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1. A key floral scent component (β‐trans‐bergamotene) drives pollinator preferences independently of pollen rewards in seep monkeyflower

   https://doi.org/10.1111/1365-2435.13246  

   Haber, Ariela I. ; Sims, James W. ; Mescher, Mark C. ; De Moraes, Consuelo M. ; Carr, David E. ; Brody, ed., Alison ( December 2018 , Functional Ecology)

   Floral odours play an important role in attracting insect pollinators. Because pollinators visit flowers to obtain pollen and nectar rewards, they should prefer floral odour profiles associated with the highest‐rewarding flowers (honest signals). In previous work, bumblebees exhibited a preference for flowers from outbred over inbredMimulus guttatusplants. Pollen is the only floral reward inM. guttatus, and pollen viability (a reliable indicator of protein content) is reduced in inbred plants. Yet, differences in pollen viability did not explain the observed preferences.

   In this study, we examined the floral volatile profiles of inbred and outbredM. guttatusto identify inbreeding effects and associations between volatile compounds and the number of viable pollen grains per flower, designated “PRQ” (pollen reward quality). We also conducted pairwise choice tests withBombus impatiensto evaluate the ability of bees to discriminate between odours of rewarding and non‐rewarding flowers and to determine whether bumblebee preferences are explained by differences in the floral odours of inbred and outbred plants.

   Inbred plants exhibited reduced emission of β‐trans‐bergamotene, the second‐most abundant compound in the volatile blend of outbred plants. Furthermore, pollen and fertile anthers emitted nonadecane. Six other compounds in the floral blend were positively correlated withPRQ. There was no overlap between compounds affected by inbreeding and compounds associated withPRQ.

   Even when given prior experience foraging onM. guttatus, bumblebees did not distinguish between the floral odours of rewarding and non‐rewarding outbred plants. However, they preferred floral odours from non‐rewarding outbred plants over rewarding inbred plants. Bumblebees without prior experience of flowers preferred volatile blends with higher versus lower amounts of β‐trans‐bergamotene.

   Taken together, these results suggest that the volatile emissions ofM. guttatusprovide reliable indicators of pollen rewards (potential honest signals), but that the preference of bumblebees for outbred plants is not driven by these cues but rather by a sensory bias for β‐trans‐bergamotene. This may represent a subtle form of deceit‐pollination that allows plants to attract pollinators while minimizing investment in costly rewards.

   Aplain language summaryis available for this article.

    

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2. What makes a good pollinator? Abundant and specialised insects with long flight periods transport the most strawberry pollen

   https://doi.org/10.1002/2688-8319.12253  

   Villa‐Galaviz, Edith ; Cirtwill, Alyssa R. ; Gibson, Rachel ; Timberlake, Thomas ; Roslin, Tomas ; Memmott, Jane ( July 2023 , Ecological Solutions and Evidence)

   Despite the importance of insect pollination to produce marketable fruits, insect pollination management is limited by insufficient knowledge about key crop pollinator species. This lack of knowledge is due in part to (1) the extensive labour involved in collecting direct observations of pollen transport, (2) the variability of insect assemblages over space and time and (3) the possibility that pollinators may need access to wild plants as well as crop floral resources.

   We address these problems using strawberry in the United Kingdom as a case study. First, we compare two proxies for estimating pollinator importance: flower visits and pollen transport. Pollen‐transport data might provide a closer approximation of pollination service, but visitation data are less time‐consuming to collect. Second, we identify insectparametersthat are associated with high importance as pollinators, estimated using each of the proxies above. Third, we estimated insects' use of wild plants as well as the strawberry crop.

   Overall, pollinator importances estimated based on easier‐to‐collect visitation data were strongly correlated with importances estimated based on pollen loads. Both frameworks suggest that bees (ApisandBombus) and hoverflies (Eristalis) are likely to be key pollinators of strawberries, although visitation data underestimate the importance of bees.

   Moving beyond species identities, abundant, relatively specialised insects with long active periods are likely to provide more pollination services.

   Most insects visiting strawberry plants also carried pollen from wild plants, suggesting that pollinators need diverse floral resources.

   Identifying essential pollinators or pollinator parameters based on visitation data will reach the same general conclusions as those using pollen transport data, at least in monoculture crop systems. Managers may be able to enhance pollination service by preserving habitats surrounding crop fields to complement pollinators' diets and provide habitats for diverse life stages of wild pollinators.

    

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3. Plant–hummingbird pollination networks exhibit limited rewiring after experimental removal of a locally abundant plant species

   https://doi.org/10.1111/1365-2656.13935  

   Leimberger, Kara G. ; Hadley, Adam S. ; Betts, Matthew G. ( May 2023 , Journal of Animal Ecology)

   Mutualistic relationships, such as those between plants and pollinators, may be vulnerable to the local extinctions predicted under global environmental change. However, network theory predicts that plant–pollinator networks can withstand species loss if pollinators switch to alternative floral resources (rewiring). Whether rewiring occurs following species loss in natural communities is poorly known because replicated species exclusions are difficult to implement at appropriate spatial scales.

