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California's almond industry, valued at $2.3 billion per year, depends on the pollinator services of honey bees, although pollination by other insects, mainly solitary wild bees, is being investigated as an alternative because of recent declines in the number of honey bee colonies. Our objective is to model the movements of honey bees and determine the conditions under which they will forage in less favorable areas of a tree and its surroundings when other pollinators are present. We hypothesize that foraging in less favorable areas leads to increased movement between trees and increased cross pollination between varieties which is required for successful nut production. We use the Shigesada-Kawasaki-Teramoto model (1979) which describes the density of two species in a two-dimensional environment of variable favorableness with respect to intrinsic diffusions and intra- and interspecific interactions of species.
California's almond industry, valued at $2.3 billion per year, depends on the pollinator services of honey bees, although pollination by other insects, mainly solitary wild bees, is being investigated as an alternative because of recent declines in the number of honey bee colonies. Our objective is to model the movements of honey bees and determine the conditions under which they will forage in less favorable areas of a tree and its surroundings when other pollinators are present. We hypothesize that foraging in less favorable areas leads to increased movement between trees and increased cross pollination between varieties which is required for successful nut production. We use the Shigesada-Kawasaki-Teramoto model (1979) which describes the density of two species in a two-dimensional environment of variable favorableness with respect to intrinsic diffusions and intra- and interspecific interactions of species.
Honey bees have garnered much attention in recent years. Concerns about long-term sustainability of pollinator populations have been coupled with concerns about implications for food supplies. We use a novel formulation of a multiple input, multiple output, two season equilibrium simulation model to explore economic linkages across the markets of buyers and sellers of pollination services and honey. We specify and calibrate in a tractable way the empirical relationships between pollinators and the crops they pollinate, especially almonds. Our model highlights the sequential nature of the pollination season and implication for revenue from pollination and honey production. We demonstrate how shifts in almond supply and demand and the much-discussed honey bee hive health problems cause price and quantity adjustments in horizontally and vertically related markets and quantify these effects. We show that the economic fortunes of the almond industry, including demand growth, cost concerns, and the potential for new almond varieties that use fewer bees, crucially affect the returns to beekeeping and the number of hives. These drivers of almond economics also have substantial effects on the cost of pollination for crops that are pollinated later.
Pollinators-insects, birds, bats, and other animals that carry pollen from the male to the female parts of flowers for plant reproduction-are an essential part of natural and agricultural ecosystems throughout North America. For example, most fruit, vegetable, and seed crops and some crops that provide fiber, drugs, and fuel depend on animals for pollination. This report provides evidence for the decline of some pollinator species in North America, including America's most important managed pollinator, the honey bee, as well as some butterflies, bats, and hummingbirds. For most managed and wild pollinator species, however, population trends have not been assessed because populations have not been monitored over time. In addition, for wild species with demonstrated declines, it is often difficult to determine the causes or consequences of their decline. This report outlines priorities for research and monitoring that are needed to improve information on the status of pollinators and establishes a framework for conservation and restoration of pollinator species and communities.
This dissertation concerns itself with the role of flower shape in affecting the foraging performance of pollinating animals. The pollinator used in this study is a model organism representing crepuscular hawkmoths in research involving the study of flight neuromuscular physiology and plant-pollinator interactions, Manduca sexta (hereafter Manduca). The broader goal of the work is to develop a new experimental framework for investigating the ecological and evolutionary consequences of plant-pollinator interactions. To that end, I have combined 3D-printing technology and mathematical modelling to construct artificial flowers, which can be manufactured with great precision and with objective, quantitatively describable shapes. First, I present a proof-of-concept study to demonstrate the feasibility of collecting foraging data from a real animal pollinator attempting to feed from 3D-printed artificial flowers. I show that Manduca’s foraging performance is extremely sensitive to variation in floral corolla curvature and nectary diameter. These results validate the experimental approach that I describe, justifying a large investment of time and financial resources into a major iterative improvement of my experimental apparatus. Next, I describe the improved experimental apparatus and use it to construct a performance landscape of Manduca’s innate foraging performance as a function of variation in flower morphology. This landscape suggests that Manduca’s foraging performance is contingent on a context-dependent interaction between corolla curvature and nectary diameter. Finally, I use data from infrared sensors attached to each artificial flower and custom computer vision software (both improvements over the proof-of-concept apparatus) to identify putative proxies of fitness for both the pollinator and the plant (artificial flower). The goal is to examine whether the pollination mutualism between Manduca and the flowers that it visits in nature could represent a scenario of evolutionary conflict or harmony. The results are inconclusive due to opposing conclusions that the various indirect proxies of flower fitness point to. As a result, I make suggestions for improving the experimental apparatus even further by including a physical touch-sensitive sensor into the design of the artificial flowers. Such a sensor would act as a physical analogue for a real flower’s reproductive structures, allowing the apparatus to yield a direct rather than indirect measure of flower fitness. Still, the general framework of using 3D-printed flower whose shapes are mathematically specified shows great promise for opening up new areas of experimental inquiry in the field of plant-pollinator interactions.
