Climate-driven interannual variability of water scarcity in food production potential: A global analysis

Interannual climatic and hydrologic variability has been substantial during the past decades in many regions. While climate variability and its impacts on precipitation and soil moisture have been studied intensively, less is known on subsequent implications for global food production. In this paper we quantify effects of hydroclimatic variability on global "green" and "blue" water availability and demand in global agriculture, and thus complement former studies that have focused merely on long-term averages. Moreover, we assess some options to overcome chronic or sporadic water scarcity. The analysis is based on historical climate forcing data sets over the period 1977-2006, while demography, diet composition and land use are fixed to reference conditions (year 2000). In doing so, we isolate the effect of interannual hydroclimatic variability from other factors that drive food production. We analyse the potential of food production units (FPUs) to produce a reference diet for their inhabitants (3000 kcal cap-1 day -1, with 80% vegetal food and 20% animal products). We applied the LPJmL vegetation and hydrology model to calculate the variation in green-blue water availability and the water requirements to produce that very diet. An FPU was considered water scarce if its water availability was not sufficient to produce the diet (i.e. assuming food self-sufficiency to estimate dependency on trade from elsewhere). We found that 24% of the world's population lives in chronically water-scarce FPUs (i.e. water is scarce every year), while an additional 19% live under occasional water scarcity (water is scarce in some years). Among these 2.6 billion people altogether, 55% would have to rely on international trade to reach the reference diet, while for 24% domestic trade would be enough. For the remaining 21% of the population exposed to some degree of water scarcity, local food storage and/or intermittent trade would be enough to secure the reference diet over the occasional dry years

Effects of initial aquifer conditions on economic benefits from groundwater conservation

Worldwide, there is growing recognition of the need to reduce agricultural groundwater use in response to rapid rates of aquifer depletion. To date, however, few studies have evaluated how benefits of conservation vary along an aquifer's depletion pathway. To address this question, we develop an integrated modeling framework that couples an agro-economic model of farmers' field-level irrigation decision-making with a borehole-scale groundwater flow model. Unique to this framework is the explicit consideration of the dynamic reductions in well yields that occur as an aquifer is depleted, and how these changes in intraseasonal groundwater supply affect farmers' ability to manage production risks caused by climate variability and, in particular, drought. For an illustrative case study in the High Plains region of the United States, we apply our model to analyze the value of groundwater conservation activities for different initial aquifer conditions. Our results demonstrate that there is a range of initial conditions for which reducing pumping will have long-term economic benefits for farmers by slowing reductions in well yields and prolonging the usable lifetime of an aquifer for high-value irrigated agriculture. In contrast, restrictions on pumping that are applied too early or too late will provide limited welfare benefits. We suggest, therefore, that there are ‘windows of opportunity’ to implement groundwater conservation, which will depend on complex feedbacks between local hydrology, climate, crop growth, and economics

Floral abundance and resource quality influence pollinator choice

1. Pollinator declines caused by forage habitat loss threaten insect pollination services. Pollinating insects depend on adequate floral resources, and their ability to track these resources. Variability of these resources and the effect on insect foraging choice is poorly understood. 2. We record patterns of visitation to six wildflower species and test the hypotheses that: pollinators preferentially visit the most rewarding flowers; nectar diurnal variations affect foraging preferences; pollinators respond most strongly to nectar rewards. 3. Nectar volume and sugar concentration were negatively correlated within plant species over time of day where greater concentration and lower volume was evident in the afternoon, but this did not correspond to pollinator visitation. Both floral abundance and nectar quality (total sugar per inflorescence) positively affect insect visitation. For some foragers, the positive effects of high quality rewards were only evident when floral abundance was high (>50 inflorescences per patch), perhaps reflecting the low probability of pollinators detecting scarce rewards. Pollen quality (total protein per inflorescence) was negatively related to visitation of Apis mellifera and Bombus pascuorum. 4. Fewer pollinators visiting flowers of higher pollen quality could reflect plant allocation trade-offs or the presence of secondary metabolites in pollen, meaning pollen foraging is likely affected by factors other than protein concentration. Nectar rather than pollen appeared to be the main driver of floral choice by insects in this system. 5. Conservation schemes for bees in farmland or gardens might benefit from ensuring that rewarding plant species are present at high density and/or are aggregated in space

