Mae Rennick*, Bartholomew DiFiore*, Joseph Curtis, Daniel Reed, and Adrian Stier
* Equal contributors
This repository houses code and data related to [Rennick et al. 20XX](insert link to published manuscript here)
The biomass of primary producers is ultimately determined by the rate at which they grow and how quickly they die or are eaten. In some instances, consumers disturb communities, dramatically reducing primary producer biomass and driving communities towards alternative ecosystem states. Yet the mechanisms behind consumer-driven disturbances remain unclear. Here, we tested how changes in the biomass and foraging habits of an important group of marine herbivores— sea urchins— triggers disturbance to a foundation species— giant kelp (Macrocystis pyrifera)— on temperate rocky reefs. Specifically, we demonstrated that urchin foraging rates increased linearly with urchin biomass in mesocosm foraging trials. We applied these results to 21 years of spatially explicit observational data on kelp community dynamics to test the long-standing hypothesis that deforestation of kelp communities occurs when the consumptive capacity of urchin populations exceeds the production of kelp detritus. We found a 50-fold reduction in giant kelp biomass when the consumptive capacity of sea urchins exceeded detrital production. Furthermore, the annual change in kelp biomass was dissociated from urchin biomass when detrital kelp was plentiful but as detrital supply became more limited, the annual change in kelp became increasingly negative. Our results suggest that the balance between detrital production and the consumptive capacity of sea urchins is critical to predicting when and where consumers are likely to force state transitions in kelp forest ecosystems.
This repo is maintained by Bart DiFiore (GitHub: @bartdifiore) and Mae Rennick (Github: @maerennick) at the University of California, Santa Barbara in the Department of Ecology, Evolution, & Marine Biology. For questions or inquires please contact bdifiore@ucsb.edu or maerennick@ucsb.edu.
| File | Description |
|---|---|
| 1_biomasshistograms.R | Script assessing historical variation in the biomass (g m2) or uchins based on Santa Barbara Coastal Long-term Ecological Research (SBC-LTER) data. |
| 2_density_analysis.R | Script to analyze mescosm foraging trials in which we manipuated the biomass (g m2) of sea urchin consumers. |
| 3_spatio_temporal.R | Core portion of the analysis to analyze spatiotemporal trends in the consumptive capacity of urchin populations, detrial supply, and standing kelp biomass. |
| 4_maps.R | Script to build the map used in the publication. |
| S1_Appendix_sizeanalysis.R | Code to analyze mesocosm foraging trials in which we manipuated the size of sea urchin consumers. |
| S1_Appendix_sizecomparison.R | Code comparing the size-frequency distribution of urchins used in foraging trials with the population of urchins observed at local sites. |
| S2_Appendix_detrialsupply.R | Code to examine trends in detrial production. |
| Functions.R | Misc. functions for model validation. |