The myriad ways species interact with each other have always captivated biologists. These interactions-predation, competition, parasitism, and mutualism-are fundamental to the stability of ecological communities and drive the evolution of species they contain. Some mutualistic systems consist of mutually dependent partners that strongly influence each other's survival, while other mutualistic systems consist of many, diffuse relationships between large assemblages of partners. Critical ecological processes like pollination and seed dispersal are prime examples of such complex systems. Plant-pollinator communities are characterized by extensive pollinator sharing among plant species. My dissertation explores some of the consequences of this reliance on shared pollinators on the structure of plant-pollinator interaction networks, the foraging decisions of pollinators, and the fitness outcomes of plant species. Through several comprehensive field studies, I contribute to our understanding of mutualist interaction patterns at multiple levels of biological hierarchy: the community, species, and individuals. My first chapter examines the forces driving the change in interaction patterns of an entire plant-pollinator community and individual species throughout the flowering season. Nearly all studies of plant-pollinator interaction networks ignore potential intra-annual variation, and in doing so may be missing critical mechanisms contributing to overall community stability. I find that the overall turnover of interactions is high and driven by a process of interaction rewiring in which species frequently shuffle between available partners. Furthermore, I distinguish pollinator species whose interactions are driven by an abundance-based neutral process versus those that change their interactions beyond what is predicted by a neutral, abundance-driven null model. My second chapter uses a network-based framework to consider the fitness consequences for plants participating in a diffuse plant-pollinator network. I analyze the relationship between plant species' network metrics and pollen deposition. Empirical examples that link patterns of interactions and functional outcomes (e.g., pollination) are scarce, but necessary to establish the utility of characterizing species interaction patterns. My final chapter explores how pollinator composition, local floral neighborhoods, and timing of flowering influence the pollination outcomes of individual Oenothera fruticosa flowers. I demonstrate extensive intraspecific variation in receipt of pollen from other species ('heterospecific pollen receipt') and find that this heterospecific pollen has a negative fitness effect if present in sufficiently high amounts. Together, the chapters of my thesis provide novel insights into the consequences of pollinator sharing among co-flowering plant species.
