Do Behavioral Foraging Responses of Prey to Predators Function Similarly in Restored and Pristine Foodwebs?

Efforts to restore top predators in human-altered systems raise the question of whether rebounds in predator populations are sufficient to restore pristine foodweb dynamics. Ocean ecosystems provide an ideal system to test this question. Removal of fishing in marine reserves often reverses declines in predator densities and size. However, whether this leads to restoration of key functional characteristics of foodwebs, especially prey foraging behavior, is unclear. The question of whether restored and pristine foodwebs function similarly is nonetheless critically important for management and restoration efforts. We explored this question in light of one important determinant of ecosystem function and structure – herbivorous prey foraging behavior. We compared these responses for two functionally distinct herbivorous prey fishes (the damselfish Plectroglyphidodon dickii and the parrotfish Chlorurus sordidus) within pairs of coral reefs in pristine and restored ecosystems in two regions of these species' biogeographic ranges, allowing us to quantify the magnitude and temporal scale of this key ecosystem variable's recovery. We demonstrate that restoration of top predator abundances also restored prey foraging excursion behaviors to a condition closely resembling those of a pristine ecosystem. Increased understanding of behavioral aspects of ecosystem change will greatly improve our ability to predict the cascading consequences of conservation tools aimed at ecological restoration, such as marine reserves

Measurement of the cosmic ray spectrum above 4×10184{\times}10^{18} eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$ eV, the "ankle", the flux can be described by a power law $E^{-\gamma}$ with index $\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by a smooth suppression region. For the energy ($E_\text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$ eV.Comment: Replaced with published version. Added journal reference and DO

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI. Supplemental material in the ancillary file

Differences in prey (<i>P. dickii</i>) movement in relation to differences in piscivorous fishes encountered between reef pairs.

<p>Points (±SE) represent differences in both independent and dependent variables between paired reefs in each of the four regions included in the study. Note that differences were calculated as unfished - fished reef values for x-axis (predation risk) and fished - unfished reef values for y-axis (prey behavior) for the reason outlined in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032390#s4" target="_blank"><i>Materials and Methods</i></a> above.</p

Prey excursion size in relation to protection status.

<p>Upper panel (a) is bullethead parrotfish (<i>C. sordidus</i>); lower panel (b) is blackbar damselfish (<i>P. dickii</i>). Points are means (±SE).</p

Prey excursion size and rate of movement in relation to acute predation risk for <i>C. sordidus</i> and <i>P. dickii</i>.

<p>Left-hand panels (a, c) show data from the Eastern Indo-Pacific (Line Islands); right-hand panels (b, d) are from the Central Indo-Pacific (GBR). Lines show best-fit upper 95% prediction intervals (dashed) and linear regressions (solid) based on a negative log-likelihood optimization function. Points are values for individual prey where predation risk is measured by predator biomass for <i>C. sordidus</i> and predator (biomass×duration) for <i>P. dickii</i>. Eastern Indo-Pacific (right-hand) panels are reproduced with permission from Madin et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032390#pone.0032390-Madin1" target="_blank">[13]</a>.</p

History of fishing pressure on reef fishes for reef pairs used in this study.

<p>X-axis indicates reef pair. Y-axis indicates the amount of time elapsed since either onset (Line Islands) or cessation (GBR) of fishing in each of the reef pairs, in years. Negative values therefore represent the length of time that the Eastern Indo-Pacific (Line Islands) fished site has been exploited (i.e., indicated as “decline” by dashed arrow on right-hand y-axis), whereas positive values represent time since cessation of fishing at protected Central Indo-Pacific (GBR) sites (i.e., as indicated by the “recovery” side of dashed arrow). “Decline” and “recovery” refer to the presumed trajectory of reefs' exploited fish populations due to fishing pressure, not to structural changes in reefs.</p

Biomass of piscivorous fishes.

<p>Piscivorous fish biomass (per unit reef area) at reefs used in this study. Bars are means (±SE).</p