Day 22 december 2 chapter 15
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Day 22 december 2 chapter 15
- 1. Day 22 December 2 Chapter 15 Dr. Amy B Hollingsworth The University of Akron Fall 2014
- 2. 15.9 Interacting species evolve together.
- 3. Natural Selection Causes organisms to become better adapted to their environment Does not distinguish between biotic and abiotic resources as selective forces
- 4. 15.10. Each species’ role in a community is defined by its niche.
- 5. More than just a place for living, a niche is a complete way of living.
- 6. “You can’t always get what you want.” Fundamental niche • the full range of environmental conditions under which a species can live Realized niche • where and how a species is actually living
- 7. 15.11 Competition can be hard to see, but it still influences community structure.
- 10. Why is competition hard to see in nature? The “ghost of competition past”
- 11. 15.12 Predation produces adaptation in both predators and their prey.
- 12. Predation One of the most important forces shaping the composition and abundance of species in a community
- 13. Why do exotic species often flourish when released into novel habitats, even though natural selection has not adapted them to this new environment?
- 14. Prey Adaptations for Reducing Predation There are two broad categories of defenses against predators: • Physical • Behavioral
- 15. Physical Defenses Include mechanical, chemical, warning coloration, and camouflage mechanisms
- 20. 4. Camouflage
- 21. Behavioral defenses Include both seemingly passive and active behaviors: hiding or escaping, or alarm calling or fighting back
- 23. Predator adaptations for enhancing predation
- 25. Why don’t predators become so efficient at capturing prey that they drive the prey to extinction? The “life-dinner hypothesis”
- 27. Parasite Predators Parasites have some unique features and face some unusual challenges: • The parasite generally is much smaller than its host and stays in contact with the host for extended periods of time. • Complicated life cycles as means of getting from host to host.
- 28. Case 1: Parasites can induce foolish, fearless behavior in their hosts. Toxoplasma Rats and cats
- 29. Case 2: Parasites can induce inappropriate aggression in their hosts.
- 30. Case 3: Parasites can induce bizarre and risky behavior in their hosts. The lancet fluke
- 31. 15.14. Not all species interactions are negative: mutualism and commensalism.
- 34. 15.15–15.16 Communities can change or remain stable over time.
- 35. 15.15. Many communities change over time.
- 37. Secondary Succession Much faster than primary succession • life and soil are already present
- 38. 15.16. Some species are more important than others within a community.
- 40. Chapter 16: Conservation and Biodiversity Human influences on the environment Lectures by Mark Manteuffel, St. Louis Community College
- 41. 16.1–16.4 Measuring and defining biodiversity is complex.
- 42. 16.1 Biodiversity benefits humans in many ways.
- 44. Consider also the following: Vinblastine and vincristine Ancrod Epibatidine
- 47. 16.2 Biodiversity is not easily defined.
- 49. 16.3 Where is most biodiversity?
- 51. Why are there more species in an acre of tropical rain forest than in an acre farther from the equator, such as in a temperate forest or prairie? Latitudinal Biodiversity Gradient
Notes de l'éditeur
- There is a moth in Madagascar with a tongue that is 11 inches long! This might seem absurdly long—until the moth approaches a similarly odd-looking orchid. The orchid’s flower has a very long tube, also about 11 inches long, that has a bit of nectar at the very bottom. The moth’s tongue, although usually rolled up, straightens out as fluid is pumped into it and can be inserted into the long nectar tube. As its tongue reaches the bottom, the moth slurps up the nectar, gaining nourishment and energy. The moth also gets a bit of pollen stuck to it in the process, pollen that gets brushed onto the reproductive parts of the next orchid flower it visits. But how did such a system ever originate? Which came first, the long-tongued moths or the long-tubed flowers? Each trait only seems to make sense in a world in which the other already exists. The answer is that neither came first. They both evolved—coevolved—together.
