RESUMEN
Predator-prey interactions shape ecosystem stability and are influenced by changes in ecosystem productivity. However, because multiple biotic and abiotic drivers shape the trophic responses of predators to productivity, we often observe patterns, but not mechanisms, by which productivity drives food web structure. One way to capture mechanisms shaping trophic responses is to quantify trophic interactions among multiple trophic groups and by using complementary metrics of trophic ecology. In this study, we combine two diet-tracing methods: diet DNA and stable isotopes, for two trophic groups (top predators and intermediate predators) in both low- and high-productivity habitats to elucidate where in the food chain trophic structure shifts in response to changes in underlying ecosystem productivity. We demonstrate that while top predators show increases in isotopic trophic position (δ15N) with productivity, neither their isotopic niche size nor their DNA diet composition changes. Conversely, intermediate predators show clear turnover in DNA diet composition towards a more predatory prey base in high-productivity habitats. Taking this multi-trophic approach highlights how predator identity shapes responses in predator-prey interactions across environments with different underlying productivity, building predictive power for understanding the outcomes of ongoing anthropogenic change.
Asunto(s)
Ecosistema , Cadena Alimentaria , Animales , Conducta Predatoria/fisiología , Invertebrados , DietaRESUMEN
BACKGROUND: Patient characteristics, higher device cost, and vendor contracts likely prevent use of magnetic resonance imaging (MRI)-conditional pacemakers (MRC) in all pacemaker (PM)-eligible patients. We sought to identify the incidence and predictors of MRI scan utilization in MRC recipients. METHODS: Patients receiving an MRC or non-MRI-conditional PM (NMRC) at four centers were included. Incidence of MRI scans following PM insertion was obtained from hospital records and patient phone calls. RESULTS: Of 1,244 patients (74 ± 12 years, 54.6% male), 927 had MRC and 317 had NMRC. At baseline, MRC recipients had a higher incidence of atrial tachycardia and MRI risk factors (syncope, recurrent falls, neurological disease, severe musculoskeletal disease, malignancy). In the MRC group, more patients had commercial health insurance (26% vs 15%, P < 0.001). Sixty MRC patients (6.5%) had an MRI during 21 ± 17 months' follow-up. Using the Weilbull parametric survival model, the projected percentage of MRC patients receiving an MRI scan at 7- and 11-year follow-up were 45% and 73%, respectively. By multivariate regression, a prior history of MRI (odds ratio [OR] 4.5, 95% confidence interval [CI] 2.2-9.1, P < 0.001) and active smoking (OR 2.65, 95% CI 1.1-6.7, P = 0.039) independently predicted the performance of an MRI following MRC implant. CONCLUSIONS: In this MRC cohort, MRI scan utilization during follow-up was low but projection analyses showed a higher incidence over the lifetime of the MRC. A history of prior MRI and active smoking independently predicted the performance of an MRI scan during follow-up.