Monitoring Approaches – Part III

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Ecological Methodology LEC-06 Althoff

Occupancy Estimation

• Fundamental goal: model detection (i.e., = detection probability) and occupancy ( )

• Recall: need ________ sampling efforts within the specified timeframe

• In ________ form, the data is collected by one individual, in one habitat type, under uniform weather conditions, with identical presence/influence of other species (plants or animals or both) from survey site to survey site, etc.

Occupancy Estimation….but when not “uniform” sampling/survey conditions:

• Observers can impact vary in their ability to detect the target species

• Weather conditions can alter one’s ability to detect species from site to site

• Habitat: structure and plant species composition can alter detection rates and occupancy

• Presence (or absence) of other animal species can alter detection rates and occupancy

How do we “__________” or “_______” our estimates (i.e., models of occupancy estimation when these

Conditions exists…because they will always exist….?

Accounting for / Adjusting for varying situations during surveys:

• Determine ___________________

• These are factors (i.e., effects) that help explain possible _____________ in the raw data--even if densities are equal between two areas.

• The covariate data can be “__________” to account for the influence of these factors to provide more reliable estimates of occupancy

Example: Mountain Plovers and Burrowing Owls

Tipton, H.C., V. J. Dreitz, and P.F. Doherty, Jr. 2008. Occupancy of mountain plover and burrowing owl inColorado. Journal of Wildlife Management 72(4):1001-1006.

• Mountain Plovers: Hypothesized the occupancy would be higher on prairie dog colony and dryland agricultural plots than on grassland plots

• Burrowing Owls: Hypothesized the occupancy would be higher on active prairie dog colony and non-active plots and grassland and dryland agricultural plots

Field Method

• Selected plots using an ArcGIS design called spatially balanced sampling (SBS).

• Surveyed 282 plots: 90 in prairie dog colonies92 in dryland agriculture

100 in grasslands• Each plot was 500m x 500m • Each plot was surveyed 2-4 times each (most

surveyed). The model used for occupancy accommodates unequal number of surveys

• Used visual and auditory cues

500 m

125 m 125 m

500

m

Begin survey

Plotlayout

& travel path for

observers

125

m

“Suspected” covariate (i.e., factor)

• ____________ was a factor that would affect detectability of each species:prairie dog colony

vs. grassland

vs. dryland agriculture

MOUNTAIN PLOVER

BURROWINGOWL

Prairie dog colony

Yes…other “factors” matter in occupancy estimation, so adjust accordingly

• In this study, habitat type mattered• Higher probability of occupancy for burrowing

owls on active vs. inactive prairie dog towns…and both were higher than grassland or dryland ag sites

• For mountain plovers, prairie dog towns (active or inactive) had higher probability of occupancy than dryland ag sites, which had slightly higher than grassland sites.

• Important info for _________ monitoring protocols and “________” occupancy estimation models !!

Sampling Schemes

• _________________: incorporating a random, stratified, and/or systematic sampling design to avoid bias

• ________________ design….cannot with good conscience come up with estimate of precision because __________-based assumptions are usually violated

vs.

Probability-based designs (survey “points” = )

• Random

• Stratified

• Systematic

Convenience sampling design (survey “points”= )

• _______ roads, trails, contours of a hill or mountain, etc.

• Assumes that what is “near” these easy-to-travel routes (i.e., transects?) is the _______ throughout the survey site

Bottomline….• The past….most sampling efforts were based on

“convenience”-based designs. Still used today for various reasons (cheaper, match long-term data sets, etc.) but require _____________________ about how precise the resulting estimates and/or indices are

• The future….more and more sampling efforts will be based on probability-based designs because they minimize biased estimates and allow for statistical analysis—usually without violation of major assumptions– to make ____________________ __________. For occupancy estimates that would be