- Natural selection causes organisms to become better adapted to their environment. As long as there is variation for a trait, and the trait is heritable (for a refresher on heritability, see Chapter 7), differential reproductive success will lead to a change in the population. It is easy to imagine populations becoming more and more efficient at utilizing non-living resources. But natural selection does not distinguish between biotic and abiotic resources as selective forces. Either can cause individuals with certain traits to reproduce at a higher rate than others, and so either can cause evolution. So small changes in the moth lead to small changes in the orchid, which select for further small changes in the moth… and the process continues on. In the end, species become adapted not just to their physical environment, but also to the other species around them.
- Within a society, most humans seem to find their niche. Each person plays a particular role, defined by the nature of his or her work, activities, and interactions with others. Other species do the same thing. Within their communities—geographic areas defined as loose assemblages of species, sometimes interdependent, with overlapping ranges—each species has its own niche.
- We can define an organism’s niche in terms of the ways in which the organism utilizes the resources of the environment. More than just a place for living, a niche is a complete way of living. In other words, an organism’s niche encompasses: 1) the space it requires, 2) the type and amount of food it consumes, 3) the timing of its reproduction (its life history), 4) its temperature and moisture requirements, and virtually every other aspect that describes the way the organism uses its environment . Figure 15-21 A way of living.
- Although a niche describes the role a species can play within a community, the species doesn’t always get to have that exact role. Consider the rats of Boston. Until the 1990s, they lived in relative peace in the sewers beneath the city’s streets. But when the city embarked on the largest underground highway construction project in U.S. history, engineers displaced and forcibly drove out thousands of rats from much of their habitat. In essence, there was suddenly an overlap between the rat niche and the human niche, and the rats were now restricted to just some portions of the sewer. As a result, the rats’ realized niche, where and how they are actually living, is now just a subset of their fundamental niche, the full range of environmental conditions under which they can live.
- Some species, particularly closely related species, have similar niches. This can lead to conflict as they try to exploit the same resources.
- Almost invariably, when the fundamental niches of two species overlap, competition occurs. This competition doesn’t last forever, though. Inevitably, one of two outcomes occurs: competitive exclusion or resource partitioning. In competitive exclusion, two species battle for resources in the same niche until the more efficient of the two wins and the other species is driven to extinction in that location (“local extinction”). In the 1930s, this was demonstrated in simple laboratory experiments using Paramecium, a single-celled organism. Populations of two similar Paramecium species were grown either separately or together in test tubes containing water and their bacterial food source. When grown separately, each species thrived. When grown together, though, one species always drove the other to extinction. Resource partitioning is an alternative outcome of niche overlap. Individual organisms and species can adapt to changing environmental conditions, and resource partitioning can result from an organism’s behavioral change or a change in its structure. When this occurs, one or both species become restricted in some aspect of their niche, dividing the resource. In other experiments with Paramecium, for example, one of the two species was replaced with a different species. As in the initial experiment, either species thrived when grown alone. But when the two species were grown together in the same test tube, they ended up dividing the test tube “habitat.” One species fed exclusively at the bottom of the test tube, and the other fed only at the top. Simple behavioral change made coexistence possible. Figure 15-22 Overlapping niches: competitive exclusion and resource partitioning.
- In many situations, resource partitioning is accompanied by character displacement, an evolutionary divergence in one or both of the species that leads to a partitioning of the niche. A clear example occurs among two species of seed-eating finches on the Galápagos Islands. On islands where both species live, their beak sizes differ significantly. One species has a deeper beak, better for large seeds, while the other has a shallower beak, better for smaller seeds, and they do not compete. On islands where either species occurs alone, beak size is intermediate between the two sizes. Figure 15-23 Allowing organisms to divide resources.
- Competition between species has one very odd feature: It is very hard to actually see it occurring because it causes itself to disappear. That is, after only a short period of competition, either one of the species becomes locally extinct or leaves the area where the niches overlap, or character displacement occurs, largely reducing the competition. In either case, the net result is that the level of competition is significantly reduced or wiped out altogether. For this reason, biologists often have to look for character displacement—the “ghost of competition past”—to identify areas where competition has occurred in the past. Moreover, even while it is occurring, competition tends to be indirect, rather than head-to-head battles. Like a game of musical chairs, it’s more a question of both species trying to utilize a particular resource, with one being a bit better at it.
