Two Great Black-backed Gulls, Larus marinus, Kill Male Longtailed Duck, Clangula hyemalis

At Presqu’ile Point, Presqu’ile Provincial Park, Ontario on 23 March 2003, while interpreting the waterfowl migration for park visitors, we witnessed two adult Great Black-backed Gulls attack and kill a male Long-tailed Duck

Stable motifs delay species loss in simulated food webs

Some three-species motifs (unique patterns of interactions between three species) are both more stable when modelled in isolation and over-represented in empirical food webs. This suggests that these motifs may reduce extinction risk for species participating in them, ultimately stabilising the food web as a whole. We test whether a species' time to extinction following a perturbation is related to its participation in stable and unstable motifs and assess how motif roles co-vary with a species' degree or trophic level. We found that species' motif roles are related to their times to extinction following a disturbance. Specifically, having a larger proportion of the motif role made up by the omnivory motif was associated with longer times to extinction, even though the omnivory motif is less stable than the others when modelled in isolation. While motif roles were associated with extinction risk, they also varied strongly with degree and trophic level. This means that these simpler measures of a species' role may be sufficient to roughly predict which species are most vulnerable to disturbance (though motif roles can be used to refine these predictions), but that studies of species' motif participation can also reasonably comment on vulnerability to extinction.Peer reviewe

A sprinkling of gold dust : Pine pollen as a carbon source in Baltic Sea coastal food webs

Allochthonous subsidies to marine ecosystems have mainly focused on biogeochemical cycles, but there has also been recent interest in how terrestrial carbon (C) influences marine food webs. In the Baltic Sea, pine (Pinus sylvestris) pollen is found in large amounts in shallow bays in early summer. Pollen is a significant C-source in freshwater ecosystems and may also be important in coastal food webs. We examined the consumption of pollen and autochthonous resources by benthic invertebrates in shallow bays of the Baltic Sea. We used stable isotopes to estimate diets and reconstructed consumer-resource networks (food webs) for grazers and particulate organic matter (POM)-feeders to compare how these different guilds used pollen. We found that P. sylvestris pollen was consumed in small amounts by a variety of animals and in some cases made up a sizeable proportion of invertebrates' diets. However, invertebrates generally depended less on pollen than other resources. The degree of pollen consumption was related to feeding traits, with generalist invertebrate grazers consuming more pollen (> 10% of diet) than the more specialist POM-feeders (< 5% of diet contributed by pollen). POM-feeders may consume additional microbially-degraded pollen which was not identifiable in our model. We suggest that pollen is a small but substantial allochthonous C-source in shallow bay food webs of the Baltic Sea, with the potential to affect the dynamics of these ecosystems.Peer reviewe

Species composition of shoreline wolf spider communities vary with salinity, but their diets vary with wrack inflow

Wolf spiders are typically the most common group of arthropod predators on both lake and marine shorelines because of the high prey availability in these habitats. However, shores are also harsh environments due to flooding and, in proximity to marine waters, to toxic salinity levels. Here, we describe the spider community, prey availabilities, and spider diets between shoreline sites with different salinities, albeit with comparatively small differences (5‰ vs. 7‰). Despite the small environmental differences, spider communities between lower and higher saline sites showed an almost complete species turnover. At the same time, differences in prey availability or spider gut contents did not match changes in spider species composition but rather changed with habitat characteristics within a region, where spiders collected at sites with thick wrack beds had a different diet than sites with little wrack. These data suggest that shifts in spider communities are due to habitat characteristics other than prey availabilities, and the most likely candidate restricting species in high salinity would be saline sensitivity. At the same time, species absence from low-saline habitats remains unresolved.Peer reviewe

Landscape composition and pollinator traits interact to influence pollination success in an individual-based model

The arrangement of plant species within a landscape influences pollination via changes in pollinator movement trajectories and plant-pollinator encounter rates. Yet the combined effects of landscape composition and pollinator traits (especially specialisation) on pollination success remain hard to quantify empirically.We used an individual-based model to explore how landscape and pollinator specialisation (degree) interact to influence pollination. We modelled variation in the landscape by generating gradients of plant species intermixing-from no mixing to complete intermixing. Furthermore, we varied the level of pollinator specialisation by simulating plant-pollinator (six to eight species) networks of different connectance. We then compared the impacts of these drivers on three proxies for pollination: visitation rate, number of consecutive visits to the focal plant species and expected number of plants pollinated.We found that the spatial arrangements of plants and pollinator degree interact to determine pollination success, and that the influence of these drivers on pollination depends on how pollination is estimated. For most pollinators, visitation rate increases in more plant mixed landscapes. Compared to the two more functional measures of pollination, visitation rate overestimates pollination service. This is particularly severe in landscapes with high plant intermixing and for generalist pollinators. Interestingly, visitation rate is less influenced by pollinator traits (pollinator degree and body size) than are the two functional metrics, likely because 'visitation rate' ignores the order in which pollinators visit plants. However, the visitation sequence order is crucial for the expected number of plants pollinated, since only prior visits to conspecific individuals can contribute to pollination. We show here that this order strongly depends on the spatial arrangements of plants, on pollinator traits and on the interaction between them.Taken together, our findings suggest that visitation rate, the most commonly used proxy for pollination in network studies, should be complemented with more functional metrics which reflect the frequency with which individual pollinators revisit the same plant species. Our findings also suggest that measures of landscape structure such as plant intermixing and density-in combination with pollinators' level of specialism-can improve estimates of the probability of pollination

Decline in Honeybees and Its Consequences for Beekeepers and Crop Pollination in Western Nepal

