Effects of Temporal variability of two ecological processes

Transcript

1. Javier Atalah Supervisors : Dr. Mark Costello Dr. Marti Anderson Effect of temporal variability of two ecological processes on benthic communities
2. Overview  Introduction  Factors affecting diversity  Role of temporal variability  Physical disturbance experiment  Grazing experiment  Summary
3. Introduction  Nature is variable in  Time  space.  Variation in  population abundance  Species composition  Factors causing variation (e.g. predation, disturbance)  Understanding such variations is a primary objective of ecology
4. An external force which results in loss of biomass (Grime 1977) o Physical: storms o Biological: grazing, predation. o Anthropogenic: fishing, tramping Disturbance Diversity
5. Area Intensity Frequency Temporal spacing of the events have been ignored! Many experiments have been focused on the effect of disturbance regimes
6. Temporal occurrence A larva A competent After succession Temporal occurrence B Larva B competent After succession
7. Objective  To test the effects of the temporal variability of disturbance on the diversity of macrobenthic assemblages
8. Methods  PVC panels (15x15 cm) were used as settlement substrata.  90 d maturing phase  150 d experimental phase
9. Study sites Ti Point
10. . . . . Chile Brasil Australia New Zealand . Kiel
11. Experimental design  Multi-factorial ANOVA :  Temporal variability: constant, low and high  Sequence: nested in low and high levels  Block: five rings at each sites  Response variables:  Species richness, multivariate data, taxa cover.  Analysis: PERMANOVA
12. Disturbance regimes Variability Sequence constant 1 1 2 3 1 2 3 Time low high Frequency = 10 events/150 d Mean time interval = 1 event/15 days Constant sd = 0 Low sd = 5.77 High sd = 16.33
13. Disturbance event  Complete removal of 20% of the community  Random position
14. Sampling  Visual estimation of percentage cover of each taxa  3 sampling dates: day 0, 75 and 150.
15. Results: Community composition Leigh Harbour Ti Point Green algae 3 4 Brown algae 3 5 Red algae 4 5 Sponges 0 2 Cnidarians 2 2 Polychaetes 3 3 Crusteceas 4 4 Bryozoans 3 4 Ascidians 1 2 Total 23 31
16. Number of taxa 0 2 4 6 8 10 12 14 Leigh Harbour TiPoint Constant Low High Undisturbed Levels of variability
17. Taxa % cover Constant Low High Undisturbed 0 20 40 60 80 100 Biofilm Ulvella sp. Ralfsia verrucosa Crustose coralline Balanus trigonus
18. Community structure Stress=0.14 Constant Low High Undisturbed
19. Time Abundance μconst = μvariable σ2 const << σ2 variable Temporal heterogeneity of disturbance may increase abundance fluctuations over time Sampling μoverall constant Variable
20. 2nd Experiment: Variable grazing  Effect of intensity and temporal variability of grazing on macroalgae assemblages  Communities were exposed to regimes of grazing by the gastropod Cantharidus purpureus
21. Methods  Caging experiment  Weekly sampling
22. Experimental design Low Constant G G G G G G G Variable 2G 2G 2G 2G High Constant 2G 2G 2G 2G 2G 2G 2G Variable 4G 4G 4G 4G Week 0 1 2 3 4 5 6
23. 0 40 80 120 160 0 1 2 3 4 5 6 Week Cover (%) High-Constant High-Variable Low-Constant Low-Variable Undisturbed Percentage cover by treatment
24. 0 200 400 600 800 1000 1200 Temporal variance HC HV LC LV Undisturbed Effect on the temporal variance of cover
25. Stress = 0.05 Community structure Undisturbed Constant Variable
26. Summary  Experimental design was novel in assessing the effect of temporal variability in disturbance  No consistent effect of variability of physical disturbance  Variable grazing regimes did change community structure  Reduce percentage cover  Increase temporal variance
27. Acknowledgments  Saskia Otto  Leigh Marine Lab staff  IFM – GEOMAR, University of Kiel  All researcher from GAME network  NZODA Study Awards scholarship  Foundation Mercator