Smithsonian Science » botany

Tropical tree study shows interactions with neighbors plays an important role in tree survival

John Barrat — Thu, 08 Jul 2010 11:29:16 +0000

Home to jaguars, harpy eagles and red-eyed tree frogs, tropical forests support some of the rarest species on the planet and are the most biodiverse ecosystems on land. Understanding why some species are common while others are exceedingly rare has been a challenge in these mega-diverse forests. New results from a massive study at the Smithsonian Tropical Research Institute show that interactions among community members play an important role in determining which organisms thrive.

“Based on information about the survival of more than 30,000 seedlings of 180 species of tropical trees, we found that seedlings of rare species are much more sensitive to the presence of neighbors of their own species than seedlings of common species are,” said Liza Comita, the primary author on the study and now a postdoctoral fellow at the U.S. National Center for Ecological Analysis and Synthesis. “Not only does this tell us where to look for the mechanisms that explain why certain species are rare, but it also provides potential clues about how to conserve rare species that are most vulnerable to extinction.”

Photo left: Botanist Liza Comita measures the stem diameter of a seedling on the Smithsonian Tropical Research Institute’s Barro Colorado Island in the Panama Canal. (Christian Zieglar photo)

The lowland tropical forest on Panama’s Barro Colorado Island is the site of a huge long-term study focusing on plant diversity: more than 400,000 individual trees and shrubs of more than 300 species have been marked, mapped and measured every five years for the past 30 years. A unique window on climate change and other large-scale processes, the experiment was originally set up because two ecologists, Robin Foster, now at Chicago’s Field Museum, and Stephen Hubbell at UCLA, a co-author on this paper, had an argument about how life organizes itself.

What determines the members of a community? The study site—a patch of forest the size of nearly 100 football fields—is large enough to include individuals of many rare species that would not be present in smaller studies. After realizing that many of the processes that shape diversity happen early in a tree’s life, researchers decided to expand the study to include an annual survey of seedlings growing in the forest understory. This study of seedlings, led by Comita, Hubbell and Panamanian botanist and co-author Salomón Aguilar, has now been going for nearly a decade and has yielded new insights into this diverse forest.

For years, researchers have noticed that individual plants surrounded by neighbors of the same species do not grow and survive as well as individual plants surrounded by other species. Some evidence suggests that this is either because pests and pathogens move more readily among individuals of the same species or because they are competing with each other for the same resources.

“It became clear with this seedling survival survey that even though neighbors can be shaded out by individuals of the same or of other species, there are real differences in the survival of different species depending on how many of their neighbors are the same species,” said Helene Muller-Landau, staff scientist at the Smithsonian and adjunct professor at the University of Minnesota. “Some of our colleagues are working on the specific mechanisms that explain these differences, and we look forward to seeing their results, which will be published soon.” –Beth King

Honeybees fascinate visitors at the National Zoological Park

John Barrat — Wed, 07 Jul 2010 11:51:01 +0000

Scientists find excess nitrogen favors plants that respond poorly to rising CO2

John Barrat — Wed, 30 Jun 2010 17:09:21 +0000

As atmospheric carbon dioxide levels rise, so does the pressure on the plant kingdom. The hope among policymakers, scientists and concerned citizens is that plants will absorb some of the extra CO2 and mitigate the impacts of climate change. For a few decades now, researchers have hypothesized about one major roadblock: nitrogen.

Photo right: Scientist Adam Langley sprays plants in a test chamber with nitrogen. The additional nutrients changed the composition of the plants inside the chamber, spurring the growth of grasses that respond weakly to elevated levels of CO2.

Plants build their tissue primarily with the CO2 they take up from the atmosphere. The more they get, the faster they tend to grow—a phenomenon known as the “CO2 fertilization effect.” However, plants that photosynthesize greater amounts of CO2 will also need higher doses of other key building blocks, especially nitrogen. The general consensus has been that if plants get more nitrogen, there will be a larger CO2 fertilization effect. Not necessarily so, says a new paper published in the July 1 issue of Nature.

