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This chapter considers methods for quantifying the importance of bees in pollinating a crop and in producing field-to-field cross-pollination and gene flow. Simple theoretical models are presented whose parameters identify key governing influences on bee pollination. The values of some parameters are known, particularly in systems involving honey bees and bumble bees, and their implications for the confinement of genetically-modified crops are discussed. Specific parameters whose values are unknown are identified as targets for future work.

This chapter examines abiotic pollination via wind or water. It begins with a discussion of wind pollination or anemophily, which is a common occurrence in modern plants, especially in most gymnosperms, in the catkin-bearing angiosperm trees, and in cereals (Poaceae and Cyperaceae). Anemophily is predominantly a derived condition in angiosperms, associated with ecological conditions where zoophily is difficult. Transition from zoophily to anemophily has occurred at least sixty-five times in such circumstances. The chapter looks at wind-pollinated angiosperm and conifer flowers and goes on to consider critical factors affecting pollen movement in anemophilous plants. It concludes with an overview of hydrophily, or water pollination.

This chapter examines the core issues raised by critiques of pollination syndromes and alternative approaches to characterizing pollination in communities, in the context of floral and pollinator specialization. It first considers theoretical arguments against syndromes and specialization before discussing practical evidence against syndromes, along with proposed alternative approaches, focusing in particular on ecological models of specialization and generalization. It then explores some problems with pollination webs, several key issues relating to specialization and generalization, and selection for specialization in flower–pollinator interactions. It also compares patterns of generalization and specialization in different ecosystems and asks whether generalization can be reversed. The chapter concludes with some reflections on the debate over generalization, specialization, and pollination syndromes.

This chapter examines brood site mutualisms, where the pollinators are florivores. In brood site mutualisms, the pollinators are sometimes referred to as nursery pollinators. Here pollination success affects not only plant fitness but also pollinator fitness, and the balance between costs and benefits may be highly variable from place to place and across seasons. There are at least thirteen known nursery pollination systems, and this phenomenon can be divided into three categories. Two of these are relatively unspecialized, where beetle or lepidopteran larvae develop in decomposing flower heads, or where thrips feed in flowers as pollen parasites. The third category is termed “active pollination,” also known as “seed-eating pollination syndrome.” The chapter first considers nursery pollination and thrips as pollen parasites before discussing active pollination, where active pollen transfer occurs and a clear mutualism results.

This chapter examines the environmental economics of pollination, with particular emphasis on the costs that may be incurred and that have to be offset against the rewards gathered. Pollination is usually regarded as a mutualism, of benefit to both partners, each of which gains in fitness. In such a relationship, both should be trying to maximize their survival and ultimately their reproductive success, which will require balancing their costs against the rewards and hence assessing the net benefits gained. Disentangling the economic aspects of the interaction for each participant has become a major area of study in pollination ecology. The chapter first considers the conflicting requirements of a plant and its pollinators before discussing the costs incurred by the plant and the costs incurred by a flower-visiting animal. It also explores the effects of the environment on flower-pollinator interactions as economic transactions.

This chapter examines competition in the context of pollination ecology. Competition is typically treated from the perspective of the plants, but it is also likely to occur among and between the pollinators. Furthermore, competition can occur at various levels—as a structuring factor in communities, as a selective force on an individual plant’s phenology, morphology, or rewards, and at a genetic level structuring competition for pollens between males, and female choice between possible mates. The chapter first considers several types of of competition in pollination ecology, potential outcomes of competition, and competition between pollinators before discussing how selection reduces intraspecific competition among plants and competition among pollinators. It also explores paternity, maternity, and gene flow in coflowering communities, focusing in particular on male competition and female choice, along with gene flow via pollen dispersal and seed dispersal.

This chapter focuses on the pollination of crops. Animal pollination is important to the large majority of important crops, including those directly eaten by humans. However, there are differing absolute and relative needs for pollination. The chapter begins with a discussion of food crop types that need animal pollination, including wheat, oats, rice, maize, rye, barley, peanut, potato, cassava, sugarcane, and banana. It then considers a fairly standard set of tests that should be applied to determine what a good pollinator will be. It also provides examples that illustrate particular problems of crop productivity or crop management, from plants grown intensively or on a small and local scale, and in a wide range of habitats. Finally, it examines general approaches to encouraging pollination, along with problems associated with hybrid crops, seed crops, and crop breeding.

This chapter introduces some of the book’s central themes on animal pollination, beginning with a discussion of animals that visit flowers. At least 130,000 species of animals, and probably up to 300,000, are regular flower visitors and potential pollinators. At least 25,000 species of bees are included in this total, all of them obligate flower visitors and often the most important pollinators in a given habitat. There are currently about 260,000 species of angiosperms and it has been traditional to link particular kinds of flowers to particular groups of pollinators. The chapter proceeds by explaining why animals visit flowers, how flowers encourage animal visitors, and what makes a visitor a good pollinator. It also considers the costs, benefits, and conflicts in animal pollination before concluding with an enumeration of reasons why pollination is worth studying.

This chapter examines flower design features related to sexual function in pollination. Flowers show remarkable variations in shape, size, and appearance, and are known for their tendency to mass together as inflorescences. In this case the overall floral display is determined by the combined appearance of a cluster of small flowers into one seemingly whole structure, which may in practice be the unit that is perceived, both by humans and by flower visitors, as the functional flower. The chapter first considers the essential flower morphology before discussing the perianth, the androecium (the male functional organs of a flower), and the gynoecium (the female organ system). It then describes flower and inflorescence features, particular floral shapes, floral size and size range, and floral sex and floral design. Finally, it provides an overview of the essentials of floral design in relation to cross-pollination.

