1,721,728 research outputs found
Nearby rainforest promotes coffee pollination by increasing spatio-temporal stability in bee species richness
No full textNatural tropical forests are highly diverse and are known to contribute to forest-based services such as pollination of nearby crops. Landscape changes cause spatial and temporal bee community changes, but consequences how the community changes affect pollination is not well analyzed. This paper addresses the effects of rainforest distance and on site flower resources in agro-forests on spatial and temporal variation in pollinator communities and the consequences for coffee pollination. The Study was conducted in 24 agro-forests dominated by coffee and cacao in Sulawesi, Indonesia differing in their distance to rainforest margin of the Lore-Lindu National Park and in flower density and its temporal variation. In all agro-forests, (1) transect surveys of the understory were obtained over a five-month period to assess bee community compositional similarity, bee diversity, and the temporal variation in bee diversity; and (2) coffee flower visitors were observed and open and bagged pollination treatments conducted over one week of coffee blooming to assess bee diversity and the spatial variation in bee diversity and coffee pollination. Mean number of shared species of the understory ranged between 40 and 60% per agro-forest and was higher in agro-forests nearby the rainforest than in agro-forests with a minimal distance of 500 m isolated from the rainforest. Mean species richness in the understory and in coffee flowers decreased with rainforest isolation and increased with flower resource availability. Temporal variation in bee species richness of the understory and spatial variation of the coffee flower-visiting bee species richness per agro-forest increased with forest distance. The variation in bee species richness decreased the mean and increased the spatial variation in bee-pollinated coffee fruit set per agro-forest. In conclusion, crops grown near intact rainforests and which profit from the pollination by many species may fluctuate less in bee-pollinated fruit set across crop plants than crop plants in isolated agriculture that receive low or even single species pollination services (C) 2009 Elsevier B.V. All rights reserved
Effects of grassland management, endophytic fungi and predators on aphid abundance in two distinct regions
No full textAims Fungal endophytes of cool-season grass species produce alkaloids toxic to herbivores, affecting food webs in agricultural and natural ecosystems. Field studies about the effects of endophytes on herbivores are rare and show contradictory results, leading to uncertain conclusions about the nature of endophyte-grass symbiosis. We asked whether the environmental contexts of local and regional scales and predation could modify the effects of endophytes on herbivores. Methods In a full factorial field experiment, we quantified the abundance of the aphid species Rhopalosiphum padi on the potted host grass Lolium perenne, which was either infected or uninfected with the endophytic fungus Neotyphodium lolii. Predators were either excluded or had free access to the pots with the aphids. One hundred and sixty grass pots were located in two regions on altogether 40 grassland sites, half of the sites intensively and half extensively managed. We tested the importance of endophyte infection, study region, management intensity of grasslands, predation and all two-way interactions on aphid abundance. Important Findings Endophyte infection reduced aphid abundance significantly in one study region only. In both regions, we found that the impacts of aphidophagous predators and grassland management intensity on aphid abundance were substantially stronger and more consistent than that of endophytes on aphid abundance. Pots excluding predators and pots placed on extensive grasslands contained higher aphid abundance. The impact of predators and management on aphid abundance were not modified by the endophyte. We conclude that the effect of endophytes on herbivores can be weak in field experiments and depends on environmental context at a regional scale. Hence, more field research efforts are necessary to detect the relative importance of endophytes and the environmental context on biotic interactions in ecosystems
Economic trade-offs between carbon sequestration, timber production, and crop pollination in tropical forested landscapes
No full textThe ecosystem service controversy: Is there sufficient evidence for a "pollination paradox"?
No full textThe ecosystem service controversy: Is there sufficient evidence for a "pollination paradox"?
No full textFunctional complementarity and specialisation: The role of biodiversity in plant–pollinator interactions
No full textEcological niche breadth (specialisation) and niche differentiation (complementarity) play a key role for species coexistence and hence biodiversity. Some niche dimensions of a species represent ecosystem functions or services such as pollination (functional niche). When species differ in their contribution to some collective function (functional complementarity), this implies that functions from several species are required for a high overall functional performance level. Applied to plant pollinator interactions, functional complementary suggests that a higher diversity of pollinators contributes to an increased pollination success of the plants or, in turn, that a higher diversity of flowers may better sustain the consumers' requirements. Complementarity can affect functioning at different scales: the collective functioning of the target community, a single species, an individual or even a part of the individual, e.g. a single flower. Recent network analyses revealed that plant pollinator interactions display a relatively high extent of complementary specialisation at the community scale. We propose several mechanisms that generate complementarity. From the consumers' viewpoint, differences in flowering phenology and/or nutritional variation in floral resources (nectar, pollen) may explain a complementary role of different flower species. From the plant's viewpoint, temporal or environmental variation in the pollinator species' activities may contribute to complementary effects on pollination of plant communities. In addition, different species may also pollinate either more exposed or more sheltered flowers from the same plant individual, or vary in their functions within single flowers. So far, empirical evidence for complementary effects in general, and particularly mechanistic explanations of such effects are scant and will require comparative investigations at multiple scales in the future. Such studies will help us to understand if and how biodiversity maintains the quality and quantity of plant pollinator functional relationships