Adam Langley and Pat Megonigal, two ecologists at the Smithsonian Environmental Research Center, conducted a four-year study on plants growing in a brackish Chesapeake Bay marsh. In 2006 they began feeding sedge-dominated plots a diet rich in CO2 and nitrogen. Just as atmospheric CO2 levels are rising, so is nitrogen pollution in estuaries due farming, wastewater treatment and other activities. Because the sedge has previously shown a large CO2 fertilization effect, Langley and Megonigal expected that adding nitrogen could only enhance it.

Photo left: The Smithsonian’s Global Change Research Marsh is a tidal system. It sits on the western shore of the Chesapeake Bay in Edgewater, Maryland.

The sedge, Schoenoplectus americanus, initially reacted as expected. However, after the first year something unanticipated happened. Two grass species that had been relatively rare in the plots, Spartina patens and Distichlis spicata, began to respond vigorously to the excess nitrogen. Eventually the grasses became much more abundant. Unlike sedges, grasses respond weakly to extra CO2 and do not grow faster. Thus, the nitrogen ultimately changed the composition of the ecosystem as well as its capacity to store carbon.

The experiment unfolded on the Smithsonian Global Change Research Wetland, located on the Chesapeake’s western shore in Maryland. The Smithsonian site has a history of climate change research that dates back to the 1980s. For this study, Megonigal and Langley placed 20 open-top chambers over random plots of plants. The chambers were 6 feet in diameter and had 5-foot-tall transparent plastic walls.

Photo right: Open-top plastic chambers allow Smithsonian researchers to control and measure the amount of carbon dioxide and nitrogen that the plants receive.

The large, plastic pods allowed the scientists to manipulate CO2 concentrations in the air and nitrogen levels in the soil. Half of the plots grew with normal, background CO2 levels; the other half were raised in an environment with CO2 concentrations roughly double that amount. Similarly, half of the chambers were fertilized with nitrogen and the other half were untreated.

Langley and Megonigal began and ended each growing season with a census of the plants in each chamber. They noted the individual plant species, measured the above-ground biomass and the root growth. In the chambers that received the high-nitrogen diet, the plant composition changed dramatically; it went from 95 percent sedge in 2005 to roughly half grass in 2009. “It’s a fact that not all plants will be able to respond optimally to all changes,” said Megonigal. “The things they do respond to reflects their strategy for making a living in the environment.”

“The study underscores the importance of considering the mix of species when you’re trying to predict how terrestrial ecosystems will react to global climate change factors,” said Langley. Rising CO2 levels will favor some plants and excess nitrogen will favor others. This lesson will be important to understand as scientists consider additional global change factors such as precipitation, temperature and, in tidal wetlands, sea-level rise. The plant species that gain a competitive edge under these evolving conditions will determine how ecosystems respond to global change.

This study was supported by the U.S. Geological Survey and U.S. Department of Energy. The Smithsonian scientists recently received funding from the National Science Foundation that will sustain the research for another 10 years. Langley and Megonigal’s paper, “Ecosystem Response to Elevated CO2 Limited by
Nitrogen-Induced Plant Species Shift,” can be accessed on Nature’s website http://www.nature.com/nature/journal/v466/n7302/full/nature09176.html.

Slide Show: Smithsonian’s National Museum of Natural History is 100!

John Barrat — Tue, 22 Jun 2010 17:24:14 +0000

Since its doors first opened in 1910, the National Museum of Natural History has inspired curiosity and learning about the natural world and our place in it. Building upon the strong foundation of our extensive collections, the staff of the museum have been at the forefront of essential scientific exploration and research, and groundbreaking public exhibition and education. This slideshow and the website (www.mnh.si.edu/onehundredyears/) is a living documentary of the Museum’s 100-year history.

