Population dynamics across multiple sites

2. Population dynamics across multiple sites

3. Multiple populations • How many populations are needed to ensure a high probability of survival for a species? • To what extent should multiple populations be clumped together in space versus spread apart? • Can small populations or those occupying sites with low habitat quality substantially add to the regional viability of a species?

4. Terminology • Site: a discrete piece of habitat that has some potential of maintaining a population of the species of interest. Separated Juxtaposed

5. Terminology • Population: the group of individuals living on a site • While the individuals across all sites will be called the Total or multi-site population

6. Terminology • Metapopulation: sets of discrete, largely (but not entirely) independent populations whose dynamics are driven by local extinction and recolonization via movement from other populations (Levin 1969)

7. Data needs • Modeling the operation of a set of populations requires all the information to do a good job of a single-population PVA for each site, plus data on movement rates between populations, plus estimates of how temporal fluctuations in population processes are correlated between population

8. Characteristics of plant PVAs (n=90) Modified from Menges 2000, TREE 15: 51-56

9. Requirement 1: • Site specific Population dynamics. • Information about the quality of the population • But how likely is that for every population of an endangered species, many years of census data, let alone estimates of all vital rates, will be available?

10. Common approaches: • Assume that population growth rates or vital rates are identical at all sites, but carrying capacities differ among sites. • Assume that most demographic rates are identical across sites, but to allow a handful of rates, about which more information is available to differ.

11. Cowbird parasitism

12. Requirement 2: • The importance of correlations. • Through “safety in numbers” multiple populations can strikingly decrease the risk of total extinction of a species. • However, this benefit critically relies on a lack of correlation in the dynamics, and hence risks of extinction, of the different populations

13. Hypericum cumulicola

14. The California clapper rail

15. The California clapper rail 0.06*0.79*0.72=0.034 Harding et al. 2001

16. Pearson correlation coefficients

17. Among sites Pearson correlation coefficients of H. cumulicola vegetative-small adult transition (TSF>15 years)

18. Correlations in population growth rates

19. Correlations in population growth rates

20. Joint-rank correlations for Delphinium uliginosum patch level data

21. The Lake Wales Ridge World distribution ofHypericum cumulicola Archbold

22. Patch level: Archbold Biological Station 110 Rosemary scrub patches Patch 45 H. cumulicola occupancy = 58 %

23. occupied unoccupied Large-Aggregated = 84 % Large-Isolated = 57 % Small-Aggregated = 52 % Small-Isolated = 41 % Hypericum cumulicolaoccupancy related to patch size and patch isolation (p<0.001) Quintana-Ascencio & Menges. (1996)

24. Fire intensity and location in burn unit 58 E, 1967, 1968, 1976 and 1980

25. Requirement 3: • The importance of movement. • If movement rates are quite high, then multiple sites do not truly harbor multiple populations, but instead a single one that utilizes a dispersed set of habitat patches. • If movement occurs at low rates, it may nevertheless play an important role in supporting multi-site viability by allowing rescue of populations

26. How to quantify movement? • Capture-recapture analysis

27. Capture-recapture methods • use resighting data to estimate the actual numbers of individuals in each class including those not directly seen • To accomplish this, you must not only count and relocate the marked animals, but also estimate the number of unmarked animals in each site

28. Fitting functions Fitted Dispersal Observed

29. A classification of multi-site scenarios