Lemurs: Gardeners of Madagascar rainforest at risk

Onja Razafindratsima, a graduate student at Rice University, observes a lemur in a Madagascar rainforest. Razafindratsima led a three-year study to explore the relationship between lemurs and trees. Lemurs eat the fruit and spread its seeds far from the parent tree to help ensure its survival. Credit: Photo courtesy of Onja Razafindratsima/Rice University

A majority of Madagascar's 101 species of lemurs are threatened with extinction, and that could have serious consequences for the rainforests they call home. A new study by Rice University researchers shows the positive impacts lemurs can have on rainforest tree populations, which raises concerns about the potential impact their disappearance could have on the region's rich biodiversity.

A large proportion of trees in Madagascar's rainforest have fruits eaten by lemurs. Lemurs in turn disperse the seeds of their fruit trees throughout the forest with their scat. Such dispersal can play a crucial role for a tree species' ability to regenerate, but effects are poorly understood, especially when there are multiple dispersers.

For the tree, the evolutionary advantage of having animal-dispersed seeds may be that the seeds land well away from their parent trees where survival is low or that seeds are directed into spots where they are the most likely to sprout and survive.

Amy Dunham, an assistant professor of biosciences, and graduate student Onja Razafindratsima set out to detail the symbiotic relationship between fruit-eating lemurs and the trees that feed them through a three-year study in a rainforest in southeastern Madagascar.

Their data from observations, experiments and mathematical models demonstrate that seeds of a common canopy tree have a 300 percent higher chance of sprouting and becoming a sapling when dispersed by lemurs versus simply falling to the ground. One of the three lemur species is particularly good at dropping seeds in spots that are most advantageous for sprouting and survival. Other lemurs are not so selective, but still benefit the tree by moving seeds away from the parent tree. By acting as forest gardeners, these animals give the tree's population a boost.

The study appeared online in the Ecological Society of America journal Ecology.

As part of the study, the researchers followed the seed-dispersal patterns of three of Madagascar's lemur species: the red-fronted brown lemur, the red-bellied lemur and the southern black-and-white ruffed lemur. That meant tracking and observing groups of lemurs as the animals leaped from tree to tree through the forest, dined in the 65-foot-high canopies and dropped their undigested seeds at ground level.

Razafindratsima led the study as part of a thesis project she expects to complete early next year. She built a team of local researchers near Ranomafana National Park, the home of Centre ValBio, a research station founded by Dunham's former Ph.D. adviser, primatologist Patricia Wright.

"We have a team of up to 10 local villagers who are trained to do research," said Razafindratsima, a native of Madagascar. "Their exceptional knowledge of the forest is very important to us when we're trying to track lemurs and identify seeds and seedlings in a forest with over 300 species of trees."

The research team tracked 24 groups of lemurs over a year without the benefit of radio collars, said Razafindratsima, who keeps in touch with her team via phone and Skype when she's at Rice. She said the study sites were as close as a short hike from Centre ValBio and as far as a two-day trek through steep terrain that entailed camping overnight.

In addition to tracking lemurs and their dispersed seeds, the research team spent three years carrying out experiments on seed sprouting and survival. They found that dispersal by lemurs dramatically increased the odds that seeds would take root and survive. In particular, the red-fronted brown lemurs tended to drop seeds away from their parent trees and in places where there were gaps in the canopy. This gave individual seeds the best shot at taking root.

Dunham said trees benefit from the wide dispersal of their seeds, and for some species in Madagascar, lemurs are the primary or only animal that can distribute those seeds. As the largest fruit-eaters in the system, these lemurs swallow seeds that may be too large for other fruit-eating animals, such as birds or bats.

"Seeds away from the parent tree survive better because there's less competition among seedlings," Razafindratsima said. "If they're close by the parent, they may also share the same natural enemies, like soil pathogens and seed predators, so there's higher mortality."

Trees that lose their dispersers will simply drop their seeds to the ground beneath their canopies, where chances of survival are slim, Dunham said. "Lemurs fill an important role as the gardeners for these trees. By ensuring that some seeds land in spots suitable for germination and survival, they increase the ability of these trees to replace themselves"

Dunham hopes the study will contribute to growing efforts to protect lemurs, and therefore the rainforest, which has been impacted in recent years by economic and political instability.

