Pollinator responses to farmland habitat features: one-size does not fit all

 By Maher et al.

orange-legged furrow bee

In a world where pollinators are increasingly under threat, largely due to the intensive nature of modern agriculture, understanding the impact of farming practices on this group is more crucial than ever. A study conducted in Ireland across twenty-nine diverse farming sites—ranging from livestock to crop systems and varying in intensity—sought to uncover how different farm habitats affect pollinator communities. This research assessed pollinators, plants, and habitat features to explore the nuanced relationships between farm habitats and the abundance and diversity of pollinating insects.

The study revealed that responses of pollinators to farm environments vary significantly across species. Hoverflies, for example, showed a preference for less structured farms with more drainage ditches, whereas bumblebees were more abundant in areas with a rich mix of grassy margins, ditches, and hedgerows, especially on crop farms. Solitary bees, on the other hand, favoured areas with high floral diversity but were less common on crop farms. Intriguingly, within each pollinator group, different species showed unique responses to the same environmental factors.

This research underscores the complexity of pollinator conservation in agricultural landscapes, highlighting that a one-size-fits-all approach is not effective. Conservation strategies need to be tailored to the specific needs of different pollinator groups, taking into account the quantity, diversity, and quality of habitats to truly benefit these essential insects.

Read the scientific publication in JPE.

Insect pollinators are critical not only for producing crops to feed humans, but also for producing food to feed wildlife

A female ivy bee (Colletes hederae) feeding
on ivy flower (Photo by Steven Falk).

by M. Lam, I. Ryan, L.V. Dicks

Climate change and human activities are causing insect pollinator declines in many parts of the world. This has direct consequences for human food production, since many crop species require insect pollination to produce seeds_ and fruits (termed “pollinator dependence”). Pollination can also improve the quality of crop harvests, such as larger and/or more nutritious fruits. However, declining pollinator populations can negatively impact food chains in nature too. Many wild flowering plants also rely on insect pollination to produce fruits, which feed other animals. In the UK, ivy fruits feed some of our best-loved birds, including song thrushes and winter visitors like the fieldfare. Previous research suggests that ivy shows pollinator dependence – if this is true, then pollinator declines can reduce the food supply for many fruit-eating animals. However, the extent of such dependence and whether pollination affects the quality of fruit remains unknown. 

To address this missing knowledge, we investigated the importance of pollination to ivy fruit production in terms of quantity and quality, as well as how that can affect the feeding choices of animals. We conducted this study in a mixed woodland-meadows nature reserve and a botanical garden in Cambridge. We manipulated the level of pollination received by ivy plants and found that the quantity and quality of fruit depends strongly on insect pollination. Without the help of insect pollinators, the production of fruits in ivy dropped dramatically by 90%, and the fruits were also smaller. Monitoring the survival of ivy fruits revealed that animals can prefer well-pollinated fruits. At the woodland site, over 99% of fruits which received extra pollen were eaten, whereas over half of the unpollinated fruits remained untouched. Hence, the initial level of pollination also influences animal feeding choices.

This study highlights how pollinator declines can have far-reaching effects in ecosystems by reducing the fruit supply for animals. It is therefore necessary for us to maintain the health of pollinator communities, so that food supply for animals and the stability of food chains are protected in nature.

 

 Read the scientific article in JPE!

The tripping mechanism of flowers affects pollen transfer dynamics

by Dieterich Mabin et al.

Bumble bee on alfalfa with some tripped flowers

 

 

Insect pollinators move pollen between flowers and plants, and therefore affect pollen transfer, pollen movement, and pollen dispersal. Two important components of pollen transfer dynamics include the accumulation of pollen on a bee’s body as a bee visits flowers in succession, and the number of pollen grains deposited on the stigma as a bee revisits a flower. These characteristics have typically been described in plants without a tripping mechanism. However, the flowers of many plant species in the families Labiatae and Fabaceae have closed flowers that require a pollinator or other force to exert pressure on the keel of a flower in order to release the anthers and stigmas. In this study, we investigate the two fundamental aspects of pollen transfer dynamics mentioned above for a bumble bee species visiting flowers with a tripping mechanism. The number of pollen grains on a bee’s body increased with the number of flowers tripped by a bee. In fact, for each flower tripped in a foraging bout, the number of pollen grains on a bee’s body increased by an average of 954 grains. However, revisiting tripped flowers did not increase the number of pollen grains deposited on a stigma. This contrasts with flowers that do not have a tripping mechanism where the number of pollen grains deposited on a stigma increases with the number of pollinator visits to a flower. Moreover, plants with a tripping mechanism can be categorized into two groups, one where the flowers remain open after tripping such as the plant species used in this study, Medicago sativa, commonly known as alfalfa or lucerne, and the other where the flowers close after tripping as occurs in clover or Trifolium species. We hypothesize that staggered anther dehiscence, where pollen is released over time from a flower, would be beneficial in plant species whose flowers close after tripping. Moreover, revisits to a flower could increase pollen deposition on stigmas in flowers that close after tripping especially if staggered anther dehiscence is present. Tripping of a flower affects pollen transfer dynamics, and the effect may vary with the mode of tripping.

Read the scientific publication in JPE here.