Transmitters unveil long-distance movements of orchid bees

John Barrat — Thu, 27 May 2010 17:42:51 +0000

In their daily search for food, blue-green orchid bees zip through increasingly scarce patches of tropical forest pollinating rare flowers. Now, for the first time ever, researchers at the Smithsonian Tropical Research Institute are able to track the routes of these creatures by gluing tiny transmitters to the backs of individual bees. The data they are collecting is yielding new insight into the role bees play in tropical forest ecosystems.

“When people disturb and destroy tropical forest they disrupt pollination systems,” says entomologist David Roubik, senior staff scientist at the Tropical Research Institute. “Now we can track orchid bees to get at the distances and spatial patterns involved in pollination—vital details which have completely eluded us in the past.”

The team trapped 17 iridescent blue-green orchid bees called Exaerete frontalis –a species common in the rainforest. “These bees easily carry a 300-milligram radio transmitter glued onto their backs,” says Martin Wikelski, director of the Max Planck Institute of Ornithology and a research associate at the Smithsonian. “By following the radio signals with a hand-held antenna, we have discovered that male orchid bees spend most of their time in small core areas, but will take off and visit areas farther away.

One male even crossed over the shipping lanes in the Panama Canal, flew 5 kilometres, and returned to Barro Colorado Island a few days later. Such long distance flights, the researchers say, support the claim that bees are major agents of gene flow, connecting widely-dsipersed orchids or other plants which they alone pollinate, over fragmented landscapes and for an extended time. This study proves that “bees are key evolutionary players in allowing orchids and other tropical plants to evolve into diverse taxa that are each spatially rare and thus require long-distance pollination,” the researchers write.

In the past, researchers have struggled to determine the distances that bees travel by following individuals marked with paint, or using radar, which doesn’t work well when trees are in the way. “Carrying a transmitter may reduce the distance that the bees travel. But even if the flight distances we record are the minimum distances that these orchid bees can fly, they are impressive, long-distance movements,” said Roland Kays, curator of mammals at the New York State Museum and a STRI research associate. “These data help to explain how the orchids these bees pollinate can be so rare.”

The Smithsonian Tropical Research Institute, the U.S. Environmental Protection Agency, the New York State Museum and the National Geographic Society all provided support for this study. Its co-authors are affiliated with the University of Arizona, Tucson, Cornell University, EcolSciences, Inc. and the New York State Museum.

Amazon farmers who vanished centuries ago were remarkably innovative

John Barrat — Mon, 19 Apr 2010 05:28:35 +0000

Little is known about the long-vanished Arauquinoid, an Indian culture that thrived centuries ago in French Guiana, other than they were innovative farmers. The Arauquinoid were gone long before Columbus landed in the new world, yet what archaeologists and other scientists have recently learned about their farming methods comes through the auspices of some unlikely collaborators—ants, termites and earthworms. In addition, what scientists are learning about Arauquinoid farming methods may have important implications for today’s sustainable farms.

Image right: A pre-Columbian raised field in French Guiana filled with small, round mounds for growing crops.

Centuries ago these natives grew maize, manioc and squash upon a matrix of raised beds in flat, regularly flooded coastal marshes. Scooping slices of topsoil from the marsh they flipped them together and upside down, creating mounds which they topped with soil from other areas. Crops were planted, tended and harvested on this matrix of small islands.

Using aerial photographs, researchers have recently located a number of long abandoned “fossil” agricultural fields used by the Arauquinoid in coastal French Guiana. Follow-up examination of the soil and associated fragments from cooking implements, done in part by scientists at the Smithsonian Tropical Research Institute in Panama, have revealed microscopic starch grains from corn and manioc. Squash phytoliths also were recovered from soil analysis.

Image left: The aerial photograph at top shows different types of raised fields in a complex in French Guiana. The bottom image is an interpretation of these earthworks based on stereoscopic ananlysis and field studies.

