638 research outputs found
Seed set of male-sterile and male-fertile oilseed rape (Brassica napus) in relation to pollinator density
No full textThe effects of pollinator density on the seed set of a male-sterile (MS) and a
male-fertile (MF) line of winter oilseed rape (Brassica napus) were studied in 24
isolation cages (7.5 m). Pollinator treatments comprised of high pollinator density
(a small honeybee colony and 10 mason bees, Osmia rufa), and a gradient of increasing
O. rufa densities from zero (control) up to 100 bees per cage. High pollinator densities
increased the seed weight per plant from 6.5 g to 56.9 g for the MS line. However seed
weight did not differ between high pollinator densities and controls for the MF line.
Increasing densities of O. rufa had a significant effect on almost all yield components
of the MS line, but only marginal effects on the MF line. The number of seeds per pod,
the seed weight per plant and the harvest index (seed weight/plant dry weight)
of the MS line showed a significantly steeper increase with increasing bee density
than that of the MF line. The results suggest that solitary bees could be used
successfully to replace honeybees as pollinators of MS oilseed rape in isolation cages
Importance of habitat area and landscape context for species richness of bees and wasps in fragmented orchard meadows
No full textI investigated how habitat area, habitat connectivity, and landscape context affect the species richness and abundance of trap-nesting bees, wasps, and their natural enemies. The research was done on 45 orchard meadows ranging in size from 0.08 to 5.8 ha and differing in habitat connectivity and the surrounding landscape matrix. Effects of the surrounding landscape matrix were restricted to circles with a radius of 250 m. Only the species richness of natural enemies increased with landscape diversity in the surrounding matrix. Population densities of bees increased with habitat connectivity. Total species richness and species richness of bees, eumenid wasps, and natural enemies significantly increased with habitat area. Significant species-area relationships existed for insect groups but not for plants, thereby confirming the hypothesis that higher trophic levels are more affected by habitat fragmentation than lower trophic levels. The slope of species-area relationships was steeper for mutualistic bees than for predatory wasps and natural enemies. In contrast to expectations, the rate of parasitism did not depend on habitat area but only on the local and regional abundance of hosts. My results suggest that the area and connectivity of habitat fragments is most important for the conservation of habitat specialists, whereas generalists may profit from a diverse surrounding landscape matrix
Honeybee foraging in differentially structured landscapes
No full textHoneybees communicate the distance and location of resource patches by bee dances, but this spatial information has rarely been used to study their foraging ecology. We analysed, for the first time to the best of the authors' knowledge, foraging distances and dance activities of honeybees in relation to landscape structure, season and colony using a replicated experimental approach on a landscape scale. We compared three structurally simple landscapes characterized by a high proportion of arable land and large patches, with three complex landscapes with a high proportion of semi-natural perennial habitats and low mean patch size. Four observation hives were placed in the centre of the landscapes and switched at regular intervals between the six landscapes from the beginning of May to the end of July. A total of 1137 bee dances were observed and decoded. Overall mean foraging distance was 1526.1 +/- 37.2 m, the median 1181.5 m and range 62.1-10 037.1 m. Mean foraging distances of all bees and foraging distances of nectar-collecting bees did not significantly differ between simple and complex landscapes, but varied between month and colonies. Foraging distances of pollen-collecting bees were significantly larger in simple (1743 +/- 95.6 m) than in complex landscapes (1543.4 +/- 71 m) and highest in June when resources were scarce. Dancing activity, i.e. the number of observed bee dances per unit time, was significantly higher in complex than in simple landscapes, presumably because of larger spatial and temporal variability of resource patches in complex landscapes. The results facilitate an understanding of how human landscape modification may change the evolutionary significance of bee dances and ecological interactions, such as pollination and competition between honeybees and other bee species
Pollination, seed set and seed predation on a landscape scale
