3 What is a Population?Population: a group consisting of members of the same species that live together in a certain area at the same timePopulations live in a particular habitat, that provides them with the resources they needCommunity: consists of all populations of all species that live and interact in the same areaEcosystem: A community plus it’s abiotic environmentPopulation Dynamics: the study of changes in populations
4 TerminologyBrainstorm with your lab partner to define the following terms in your own words AND provide an example.Population size (N)The number of individuals of the same species living within a specific geographical area.Population density (Dp)Number of individuals of the same species that occur per unit of area or volume.Think-Pair-Share
5 How many daisies in the field? You have 15 seconds…78
6 How many did you count? How did you estimate the number of daisies? Did you try to count them all?Or did you use another method?We need a quantitative estimate for the number of daisies – it doesn’t have to be perfect but it should be as close as possible to the real number.Write your first estimate down, then try again, seeing if this will help…
8 Is your estimate the same? How did you use the grid to estimate the number of daisies? Did it help?There are 78 daisiesIf you were asked to count the number of daisies in the school field, it would be impractical to count each one.How could you use the grid method to get an accurate, reproducible estimate? Make a rough plan.Use your plan to make an estimate for the next field:
10 How many daisies were there? There were 103 daisies in the field. How close were you?Your plan should have involved the following steps:Select at least three quadrats and count how many daisies are in each (eg 4, 8, 3)Add them to get a total and divide by the number of samples to find the mean number of daisies per quadrat ( = /3 = 5 daisies per quadrat)Multiply the mean by the number of quadrats that would fit into the field to get your estimated total number of daisies. (5 x 20 = 100 daisies estimated in the field)
12 Characteristics of Populations – Population Density Who cares how big or dense a population is?The density of a population can be related to how healthy the population is. We will talk about this and what influences population size/density in more detail later.....
13 measuring Population Size and Density How do we determine the human population?Can we use the same methods with other species? Why or why not?Instead of counting individuals in a populations inefficiently, ecologists estimate population size by studying smaller samples extrapolation3 methods:TransectsQuadratsMark-Recapture
14 TransectsTransect – a long line or narrow area used for population samplingResearchers choose a line of specific length (i.e. 100m)Walk along the line and count number of individuals of each species being monitored within the areaFor sessile organisms – within 1mMobile organisms – within 50mExample:
15 Transects Useful for: low population densities or larger organisms like trees
16 Quadrats Quadrat – a box used to sample a population Location is chosen at randomQuadrat is drawn area can be large or small depending on size of species under study (A)Number of individuals are counted within quadrat boundaries (N)
17 QuadratsInformation can be used to calculate population density:DP = N/ASample Problem:Ecologists are sampling the distribution of flowering white trillium plants in a section of forest covering 100m x 100m (so what is the area)?They place four 1m by 1m quadrats randomlyThey find 5, 4, 3, and 1 individuals in the four quadratsCalculate the population density
18 QuadratsThe calculated population density can be used to determine the estimated population size Estimated Population Size = DP x total study area What is the estimated population of trilliums?
19 QuadratsWhat type of species do you think this method would be most useful for?Useful for:Sessile organisms orOrganisms with low motility
20 Mark-Recapture Population size (N) = Animals are capturedThen, marked with a tag/collar/bandReleased back into their habitatRecaptured at later time (days/weeks) Watch this captureData is used to estimate the population size according to the following formula:Population size (N) =M (number originally marked) x n (total individuals in recapture)/m (marked individuals in recapture)
21 Mark-Recapture Sample Problem 1 A group of researchers captured 20 warblers, which were marked with leg bands. They were released soon after. One week later, 50 warblers were captured. Of the 50 birds, 10 had bands on them. What would be their estimated population size?
22 Mark-RecaptureWhat type of species do you think this method would be most useful for? Useful for: Highly mobile populations
23 Population Dispersion Dispersion:The population dispersion for a species is the pattern in which individuals in a population are distributed or spaced throughout an area.Often related to densityClumped Dispersion: occurs when individuals are concentrated in specific parts of the habitatOften due to patchy resource distributionMay be social benefits ie. schooling fish
24 Population Dispersion Uniform Dispersion: Individuals are spaced evenly throughout the habitatOften due to intense competition. Eg. Nesting, feeding or mating territoriality, toxins released by plant roots
25 Population Dispersion Random Dispersion: The population is spread out in an unpredictable manner that is unrelated to the presence of othersLeast common and hardest to observeResources are not often distributed randomly
27 Hold up! Dispersal patterns Resource distribution is uniformResource distribution is clumpedResource abundance variesResource abundance is scarceResource abundance is abundantInteraction between members of a population is positiveInteraction between members of a population is negativeInteraction between members of a population is random.Answers:Random or uniformClumpedUniformRandomrandom