Floral sonication is an innate behaviour in bumblebees that can be fine-tuned with experience in manipulating flowers

Bumblebees demonstrate an extensive capacity for learning complex motor skills to maximise exploitation of floral rewards. This ability is well studied in nectar collection but its role in pollen foraging is less well understood. Floral sonication is used by bees to extract pollen from some plant species with anthers which must be vibrated (buzzed) to release pollen. Pollen removal is determined by sonication characteristics including frequency and amplitude, and thus the ability to optimise sonication should allow bees to maximise the pollen collection. We investigated the ability of the buff-tailed bumblebee (Bombus terrestris) to modify the frequency and amplitude of their buzzes with increasing experience manipulating flowers of the buzz-pollinated plantSolanum rostratum. We analysed flight and feeding vibrations generated by naïve workers across feeding bouts. Feeding buzzes were of a higher frequency and a lower amplitude than flight buzzes. Both flight and feeding buzzes had reduced amplitudes with increasing number of foraging trips. However, the frequency of their feeding buzzes was reduced significantly more than their flight buzzes as bumblebee workers gained experience manipulating flowers. These results suggest that bumblebees are able to modify the characteristics of their buzzes with experience manipulating buzz-pollinated flowers. We discuss our findings in the context of bumblebee learning, and the current understanding of the optimal sonication characteristics for releasing pollen in buzz-pollinated species. Our results present a tantalising insight into the potential role of learning in floral sonication, paving the way for future research in this area

Divergent Rules for Pollen and Nectar Foraging Bumblebees – A Laboratory Study with Artificial Flowers Offering Diluted Nectar Substitute and Pollen Surrogate

Almost all bees collect nectar and pollen from flowers. Female bees collect pollen to provision their nest cells, whereas they use nectar for individual energy supply and nest cell provisioning. Bees fine-tune nectar foraging to the amount and to the concentration of nectar, but the individual bees' response to variability of amount and concentration of pollen reward has not yet been studied thoroughly in laboratory settings. We developed an experimental set-up in which bumblebees simultaneously collected sugar solution and pollen from artificial flowers; natural pollen was mixed with cellulose powder or glass powder as a pollen surrogate. Here we show that bumblebee (Bombus terrestris) workers do not specialise in nectar or pollen collection, but regularly collect both rewards on the same day. When offered a fixed pollen reward and varied amounts and concentrations of sugar solution, the bumblebees fine-tuned sugar solution foraging dependent on both the volume and concentration, with strong preferences for the highest concentration and the greatest volume. In the reciprocal tests, when offered a fixed sugar reward and varied amounts and concentrations of pollen mixed with a nutrient-free pollen surrogate, the bumblebees follow more an all-or-none rule for pollen, accepting all amounts and concentrations except pure surrogate. It is discussed how the bumblebees' ability to sense sugar, and their apparent inability to sense the pollen protein content, shaped their foraging behaviour. It is argued that the rarity of nectar mimicry and the frequency of pollen mimicry in natural flowers might be interpreted in the context of divergent abilities of nectar and pollen recognition in bees

Combinations of rewards in the individual foraging on resources varying in both quality and quantity experiment.

<p>Quantity and quality of sugar solution and pollen rewards offered simultaneously in four series of tests, each of them comprising five tests with a varied reward – different quantities or qualities – of one resource and a standard reward of the other resource.</p

Summary of foraging behaviour for 48 tagged bumblebee workers.

<p><b>A</b>: Mean amount of days that the bumblebee workers perform specific foraging tasks. Each bumblebee was observed on 20–41 days (mean number of days observed  = 26.52±1.29 SE). Note that while collecting pollen, bumblebees also gathered small amounts of sugar solution to pack the pollen; the column “pollen” thus excludes foraging bouts just for sugar solution. <b>B</b>: Summary of all foraging tasks performed by each bumblebee in the course of the observation period. 7 bumblebees only ever collected sugar solution, 41 bumblebees collected sugar solution, pollen, or both sugar solution and pollen on different days.</p