It is clear that the majority of flowering plants are pollinated by insects and other animals, with a minority utilising abiotic pollen vectors, mainly wind. However there is no accurate published calculation of the proportion of the ca 352 000 species of angiosperms that interact with pollinators. Widely cited figures range from 67% to 96% but these have not been based on firm data. We estimated the number and proportion of flowering plants that are pollinated by animals using published and unpublished community‐level surveys of plant pollination systems that recorded whether each species present was pollinated by animals or wind. The proportion of animal‐pollinated species rises from a mean of 78% in temperate‐zone communities to 94% in tropical communities. By correcting for the latitudinal diversity trend in flowering plants, we estimate the global number and proportion of animal pollinated angiosperms as 308 006, which is 87.5% of the estimated species‐level diversity of flowering plants. Given current concerns about the decline in pollinators and the possible resulting impacts on both natural communities and agricultural crops, such estimates are vital to both ecologists and policy makers. Further research is required to assess in detail the absolute dependency of these plants on their pollinators, and how this varies with latitude and community type, but there is no doubt that plant–pollinator interactions play a significant role in maintaining the functional integrity of most terrestrial ecosystems.

One view of pollination systems is that they tend toward specialization. This view is implicit in many discussions of angiosperm evolution and plant—pollinator coevolution and in the long—standing concept of pollination syndromes. But actual pollination systems often are more generalized and dynamic than these traditions might suggest. To illustrate the range of specialization and generalization in pollinators' use of plants and vice versa, we draw on studies of two floras in the United States, and of members of several plant families and solitary bee genera. We also summarize a recent study of one local flora which suggests that, although the colors of flowers are aggregated in phenotype space, there is no strong association with pollinator types as pollination syndromes would predict. That moderate to substantial generalization often occurs is not surprising on theoretical grounds. Plant generalization is predicted by a simple model as long as temporal and spatial variance in pollinator quality is appreciable, different pollinator species do not fluctuate in unison, and they are similar in their pollination effectiveness. Pollinator generalization is predicted when floral rewards are similar across plant species, travel is costly, constraints of behavior and morphology are minor, and/or pollinator lifespan is long relative to flowering of individual plant species. Recognizing that pollination systems often are generalized has important implications. In ecological predictions of plant reproductive success and population dynamics it is useful to widen the focus beyond flower visitors within the correct" pollination syndrome, and to recognize temporal and spatial fluidity of interactions. Behavioral studies of pollinator foraging choices and information—processing abilities will benefit from understanding the selective advantages of generalization. In studies of floral adaptation, microevolution, and plant speciation one should recognize that selection and gene flow vary in time and space and that the contribution of pollinators to reproductive isolation of plant species may be overstated. In conservation biology, generalized pollination systems imply resilience to linked extinctions, but also the possibility for introduced generalists to displace natives with a net loss of diversity.

By facilitating plant reproduction, pollinators perform a crucial ecological function that supports the majority of the world's plant diversity, and associated organisms, and a significant fraction of global agriculture. Thus pollinators are simultaneously vital to supporting both natural ecosystems and human food security, which is a unique position for such a diverse group of organisms.The past couple of decades have seen unprecedented interest in pollinators and pollination ecology, stimulated in part by concerns over the decline of pollinator abundance and diversity in some parts of the world. This review synthesizes what is currently understood about the taxonomic diversity of organisms that are known to act as pollinators; their distribution in both deep time and present space; the importance of their diversity for ecological function (including agro-ecology); changes to diversity and abundance over more recent timescales, including introduction of non-native species, and a discussion of arguments for conserving their diversity.

The pollination syndrome hypothesis as usually articulated does not successfully describe the diversity of floral phenotypes or predict the pollinators of most plant species. Caution is suggested when using pollination syndromes for organizing floral diversity, or for inferring agents of floral adaptation. A fresh look at how traits of flowers and pollinators relate to visitation and pollen transfer is recommended, in order to determine whether axes can be identified that describe floral functional diversity more successfully than the traditional syndromes.

