Human land use threatens global biodiversity and compromises multiple ecosystem functions critical to food production. Whether crop yield–related ecosystem services can be maintained by a few dominant species or rely on high richness remains unclear. Using a global database from 89 studies (with 1475 locations), we partition the relative importance of species richness, abundance, and dominance for pollination; biological pest control; and final yields in the context of ongoing land-use change. Pollinator and enemy richness directly supported ecosystem services in addition to and independent of abundance and dominance. Up to 50% of the negative effects of landscape simplification on ecosystem services was due to richness losses of service-providing organisms, with negative consequences for crop yields. Maintaining the biodiversity of ecosystem service providers is therefore vital to sustain the flow of key agroecosystem benefits to society.
79 40 INRA, UR 1115, Plantes et Systèmes de culture horticoles, ABSTRACT 138
Land-use change and intensification threaten bee populations worldwide, imperilling pollination services. Global models are needed to better characterise, project, and mitigate bees' responses to these human impacts. The available data are, however, geographically and taxonomically unrepresentative; most data are from North America and Western Europe, overrepresenting bumblebees and raising concerns that model results may not be generalizable to other regions and taxa. To assess whether the geographic and taxonomic biases of data could undermine effectiveness of models for conservation policy, we have collated from the published literature a global dataset of bee diversity at sites facing land-use change and intensification, and assess whether bee responses to these pressures vary across 11 regions (Western, Northern, Eastern and Southern Europe; North, Central and South America; Australia and New Zealand; South East Asia; Middle and Southern Africa) and between bumblebees and other bees. Our analyses highlight strong regionally-based responses of total abundance, species richness and Simpson's diversity to land use, caused by variation in the sensitivity of species and potentially in the nature of threats. These results suggest that global extrapolation of models based on geographically and taxonomically restricted data may underestimate the true uncertainty, increasing the risk of ecological surprises.
<p>Multivariate and ordered Probit models were used to study the determinants of the adoption and extent of adoption of agronomic practices among cacao farmers in Nariño, Colombia, with data from 353 farmers in the mountain region. Results suggest that farmers’ adoption decisions are made on a joint basis, further validating the use of a multivariate approach. The presence of illegal crops creates strong disincentives that affect the possibility of more significant technological improvements. Adequate access to agricultural technical assistance strongly increases rates of adoption. Evidence suggests that efforts are necessary to better target resource-poor farmers.</p>
Introducción. En Colombia se han realizado esfuerzos por masificar el uso de semilla certificada, sin embargo, el desconocimiento de los productores en sus ventajas, la inexistencia de una oferta estable y la dependencia al precio de papa comercial, limitan la sostenibilidad de su producción. Objetivo. Evaluar financiera y biofísicamente la producción de semilla de papa en el departamento de Nariño, (Colombia). Materiales y Métodos. Se evaluó el uso, evolución, adopción y costos de semilla, entre mayo de 2016 y abril de 2018, para consolidar bases que permitan crear modelos de producción sostenibles. Dicha información fue recopilada por encuestas a 1018 hogares productores en veintiún municipios de la localidad. Para definir los parámetros biofísicos se utilizó una entrevista semiestructurada para extraer rangos y aptitudes en capas cartográficas, que se enmarcaron en un área con precipitación entre 800 a 1600 mm año-1, suelos francos con pendientes del 15 %, altitud entre 2800 a 3200 msnm y temperatura de 8 a 15 °C. El comportamiento del agronegocio se estableció con proyección de costos de producción a siete años, a partir de revisión de fuentes primarias y cifras de áreas sembradas durante los últimos diez semestres, que fue cotejada con la estimación del porcentaje de uso actual de semilla en la región para establecer la demanda potencial. Resultados. La carga económica no permitió generar rendimientos significativos en una sola hectárea (: 6 %), porque fueron inferiores al de la producción de papa comercial (: 18 %), con un promedio 20 % y una tasa interna de retorno (TIR) del 28 %. Conclusión. El área mínima para superar la rentabilidad de la producción de papa comercial fue de tres hectáreas, logrando suministrar el 3 % de la demanda de semilla. Las zonas con mayor potencial para producción fueron los Municipios de Pasto, Tangua y Sapuyes.
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