"That is no ordinary cat," said George. We were standing at our back door in the middle of the night, watching a tawny-colored cat fly over the eight-foot-high stucco wall that separates us from the mega-home next door. We live in one of the last little cottages left on Siesta Key; a few years ago, the fishing captain next door sold his property to a developer, who replaced the modest home and surrounding fig and mango trees with two three-story structures that fill almost every inch of their lots. We used to see raccoons scrambling over the captain's chain-link fence to explore our yard by moonlight, but they don't seem able to get over the wall.

But a few nights before this, I'd heard our cat, Tom, a gentle Himalayan who loves to patrol the borders of our back yard, yowling outside. I ran to open the back door; and Tom streaked in, tufts of white fur floating behind him, while a big cat jumped over the stucco wall. A few nights later, a bone-chilling growl startled us out of bed. On the inside of our glass-paned door was Tom, emitting that terrible noise, and on the outside, looking in, was the red cat. They were standing on their hind legs and striking the glass, hissing and growling at each other. The cat saw us and fled, but not before I saw its dark spots and powerful haunches, which again launched it over the wall.

I realized George was right when I opened the Pelican Press a few days later and read that a bobcat had been reported on the south end of the key. There was even a picture of the cat we'd seen, right down to its spots, standing on an elegant pool terrace. I haven't seen the bobcat again, but that image haunts me-a last, lonely survivor, foraging in this sterile new landscape we're creating.

Our environment has always been the engine of our fame and prosperity, the reason so many people have pulled up their roots and started over here. The early settlers wrote about a Sarasota of breathtaking beauty, where huge flocks of birds darkened the skies and the bays teemed with so many fish you could almost walk across on their backs. During World War II, when my father was shipped overseas, my mother came to stay with my grandmother, who spent the winters in a pink, Spanish-style cottage on Oak Street. They would drive out to south Siesta Key-from the bridge, you could see the entire white sweep of Crescent Beach, without a condominium in sight-to my grandmother's cabana and dock, on a Gulf-front piece of land that stretched all the way to the bay. (A much-lamented family legend has it that Gramie, who was both meticulous and quick-tempered, sold it for a song one year because none of her visiting children had bothered to replace the cabana screens, which raccoons and Gulf breezes kept ripping to shreds.)

In those days, Mother says, they never dreamed how quickly growth would transform that wild little island, or the rest of Sarasota, for that matter; and to those of us who live here today, those changes seem to be accelerating every year.

But though we've lost much of our natural environment, we've won some battles, too. What Wayne Daltry, director of Lee County's Smart Growth Initiative, calls "a rising environmental ethic" in the late '60s and '70s halted some of the most destructive development practices. (The war kicked off most famously in Sarasota when an armada of retirees gathered in Sarasota Bay to successfully protest the mighty Arvida Corporation's plans to dredge and fill large parts of the bay). My bobcat may be doomed, but brown pelicans once again fill our skies; we seem to be reversing the decline of Sarasota Bay; and thanks to the willingness of voters to tax themselves, thousands of acres of wild land that might have been developed have been acquired and preserved in recent years.

In his provocative new Collapse, Jared Diamond explains how societies that ignore the limits of their natural resources can destroy themselves. If we ruin Sarasota's environment, we won't starve to death, as the Norse settlers in Greenland did a thousand years ago when they stripped away their fragile grasslands, or commit genocide, as Rwandans did after they deforested their hills. But we will lose the well-heeled visitors and newcomers who drive every aspect of our economy.

And, as any environmental activist can tell you, eternal vigilance is the price of preserving our future. You can win a dozen battles to save a forest; lose one and it's gone. The inexorable pressures of the sheer numbers of people pouring into the region can overcome officials, government agencies and all our best intentions. And though these days almost everybody, from developers to politicians, understands the importance of preserving our environment, there's just not as much left to protect. And that worries Daltry. "We have better science and laws than we did 35 years ago," he says. "But we have way less room to make mistakes."