Dam Good Research on Invasive Beavers in Patagonia

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Alejandro Pietrek and a subject of his research. Photo by Duke Forward.

 

For three years, Duke student Alejandro Pietrek has bravely grappled with some unusual marauders of the forests and steppes of Patagonia: invasive beavers. A biology graduate student, Pietrek recently presented his dissertation on the “Demography of invasive beavers in the heterogeneous landscapes of Patagonia.” Pietrek has studied over two dozen colonies of beavers in order to answer three questions:

  • “How do differences between habitats affect the demography of invaders?”
  • “How does density dependence affect the abundance and distribution of invaders post-establishment?”
  • “How can we manage biological invasions?”

Pietrek began by explaining how the furry rodents started ravaging the natural habitat of Patagonia, beginning with 20 beavers intentionally introduced into the forests of Tierra del Fuego in 1946. By the late 1960s, the growing colonies spread to the continent.

Today there are an estimated 100,000 individuals in Patagonia, disrupting the regional habitats and destroying biodiversity.

The biologist tackled his first question via quantitative science. “Very simply mathematical models have shown that speed of invasion is determined by two main things: population growth rate and movement,” he said. How the different habitats of Patagonia affected this invasion was what he worked to find out, by measuring colony size and the number of kits. Pietrek directly observed 25 colonies in each habitat over three years, using binoculars and seemingly endless patience. “It was very fun,” he said. He found that steppe habitats tended to have higher numbers of beavers and kits compared to forest.

Beaver Dam - Tierra del Fuego National Park, Argentina - Photograph by Anne Dirkse via Wikimedia Commons

Beaver Dam – Tierra del Fuego National Park, Argentina – Photograph by Anne Dirkse via Wikimedia Commons

Pietrek believed that the answer to the first question was counterintuitive, and he explored the possible reason in the second, where he figured the cause to be density dependence, as beavers in the steppe were more likely to survive in higher populations, and thus were dependent on living in large colonies for survival. In the forest, colony size wasn’t as important to the survival of the beavers. Pietrek found that as population density increased, the animals’ choice of landform changed: with denser numbers, the beavers were more likely to choose u-shaped valleys and plains than canyons. He noted the importance of identifying the preferred habitat of beavers, as it may allow easier detection of the presence of the invasive species.

Finally, Pietrek applied his findings toward the management of biological invasions. “One thing we can do is to build a model to predict the spread of beavers,” he said. He observed that beavers spread on average 7.8 km per year, though he also used individual-based models as well in order to track juvenile beavers. He found that young beavers tended to disperse and form new colonies, and formed another model in order to track this dispersal pattern. Juvenile beavers will first search for mates within their original colonies, only moving along if none can be found. These findings make for easier tracking of beavers across the landscape, allowing for easier management of their population growth.

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Post by Devin Nieusma, Duke 2019

Science a waste of money? “Wastebook” misses big picture

Duke biologist Sheila Patek explains the big picture behind a recent study on sparring mantis shrimp. Photograph by Roy Caldwell.

Duke biologist Sheila Patek explains the big picture behind a recent study on sparring mantis shrimp. Photograph by Roy Caldwell.

Sheep in microgravity. An experiment involving a monkey in a hamster ball on treadmill. These are among more than 100 descriptions of what Senator Jeff Flake, Republican of Arizona, deems wasteful federal spending in “Wastebook: The Farce Awakens,” released on Tuesday, Dec. 8. The latest in a series originally launched by retired Senator Tom Coburn, each “Wastebook” targets a range of federally-funded projects, many of them science-related, which the authors declare a waste of taxpayers’ money.

But what do the researchers behind these projects have to say? We asked Duke biologist Sheila Patek, whose work on fighting mantis shrimp was singled out in Flake’s latest report, to tell us her side of the story:

“What do we stand to learn from basic research on mantis shrimp? It turns out, a lot,” Patek said.

“First, mantis shrimp strike with weapons operating at the same acceleration as a bullet in the muzzle of a gun, yet they achieve high performance without explosive materials. They use a system based on muscles, springs and latches and neutralize their opponents with impact-resistant armor. This research helps us understand how animals survive when they have lethal weapons at their disposal but do not actually kill the opponent — something that could change the way we look at future defense systems,” Patek said.

