Mega experiment shows that species interact more with the tropics and the lowlands

One of the most important field experiments ever conducted provides the best evidence to date, in support of a key Darwinian theory that species interactions are stronger towards the tropics and the tropics. lower altitude.

An international research team used a simple experiment that mimics the way plants and animals interact with each other, leaving the seeds 24 hours a day to determine how many plants are being consumed by the animals. Seven thousand sprouting beds were deployed in a vast geographical area, with 70 sites crossing 18 mountains from Alaska to the Equator.

"The theory predicts that interactions between species – such as predation and competition – will be stronger in warm, productive and biodiversity-rich ecosystems of the tropics and at lower altitudes," said lead author Anna Hargreaves. who initiated the project at the UBC Biodiversity Research Center. She is now a professor at McGill University.

"For example, it is thought that the dramatic diversity of tropical trees results in part from the stronger interactions between plants and animals that feed on their seeds, which determines how plants grow and adapt."

But until recently, the evidence for this key ecological theory was inconclusive and came from small-scale studies using different methods.

The new study found that seed consumption, or predation, increased by 2.6% every 10 degrees of latitude relative to the equator and by 0.4% every 100 meters of elevation gain. In total, seed predation increased by 17% between Alaska and Ecuador and by 17% from 4,000 meters above sea level.

Researchers used consistent methods from the Arctic to the Equator and repeated the 24-hour experiment over and over during the natural seed production period of each latitude.

"These interactions are at the root of the functioning of ecosystems and their direct benefits to human society," said Santiago David, Ph.D. student at UBC who ran one of the study sites in Colombia. "Understanding global patterns in key interactions between species, such as seed predation, is essential when we think about ecosystem management or restoration, especially in the face of climate change."

Predation by insects, other invertebrates

By protecting some mammalian seeds, researchers have shown that large-scale patterns of study are dictated by the smallest seed predators: insects and other invertebrates.

The only other comparable scale standardized experiment used model clay caterpillars and found that model crawling attack rates increased to lower latitudes – an interaction also generated by invertebrates.

"Taken together, these experiments suggest that invertebrates play an inordinate role in the dynamics and evolution of tropical and lowland ecosystem communities," Hargreaves said. "And yet, we know relatively little about invertebrates, for example, about the impact of climate change on their populations."

Researchers now combine false caterpillars with seeds to determine if the models they found with one form of predation apply with another.

The study, "Seed predation increases from the Arctic to the Equator and high altitudes to low," implicated researchers from 13 institutions of the Americas, was published today. hui in Progress of science.

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More information:
A.L. Hargreaves et al., "Seed predation increases from the Arctic to the equator and from high to low altitude" Progress of science (2019). DOI: 10.1126 / sciadv.aau4403, http://advances.sciencemag.org/content/5/2/eaau4403