- Predation—an interaction between two species in which one species eats the other—is one of the most important forces shaping the composition and abundance of species in a community. Predation, though, isn’t restricted to the obvious interactions involving one animal chasing down and killing another. Herbivores eating leaves, fruits, or seeds is a form of predation, even though it doesn’t necessarily kill the plant. And predators are not necessarily physically imposing. Each year, more than a million humans die as a result of disease from mosquito bites, compared with fewer than a dozen from shark attacks.
- Predators are a potent selective force: Organisms eaten by predators tend to have reduced reproductive success. Consequently, in prey species, a variety of features have evolved (and continue to evolve) that reduce their predation risk. But as prey evolve, so do predators. This coevolution is a sort of arms race with ever-changing and escalating predation-effectiveness adaptations causing more effective predator-avoidance adaptations, and vice versa. In this light, it may seem unexpected that exotic species often flourish when released into novel habitats, even though natural selection has not adapted them to their new environment. As it turns out, just as these species are not fully adapted to their new environment, they also have few predators there. And with low predation risk, they often are able to flourish.
- Figure 15-24 Prey defenses: some physical means for avoiding predation. Shown (from top left, clockwise) are Cape porcupine, azure poison dart frog, praying mantis, and monarch butterfly.
- 1. Mechanical defenses. Predation plays a large role in producing adaptations such as the sharp quills of a porcupine, the prickly spines of a cactus, the wings of a bird or bat, or the tough armor protecting an armadillo or sow bug. These features, as well as claws, fangs, stingers, and other physical structures, can reduce predation risk. Figure 15-24 part 1 Cape porcupine.
- 2. Chemical defenses. Further prey defenses can include chemical toxins that make the prey poisonous or unpalatable. Plants can’t run from their predators, so chemical defenses are especially important to them. Virtually all plants produce some chemicals to deter organisms that might eat them. The toxins can be severe, such as strychnine from plants in the genus Strychnos, which kills most vertebrates, including humans, by stimulating non-stop convulsions and other extreme and painful symptoms leading to death. At the other end of the spectrum are chemicals toxic to some insects but relatively mild to humans, such as those found in cinnamon, peppermint, and jalapeno peppers. Ironically, many plants that evolved to produce such chemicals to deter predators are now cultivated and eaten specifically for the chemicals they produce. One organism’s toxic poison is another’s spicy flavor. Some animals can also synthesize toxic compounds. The poison dart frog has poison glands all over its body, making it toxic to the touch. The fire salamander, too, is toxic, with the capacity to squirt a strong nerve toxin from poison glands on its back. Some animals, including milkweed bugs and monarch butterflies, are able to safely consume toxic chemicals from plants and sequester them in their tissues, becoming toxic to predators who try to eat them. Figure 15-24 part 2 Azure poison dart frog.
- 3. Warning coloration. Species protected from predation by toxic chemicals frequently have evolved bright color patterns to warn potential predators. They are essentially carrying a sign that says: “Warning, I’m poisonous, so keep away.” To make it as easy as possible for predators to learn, different poisonous species often have the same color patterns. It’s as if devising a single common sign saying “Danger: poison” is more effective than multiple species coming up with their own specific sign (see Figure 15-24). In a clever twist on this, some species that are perfectly edible to their predators also have evolved the same bright colors, in a phenomenon known as mimicry. Their coloration mimics the same warning sign but without the toxins. As long as they are relatively rare compared with the toxic individuals they mimic—reducing the chance that predators might catch on to their trickery—the evolutionary ruse is quite successful. Figure 15-24 part 3 Monarch butterfly.
- 4. Camouflage. An alternative to warning coloration, and one of the most effective ways to avoid being eaten, is simply to avoid being seen. An adaptation in many organisms is patterns of coloration that enable them to blend in to their surroundings. These include insects that look like leaves or twigs and hares that are brown for most of the year but turn white when there is snow on the ground. Figure 15-24 part 4 Praying mantis.
