DOI: 10.5061/dryad.50t6sq6
title: Data from: Experiments reveal limited top-down control of key herbivores in southern California kelp forests

description: Predator responses to gradients in prey density have important
 implications for population regulation and are a potential structuring
 force for subtidal marine communities, particularly on rocky reefs where
 herbivorous sea urchins can drive community state shifts. On rocky reefs
 in southern California where predatory sea otters have been extirpated,
 top-down control of sea urchins by alternative predators has been
 hypothesized but rarely tested experimentally. In laboratory feeding
 assays, predatory spiny lobsters (Panulirus interruptus) demonstrated a
 saturating functional response to urchin prey, whereby urchin proportional
 mortality was inversely density-dependent. In field experiments on rocky
 reefs near San Diego, CA, predators (primarily the labrid fish California
 sheephead, Semicossyphus pulcher) inflicted highly variable mortality on
 purple urchin (Strongylocentrotus purpuratus) prey across all density
 levels. However, at low to moderate densities commonly observed within
 kelp forests, purple urchin mortality increased to a peak at a density of
 ~11 m-2. Above that level, at densities typical of urchin barrens, purple
 urchin mortality was density-independent. When larger red urchins
 (Mesocentrotus franciscanus) were offered to predators simultaneously with
 purple urchins, mortality was density-independent. Underwater videography
 revealed a positive relationship between purple urchin density and both
 the number and richness of fish predators, but these correlations were not
 observed when red urchins were present. Our results demonstrate highly
 variable mortality rates across prey densities in this system and suggest
 that top-down control of urchins can occur only under limited
 circumstances. Our findings provide insight into the dynamics of alternate
 community states observed on rocky reefs.
description: ReadMe File describing
 all scripts and datasetsThis text file provides
 a description and some metadata for each of the datasets and analysis
 scripts associated with the paper: Experiments reveal limited top-down
 control of key herbivores in Southern California kelp forests by Dunn
 & Hovel in Ecology1
 DunnHovel_Scripts_Data_ReadMe.txtSpiny lobster functional response analysisFunctional response analysis for California spiny lobsters consuming purple and red sea urchinsFunctional_Response_Analysis_DunnHovel.RSpiny lobster functional response to purple urchinsCalifornia spiny lobsters consuming purple urchins in functional response experiments conducted in at San Diego State Coastal & Marine Institute Lab.LobsFuncRespData.txtSpiny lobster functional response to purple + red urchinsCal. spiny lobsters consuming purple and red urchins simultaneously, experiments conducted at SDSU Coastal & Marine Institute LabLobsFuncRespDataBoth2.txtSize-dependent mortality of urchins due to spiny lobster predationCalifornia spiny lobsters consuming purple urchins and purple + red urchins in functional response experiments. Size-dependent mortality analysis script.Functional_Response_SizeDependentMortality_DunnHovel.RPurple urchin size-dependent survivalPurple urchin survival data following spiny lobster functional response experiments. Used to test size-dependent mortality.Survival by TD Logistic Reg Data.txtPurple + red urchin size-dependent survivalPurple urchin survival data following spiny lobster functional response experiments. Used to test size-dependent mortality.Survival by TD Logistic Reg Data Both2.txtField experiment GLMM analyses of urchin mortalityGLMM analyses (binomial distribution) to test for density-dependent mortality of purple and purple + red sea urchins due to predation. Experiments conducted in Pt Loma and S. La Jolla kelp forests in 2014 and 2017.Field_Experiment_Binomial_Analyses_DunnHovel.RGLMM Binomial Analysis Data for Field ExperimentData from field experiment testing for density-dependent mortality of urchins using a GLMM (Binomial distribution)BinomialAnalysisData.txtField experiment, analysis to visualize urchin mortality with LOESSScript to use loess models to visualize urchin mortality patterns in field experiment, conducted in Pt Loma and S La Jolla kelp forests in 2014 and 2017Field_Experiment_LOESS_DunnHovel.RPurple urchin mortality data for use with LOESS scriptData from field experiment, use to visualize mortality patterns of purple urchins with LOESS modelsFieldDDdataPurpleAll.txtRed + Purple urchin mortality data for loess analysisData set to visualize red + purple urchin mortality patterns using LOESSFieldDDdataBoth.txtPredator aggregation and species richness analysesScript to analyze predator aggregation and species richness datasets from field experiment conducted in Pt Loma and S La Jolla in 2014 and 2017Predator_Video_Analysis_DunnHovel.RPredator video dataData set from video recordings of predators foraging in field experiment conducted in Pt Loma and S La Jolla kelp forests in 2014 and 2017PredVideoDataAll.txt