Patterns of bee diversity in mosaic agricultural landscapes of central Uganda: implication of pollination services conservation for food security

Little is known about bee communities and pollination services conservation strategies in sub-Sahara Africa. A study was conducted at 26 different sites with varying local landscape characteristics in farmlands of central Uganda in 2006. Bees were sampled using coloured pantraps, handnet and line transect counts. Overall 80,883 bee individuals from 6 families and 652 species were encountered. The bee fauna was characterized by a lower diversity of Melittidae and Andrenidae and a high diversity of Apidae, Megachilidae and Halictidae. Megachile and Lasioglossum were the two most species-rich genera. The most abundant species was Apis mellifera adansonii Linnaeus (23 % of total individuals) followed by Hypotrigona gribodoi Magretti (19 %), Meliponula ferruginea Lepeletier (13 %), Lasioglossum ugandicum Cockerell (7 %), Apis mellifera scutellata Latreille (6 %), Allodapula acutigera Cockerell (6 %), Ceratina rufigastra Cockerell (5 %), Ceratina tanganyicensis Strand (5 %), Braunsapis angolensis Cockerell (5 %), Megachile rufipes Fabricius (5 %), Meliponula bocandei Spinola (5 %) and Seladonia jucundus Smith (5 %). The mean number of species recorded per study site per day ranged between 14 and 49, whereas the abundance ranged between 188 and 1,859 individuals. Study sites in areas with intense land-use had species-poor bee communities compared to sites with medium to low land-use intensities. Study sites with riparian forest fragments and wetlands, or with forest fallows in their vicinity had significantly (P < 0.05) higher species richness and diversity than sites dominated by small-scale monoculture/polyculture fields or sites dominated by either simple or complex traditional agroforestry systems. An ordination analysis also revealed that bee communities were significantly (P < 0.01) influenced by the presence of semi-natural habitats (woodlands, fallows) and forest fragments in the surrounding of fields. Thus, natural and semi-natural habitats are of great value for afrotropical farmland bee communities. There is a need to put in place strategies and policies for semi-natural and forest fragments preservation for spatio-temporal stability of pollination services in rural landscapes. Farmers are recommended to increase on-farm trees cover to safeguard and enhance pollination function and services in fields. Mimicking natural vegetation through promoting establishment of forest plantations and village community forestry in rural landscapes is also critical for conserving pollination services.     

Modelling animal populations in changing landscapes

Models of Mobile Animal Populations (MAP models) simulate long-term land use changes, population trends and patterns of biological diversity on landscapes of 10³-10⁵ ha. MAP models can incorporate information about past land-use patterns and management practices and can project future patterns based on management plans. We illustrate this approach with an example of how implementation of a U.S. Forest Service management plan at the Savannah River Site in South Carolina, U.S.A., might influence population trends of Bachman's Sparrow Aimophila aestivalis, a relatively rare and declining species in southeastern pine forests. In this case, a management plan, largely designed to improve conditions for an endangered species, Red-cockaded Woodpecker Picoides borealis, may have a negative impact, at least in the short term, on another species of management concern, Bachman's Sparrow.
In a parallel processing version of the MAP models, a single landscape that would ordinarily be too large or detailed to be simulated on a single computer is subdivided into a number of smaller landscapes, and each landscape is simulated in parallel, either on a single multi-tasking machine or on a group of networked machines. With this approach we are attempting to determine just how large a landscape must be before the dynamics of a population within it are more or less independent of factors beyond the landscape boundaries.     

Movement of insect pests in agricultural landscapes

Insect pests continue to exact a high toll on agricultural production, in spite of intense agrochemical input. The movement of insect pests from one place to another underlies their abundance and distribution in space and time, hence, ultimately, the extent of the inflicted crop damage. An improved understanding of dispersal mechanisms assists the deployment of sustainable pest management practices. Here, we review the latest advances in the study of the dispersal of herbivore insect pests in contemporary agro‐ecosystems. We address the factors triggering dispersal in typical agricultural landscapes, the contribution of agro‐ecosystem design and management to dispersal patterns, and the wider implications of natural and human‐mediated dispersal. Integrating practical knowledge with evolutionary theory holds the potential to improve predictions on how insect pests respond to present and future challenges imposed by changes of climate and land use.     