   We experimentally removed a hummingbird‐pollinated plant,Heliconia tortuosa, from within tropical forest fragments to investigate how hummingbirds respond to temporary loss of an abundant resource. Under therewiring hypothesis, we expected that behavioural flexibility would allow hummingbirds to use alternative resources, leading to decreased ecological specialization and reorganization of the network structure (i.e. pairwise interactions). Alternatively, morphological or behavioural constraints—such as trait‐matching or interspecific competition—might limit the extent to which hummingbirds alter their foraging behaviour.

   We employed a replicated Before‐After‐Control‐Impact experimental design and quantified plant–hummingbird interactions using two parallel sampling methods: pollen collected from individual hummingbirds (‘pollen networks’, created from >300 pollen samples) and observations of hummingbirds visiting focal plants (‘camera networks’, created from >19,000 observation hours). To assess the extent of rewiring, we quantified ecological specialization at the individual, species and network levels and examined interaction turnover (i.e. gain/loss of pairwise interactions).

   H. tortuosaremoval caused some reorganization of pairwise interactions but did not prompt large changes in specialization, despite the large magnitude of our manipulation (on average, >100 inflorescences removed in exclusion areas of >1 ha). Although some individual hummingbirds sampled through time showed modest increases in niche breadth followingHeliconiaremoval (relative to birds that did not experience resource loss), these changes were not reflected in species‐ and network‐level specialization metrics.

   Our results suggest that, at least over short time‐scales, animals may not necessarily shift to alternative resources after losing an abundant food resource—even in species thought to be highly opportunistic foragers, such as hummingbirds. Given that rewiring contributes to theoretical predictions of network stability, future studies should investigate why pollinators might not expand their diets after a local resource extinction.

    

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4. Competition for nectar resources does not affect bee foraging tactic constancy

   https://doi.org/10.1111/een.12866  

   Lichtenberg, Elinor M. ; Richman, Sarah K. ; Irwin, Rebecca E. ; Bronstein, Judith L. ( March 2020 , Ecological Entomology)

   1. Competition alters animal foraging, including promoting the use of alternative resources. It may also impact how animals feed when they are able to handle the same food with more than one tactic. Competition likely impacts both consumers and their resources through its effects on food handling, but this topic has received little attention.

   2. Bees often use two tactics for extracting nectar from flowers: they can visit at the flower opening, or rob nectar from holes at the base of flowers. Exploitative competition for nectar is thought to promote nectar robbing. If so, higher competition among floral visitors should reduce constancy to a single foraging tactic as foragers will seek food using all possible tactics. To test this prediction, field observations and two experiments involving bumble bees visiting three montane Colorado plant species (Mertensia ciliata,Linaria vulgaris,Corydalis caseana) were used under various levels of inter‐ and intra‐specific competition for nectar.

   3. In general, individual bumble bees remained constant to a single foraging tactic, independent of competition levels. However, bees that visitedM. ciliatain field observations decreased their constancy and increased nectar robbing rates as visitation rates by co‐visitors increased.

   4. While tactic constancy was high overall regardless of competition intensity, this study highlights some intriguing instances in which competition and tactic constancy may be linked. Further studies investigating the cognitive underpinnings of tactic constancy should provide insight on the ways in which animals use alternative foraging tactics to exploit resources.

    

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5. Collective decision‐making when quantity is more important than quality: Lessons from a kidnapping social parasite

   https://doi.org/10.1111/1365-2656.13423  

   Miller, Julie S. ; Dussutour, ed., Audrey ( January 2021 , Journal of Animal Ecology)

   Identifying the general principles that shape mechanisms of collective decision‐making requires studies that span a diversity of ecological contexts. However, collective decision‐making has only been explored in a handful of systems.

   Here, I investigate the ecologically mediated costs and benefits of collective decisions by socially parasitic kidnapping antsTemnothorax americanusover where to launch raids to steal host brood.

   I first investigate their sampling strategies and preferences with choice tests. Using more realistic spatial scales, I confirm the findings of others that colonies use a sequential choice strategy, and do not compare options simultaneously. I then ask which ecological conditions could favour the evolution of this strategy by testing the following hypotheses from optimal foraging and mate choice theories: (a) raiding decisions are time constrained or (b) search payoffs are low due to resource uniformity.

   Spatial distribution and phenological data on nest contents support the time constraints hypothesis. Host nests contain an optimal ratio of brood and workers for a brief period relative to discovery rates. Colonies therefore benefit from raiding most nests they find in this period rather than deliberating over the best choice, favouring host quantity over quality.

   The decision strategy for raids uncovered here contrasts with best‐of‐n collective decision‐making found in other systems. These findings demonstrate that ecological constraints on information acquisition can alter how collectives process information.

    

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