Ecology Lab Week 1 Population Estimation

Ecology Lab Population Estimation (Week 1)

1Population EstimationPURPOSE: To compare the three different population estimation methodsEnumerationMark/RecaptureDepletion

HYPOTHESES: Null (H0): Enumeration = Mark/Recap = DepletionAlternative (HA): Enumeration Mark/Recap Depletion 2Method 1: EnumerationP = sum of all individualsMINIMUM estimation

AssumptionsAll individuals are capturedRemoval of individuals did not attract others into study area (vacuum effect)No births or deaths during the study3Method 2: Mark/Recapture P = M x C R

M : # collected and marked during first sampleC : # collected during second week sampleR : # marked in the second sample

Assumptions:All individuals are equally likely to be caughtMarked individuals are randomly dispersedMarked individuals must not become easier or more difficult to catch than unmarked individuals.No births, deaths, or migration

4Method 3: DepletionCollect and remove Collect and removeCollect and remove

(a constant fraction of the remaining population is taken with each sample)

Apply a trendline and predict total population

P = where the trendline crosses the x-axis

AssumptionsNo births, deaths, or migrationProbability of capture does not changeProbability of capture is the same for each individual5Method 3: DepletionCollect and remove

Collect and remove

Collect and remove8/205/123/7= 0.40= 0.41= 0.426Depletion GraphX-axis: # snails collected so farY-axis: #of snails collected in current sample

* Where trendline crossed X-axis is your population estimate!Total # harvested todayTotal # harvested previous1009108197277346415477Why are we using snails?Yellow elimia (Elimia flava)

Small home rangefew square meters

Pop sizes stablelive for several years

Easy to catch and mark

Abundant unless Eco lab has been collecting them all week

8Snail Sampling Method200 collection minutes5 groups of 4 10 min eachVolunteer group of 4 to go twice

ProcessCollect snailsDry snailsMark all snails with paint pen (on bottom of the shell!)Bring all snails back to lab

Last lab of the week will release ALL the snails collected all week.

9Creek CharacteristicsMeasure:

Air temp

Water temp

Water clarity (can you see the bottom?)

Depth using meter stick at designated place

Velocitymeter stick and leaf in designated place

10Same as week 1 except: No marking snails

Keep track of:# marked (and what color)# unmarked

200 minutes of search time outside study area (to test for emigration):10 people search upstream for 10 minutes10 people search downstream for 10 minutes

Bring all snails from study plot back to lab (but only the marked migrants!) for Friday release!Week Two MethodsCreek CharacteristicsMeasure (Again):

Air temp

Water temp

Water clarity (can you see the bottom?)

Depth using meter stick at designated place

Velocitymeter stick and leaf in designated place

13Ecology Lab Population Estimation (Week 3)14PURPOSE: To compare the three different population estimation methodsEnumerationMark/RecaptureDepletion

HYPOTHESES: Null (H0): Enumeration = Mark/Recap = DepletionAlternative (HA): Enumeration Mark/Recap Depletion Review: Population Estimation15Can be an indicator of:species healthhabitat qualityecosystem or community health

If done repeatedly over time, changes in population and its surroundings can be trackedespecially threatened/endangered species

Used in management decisionsHunting/fishing licensesHow areas are used in state/national parksWhy estimate population size?How is this tool valuble?Method 1: EnumerationP = sum of all individualsMINIMUM estimation

AssumptionsAll individuals are capturedRemoval of individuals did not attract others into study area (vacuum effect)No births or deaths during the study17Method 2: Mark/Recapture P = M x C R

M : # collected and marked during first sampleC : # collected during second week sampleR : # marked in the second sample

Assumptions:All individuals are equally likely to be caughtMarked individuals are randomly dispersedMarked individuals must not become easier or more difficult to catch than unmarked individuals.No births, deaths, or migration

18Method 3: DepletionCollect and remove Collect and removeCollect and remove

(a constant fraction of the remaining population is taken with each sample)

Apply a trendline and predict total population

P = where the trendline crosses the x-axis

AssumptionsNo births, deaths, or migrationProbability of capture does not changeProbability of capture is the same for each individual19Depletion Graph* Where trendline crossed X-axis is your population estimate!Total # harvested todayTotal # harvested previous10091081972773464154720