Chapter 52 Population Ecology Population individuals of a species in a given area Populations defined by two factors Density number of individuals per unit of space area or volume Dispersion pattern of spacing of individuals within the geographic boundaries of the population Census taking impractical alternate approach mark recapture Assumption 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 density Limitations Individual patterns of movement Some way avoid traps via learning Indirect population measurements also possible Is the sea otter decline really due to orcas Evidence for it being orcas o Increase in observed attack on sea otters concurrent with decline o No decline in areas inaccessible to orcas Alternate 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 out Two Orca Groups harass marine mammals Kuluk Bay greater deline 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 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 Lagoon What 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 night Patterns of Dispersion May be due to behavior resources or combo of the two 1 Clumped 2 Uniform 3 Random Demography 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 52 Life Table age specific summary of survival pattern of population Cohort defined group of individuals of same age followed from birth to death Survivorship proportion of offspring that survive to a particular age Survivorship Curve life table data put into graphic form Population size vs age o Type I flat start steep decline o Type II intermediate o Type III sharp drop at start flattens as death rate stabilizes for survivors Two class of death rates and the mortality rate 1 Density Dependent strong correlation with the concentration of the population 2 Density Independent population is separate from the mortality rate a Ex correspond to weather effects Second factor affecting population Reproductive Rates o Tally is of females giving birth and number of females born Males considered to be gene distributors only for purposes of statistics o Fecundity number of female offspring produced by each female in a population Reproductive Table Reproductive Strategies Big bang reproduction AKA semelparity o Copulate once at the end of your life Repeated Reproduction AKA iteroparity o Continuous reproduction Life History How organisms allocates time and energy Survival vs Fecundity Both cannot be high because each has a cost Fitness Trade Off Population 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 stable In Utopia what is the growth rate Rmax What is r in Utopia of increase o Rmax is fixed for each species Exponential Growth dN dt rmaxN Growth rate is at its maximum rmax called the intrinsic rate of growth Change in population over time growth rate times population number There is always potential for exponential population growth Limitations of Exponential Model Assumes there is infinite space infinite resources o Highest possible birthrate lowest possible death rate rmax or the intrinsic rate Logistic Population Growth S Curve Population Growth Function of population Size and Density Dependent Carrying Capacity K maximum population size that a particular environment can support without degrading the habitat K is maximum number of individuals K 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 unsustainable Limitations to Logistic Model it assumes that Each individual has equal fitness No catastrophe will occur in environment Populations adjust instantly Social structures are irrelevant Population Growth Patterns K Selection R Selection Population is sensitive to density Few young Large young Slow maturation Intensive parental care Reproduce many times Population maximizes reproduction success when not crowded Many young Small young Rapid maturation Little no parental care Big bang reproduction Density 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 increases o 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 density
View Full Document
Unlocking...