She noted grassroots efforts within Madagascar led to the first World Lemur Festival in late October to celebrate and protect the animals and their habitats in Madagascar.

"What got us interested is that frugivorous lemur populations are declining across the island, and we know very little about how these seed dispersers actually affect tree populations," she said. "Once we understand that better, maybe we'll have a better idea of how the community might change if the lemurs disappear.

"If some species suddenly lose their dispersers, but others dispersed by birds or the wind are doing fine, it may change population trajectories and alter which tree species are dominant in a community. To understand what happens when these species are lost, we need to understand their role in the ecosystem," she said.

Source: Rice University

Potential biological control for avocado-ravaging disease

University of Florida scientists think they’ve found the first potential biological control strategy against laurel wilt, a disease that threatens Florida’s avocado industry. The redbay ambrosia beetle, see here, bores holes into avocado trees, bringing the disease that causes laurel wilt. Credit: Lyle Buss, UF/IFAS

University of Florida scientists believe they've found what could be the first biological control strategy against laurel wilt, a disease that threatens the state's $54 million-a-year avocado industry.

Red ambrosia beetles bore holes into healthy avocado trees, bringing with them the pathogen that causes laurel wilt. Growers control the beetles that carry and spread laurel wilt by spraying insecticides on the trees, said Daniel Carrillo, an entomology research assistant professor at the Tropical Research and Education Center in Homestead.

But a team of researchers from the Tropical REC and the Indian River Research and Education Center in Fort Pierce have identified a potential biological control to use against redbay ambrosia beetles that could help growers use less insecticide.

First, they exposed beetles to three commercially available fungi, and all of the beetles died. Then they sprayed the fungi on avocado tree trunks, and beetles got infected while boring into the trunk. About 75 percent of those beetles died, said Carrillo, an Institute of Food and Agricultural Sciences faculty member.

Ideally, the fungal treatments could prevent beetles from boring into the trees, eliminating the risk that the pathogen would enter the trees, the study said. But tests showed female beetles bored into the trees and built tunnels regardless of the treatment. Still, researchers say their treatment can prevent the female beetles from laying eggs.

UF/IFAS scientists don't know yet how much less chemical spray will be needed to control the redbay ambrosia beetle. But Carrillo sees this study as the first step toward controlling the beetle in a sustainable way.

"When you want to manage a pest, you want an integrated pest management approach," Carrillo said. "This provides an alternative that we would use in combination with chemical control."

The redbay ambrosia beetle -- native to India, Japan, Myanmar and Taiwan -- was first detected in 2002 in southeast Georgia. It was presumably introduced in wood crates and pallets, and its rapid spread has killed 6,000 avocado trees in Florida, or about 1 percent of the 655,000 commercial trees in Florida. The beetle was first discovered in South Florida in 2010.

Most American-grown avocados come from California, with the rest coming from Florida and Hawaii. The domestic avocado market is worth $429 million, according to Edward Evans, a UF associate professor of food and resource economics, also at the Tropical REC. Florida's avocados are valued at about $23 million, or about 5 percent of the national market.

The redbay ambrosia beetle is not an issue with California avocados, so the new tactic found by Florida scientists wouldn't apply to this pest in the Golden State, said Mark Hoddle, a biological control Extension specialist with the University of California-Riverside. Hoddle studies biological pest control for California avocados. Scientists there are exploring ways to control a different ambrosia beetle, he said, and bug-killing fungi may be useful for the new California pest.

More than 95 percent of Florida's commercial avocados grow in Miami-Dade County, although many Floridians have avocado trees in their yard.
The redbay ambrosia beetle feeds and reproduces on a very wide variety of host plants, native oaks, sycamores, and of course it is very detrimental to avocados.

Source:University of Florida Institute of Food and Agricultural Sciences

Live fast, die young: Soil microbes in a warmer world

Aerial view of the Northern Minnesota landscape including numerous conifer peatlands, deciduous uplands and lakes. Credit: USDA Forest Service Northern Research Station

Warmer temperatures shorten the lifespan of soil microbes and this may affect soil carbon storage, according to a new NSF-funded study published in Nature Climate Change this week.

