Bee Species in Wake County: Are They Missing or Just Hard to Find?

What happens to bee populations in areas of massive human population growth like Wake County, North Carolina, where the population is more than 16 times greater than it was at the turn of the 20th century?

Examining historical museum specimens along with online bee repositories and university bee collections, researchers at North Carolina State University show that bee species richness – the number of different bee species – has varied over the past 118 years, with no clear downward trend emerging over time, said Selina Ruzi, a postdoctoral researcher in biological sciences at NC State and corresponding author of a paper describing the research.

With that good news, though, comes some not-so-great news. The study showed that, of 328 bee species collected in Wake County over the study period (1900-2018), 195 species have not been collected since 1969; many of these missing species are bees that nest underground.

“Our hypothesis was that bee species richness would decline in Wake County over time due to effects from urbanization and population growth,” Ruzi said. “But, while we saw some variance, there was no clear trend over time. It’s hard to know, without a new monitoring program to sample different locations in Wake County, whether the ‘missing’ bee species are really missing or if we’re just not detecting them.”

Burrowing bees could have a hard time in areas with growing populations of humans. Population growth and urbanization bring housing developments, which generally means more concrete in the form of roads and driveways. More housing also means more turfgrass on lawns, which means compacted soils. All of these factors represent impediments for bees that nest underground. Climate change and interactions among bees can also have effects on bee species richness, the researchers say.

“Specialist bee species need pollen from specific plant species to feed their young; bees can’t suddenly switch pollen sources,” said Rebecca Irwin, professor of applied ecology at NC State and co-author of the paper. “If these specific flowers are absent, bees will be absent as well.”

The researchers also noted other collection factors that could contribute to the seemingly missing species.

“The reasons why collecting occurred could affect the representation of species richness,” Irwin said. “A lot of historical collectors were taxonomists, so they would travel to particular places at particular times to look for certain bees. As ecologists, we may be trying to sample a whole area and look at how some aspect of the environment may affect the number of species we find.”

Ruzi noted that all of the bee specimens included in the study were collected by netting; bees caught by other more recent techniques were excluded to reduce any study bias.

The researchers add that going back to museum or historical collections could help fill some gaps in the absence of systematic population studies.

In all, the study reflects a ray of hope amid gloomy reports documenting declining bee populations over the past few decades.

“This study suggests there’s some resilience in bee species to habitat change,” Irwin said. “Yet certain species with certain life history traits are missing. When we think about conservation and what we can do in urban habitats, making sure that there are appropriate places for ground-nesting bees to nest rises to the top of the list.”

The paper, “Bee species richness through time in an urbanizing landscape of the southeastern United States,” is published open access in the journal Global Change Biology. Elsa Youngsteadt, April Hamblin Cherveny, Jessica Kettenbach, Hannah K. Levenson, Danesha Seth Carley and Jaime A. Collazo co-authored the paper.

The research was supported by the National Science Foundation Division of Biological Infrastructure Postdoctoral Fellowship in Biology under award 1906242 and by the USGS Southeast Climate Adaptation Science Center under award G17AC00204.

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Note to editors: The abstract of the paper follows.

“Bee species richness through time in an urbanizing landscape of the southeastern United States”

Authors: Selina A. Ruzi, Elsa Youngsteadt, April Hamblin Cherveny, Jessica Kettenbach, Hannah K. Levenson, Danesha Seth Carley, Jaime A. Collazo and Rebecca E. Irwin, North Carolina State University

Published: Dec. 11, 2023 in Global Change Biology

DOI: 10.1111/gcb.17060

Abstract: Compared to non-urban environments, cities host ecological communities with altered taxonomic diversity and functional trait composition. However, we know little about how these urban changes take shape over time. Using historical bee (Apoidea: Anthophila) museum specimens supplemented with online repositories and researcher collections, we investigated whether bee species richness tracked urban and human population growth over the past 118 years. We also determined which species were no longer collected, whether those species shared certain traits, and if collector behavior changed over time. We focused on Wake County, North Carolina, United States where human population size has increased over 16 times over the last century along with the urban area within its largest city, Raleigh, which has increased over four times. We estimated bee species richness with occupancy models, and rarefaction and extrapolation curves to account for imperfect detection and sample coverage. To determine if bee traits correlated with when species were collected, we compiled information on native status, nesting habits, diet breadth, and sociality. We used non-metric multidimensional scaling to determine if individual collectors contributed different bee assemblages over time. In total, there were 328 species collected in Wake County. We found that although bee species richness varied, there was no clear trend in bee species richness over time. However, recent collections (since 2003) were missing 195 species, and there was a shift in trait composition, particularly lost species were below-ground nesters. The top collectors in the dataset differed in how often they collected bee species, but this was not consistent between historic and contemporary time periods; some contemporary collectors grouped closer together than others, potentially due to focusing on urban habitats. Use of historical collections and complimentary analyses can fill knowledge gaps to help understand temporal patterns of species richness in taxonomic groups that may not have planned long-term data.

This post was originally published in NC State News.