This new research has revealed that in areas considered unsuitable for farming today, “pre-Columbian farmers constructed thousands of raised fields in the seasonally flooded coastal savannas of the Guianas,” scientists write in a paper published recently in the Proceedings of the National Academy of Sciences. ”They built conspiciuous earthworks, including raised fields, canals and ponds, that enabled them to practice intensive permanent agriculture in this low-lying region with highly seasonal rainfall.” The study combined archeology, archeobotany, paleoecology, soil science, ecology and aerial imagery and was carried out by scientists from a number of organization, including the University of Bayreuth in Germany, the University of Montpellier II and Centre d’Ecologie Fonctionnelle et Evolutive in France, the University of Exeter, and the Smithsonian Tropical Research Institute in Panama.

Image right: A matrix of raised mounds in an abandon field in a part of French Guiana named Savane Grande Macoua. Only the mounds are above water level.

In a region that receives on average four meters of rain each year, scientists were puzzled why the mounds have not eroded into obscurity over the centuries. They discovered that ants and termites, living in the raised mounds since before they were abandoned by the Arauquinoid, have continually rebuilt them with large quantities of new organic matter. Earthworms, attracted to this rich soil, kept the mounds porous, allowing rain to percolate through without washing them away. Grasses and other plants keep the mounds stable. A survey of the ants and termites in these former agricultural swamps, revealed that their nests occur entirely on the mounds, with none in the low, often submerged, areas surround them.

Researchers now speculate that as the fertility of the mounds decreased with continued crop growing, these ancient farmers may have let their mound-matrix fields lay fallow, allowing ants, termites and worms to replenish the soil’s nutrients. This largely forgotten practice of growing crops in marshes and allowing ecological engineers such as ants and termites to replenish nutrients is a technique that may have practical uses in modern sustainable farms, the researchers write.

A well-defended territory is what some female hummingbirds find most attractive in a mate

John Barrat — Wed, 31 Mar 2010 17:20:21 +0000

When it comes to attracting a mate, flowers and sweets often do the trick—even for one of the world’s smallest birds—the purple throated carib, a hummingbird species native to the mountainous islands of the Eastern Caribbean. Scientists recently discovered that it is in the best interest of male purple-throated caribs to defend and maintain a territory with a high density of nectar-producing flowers. Why? Because it is the quality of this territory—rather than flashy plumage or elaborate courtship displays—that attracts the most females.

Image right: A male purple-throated carib perches on a Caribbean heliconia plant. Click to enlarge. (Photo by John Kress)

John Kress, a botanist at the Smithsonian’s National Museum of Natural History, and Ethan Temeles, an ornithologist and biology professor at Amherst College in Massachusetts, have spent several years researching purple throated caribs (Eulampis jugularis) in the wild on the island of Dominica. What they observed was unique among all bird species: successful male caribs maintained and defended territories with nectar supplies that were two to five times greater than their daily needs and also isolated part of their crop for the exclusive feeding rights of visiting females. The key to this female-only feeding area was the presence of heliconia flowers.

“This is the first time such behavior has ever been observed in a bird species,” said Kress. “Not only is the male defending a huge territory from competing males, but he’s also defending a big chunk of it exclusively for females who he is trying to attract as potential mates. He is farming the nectar for these dual purposes.”

Image left: A female purple-throated carib (Photo by Ethan Temeles)

Male and female purple throated caribs are alike in plumage, but males are considerably larger and have longer wings than females. Females, however, have bills that are 20 percent longer and 30 percent more curved than the bills of the males, meaning that they are physically able to feed from flowers that males cannot. This is also known as “sexual resource partitioning” and for the purple throated carib it applies to two species of Heliconia, a primarily neotropical genus of plants. Male caribs feed from the Caribbean heliconia (Heliconia caribaea), while females feed primarily from the lobster claw heliconia (Heliconia bihai).

This close correspondence between the physical traits of the two different heliconia flowers and the bill morphology of each sex of purple-throated carib strongly suggests that the process of coevolution (the evolution of two or more species that interact closely with one another, with each species adapting to changes in the other) is the cause of this fit between the birds and the flowers. Furthermore, this process is strongly reinforced by the fact that the different energy requirements of the male and female carib are uniquely matched by the energy rewards in the nectar of their respective heliconia flowers.

