bs148h 29 November 2007Read: Text ch 52 • population ecology• limiting factors• spatial patterns• dynamic demographics• geometric pop growth• looking back• exponential growth• logistic growth• maximum sustainable yield• chaos!• the human footprint10Molecules9Organelles8Cells7Tissues6Organs & organ systems5OrganismsPopulations Populations 4Communities of populations living together& exchanging resourcesform Ecosystems 321the BiosphereOrganismsOrganisms live in populationspopulations{& kin groups & social groups}a PopulationPopulationis a group of individuals in the same species living in the same general areainteracting w/ each other through common resources &/or predators, parasites etcand social (ex: mating) behavior. Not as tightly integrated as an organism,but more tightly integrated than a community of populations.Characteristics of a pop’s ecology include(1) rangerange, (2) spacingspacing & (3) sizesize, all may vary over timetime& across age, sex, demographicsdemographicsWe begin with the current distribution map for each tree species, to characterize and define the occupied (or occupiable) volume of environmental space by statistically cataloging all combinations of env conditions which are habitable by this species.To predict a new distribution for the species under altered environmental conditions, we re-cluster using all cells from a map ... the altered spatial distribution now habitable by this species under the new env conditions will be shown ...Most species have relatively limited geographic rangesMost species have relatively limited geographic ranges - limited by what?I. Environmental conditionsI. Environmental conditions: each species & pop is adapted to a limited range of abioticabioticconditions conditions incl. temp, humidity, mineral nutrients etc {fundamental niche}& biotic interactionsbiotic interactions, incl. prey, competitors, predators, parasites etc {realized niche}Oak Ridge National Laboratory (ORNL) Environmental Sciences Division (ESD)... Predicting Changes in a Species Distribution Map Following Changes in Environmental Conditions {ex global warming}William W. Hargrove and Forrest M. Hoffman http://research.esd.ornl.gov/~hnw/esri99/G.E. Hutchinson (1957,1965) suggested that an organism's nicheniche could be visualized as a multidimensional hypervolume comprised of all combinations of the env. conditions which permit an individual of that species to survive and reproduce indefinitely. ... fundamental nichefundamental niche: the inhabitable hypervolume w/o competition, predation, & parasitism, ... realized nicherealized niche: a smaller hypervolume occupied when the species is under biotic constraints. {assuming what about time, luck & adaptation?}II. Time, luck & adaptationII. Time, luck & adaptation: pop ranges are changing over time, w/ luck & adaptationPotential processes include aggregation at patchy resourcesand/or social attraction to each otherThe distribution pattern is Clumped.Clumped.Begin w/ a null modelnull model - the distribution is ‘randomrandom’’If we know abundance (n = 16) & area (& a little probability theory)we can construct expected random distribution ofIf there are too many short nearest neighbor distances, orthe variance in # indiv’s per quadrat is too high, thenreject the null model that the distribution is random. The distribution pattern is UniformUniform (or hyperdispersed)Potential processes include resource competition and aggression.Nonrandom spatial distribution patternspatterns suggest causal processesprocesses.Demographic processesprocesses (ex: Birth, Immigration, Death, EmigrationBirth, Immigration, Death, Emigration) (text Fig 52.2) within Populations create patternspatterns of DistributionDistribution and AbundanceAbundance (text Fig 52.3) If there is too little variation in nearest neighbor distances, orin # indiv’s per quadrat, then reject the null model. a) nearest neighbor distances, orb) number indiv’s in small sample quadrats(like expected chocolate chips per cookie if Poisson) {consider seating pattern in a bar: might be some clumping & some hyperdispersal}In general,if you look at a big enough scale, things tend to be clumpedbut if you look at a small enough scale they tend to be hyperdispersed.At continental scale,breeding birds clumpedin regions, biomes, habitats(grasslands, pastures)Within habitats,aggregate atprofitable patches(heavily grazed)Within patches,territoriesuniformWithin territories,behaviors‘aggregated’over microhabitatsMost organism spatial distribution patterns are Most organism spatial distribution patterns are ‘‘scale sensitivescale sensitive’’{fractal patterns (“chaos in space” – later) are scale insensitive} We use population growth modelspopulation growth models to describe pastdescribe past patterns andto predict futurepredict future patterns.These demographic processes depend on ecological interactions, ecological interactions, likeresource competition, predation, disease etc,resource competition, predation, disease etc,and on details ofpopulation structure, population structure, likeproportion of mature femalesproportion of mature femalesand life history characteristics, life history characteristics, likeage at 1st repro, offspring per age at 1st repro, offspring per ‘‘clutchclutch’’etc.,etc.,that we will consider later.Begin w/ simple binary fission in bacteria.One of the most fundamental patterns in a population is Abundance through TimeAbundance through Time.Population growth or decline depends on demographic processes ofBirth, Immigration, Death & Emigration (BIDE)Birth, Immigration, Death & Emigration (BIDE)Then N0 = 1Begin with geometric growthgeometric growth:Suppose we start w/ 1 bacteria at time t = 0: N0 = 1, and at each unit of time the bacteria undergoe binary fission and the number of bacteria doubles.{obviously something is missing from this simple model of geometric growth}The geometric growth rategeometric growth rate per unit time is λλ = ( Nt/ Nt-1).For bacteria in lab, λλ ~ 2 per 20 min. = λλ20min 20min Can you figure out λλ per hour? λλhr hr =2 N0= N1 = 2 = 212 N1= N2= 4 = 222 N2= N3 = 8 = 23…2 Nt-1 =NNtt= N= N0022tt…2(60/20)= 23= 8 per hrCan you figure out λλ per day? λλday day =2(3⋅24)= 272= ?"The mathematics of uncontrolled growth are frightening.... in a single day, one cell of E. coli could produce a super-colony equal in size and weight to the entire