This chapter discusses the role of flower-visiting species richness for crop pollination services. General arguments why flower-visitor species richness can be important for the mutualistic plant partners are described; highlighting the mechanisms that underlie flower-visiting species richness-pollination services relationships. The visualization and quantification of plant-flower visitor interaction webs are demonstrated and linked to crop pollination research. Current knowledge about the consequences of pollinator decline for the global food supply are presented and pollination markets for honey bees and other bee species are discussed using alfalfa as a case study. This chapter shows that conservation and restoration for high species richness is important to provide insurance and stabilise for pollination services interacting with nature in a changing world.

Perfect (hermaphrodite) flowers can, assuming no other constraints, self-pollinate, and fertilize their own ovules. This guaranteed sexual reproduction gives self-pollinating plants the ability to colonize new habitats, and it is a common trait in weedy species. However, self-fertilization does carry a disadvantage relative to outcrossing, which is that the genetic variability produced, although greater than in an asexual population, is considerably less than that seen in an outbreeding population. The balance between the relative importance of assured reproduction and genetic variability differs in different species, largely as a result of their habitats, lifecycles, and the niches that they occupy. This chapter considers the ways in which self-fertilization can be reduced or prevented through dichogamy, herkogamy, monoecy, dioecy, and biochemical self-incompatibility.

The underlying assumption of much of the work on flower development and morphology is that these features serve to increase the attractiveness of the flower to pollinating animals, thus maximizing pollinator attention, and consequently seed set and fitness. It has long been believed that these elaborations are the consequence of adapting to attract particular pollinating animals, resulting in pollination syndromes. Before the existence of pollination syndromes and how frequently they are needed are examined, this chapter considers whether there is evidence that the underlying assumptions are met. This chapter addresses one fundamental issue: do plants actually benefit from increased pollinator attention and should floral attractiveness therefore be expected to increase across generations?

The concept of the pollination syndrome has underlain much of floral biology for many years. This chapter assesses the usefulness of the concept in understanding flowers and flowering. It begins by considering why and how the pollination syndrome concept has become so entrenched in the literature on flowering, and then examines whether the key assumptions that underlie it are met. Finally, it assesses the experimental evidence that pollination syndromes do exist, and the experimental evidence which shows them to be false — those cases where the major pollinator in the native habitat is not that which the flower's morphology would lead you to predict. The chapter also provides a brief overview of the relative importance of generalization and specialization in pollination ecology.

This chapter introduces the natural history and evolution of bees, why bees are important for pollination, and why plants are important to bees. It presents the intent of the book and a summary of its contents.

Historically, farmers obtained pollination services from wild, unmanaged bees or made habitat modifications to attract them. Today, agriculture demands the use of managed bees, usually honey bees, although their availability is becoming uncertain due to diseases, pests, and other unknown causes of mortality. This chapter addresses the roles that wild bees play in agriculture today, and what roles they could play in the future. Research has shown that in some circumstances, wild bees can partially or fully replace managed bees or actually enhance their effectiveness as pollinators. Land use changes and habitat loss impact wild bee communities and their ability to provide pollination services within agricultural systems, and agricultural intensification can affect wild bee diversity and abundance in both positive and negative ways. The economic value of wild bee services is discussed, and the ways in which agricultural lands can be managed to restore healthy communities of wild bees.

Federal land managers desire seed of Great Basin perennial wildflowers, mixed with grass and shrub seed, for restoration of millions of acres of sagebrush communities degraded by altered wildfire regimes and exotic grasses and forbs. For fifteen candidate wildflower species to be farmed for seed production, all were found to need pollinators, typically bees (Apiformes), for fruit and seed production. Some can be pollinated with currently managed bees (honey bees, alfalfa leafcutting bees), but for others, management protocols and starting populations are being developed for suitable species of native Osmia bees.

Several solitary bee species in the genus Osmia have been studied as potential pollinators of fruit trees and other early-blooming crops. Methods to manage large populations in agro-ecosystems have been developed for at least three species. This chapter reviews current knowledge on the life cycle of Osmia and emphasizes the need to establish a solid ecophysiological basis to develop adequate rearing methods for these species. Two phenological events — the timing of adult diapause in the autumn, and the timing of emergence in the spring — require particular attention when managing Osmia populations. The timing of adult diapause is critical because pre-wintering temperatures have a profound effect on fat body depletion, winter survival, and vigor at emergence. Timing of emergence and its synchronization with bloom of the target crop is important to maximize pollination and production of bee progeny. Both events can be adjusted with proper temperature management.

Genetic modification (GM) of crops has been accompanied by concerns of environmental impact, including effects to beneficial organisms such as bees. Currently, most commercial GM crops are modified for pest and/or herbicide resistance. Transgenes such as Bt may be expressed in pollen, resulting in exposure to bees. However, studies to date indicate that crops transformed with genes coding for Bt proteins will not harm bees. Herbicide resistant crops are not likely to pose direct toxicity effects to bees; yet, greater weed control in herbicide resistant crops may be responsible for a lower bee abundance in these crops than non-transformed crops. Reduced pesticide use associated with insect resistant GM crops, and reduced tillage that is possible with herbicide tolerant crops, could be beneficial to bee populations compared to conventional agriculture. Risk of GM crops to bees should be assessed on a case-by-case basis in relation to feasible alternatives.