农业景观的生态规划与设计

从景观生态学的基本理论出发,探讨农业景观的生态规划与设计原理及方法,认为因涉及问题的宏观空间性、关联性及综合性等特点,使农业景观的生态规划与设计成为景观生态学的重要应用领域,进而以地处我国半干旱半湿润地带冀西北涿盆地进行了案实践。     

Constructed wetlands support bats in agricultural landscapes

Bats are known to use aquatic habitats as foraging habitats. Agricultural intensification is perceived to be a main reason for the loss of wetlands. However, artificial wetland creation (i.e. the construction of retention-ponds) in the agricultural landscape aiming at water or nutrient retention has recently gained importance. We evaluated to what extent bats use these artificial wetlands as foraging habitats in an agricultural landscape.Bat activity and prey density were compared in matched pairs at retention-ponds and neighbouring vineyard sites using stationary bat-detectors and sticky-traps, respectively. To examine if bat activity is related to the number of bat individuals, a thermal infrared imaging camera was used. Pipistrellus pipistrellus, the dominant species, served as an example to assess habitat selection between retention-ponds and vineyards. This was performed by relating foraging activity to the available area available within the potential home-range.Total bat activity and nocturnal prey density were significantly higher above the retention-ponds than above vineyards. High differences of activity levels between the ponds and the respective vineyard sites were found for Pipistrellus spp. (P. pipistrellus and P. nathusii) and Myotis spp. (M. daubentonii and M. mystacinus), being about 180 times and 50 times higher above the retention-ponds, respectively. A significant correlation was found between recorded bat activity and the maximum number of bat individuals observed with a thermal infrared imaging camera. When relating foraging activity to habitat availability within the assumed home-range of P. pipistrellus, retention-ponds had on average a higher importance as a foraging habitat than the complete vineyard area although they covered less than 0.1% of its area.This study indicates that artificial wetlands such as retention-ponds provide foraging habitats for bats. Therefore, creation of wetlands in intensively used agricultural landscapes benefits bats.     

Integrating biodiversity and conservation with modern agricultural landscapes

To achieve food security and meet the demands of the ever-growing human populations, farming systems have assumed unsustainable practices to produce more from a finite land area. This has been cause for concern mainly due to the often-irreversible damage done to the otherwise productive agricultural landscapes. Agro-ecology is proclaimed to be deteriorating due to eroding integrity of connected ecological mosaics and vulnerability to climate change. This has contributed to declining species diversity, loss of buffer vegetation, fragmentation of habitats, and loss of natural pollinators or predators, which eventually leads to decline in ecosystem services. Currently, a hierarchy of conservation initiatives is being considered to restore ecological integrity of agricultural landscapes. However, the challenge of identifying a suitable conservation strategy is a daunting task in view of socio-ecological factors that may constrain the choice of available strategies. One way to mitigate this situation and integrate biodiversity with agricultural landscapes is to implement offset mechanisms, which are compensatory and balancing approaches to restore the ecological health and function of an ecosystem. This needs to be tailored to the history of location specific agricultural practices, and the social, ecological and environmental conditions. The offset mechanisms can complement other initiatives through which farmers are insured against landscape-level risks such as droughts, fire and floods. For countries in the developing world with significant biodiversity and extensive agriculture, we should promote a comprehensive model of sustainable agricultural landscapes and ecosystem services, replicable at landscape to regional scales. Arguably, the model can be a potential option to sustain the integrity of biodiversity mosaic in agricultural landscapes.     

Valuing insect pollination services with cost of replacement

Value estimates of ecosystem goods and services are useful to justify the allocation of resources towards conservation, but inconclusive estimates risk unsustainable resource allocations. Here we present replacement costs as a more accurate value estimate of insect pollination as an ecosystem service, although this method could also be applied to other services. The importance of insect pollination to agriculture is unequivocal. However, whether this service is largely provided by wild pollinators (genuine ecosystem service) or managed pollinators (commercial service), and which of these requires immediate action amidst reports of pollinator decline, remains contested. If crop pollination is used to argue for biodiversity conservation, clear distinction should be made between values of managed- and wild pollination services. Current methods either under-estimate or over-estimate the pollination service value, and make use of criticised general insect and managed pollinator dependence factors. We apply the theoretical concept of ascribing a value to a service by calculating the cost to replace it, as a novel way of valuing wild and managed pollination services. Adjusted insect and managed pollinator dependence factors were used to estimate the cost of replacing insect- and managed pollination services for the Western Cape deciduous fruit industry of South Africa. Using pollen dusting and hand pollination as suitable replacements, we value pollination services significantly higher than current market prices for commercial pollination, although lower than traditional proportional estimates. The complexity associated with inclusive value estimation of pollination services required several defendable assumptions, but made estimates more inclusive than previous attempts. Consequently this study provides the basis for continued improvement in context specific pollination service value estimates.     