Image right: A male purple-throated carib sips nectar from a Caribbean heliconia plant. (Photo by Ethan Temeles)

The scientists report that a female’s choice of a male depends on the nectar supplies within his territory, which in turn depended on his prevention of nectar losses to competing male purple-throated caribs and other nectar feeding intruders.

“One of the most important aspects of maintaining an abundant nectar crop for the male carib is keeping intruders out,” Temeles said. “We found that males that were most successful at defending their territories from intruders also were the ones that were most successful at dominating neighboring males and at feeding on neighbors’ territories.”

The male’s reward for spending the time and energy in defending his territory was, of course, the attraction of potential mates. Temeles and Kress observed that the rates of female intrusions to feed on defended territories were highest in late morning and early afternoon, at times when the amount of nectar in undefended plants was lowest. “Once the females are in the territories they are allowed to “sip from the male’s wine cellar.” If she likes what she is sampling, then mating takes place,” Temeles said.

Kress and Temeles plan to extend their studies to other islands in the Eastern Caribbean to test how this plant-pollinator system has evolved in different regions and in different ecosystems. —Johnny Gibbons

Medieval book is important resource for how plants were once collected, treated and used

John Barrat — Thu, 04 Mar 2010 17:52:09 +0000

Among its treasures, the Bibliothèque de France in Paris holds a great many splendidly illustrated books on medieval herbs and medicines. One of these manuscripts is latinus 9333, which recently was reproduced in facsimile with a volume of study. Alain Touwaide, Historian of Sciences in the Department of Botany at the Smithsonain’s National Museum of Natural History, contributed three chapters in the study volume highlighting the history, importance and originality of the manuscript.

Latinus 9333 is the Latin translation of the so-called Tacuinum sanitatis, a medieval handbook on wellness written in Arabic by the 11th-century physician ibn Butlan. It deals with factors influencing human health: from the air, the environment and food, to physical exercise and sexual activity.

Image: The manuscript of Paris, Bibliothe`que nationale de France, latinus 9333: f. 36 verso: Ocimum basilicum L.; and f. 37 recto: Mandragora officinarum L.

In contrast to the Arabic original, several copies of the Latin version are illustrated. Characteristically, these illustrated Tacuinum sanitatis come from northern Italy and date to the 14th century. Their illustrations include scientific representations of plants and other substances used as medicines, as well as illustrations featuring other factors that influence human health. The illustraions offer snapshots of medieval daily life, environment and activities.

Such images are of particular importance to the history of botanical knowledge and illustration, Touwaide points out in the study volume. Plants are represented here in great detail, inserted into their environment, be it natural or human. Many of the images include human figures and illustrate the way plants were collected, treated, used, or were embued with cultural meanings. They constitute material of great interest for the study of the interaction between men and plants.

The manuscript encapsulates a knowledge and wisdom gained by trial and error over centuries, often going back to a much earlier period. The archeology of its text brings to light the odyssey of medicine and science in the Mediterranean and beyond, as latinus 9333 moved from Italy further north, where its Latin text was translated into German.

Researchers compile colorful on-line guide to marine algae of Panama

John Barrat — Fri, 26 Feb 2010 19:32:44 +0000

A new, online identification guide to more than 120 marine algae of the Pacific Panama has been developed by Smithsonian marine biologists Diane and Mark Littler in conjunction with the bioinformatics office at the Smithsonian Tropical Research Institute in Panama. The guide is designed to make it easy for non-specialists to accurately identify seaweed species around Panama´s offshore islands from Las Perlas in the Bay of Panama to the Gulf of Chiriqui. More than 158 stunning underwater photographs and 445 photomicrographs showcase the major seaweeds. The treatment also documents 87 new records of marine macroalgae for Panama and 32 new records for the Eastern Pacific Ocean. The database can be accessed at the Web address: http://biogeodb.stri.si.edu/pacificalgae/

Image right: Mark and Diane Littler (Photo by Barrett L. Brooks)

“We have seen rapid degradation of reefs worldwide. It is of paramount importance scientists–from geologists to chemists–and for school kids, tourist guides and conservationists to understand the local reef environment and its foundation species,” say the Littlers. “Our guide celebrates the beauty of some of the most attractive inhabitants of Panama’s undersea realm and provides an indispensable, easy-to-use tool for their identification.”