In understudied regions of the world, beekeeper records can provide valuable insights into changes in pollinator population trends. We conducted a questionnaire survey of 116 beekeepers in a mountainous area of Western Nepal, where the native honeybee Apis cerana cerana is kept as a managed bee. We complemented the survey with field data on insect–crop visitation, a household income survey, and an interview with a local lead beekeeper. In total, 76% of beekeepers reported declines in honeybees, while 86% and 78% reported declines in honey yield and number of beehives, respectively. Honey yield per hive fell by 50% between 2012 and 2022, whilst the number of occupied hives decreased by 44%. Beekeepers ranked climate change and declining flower abundance as the most important drivers of the decline. This raises concern for the future food and economic security of this region, where honey sales contribute to 16% of total household income, and where Apis cerana cerana plays a major role in crop pollination, contributing more than 50% of all flower visits to apple, cucumber, and pumpkin. To mitigate further declines, we promote native habitat and wildflower preservation, and using well-insulated log hives to buffer bees against the increasingly extreme temperature fluctuations

More intraguild prey than pest species in arachnid diets may compromise biological control in apple orchards

Publisher Copyright: © 2021 The AuthorsUnderstanding the full diet of natural enemies is necessary for evaluating their role as biocontrol agents, because many enemy species do not only feed on pests but also on other natural enemies. Such intraguild predation can compromise pest control if the consumed enemies are actually better for pest control than their predators. In this study, we used gut metabarcoding to quantify diets of all common arachnid species in Swedish and Spanish apple orchards. For this purpose, we designed new primers that reduce amplification of arachnid predators while retaining high amplification of all prey groups. Results suggest that most arachnids consume a large range of putative pest species on apple but also a high proportion of other natural enemies, where the latter constitute almost a third of all prey sequences. Intraguild predation also varied between regions, with a larger content of heteropteran bugs in arachnid guts from Spanish orchards, but not between orchard types. There was also a tendency for cursorial spiders to have more intraguild prey in the gut than web spiders. Two groups that may be overlooked as important biocontrol agents in apple orchards seem to be theridiid web spiders and opilionids, where the latter had several small-bodied pest species in the gut. These results thus provide important guidance for what arachnid groups should be targets of management actions, even though additional information is needed to quantify all direct and indirect interactions occurring in the complex arthropod food webs in fruit orchards.Peer reviewe

Agricultural specialisation increases the vulnerability of pollination services for smallholder farmers

1. Smallholder farms make up 84% of all farms worldwide and feed 2 billion people. These farms are heavily reliant on ecosystem services and vulnerable to environmental change, yet under-represented in the ecological literature. The high diversity of crops in these systems makes it challenging to identify and manage the best providers of an ecosystem service, such as the best pollinators to meet the needs of multiple crops. It is also unclear whether ecosystem service requirements change as smallholders transition towards more specialised commercial farming—an increasing trend worldwide. 2. Here, we present a new metric for predicting the species providing ecosystem services in diverse multi-crop farming systems. Working in 10 smallholder villages in rural Nepal, we use this metric to test whether key pollinators, and the management actions that support them, differ based on a farmers' agricultural priority (producing nutritious food to feed the family vs. generating income from cash crops). We also test whether the resilience of pollination services changes as farmers specialise on cash crops. 3. We show that a farmers' agricultural priority can determine the community of pollinators they rely upon. Wild insects including bumblebees, solitary bees and flies provided the majority of the pollination service underpinning nutrient production, while income generation was much more dependent on a single species—the domesticated honeybee Apis cerana. The significantly lower diversity of pollinators supporting income generation leaves cash crop farmers more vulnerable to pollinator declines. 4. Regardless of a farmers' agricultural priority, the same collection of wild plant species (mostly herbaceous weeds and shrubs) were important for supporting crop pollinators with floral resources. Promoting these wild plants is likely to enhance pollination services for all farmers in the region. 5. Synthesis and applications. We highlight the increased vulnerability of pollination services when smallholders transition to specialised cash crop farming and emphasise the role of crop, pollinator and wild plant diversity in mitigating this risk. The method we present could be readily applied to other smallholder settings across the world to help characterise and manage the ecosystem services underpinning the livelihoods and nutritional health of smallholder families

Stable pollination service in a generalist high Arctic community despite the warming climate

Insects provide key pollination services in most terrestrial biomes, but this service depends on a multistep interaction between insect and plant. An insect needs to visit a flower, receive pollen from the anthers, move to another conspecific flower, and finally deposit the pollen on a receptive stigma. Each of these steps may be affected by climate change, and focusing on only one of them (e.g., flower visitation) may miss important signals of change in service provision. In this study, we combine data on visitation, pollen transport, and single-visit pollen deposition to estimate functional outcomes in the high Arctic plant-pollinator network of Zackenberg, Northeast Greenland, a model system for global warming–associated impacts in pollination services. Over two decades of rapid climate warming, we sampled the network repeatedly: in 1996, 1997, 2010, 2011, and 2016. Although the flowering plant and insect communities and their interactions varied substantially between years, as expected based on highly variable Arctic weather, there was no detectable directional change in either the structure of flower-visitor networks or estimated pollen deposition. For flower-visitor networks compiled over a single week, species phenologies caused major within-year variation in network structure despite consistency across years. Weekly networks for the middle of the flowering season emerged as especially important because most pollination service can be expected to be provided by these large, highly nested networks. Our findings suggest that pollination ecosystem service in the high Arctic is remarkably resilient. This resilience may reflect the plasticity of Arctic biota as an adaptation to extreme and unpredictable weather. However, most pollination service was contributed by relatively few fly taxa (Diptera: Spilogona sanctipauli and Drymeia segnis [Muscidae] and species of Rhamphomyia [Empididae]). If these key pollinators are negatively affected by climate change, network structure and the pollination service that depends on it would be seriously compromised