Economists have been interested in markets for pollination services since Meade (1952) described the reciprocal benefits of pollination. However, the California almond pollination market does not fit the typical reciprocal benefits perspective because beekeepers and almond growers have diverging preferences. It is not profitable for beekeepers to extract and market almond honey, because it is not palatable to humans. Furthermore, California almonds bloom in mid-February, a time when colonies are naturally at their smallest size in a state of winter dormancy. Honey bee colonies exhibit increasing returns to scale in pollination, so almond growers prefer high colony strength. Beekeepers must invest inputs into colonies to increase colony strength for almond pollination. During and immediately after almond bloom very little is blooming elsewhere. Because California almond pollination now requires over three-fourths of all colonies in the United States, immediately following almond bloom most beekeepers must either feed their colonies food supplements or compete for the small number of other crop pollination contracts in California and the Pacific Northwest. An incentive problem thus exists in almond pollination: delivering colonies with high colony strength is costly to the beekeeper while high colony strength is desired by the almond grower. I develop a principal-agent model in Chapter 2 to show that a profit-maximizing almond grower conditions the per-colony fee on delivered colony strength to incentivize beekeepers to invest effort into increasing colony strength. I then explore the types of contracts used during the 2015 almond pollination season using a grower survey that I conducted at the Almond Board of California's 2015 Almond Conference. Although I find variation in the contract provisions used, nearly 90 percent of the 74 analyzed respondents had contracts which included a minimum colony strength requirement. Chapter 3 is a complete summary of the almond grower survey, which provides the first formal information on provisions used in almond pollination contracts reported publicly. In this chapter, I find that almond pollination agreements are often relational in nature and repeated over many pollination seasons. I conclude that growers likely vary in preferences for almond pollination contract provisions and enforcement based on their trust and relationships with beekeepers, expectations regarding yield benefits, experience in the industry, and monitoring costs due to the amount of acreage they own. In Chapter 4, I explore outcomes of the contract provisions discussed in Chapters 2 and 3. I estimate the effect of delivered colony strength on per-colony almond pollination fees using the California State Beekeeper's Association survey responses from years 2008-2016. Because a beekeeper's colony mortality rate over the winter and her delivered colony strength for almond pollination should be related through exogenous colony health issues, I use a beekeeper's reported winter mortality rate as a proxy for her delivered colony strength. I estimate that a 10 percentage point increase in a beekeeper's winter mortality rate leads to an average decrease of 16 percent in total revenues from almond pollination, due to the beekeeper having fewer colonies to rent and receiving lower per-colony fees for her surviving colonies. Chapter 5 highlights the interdependent relationship of almond production and honey bee colony health caused by the large demand for colonies for almond pollination relative to the U.S. honey bee colony population. I analyze data provided by the California Department of Food and Agriculture, which contains information on each out-of-state apiary shipment entering California. I determine that shipments into California are concentrated in major almond-producing counties, often at densities over 35 colonies per square mile. In 2016, roughly 76 percent of colonies shipped into California for almond pollination came from eight states, most of which are in the northwestern U.S. Since 2008, the state with the largest increase in colony shipments into California was Florida, whose shipments increased by 278 percent. Florida has relatively high transportation costs of supplying colonies to California, suggesting that the per-colony cost of the marginal supplier of colonies for almond pollination has increased since 2008. I find that when a state's winter mortality rate is above average, the number of colony shipments into California from that state is often below average. Alternatively, when California beekeepers experience higher than average winter mortality rates, out-of state shipments increase to make up for the smaller in-state supply of colonies. The conclusions of this dissertation provide many contributions to the economic literature on pollination services, as well as to policy regarding the improvement of pollinator health. Chapters 2, 3, and 4 show that colony strength is an important consideration for beekeepers and almond growers alike. Because colony strength varies and fees are conditional on colony strength, averaging almond pollination fees is equivalent to averaging prices of heterogeneous products which can result in incorrect inference regarding supply and demand. Thus, it is important to collect survey data on colony strength requirements as well as pollination fees to get an accurate representation of market conditions. Ignoring the role of colony strength underestimates the economic impacts of colony health issues. First, such issues often lead to low delivered colony strength in addition to high winter mortality rates. Thus, beekeepers' returns per surviving colony are reduced. These losses can be substantial given that almond pollination is a large share of commercial beekeepers' revenues. Second, the findings of Chapter 5 highlight the sizable risks faced by beekeepers and almond growers due to the interdependent relationship between honey bee colony health and almond production. High concentrations of honey bee colonies in California almond-producing counties could lead to the rapid spread of pest and diseases among colonies, while colony health issues in regions that are main suppliers of colonies for almond pollination could significantly decrease the number and strength of colonies available for almond pollination.
Reviews of Environmental Contamination and Toxicology attempts to provide concise, critical reviews of timely advances, philosophy and significant areas of accomplished or needed endeavor in the total field of xenobiotics, in any segment of the environment, as well as toxicological implications.
This is the third of three volumes based on the 2nd Pan-Pacific Conference on Pesticide Chemistry. The proposed title examines metabolism and residue analysis methods of environmental pesticides.