Population Parameters 1 Population a group of conspecifics occupying the same location at the same time facing common conditions using common resources and capable of interbreeding a Utility in ecology Central concept In practice extent of population is space and time set by interests of the investigator b Subdivisions neighborhoods and demes Population genetic concepts Form clear link between ecology and genetics Focus on reproduction and gene flow Deme group of conspecifics in direct reproductive contacts o EX song sparrows hear each other Neighborhood set of demes linked by gene flow o EX song sparrows disperse to other demes within dispersal limits 2 Absolute density the number of individuals per unit area or volume a Usually straightforward EX humans o Density of humans in Allegheny county of individuals EX jewelweed EX diatoms o Measured by volume Problem crude v ecological density volume o Ecological density of interactions Problem dispersion influences density o Crude absolute density number of organisms per unit o Dispersion spatial array or pattern distribution of organisms in a population Uniform evenly spaced pretty common could be caused by territory Random no ecological interaction rarest pattern few examples tropical forest trees location of an individual is independent of the location of another individual independently and identically distributed Clumped aggregated could be caused by patchy resources flocking herding to prevent predation most common by far clumps are uniform and arbitrary b More complex with modular organisms Many plants have ramets o Ramet module capable of independent existence o Consists of an internode leaf and axillary bud Internode region of stem between two leaves Axillary bud meristimatic tissue between leaf and internode capable of cell divison growth o EX spider plants Concept of individual does not apply Ramets grow and make more ramets Modular not unitary i Population and biomass does not increase o For modular organisms biomass is the best measure of density o Genet group of genetically identical ramets i e clones Operates under natural selection with modulatory organisms Some animals e g hydroids are modular c Biomass per unit area or volume 3 Primary population parameters a Natality addition of individuals to a population by birth b Mortality loss of individuals from a population by death c d Emigration dispersal of individuals out of the population e Nx 1 Nx b d I e dN dt rN Immigration addition of individuals to a population by dispersal N number of individuals X time B births D deaths I immigrations E emigrations 4 Measuring density a Absolute density Quadrat methods o Establish a set of sampling plots same size and shape o Count individuals in each part o Calculate the mean number of individuals per sampling plot o Divide mean by area of one plot to get estimate of density o Calculate variance of estimate to determine the precision repeatability of estimate o Critical assumption plots are representative of population o Walk distance of known length and width long quadrats as a whole Line transects Aerial surveys o Fly a series of line transects EX whales in ocean Mark recapture methods o Used for organized that are mobile sampling across time rather than space o Capture mark and release a sample M o Recapture a sample n o Count number marked in recaptured sample o Use equivalence of proportionality to estimate population size N o Equation R n M N N nM R Let M 30 individuals n 100 R 10 individuals N 300 individuals direct censusing o count all individuals in a population o rarely used hard to complete for large populations b Relative density e g light trap EX U S Census Density expressed without respect to specific numeric values Light trap insects attracted to light and fall into a jar