RAVEN 9/e
CHAPTER 57: INTESPECIFIC INTERACTIONS AND THE ECOLOGY OF COMMUNITIES
WHERE DOES IT ALL FIT IN?
Chapter 57 builds on the foundations of biodiversity and provides detailed information about environmental interactions of organisms. Students should be encouraged to recall the principles of organismic classification and comparative anatomy. The information in chapter 57 does not stand alone. It connects the information on organismic diversity to evolution and ecology coverage. Students should know that animals and other organisms are interrelated and originated from a common ancestor of all living creatures on Earth.
SYNOPSIS
Moving toward increased complexity, biological communities follow populations. Biological communities, simply referred to as communities, are all of the species or organisms occurring in a particular area. Among the most complex concepts of populations is that of the niche. Niche is not synonymous with habitat as it includes behavioral, reproductive, and seasonal factors. The principle of competitive exclusion can be restated in terms of the niche; two species cannot occupy the same niche indefinitely. They can coexist while competing for the same resources, but at least one feature of their niches must differ or one will succeed and the other will go extinct.
Interspecific competition limits population size when two kinds of organisms use the same resource, which is limited in supply. The principle of competitive exclusion states that when two species compete for the same limited resource, one will utilize the resource more efficiently which results in the elimination of the other. Continued competition between species rarely occurs. Either one or the other species is driven out or natural selection reduces the competition between them. Competition is also avoided through geographical partitioning. Although sympatric species live in the same area, they utilize different resources. Sometimes when niche overlap appears, the two species are able to partition the resource and thus coexist. Character displacement occurs when co-occurring species exhibit greater morphological differences and resource use. It is often hard to determine interspecific competition without constructing complex experiments. Even then, interpretations suggesting negative results do not always indicate competition. Detailed studies of ecological requirements often best explain interspecific interactions.
Predators have major effects on prey populations. Predation limits population size and is an important form of biological control. It places selective pressure on prey often causing a co-evolutionary arms race with prey and predators constantly evolving strategies to defeat each other. Many plants produce physical structures or chemicals to discourage or prevent animals from herbivory activities. Such chemicals are called secondary compounds to differentiate them from primary chemicals involved in normal metabolic pathways. Some animals have been able to adapt secondary plant compounds for use in their own defense. The distastefulness of the monarch butterfly is perhaps the best known example. Its taste results from eating alkaloid-producing milkweed as a larva. Larvae that do not feed on these plants are quite tasty to birds. Animals develop defenses against predators, often by defensive coloration or chemical defenses. The monarch is an excellent example of aposematic coloration, bright warning coloration that tells predators to stay away. They advertise their toxicity to increase their survival. Cryptic coloration, on the other hand, allows an animal to blend in with its surrounding; its survival depends on hiding. The viceroy butterfly is a Batesian mimic that depends on its similarity to the toxic monarch for survival. Muellerian mimics are frequently unrelated, but protected, species that all look alike, providing a sort of group defense. Organisms evolve in a positive manner as well. An excellent example is the co-evolution that has occurred between flowering plants and their pollinators. Among the best known symbiotic relationships are those found in lichens, mycorrhizae, and legumes. If the one partner benefits with no change to the other, the relationship is commensalism. If both participants benefit, it is mutualism. If one benefits and the other is harmed, the relationship is parasitic. Gray areas exist among these relationships as it is often difficult to determine whether a partner truly benefits by the actions of the other. Both commensalism and mutualism can readily turn into parasitism if even the slightest, unintentional damage occurs to the non-benefiting partner. Parasites that eliminate their source of food, that is kill their host, are not successful since they cause their own demise as well. Organisms that cause lethal disease are similarly not successful. Both predation and parasitism may counter the effects of competition by influencing the outcome of interspecific interactions.
The plants and animals that make up ecosystems change over time as the physical nature of the ecosystem changes. Secondary succession occurs in inhabited areas that are disturbed in some manner: Such disturbances are often initiated by humans. Primary succession occurs in areas made devoid of all life. It is readily seen on new volcanic islands, but also occurred millions of years ago when glaciers retreated from the northern hemisphere.
Biodiversity, species richness, and species diversity promote community stability. Factors that promote species richness include ecosystem productivity, spatial heterogeneity, and climate. The tropics exhibit a greater number of species than any other biome. This may be due to the long evolutionary age of the tropics combined with high productivity, predictability of climate, intense predation, and spatial heterogeneity. A predictable species-area relationship has been observed as one of the most predictable patterns in ecology. The equilibrium model of island biogeography proposes that, in time, the number of species extinctions and colonizations balance each other out and the number of species remains constant. In addition, distance to sources (other islands or to a mainland) for colonizers and island size play important roles in supporting the colonization/extinction events that occur on islands. Islands should not just be though of as “somewhere” in the Pacific Ocean but also mountain tops and other isolated areas on the planet.
LEARNING OUTCOMES
57.1 Biological Communities: Species Living Together
· Define community.
· Describe how community composition may change across a geographic landscape.
57.2 The Ecological Niche Concept
· Define niche and resource partitioning.
· Differentiate between fundamental and realized niches.
· Explain how the presence of other species can affect a species’ realized niche.
57.3 Predator–Prey Relationships
· Define predation.
· Describe the effects predation can have on a population.
57.4 The Many Types of Species Interactions
· Explain the different forms of symbiosis.
· Describe how coevolution occurs between mutualistic partners.
· Explain how the occurrence of one ecological process may affect the outcome of another occurring at the same time.
57.5 Ecological Succession, Disturbance, and Species Richness
· Define succession and distinguish primary versus secondary.
· Describe how early colonizers may affect subsequent occurrence of other species.
