In 2004 a current of excitement ran through the world of ornithology. A kayaker paddling the Cache River had spotted a bird he believed was an ivory-billed woodpecker. Soon afterward two others caught on film a brief glimpse of a bird having the woodpecker’s characteristic markings. The director of the Cornell Lab of Ornithology, John Fitzpatrick, told
National Geographic, “Through the 20th century it’s been every birder’s fantasy to catch a glimpse of this bird, however remote the possibility. This really is the holy grail.” Recordings taken in the densest parts of the bottomlands gave evidence of the ivory-bill’s distinctive double rap-rap on tree trunks. Birdwatchers converged on the Cache River and nearby White River National Wildlife Refuge, the last remaining places believed to support the special bird. Frank Gill of New York’s Audubon Society remarked, “It is kind of like finding Elvis.” Since 2004 persistent volunteers have made
no additional sightings, though the Cornell group and the Nature Conservancy have devoted 3,000 hours of in-person searches and movementcontrolled photography. Robotic sensors scan the woods for any and all movements, while the Automated Collaborative Observatory for Natural Environments (ACONE) searches the Arkansas skies on the lookout for
birds of any type.
Did a species thought to be extinct somehow manage to recover and begin to repopulate the area? The last tentative sighting occurred in 2005, but ecologists have wisely gone on the offensive in preserving what is left of the woodpecker’s habitat. Mr. Fitzpatrick told the Boston Globe in 2008, “The decline of the ivory-billed is an unspeakable American tragedy. This country was unable to save even a single square meter of pristine bottomland habitat. It all went under the ax and chainsaw. We may have lost this iconic bird, but, by God, we owe the ivory-billed this sort of exhaustive, scientific search. . . . If they are there, we also owe them a recovery program.” The Nature Conservancy has worked jointly with the FWS to set aside thousands of acres of woodpecker habitat. “The successful history of conservation in the Big Woods of Arkansas,” said the Nature Conservancy’s Scott Simon, “is the result of great partnerships—federal and state agencies working with other organizations, local communities, hunters and landowners.” The emotional support from people like Fitzpatrick plus government support provide the best chance for saving critically endangered species.
In 2007 the FWS designed a recovery plan for the ivory-billed woodpecker, should it indeed still hide in the swamps. The agency focuses on the following three goals: verify the existence of the bird by sightings, recordings, or nest cavities in trees; protect or add to current habitat; and study all factors that would threaten a potential ivory-billed colony. In an encouraging example of positive thinking, the FWS has set a goal of 2075 for the year in which the ivory-billed woodpecker will be removed from the endangered species list, a step called delisting.
The scientific community’s and the public’s reaction to the ivory-billed woodpecker sighting attests to the current state of many species that were once abundant. The ivory-billed woodpecker experience—whether or not the bird still lives—has offered good examples of the quick reactions and sound planning needed to preserve disappearing species.
To conserve the Earth’s nutrients and make them available to other species, the Earth relies on organisms called decomposers. Decomposers are living things, usually microbes, that break down matter so it can be recycled. Radiant energy from the Sun does not recycle and is lost, but due to the action of decomposers nutrients cycle continuously through soil, water, and the atmosphere. These producer-consumer-decomposer relationships collectively make up ecosystems. On a larger scale, the many interrelationships between nonliving matter and living things make up what is known as a web of life or a food web.
Diversity among the members of a food web contributes to ecosystem survival. Food webs are complex networks of interconnected food chains. These webs depend on a diverse collection of biota, a term for living things,
All plant life, animal life, and microorganisms contribute to the continual recycling of the Earth’s elements. According to the second law of thermodynamics, energy as heat is lost with each step in the cycle. Organisms that perform photosynthesis capture energy from the Sun and so replenish the energy-matter cycle.
to make the web stable and resilient. (A food chain is a series of organisms, usually increasing in size, in which each one eats the preceding, or smaller, member.) Species diversity in a food web helps make the web resilient in case part of the web becomes damaged. If one nutrient-energy route were to be shut down, by pollution, for instance, other routes continue to provide nutrients and energy all the way to the top of the web’s food chains. By contrast simple food webs make life riskier for their members because simple webs leave each animal up the food chain more and more vulnerable should anything go wrong.
Energy always flows in food chains from the first member toward the last member in an upward direction, meaning from producers to consumers all the way to the consumer at the top of the chain. Examples of simple food chains from different habitats are shown as follows:
Aquatic food chain:
- Phytoplankton → zooplankton → mackerel → tuna
Woodland food chain:
- Grasses → rodent → snake → hawk
Arctic food chain:
- Phytoplankton → zooplankton → various fish → seals → polar bear
African savanna food chain:
- Grasses → wildebeest → lion
Producers serve as a critical first step in food chains because they capture the Sun’s energy. Earth’s producers are its photosynthetic plants (grasses and phytoplankton). Primary consumers consist of herbivores: grasshoppers, rabbits, or grazing zebra. Once the primary consumers transfer the plant’s energy to animal tissue, secondary and higher consumers
continue the flow of energy transfer. Each consumer level above primary consumers contains either a carnivore or an omnivore. Small mammals, small fish, and birds tend to act as secondary consumers, for example, foxes, raccoons, gulls, or freshwater perch and catfish. The top of each food chain contains large predators: white sharks, killer whales, grizzly bears, polar bears, eagles, and owls. Food chains also depend on scavengers such as vultures that feed on carcasses. By doing so, the scavenger exposes the carcass to the air, which hastens decomposition by bacteria
and fungi.
The rate at which producers convert the Sun’s energy into biomass (any matter of biological origin) is called gross primary productivity. Producers first build up enough biomass to meet their own needs for growth, then the extra biomass supplies the food chain. Net primary productivity
An ecological pyramid, also called an energy pyramid, illustrates how energy is lost with each step up from energy producers to consumers, and from prey to predators. Top predators adjust to a lowered availability of food and energy by having small numbers of offspring, compared with species lower on the pyramid that produce large numbers of fast-growing offspring.
equals the rate in which producers store sufficient energy to supply food chains, minus the producers’ own energy needs, as follows:
gross primary productivity – producer’s needs = net primary productivity
Food chains follow the second law of thermodynamics—they progress toward an increased state of entropy, that is, a state of unavailable energy. Secondary consumers recover a fairly large portion of the energy stored in plant tissue, but consumers higher up the chain have access to a smaller proportion of usable energy. The unavailable energy dissipates as heat, and this energy loss puts increased pressure on tertiary and quaternary consumers to meet their own energy requirements. Food chains rarely contain more than four levels because the inefficiencies simply become too great at each step to sustain more levels.
Secondary consumers play two important roles: they convert plant tissue to animal tissue, as discussed above, and they are prey for other species. Prey species usually have large populations for the following reasons: energy is readily available to them, and large population size offsets the amount of individuals caught by predators. Diagrams called energy pyramids depict the energy transfers from numerous prey animals in food chains to lesser numbers of predator animals. Energy pyramids also explain why some species are more vulnerable to extinction than others.
Even in perfect conditions, predators have much less energy available to them for survival, breeding, raising young, and sustaining a population. These animals, therefore, depend on the well-being of all the biota lower on the chain. As a consequence predators such as eagles, tigers, sharks, wolves, grizzlies, and polar bears become vulnerable to extinction when their environment undergoes damage.
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