Scholarship & Creativity

Updated 9:30 AM January 10, 2007

Scholarship & Creativity

Predators and prey: The ecology of coupled oscillations

Connect one pendulum to another with a spring and in time the motion of the two swinging levers will become coordinated.

This behavior of coupled oscillators—long a fascination of physicists and mathematicians—also can help biologists seeking to understand such questions as why some locations overflow with plants and animals while others are bereft.

In the December cover article of the journal BioScience, theoretical ecologist John Vandermeer summarizes a decade of work leading to his conclusion that ecologists seeking to understand complex interactions in nature should pay closer attention to coupled oscillations.

"We know that any predator-prey system, say lions and zebras for example, shows oscillations," says Vandermeer, the Margaret Davis Collegiate Professor of Ecology and Evolutionary Biology. "If there are lots of lions preying on zebras, numbers of zebras decline; then because zebras are scarce, lions starve and their numbers dwindle, allowing the zebra population to build up again. You see this oscillation, changing on a regular basis from lots of predators with few prey to lots of prey with few predators. The pattern is like waves or pulsations."

What gets interesting is when two independently oscillating systems, such as lions preying on zebras and cheetahs preying on impalas, become connected through the invasion of a third predator—leopards, for instance.

"When they become connected, the situation is very much like connecting two springs together—the ups and downs get into regular patterns," Vandermeer says. In the case of lions, cheetahs and leopards, bringing leopards into the system causes lion and cheetah populations to oscillate in phase with each other—peaking and declining at the same time. That works to the leopard's advantage—when both lion and cheetah populations are low, leopards can pounce on the plentiful prey.

But then lions and cheetahs increase again, eventually building up their numbers and combined competitive strength enough to drive out the leopards—at least until the next low point in the lions' and cheetahs' population cycles.

Predator-prey systems also can become coupled when a new species invades and competes for resources with prey species in two previously unconnected predator-prey systems.

Considering such scenarios with the aid of mathematical simulations can help address questions biologists have wrestled with for decades, such as how species that appear to be exploiting the same resources can coexist and why some predator-prey systems are particularly resistant to invaders.
—Nancy Ross-Flanigan, News Service

Local TV stations less likely to offer public affairs programming

Commercial television stations that are locally owned too often are leaving the majority of community programming to public television stations, a new study says.

The finding is contrary to the notion that local station owners are more likely than large network-owned operations to broadcast informational programming, such as local public affairs, says Michael Yan, an assistant professor of communication studies and study's lead author. Philip Napoli, director of the Donald McGannon Communication Research Center at Fordham University, co-authored the study.

Yan examined the relationship between competitive conditions in television markets, ownership characteristics and local public affairs programming. His study focused on 285 television stations and found that half of them did not air any local public affairs programming during the two-week sample period.

A commercial station aired about 45 minutes of local public affairs programming during the two weeks compared with seven hours during the same period by public stations, he says.

"It would seem, then, that the commercial imperatives of ad-supported broadcast television inhibit the production of local public affairs programming," Yan says.

The study found that stations owned by one of the four major broadcast networks (ABC, CBS, Fox and NBC) were less likely to air local public affairs programming.

Increased market competition does not spur individual stations to provide public affairs programming. The main reason, Yan says, is that competition may discourage profit-driven stations from taking the financial risk of providing such programming.

"Commercial broadcasters are ceding public affairs programming to their noncommercial counterparts," he says.

If public television is expected to be the primary source to broadcast public affairs, Yan says policy-makers should be concerned about this type of programming migrating to outlets that are in an increasingly precarious financial position.

The study appears in the December issue of the Journal of Communication.
—Jared Wadley, News Service

Outdoor settings help enhance walking routines

U-M environmental psychologists suggest that walking in more natural, less built-up environments tends to prolong the duration of physically and mentally healthy outdoor exercise.

In a 2004 survey of experienced walkers, researchers at the School of Natural Resources and Environment (SNRE) report that respondents who walked in natural settings with woods, water and vegetation on average spent 10 minutes longer on their outings—a 12.5 percent increase over those who exercised in urban areas or neighborhoods.

"What our survey results show is that certain types of environments facilitate extended walking," says Jason Duvall, a doctoral student specializing in resource policy and behavior. "The fact that people who walk in natural settings tend to walk for longer periods of time suggests there is something special about those settings."

Environmental psychologists study the interactions between humans and their surrounding environment. They theorize that people who spend time in nature reap the dual benefits of physical exercise and mental revitalization.

"One goal of this research initiative is to help increase the number of people who are sustaining a year-round walking routine in northern climates, thus improving the general quality of public health," says Raymond De Young, associate professor of environmental psychology and conservation behavior.

Outcomes researchers hope for include improved physical health and mental wellbeing, and possibly deeper connections with the local environment.

Duvall and De Young gave written surveys to 71 individuals classified as regular walkers, meaning they spent at least 30 minutes three days a week walking. Sixty-one returned surveys. On average participants report walking for more than 14 years, take about six walks per week and spend just over 40 minutes on each outing. Participants predominantly were women ages 20-60+.

Among the three top strategies the respondents endorsed as being most helpful for maintaining a regular walking routine were seeking good routes, using health goals as a motivation and preparing for bad weather.
—Claudia Capos, SNRE

Worry patterns vary for elderly ages 85 and older

A new study indicates that the elderly ages 85 and older worry about health and memory, and that some will seek more social contact as their worries increase with age.

The results could provide guidance for social work practitioners who help the elderly cope with aging-related issues and who can influence them to seek medical diagnosis when necessary.

The social contact involved other elderly people, as well as family, friends and neighbors, says Ruth Dunkle, the Wilbur J. Cohen Collegiate Professor of Social Work in the School of Social Work.

"The social support from family and friends could have been a reaction to the increasing worry," she says.

Dunkle—an expert in gerontology—co-authored the study that examined what worried the elderly and what patterns developed.

The study sampled 193 Midwesterners ages 85 and older between 1986 and 1995. Only 23 survivors completed the research. Despite the small sample size, the study allowed for the examination of worry patterns and how physical, psychological and social factors contributed to these patterns, Dunkle says.

Elderly subjects were followed for the nine years in order to identify what they worried about, such as concerns about sleep, taking medications, difficulties with friends and the health of family members. A dramatic increase in frequency and severity of worry occurred for all elders over the study period for all aspects of worry. The increase among this elderly group is related to issues of decreasing sense of control triggered by growing memory and physical limitations, researchers say.

While worry increased for all over the study period, the pattern was not consistent for each person, Dunkle says. For some, the worry ebbed and flowed.

Practitioners can provide information to help the elderly cope with the fears that fuel their worries, Dunkle says. When social workers serve very old clients, the patients' concerns about health- and memory-related issues must be assessed, possibly referring them to a doctor to get an accurate diagnosis.

The findings appear in a recent issue on aging in Health & Social Work.
—Jared Wadley, News Service

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