Differential pollinator effectiveness and importance in a milkweed (<i>Asclepias</i>, Apocynaceae) hybrid zone

Stoepler, Teresa M.; Edge, Andrea; Steel, Anna E.; O’Quinn, Robin; Fishbein, Mark

doi:10.3732/ajb.1100272

Cited by 18 publications

(10 citation statements)

References 65 publications

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“…Wilson & Thomson 1991) made exactly this point but have been insufficiently built upon. More recent studies have paralleled our own in comparing visitor PE for just one plant genus (Kandori 2002;Stoepler et al 2012), reaching similar conclusions regarding problems with proxies, and reinforcing the value of SVD (or a near equivalent) as a measure of effectiveness.…”

Section: W H Y D I S T I N G U I S H I N G P O L L I N a T O R S A N supporting

confidence: 61%

Why flower visitation is a poor proxy for pollination: measuring single‐visit pollen deposition, with implications for pollination networks and conservation

2013

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Summary1. The relative importance of specialized and generalized plant-pollinator relationships is contentious, yet analyses usually avoid direct measures of pollinator quality (effectiveness), citing difficulties in collecting such data in the field and so relying on visitation data alone. 2. We demonstrate that single-visit deposition (SVD) of pollen on virgin stigmas is a practical measure of pollinator effectiveness, using 13 temperate and tropical plant species. For each flower the most effective pollinator measured from SVD was as predicted from its pollination syndrome based on traditional advertisement and reward traits. Overall, c. 40% of visitors were not effective pollinators (range 0-78% for different flowers); thus, flower-pollinator relationships are substantially more specialized than visitation alone can reveal. 3. Analyses at species level are crucial, as significant variation in SVD occurred within both higher-level taxonomic groups (genus, family) and within functional groups. 4. Other measures sometimes used to distinguish visitors from pollinators (visit duration, frequency, or feeding behaviour in flowers) did not prove to be suitable proxies. 5. Distinguishing between 'pollinators' and 'visitors' is therefore crucial, and true 'pollination networks' should include SVD to reveal pollinator effectiveness (PE). Generating such networks, now underway, could avoid potential misinterpretations of the conservation values of flower visitors, and of possible extinction threats as modelled in existing networks.

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Section: W H Y D I S T I N G U I S H I N G P O L L I N a T O R S A N supporting

confidence: 61%

Why flower visitation is a poor proxy for pollination: measuring single‐visit pollen deposition, with implications for pollination networks and conservation

2013

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“…The frequency of floral visitors' groups (hummingbirds, large bees and small bees) varied between reproductive events of E. lindenii and this variation resulted in a reduction in the natural pollination in one year, when pollen limitation was also recorded. The existence of year-to-year changes in the composition of floral visitors has been found in several Full-size  DOI: 10.7717/peerj.8836/ fig-4 systems (Schemske & Horvitz, 1984;Traveset & Sáez, 1997;Price et al, 2005;Olesen et al, 2008;Petanidou et al, 2008), while in others, pollination efficacy between different years was studied (Fishbein & Venable, 1996;Stoepler et al, 2012). However, there are fewer studies that consider both plant reproductive success and variations in the pollinator assemblages along time (Herrera, 1990;Fleming et al, 2001;Salas-Arcos, Lara & Ornelas, 2017).…”

Section: Discussionmentioning

confidence: 99%

Temporal changes in the most effective pollinator of a bromeliad pollinated by bees and hummingbirds

Leal

Moreira

Pinto

et al. 2020

PeerJ

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A generalist pollination system may be characterized through the interaction of a plant species with two or more functional groups of pollinators. The spatiotemporal variation of the most effective pollinator is the factor most frequently advocated to explain the emergence and maintenance of generalist pollination systems. There are few studies merging variation in floral visitor assemblages and the efficacy of pollination by different functional groups. Thus, there are gaps in our knowledge about the variation in time of pollinator efficacy and frequency of generalist species. In this study, we evaluated the pollination efficacy of the floral visitors of Edmundoa lindenii (Bromeliaceae) and their frequency of visits across four reproductive events. We analyzed the frequency of the three groups of floral visitors (large bees, small bees, and hummingbirds) through focal observations in the reproductive events of 2015, 2016, 2017, and 2018. We evaluated the pollination efficacy (fecundity after one visit) through selective exposure treatments and the breeding system by manual pollinations. We tested if the reproductive success after natural pollination varied between the reproductive events and also calculated the pollen limitation index. E. lindenii is a self-incompatible and parthenocarpic species, requiring the action of pollinators for sexual reproduction. Hummingbirds had higher efficacy than large bees and small bees acted only as pollen larcenists. The relative frequency of the groups of floral visitors varied between the reproductive events. Pollen limitation has occurred only in the reproductive event of 2017, when visits by hummingbirds were scarce and reproductive success after natural pollination was the lowest. We conclude that hummingbirds and large bees were the main and the secondary pollinators of E. lindenii, respectively, and that temporal variations in the pollinator assemblages had effects on its reproductive success. Despite their lower pollination efficacy, large bees ensured seed set when hummingbirds failed. Thus, we provide evidence that variable pollination environments may favor generalization, even under differential effectiveness of pollinator groups if secondary pollinators provide reproductive assurance.

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“…Other recent studies have compared PE for visitors with single flower species or a few congeneric species (e.g. [ 38 , 39 ]). Here we show that SVD is feasibly incorporated in community-level field studies with low plant diversity, and present the first explicit PE and PI networks, specifically addressing the following questions: (i) how does PE (SVD) vary between different flower visitors?…”

Section: Introductionmentioning

confidence: 99%

Constructing more informative plant–pollinator networks: visitation and pollen deposition networks in a heathland plant community

2015

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Interaction networks are widely used as tools to understand plant–pollinator communities, and to examine potential threats to plant diversity and food security if the ecosystem service provided by pollinating animals declines. However, most networks to date are based on recording visits to flowers, rather than recording clearly defined effective pollination events. Here we provide the first networks that explicitly incorporate measures of pollinator effectiveness (PE) from pollen deposition on stigmas per visit, and pollinator importance (PI) as the product of PE and visit frequency. These more informative networks, here produced for a low diversity heathland habitat, reveal that plant–pollinator interactions are more specialized than shown in most previous studies. At the studied site, the specialization index was lower for the visitation network than the PE network, which was in turn lower than for the PI network. Our study shows that collecting PE data is feasible for community-level studies in low diversity communities and that including information about PE can change the structure of interaction networks. This could have important consequences for our understanding of threats to pollination systems.

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Differential pollinator effectiveness and importance in a milkweed (Asclepias, Apocynaceae) hybrid zone

Cited by 18 publications

References 65 publications

Why flower visitation is a poor proxy for pollination: measuring single‐visit pollen deposition, with implications for pollination networks and conservation

Why flower visitation is a poor proxy for pollination: measuring single‐visit pollen deposition, with implications for pollination networks and conservation

Temporal changes in the most effective pollinator of a bromeliad pollinated by bees and hummingbirds

Constructing more informative plant–pollinator networks: visitation and pollen deposition networks in a heathland plant community

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