How species live together in climate change

How species live together in climate change

Understanding how species live together in changing ecosystems has been a difficult subject for scientists to attack.

Researchers have been working towards understanding their origins, how they coexist and what that might mean in a world threatened by climate change.

The research was carried out at Stanford University and led by Andrew D. Letten (University of Canterbury), and co-authored by Manpreet K. Dhami (Manaaki Whenua – Landcare Research), Po-Ju Ke and Tadashi Fukami (Stanford University). The study was published in June 2018 in the Proceedings of the National Academy of Sciences of the United States of America.

Born from a curiosity about how species coexist, the paper takes a comprehensive look at how species live together. In most ecosystems, different species coexist even when they seem to require the same limiting resources to sustain their populations. When resources are limited, species good at using them can drive others to extinction through competing for resources, thus reducing biodiversity.

So, how do species manage to coexist?

“It is well established in the field of ecology that competing species can coexist when environmental conditions fluctuate over time,” says Tadashi Fukami. “For example, in our study, different species of yeasts found in flower nectar coexist when the concentration of sugars and other chemicals in nectar vary over time.”

In a previous study by Caroline Tucker (University of North Carolina, Chapel Hill) and Tadashi, published in the Proceedings of the Royal Society of London, the researchers also found that fluctuations in temperature help these species of yeasts to coexist.

Tadashi says the main point of the new study– which used new mathematical tools to analyse experimental data to tease apart the intricate ways in which species interact in ecosystems – is that there are two ways in which fluctuations promote coexistence, and that sometimes species need both ways to coexist.

These findings are important to biodiversity management because of what humans are doing to the environment. Climate change is causing more and more environmental fluctuations, notably extreme weather events. But how environmental fluctuations promote species coexistence has been difficult to know because ecosystems are complex and many things affect species in ecosystems.

“To understand the fate of species under climate change, our study indicates that we will need to pay more attention to how exactly fluctuating environments allow species to coexist. In our study, we saw that increased fluctuations help some species, but not others, and it depends on which mechanism of coexistence is possible – storage effect or nonlinearity (or both),” says Tadashi.

In addition, nectar-colonizing yeasts can also affect plant reproduction.
“Microbes in nectar are an important component of the plant-pollinator interface. These microbes, especially yeasts, compete for limited nectar resources,” says Manpreet Dhami. “This study explores the mechanisms of such species interactions in greater detail”

Andrew Letten says high resolution data is required to divide the mechanisms.
“This meant setting up thousands of microcosms over an almost two-year period, including an enormous amount of trouble-shooting and method refinement,” says Andrew.

Depending on what microbes end up on these flowers, there could be significant implications for pollination. For example, some bacteria can rapidly alter nectar quality and effect pollinator behaviour.
“While such bacteria can have negative implications, certain yeasts have been shown to interact positively with plants, including possibly attracting pollinators. This research is still a new area, but there is clear evidence in some systems that microbes do affect pollination and the reproductive fitness of the plant,” says Manpreet.

This work shows that microbes have coexistence mechanisms that have a broader implication for plant fitness. While there are many variables, and it is hard to track these interactions at larger levels, in the relatively simplified community that the team tested, they have found a coexistence mechanism that can have follow-on effect for plant reproductive fitness.

The most exciting thing for Andrew is where the research will take them in the future.
“There is so much rich unexplored territory in exploring the effect of nonlinear feedbacks on the maintenance of species diversity,” he says, “How do we explain the richness of life? Microbial systems like nectar yeasts, and other even more high throughput bacterial systems, provide the exciting prospect of really being able to push against these questions.”

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