A research team led by Shannon Hagerty and Paul Dijkstra from Northern Arizona University measured two key characteristics of soil microbes that determine their role in the soil carbon cycle: how efficiently they use carbon to grow and how long they live. "Higher temperatures make microbes grow faster, but they also die faster," said Hagerty, who conducted the research as part of her master's degree and was lead author on the study.

Soil microbes consume organic carbon compounds in soil, use some of it to make more microbes and release the rest to the atmosphere as carbon dioxide. The efficiency with which microbes use their food to make new microbes affects how much carbon remains in soil, and how much is released back to the atmosphere. The accepted idea before this study was that microbes would become less efficient at warmer temperatures.

The scientists incubated soil from a peatland and a forest in Minnesota at different temperatures and measured the efficiency with which microbes grew. They used a new method to measure microbial efficiency: they added small amounts of sugar and tracked how individual atoms in this sugar were turned into carbon dioxide.

"Microbes process sugars in similar ways as we do," says Paul Dijkstra. "We know very well how these processes work in laboratory studies, and can predict which carbon atoms in sugar molecules end up as carbon dioxide, and which are used to build new microbes. We applied this knowledge to the microbes living in soil."

The researchers found, contrary to expectation, that temperature had no effect on how microbes utilized their food, but instead boosted microbial death. "We don't yet know why microbes are dying faster at higher temperatures. Maybe they are eaten by nematodes or mites, or they die because of viruses," said Hagerty. "We need to know more about how temperature affects microbial death."

To explore what these new findings could mean for soil carbon storage in a warming world, the team compared output from a soil model that includes the effect of temperature on microbial lifespan to models unaffected by temperature change. "Models are used to predict how soil processes change, for example, in response to climate change," said Steve Allison, coauthor from the University of California, Irvine. "If we want to predict the future correctly, we'd better use models that accurately describe these microbial processes."

Including a temperature-dependent lifespan to the model increased the amount of carbon retained in soils at warmer temperatures compared to estimates from traditional models. The study concludes that incorporating this new insight into soil models will improve our understanding of how soils influence atmospheric carbon dioxide levels and global climate.

Does this mean that with climate change, more carbon will stay in the soil? "Too early to tell," said Bruce Hungate, Director of the Center for Ecosystem Science and Society at NAU. 

"The results suggest that the biochemistry of the microbes remains the same with warmer temperature, but that predation and death become more important. This laboratory study is just the first step, identifying a potential mechanism. Now we need to study how, in the real world, and in the long-term, the processes of biochemical efficiency and lifespan will change. And nobody has done that yet."

Source: Northern Arizona University

If trees could talk: Forest research network reveals global change effects

In addition to identifying, mapping, measuring and monitoring trees in the CTFS-ForestGEO study plots, researchers describe the relatedness of trees, track flower and seed production, collect insects, survey mammals, quantify carbon stocks and flows within the ecosystem, take soil samples and measure climate variables like rainfall and temperature. The thorough study of these plots provides insights into not only how forests are changing but also why. Credit: Beth King, STRI

Permafrost thaw drives forest loss in Canada, while drought has killed trees in Panama, southern India and Borneo. In the U.S., in Virginia, over-abundant deer eat trees before they reach maturity, while nitrogen pollution has changed soil chemistry in Canada and Panama. Continents apart, these changes have all been documented by the Smithsonian-led Center for Tropical Forest Science-Forest Global Earth Observatory, CTFS-ForestGEO, which released a new report revealing how forests are changing worldwide.

"With 107 collaborators we've published a major overview of what 59 forests in 24 countries, where we monitor nearly 6 million trees teach us about forest responses to global change," said Kristina Anderson-Teixeira, first author of the report and CTFS-ForestGEO and ecosystem ecologist based at the Smithsonian Conservation Biology Institute.

Many of the changes occurring in forests worldwide are attributable to human impacts on climate, atmospheric chemistry, land use and animal populations that are so pervasive as to warrant classification of a new geologic period in Earth's history -- the Anthropocene, the Age of Humans.

Measuring and understanding the effects of all these changes -- collectively termed "global change" -- are easier said than done. Some of the best information about these global-scale changes comes from CTFS-ForestGEO, the only network of standardized forest-monitoring sites that span the globe.