“Second, these crustaceans have properties of extreme acceleration that are of great interest to military and manufacturing engineers. Mantis shrimp use a toothpick-sized hammer that can break snail shells in water that humans can only break with a larger hammer in air. Their small, lightweight hammer resists fracture over thousands of uses. Our research has already led to the development of novel engineered materials that resist impact fracture, based directly on mantis shrimp hammers,” Patek said.

“Third, mantis shrimp do something else that humans cannot: strike in water at the speed of cars on a major highway without causing cavitation, a phenomenon that occurs in systems with rapid motion (like propellers) where implosive bubbles emit heat, light and sound with energy sufficient to wear away steel. Naval engineers have been trying to solve this problem since the invention of the submarine. When we understand how mantis shrimp avoid cavitation during the rotation phase of their strikes while effectively using cavitation during their impact phase, the knowledge will undoubtedly improve the capabilities of ships, submarines, torpedoes and other machines,” Patek said.

“Research that helps us understand and apply the mechanics and evolutionary diversity of natural systems to create a better and safer society for all of us is a wise investment for this country.”

RobinSmith_hed100Post by Robin A. Smith, Senior Science Writer

Geography and the Web: A new frontier for data vizualization

A GIS Day earth cake made by the Collegiate Baker

You might be forgiven if you missed GIS Day at The Levine Science Research Center Nov. 18, but it was your loss. Students and faculty enjoyed a delightful geography-themed afternoon of professional panels, lightning talks, and even a geospatial research-themed cake contest.

What is GIS and why is it important?

Geographic information systems (GIS) give us the power to visualize, question, analyze, and interpret data to understand relationships, patterns, and trends in the world around us. Those who work with data and analytics have a responsibility to contribute to this change by helping us make the right decisions for our future. As noted during ESRI’s 2015 User Conference in the video below, “We have a unique ability to impact and shape the world around us. [Yet] for all of our wisdom, our vast intellectual marvels, we still choose a path of unsustainability and continue to make decisions that negatively impact the Earth and ourselves. […]We must accept our responsibility as stewards of the Earth. […] We must apply our best technology, our best thinking, our best values. Now is the time to act. Now is the time for change.”

 

How does GIS help?

Doreen Whitley Rogers, Geospatial Information Officer for the National Audubon Society, led a lively discussion about GIS and the World Wide Web at Duke’s GIS Day. She said GIS is essential to understand what is happening in the geographic space around us. As GIS becomes increasingly web-based, efficiently distributing the system to other people is crucial in a time when new data about the environment is being created every second.

3D map displaying the height of buildings that birds hit windows

3D map displaying the height of buildings at which birds fly into windows in Charlotte, NC

Rogers and her team are aiming to move authoritative GIS data to web for visualizations and create a centralized system with the potential to change our culture and transform the world. As the technology manager, she is working on bringing the information to people with proper security and integrity.

In order to get people to use GIS data in a generalized way, Rogers needed to implement several core capabilities to assist those integrating GIS into their workflow. These include socializing GIS as a technology to everybody, creating mobile apps to work with data in real time, and 3D maps such as this one of bird-strikes in downtown Charlotte.

Case Studies

ClimateWatch helps us predict the seasonal behaviour plants and animals.

Mobile apps connecting to the GIS platform promise a strong “return on mission” due to the vast number of people using maps on phones. By mobilizing everyone to use GIS and input data about birds and geography in their area, the platform quickly scales over millions of acres. In the Bahamas, an  app allows users to take pictures to support bird protection programs.

ClimateWatch is an app that gives us a better understanding of how bird habitats are affected during temperature and rainfall variations – motivating people to speak up and act towards minimizing anthropogenic climate change. Developed by Earthwatch with the Bureau of Meteorology and The University of Melbourne, the app enables every Australian to be involved in collecting and recording data to help shape the country’s scientific response to climate change.

Virtual simulation of scenic flights as an endangered bird.

Virtual simulation of scenic flights from the perspective of an endangered bird.

Apps such as the 3-D flight map give users the vicarious thrill of cruising through nature landscapes from the view of endangered birds.

With the movements toward cleaning air and water in our communities, our planet’s birds will once again live in healthier habitats. As the Audubon Society likes to say: “Where birds thrive, people prosper.”

