Presentation given in April 2010 at Willamette University.

1. Expansion and Decline of Southern California Populations of Yucca Brevifolia (Agavaceae) Jeffrey Collins and Chris Smith

2. Global climate change From Climate Change Art

3. Global climate change Organisms that can neither migrate nor adapt will go extinct.

4. Mojave community

5. Mojave community

6. Mojave community

7. Mojave community

8. Mojave community

9. Mojave community

10. Mojave community

11. Ecological niche modeling After Dole et al., 2003

12. Research questions Do some Joshua tree populations show signs of population decline? Does population decline correlate with any environmental variables?

13. Demographic structure

14. Survey methods 9 study sites Elevation Predicted fate Previous observations

15. Survey methods 9 study sites Demographic survey 2-3 transects per site 50 m wide 50 trees

16. Survey methods 9 study sites Demographic survey 2-3 transects per site Surveyed each tree Number of branches Number of inflorescences Location (via GPS) Height

17. Survey methods 9 study sites Demographic survey 2-3 transects per site Surveyed each tree Tissue samples ≥10 trees per site Labeled Frozen

18. Survey methods 9 study sites Demographic survey Genotyping 13 polymorphic microsatellite loci Genotyped using PCR multiplexes

19. Demography Size classes Height Number of branches

20. Demography Size classes Stepwise Linear regression DV: Median size class IVs: Environmental normals February Precipitation Annual Precipitation July max temperature Elevation

21. February precipitation vs. size class

22. Population genetics 7 polymorphic microsatellite loci Wilcoxan sign rank test Null hypothesis: no genetic bottleneck has occurred Calculates distribution of Hexp based on n and k

23. Population genetics p2 + 2pq + q2 = 1

24. Population genetics 7 polymorphic microsatellite loci Wilcoxan sign rank test Null hypothesis: no genetic bottleneck has occurred Calculates distribution of Hexp based on n and k Compares He to the distribution of Hexp If He < Hexp, reject the null hypothesis

25. Population genetics

26. Conclusions Evidence for current population decline Correlates with precipitation

27. Conclusions Evidence for current population decline No evidence of genetic bottlenecks Possible explanations: No bottlenecks Low sample size Low power of Wilcoxan sign rank test

28. Conclusions Evidence for current population decline No evidence of population bottlenecks Further work Further genetic analysis Analysis of population structure MSVAR Other methods of classifying age distributions Leslie matrices