Showing posts with label predator-prey interactions. Show all posts
Showing posts with label predator-prey interactions. Show all posts

Wednesday, April 4, 2012

Rattlelsnake-Squirrel Interactions

From the University of California at Davis.

Robot squirrels from the University of California, Davis, are going into rattlesnake country near San Jose, continuing a research project on the interaction between squirrels and rattlesnakes.

In the lab, robot squirrels have shown how squirrels signal to snakes with heat and tail flagging. Through field experiments, researchers from San Diego State University and UC Davis aim to learn more about rattlesnake behavior.

It's not the only use of robots to study animal behavior at UC Davis. Terry Ord, a former postdoctoral researcher now at Harvard University, used robot lizards to study display behavior by anole lizards in the jungles of Puerto Rico. Gail Patricelli, professor of evolution and ecology, has used a camera-equipped robot sage grouse hen to study the mating behavior of these prairie birds.

The collaboration is giving biologists new tools for their work -- and also helping engineers design new and better machines.

The research on the long struggle between California ground squirrels and their main predator, rattlesnakes, began at UC Davis under the leadership of psychology professor Donald Owings, an expert on animal behavior, who died in 2011.

Sanjay Joshi, professor of mechanical and aerospace engineering at UC Davis, built the original "robosquirrels" for Owings, and is now working with Rulon Clark, assistant professor of biology at San Diego State University and an expert on snake behavior.

The research then and now centers on two squirrel behaviors in reaction to rattlesnakes: a tail flagging movement and the warming of the tail. Owings, with Professor Richard Coss and colleagues, observed that when adult squirrels detect a snake, they approach it head-first in an elongated posture, making flagging movements with their tails. Owings and Coss noticed that when confronting a rattlesnake, the squirrels also heated their tails.

Because rattlesnakes can "see" in the infrared, the researchers thought the squirrels might be sending a signal to the snakes. But, with live squirrels, there is no way to separate tail flagging from tail heating.

Enter the robots. Joshi's engineering lab built a squirrel with a heatable tail and a tail flagging mechanism, each controlled separately.

Using the robosquirrel, Aaron Rundus, then a graduate student in Owings' lab and now an assistant professor at West Chester University in Pennsylvania, showed that the snakes responded to the heat signal from the squirrel.

"It was the first example of infrared communication in the animal world," Joshi said. That work was published in 2008: an article published in IEEE Robotics & Automation Magazine in December, 2011, summarized much of the work to date.

Fieldwork is more challenging, he said. Ryan Johnson-Masters, a graduate student in Joshi's lab and now at the Sandia National Laboratory in Livermore, built a new robot with smaller and more robust controls that was easier to transport into the field.

The field season is fairly short, a few weeks in late spring and early summer when squirrel pups are born and rattlesnakes come hunting for them.

Then you need to find rattlesnakes in rough country.

"It's definitely an adventure," Joshi said.

Clark began collaborating with Owings and Joshi in 2007. Together, they wrote a grant proposal to the National Science Foundation to take the robosquirrel into the field. The grant was funded with $390,000 in 2010.

Once the researchers have located a foraging snake, they put down some track, set up the robosquirrel and a video camera to record the scene and retreat behind a blind. The snakes seem to accept the robosquirrel as real, Clark said. One of their videos shows a snake biting the robot's head.

Snakes will rarely strike at a flagging adult squirrel -- and if they do they almost always miss, Clark said.

"Squirrels have a remarkable ability to move out of the way of an oncoming snake strike," he said. Even adult squirrels that do not seem to be aware of a snake will often successfully dodge a strike.

Squirrel pups are much more vulnerable. They have less resistance to snake venom and seem more reckless in their behavior. They show the same displaying behavior as adults, but will get closer to snakes -- sometimes with fatal results.

Although not much is known about the mental abilities of rattlesnakes -- they are not ideal lab animals, after all -- they do behave in the field as if they are making complicated assessments about foraging behavior, Clark said. For example, they react differently to adult squirrels versus pups.

Why do squirrels approach the snakes at all? Clark says that they may be trying to assess the nature of the threat. Sometimes snakes will leave the area after encounters with squirrels.