but have declined in species richness, geographical range and abundance (2-5). Previous studies have assessed the roles played by habitat destruction and loss of flower resources (4,5), and pesticides (6) over relatively modest time scales and geographical ranges.Analyses of regions are rare (7-10) and our understanding of the effects of humanmediated actions over longer periods is limited. Here we assess the bee and flowervisiting wasp species that have gone extinct in Britain, using 494,117 records held by the Bees, Wasps and Ants Recording Society (BWARS), probably the most detailed available for a single country. We define extinct species as those that have not been recorded for at least 20 years following their last observation, despite extensive efforts by members of BWARS and other naturalists.Twenty-three bee and flower-visiting wasp species have become extinct in Britain (Table 1), including formerly widespread species. We exclude single early records that cannot be verified as representing stable breeding populations, but include one species which has recolonized Britain after an absence of six decades (see Supplementary Materials).Since the mid 19 th century the pattern of British bee and wasp extinctions has been characterized by intervals of relative stability, in which few species were lost, interspersed with times when over three species per decade went extinct ( Figure 1, Table 2). These data indicate a period of relatively sustained extinctions from the late 1920s to the late 1950s, with other isolated extinction peaks before and after this time. These features are confirmed in Figure 2, where the average gradient indicates the relative extinction rate over a period, and the period of sustained extinctions is evident as the phase of maximum gradient during the mid 20 th century.The varying rates of extinctions were quantified by applying breakpoint analysis to the cumulative record. In this analysis, a piecewise linear model is fitted to data to reveal periods of approximately constant extinction rate, separated by breakpoints where the rate changes. The analysis was iterated for up to 10 breakpoints and the Akaike Information Criterion (AIC), confirmed by coefficient of determination (multiple-R 2 ), was used to establish the best model (see Supplementary Materials). For these data, changes in AIC and muliple-R 2 level off for two models having four breakpoints (Table S2). These are very similar, sharing the latter three breakpoints, and revealing effectively identical periods of approximately uniform extinction rate for the majority of the 20 th century (Table 2).Both models must be interpreted with caution as the data for 'year last recorded' may not equate to 'year last living'. Declines in populations due to habitat changes may mean a species went unrecorded for some years prior to the actual extinction. The robustness of the breakpoints to this potential ambiguity of the probability of the 'year last living' has been assessed and, whilst there is some sensitivity in the timing of the e...

Flowering times of plants are important life-history components and it has previously been hypothesized that flowering phenologies may be currently subject to natural selection or be selectively neutral. In this study we reviewed the evidence for phenotypic selection acting on flowering phenology using ordinary and phylogenetic meta-analysis. Phenotypic selection exists when a phenotypic trait co-varies with fitness; therefore, we looked for studies reporting an association between two components of flowering phenology (flowering time or flowering synchrony) with fitness. Data sets comprising 87 and 18 plant species were then used to assess the incidence and strength of phenotypic selection on flowering time and flowering synchrony, respectively. The influence of dependence on pollinators, the duration of the reproductive event, latitude and plant longevity as moderators of selection were also explored. Our results suggest that selection favours early flowering plants, but the strength of selection is influenced by latitude, with selection being stronger in temperate environments. However, there is no consistent pattern of selection on flowering synchrony. Our study demonstrates that phenotypic selection on flowering time is consistent and relatively strong, in contrast to previous hypotheses of selective neutrality, and has implications for the evolution of temperate floras under global climate change.

Vigorous discussion of the degree of specialization in pollination interactions, combined with advances in the analysis of complex networks, has revitalized the study of entire plantÁpollinator communities. Noticeably rare, however, are attempts to quantify temporal variation in the structure of plantÁpollinator networks, and to determine whether the status of species as specialists or generalists is stable. Here we show that network structure varied through time in a montane meadow community from southern California, USA, in that pollinator species did not form the same links with plant species across years. Furthermore, composition of the generalized core group of species in the network varied among summers, as did the identity of those species involved in relationships that appeared to be reciprocally specialized within any one summer. These differences appear to be related to severe drought conditions experienced in the second summer of the 3 year study. In contrast to this variation, the pollinator community remained similarly highly nested in all three summers, even though species were packed into the nested matrix differently from year to year. These results suggest that plantÁpollinator networks vary in detail through time, while retaining some basic topological properties. This dynamic aspect of community-scale interactions has implications for both ecological and evolutionary inferences about pollination mutualisms.

Research on urban insect pollinators is changing views on the biological