- Hiding or escaping. Anti-predator adaptations need not involve toxic chemicals, physical structures, or special coloration. Many species excel at hiding and/or running. With vigilance, it is possible to get advance warning of impending predator attacks, and then quickly and effectively avoid predators. A variation of this strategy comes from safety in numbers: Many species, including schooling fish and emperor penguins, travel in large groups to reduce their predation risk. Alarm calling and fighting back. In many species, especially birds and mammals, individuals warn others with an alarm call. Although risky for the caller, such alarm calling can give other individuals—often close kin that are nearby—enough advance warning to escape. Some prey species also turn the tables, mobbing predators to keep them from successfully completing their task. This category might also include the fulmar, a seabird that defends its nest from attacks with projectile vomiting aimed at the intruder. Figure 15-25 Prey defenses: behavioral means for avoiding predation.
- Just as prey use physical and behavioral features to reduce their risk of predation, predators evolve in parallel ways to increase their efficiency. In milkweed plants, as toxic chemicals have evolved to kill their predators, so in milkweed bugs, toxic-avoidance methods have evolved that allow the bugs to eat the toxic plants without suffering harm. And as prey have become better at hiding and escaping, predators have developed better sensory perception to help them detect hiding prey, and faster running ability to catch them.
- Predators, too, make use of mimicry. The angler fish, the tasseled frogfish, and the snapping turtle all have physical structures that mimic something—usually a food item—that is of interest to potential prey. As the prey come closer to inspect, the predator snaps them up. Figure 15-26 A better predator.
- Although natural selection leads to predators with effective adaptations for capturing prey, the adaptations are rarely so efficient that the prey are driven to extinction. The explanation for this is referred to as the “life-dinner hypothesis.” It generally holds true because selection for “escape ability” in the prey is stronger than selection for “capture ability” in the predator. When a prey, such as a rabbit, for example, can’t escape from a fox, the cost is its life—and it will never reproduce again. On the other hand, when a fox can’t keep up with a rabbit, all it loses is a meal; it can still go on to capture prey and reproduce in the future. In other words, the cost of losing in the interaction is much higher for the rabbit.
- Two general types of parasites make life difficult for most organisms. Ectoparasites (“ecto,” meaning outside) include organisms such as lice, leeches, and ticks. One species of Mexican parrot is all too aware of ectoparasites: It has 30 different species of mites living on its feathers alone. And many of the parasites even have parasites of their own! Endoparasites are parasites that live inside their hosts (“endo,” meaning inside). They are equally pervasive. Endoparasites infecting vertebrates include many different phyla of both animals and protists, the single-celled eukaryotes. In all of these parasite-host interactions, as with all predator-prey interactions, the predator or parasite benefits and the prey or host is harmed.
- Even though they are considered predators, parasites have some unique features and face some unusual challenges relative to other predators. The most obvious of these features is that, in parasitism, the parasite generally is much smaller than its host and stays in contact with the host for extended periods of time, normally not killing the host but weakening it as the parasite uses some of the host’s resources. Being located right on your food source all the time can be advantageous. But this also leads to what is perhaps the greatest challenge that parasites face: how to get from one individual host to another. A parasite can’t survive long once its host dies, after all. The methods by which parasites accomplish such dispersal are unexpected and surprising. Many of their complicated life cycles involve passing through two (or more) different species (and could have come about only through coevolution with each of the host species). These life cycles are likely to give us a new appreciation for the ingenuity of these microorganisms—or rather, for the evolutionary process that has produced them. Let’s look at a few representative examples.
- Case 1: Parasites can induce foolish, fearless behavior in their hosts. Rats fear cats. During their evolution, rats have developed a protective wariness of their feline predators and areas in which cats have been roaming. Toxoplasma is an organism that changes this. This single-celled parasite of rats must also spend part of its life cycle in cats. It does this by altering the brain of its rat host so that the rat no longer fears cats. In fact, Toxoplasma-infected rats not only lose their fear of cats, they become attracted to them. Is this an accident? No. This behavioral change, while quite dangerous for the rat, is exactly the change that increases the likelihood that the rat will be attacked by a cat, spreading the parasite in the process.
