Flashcards in Lecture 5 Estimating population Size Deck (22)
What are the four measures of abundance?
Present/ Not detected
What is present / not detected measurement?
Whether or not a species is present in a given area. but conveys little useful information.
What is relative abundance measurement?
The number or proportion of individuals without specifying the size of the sampling area
ex. 7% cover of blackberry
What is Density abundance measurement?
The number of individuals per unit area or volume
What is total abundance measurement?
The total number of individuals in a specified area`
What is accuracy?
How close an estimate is to the ACTUAL value. accuracy is reduced by bias which ususally results from systemic errors in the measuring procedure or flaws in study design
What is precision?
How close measured values are to eachother. precision is affected by random errors, like poor measuring instruments
What are some examples of Bias?
Weather bias- greater accuracy is acheived by conducting surveys in standardized conditions
Season Bias- visibility of species varies by season
Observer Bias- results vary by observer. greater accuracy is achieved by calibrating observers in smaller groups
What characteristics of organisms may cause you to adjust your survey place and time?
-timing of reproduction/ death
what usually ends up being the main controling factor os surveys?
What are the 4 general approaches to estimating population size?
1. Complete Count
3. Indirect Counts
4. Mark-Recapture Methods.
What are Complete Count methods?
Entails counting every member of a population, yielding estimates of density or total abundance.
-Feasible with highly visible species that are aggregated together.
-usually expensive, impractical or impossible.
-may be needed for endangered/ sensitive species
What are incomplete Counts?
Counting part of the population, and then extrapolating those counts to the entire population.
- counting individuals within sampling units
-plots, quadrats and transects
What are 3 conditions which sampling unit type is dependant on?
1. Size of sampling unit should increase as abundance of target variable decreases
2. rectangular quadrats are more efficient at sampling items when there are clumped distributions
3. Transects are more efficient and convenient when sampling along linear features.
What are 3 main types of transect?
1. Encounter-- Used for presence/not detected. Transect along which the target variable is counted continuously or at fixed points
2. Strip-- Transect along which the target variable is counted within a fixed distance from the center
3. Line-- Individuals observed at any distance are counted, together with an estimate fo thier distance from the transect.
What are the benefits of Line transects that include the distances from the observers path of travel?
Determines detection functions, helps account for variation in detectability due to distance, observer, weather and other potential biases. Improves accuracy of density estimates
What are indirect counts?
Surveying indirect signs of animal presence: Scat, burrows, dens, nests, browsing patters, tracks.
-do not provide actual estimates of abundance.
-these indicies observered can be useful in assessing relative differences in abundance of a target variable amoung sites or time periods
What are Mark-Recapture methods
CApturing a number of animals, marking them, returnign them to that population, and then using the proportion of marked individuals in subsequent capture efforsts as a basis for estimating pop size.
What are other names for mark-recapture?
CApture-recapture, capture-mark-recapture, sight-resight, mark-release-capture, band recovery
What principle is mark recapture based on?
Proportion of animals marked in the total pop is the same as the proportion of animals marked in any subsequent capture effort
What is the derived formula for population size?