RESUMO
Mountainous grasslands in South America, characterized by their high diversity, provide a wide range of contributions to people, including water regulation, soil erosion prevention, livestock feed provision, and preservation of cultural heritage. Prior research has highlighted the significant role of grazing in shaping the diversity and productivity of grassland ecosystems, especially in highly productive, eutrophic systems. In such environments, grazing has been demonstrated to restore grassland plant diversity by reducing primary productivity. However, it remains unclear whether these findings are applicable to South American mountainous grasslands, where plants are adapted to different environmental conditions. To address this uncertainty, we conducted a meta-analysis of experiments excluding livestock grazing to assess its impact on plant diversity and productivity across mountainous grasslands in South America. In alignment with studies in temperate grasslands, our findings indicated that herbivore exclusion resulted in increased aboveground biomass but reduced species richness and Shannon diversity. The effects of grazing exclusion became more pronounced with longer durations of exclusion; nevertheless, they remained resilient to various climatic conditions, including mean annual precipitation and mean annual temperature, as well as the evolutionary history of grazing. In contrast to results observed in temperate grasslands, the reduction in species richness due to herbivore exclusion was not associated with increased aboveground biomass. This suggests that the processes governing (sub)tropical grassland plant diversity may differ from those in temperate grasslands. Consequently, further research is necessary to better understand the specific factors influencing plant diversity and productivity in South American montane grasslands and to elucidate the ecological implications of herbivore exclusion in these unique ecosystems.
RESUMO
Abstract The umbrella species concept posits that protection of a single, wide-ranging species may confer protection to a large number of sympatric species. Due to their large home ranges, widespread distribution in the Mesoamerican Biodiversity Hotspot (MBH), and status as the focal species of numerous conservation initiatives, the jaguar Panthera onca is an ideal species to evaluate the umbrella strategy. After ground-truthing jaguar corridors from 2009-2016, we tested the umbrella value of jaguars for endemic herpetofauna (Amphibia, Reptilia) in Nuclear Central America (NCA), a ~ 370 000 km² sub-region of the MBH. NCA contains the greatest density of threatened reptiles in the Western Hemisphere and harbors extraordinary high diversity of amphibians, the most threatened class of vertebrate worldwide. Of the 304 regional endemics in NCA, the distributions of 187 (61.5 %) species of amphibians and reptiles overlapped ground-truthed jaguar range. The distributions of 14 reptiles, including a critically endangered Bothriechis spp. and two endangered Norops spp., occur exclusively within jaguar distribution. Similarly, the distributions of 19 amphibians, including four critically endangered Craugastor spp. and two critically endangered Plectrohyla spp. occur entirely within jaguar distribution. Our results indicate greater effectiveness of ground-truthed jaguar distribution than modeled and randomly selected networks in overlapping the distributions of endemic herpetofauna, especially threatened amphibians, in NCA. Substantiation of multi-taxa dependence on habitat in jaguar distribution would strengthen justification for wider application of the umbrella strategy beyond NCA and aid conservation planning in the MBH.
Resumen Las especies sombrilla son aquellas cuya conservación confiere protección a un gran número de especies simpátricas. Debido a sus ámbitos hogareños extensos, a una distribución generalizada en el Hotspot de Biodiversidad de Mesoaméricana (MBH), y su estatus como especie focal de numerosas iniciativas de conservación, el jaguar Panthera onca es una especie ideal para evaluar la estrategia sombrilla. Evaluamos el valor de los jaguares como estrategia sombrilla para la herpetofauna endémica en Centro América Nuclear (NCA), una subregión de ~ 370 000 km² que se encuentra dentro del MBH. La NCA contiene la mayor densidad de reptiles amenazados en el hemisferio occidental y alberga una diversidad extraordinaria de anfibios, que es la clase de vertebrados más amenazada del mundo. De las 304 especies endémicas regionales presentes en el NCA, las distribuciones de 187 (61.5 %) se sobrepusieron al área de distribución del jaguar verificada. Las distribuciones de 14 reptiles, incluyendo una Bothriechis spp. (en Peligro Crítico) y dos Norops spp. (en Peligro de Extinción), se dan exclusivamente dentro del rango del jaguar. Similarmente, 19 especies de anfibios, incluidas cuatro Craugastor spp. (en Peligro Crítico) y dos Plectrohyla spp. (en Peligro Crítico) están presentes exclusivamente dentro del área de distribución del jaguar. Nuestros resultados indican que los corredores verificados para el jaguar coinciden mejor con las distribuciones de la herpetofauna endémica dentro del NCA, especialmente anfibios, en comparación con los corredores modelados y seleccionados al azar. La confirmación del traslape de la distribución del hábitat del jaguar con la de múltiples taxones fortalece la justificación de una aplicación más amplia de la estrategia sombrilla, aún más allá del NCA, contribuyendo también en la selección de áreas de conservación previamente subestimadas dentro del MBH.