No full textWe analysed the combined effects of pollination and seed predation on seed set of Centaurea jacea in 15 landscapes differing in structural complexity. In the centre of each landscape, a patch of Centaurea plants was established for standardized measurements of flower visitation, seed predation and seed set. Both the number of flower-visiting bees and the proportion of flower heads damaged by seed predators increased with landscape complexity, which was measured as the proportion of semi-natural habitats. The mean number of seeds per flower head did not increase with the proportion of semi-natural habitats, presumably because of the counterbalancing effects of pollination and seed predation. For a subset of undamaged flower heads, the number of seeds per flower head was positively correlated with the number of flower visits. Further reasons for the unexpected failure to detect a correlation between landscape complexity and seed set appeared to be changes in flower-visitor behaviour and the contrasting responses of honeybees and wild bees to habitat context. Landscape analyses at eight spatial scales (radius of landscape sectors, 250-3000 m) showed that different groups perceived the landscape at different spatial scales. Changes in pollinator numbers could be explained only at small scales (up to 1000 m), while the seed predators also responded to large scales (up to 2500 m)
Pollination of Coffea canephora in relation to local and regional agroforestry management
No full textPollination of crops depends on local agricultural management and the quality of adjacent habitats. Lowland coffee Coffea canephora, is an important tropical cash crop. Fruit set depends on cross-pollination by bees, so inadequate pollination leads to reduced yield. In this study we analyse the relationship between bee pollinators, fruit set in coffee, and the local and regional agroforestry systems to identify the optimal conditions for pollinators.2We analysed the abundance and species composition of coffee flower-visiting bees in 15 agroforestry systems differing in distance to forest (important for wood-nesting species), light intensity (important for ground-nesting species), blossom cover of coffee and noncoffee-flowering plants, and species richness of flowering plants (as pollen and nectar resources) in Central Sulawesi (Indonesia). We examined which factors were most important for optimal pollination success. We carried out bagged and open pollination experiments in each agroforestry system, to measure the pollination efficiency of 15 bee species.3The number of social bee species decreased with distance to forest, whereas the number of solitary bee species increased with light intensity (less shade) and greater quantities of blossoms.4Fruit set of open pollinated flowers (as opposed to manually cross-pollinated flowers) increased with the diversity and abundance of flower-visiting bees. In the agroforestry systems studied, a bee community of 20 species or more led to a higher fruit set (95%) than a species-poor bee community of six species (70% fruit set).5Pollination activity by members of the species-rich solitary bee assemblage led to higher levels of fruit set than that arising from pollination activity by members of the more abundant social bee assemblage.6Synthesis and applications. A species-rich and abundant bee assemblage will facilitate high pollination success in lowland coffee. This will increase fruit set and coffee yield. Farmers can encourage different species of bees through simple management measures such as growing coffee in shade beneath a variety of trees; by pruning trees to increase levels of sunlight and numbers of flowering herbs; and by increasing the availability of nesting sites for solitary bees. Weed control and the use of herbicides should be kept to a minimum so that a diverse nectar and pollen resource is available to bees throughout the year. Natural forests and forest fragments should be preserved in the vicinity of coffee agroforestry systems (< 500 m) so that forest-nesting social bees can travel easily to the coffee fields to pollinate the flowers
Nest-site fidelity, body weight and population size of the red mason bee, Osmia rufa (Hymenoptera : Megachilidae), evaluated by Mark-Recapture experiments