Before joining the campus in 2001, Joshi worked at NASA's Jet Propulsion Laboratory on robots for space exploration. At UC Davis, Joshi began working with psychology professors including Owings and Jeffrey Schank. With Schank, he built robots that emulated the behavior of young rat pups -- revealing new insights into both rat behavior and robot design.

"The reason I'm so excited is that with robots we can really change how animal behavior studies are done," Joshi said.

Tuesday, November 22, 2011

The Arms Race in Dendrobatid Frogs

Shape dough into frogs, that's normal in a day care. At university, it is more rare. However, the biologist Mathieu Chouteau in 3600 he made a carefully painted as part of his Ph.D. project in the Department of Biological Sciences at the University of Montreal. A month of work to which his wife had worked closely.

He then divided this bestiary in sites previously identified in the middle of the Amazon rainforest. "The hardest part was carrying my models without arousing suspicion at the airport and customs controls," says Mathieu Chouteau in an interview from Peru, where he pursued a fellowship in collaboration with the National Museum of Natural History of Paris.

In an article to be published in December in Natural History that has already been the subject of a new site ScienceNOW (Helen Fields, "Why Are There So Many Colors of Poisonous Frogs", November 4, 2011), he concludes that the Predation is a natural selection factor in the development of multiple motifs in the species Ranitomeya imitator, a frog under a centimeter in various colors. The models on clay he has documented fact in the evolution of colors and patterns of dendrobates: the role of predators.

As we learned from our first visit to the Montreal Biodome, brightly colored frogs which can be seen in the rain forests launched a clear message to predators: do not approach me because I am poisoned! But why is it some green with a pattern of leopard and other yellow lines while in the same species? Presumably because predators taste the local people they do not associate with frogs in the area, hoping that these frogs are edible. "When predators are they are dealing with a different species, they attack. In the long term, this would explain the unity of the patterns and colors, "says Bernard Angers, who led the research of Mr. Chouteau.

The methodology is rather original. Three times for three days at two sites, Mathieu Chouteau noted his false attacks on frogs - mostly pecking. The least attacked were those most closely resembles the native species, while those who were most distant showed signs of aggression. He had more than 300 fake frogs per site.

Seeing that no food, some predators attacked plasticine frog.

Why play dough to observe predation? The doc had this idea by browsing the scientific literature. "We have successfully used models in clay for snakes, salamanders and also dendrobates," said Mathieu Chouteau. It was in the Peruvian jungle terrain ideal for testing the hypothesis, as two radically different colonies of frogs have been studied: one attending the plain is dotted with green and the other on top of a mountain is yellow line ... The two settlements are separated by about 10 km. False frogs were deposited in two sites in specific locations. As for colors and patterns, they differed in several combinations.

What was most surprising in this research is "the very small spatial scale at which evolutionary processes occur." In the case of Dendrobates, a distance of 10 km is sufficient to demonstrate an adaptation clearly different. "A second surprise has been the learning capacity of the communities of predators, but also the speed with which this process begins when a new aposematic signal is massively introduced exotic," said the biologist.

"We have proved empirically that avian predators can recognize and avoid aposematic signals in various sites," he wrote in conclusion of his article.

This process could be the cause of the wide variety of color patterns observed not only in frogs but also among many species of butterflies and bees and other animals. The purpose of the postdoctoral fellowship is also to explain the polymorphism in the butterfly genus Heliconius. "Given that such a project request to be on the ground regularly, I settled in the small town of Tarapoto , where I am responsible for implementing a research center to facilitate studies of mimetic neotropical butterflies, "he says via email.

Bernard Angers admiration for his student, especially as this research is only one of four components of his doctorate. Patience, creativity and discipline were to converge to implement such a protocol. It also highlights the qualities of photographer Mathieu Chouteau (including readers of Forum can get an idea on page 1).

If they are of great beauty, dendrobates are among the most toxic animals on the planet. The student has experienced when, after a hard day's work Cainarachi, it has not taken the time to wash their hands before snack. "Error! Approximately five minutes after starting to eat, I had the lips and throat stung and it ended with a serious food poisoning that lasted two days, "he recounts.

Mathieu-Robert Sauvé