Mosaic cycles in agricultural landscapes of Northwest Europe

Mosaic cycles were originally understood as cyclical regeneration phases in forests. In this review, we shall examine how far the concept can be extended towards cyclical mosaics of habitat quality in patterned landscapes as a special case of ‘dynamic landscapes’. We will concentrate on habitats and plants in European temperate agricultural landscapes and grasslands in particular. Mosaic cycles of habitat quality are characterised by spatiotemporal shifts between disturbance and secondary succession. We found evidence for mosaic cycles in traditional agricultural systems, modern crop farming, and in recent conservation management. The relevant disturbance parameters to describe land-use drivers of mosaic cycles are spatial extent, frequency, and magnitude (biomass loss). Land-use-related drivers are usually regular and deterministic in space and time, with the exception of year-round grazing by free-ranging large herbivores. Fluctuating soil resources such as water and nutrients in interaction with climate variability add a stochastic component to these (land-use-related) drivers. The proportion of deterministic and stochastic components and their autocorrelation in time and space divides purely deterministic mosaic cycles from purely stochastic dynamic landscapes. In a second part, we briefly review plant life-history traits that may facilitate survival of plants in mosaic cycles of habitat quality. Theoretical studies emphasise (i) dispersal functions for extinction and recolonisation processes of metapopulations, (ii) storage effects as a component of buffered population growth in response to temporal fluctuations of habitat quality, and (iii) competitive ability in metacommunities. We propose a simple scheme relating these functions to the temporal and spatial correlation of patterned landscapes. There are only a very limited number of field studies available that give some support for the proposed scheme. We provide perspectives for further research in this field.     

The restoration of fish ponds in agricultural landscapes

Fish ponds in central and eastern Europe are artificial lakes of less than 1 ha to several 100 ha in size. Some of them were created around 900 years ago. These fish ponds form an important part of the hydrological system in the landscape; they also serve as water purification systems and sediment traps, provide habitat for many plant and animal species, as well as being used for recreation purposes—but above all, they are dedicated to fish production. The original oligo- or mesotrophic character of these fish ponds has been altered to one of eutrophic or even hypertrophic conditions due to the nature of the intensive management for high fish production, as well as agriculture practices within the catchment area. It can also be due to other uses of fish ponds, such as wastewater recipients. A thick layer of black anaerobic sediment invariably develops and serves as an uncontrolled internal source of nutrients. In order to stop the development of water blooms and restore the lake to reasonable healthy conditions, both the external and internal loading has to be reduced. An example of such a fish pond restoration within the Czech Republic is described. The phosphorus budget of the Vajgar fish pond (40 ha, S Bohemia) was evaluated and the dry matter, organic matter, nutrients, heavy metals and other metals content were estimated in the vertical profile of the fish pond's sediment. A precision suction dredger was designed, constructed, and used for the selective removal of 330 000 m³ black sediment from the Vajgar fish pond. The sediment was pumped to settling ponds at a distance of 2.5 km. Later, the suction dredger was used for sediment removal from other fish ponds. In one case, 40 000 m³ of eutrophic sediment was directly applied on an agriculture field. In another case, sediment containing oil products was decontaminated by using a biocatalyst and bacterial culture. Sediment removal from Vajgar fish pond resulted in a temporary negative phosphorus budget (lower concentrations in the outflow than the inflow). The temporary absence of cyanobacteria (Microcystis sp.) blooms was the result of the removal of the black sediment layer. The improvement of water quality after sediment removal was, however, temporary. A more holistic approach, aimed at the reduction of matter losses from the fish pond's catchment area, is therefore being adopted. The principles of such an holistic approach are described.     

