Distance Sampling – Part I Ecological MethodologyLEC-02 Althoff

Distance Sampling (DS): In the beginning…… Earliest development of theory and application was by David R. Anderson (Colorado State U.) in the 1960s, Kenneth P. Burnham (Colorado State U.) in the 1970s, and J.L. Laake (National Marine Mammal Laboratory) in the 1970s. S.T. Buckland (University of St. Andrews) started making contributions in the early 1980s

DS: Estimate Density or Abundance of Biological Populations Two components: ______ and ______________ Must have some understanding of theory to properly design protocols for application in the field Authors of “Distance Sampling” contend that DS provides a way to obtain _______ estimates of density of objects under fairly _______ _________________ DS is an extension of plot or quadrat sampling

Plot & Quadrat Sampling Assume with this type of sampling that ___ ______ within sample plot are counted Often use line or point ___________ to accomplish Most common use of point transects and line transects has been in the assessment and monitoring of ______ ____________…. Point Intercept Line Intercept Quadrats …see next slides

Point-Intercept Establish starting point at random May pick random direction, go with contour, or parallel lines Straight line common m in length, 100 m typical Observations made every 1 m typical At each point, record either the canopy species or the basal species or both typically for plants

Point-Intercept Measures distance (length) of plant coverage along line Or, measure GAP between plants (estimate of bare ground) Gives estimate of coverage….improve ment over point- intercept method Line-Intercept

Point-Intercept Quadrats every 5 m 0.25 m 2 frame for forb frequency, and presence/absence 0.1 m 2 frame set inside 0.25 m2 frame for grass (graminoid) frequency Compared results to point-intercept method Line-Intercept Quadrats Prosser, C.W., K.M. Skinner, and K.K. Sedivec Comparison of 2 techniques for monitoring vegetation on military lands. Journal of Range Management 56:

DS….Objects of “interest” Typically vertebrate animals—including those that typically occur in clusters (i.e., flocks, schools, etc.). Can include _______________ animals and _______ Sometimes the surveyed objects can be ________________—including bird nests, burrows, dung piles (fecal pats), or dead animals

The range of applications has included…. Songbirds (both strip transect and point counts) (we will examine data sets) Seabirds Gamebirds Terrestrial mammals Marine mammals Fish Reptiles Plants (we will explore/attempt in the field)

Basic Measurements using Line Transect Surveys Know the length of the transect ( L ) If detect “object” _____________ to transect line, then record the sighting distance ( x ) from the line to the object If detect “object” ahead or behind you, then record the sighting distance ( r ) along with the sighting angle (  ) to allow analysis of perpendicular distance ( x ), calculated as x = r sin (  ). Key to note the distance and angle at the ___________________!!!

Transect line L A Point at which observer first detects object OBJECT x = perpendicular distance

 Transect line L A Point at which observer first detects object x = perpendicular distance r OBJECT

Brings us to 3 major assumptions of DS Objects directly ___________ (or point) are always detected (i.e., they are detected with probability 1, or g(0) =1) Objects are detected at their _____________, prior to any movement in response to the observer Distances (and angles where relevant) are measured ____________ (ungrouped data) or objects are correctly counted in the proper distance interval (grouped data) 1 2 3

Transect line L 1 ASSUMPTION

 Transect line L Point at which observer first detects object r x 2 ASSUMPTION OBJECT location when _____ detects you OBJECT location when ____ detect it

 Transect line L Point at which observer first detects object r 3 ASSUMPTION if measuring r and 

Transect line L OBJECT x = perpendicular distance 3 ASSUMPTION if measuring x

Some add a 4 th major assumption for DS Objects directly on the line (or point) are always detected (i.e., they are detected with probability 1, or g(0) =1) Objects are detected at their initial location, prior to any movement in response to the observer Distances (and angles where relevant) are measured accurately (ungrouped data) or objects are correctly counted in the proper distance interval (grouped data) One must be able to identify the “object of interest” ________

Some “tidbits”….relative to the _____ major assumption In __________ communities (or where two species are difficult to easily distinguish by appearance or vocalization), this assumption may be compromised. Ex. Songbirds If estimating male vs. female and there is no sexual dimorphism, then one might have to rely on behavioral cues for proper ID, this assumption may be compromised…or simply not be possible to use for estimating densities by sex Marine mammals that often occur in _______ ________ make it difficult to get species ID correct, therefore assumption may be difficult to meet

More on assumption 2 If ____ movements of object (i.e., animal) relative to speed of the observer, then simulations have indicated relatively small problems are encountered in the analysis and subsequent estimates of density If “responsive” (i.e., alarm response to either _____ _____ or _______ the observer) movements, then serious problems result in violation of theory of DS For point transects (aka point counts), __________ movement of animals is always problematic because the observer is stationary…mainly because a moving animal is more likely to be detected when close to the point. 2

Overall considerations relative to these 3 major assumptions of DS Careful attention must be given to _________ and ___________ to maximize likelihood of meeting these 3 assumptions Equally important, ___________ should have adequate a) ___________ b) ___________ According to Buckland et al. (2001) all of these assumptions can be relaxed under “certain” circumstances. ______________ can sometimes cause difficulty !!! (think asymmetry of detection capability)