Surprise Result: Increasing Dispersal Increases Ecological Diversity

By Kathy Keatley Garvey

A study of microbes that live in the nectar of flowers has turned up an unexpected result that challenges a common assumption in ecology.

It’s been widely assumed that the more easily organisms can disperse between habitats, the more similar the mix of species in those habitats will be.

Sticky Monkeyflower

The flowers of Sticky Monkeyflower contain a mix of microbes that live on nectar. A new study shows how microbial diversity changes between flowers. (Photo by Kathy Keatley Garvey)

But Rachel Vannette, assistant professor of entomology and nematology at UC Davis, and Tadashi Fukamia at Stanford University found that the opposite held true, when the habitats they were considering were individual flowers hosting a mix of nectar-feeding microbes. The work was published recently in the journal Ecology Letters.

Nectar Microbes in Sticky Monkeyflower

Vannette and Fukamia looked at microbial communities inhabiting the nectar of the Sticky Monkeyflower, Mimulus auranticus at the Jasper Ridge Biological Preserve in California’s Santa Cruz Mountains. Sticky Monkeyflower is a native shrub common in chaparral and coastal scrub habitats of California and Oregon. It is primarily pollinated by Anna’s hummingbird but also by bees and other insects.

Pollinators and the wind carry microbes from flower to flower. By limiting access of pollinators to the flowers, the researchers could manipulate the ease of dispersal and then quantify the abundance and composition of microbes in flower nectar, as well as the effects of the bacteria and yeasts on nectar chemistry.

They found to their surprise that instead of a homogenizing effect, increasing dispersal actually increased diversity of the microbe populations between different flowers. This might be because of “priority effects,” they wrote: Early arrivals change the species that can establish in the same habitat.

Implications for Conservation

This work has direct implications for conservation of many organisms in addition to bacteria and yeast, suggesting that preserving routes of dispersal among habitat patches may be important in the maintenance of biodiversity. In contrast to previous work showing that dispersal can homogenize communities or make them more similar, the new work demonstrates that dispersal can in some cases generate communities that are more different from each other.

Why look at nectar-inhabiting microbes? Previous work by Vannette and others shows that microbial activity in nectar can alter nectar chemistry and influence plant-pollinator interactions by altering nectar chemistry. In the Ecology Letters study, microbes were also found to change nectar chemistry, explaining about 50 percent of the variation in sugar composition in the field. This suggests that nectar-inhabiting bacteria and yeast can influence the nectar rewards available to pollinators in a natural setting.

Studying the role of microbes in the environment addresses one of the biggest mysteries in science, Vannette said. In her current work, she and her lab are investigating how microbial communities form, change, and function in their interactions with insects and plants. They are also researching how microorganisms affect plant defense against herbivores and plant attraction to pollinators.

Vannette’s research was funded by the Gordon and Betty Moore Foundation through the Life Sciences Research Fellowship. The work was also supported by the National Science Foundation, the Terman Fellowship, and the Department of Biology at Stanford University, where Vannette conducted her postdoctoral research before joining UC Davis.

More information

Read the paper

Original blog post (UC Davis Dept. of Entomology and Nematology)

Not So Sweet: Pollinators Forage on Toxic or Bitter Nectar

Kathy Keatley Garvey writes about all things insect-related for the UC Davis Department of Entomology and Nematology and UC Division of Ag and Natural Resources. For more insect news, follow her Bug Squad blog. 

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