Poor nutrition spells poor prospects for pollinators

Nectar and pollen fuel pollinator life

Flowers use their showy petals and fragrant odors to attract pollinators.1 These floral signals advertise the presence of pollinator food: nectar and pollen. Nectar is a sugary liquid containing trace nutrients. Pollen is rich in proteins, fats, vitamins and minerals. The nutritional content of nectar and pollen varies by plant species, much like carrots and blueberries have different nutrients. Each pollinator's dietary needs depend on its species, life stage (immature or adult) and sex (female or male). In social bee systems, caste (reproductive queen, sterile worker or reproductive male) can also affect individuals' nutritional requirements.

Pollinators and plants form a pollination web

Some pollinators are specialists and only eat nectar and pollen from one or a handful of plant species. Without access to specific plants, these specialist pollinators would starve. Squash bees, as their name suggests, are specialist pollinators of squash and gourd plants.2 Generalist pollinators, like honey and bumble bees, forage for pollen and nectar from many plants.

Plants too may have specialist or generalist pollination strategies and may be visited by one or many species of pollinators. Together, these plant and pollinator interactions form a pollination web. A plant's or pollinator's place in this web, including its connection to and overlap with other species, can affect the web's resilience when faced with environmental threats.3 Well-connected species are central to a web's stability, and their removal can bring a web close to collapse (like pulling a brick from the bottom of a tower). On the other hand, a web might be able to withstand the loss of a poorly connected species, though the web might be destabilized (like pulling a brick from the top or middle of a tower).

Pollinator nutrition is threatened by human activity

FlowersScientists have closely studied the interactions between nutrition, behavior, environmental stress and disease in people.4 Human nutritional health does not solely hinge on what and how much we eat. Mealtimes (e.g., eating at noon versus midnight), other lifestyle habits (e.g., exercising) and environmental conditions (e.g., working long hours at a stressful job) can all affect how our bodies process food and store energy. Diseases and medications can also determine how well our bodies access, absorb and use the nutrients in the food we eat. These concepts translate to pollinator health where nutrition and environmental stressors interact: habitat loss, invasive species, pesticide exposure, disease and global warming all affect the stability of pollination webs.

Humans have reduced and fragmented pollinator habitat at the landscape level. Intensive agriculture, for example, converts natural habitat to fields of single crops. Blooming crops only providing food for a brief time. Once a crop has finished blooming, pollinators are faced with a nutritionally bare landscape. Furthermore, nectar and pollen from a single crop may not provide a balanced diet for visiting pollinators. Invasive plants can also destroy pollinator habitat by overrunning native plant communities. Nutritional deficits caused by a lack of diverse floral resources can make pollinators more susceptible to negative effects of pesticide or disease exposure. Finally, global warming is eating away at the quality of the remaining pollinator habitat. Changing weather pattens are altering where plants can successfully grow. Pollen and nectar from climate-stressed plants may not be as nutritious or attractive to pollinators.5 Finally, climate change may cause a mismatch between when plants bloom and when corresponding pollinator species are active, again destabilizing pollination webs.6

How can you support pollinator nutrition?

  1. Create pollinator habitat by planting a variety of native plants that bloom at different times throughout the growing season. Native pollinators' nutritional needs coevolved with native plants. Staggering blooms ensures that food is always available. Find recommended native plant lists for your region by visiting the Xerces Pollinator Center.
  2. Avoid using pesticides. If you must use a pesticide, select the least harmful chemical that will still control your pest problem. Do not spray plants when they are blooming since flowers will attract pollinators. If you are planting flowering plants, check that the plants or seeds that you buy are not treated with pesticides, including neonicotinoids. Neonicotinoids are absorbed by growing plants and are present in all plant tissues, including pollen and nectar.
  3. Learn about invasive plant species in your area. Your state's Department of Natural Resources or local university extension program can supply you with invasive species lists and identification materials, tell you where to report sightings and provide management recommendations. You can also participate in citizen science efforts to track invasive species by reporting sightings to EDDMaps.
  4. Participate in citizen science. Many citizen science programs are interested in determining which plants pollinator species depend upon for food. Help scientists gather this data by participating in observation programs like the Great Sunflower Project.

References

  1. Wilson, J. S. & Messinger Carril, O. J. The Bees in Your Backyard. The Bees in Your Backyard (2016). doi:10.1515/9781400874156

  2. Butzler, T. Native pollinators provide free services for growers. Penn State Extension (2019).

  3. Memmott, J., Waser, N. M. & Price, M. V. Tolerance of pollination networks to species extinctions. Proc. R. Soc. London. Ser. B Biol. Sci. 271, 2605–2611 (2004).

  4. National Center for Chronic Disease Prevention and Health Promotion. About Chronic Diseases. Centers for Disease Control and Prevention (2019). (Accessed: 14th September 2020)

  5. Descamps, C., Quinet, M., Baijot, A. & Jacquemart, A.-L. Temperature and water stress affect plant–pollinator interactions in Borago officinalis (Boraginaceae). Ecol. Evol. 8, 3443–3456 (2018).

  6. Kudo, G. & Ida, T. Y. Early onset of spring increases the phenological mismatch between plants and pollinators. Ecology 94, 2311–2320 (2013).