- Case 2: Parasites can induce inappropriate aggression in their hosts. Rabid animals don’t behave normally. They froth at the mouth and become unusually aggressive (Figure 15-28 Rabies). Is this an accident? No. Rabies is caused by a virus that infects warm-blooded animals, mostly raccoons, skunks, foxes, and coyotes. It is passed from one host to another via saliva. Inducing these “rabid” behaviors, of course, is exactly the change in behavior that will most help the virus to spread.
- Case 3: Parasites can induce bizarre and risky behavior in their hosts. The lancet fluke is a parasitic flatworm. It has also been described as a “zombie-maker.” This fluke spends most of its life in sheep and goats, but the fluke’s eggs pass into snails that graze on vegetation contaminated by sheep and goat feces. Once inside the snail, the fluke eggs grow and develop, eventually forming cysts that the snail surrounds with mucus and then excretes. Continuing on their complex life cycle, the fluke cysts find their way into ants that eat the snail mucus. The flukes’ journey back to a sheep or goat is now expedited by the so-called zombie-making. In an infected ant, the flukes grow into the ant’s brain, altering its behavior. Whereas ants normally remain low to the ground, when infected by the lancet fluke, they climb to the tops of grass blades or plant stems and clench their mandibles on leaves. Is this an accident? No. This behavioral change puts the ants much more at risk of being eaten by a grazing mammal—a bad outcome for the ant, but just what the parasite needs to complete its life cycle.
- It’s easy to get the idea that all species interactions in nature are harsh and confrontational, marked by a clear winner and a clear loser. That is largely the case when it comes to competition and predation. Nonetheless, not all species interactions are combative. Every flower you see should be a reminder that evolution produces beneficial species interactions as well. These types of interactions fall into two categories: mutualism and commensalism.
- Mutualism: everybody wins Coral that gain energy from photosynthetic algae living inside their tissues. Termites capable of subsisting on wood, only with the assistance of cellulose-digesting microbes living in their digestive system. Flowers pollinated by animals nourished by nectar. Each of these relationships is an example of mutualism, an interaction in which both species gain and neither is harmed. Mutualism is common in virtually all communities. Plants, particularly, have numerous such interactions: with nutrient-absorbing fungi, with nitrogen-fixing bacteria, and with animals that pollinate them and disperse their fruits. Figure 15-29 part 1 Not always “red in tooth and claw.”
- Commensalism: an interaction with a winner but no loser Some species interactions are one-sided. The cases in which one species benefits and the other neither benefits nor is harmed are called commensal relationships, or commensalism. Cattle egrets have just such a relationship with grazing mammals such as buffalo and elephants. As the large mammals graze through grasses, they stir up insects. The birds, which feed near the mammals—particularly near the forager’s head—are able to catch more insects with less effort this way. The grazers are neither helped nor harmed by the presence of the birds. Figure 15-29 part 2 Not always “red in tooth and claw.”
- A pair of colorful ochre starfish, keystone predators within intertidal zones in the Pacific Ocean.
- Human “progress” and development can completely transform an environment—turning a patch of desert into Las Vegas, for example. Urban landscapes, too, can obliterate any signs of the nature that was once there. This is why it can be surprising (and heartening) to observe what happens when humans abandon an area. Little by little, nature reclaims it. The area doesn’t necessarily recover completely, and change is slow. Still, this process is almost universal and virtually unstoppable. Nature responds similarly to other disturbances, too, from a single tree falling in a forest, to a massive flood or fire, to massive volcanic eruptions. The process of nature reclaiming an area and of communities gradually changing over time is called succession. It is defined specifically as a change in the species composition over time, following a disturbance. There are two types of succession. Primary succession is when the process starts with no life and no soil. Secondary succession is when an already established habitat is disturbed but some life and some soil remain.
- Primary succession Primary succession can take thousands or even tens of thousands of years, but it generally occurs in a consistent sequence. It always begins with a disturbance that leaves an area barren of soil and with no life. Frequently, the disturbance is catastrophic. The huge volcanic eruption on Krakatoa, Indonesia, in 1883, for example, completely destroyed several islands and wiped out all life and soil on others. Primary succession has also begun, in a less dramatic fashion, in regions where glaciers have retreated, such as Glacier Bay, Alaska. Although succession does not occur in a single, definitive order, several steps are relatively common. An important feature of the colonizers seen in the earliest stages of primary succession is that, while they are all good dispersers, able to move away from their original home (hence their early arrival to a newly available locale), they are not particularly good competitors. That’s why they are gradually replaced. Ultimately, it is the longer-living, larger species that tend to outcompete the initial colonizers and persist as a stable and self-sustaining community, called a climax community. The specific species present in the climax community depend on physical factors such as temperature and rainfall. Figure 15-30 Species composition of a community changes over time.