No full textMark-recapture experiments were used to examine nest-site fidelity, natural local population size and effects of body weight on dispersal strategies in the solitary bee Osmia rufa Linnaeus 1758. A total of 974 hibernated females was individually marked and weighed inside their cocoons and then released in five orchard meadows for emergence. In May 2002. colonisation of three spatially separated trap nest locations on each study site (mean distance 52 m) by marked and unmarked females of O. rufa was monitored. Only 222 (22.8 %) of all marked females (3-108 per site) were re-observed. Mortality rates varied between 2.2 and 26.4 % between study sites. Thus estimated 74 %, of emerged females leaved the parental nest-site. The number of observed unmarked females varied between 9 and 16 per-site resulting in an estimated natural Population size between 48 and 258 individuals or 15 females per 1000 m(2) on average. The mean body weight of marked recaptured females (113.0 +/- 14.9 mg) was significantly higher than the body weight of marked but not recaptured females(107.3 +/- 19.0 mg). The results give new insights into the possible densities of natural populations of a solitary bee species, its nest-site fidelity and the potential role of body weight for dispersal strategies
Nest-site fidelity, body weight and population size of the red mason bee, Osmia rufa (Hymenoptera : Megachilidae), evaluated by Mark-Recapture experiments
No full textMark-recapture experiments were used to examine nest-site fidelity, natural local population size and effects of body weight on dispersal strategies in the solitary bee Osmia rufa Linnaeus 1758. A total of 974 hibernated females was individually marked and weighed inside their cocoons and then released in five orchard meadows for emergence. In May 2002. colonisation of three spatially separated trap nest locations on each study site (mean distance 52 m) by marked and unmarked females of O. rufa was monitored. Only 222 (22.8 %) of all marked females (3-108 per site) were re-observed. Mortality rates varied between 2.2 and 26.4 % between study sites. Thus estimated 74 %, of emerged females leaved the parental nest-site. The number of observed unmarked females varied between 9 and 16 per-site resulting in an estimated natural Population size between 48 and 258 individuals or 15 females per 1000 m(2) on average. The mean body weight of marked recaptured females (113.0 +/- 14.9 mg) was significantly higher than the body weight of marked but not recaptured females(107.3 +/- 19.0 mg). The results give new insights into the possible densities of natural populations of a solitary bee species, its nest-site fidelity and the potential role of body weight for dispersal strategies
Effects of land-use intensity in tropical agroforestry systems on coffee flower-visiting and trap-nesting bees and waps
No full textThe contribution of cacao agroforests to the conservation of lower canopy ant and beetle diversity in Indonesia
No full textThe ongoing destruction of tropical rainforests has increased the interest in the potential value of tropical agroforests for the conservation of biodiversity. Traditional, shaded agroforests may support high levels of biodiversity, for some groups even approaching that of undisturbed tropical forests. However, it is unclear to what extent forest fauna is represented in this diversity and how management affects forest fauna in agroforests. We studied lower canopy ant and beetle fauna in cacao agroforests and forests in Central Sulawesi, Indonesia, a region dominated by cacao agroforestry. We compared ant and beetle species richness and composition in forests and cacao agroforests and studied the impact of two aspects of management intensification (the decrease in shade tree diversity and in shade canopy cover) on ant and beetle diversity. The agroforests had three types of shade that represented a decrease in tree diversity (high, intermediate and low diversity). Species richness of ants and beetles in the canopies of the cacao trees was similar to that found in lower canopy forest trees. However, the composition of ant and beetle communities differed greatly between the agroforest and forest sites. Forest beetles suffered profoundly from the conversion to agroforests: only 12.5% of the beetle species recorded in the forest sites were also found in the agroforests and those species made up only 5% of all beetles collected from cacao. In contrast, forest ants were well represented in agroforests, with 75% of all species encountered in the forest sites also occurring on cacao. The reduction of shade tree diversity had no negative effect on ants and beetles on cacao trees. Beetle abundances and non-forest ant species richness even increased with decreasing shade tree diversity. Thinning of the shade canopy was related to a decrease in richness of forest ant species on cacao trees but not of beetles. The contrasting responses of ants and beetles to shade tree management emphasize that conservation plans that focus on one taxonomic group may not work for others. Overall ant and beetle diversity can remain high in shaded agroforests but the conservation of forest ants and beetles in particular depends primarily on the protection of natural forests, which for forest ants can be complemented by the conservation of adjacent shaded cacao agroforests
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