Wood storks are spectacular fliers. From a perch, they spring their giant bodies into air in a single motion, then extend their necks and legs fully as they take flight. They can reach altitudes as high as 1,500 meters (5,000 feet) and can glide for miles without flapping their wings (a feat accomplished by riding vertical air currents—the currents support their weight and allow the storks to spiral upward). When foraging grounds dry up, or flood, or are converted into human developments, these aerial skills are pushed to the limit. Surveys found that some wood storks were flying farther and farther from their nesting habitat in search of foraging grounds—as much as 120 kilometers (75 miles) in some cases.

But they weren’t the only ones to struggle in the newly developed region. As the natural landscape of the Florida Everglades was modified—as cities replaced swamps and roads replaced rivers—so too were the species interactions and thus the composition of the natural communities that remained.

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Dams, dikes, and bridges installed to give humans total control over water levels—in any given portion of the Everglades at any given time—disrupted the flow of water like never before—causing some portions of the Everglades to stay too wet for too long and others to stay far too dry. As sloughs ran dry, key detritivores and decomposers like worms, grass shrimp, and microbial communities that had thrived there were decimated. This then led to the decline of the snakes, fish, alligators, turtles, and wading birds that fed on them.

Meanwhile, agricultural lands—sugar plantations, in particular—were doing as much damage as flood control efforts. The Everglades are a nutrient-poor ecosystem, especially low in phosphorus. This is fine for the plants and animals that live there; they have evolved and adapted to such conditions and are very effective at moving nutrients through the food chain. But, as early developers discovered, it’s not so good for agriculture. To grow crops, farmers must add large quantities of synthetic nutrients to the mucky wetland soil. The runoff from those nutrients has created vast algal blooms, from Lake Okeechobee and elsewhere, which have in turn choked off plant and animal life. As scientists recently discovered, phosphorus runoff is flushed into the canals, then pumped into the lake. When the lake drains, the phosphorus enters marshes and trickles through other ecosystems, changing nutrient levels and community composition of plant species along with it.

Sawgrass, typically the dominant species in the marsh, is well adapted to obtain phosphorus from the normally nutrient-poor waters. Cattail, another Everglades producer species with unique flowering spikes, normally prefers the marshes’ edges, and its growth is limited by the lack of phosphorus. However, Danish ecologist Hans Brix and his colleagues have shown that when phosphorus levels increase, cattails can quickly outcompete sawgrass. In an experiment conducted by Brix, both plants took in more phosphorus from nutrient-enriched waters. But whereas cattails increased phosphorus uptake 10-fold, sawgrass increased only 5-fold. Therefore, the cattails can grow more quickly than sawgrass. In areas with nutrient enrichment, cattails have pushed beyond their natural habitat, through ecotones and into neighboring communities, where they now grow in such dense mats that they’re outcompeting sawgrass, choking off native invertebrates on the bottom of the food chain, and physically preventing birds and alligators from nesting.

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Replacing mangrove forests with oceanfront resorts has also proven problematic. It turns out that mangrove trees are a keystone species—one that impacts its community more than its mere abundance would predict. It’s a species that many other species depend on, and one whose loss creates a substantial ripple effect, disrupting interactions for many other species and, ultimately, altering food webs. From their natural habitat at the water’s edge, mangrove “prop” roots stabilize the shoreline and provide shelter for a wide variety of fish. So when the mangrove forests are cleared, many other species suffer: the fish that hide among their roots, the fish that feed on those fish, and so on.

Alligators are also a keystone species in the Everglades, one that a great many species depend on during the dry season. As the waters recede, depressions made by alligators (gator holes) are some of the few places that still hold standing water. These holes become refuges for fish, invertebrates, and aquatic plants; they also become very attractive to the animals who feed on these aquatic creatures. Without gator holes, many species would not survive the dry season. INFOGRAPHIC 10.6

Wood storks also depend on the presence of alligators, but not just for the dry season gator holes. In the 1980s, Rodgers and his colleagues embarked on a comprehensive study of stork nests in an effort to see which types of trees the storks preferred to nest in and whether the availability of those trees was impacting their ability to breed. “We went to 20 stork colonies,” Rodgers remembers. “We measured every tree, recorded its species, size, cored it for age, noted its branching structure.” The conclusion, reached after 5 years of painstaking work, can be summed up in a single sentence, Rodgers says: Wood storks will nest in just about anything, as long as it’s surrounded by water that is patrolled by alligators. “Without the alligators, raccoons swim across, and climb up and destroy everything,” Rodgers says. “Without the alligators, when predators get in, we’ve seen [the storks] abandon entire colonies.”

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