- Secondary succession Secondary succession is much faster than primary succession because life and soil are already present. Rather than the thousands or even tens of thousands of years that primary succession may take, secondary succession can happen in a matter of centuries, decades, or even years. It frequently begins with organisms colonizing the decaying remains of dead organisms. It may involve fungi establishing themselves in the decaying trunk of a tree that has fallen, and these being replaced over time by different species of fungi. Or secondary succession may begin with weeds springing up in formerly cultivated land that is left untended. If the weeds are allowed to grow, they eventually are outcompeted and replaced by perennial species, and then shrubs, and eventually larger trees. The process is similar to primary succession, but with a head start. Ultimately, if undisturbed, secondary succession also leads to establishment of a stable, self-sustaining climax community.
- Not all species are created equal. In this chapter, we have examined the ways in which species interact with one another and with their habitats, noting the dependence of species on one another. But not all species have equal dependence on and influence over others.
- Within a community, the presence of some species, called keystone species, greatly influences which other species are present and which are not. That is, if a keystone species is removed, the species mix in the community changes dramatically. The removal of other species, conversely, causes relatively little change. Bison are a keystone species. Sea stars, too, are a keystone species. Figure 15-31 Preserving biodiversity. Keystone species can keep aggressive species in check, allowing more species to coexist in a community.
- In the Pacific Northwest of the United States, a medium-size tree grows. This conifer, the Pacific yew tree (Taxus brevifolia), isn’t the biggest tree in the forest, nor is it the most common. It’s not the sort of tree that usually warrants attention in a textbook. But within the bark of the Pacific yew there is a chemical, called taxol, that has some important properties—it acts as an anti-mitotic agent, interfering with the division of cells that come into contact with it. The role taxol plays for the Pacific yew is not clear; it may reduce the rate at which other organisms feed on the plant. But in humans, taxol is effective in the treatment of ovarian cancer, breast cancer, and lung cancer (generating more than $1 billion a year in pharmaceutical sales). Figure 16-1 Taxol is cancer medicine derived from a tree.
- The chemicals vinblastine and vincristine, isolated from the Madagascar periwinkle (Catharanthus roseus), are so effective in treating leukemia and Hodgkin’s lymphoma that both diseases, formerly incurable, now are curable in the vast majority of people. The chemical ancrod, found only in the Malayan pit viper (Agkistrodon rhodostoma), dissolves blood clots and is effective in treating some heart attack and stroke patients. Epibatidine, a poisonous compound in the saliva of a small frog (Epipedobates tricolor) that lives in Ecuador, is 200 times more effective than morphine in relieving pain and is non-addictive. These are just a few examples—there are many, many more—illustrating that medically important compounds often come from some unlikely organisms living in farflung locations around the world. Usually, toxin production evolved in these organisms as a method of protecting them from other organisms. Co-opting the chemicals for human use reveals that one important value of biodiversity is as a sort of universal medicine cabinet.
- But the beneficial effects of the world’s biodiversity aren’t limited to disease-fighting chemicals from plants and animals. This has been particularly apparent in the Gulf of Mexico during 2010 and 2011. In April of 2010, an explosion on a floating oil rig that was drilling a well about a mile under the surface of the water caused a massive leak of crude oil (Fig. 16-2). Reporting in the journal Science, researchers using sensors at 207 locations in the Gulf were surprised to find huge regions in which the large amounts of methane released in the spill were basically gone. Oxygen levels in these regions were also very low, suggesting that bacteria in those areas—which use oxygen when consuming methane—were responsible for the rapid “mopping up” of the methane. Fragments of methane consuming bacteria found by the researchers supported their hypothesis. The researchers believe that, because the bacteria were already present in the Gulf, feeding on the slow, natural seepage of oil from the ocean bottom, they were able to respond quickly to the spill. Nonetheless, not all scientists agree with the analyses suggesting rapid bacterial consumption of the oil, and the research is continuing.
