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When it comes to mammals, how big is too big?

June 13, 2013

Researchers explain maximum size in mammals

Mammals vary enormously in size, from weighing less than a penny to measuring more than three school buses in length. Some groups of mammals have become very large, such as elephants and whales, while others have always been small, like primates. A new theory developed by an interdisciplinary team, led by Jordan Okie of Arizona State University, provides an explanation for why and how certain groups of organisms are able to evolve gigantic sizes, whereas others are not. seals Download Full Image

The international research team comprised of palaeontologists, evolutionary biologists and ecologists examined information on how quickly an individual animal grows and used it to predict how large it may get over evolutionary time. Their research is published in the journal Proceedings of the Royal Society B.

The new theory developed from the observation that some animals live fast and die young, while others take their time and mature much later. This is called the slow-fast life-history continuum, where "fast" animals – such as mice – breed very quickly, while humans mature slowly and are relatively older when they first have children. The theory proposes that those species that are relatively faster are more likely to evolve a large size quicker than slow species, and that their maximum size will be greater.

The research team tested their theory using the fossil records of mammals over the last 70 million years, examining the maximum size of each mammal group throughout that time, including whales, elephants, rodents, seals and primates. They found that their theory was very well supported.

“Primates have evolved very slowly, and never got bigger than 1,000 pounds,” said Okie, an exploration postdoctoral fellow in the School of Earth and Space Exploration at ASU. “The opposite was true of whales, which evolved their large size at the fastest rates recorded.”

The theory also makes predictions about the relative risks of extinction for large animals compared to small. The maximum size of an animal is limited by the rate of mortality in the population. Because larger animals tend to breed less frequently than smaller animals, if the mortality rate doubles, the maximum size is predicted to be 16 times smaller.

“This is a really surprising finding,” said co-author Alistair Evans of Monash University (Melbourne, Australia). “It points to another reason why many of the large animals went extinct after the last Ice Age, and their high risk of extinction in modern environments.”

The research clarifies some of the differences among the main groups of mammals and makes further predictions about how changes in body size affect the evolutionary potential. In the future, this work will be extended to help explain how extinction risk may be reduced in changing climates.

The team was funded by a Research Coordination Grant from the US National Science Foundation. Financial support to Okie was provided by an Exploration Postdoctoral Fellowship from Arizona State University’s School of Earth and Space Exploration and a National Aeronautics and Space Administration Astrobiology Institute Postdoctoral Fellowship.

The School of Earth and Space Exploration is an academic unit of the College of Liberal Arts and Sciences.

Nikki Cassis

marketing and communications director, School of Earth and Space Exploration

Scholarships aid sustainability students exploring policy, diversity

June 14, 2013

Being born and raised in Tempe, Maria Eller’s decision to go to Arizona State University would seem like an automatic choice. However, the incoming freshman says she was first attracted to the university’s sustainability program.

“I knew that at ASU, I could help the community, and that’s very important to me,” Eller says. “I want to serve Tempe. I knew that I would be learning a lot that I could use for social justice and the community.” headshot of female, black-haired Maria Eller wearing striped, collared shirt Download Full Image

Eller is a recipient of the Clean Air Cab Scholarship, established in 2009 and available to School of Sustainability students that are involved in their community while pursuing innovative and entrepreneurial studies. Clean Air Cab is Arizona’s first carbon neutral taxi service with over 40 Toyota Priuses and a deep commitment to the local economy and community.

“We designed our scholarships to reward individuals who share our same values in conserving our ecology and creating sustainability within their thinking as it pertains to their actions, community projects and future business structures,” says Steve Lopez, founder and owner of Clean Air Cab. “By positioning ourselves with ASU students and awarding ASU School of Sustainability scholarships, we feel we are taking steps in becoming a part of the future and the solutions to tomorrow’s concerns, today.” 

