Warming Increases Pollen Lipid Concentration in an Invasive Thistle, with Minor Effects on the Associated Floral-Visitor Community

Shifting the paradigm: The role of introduced plants in the resiliency of terrestrial ecosystems to climate change

Current ecological communities are in a constant state of flux from climate change and from species introductions. Recent discussion has focused on the positive roles introduced species can play in ecological communities and on the importance of conserving resilient ecosystems, but not how these two ideas intersect. There has been insufficient work to define the attributes needed to support ecosystem resilience to climate change in modern communities. Here, I argue that non-invasive, introduced plant species could play an important role in supporting the resilience of terrestrial ecosystems to climate change. Using examples from multiple taxonomic groups and ecosystems, I discuss how introduced plants can contribute to ecosystem resilience via their roles in plant and insect communities, as well as their associated ecosystem functions. I highlight the current and potential contributions of introduced plants and where there are critical knowledge gaps. Determining when and how introduced plants are contributing to the resilience of ecosystems to climate change will contribute to effective conservation strategies.

Fertilizer and herbicide alter nectar and pollen quality with consequences for pollinator floral choices

Background

Pollinating insects provide economically and ecologically valuable services, but are threatened by a variety of anthropogenic changes. The availability and quality of floral resources may be affected by anthropogenic land use. For example, flower-visiting insects in agroecosystems rely on weeds on field edges for foraging resources, but these weeds are often exposed to agrochemicals that may compromise the quality of their floral resources.

Methods

We conducted complementary field and greenhouse experiments to evaluate the: (1) effect of low concentrations of agrochemical exposure on nectar and pollen quality and (2) relationship between floral resource quality and insect visitation. We applied the same agrochemcial treatments (low concentrations of fertilizer, low concentrations of herbicide, a combination of both, and a control of just water) to seven plant species in the field and greenhouse. We collected data on floral visitation by insects in the field experiment for two field seasons and collected pollen and nectar from focal plants in the greenhouse to avoid interfering with insect visitation in the field.

Results

We found pollen amino acid concentrations were lower in plants exposed to low concentrations of herbicide, and pollen fatty acid concentrations were lower in plants exposed to low concentrations of fertilizer, while nectar amino acids were higher in plants exposed to low concentrations of either fertilizer or herbicide. Exposure to low fertilizer concentrations also increased the quantity of pollen and nectar produced per flower. The responses of plants exposed to the experimental treatments in the greenhouse helped explain insect visitation in the field study. The insect visitation rate correlated with nectar amino acids, pollen amino acids, and pollen fatty acids. An interaction between pollen protein and floral display suggested pollen amino acid concentrations drove insect preference among plant species when floral display sizes were large. We show that floral resource quality is sensitive to agrochemical exposure and that flower-visiting insects are sensitive to variation in floral resource quality.

Impacts of soil nutrition on floral traits, pollinator attraction, and fitness in cucumbers (Cucumis sativus L.)

Annual plants allocate soil nutrients to floral display and pollinator rewards to ensure pollination success in a single season. Nitrogen and phosphorus are critical soil nutrients whose levels are altered by intensive land use that may affect plants' fitness via pollinator attractiveness through floral display and rewards. In a controlled greenhouse study, we studied in cucumbers (Cucumis sativus) how changes in soil nitrogen and phosphorus influence floral traits, including nectar and pollen reward composition. We evaluated how these traits affect bumble bee (Bombus impatiens, an important cucumber pollinator) visitation and ultimately fruit yield. While increasing nitrogen and phosphorus increased growth and floral display, excess nitrogen created an asymptotic or negative effect, which was mitigated by increasing phosphorus. Male floral traits exhibited higher plasticity in responses to changes in soil nutrients than female flowers. At 4:1 nitrogen:phosphorus ratios, male flowers presented increased nectar volume and pollen number resulting in increased bumble bee visitation. Interestingly, other pollinator rewards remained consistent across all soil treatments: male and female nectar sugar composition, female nectar volume, and pollen protein and lipid concentrations. Therefore, although cucumber pollination success was buffered in conditions of nutrient stress, highly skewed nitrogen:phosphorus soil ratios reduced plant fitness via reduced numbers of flowers and reward quantity, pollinator attraction, and ultimately yield.

A biophysical approach to assess weather impacts on honey bee colony winter mortality

The western honey bee (Apis mellifera) is one of the most important insects kept by humans, but high colony losses are reported around the world. While the effects of general climatic conditions on colony winter mortality were already demonstrated, no study has investigated specific weather conditions linked to biophysical processes governing colony vitality. Here, we quantify the comparative relevance of four such processes that co-determine the colonies' fitness for wintering during the annual hive management cycle, using a 10-year dataset of winter colony mortality in Austria that includes 266 378 bee colonies. We formulate four process-based hypotheses for wintering success and operationalize them with weather indicators. The empirical data is used to fit simple and multiple linear regression models on different geographical scales. The results show that approximately 20% of winter mortality variability can be explained by the analysed weather conditions, and that it is most sensitive to the duration of extreme cold spells in mid and late winter. Our approach shows the potential of developing weather indicators based on biophysical processes and discusses the way forward for applying them in climate change studies.