Integrated assessment of agricultural production practices to enhance sustainable development in agricultural landscapes

This study presents an integrated assessment approach for the sustainable development of agricultural landscapes. The approach evaluates single agricultural production practices by means of environmental, economic and social indicators. To implement the approach, a mixed method was employed that combines modelling techniques and survey methods. The economic and environmental indicators were implemented within the bio-economic modelling system MODAM (Multi-Objective Decision support system for Agro-ecosystem Management) in order to assess economic performance and the effects on the abiotic and biotic environments. The modelling approach was applied to a case study in a region of north-eastern Germany, within the state of Brandenburg. In addition, the acceptance by farmers of different production alternatives that are known to have environmental benefits was examined in the case study. To allow for a direct comparison between different indicators, the results of the assessment are dimensionless index values that indicate the suitability of certain agricultural production practices with respect to an indicator. The indicator-related indices are then aggregated into an overall index of sustainability differentiating between ‘strong’ and ‘weak’ sustainability. Results are presented for exemplarily chosen production practices for sugar beet, potato and winter rape production and set aside. Depending on the underlying concept of sustainability (‘weak’ vs. ‘strong’), different production practices were identified as the most suitable ones in a given situation. This integrated assessment enables determination of positive and negative correlations between indicators. The approach allows for the identification of production alternatives that are assessed to be economically and environmentally beneficial as well as socially accepted, although at different levels.     

Genetic mosaics of ecosystem functioning across aspen-dominated landscapes

Genetic diversity is the foundation of all biodiversity, and the genetic variation within species is increasingly recognized as being important to ecosystem level processes. Recent research demonstrates that plant genotype influences above- and belowground communities as well as basic ecosystem functions. However, the extent to which plant genotypes create spatial mosaics of genetically mediated ecosystem processes in natural forests is uncertain. We use Populus tremuloides as a model system to demonstrate the importance of plant genotype on carbon and nitrogen cycling in natural systems. We identified 24 distinct P. tremuloides clones with multiple ramets across 25 km² in southern Wisconsin, United States, using microsatellite makers. We then sampled clone leaf chemistry and belowground nutrient content and microbial extracellular enzyme activity. Aspen-induced variation in belowground carbon and nitrogen content, and microbial activity, varied widely among clones. Variation in green leaf chemistry and belowground microbial activity were correlated with genetic distance among clones, such that more genetically distant clones created more divergent patches of ecosystem processes. These data suggest that aspen genotypes create spatial mosaics of genetically mediated ecosystem functioning across natural landscapes and can therefore have evolutionary consequences for co-occurring species.     

Durable strategies to deploy plant resistance in agricultural landscapes

The deployment of resistant crops often leads to the emergence of resistance-breaking pathogens that suppress the yield benefit provided by the resistance. Here, we theoretically explored how farmers' main leverages (resistant cultivar choice, resistance deployment strategy, landscape planning and cultural practices) can be best combined to achieve resistance durability while minimizing yield losses as a result of plant viruses. Assuming a gene-for-gene type of interaction, virus epidemics are modelled in a landscape composed of a mosaic of resistant and susceptible fields, subjected to seasonality, and a reservoir hosting viruses year-round. The model links the genetic and the epidemiological processes, shaping at nested scales the demogenetic dynamics of viruses. The choice of the resistance gene (characterized by the equilibrium frequency of the resistance-breaking virus at mutation-selection balance in a susceptible plant) is the most influential leverage of action. Our results showed that optimal strategies of resistance deployment range from 'mixture' (where susceptible and resistant cultivars coexist) to 'pure' strategies (with only resistant cultivar) depending on the resistance characteristics and the epidemiological context (epidemic incidence and landscape connectivity). We demonstrate and discuss gaps concerning virus epidemiology across the agro-ecological interface that must be filled to achieve sustainable disease management.     

