Favorable adaptations pass from parents to offspring until the new traits become part of the genetic makeup of all successive generations. In a threatened habitat, the individuals most likely to survive are those possessing the advantageous traits. Animals and plants develop the following adaptations to gain a measure of protection against predators: camouflage, poisons, warning colors, smells, stingers, thorns, quills, bad taste, and mimicry. Microbes also adapt protective mechanisms, but they do this much quicker than multicellular organisms because microbes need only a few hours to produce a new generation; thousands of generations from a single microbe can grow literally overnight. The current problem of bacterial resistance to antibiotics illustrates the adaptive nature of bacteria.
Doctors began using antibiotics to treat infections in the 1940s, and within 20 years numerous pathogens had developed resistance to these antibiotics. The majority of today’s common pathogens are resistant to almost all antibiotics.
The American crow is one of the most adaptable generalists in the animal kingdom. Crows are scavenger omnivores, meaning they eat plants and animals and also feed on carrion. Some inventive crows have been known to stand on a sidewalk, waiting for traffic to roll over acorns in the road. The crow then saunters out to pick up an easy meal. (Jason Finley)
Adaptive species in the animal kingdom possess characteristics enabling them to remain healthy and reproduce in spite of damaged habitats, noise, traffic, pollution, or other disturbances. In many ways, the characteristics of adaptive species resemble those of invasive species: Adaptive species breed prolifically, produce many offspring, grow fast,
possess genetic variability, and are generalists. Generalist adaptive species live in many different habitats, tolerate wide ranges in climate, eat a variety of foods, and resist disease and parasites. Familiar examples of adaptive species found living in proximity to people are cockroaches, flies, mice, rats, raccoons, coyotes, and crows.
The Galápagos Islands were one of many places that Charles Darwin visited to observe the world’s wildlife. Several subpopulations of finches have been associated with Darwin’s studies because they demonstrate the principles of evolution and adaptation. In general, the size and shape of related finches differ depending on the islands on which they live and the type of food they eat on each of those islands. Of about 13 different types of Galápagos finches, sharp-billed varieties probe for insects in tree bark, medium-billed birds catch insects on leaves, and stout-billed finches crack open cactus seeds as their main diet.
Humans are generalists, adaptive, and also invasive. People live in virtually every place on Earth, exist on a variety of diets and in a wide range of living conditions, and can adjust their behavior to avoid predation, pollution, and disease. To withstand changes in the environment, humans simply invent a new technology that ensures their survival. Humans
are predators in a number of food chains, and they invade habitats because they proliferate to large numbers rapidly and outcompete native species. Finally, humans play the role of pioneer species when urban areas encroach into pristine wilderness. Mountain lions, grizzly bears, wolves, lions, and sharks are all predators that naturally steer clear of humans. Rare attacks from these animals on humans usually involve mistakes or because the animal feels that a person threatens it or its young. The familiar phrase “He is more afraid of you than you are of him” describes the reaction of most natural predators when confronted with the novel sight of a human.
Adaptations having the most effect on biodiversity are changes that lead to adaptive radiation. Charles Darwin noted in the Galápagos Islands in 1835 that characteristics of one bird species was common to all the islands. The birds—ornithologists later identified them as finches—seemed to be of the same species, yet each had slightly differentshaped
beaks, depending on the island on which they lived. Darwin had surmised that an ancestor of the finches had once lived on one of the islands, but occasionally visited the other islands. Darwin wrote in his 1839 memoir The Voyage of the Beagle, “One might really fancy that, from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.” Darwin had drawn his conclusion from his observation that all the islands’ finches possessed slight variations in beak size and shape to master the food in their local habitats. “Darwin’s finches,” as they became known, adapted to their local habitat, yet they shared the entire archipelago without interfering with each other’s well-being.
