2 Flashcards
(37 cards)
Define Catchability
the rate at which the trap catches animals which is the slope
Data required for Leslie plot
Catch data and effort to calculate CPUE. accumulated catch
What baggage comes with a Leslie plot?
On top of the assumptions of a leslie plot, it is a parametric test so it comes with the parametric assumptions
Leslie assumptions
- closed population
- all animals have the same probability of being caught
- all animals can be harvested to the point of extinction
parametric assumptions
- random sampling
- independence
- homoscedasticity
- normal distribution
- no bias
problems with aerial survey
it uses relative density to estimate the population density which consistently over and under estimates
Factors that contribute to relative density
- counting error - observer over counts some samples and under counts other. cancel each other out.
counting bias: observer consistently under counts and bias increases when there are lots of animals and must be counted quickly
low precision: can be improved with stratification and high replication
types of aerial surveys
transect, quadrat, and block
transect sampling
perpendicular lines to a baseline are flown with one pass per transect
quadrat sampling
the census area has a grid superimposed onto it and quadrats are randomly chosen. incomplete quadrats cannot be chosen.
block sampling
blocks are defined the topographic features and then randomly chosen.
what is 2R(sum)xz used for?
it is used to lower the variance. z is the area of the transect multiplied by the # of animals on the transect.
Interpret 2R(sum)xz
if you add more transect lines (z) and there are zero animals in these lines then the variance will remain high. if there are a large number of animals on the transects then the variance will come down
what does summing the inverse of sighting distances do?
by taking the inverse of the sighting distances; it will cause the longer (less accurate) distance to be less of an influence, while the shorter (more accurate) distances to have more of an influence and can lower the overall variance
assumptions of the haynes estimator of density
- all animals directly on the transect line are seen
- all animals are fixed at the initial sighting position and are not counted twice
- distances and angles are measured exactly
- sighting of individuals are independent events
- critical assumption: the average sighting angle is 32.7
state the Ho and what is the critical assumption used for?
Ho: the average sighting angle is no different than 32.7. reject if outside +1.96 and -1.96. We use the critical assumption to decide whether or not the haynes estimator is a appropriate estimator
What is f hat?
it is the estimated population density function for the detection of an animal. It is the perpendicular distance from the transect line
what is g hat?
it is the probability of detection function for the detection of an animal. i.e seeing animal directly on the transect line
what is the edge effect?
the more edges there are the more decisions must be made to whether an organism is inside or out of the quadrat
which order does the shape of the quadrat go?
circle>square>rectangle
what does nested quadrat sampling do that is so important?
it takes into account the ecological scale of the organism/habitat in order to determine the minimal sample area size
defined quadrat sizes
trees - 10x20
shrubs - 5x5
herbs - 1x1
lichens and moses - 0.1x0.1
how does the nested quadrat system work with the sample area curve?
it determines the minimum area of a quadrat by starting out with the smallest size quadrat and counting the organisms then doubling the size until no more new organisms are found. this is when the sample are curve plateaus
what problem can occur with the nested quadrat sampling?
if a species is counted only in the first quadrat and nowhere else