 

 

 

For more information about bird-friendly community programs, you can visit Audubon‘s site or send them a message.

Doreen Rogers after her presentation on National GIS day.

 

 

To learn more about data visualization in GIS, you can contact Doreen Whitley Rogers via email here.

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Post by Anika Radiya-Dixit

Iridescent Beauty: Development, function and evolution of plant nanostructures that influence animal behavior

Iridescent wings of a Morpho butterfly

Iridescent wings of a Morpho butterfly

Creatures like the Morpho butterfly on the leaf above appear to be covered in shimmering blue and green metallic colors. This phenomenon is called “iridescence,” meaning that color appears to change as the angle changes, much like soap bubbles and sea shells.

Iridescent behavior of a soap bubble

Iridescent behavior of a soap bubble

In animals, the physical mechanisms and function of structural color have been studied significantly as a signal for recognition or mate choice.

On the other hand, Beverley Glover believes that such shimmering in plants can actually influence animal behavior by attracting pollinators better than their non-iridescent counterparts. Glover,Director of Cambridge University Botanic Garden,  presented her study during the Biology Seminar Series in the French Family Science Center on Monday earlier this week.

Hibiscus Trionum

Hibiscus Trionum

The metallic property of flowers like the Hibiscus Trionum above are generated by diffraction grating – similar to the way CD shines – to create color from transparent material.

In order to observe the effects of the iridescence on pollinators like bees, Glover created artificial materials with a surface structure of nanoscale ridges, similar to the microscopic view of a petal’s epidermal surface below.

Nanoscale ridges on a petal's epidermal surface.

Nanoscale ridges on a petal’s epidermal surface.

In the first set of experiments, Glover and her team marked bees with paint to follow their behavior as they set the insects to explore iridescent flowers. Some were covered in a red grating – containing a sweet solution as a reward – and others with a blue iridescent grating – containing a sour solution as deterrent. The experiment demonstrated that the bees were able to detect the iridescent signal produced by the petal’s nanoridges, and – as a result – correctly identified the rewarding flowers.

Bees pollinating iridescent "flowers"

Bees pollinating iridescent “flowers”

With the evidence that the bees were able to see iridescence, Glover set out for the second experiment: once the bees find a specific type of flower, how long does it take them to find the same flower in a different location? Using the triangular arrangement of shimmering surfaces as shown below, Glover observed that iridescence produced by a diffraction grating leads to significant increase in foraging speed as compared to non-iridescent flowers.

Triangular formation of iridescent disks used for experimentation on bees

Triangular formation of iridescent disks used for experimentation on bees

While iridescence in plants is difficult to spot by a casual stroll through the garden, pollinators such as bees definitely can see it, and scientists have recently realized that insect vision and flower colors have co-evolved.

In order to ensure that pollen is transferred between flowers of the same species, these flowers have developed a unique structure of iridescence. As scientists work on understanding which plants produce these beautiful colors and how the nanoscale structure is passed down through reproduction, we can only look at our gardens in wonder at the vast amount of nature that still remains to be explored and learned.

Wonder of nature

Wonders of nature in an everyday garden

 

 

Beverley Glover is the Director of Cambridge University Botanic Garden and is currently accepting applications for PhD students

 

 

 

 

 

Post written by Anika Radiya-Dixit

 

Relationship Between Domestication and Human Social Skills

Brian Hare wants to know why humans are such big babies.  

Well,  that was just the provocative title for his Center for Cognitive Neuroscience talk on Oct. 2. What he wants to know is what happens in the development of human babies that socially advances and separates them from their animal counterparts.

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Hare, an associate professor of evolutionary anthropology, discussed human evolution and comparisons to our ancestors and chimpanzees, bonobos and even dogs. He explained that the idea of comparing humans to other species suggests that “something very fundamental happened during human evolution that makes us human– a shift in human development.”

First Hare attempted to evaluate whether certain advanced capabilities of humans are present in other species. One means of doing this was by examining if other species think about the thoughts of others. In a video from an experiment  “Gaze” that Hare conducted, he looks at a chimpanzee named Dorene, and then suddenly glances upwards. The chimp follows suit, gazing up at the ceiling to see what Hare is looking at. From this behavior, Hare inferred that chimpanzees are in fact capable of thinking about the thoughts of others, like the human species.