Landscape context and management effects on an important insect pest and its natural enemies in almond
No full textEilers E, Klein A-M. Landscape context and management effects on an important insect pest and its natural enemies in almond. Biological Control. 2009;51(3):388-394.Pest control mediated by organisms such as parasitoids is a valuable ecosystem service, particularly with regard to high costs, low effectiveness, and detrimental effects of some agrochemicals. This study examined infestation rates and abundance of pests and their natural enemies in organic and conventional almond orchards in California, differing in landscape context, understory plant cover, and plant species richness. Parasitoids of the commercially most important insect pest of almond, the Navel Orangeworm (NOW) were studied by rearing NOW in collected overwintering nuts. The indirect impact of vertebrate natural enemies of NOW were estimated by counting empty nut shells with feeding marks by wild birds and various mammals, found at the orchard floor. Mean nut infestation by NOW ranged from 0.8% to 37% per orchard and was reduced by parasitism rates, ranging from 0% to 22%, and vertebrate nut damage, ranging from 2% to 96% per orchard. The parasitoids were facilitated by a high proportion of natural habitat surrounding the orchards and high proportion of understory ground cover with vegetation. The vertebrate natural enemies were facilitated by a high proportion of natural habitat surrounding the orchards and plant species richness in the orchard understory. In conclusion, this study shows that pest control mediated by vertebrates and invertebrates promoted by near natural habitats can lower pest pressure by NOW larvae in overwintering almond. In case of the vertebrate nut damage this service might only be temporal and turn into a dis-service during and after harvest because the vertebrates continue to feed on the nuts and may also cause injuries to the trees
Environmentally mediated coffee pest densities in relation to agroforestry management, using hierarchical partitioning analyses
No full textRain forest promotes trophic interactions and diversity of trap-nesting Hymenoptera in adjacent agroforestry
No full text1. Human alteration of natural ecosystems to agroecosystems continues to accelerate in tropical countries. The resulting world-wide decline of rain forest causes a mosaic landscape, comprising simple and complex agroecosystems and patchily distributed rain forest fragments of different quality. Landscape context and agricultural management can be expected to affect both species diversity and ecosystem services by trophic interactions. 2. In Central Sulawesi, Indonesia, 24 agroforestry systems, differing in the distance to the nearest natural forest (0–1415 m), light intensity (37·5–899·6 W/m−2) and number of vascular plant species (7–40 species) were studied. Ten standardized trap nests for bees and wasps, made from reed and knotweed internodes, were exposed in each study site. Occupied nests were collected every month, over a period totalling 15 months. 3. A total of 13 617 brood cells were reared to produce adults of 14 trap-nesting species and 25 natural enemy species, which were mostly parasitoids. The total number of species was affected negatively by increasing distance from forest and increased with light intensity of agroforestry systems. The parasitoids in particular appeared to benefit from nearby forests. Over a 500-m distance, the number of parasitoid species decreased from eight to five, and parasitism rates from 12% to 4%. 4.The results show that diversity and parasitism, as a higher trophic interaction and ecosystem service, are enhanced by (i) improved connectivity of agroecosystems with natural habitats such as agroforestry adjacent to rain forest and (ii) management practices to increase light availability in agroforestry, which also enhances richness of flowering plants in the understorey
Spatial scale of observation affects alpha, beta and gamma diversity of cavity-nesting bees and wasps across a tropical land-use gradient
No full textAim Anthropogenic changes in land use may have major consequences for global biodiversity. However, species diversity is determined by a suite of factors that may affect species differently at different spatial scales. We tested the combined effects of land use and spatial scale on α, β and γ diversity in the tropics using experimental communities of cavity-nesting bees and waSPS (Hymenoptera: Aculeata). We aimed to determine whether: (1) land-use intensity negatively affects species richness of cavity-nesting Hymenoptera, (2) β diversity, both within and between plots, is higher in more natural systems, (3) species richness of flowering herbs correlates positively with species richness of Hymenoptera within and across habitats, (4) richness of cavity-nesting Hymenoptera in highly modified habitats declines with increasing distance from natural or semi-natural habitats, (5) the effects of land use, herb diversity and forest distance on Hymenoptera α and β diversity vary at different spatial scales, and (6) bees and waSPS respond to land use in a similar way.Location Manabi, south-west Ecuador.Methods We examined diversity (species richness) within 48 plots of five habitat types that comprised a gradient of decreasing agricultural intensity from rice and pasture to coffee agroforests, unmanaged abandoned agroforests and forest fragments, using standardized nesting resources for reproducing communities of cavity-nesting bees and waSPS.Results (1) Land use significantly affected α diversity of trap-nesting bees and waSPS at the subplot (per trap) scale, but not subplot β diversity or plot-scale species richness (γ diversity). (2) Beta diversity was surprisingly higher between plots within a land-use type than between land-use types. (3) Species richness of bees and waSPS increased with diversity of flowering herbs at the subplot (trap) scale only. (4) Forest distance correlated positively with bee species richness at the plot scale only. (5) Land use, herb diversity and forest distance each showed significant correlations with bee and wasp diversity at only one spatial scale. (6) Despite differences in life history, bees and waSPS responded to land-use intensity in a similar way.Main conclusions The effects of land use on species richness were highly dependent on spatial scale. Subplot-scale analyses showed that rice and pasture contained the highest species diversity, whereas plot-scale analyses showed no significant difference in the diversity of different land-use types. We emphasize caution in the estimation of biodiversity at only one spatial scale, and highlight the surprisingly large contribution of managed land to the regional biodiversity of these species
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