- Biodiversity is the variety of genes, species, and ecosystems on earth. There is tremendous value that can come from earth’s biodiversity, and the loss of biodiversity can be hugely detrimental to humans. Biodiversity provides significant, perhaps less tangible, benefits by helping regulate the climate, in the form of trees that both create shade and take up carbon dioxide from the atmosphere. Biodiversity also benefits humans in numerous other ways that are difficult to quantify, but are no less valuable than medicinal plants and oil- and sludge-eating bacteria. Many of the ways in which people value biodiversity are not easily quantified (in dollars, for example), but represent value just the same
- It’s not clear exactly what a person means when using the term “biodiversity.” Discussions in the media make it appear that there is a consensus on what biodiversity means, but there is not. All definitions of biodiversity refer, in a general sense, to the variety of living organisms on earth, and most reflect that biodiversity can be considered at multiple levels, from entire ecosystems to species to genes and alleles.
- Conservation biology is the interdisciplinary field that addresses how to preserve the natural resources of earth. Drawing on knowledge, data, and insights from biology, economics, psychology, sociology, and political science, one of the goals of conservation biology is the preservation and protection of biodiversity. For this reason, the complexities of defining biodiversity directly affect the decisions that conservation biologists make. In this chapter, we explore how the actions of humans can have significant, even disastrous, consequences for biodiversity and other natural resources, and we also explore the strategies that have been developed for effective conservation.
- If you were to stand at the equator in South America and identify the number of land mammals, you would count about 400 different species. If you then started walking south, away from the equator, and assessed the diversity of land mammals when you go to 25° latitude, you would find about 300 different species. Continuing your long walk south, when you got to 30° latitude, you would find only 200 different species. And the trend would continue for as far south as you could go, with 100 species at 40° latitude and fewer than 50 species at 50° latitude. On a similar walk north from the equator, through North America, you would observe the same trend, with more than 300 species of land mammals at 15° latitude reduced to only 15 species in northern Canada. Biodiversity is not evenly distributed throughout the world. And perhaps the strongest trend in biodiversity distribution is that, as you move away from the equator in either direction, diversity is reduced with increasing latitude.
- The strong biodiversity gradient from the tropics to the poles occurs not just in land mammals, but in nearly any group of plants or animals observed. Interestingly, even the diversity of organisms in the oceans follows this trend. One survey of marine copepods—tiny crustacean animals, including plankton—found the exact same trend moving north from the tropical region of the Pacific Ocean (80 species present) to the Arctic Ocean (fewer than 10 species).
- Numerous factors that influence species richness are responsible for producing the tropical-to-temperate-to-polar gradient in biodiversity. Three, in particular, play strong roles: 1. Solar energy available. Perhaps the simplest predictor of species diversity is climatic favorability, the amount of solar energy available in an area. In a variety of species of plants and animals, researchers have documented strong relationships between energy availability and species richness. 2. Evolutionary history of an area. Communities diversify over time. Consequently, the more time that passes, generally speaking, the greater the diversity in an area. A high level of biodiversity in an area, however, can be knocked back down by climatic disasters such as glaciations. This biodiversity decline may occur in temperate and polar regions. 3. Rate of disturbance. Over time, the best competitor for a resource is expected to outcompete other species, excluding them from the community and thus reducing species richness. Communities may be kept from reaching this state, though—in a number of ways. Factors such as predation, or environmental perturbations such as fires, can prevent any one species from excluding others. For this reason, a habitat with an intermediate amount of disturbance is expected to have the greatest species richness.
- Conservation biologists are increasingly interested in biodiversity hotspots, those regions of the world having significant reservoirs of biodiversity that are under threat of destruction. Twenty-five biodiversity hotspots have been identified around the globe that, while covering less than 1% of the world’s area, have 20% or more of the world’s species. Habitats included among the biodiversity hotspots are tropical rain forests, coral reefs, islands, and deep oceans.