The second recipient, Sean Martin, is a student in the School of Sustainability. Approaching his senior year, the Tucson native will graduate with two degrees: a bachelor’s in sustainability and a bachelor’s in business with a concentration in legal studies from the W.P. Carey School of Business.

Martin is interested in becoming a sustainability consultant. His policy and governance concentration in the School of Sustainability will allow him to see both the corporate and political sides of the sustainability argument.

“Combining business, law and sustainability gives me the right perspective to understand how people create synergic relationships between the community and business, and how they support policy so we can start moving towards progressive energy,” Martin says.

An early introduction to sustainability

Eller first learned about sustainability through music, listening to Jack Johnson sing about waste, recycling and conservation. Growing up, she hiked the Grand Canyon with her family and participated in the Habitat Club in elementary school.

As a top student at McClintock High School, Eller and her friends wanted to create enthusiasm for conservation so they started her school’s first sustainability student group, EcoClub. She also was an intern at the Global Institute of Sustainability’s education outreach department, developing a water conservation game for the Arizona Historical Society Museum.

“Through education, you can show people how to make a difference by choosing alternatives that make our community more sustainable,” she says. “It’s really important to integrate and involve the community in the problem-solving.”

Martin admits that after high school, he didn’t know where to start or what to study. After doing some research, he found he was most interested in clean energy like solar power.

“The more I read about sustainability, the more I realized it was a field that could expand to whatever I wanted it to be,” he says. “I could define what my education would be, but with the right structure, people and open mentality.”

While in the school, Martin became the director of recruitment for Greenlight Solutions, a student club providing pro-bono sustainability consulting to local businesses. Student consultants come from all campus departments, delivering well-rounded corporate sustainability analyses and missions. Martin will be able to use this experience once he graduates.

“The thing about consulting is you can take on any project and really challenge yourself to use your skills in a new way,” he says.

Students develop own definitions of ‘sustainability’

Both students are using their sustainability education in different, but admirable ways. While sustainability is not fully accepted or adopted, Eller and Martin believe they can be the change they wish to see in the world.

“Sustainability is not a field; it’s not a tack-on to a new business department. It’s a way of thinking,” Martin says. “That’s one of the greatest challenges of sustainability: opening people up to what it is. Once people understand its value, that’s when the real progress will be made.”

Quoting a famous Native American phrase, Eller believes that “we do not inherit the Earth from our ancestors; we borrow it from our children."

"Sustainability for me is about preserving and understanding the different systems and connections between the nonliving and the living,” she says.

What’s next

This fall, Eller will begin her freshmen courses and wants to infuse diversity issues within her sustainability studies.

“I hope to learn about how human behavior and habits alter and affect ecosystems,” she says. “There are so many aspects to climate and environmental issues, but having perspectives from different cultures can help find solutions. I feel like you need to know about different cultures in order to adapt those solutions so that they can be implemented everywhere.”

An avid scuba diver and ocean lover, Eller hopes to advance to graduate school where she can study marine biology.

Martin wants to intern with ASU LightWorks, a research and education initiative focusing on Arizona’s renewable energy options. If chosen, he will help develop a measurement system for the university’s solar usage. After graduation, Martin plans to explore graduate programs in Europe.

“I want a new way of looking at sustainability,” he says. “I think if I went to a sustainability program in a different country, it would give me a wider perspective. I want to open my mind to the largest spectrum of fresh ideas as possible.”

Funding fuels the future

Thanks to the Clean Air Cab Scholarship, Eller and Martin will be able to turn their aspirations into realities.

“I want to thank the donors at Clean Air Cab and the School of Sustainability’s Academic Services director, Lisa Murphy,” Eller says. “I am totally responsible for paying for school and this scholarship will take the pressure off so I can focus on my classes and on any possible internships and research.”

“The scholarship enables me to steer my future in the direction I see best,” adds Martin. “Because sustainability is such an amorphous career and has the potential to go anywhere, being financially enabled by Clean Air Cab lets me be fully focused on my learning and advancement.”