1. Multiple Season Study Design

2. 2 Recap All of the issues discussed with respect to single season designs are still pertinent.  why, what and how  how to define a ‘sampling unit’?  selecting sampling units  what is a ‘season’?  repeat surveys  avoiding heterogeneity  more units vs. more surveys per season? How to best survey units over time?

3. 3 Selecting sampling units An ‘unrepresentative’ sample of units could result in biased estimates of initial level of occupancy and trend. Avoid selecting units based upon knowledge of the occupancy status of sampling units.  e.g., surveying only places where the species was known to be historically.

4. 4 Selecting sampling units Seasons ψ

5. 5 Selecting sampling units Seasons ψ

6. 6 Selecting sampling units Seasons ψ

7. 7 Selecting sampling units Not so important if interest lies in the dynamic processes of colonization and extinction.  these are conditional on a unit’s occupancy status in the previous season.  although estimate of occupancy in first season may still be biased. Stratify units into known and unknown historic status.

8. 8 Selecting sampling units Are sampling units/habitat static? If not, selection should include areas of non-habitat as could possibly be habitat in future

9. 9 Time between seasons? A natural definition? What is the objective? Determines the timescale at which colonization and extinction probabilities relate to.  e.g., if units are surveyed in the same month each year, estimates are annual: can’t say anything about what may happen at 6 month intervals. in contrast to metapopulation ‘rescue effects’

10. 10 General designs 1. Survey the same units each season. 2. Survey different units each season (rotating panel design). 3. Hybrid design.

11. 11 General designs Simulation suggests all designs give similar results for trends in occupancy under simple situations.  key is number of units surveyed per season. In practice, rotating panel-type designs may introduce additional sources of variation that should be modeled.  spatial and temporal changes may be confounded.

12. 12 General designs Recommend that studies be designed such that the same units are surveyed each season.  unless monitoring is invasive and will result in the degradation of the units.

13. 13 Allocation of effort If focus on trend in occupancy, tradeoff between number of units and length of study.  short studies require surveying more units per season. How quickly is reliable information required?

14. 14 Allocation of effort SE logit (ψ trend) Seasons # Sites

15. 15 Allocation of effort What if interest lies in dynamic processes?  Precision determined by expected number of occupied/unoccupied units. If interested in overall occupancy each year (as state variable)?  Precision determined by total number of units surveyed each year.

16. 16 Investigating different designs: GENPRES Software Flexible: explore a wide variety of design options. Tailor to biological system of interest. Can be used to assess power to detect effects. Support material available (Bailey et al. 2007).

17. 17 General comments Drawing reliable conclusions about a system will always require some minimal level of information. The trick is to extract maximal information with minimal effort.  careful study design and up-front thinking. What is the cost of not having reliable information about a system?

18. 18 Summary Study objective is of overriding importance when considering:  selection of sampling units.  time between seasons.  general design.  allocation of effort.

19. Exercise 19 Compare the precision of occupancy estimates from a ‘Standard’ design vs, a ‘Rotating Panel’ design. Which design yields a more precise estimate of occupancy?  =.6,  =.2,  =.25, p=.25, Standard design Rotating Panel design Season Season sites 1 2 3 4 1 2 3 4 24 xx xx xx xx 12 xx xx xx xx 24 -- xx -- xx