Validation of plant functional types across two contrasting landscapes

Abstract. The validation of plant functional type models across contrasting landscapes is seen as a step towards the claim that plant functional types should recur regionally or even globally. I sampled the vegetation of an urban landscape on a range of sites representing gradients of resource supply and disturbance intensity. A group of plants with similar attributes was considered a ‘functional type’, if the species significantly co‐occurred in a certain segment of the gradient plane of resource supply and disturbance intensity. Vegetative and regeneration traits were considered. A similar study was performed in a nearby agricultural landscape (Kleyer 1999). The logistic regression models from the urban landscape were applied to the data set of the agricultural landscape and vice versa. Although the overall environment of the two landscapes was very different, recurrent patterns of several functional types were found. At high fertility and high disturbance levels, annual species predominated with a persistent seed bank, high seed output, and short vertical expansion. When disturbances changed from below‐ground to above‐ground, the sexual regeneration mode was replaced by the vegetative mode, while vertical expansion remained low. At medium disturbance intensities, the vertical expansion and vegetative regeneration increased with fertility, while the seed bank remained mostly transient to short‐term persistent and lateral expansion and sexual regeneration was intermediate. At low disturbances and low resource supplies, seed bank longevity, and vertical and lateral expansion tended to be long. Diversity of groups of plants with similar attributes was highest at intermediate disturbance levels and low fertility. These results correspond with Grime's humped‐back model and Connell's intermediate disturbance hypothesis.     

Measuring biodiversity and sustainable management in forests and agricultural landscapes

Most of the world's biodiversity will continue to exist outside protected areas and there are also managed lands within many protected areas. In the assessment of millennium targets, there is therefore a need for indicators to measure biodiversity and suitability of habitats for biodiversity both across the whole landscape/seascape and in specific managed habitats. The two predominant land uses in many inhabited areas are forestry and agriculture and these are examined. Many national-level criteria and indicator systems already exist that attempt to assess biodiversity in forests and the impacts of forest management, but there is generally less experience in measuring these values in agricultural landscapes. Existing systems are reviewed, both for their usefulness in providing indicators and to assess the extent to which they have been applied. This preliminary gap analysis is used in the development of a set of indicators suitable for measuring progress towards the conservation of biodiversity in managed forests and agriculture. The paper concludes with a draft set of indicators for discussion, with suggestions including proportion of land under sustainable management, amount of produce from such land, area of natural or high quality semi-natural land within landscapes under sustainable management and key indicator species.     

Testing the transferability of a marsh-inundation model across two landscapes

The effect of water-level (WL) fluctuations on both the structure and functioning of coastal marshes is well documented, and in the past, scientists have demonstrated this by relating historical changes in the areal cover of emergent vegetation (EM) of a particular site to corresponding WL data. This approach of relating areal cover to WL cannot be applied to multiple sites from a region experiencing the same WL because in that instance, WL would be a constant and cannot be used as an explanatory variable for emergent cover. In a previous study of Cootes Paradise Marsh, we proposed the use of a Digital Elevation Model (DEM) to examine the effect of WL fluctuations on emergent plant cover over a 60-year period (1934–1993), and found that the inundated area (IA) was a better predictor of emergent cover than WL. However, the transferability of the marsh-inundation model and the related uncertainty has not yet been tested in a distinct geographic region. In the present article, we test the transferability of the model and develop a regional model of vegetation response to validate the DEM-based method. We confirm the existence of a highly significant relationship between percent IA and percent emergent cover over a large spatial scale in Eastern Lake Ontario. Additionally, we showed that this general relationship might be modified by the degree of urbanization in wetland watersheds. Our results suggest that this DEM-based approach is useful for predicting the aggregate response of EM to annual WL fluctuations and is transferable from local to regional scales. Handling editor: L. M. Bini     

Dispersal of adult aquatic Chironomidae (Diptera) in agricultural landscapes

• 1 This study investigates the possible influence of terrestrial landscape structure on the spatial distribution of adult Chironomidae emerging from water bodies in three agricultural areas, each with hedgerow networks, in Brittany (France).
• 2 Using spatially explicit data from 128 yellow pan traps set in pairs at the bottom of hedges throughout the three study areas, we show that landscape structure and heterogeneity must be considered at two different spatial scales.
• 3 At a global scale, distance to water bodies was the main factor explaining the spatial distribution of adult chironomids: both species richness and abundance changed beyond a critical distance to the stream, resulting in different species assemblages of flying insects.
• 4 At a local scale, the abundance of species and individuals at rest in hedges changed with the quality of the hedge (mainly determined by canopy width and cover of the different vegetation layers).
• 5 The density of the hedgerow network, and landscape openness, both influenced the dispersal of chironomid species from water bodies.
• 6 This study, which provides the first estimate of the dispersal capabilities of chironomids in particular landscapes, suggests that the terrestrial environment is an essential component of population dynamics and community structure in aquatic Chironomidae.