DOI: 10.5061/dryad.59zw3r261
title: Archive data for: Loss of predation risk from apex predators can exacerbate marine tropicalization caused by extreme climatic events

description: 1. Extreme climatic events (ECEs) and predator removal represent some of
 the most widespread stressors to ecosystems. Though species interactions
 can alter ecological effects of climate change (and vice versa), it is
 less understood whether, when, and how predator removal can interact with
 ECEs to exacerbate their effects.  Understanding the
 circumstances under which such interactions might occur is critical
 because predator loss is widespread and ECEs can generate rapid phase
 shifts in ecosystems which can ultimately lead to tropicalization. 2. Our
 goal was to determine whether loss of predation risk may be an important
 mechanism governing ecosystem responses to extreme events, and whether the
 effects of such events, such as tropicalization, can occur even when
 species range shifts do not.  Specifically, our goal was to
 experimentally simulate loss of an apex predator, the tiger shark
 (Galeocerdo cuvier) effects on a recently damaged seagrass ecosystem of
 Shark Bay, Australia by applying documented changes to risk sensitive
 grazing of dugong (Dugong dugon) herbivores.  3. Using a 16-month
 field experiment established in recently disturbed seagrass meadows, we
 used previous estimates of risk-sensitive dugong foraging behavior to
 simulate altered risk-sensitive foraging densities and strategies of
 dugongs consistent with apex predator loss, and tracked seagrass responses
 to the simulated grazing. 4. Grazing treatments targeted and removed
 tropical seagrasses, which declined. However, like in other mixed-bed
 habitats where dugongs forage, treatments also incidentally accelerated
 temperate seagrass losses, revealing that herbivore behavioral changes in
 response to predator loss can exacerbate ECE effects and promote
 tropicalization, even without range expansions or introductions of novel
 species.  5. Our results suggest that changes to herbivore
 behaviors triggered by loss of predation risk can undermine ecological
 resilience to ECEs, particularly where long lived herbivores are
 abundant.  By implication, ongoing losses of apex predators may
 combine with increasingly frequent ECEs to amplify climate change impacts
 across diverse ecosystems and large spatial scales.
description: This dataset was collected over 16 months from 2013-2014 in
 degraded seagrass beds of Shark Bay, Western Australia.  Each row refers
 to a visit to an experimental plot, each measuring 3x3m and consisting of
 three main macrophyte types: the seagrasses <em>Amphibolis
 antarctica </em>and <em>Halodule uninervis </em>as well
 as benthic macroalgae.  At each plot, percent cover was assessed via diver
 by using a single 60 cm quadrat overlaid on the plot in a 5 x 5 pattern to
 cover the entire plot.  Because each quadrat measurement is strongly
 correlated in space to others within the same plot, the percent cover
 across all 25 quadrats was averaged to generate a single percent cover
 value for each macrophye group in the plot. As such, each row contains the
 average percent cover in that plot for that time point.  Later columns
 also group the data collected in a specific month by treatment group, and
 by treatment x bank subgroup.  The data are otherwise unprocessed; full
 details can be found in the methods of the manuscript.  There is also a
 column key on the second sheet.
description: There are some missing values in the dataset at experiment start
 for benthic macroalgae, which were initially not measured because their
 cover was negligible.  Soon after experimental establishment, however,
 algae measurement began upon realizing that algae may exhibit strong
 seasonal cover effects and may be important later in the experiment.
 Likewise, plots that were destroyed by time a visit occured were not
 measured from that time point onward; one plot was removed entirely
 because it was destroyed too early in the experiment to warrant inclusion
 in the datset as a whole.