· Explain how disturbance can either positively or negative affect species richness.
COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 57 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature.
· Students oversimplify intraspecific competition effects
· Students oversimplify interspecific competition effects
· Students are unaware of the complexity of organismic interactions
· Students believe that predator-prey population fluctuations are uniform over time
· Students do not account that predators seek many types prey when looking at population fluctuations
· Students do not account that prey are taken by several types of predators when looking at population fluctuations
· Students believe that population behavior is not subject to selection
· Students believe artificial selection produces new traits
· Students are unaware of evolution at the population level
· Student think that selection is directional and produces superior characteristics
· Students are unaware that mate selection drives population genetics
· Students do not believe that random genetic drift produces population differences
· Students think that all animals and plants evolved at about the same time
· Students believe that most animals are vertebrates
· Students believe that most plants are angiosperms
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
Many students may not realize that a vast majority of medicinal compounds were initially extracted from plants, i.e., aspirin from willow bark, digitalis from foxglove plants, and leukemia treatment from the periwinkle plant. Humans have used secondary plant compounds to their benefit as have other animals. Traditional medicine of the Appalachian peoples and of China is being studied to determine the active ingredients behind the many beneficial folk treatments. These compounds may be isolated and synthesized commercially. Unfortunately many traditional remedies fail, not because they are inherently bad, but because the plant chemicals are not always produced, or are not produced in uniform amounts. A great amount of variation is dependent on seasonal temperature and rainfall as well as natural soil conditions. Many insects have evolved unique behaviors to cope with the stimulated production of plant chemicals. Some nip the midrib to keep them from entering the leaf they are eating; others chew circles on the leaves, eating only the inside. Recent research shows that plants communicate over great distances, presumably by airborne chemicals. Thus, a tree may begin to produce secondary compounds even though it is far removed from the actual herbivore attack.
Tobacco plants, for example, produce salicylic acid (aspirin) to alert their immune system to fight an infection of TMV. Some of the acid is converted to methyl salicylate and evaporates from the damaged plants. When this air wafts over non-infected tobacco plants, the salicylate is absorbed and turned into salicylic acid. Many frogs in the Amazon are poisonous, though they possess absolutely no poisons on their skins when they are born. They only secrete the poisons as adults. Examination of the stomachs of these frogs revealed the presence of ants. The ants contain up to 20 different toxic alkaloids.
The most dangerous of these frogs, Dendrobates auratus has a diet that is 70% toxic ants!
Use hypothetical social examples to explain various forms of coloration and mimicry. One of the best ways to avoid being mugged is to act slightly crazy—similar to aposematic coloration. The use of camouflage in hunting is obvious. Another is to have students think about various traffic control signs (yellow-black, red-white, orange-black), which are colored distinctly to display warnings. There are increasing numbers of pan-handlers in most cities; as residents discover that many are actually making a decent living from such activity, they are less likely to give money to anyone—similar to Batesian mimicry. Another example of brood parasitism occurs in a species of mouth brooding catfish. Another species of fish (analogous to the catbird) presents its young near the catfish mother, who sucks them up as though they were her own young.
Over time her true young and the intruders both grow and develop. Unfortunately, the catfish young provide an additional food source for the intruders who grow too much greater proportions. After the normal brooding period, the catfish mother releases her “young,” which turn out to be only a few individuals of the brood parasite species. She has expended substantial energy to raise another species and has no new generation of her own species!
Have students discuss the consequences to removing a forested area and converting it to grassland. What animals will disappear and what new animals will colonize the new grass area. This should lead them in the direction of how different species of animals and their distributions are directly related to the types of vegetation in the area.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 57.
Application / · Have students explain the impact of wild dogs on biodiversity in your area.· Have students describe how the dying off of one type of tree affects biodiversity of a forested area.
· Ask students to explain one impact of introducing a non-native bird into an area where it competes for food with another species of bird.
Analysis / · Have students compare and contrast a parasite and a pathogen.
· Have student describe the pros and cons of brood parasitism in birds.
· Ask students to explain the evolutionary effect on a prey species when its major predator becomes extinct.
Synthesis / · Ask students to design an experiment to test if an invasive fish is competing for resources with native fish.
· Have students design an experiment to test the origins of toxins produced by tropical frogs.
· Ask the students come up with an agricultural application of a pathogenic virus that exclusively kills parasitic worms of animals.
Evaluation / · Ask students evaluate the use of non-native parasitic wasps to control populations of invasive moths that are devastating crops.
· Ask students weight the environmental impacts of eradicating the disease rabies from local populations of wildlife.
· Ask students investigate the pros and cons of introducing non-native organisms in an area to replace fill the role of a native one that died off.
VISUAL RESOURCES
Slides of various forms of mimicry are a necessity. One can include various poisonous animals, including rattlesnakes, and coral snakes and the others that mimic them (hognose snake and scarlet king snake respectively).
Bring various colored photographs (for example, from entomology books) and discuss some of the common colors that appear between unrelated insects. This can also be done with botany books (photos of colored flowers) and then see if students can put together the idea of co-evolution between insect and the flowers that demand their attention by advertising with color and fragrance. The co-evolution of flowers and their pollinators is especially interesting and highly specialized.
Among the most specific relationships are between wasps and tropical orchids. As a result of intense co-evolution, the extinction of one partner will likely result in the extinction of the other. This is especially true if the extinction is caused by humans and happens over a short time span. Under natural circumstances the second partner might have the time and opportunity to evolve less dependency on the first partner. The animated film “Antz” has a really cute part where the worker and soldier ants are in an ant “bar” and the worker ant (Woody Allen’s voice) refuses the glob of “honeydew” commenting it doesn’t drink stuff that comes out of another insect’s anus!