This led Hare to examine another behavior that is advanced in humans: cooperation. Hare explained that in previous laboratory research, chimpanzees were found to be incredibly uncooperative. Hare’s studies in the field, however, proved the opposite. In an experiment with Alicia Melis and Michael Tomasello, two chimps were put in adjacent, but separate rooms. A treat was visible with a string leading to each chimpanzee. If one animal pulled the string, it just got the string. But if both pulled cooperatively, they ended up with the food. The researchers found that 95% of the chimps could work together to solve this problem to get an equal payoff for both of them. Hare did note, however, that if the chimps had communicated, they could have solved the problem more efficiently.

This showed that where chimpanzees might differ from the human species is in their inability integrate cooperation and communication. With children, Hare explains, this is a fundamental part of development that is established early in life. Because of this, Hare wondered if there is something motivationally different about the structure of cooperation between humans and other species, something that also shows early in development.

When humans work together, Hare said, they understand they have a shared goal and will adjust to different roles to complete the task. This has led to, from an evolutionary perspective, a very “strange” behavior in humans, in which they do things together simply because they like to. Hare calls this “we psychology.” Hare showed two videos side by side: one of his son rolling a ball to his mother, Vanessa Woods, and another of a chimp in a cage rolling a ball with Woods. When Woods stopped playing the game, the chimp reached out of the cage and grabbed her arm and pushed the ball so it would roll back to him. From this, Hare inferred that, like humans, chimps may also have a small tendency for “we psychology.”

In another study, Hare compares two-year-old children to adult and juvenile chimpanzees. In terms of physical cognition, the species were very similar to one another. On the social problem solving front, however, human children were already outperforming juvenile and adult chimpanzees. This study, along with the culmination of his earlier research, reinforced Hare’s idea that something very fundamental happens early in human development that differentiates human’s social and communicative capabilities from other species: domestication.  

“It’s not just that kids are solving problems better, but it may even be that the way kids cognitively organize has changed,” he said.

Hare explains that just knowing the cause to be domestication was not enough, however. He wanted to understand how this worked. Hare referenced extensive breeding research conducted by Dmitri Konstantinovich Belyaev, in which he studied the domestication of the fox. Not only did these foxes show behavioral changes due to domestication, they also displayed morphological and physiological changes: floppy ears, curly tails and high levels of serotonin. Belyaev also found that, like humans, foxes use gestures and communicative cues. So, Hare concluded that the process of domestication influences a realm of social and biological characteristics and could be manipulated and interpreted in many different ways, especially in our own development.

experimental-fox

“This doesn’t just happen as a result of artificial selection, or human selection. It can happen as a result of natural selection,” Hare said. “So then we turn to our own species and start looking at whether there’s any evidence in our own evolution for this.” he said.

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By Madeline Halpert, Class of 2019

Fisticuffs Among the Mantis Shrimp

When mantis shrimp (Stomatopoda) dispute territory or mating rights, they use the tools at hand – namely two super-sonic bludgeons powerful enough to dismember a live crab or break through a clam shell.

Mantis shrimp are pugnacious pugilistic crustaceans . (Photo by Nazir Amin via Wikimedia Commons.)

Mantis shrimp are pugnacious and pugilistic. (Photo by Nazir Amin via Wikimedia Commons.)

Fortunately, they’ve developed a way to use these deadly clubs on each other without causing too many fatalities. In a ritualized battle called “telson sparring,” the combatants take turns hammering on each other’s tail-plate, which is raised up like a shield.

Graduate student Patrick Green watched more than 30 such contests in captive Panamanian mantis shrimp to discover that it wasn’t the shrimp who hit hardest who won the bout, but the one who hit the most frequently.

Green and his Ph.D. supervisor, biology professor Sheila Patek, hypothesize that the ritualized fighting could be a display of overall vigor and tenacity rather than outright punching power.

CITATION: “Contests with deadly weapons: telson sparring in mantis shrimp (Stomatopoda),” Green PA, Patek SN. Biology Letters, Sept. 2015. DOI:10.1098/rsbl.2015.0558

Karl Leif Bates

Post by Karl Leif Bates, Director of Research Communications