Abstract
Understanding diversity in flower-visitor assemblages helps us improve pollination of crops and support better biodiversity conservation outcomes. Much recent research has focused on drivers of crop-visitor diversity operating over spatial scales from fields to landscapes, such as pesticide and habitat management, while drivers operating over larger scales of continents and biogeographic realms are virtually unknown. Flower and visitor traits influence attraction of pollinators to flowers, and evolve in the context of associations that can be ancient or recent. Plants that have been adopted into agriculture have been moved widely around the world and thereby exposed to new flower visitors. Remarkably little is known of the consequence of these historical patterns for present-day crop-visiting bee diversity. We analyse data from 317 studies of 27 crops worldwide and find that crops are visited by fewer bee genera outside their region of origin and outside their family's region of origin. Thus, recent human history and the deeper evolutionary history of crops and bees appear to be important determinants of flower-visitor diversity at large scales that constrain the levels of visitor diversity that can be influenced by field- and landscape-scale interventions.
Highlights
Flowers that attract insects have been a feature of most angiosperm lineages since the Cretaceous [1], and with the rise and diversification of angiosperms, they have become the dominant reproductive mode for terrestrial plant life, including those plants we have domesticated as crops
Because insect pollination is important to so many angiosperms [2], and pollinator taxa differ in the ways they interact with flowers, it has been argued that the diversity of angiosperm lineages and their many floral forms arises in part from differential selection driven by different pollinator taxa [3]
Observed declines of insect pollinators [45,46] have motivated much research into the drivers of crop-visitor diversity, which has revealed important factors such as habitat and pesticide management that operate over spatial scales from fields to landscapes [17,18]
Summary
Flowers that attract insects have been a feature of most angiosperm lineages since the Cretaceous [1], and with the rise and diversification of angiosperms, they have become the dominant reproductive mode for terrestrial plant life, including those plants we have domesticated as crops. Exotic plants have been shown to attract fewer pollinator taxa compared to native plants in one north American study [15] If this pattern proves to be general, it would help to explain why typically only 12–13% of the bee species within a region are observed exploiting agricultural crops [16]. The deeper biogeographic histories of crop lineages might give rise to another level of geographical variation in crop-visitor diversity, in which the presence of confamilial species influences pollinator availability This idea is similar 2 to the observation that specialist natural enemies native to the invaded range can be pre-adapted to exotic plants through adaptation to the native relatives of these plants in the invaded range [25]. The sample-based rarefaction method ‘exact’ in R package ‘vegan’ [42] was used to generate these curves as it is suitable for presence/absence data
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