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Population Parameters1. Population: a group of conspecifics occupying the same location at the same time, facing common conditions, using common resources, and capable of interbreedinga. Utility in ecology- Central concept- In practice, extent of population is space and time set by interestsof the investigatorb. 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 contactso EX: song sparrows hear each other- Neighborhood: set of demes linked by gene flowo EX: song sparrows disperse to other demes within dispersal limits2. Absolute density: the number of individuals per unit area or volumea. Usually straightforward- EX: humanso Density of humans in Allegheny county—# of individuals- EX: jewelweed- EX: diatomso Measured by volume- Problem: crude v. ecological densityo Crude: absolute density; number of organisms per unit volumeo Ecological: density of interactions- Problem: dispersion influences densityo 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 arbitraryb. More complex with modular organisms- Many plants have rametso Ramet: module capable of independent existenceo 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/growtho EX: spider plants Concept of individual does not apply Ramets grow and make more ramets Modular, not unitaryi. Population and biomass does not increaseo For modular organisms, biomass is the best measure of densityo Genet: group of genetically identical ramets (i.e. clones) Operates under natural selection with modulatory organisms Some animals (e.g. hydroids) are modularc. Biomass per unit area or volume3. Primary population parametersa. Natality—addition of individuals to a population by birthb. Mortality—loss of individuals from a population by deathc. Immigration—addition of individuals to a population by dispersald. Emigration—dispersal of individuals out of the populatione. Nx+1 = Nx + b – d + I – e  dN/dt = rN- N= number of individuals- X= time- B= births- D=deaths- I=immigrations- E=emigrations4. Measuring densitya. Absolute density- Quadrat methodso Establish a set of sampling plots (same size and shape)o Count individuals in each parto Calculate the mean number of individuals per sampling ploto Divide mean by area of one plot to get estimate of densityo Calculate variance of estimate to determine the precision/repeatability of estimateo Critical assumption: plots are representative of population as a whole- Line transectso Walk distance of known length and width; long quadrats- Aerial surveyso Fly a series of line transects EX: whales in ocean- Mark-recapture methodso Used for organized that are mobile; sampling across time rather than spaceo Capture, mark, and release a sample (M)o Recapture a sample (n)o Count number marked ® in recaptured sampleo 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 censusingo count all individuals in a populationo rarely used; hard to complete for large populations  EX: U.S. Censusb. Relative density (e.g. light trap)- Density expressed without respect to specific numeric values- Light trap—insects attracted to light and fall into a


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Pitt BIOSC 0370 - Population Parameters

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