Metabolic rate models and the substitutability of predator populations

• Much of the debate surrounding the consequences of biodiversity loss centres around the issue of whether different species are functionally similar in their effects on ecological processes. In this study, we examined whether populations consisting of smaller, more abundant individuals are functionally similar to populations of the same species with larger, fewer individuals. • We manipulated the biomass and density of banded sunfish (Enneacanthus obesus) and measured their impact on populations of Southern leopard frog (Rana sphenocephala) larvae. We also evaluated the ability of models relating metabolic rate to body size to predict the relative impacts of populations that differ in average body size and population density. • Our results indicate that population biomass, density and their interaction each play a large role in determining the effect of a predator population on its food resource. Populations with smaller but more abundant individuals had effects as large or larger than those populations with larger but fewer individuals. • Although we found qualitative agreement between the observed relative effects of populations with that predicted by allometric models, we also found that density-dependence can cause effects of a population to differ from that expected based on allometry. • The substitutability of populations differing in average body size appears to depend on complex relationships between metabolic rate, population density and the strength of density-dependence. The restrictive conditions necessary to establish functional equivalence among different populations of the same species suggests that functional equivalence should be rare in most communities

Multi-messenger Observations of a Binary Neutron Star Merger

International audienceOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta