In studying Handroanthus guayacan,a common tropical tree species, over a 10-year period, they found that the tree population increased mainly in locations where the tree is rare, rather than in locations where it is common.

“There are more tree species living in an area not much larger than a few football fields in Panama than in all of North America north of Mexico combined,” said Jim Kellner, first author on the paper and an assistant professor of ecology and evolutionary biology at Brown. “How this diversity originated, and why it persists over time is a paradox that has challenged naturalists for more than a century.”

Until now.

“The take-home of the study is that there is a ‘negative feedback’ on population growth,” Kellner said, which puts the brakes on population growth in locations where the species is common.

The findings confirm a prediction from the 1970s, which posited that tropical forests are diverse because natural enemies keep populations in check. An enemy could be a seed eater, an herbivore or a pathogen, said Kellner, who is affiliated with the Institute at Brown for Environment and Society.

For example, consider an oak tree and a squirrel. The squirrel eats acorns and prefers to forage where oak trees are abundant. A lone acorn in the middle of a grove of maples is likely to go unnoticed by a squirrel, whereas many acorns in an oak grove will be eaten. If this kind of behavior is widespread in tropical rainforests, it could keep species from becoming too common, Kellner said.

Earlier studies have shown that this negative feedback phenomenon holds true among young trees — seeds, seedlings and saplings — but ecologists hadn’t been able to determine whether it influences adult trees, the reproductive portion of populations, he said.

“It takes decades for trees to become reproductive in tropical forests, and the problem is compounded by how rare each species is,” Kellner said. “We found that for this species, you would have to search about 250 acres to find one new adult tree every year.”

That challenge isn’t feasible on foot, but remote sensing can overcome the challenges of observing large areas.

Kellner and co-author Stephen Hubbell, an ecology professor emeritus at UCLA, used high-resolution satellite images to track individuals on Barro Colorado Island, a six-square-mile island in the middle of the Panama Canal, over 10 years. They looked for Handroanthus guayacan, a tropical rainforest tree that produces bright yellow flowers for a few days a year.

“By timing the satellite image acquisition with seasonal flowering, we were able to identify most of the adults for this species on the island,” said Kellner.

They found 1,006 adult trees. Starting in 2012 and looking backward over the 10-year study period, Kellner and Hubbell were able to identify when new trees joined the adult population for the first time. They used advanced statistical methods to make sure that they were in fact identifying new adults and not just trees that had skipped a year of flowering or had flowered early or late.

The researchers found that negative feedback affected the abundance of new adult trees and that it can influence the population of new adult trees in an area of almost 100 football fields. This contrasts with prior studies of juvenile trees, which found the effects of host-specific enemies are usually restricted to small areas, Kellner said.

To confirm the locations of trees from the satellite data, they went to the island and independently found 123 adult trees of the same species. Of these, 89 percent had been detected in the high-resolution images, suggesting that their data are a nearly complete census of the species.

Kellner said the implications could be broad.

“I can’t think of any idea in ecology that is more important than population dynamics,” he said. “It’s important for everything from fishing licenses to forecasting disease outbreaks.”

One strategy is to border crops with wildflower plantings to attract pollinators and pest predators. But scientists have suggested that such plantings may only be effective when farms are surrounded by the right mix of natural habitat and agricultural land.

For the first time, a Cornell University study of strawberry crops on New York farms tested this theory and found that wildflower strips on farms added pollinators when the farm lay within a “Goldilocks zone,” where 25 to 55 percent of the surrounding area contained natural lands. Outside this zone, flower plantings also drew more strawberry pests, while having no effect on wasps that kill those pests.

Still, more pollinators in this ideal landscape zone boosted strawberry yields overall. The analysis has implications for many types of state and federal programs in the United States and abroad that promote establishing pollinator habitats on farms.

“We’re investing huge amounts of money on these programs and right now it’s not part of the policy to think about the landscape context of where these habitats are placed,” said Heather Grab, Ph.D. ’17, the paper’s first author and a postdoctoral researcher in the lab of Katja Poveda, associate professor of entomology and a co-author of the study.

The paper, “Landscape Context Shifts the Balance of Costs and Benefits From Wildflower Border on Multiple Ecosystem Services,” published Aug. 1 in Proceedings of the Royal Society B, suggests targeting wildflower borders to farms with the right conditions and modifying wildflower plant species could maximize success.

The rationale behind the Goldilocks zone theory: wildflower strips surrounded by too much natural land would not add additional beneficial insects, because ample habitat would drown out a small strip of flowers. On the other hand, farms surrounded by other farms are already low on natural habitat and beneficial insects, making a wildflower strip too small to attract more insects.

“It’s in this zone in the middle, where there’s enough natural habitat around, and there are beneficial insects there, and you can attract them [insects] from the natural habitat into the crop habitat to actually see a benefit in terms of crop production,” Grab said.

In the study, the researchers planted strawberry plots on 12 small New York state farms that represented a gradient of landscapes, from farms surrounded by natural habitat to farms next to agricultural lands. Each farm had two strawberry plantings, one plot bordered by a wildflower strip, and another control plot on the other side of the farm, edged with mowed grass.

The researchers conducted surveys of pollinators, pests, wasps that parasitize pests, fruit yield and fruit damage over three years. The tiny parasitizing wasps lay their eggs inside tarnished plant bug nymphs — a pest that costs New York strawberry growers 30 percent of their annual yield. When the eggs hatch, the larvae feed on the nymphs.

The wildflower strips were increasingly effective at attracting pollinators as each year passed. The result that “between 25 and 55 percent [surrounding natural landscapes] was the best range in terms of promoting bees,” closely matched what the Goldilocks theory predicted, Grab said.

But when it came to pests, wildflowers outside the Goldilocks zone attracted the most pests and didn’t add more wasps. “It suggests the parasitoids are not responding to wildflower strips at all,” Grab said. More study is needed to understand why.

Analyses revealed many wildflower species attracted both pests and bees, but some species like fleabane (Erigeron annuus) lured the most pests and were least effective at drawing bees.

“If you wanted to optimize the wildflower patches, I would suggest we eliminate some of those from the list of recommended species in the plantings,” Grab said.

Future work will investigate how floral habitats influence pathogen transmission for bees, the leading driver of bee declines.

Bryan Danforth and Greg Loeb, Cornell professors of entomology, co-authored the study, which was funded in part by a Northeast Sustainable Agriculture Research and Education grant.

There have been five upheavals over the past 450 million years when the environment on our planet has changed so dramatically that the majority of Earth’s plant and animal species became extinct. After each mass extinction, evolution has slowly filled in the gaps with new species.

The sixth mass extinction is happening now, but this time the extinctions are not being caused by natural disasters; they are the work of humans. A team of researchers from Aarhus University and the University of Gothenburg has calculated that the extinctions are moving too rapidly for evolution to keep up.

If mammals diversify at their normal rates, it will still take them 5-7 million years to restore biodiversity to its level before modern humans evolved, and 3-5 million years just to reach current biodiversity levels, according to the analysis, which was published recently in the scientific journal, PNAS.

Some species are more distinct than others

The researchers used their extensive database of mammals, which includes not only species that still exist, but also the hundreds of species that lived in the recent past and became extinct as Homo sapiens spread across the globe. This meant that the researchers could study the full impact of our species on other mammals.

However, not all species have the same significance. Some extinct animals, such as the Australian leopard-like marsupial lion Thylacoleo, or the strange South American Macrauchenia (imagine a lama with an elephant trunk) were evolutionary distinct lineages and had only few close relatives. When these animals became extinct, they took whole branches of the evolutionary tree of life with them. We not only lost these species, we also lost the unique ecological functions and the millions of years of evolutionary history they represented.

“Large mammals, or megafauna, such as giant sloths and sabre-toothed tigers, which became extinct about 10,000 years ago, were highly evolutionarily distinct. Since they had few close relatives, their extinctions meant that entire branches of Earth’s evolutionary tree were chopped off” says palaeontologist Matt Davis from Aarhus University, who led the study. And he adds:

“There are hundreds of species of shrew, so they can weather a few extinctions. There were only four species of sabre-toothed tiger; they all went extinct.”

Long waits for replacement rhinos

Regenerating 2.5 billion years of evolutionary history is hard enough, but today’s mammals are also facing increasing rates of extinction. Critically endangered species such as the black rhino are at high risk of becoming extinct within the next 50 years. Asian elephants, one of only two surviving species of a once mighty mammalian order that included mammoths and mastodons, have less than a 33 percent chance of surviving past this century.

The researchers incorporated these expected extinctions in their calculations of lost evolutionary history and asked themselves: Can existing mammals naturally regenerate this lost biodiversity?

Using powerful computers, advanced evolutionary simulations and comprehensive data about evolutionary relationships and body sizes of existing and extinct mammals, the researchers were able to quantify how much evolutionary time would be lost from past and potential future extinctions as well as how long recovery would take.

The researchers came up with a best-case scenario of the future, where humans have stopped destroying habitats and eradicating species, reducing extinction rates to the low background levels seen in fossils. However, even with this overly optimistic scenario, it will take mammals 3-5 million years just to diversify enough to regenerate the branches of the evolutionary tree that they are expected to lose over the next 50 years. It will take more than 5 million years to regenerate what was lost from giant Ice Age species.

Prioritizing conservation work

“Although we once lived in a world of giants: giant beavers, giant armadillos, giant deer, etc., we now live in a world that is becoming increasingly impoverished of large wild mammalian species. The few remaining giants, such as rhinos and elephants, are in danger of being wiped out very rapidly,” says Professor Jens-Christian Svenning from Aarhus University, who heads a large research program on megafauna, which includes the study.

The research team doesn’t have only bad news, however. Their data and methods could be used to quickly identify endangered, evolutionarily distinct species, so that we can prioritise conservation efforts, and focus on avoiding the most serious extinctions.

As Matt Davis says: “It is much easier to save biodiversity now than to re-evolve it later.”

Following the discovery of Higgs, a primary scientific goal of high energy physicits has been to characterize the properties of this new particle and to discover oher high-energy physics phenomenon. As a result, there have been some rapid developments in high-energy particle accelerator technology to support high-energy physics research. However, the technologies used to date can only be improved and expanded at great expense. For this reason, making high-energy accelerators more affordable is urgently needed.

An international team of physicists, working on the Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) at CERN, reported that they have conducted a groundbreaking experiment demonstrating a new way of accelerating electrons to high energies — one that could dramatically shrink the size of future particle accelerators and lower their costs. A paper describing this important result was published in Nature on August 29, 2018.

AWAKE is an international scientific collaboration, made up of engineers and scientists from 18 institutes, including CERN and the Max Planck Institute for Physics in Germany. A UNIST-based research group, led by Professor Moses Chung in the Department of Physics is also part of this AWAKE collaboration and made a number of important contributions to AWAKE. This includes the design of beamlines and the optimization of electron beam injection.

“AWAKE’s technology will bring about a paridigm shift in the development of future high-energy particle accelerators, following LHC,” says Professor Chung. “The latest achievement could enable engineers to drastically reduce the size of future particle accelerators, cutting down on the vast amounts of money normally required to build them.” He adds, “The high-energy particle collisions these facilities produce enable physicists to probe the fundamental laws of nature, providing the basis for advancements in a huge variety of different fields.”

Typically, particle physics experiments use oscillating electric fields, called radiofrequency cavities, and high-powered magnets to accelerate particles to high energies. But these experiments must grow quite large — they have to be, in order to accelerate particles with enough energy to properly study them.

As an alternative cost-cutting option to accelerate particles more efficiently, the wakefield accelerator has been suggested. Physicists send a beam of either electrons, protons, or a laser through a plasma. Free electrons in the plasma move toward the beam, but overshoot it, then come crashing back, creating a bubble structure behind the beam and intense electric fields. If you inject particles, like more electrons, into the wake, it can accelerate the injected particles in a shorter amount of time with an electric field 10 or more times stronger.

In the study, proton-driven plasma wakefield acceleration has been demonstrated for the first time. The strong electric fields, generated by a series of proton microbunches, were sampled with a bunch of electrons. These electrons were accelerated up to 2 GeV in approximately 10 m of plasma and measured using a magnetic spectrometer. This technique has the potential to accelerate electrons to the TeV scale in a single accelerating stage.

Although still in the early stages of its programme, the AWAKE collaboration has taken an important step on the way to realising new high energy particle physics experiments.