Growing and Flowering in a Changing Climate: Effects of Higher Temperatures and Drought Stress on the Bee-Pollinated Species Impatiens glandulifera Royle

Drought and higher temperatures caused by climate change are common stress conditions affecting plant growth and development. The reproductive phase is particularly sensitive to stress, but plants also need to allocate their limited resources to produce floral traits and resources to attract pollinators. We investigated the physiological and floral consequences of abiotic stress during the flowering period of Impatiens glandulifera, a bee-pollinated species. Plants were exposed to three temperatures (21, 24, 27 °C) and two watering regimes (well-watered, water stress) for 3 weeks. Not all parameters measured responded in the same manner to drought and/or heat stress. Drought stress induced leaf senescence, decreasing leaf number by 15-30% depending on growth temperature. Drought also reduced photosynthetic output, while temperature rise affected stomatal conductance. The number of flowers produced dropped 40-90% in response to drought stress, while higher temperatures shortened flower life span. Both stresses affected floral traits, but flower resources diminished in response to higher temperatures, with lower nectar volume and pollen protein content. We conclude that increased temperatures and drought stress, which are becoming more frequent with climate change, can negatively affect flowering, even if plants deploy physiological resistance strategies.

Climate Change-Induced Stress Reduce Quantity and Alter Composition of Nectar and Pollen From a Bee-Pollinated Species (Borago officinalis, Boraginaceae)

In temperate ecosystems, elevated temperatures, and drought occur especially during spring and summer, which are crucial periods for flowering, pollination, and reproduction of a majority of temperate plants. While many mechanisms may underlie pollinator decline in the wake of climate change, the interactive effects of temperature and water stress on the quantity and quality of floral nectar and pollen resources remain poorly studied. We investigated the impact of temperature rise (+3 and +6°C) and water stress (soil humidity lower than 15%) on the floral resources produced by the bee-pollinated species Borago officinalis. Nectar volume decreased with both temperature rise and water stress (6.1 ± 0.5 μl per flower under control conditions, 0.8 ± 0.1 μl per flower under high temperature and water stress conditions), resulting in a 60% decrease in the total quantity of nectar sugars (mg) produced per flower. Temperature rise but not water stress also induced a 50% decrease in pollen weight per flower but a 65% increase in pollen polypeptide concentration. Both temperature rise and water stress increased the total amino acid concentration and the essential amino acid percentage in nectar but not in pollen. In both pollen and nectar, the relative percentage of the different amino acids were modified under stresses. We discuss these modifications in floral resources in regards to plant-pollinator interactions and consequences on plant pollination success and on insect nutritional needs.

Mechanisms of Nutritional Resource Exploitation by Insects

Insects have evolved an extraordinary range of nutritional adaptations to exploit other animals, plants, bacteria, fungi and soils as resources in terrestrial and aquatic environments. This special issue provides some new insights into the mechanisms underlying these adaptations. Contributions comprise lab and field studies investigating the chemical, physiological, cognitive and behavioral mechanisms that enable resource exploitation and nutrient intake regulation in insects. The collection of papers highlights the need for more studies on the comparative sensory ecology, underlying nutritional quality assessment, cue perception and decision making to fully understand how insects adjust resource selection and exploitation in response to environmental heterogeneity and variability.

Pollen Protein: Lipid Macronutrient Ratios May Guide Broad Patterns of Bee Species Floral Preferences

Pollinator nutritional ecology provides insights into plant–pollinator interactions, coevolution, and the restoration of declining pollinator populations. Bees obtain their protein and lipid nutrient intake from pollen, which is essential for larval growth and development as well as adult health and reproduction. Our previous research revealed that pollen protein to lipid ratios (P:L) shape bumble bee foraging preferences among pollen host-plant species, and these preferred ratios link to bumble bee colony health and fitness. Yet, we are still in the early stages of integrating data on P:L ratios across plant and bee species. Here, using a standard laboratory protocol, we present over 80 plant species’ protein and lipid concentrations and P:L values, and we evaluate the P:L ratios of pollen collected by three bee species. We discuss the general phylogenetic, phenotypic, behavioral, and ecological trends observed in these P:L ratios that may drive plant–pollinator interactions; we also present future research questions to further strengthen the field of pollination nutritional ecology. This dataset provides a foundation for researchers studying the nutritional drivers of plant–pollinator interactions as well as for stakeholders developing planting schemes to best support pollinators.