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This Issue

Limiting Factors

This issue's story for Young Naturalists, "Life of a Pike," got me thinking about life cycles, limiting factors, and longevity. Being past middle age, I'm inclined toward a self-interested view of life expectancy. Recently, I heard health economist Tor Dahl discuss a study of 10 common causes of death and their relationships to behavior, environment, biology, and medical care. Turns out, behavior—that is, lifestyle—was a contributing factor more than half the time. Study after study has implicated behavior as an important variable in disease and in health. A 2009 Harvard School of Public Health study found the leading risk factors for premature mortality of Americans—smoking, having high blood pressure, and being overweight.

Every life has its limiting factors, as "Life of a Pike" helps show. The story's author, DNR aquatic education specialist Scott Moeller, suggests that people might gain some perspective from considering the northern pike's perilous path. Fortunate is the fish that lives long enough to reproduce despite dangers, obstacles, and other limiting factors in its environment. We learn, for example, that water temperature affects the pike's growth and activity. Migrating to relatively warm waters to spawn improves the odds of survival for newly hatched pike because they can grow faster. If a northern pike population reaches a high density, pike compete among themselves for prey. The competition reduces growth rates of individual fish.

Human activities can also influence fish population dynamics, as other stories in this issue help illustrate. "Hungry for Hex" discusses the delicate balance between the Straight River's hydrology and potato farm irrigation. "Wild Country . . . Still" explains the positive changes for the St. Louis River and its tributaries that accompanied changes in hydropower operations. "Minding Our Shores" outlines the proposed new rules for protecting shorelines from soil erosion, nutrient runoff, and other hazards of development. And "Eco Yard" offers a look at home landscaping that treats rain and snowmelt as natural resources to be harvested and used (and thus prevented from carrying contaminants to public waters).

All habitats, lawns and gardens included, become more critical for all species as human population grows. The number of Minnesotans is projected to increase from 5.2 million today to more than 6 million by the year 2025. Worldwide population will likely climb from 6.8 billion people today to more than 9 billion by 2050.

What are the limiting factors for human population? Natural disasters such as the recent earthquakes in Haiti and Chile remind us that we, like all creatures, are vulnerable. To respond effectively to the crisis, people marshal their resources.

With similar urgency, the Institute on the Environment at the University of Minnesota is enlisting researchers and forming partnerships to find solutions to "the Earth's most pressing environmental problems." Director Jonathan Foley wants people to see the big issues and not get distracted by smaller things. In the winter issue of Momentum magazine, he offers this example: "A lot of people think that expanding urban areas are gobbling up the world's natural areas and farmlands. But on the global scale, urban areas are tiny—less than 1 percent of the earth's land surface—agriculture covers more than 35 percent. . . . Reality check: If you're concerned with preserving biodiversity and protecting ecosystems, focus on expanding agriculture, not suburbia."

To keep a balanced perspective, a person needs to be able to shift focus back and forth from a big-picture view to the ever-present now. A Minnesota Conservation Volunteer reader recently sent a letter offering a kind of daily reality check, words that he attributed to the Inuit: "I think over again my small adventures, my fears, those small ones that seemed so big, for all the vital things I had to reach. And yet there is only one great thing, the only thing, to live to see the great day that dawns and the light that fills the world."

Kathleen Weflen, editor
lettertoeditor.dnr@state.mn.us

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