Zoology 101 – McIntyre – Population Ecology - 2 May 2012Goal of Population Ecology: To understand how biotic and abiotic factors influence the density, distribution, size, and age structure of populations Population – a group of individuals of the same species that live in the same areaDensity - # of individuals per unit area or volumeDispersion – spatial distribution; spacing among individuals in population (not tobe confused with dispersal)Observation #1: Population dynamics show change through timeElephants hunted to the point of extinction during the early 20thcentury, and protections were put in place to protect them. Theelephant population had a slow growth phase and then a hugeexplosion in the 1960s (J-shaped curved). Populations do begin to plateau when they reach the carryingcapacity. The graph to the right shows a S-shaped curveSlow growth – fast growth – stable plateauObservation #2: Reproductive rate (births) depend onpopulation size. High population means low births, and lowpopulation means more births (rapid population growth)MEANING EXAMPLERANDOM Random dispersion with no or fewconstraints Dandelions UNIFORM Territorial partitioning and it has too even dispersion with uniform spacingPenguinsCLUMPED Clumps/aggregations; patchy resources Starfish/Sea stars (they focus on chemical cues from food)Observation #3: Deaths are not randomSurvivorship curve – a plot of the proportion or numbers in a cohort still alive at each age.In the Belleville brown squirrel, females live longer than males. Males don’t live more than 5 years, and females live up to approximately 9.7 years. Observation #4: Survival differs among species Range of variation across species. Humans have low mortality atearlier ages. At around 35-40 years of age the decline starts.Humans have high parental investment.Brown squirrel has moderate parental investment. Oysters havelow parental investments, and they have high young mortalityrates. BIDE conceptual model: [Birth, Immigration, Death, Emigration]Births + Immigration = Deaths + Emigration (they have to equal) Population growth is usually limited Exponential growth – geometric population growth Logistic population growth – the per capita rate of increaseapproaches zero as the carrying capacity is reachedr = B-D = intrinsic rate of population growth per capita pergeneration More information on equations on separate sheet!!(GRAPH TO THE RIGHT)Long generation time – slow population growth Short generation time – fast population growth Predators can cause stable cycles of population sizes (i.e., lynxpopulation correlates with their prey’s population, the hare)Regulations in populations:Density-independent regulating factors: chance events whose impact doesn’t depend on population density (i.e., tornado, lighting storm)Density-dependent regulating factors: chance events ordeterministic processes whose impact depends on populationdensityDominates population dynamics (i.e., Crustaceous period withhuge periods of extinctions)Competition for scarce resources (food, space, light, water, etc.)Predation, disease, toxic wastes, behaviorPopulation structure:Sex ratio – # of males:# of femalesAge structure – % of individuals in different agegroupsSometimes grouped by reproductive status (pre-reproductive, reproductive, post-reproductive)Size structure – % of individuals in different sizegroupsSweden – (Urn-shaped) few kids, many parents, even more seniors, and no growth or decline USA – (Bell-shaped) some kids, more parents, few seniors, and slow or no growthMexico – (Pyramid-shaped) lots of kids, some parents, fewer seniors, rapid population growth(Reproductive ages range from 15-44 years)Is the human population growth limited? Density-dependent factor (The Black Plague) caused a dip inthe human population (1300s), and now we’re in anexponential growth phase.% increase is declining through time; decrease in annualpercent increase, and maybe now we’re entering a logisticgrowth phase (a “plateau”)Semelparity – reproduction in which an organism produces all of its offspring in a single event; also known as big-bang reproductionIteroparity – reproduction in which adults produce offspring over many years; also known as repeated reproductionK-selection – selection for life history traits that are sensitive to population density; also called density-dependent selectionr-selection – selection for life history traits that maximize reproductive success in uncrowded environments; also called density-independent selectionBig-Picture Conclusions:1) Populations are dynamic – their size reflects balance of BIDE2) Both density-dependent & density-independent factors limit populations3) Population growth is not unlimited in any species (including humans)PRE-LECTURE QUIZ1) Demographic analysis of sexually reproducing species generally focuses on which segment of a population? Females only2) What is the general association between reproductive rate (young produced per adult) and population growth? Only when conditions are ideal for new recruits will high reproductive ratetranslate into high population growth 3) The zero population growth point occurs under what conditions? Any time that per capita birth and death rates are equal 4) The symbol K signifies the carrying capacity of a site for a particular population, which means:The maximum population size that can be supported by that environment5) Which of the following taxa is an example of semelparous life history? Pacific salmon & Agave century plants 6) The inverse relationship between the number and size of offspring exemplifies what tradeoff in the evolution of life history strategies? Reproduction vs. survival of offspring7) Which of the following is not a mechanism of density-dependent regulation of population size? a. Predationb. Territoriality and other aggressive interactionsc. Disease d. Toxic metabolic wastese. All of these are mechanisms of density-dependent regulations8) What is a metapopulation? A network of linked populations9) What is the pattern of global human population size over the last century? Initial exponential growth followed by slowing growth rate since the 1960s10) The ecological footprint concept summarizes the resource consumption per person in a society. How does the average American’s ecological footprint compare to the global average? Roughly 5 times higher in the
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