Along with the coelenterate corals, the algae are the major primary producers and builders of Panamanian Eastern Pacific reef systems. Marine plants from four diverse evolutionary lines dominate. Now there is a way to accurately identify the marine plants that form the basis of this food web and maintain living reef structures.

Image left: Spectacular marine algae like this specimen of Dictyota humifusa are easily identified using the new marine plant guide. (Photo by Dianne Littler)

Image left: Identification keys distinguish one species from another based on easily observed characters. This guide provides keys to genera and species within each phylum of macroalgae. The keys utilize a double numbering system that enables the user to work a key backwards as well as forwards. A specimen can be “picture-keyed” initially, then positively identified by using the dichotomous keys and the photomicrographs.

Prehistoric pollination: Sawfly mouthparts fit tubular channels of gymnosperm cones

John Barrat — Fri, 06 Nov 2009 17:40:15 +0000

Scientific evidence shows that almost all of the earliest angiosperms (flowering plants) were pollinated by insects. Whether such a relationship existed between insects and early gymnosperm species (non-flowering plants with exposed seeds, such as conifers) has been widely disputed. Smithsonian scientists and colleagues, however, have recently found evidence that gymnosperm plants shared an intricate pollination relationship with scorpionfly insects 62 million years before flowering plants appear in fossil records. The team’s findings are published in the scientific journal Science, Friday, Nov. 6.

Illustration: Eurasian mid Mesozoic scorpionflies feeding on gymnosperm ovulate organs, each with tubular access to deeper-seated rewards such as nectar or pollination drops. (Illustration by Mary Parrish)

Conrad Labandeira, paleoentomologist at Smithsonian’s National Museum of Natural History, and team members examined both the specialized features of scorpionfly mouthparts and the unique reproductive features of coexisting gymnosperm plants. The proboscis (elongated tubular mouthparts) of these insects, which was up to 1.3 centimeters long, was either hairy or had ridges, and frequently had pads at the tip to suck up fluids, similar to the structure of modern hoverflies, moths and butterflies. The presumed gymnosperm hosts bore deep funnel-like or tubular channels, also up to 1.3 centimeters long, containing nectar-like pollen drops.

The reproductive anatomy of the plants was typically gymnospermous, but show important modifications for insect attraction, similar to modern flowering plants. However the lineages of these plants and their scorpionfly pollinators became extinct during the mid-Cretaceous period (approximately 105 million years ago) just as flowering plants and their newly evolved pollinators, such as moths and butterflies, came on the scene.

Photos: Lichnomesopsyche gloriae (Mecoptera: Mesopsychidae), from the late Middle Jurassic of northeastern China, showing head and long, hairy proboscis. (Photos by Wenying Wu)

“This exciting discovery now answers the conclusions that paleobotanists were making recently regarding ‘strange’ structures occurring in the ovulate organs of some Mesozoic gymnospermous plants,” said Labandeira. “One such fructification of an extinct Early Cretaceous cheirolepidiaceous conifer family, Alvinia bohemica, is the best example of an anatomically complicated, jerry-rigged device to achieve insect pollination. There were contemporaneous, matching, elongate insect mouthparts, and other evidence, that indicate presence of a gymnosperm-based pollination mode from the deep past.”

The evolution of this type of elongated mouthpart among insects occurred at least five separate times during a 13-million-year span during the Middle Jurassic period. The pollinating relationship between modern pollinators and flowering plants was an independent evolutionary occurrence, separate from the scorpionfly and gymnosperm plants.