Long-term effects of nitrogen enrichment on pollen chemistry of a plant species from Brazilian savannas, Pavonia rosa-campestris

by Luísa Gigante Carvalheiro, Maryse Vanderplanck and Mercedes M. C. Bustamante

Brazilian savannas (Cerrado), a hotspot of biodiversity
© Luísa G. Carvalheiro

Human activities, such as farming and fossil fuel burning, are rapidly increasing environmental nutrient availability. While the impacts on plants, such as community composition and nutritional content changes, are better known, the study on how such effects propagate to higher trophic levels is still mainly focused on foliar herbivory. Yet, pollinators feed on floral resources (pollen and/or nectar) and can also be affected by such changes in plant quality.  This study reduced the knowledge gap on how nutrient input affects floral resources, initiating evidence-building for tropical regions.       

We conducted this study in an experimental area of the Brazilian savannas (Cerrado). In this region, soils are mostly naturally dystrophic, and natural areas are highly exposed to fertilizer leaching and nitrogen deposition due to the importance of this region for global food production. We focused on pollen, the main source of larval diet for bees, an important group of pollinators. Several amino acids found in pollen affect the development, health, and behavior of bees. Therefore, a better understanding of the consequences of nutrient input on pollen amino acid content can help explain and predict future impacts of global, ongoing changes on bee populations and diversity.

Pollen of Pavonia rosa-campestris (Malvaceae), a species known to be important for the diet of several native bee species, was collected from individual plants growing in parcels that are part of a long-term controlled fertilization experiment that started in 1998, involving manipulation of nitrogen (N) and phosphorous (P) levels. We found that ten years after the last fertilization addition, effects were still detectable on the leaf and pollen chemical content of P. rosa-campestris. Overall, amino acid (AA) content was higher in plants growing on parcels subjected to increased N input. Yet, this increase was not similar across the different AA, and the pollen AA profile was substantially affected. More specifically, the proportion of isoleucine, leucine, serine, and threonine increased, while the proportion of cysteine decreased. As these amino acids can affect larval development and flower visitor behavior, impacts on floral visitor assembly are expected. Further studies evaluating the effects on a diverse set of plant species and the consequent impacts on flower visitation and bee fitness are essential to understand better the full consequences of increased nitrogen availability in nutrient-limited ecosystems.

Read the scientific publication in JPE here!

Portuguese version:

 Efeitos a longo prazo de aumento da disponibilidade de azoto (nitrogênio) na química do pólen de uma espécie do Cerrado, Pavonia rosa-campestris

As atividades humanas, como a agricultura e a queima de combustíveis fósseis, estão causando um rápido aumento da disponibilidade de nutrientes no meio ambiente. Enquanto os impactos sobre as plantas são bem conhecidos, como os efeitos sobre a composição da comunidade e no conteúdo nutricional das plantas, o estudo de como tais mudanças se propagam para outros níveis tróficos focam principalmente em herbívoros foliares. No entanto, os polinizadores alimentam-se de recursos florais (pólen e/ou néctar) e, portanto, também podem ser afetados por tais alterações na qualidade nutricional das plantas.  Este estudo reduz a existente lacuna de conhecimento sobre como o aporte de nutrientes afeta a qualidade dos recursos florais, iniciando o processo de acúmulo de evidências sobre este tópico para regiões tropicais. 

O estudo foi realizado em uma área experimental do Cerrado. Neste bioma os solos são naturalmente distróficos e, devido à importância dessa região para a produção global de alimentos, as áreas naturais estão altamente expostas à lixiviação de fertilizantes e deposição de nitrogênio. O estudo foca no pólen, a principal fonte de dieta larval para as abelhas, um importante grupo de polinizadores. Vários aminoácidos encontrados no pólen afetam o desenvolvimento, a saúde e o comportamento das abelhas e, portanto, uma melhor compreensão das consequências da entrada de nutrientes sobre o conteúdo polínicos de aminoácidos pode ajudar a explicar e prever os impactos futuros das mudanças globais em curso sobre as populações e a diversidade de abelhas. 

O pólen de Pavonia rosa-campestris (Malvaceae), espécie conhecida por ser importante para a dieta de várias espécies de abelhas nativas, foi coletado de plantas individuais que cresceram em parcelas que fazem parte de um experimento de adubação controlada de longo prazo iniciado em 1998. Esse experimento envolveu a manipulação de doses de nitrogênio (N) e fósforo (P). Verificou-se que 10 anos após a última adição de adubação, os efeitos sobre a química foliar e polínica de P. rosa-campestris ainda eram detetáveis. O teor total de aminoácidos foi maior em pólen de plantas estabelecidas em parcelas que foram submetidas ao incremento de N. No entanto, esse aumento não foi semelhante entre os diferentes AA, e o perfil de AA polínico foi substancialmente afetado. Mais especificamente, a proporção de isoleucina, leucina, serina e treonina aumentou, enquanto a proporção de cisteína diminuiu. Como esses aminoácidos podem ter efeitos importantes no desenvolvimento larval e no comportamento do visitante floral, impactos na composição das comunidades de visitantes florais são esperados. Novos estudos avaliando os efeitos em um conjunto diversificado de espécies de plantas e os consequentes impactos na visitação floral e saúde das abelhas são essenciais para melhor compreender as consequências do aumento da disponibilidade de nitrogênio em ecossistemas naturalmente distróficos.