife History – How organisms allocates time and energyFitness Trade-Off- Survival vs. Fecundity. Both cannot be high because each has a costPopulation Growth- Assume no migration- Examine difference in birth and death rates (b-d=r)- +r births > deaths  population growth- -r births < deaths  population declining- r = 0 the population is stableIn Utopia, what is the growth rate? Rmax- What is r in Utopia?o Highest possible birthrate + lowest possible death rate = rmax or the intrinsic rate of increaseo Rmax is fixed for each speciesExponential Growth- Growth rate is at its maximum (rmax) called the intrinsic rate of growth- dN/dt = rmaxN- Change in population over time = growth rate times population number- There is always potential for exponential population growthLimitations of Exponential Model- Assumes there is infinite space, infinite resourcesLogistic Population Growth S Curve Population Growth – Function of population Size and Density DependentCarrying Capacity (K): maximum population size that a particular environment can support without degrading the habitatK is maximum number of individualsK-N = how many more individuals can join population- Ex. Human population hit a J curve – will ultimately hit a carrying capacity, steep upward trajectory – will become unsustainableLimitations to Logistic Model (it assumes that)- Each individual has equal fitness- No catastrophe will occur in environment- Populations adjust instantly- Social structures are irrelevantPopulation Growth PatternsK-Selection R-SelectionPopulation is sensitive to density Population maximizes reproduction successwhen not crowdedFew young Many youngLarge young Small youngSlow maturation Rapid maturationIntensive parental care Little/no parental careReproduce many times Big-bang reproductionDensity Dependent Birth and Death Rates are example of negative feedback- Many populations cycle through periods of high and low density- Negative feedback prevents unlimited population growth- Competition for resources increases as population increaseso Food, nesting sites- Health suffers as result of competition- Reproduction may decrease and mortality increase for those in poor health- Predation – predators may focus on high-density populations as “easy catch” and also may target those in poor health- Disease transmission likely increased by close contact- Population may fill habitat with toxins- Many populations cycle through periods of high and low


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Pitt BIOSC 0160 - Chapter 52 Population Ecology

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