Since the censuses began at the first site on Barro Colorado Island in Panama in 1981, atmospheric carbon dioxide has increased by 16 percent. The forest sites in the network have warmed by an average of over 1 degree F (0.6 degree C) and experienced up to 30 percent changes in precipitation. Landscapes around protected sites experience deforestation.
The plot network now includes forests from Brazil to northern Canada, from Gabon to England and from Papua New Guinea to China.

In addition to identifying, mapping, measuring and monitoring trees, researchers describe the relatedness of trees, track flower and seed production, collect insects, survey mammals, quantify carbon stocks and flows within the ecosystem, take soil samples and measure climate variables like rainfall and temperature. The thorough study of these plots provides insights into not only how forests are changing but also why.

Climate change scenarios predict that most of these sites will face warmer and often drier conditions in the future -- some experiencing novel climates with no modern analogs. Forests are changing more rapidly than expected by chance alone, and shifts in species composition have been associated with environmental change. Biomass increased at many tropical sites across the network.

"It is incredibly rewarding to work with a team of forest scientists from 78 research institutions around the world, including four Smithsonian units" Anderson-Teixeira said. "CTFS-ForestGEO is a pioneer in the kind of collaborative effort it takes to understand how forests worldwide are changing."

"We look forward to using the CTFS-ForestGEO network to continue to understand how and why forests respond to change, and what this means for the climate, biodiversity conservation and human well-being," said Stuart Davies, network director.

Source: Smithsonian Tropical Research Institute

Seeing the forest for the trees: Youngest trees in a forest tell the biggest story

LSU ecologist Kyle Harms co-authors first study to quantify the process of diversification in forests and likely all other sessile ecosystems. Credit: Louisiana State University

The largest trees in a forest may command the most attention, but the smallest seedlings and youngest saplings are the ones that are most critical to the composition and diversity of the forest overall. While many people gaze up into the forest canopy, scientist Joseph Connell has spent much of his career looking down quite closely at the forest understory. Connell, who is a professor emeritus in the Department of Ecology, Evolution and Marine Biology at the University of California at Santa Barbara, established one of the world's longest, in-depth ecological research studies on the planet. The Connell Plots Rainforest Network has thus far produced a 50-year collection of data on individual trees in Australia's protected rainforests.

"Having such a long-term, detailed dataset is highly unusual. It's the kind of temporal depth we need to answer some of the big questions such as, what are the ecological processes that maintain diversity?" said Kyle Harms, professor in the LSU Department of Biological Sciences and a collaborator with Connell.

Early in his career, Harms was a post-doctoral researcher in Connell's lab at U.C. Santa Barbara. There, he met former fellow post-doctoral researcher and current collaborator Peter Green, who is a senior lecturer at La Trobe University in Melbourne, Australia.

Harms and Green were inspired to use their mentor's dataset; therefore, they devised an analysis to test the long-standing hypothesis that the patterns of composition and diversity among a forest's mature trees are largely set by processes that occur in trees' earliest life stages. Harms ran statistical analyses on 7,977 individual trees across 186 species that were censused in one of Connell's tropical Australian forest plots from 1971-2013.

He repeatedly ran simulation analyses on six tiers of trees based on size in order to predict the expected outcome of diversity at each tier. Then he compared the expected levels of diversity in each tier with the true collected data.

"What we found was that the seedlings are more diverse than the statistical expectations predicted them to be, but the larger trees' levels of diversity were about the same as the predictions" he said.

These results are the first quantitative evidence that the earliest life cycle stages of individual trees are more critical than later stages to the overall relative abundances of mature trees in a forest. Their findings will be published online in the Proceedings of the National Academy of Sciences this week.

The stronger influence of ecological sorting processes operating at the earliest life cycle stages compared to later life stages, which they quantified, also likely occurs in other highly diverse ecosystems with rooted, or sessile, organisms including grasslands, herbaceous plant communities and marine communities of coral.

"I think this is something that is happening broadly in ecosystems across the planet," Harms said.

He and his collaborators' results underscore the importance of support for long-term, in-depth datasets, as well as the need to investigate the early life stages -- for example, the smallest, newly germinated seedlings -- where the most critical processes are occurring.

"I think it helps us understand where to focus in order to really understand the biased sorting processes that create the composition and diversity patterns in the forest overall," he said.

Source: Louisiana State University