Global and regional ecological boundaries explain abrupt spatial discontinuities in avian frugivory interactions

Species interactions can propagate disturbances across space via direct and indirect effects, potentially connecting species at a global scale. However, ecological and biogeographic boundaries may mitigate this spread by demarcating the limits of ecological networks. We tested whether large-scale ecological boundaries (ecoregions and biomes) and human disturbance gradients increase dissimilarity among plant-frugivore networks, while accounting for background spatial and elevational gradients and differences in network sampling. We assessed network dissimilarity patterns over a broad spatial scale, using 196 quantitative avian frugivory networks (encompassing 1496 plant and 1004 bird species) distributed across 67 ecoregions, 11 biomes, and 6 continents. We show that dissimilarities in species and interaction composition, but not network structure, are greater across ecoregion and biome boundaries and along different levels of human disturbance. Our findings indicate that biogeographic boundaries delineate the world’s biodiversity of interactions and likely contribute to mitigating the propagation of disturbances at large spatial scales.The authors acknowledge the following funding: University of Canterbury Doctoral Scholarship (L.P.M.); The Marsden Fund grant UOC1705 (J.M.T., L.P.M.); The São Paulo Research Foundation - FAPESP 2014/01986-0 (M.G., C.E.), 2015/15172-7 and 2016/18355-8 (C.E.), 2004/00810-3 and 2008/10154-7 (C.I.D., M.G., M.A.P.); Earthwatch Institute and Conservation International for financial support (C.I.D., M.G., M.A.P.); Carlos Chagas Filho Foundation for Supporting Research in the Rio de Janeiro State – FAPERJ grant E-26/200.610/2022 (C.E.); Brazilian Research Council grants 540481/01-7 and 304742/2019-8 (M.A.P.) and 300970/2015-3 (M.G.); Rufford Small Grants for Nature Conservation No. 22426–1 (J.C.M., I.M.), No. 9163-1 (G.B.J.) and No. 11042-1 (MCM); Universidade Estadual de Santa Cruz (Propp-UESC; No. 00220.1100.1644/10-2018) (J.C.M., I.M.); Fundação de Amparo à Pesquisa do Estado da Bahia - FAPESB (No. 0525/2016) (J.C.M., I.M.); European Research Council under the European Union’s Horizon 2020 research and innovation program (grant 787638) and The Swiss National Science Foundation (grant 173342), both awarded to C. Graham (D.M.D.); ARC SRIEAS grant SR200100005 Securing Antarctica’s Environmental Future (D.M.D.); German Science Foundation—Deutsche Forschungsgemeinschaft PAK 825/1 and FOR 2730 (K.B.G., E.L.N., M.Q., V.S., M.S.), FOR 1246 (K.B.G., M.S., M.G.R.V.) and HE2041/20-1 (F.S., M.S.); Portuguese Foundation for Science and Technology - FCT/MCTES contract CEECIND/00135/2017 and grant UID/BIA/04004/2020 (S.T.) and contract CEECIND/02064/2017 (L.P.S.); National Scientific and Technical Research Council, PIP 592 (P.G.B.); Instituto Venezolano de Investigaciones Científicas - Project 898 (V.S.D.)

Relación entre la abundancia de tres especies de playeros del género \u3cem\u3eCalidris\u3c/em\u3e Merren 1804 (Aves: Scolopacidae) y sus recursos alimenticios en la Laguna de Punta de Mangle, Isla de Margarita, Venezuela / Relationship Between the Abundance of Three \u3cem\u3eCalidris\u3c/em\u3e Sandpipers (Aves: Scolopacidae) and Their Food Resources in Punta de Mangle Lagoon, Margarita Island, Venezuela

Los humedales costeros son áreas importantes para las aves playeras migratorias, especialmente durante el período no reproductivo, ya que permiten suplir las demandas energéticas asociadas a la migración. La laguna de Punta de Mangle, en la isla de Margarita, es utilizada por Calidris pusilla, C. mauri y C. minutilla durante la migración post-reproductiva (septiembre-diciembre); sin embargo, se conoce poco acerca de su dieta, oferta de presas y condiciones abióticas que enfren-tan en este período. Este trabajo se enfocó en describir algunas condiciones abióticas y la dieta de las aves; además de esti-mar la riqueza y abundancia de presas y examinar su relación con los calidrinos pequeños. La recolección de datos se realizó quincenalmente (septiembre-diciembre 2016), en un transecto de 650 m en la planicie intermareal más utilizada por las aves. Las condiciones abióticas fueron descritas en términos de salinidad, amplitud intermareal, profundidad de la lámina de agua y granulometría y la abundancia de playeros se estimó mediante censos visuales. Para la descripción de la dieta, se analizaron muestras de heces, mientras que la riqueza y abundancia de presas se determinó analizando muestras de sedimento colecta-das para cada tamaño de presa (macrofauna y meiofauna) y la incidencia de biopelículas. Los resultados sugieren que Punta de Mangle es un sitio de parada importante en el Caribe, recibiendo un máximo de 548 individuos durante el pico de migración post-reproductiva, en noviembre. En el periodo de estudio, se observaron mejoras en la calidad del hábitat con el progreso de la migración y una abundancia y riqueza de recursos elevada, aunque variable espaciotemporalmente. Los recursos más frecuentemente consumidos por los Calidris fueron biopelículas, ostrácodos, copépodos, anfípodos, poliquetos y dípteros, y la dieta se ajustó a su disponibilidad, a pesar de la ausencia de relaciones estadísticamente significativas entre aves y recursos. Sin embargo, las sincronías fenológicas entre la abundancia de aves y algunas presas sugieren la existencia de relaciones que podrían no haberse detectado debido al efecto denso-dependiente de la depredación ejercida por las aves durante el pico migratorio. Esta investigación representa una aproximación integral a la ecología de parada de estas especies en el Caribe. Coastal wetlands are important areas for migratory shorebirds, especially during the non-breeding season, serving as fueling areas where birds get to meet the energy demands associated with migration. Punta de Mangle lagoon, in Margarita island, is used by Calidris pusilla, C. mauri and C. minutilla during fall migration (September-December); however, little is known about their diet, prey availability, or the abiotic condi-tions they face in this period. This work focused on describing some abiotic conditions and the diet of the birds; in addition to estimate prey richness, abundance and their relationship with small calidrine sandpipers abundance. Data collection was carried out biweekly (September-December 2016), in a 650 m transect on the intertidal mudflat most heavily used by birds. Abiotic conditions were described in terms of salinity, exposed intertidal amplitude, water depth and granulometry. Shorebird abundance was assessed by direct counts of flocks. Dropping samples were analyzed for diet description while prey richness and abundance was determined from core samples collected for each prey size (macrofauna and meiofauna) along with bio-film incidence data. Our results suggest Punta de Mangle is an important stopover site in the Caribbean, receiving a maximum of 548 individuals during the fall migration peak, in November. Over the analyzed period, an enhancement in habitat condition with the progress of migration was evident, and resource abundance and richness were high but variable at spatial and temporal scales. The resources more frequently consumed by birds were biofilms, ostracods, copepods, amphipods, polychaetes and dipteran. Overall, shorebird diet greatly matched resource availability despite the absence of statistically significant relationships between shorebird and feeding resources. However, the phenological synchronies between the abundance of birds and some prey suggest the existence of relationships that could not have been detected probably due to a denso-dependent effect of predation exerted by birds on prey stocks during migration peak. This research represents a comprehensive approach to the staging ecology of these species in the Caribbean