COMMUNITY ECOLOGY

45 Community ecology Chapter Outline fighting foreign fire ants Which Factors Shape Community Structure? Mutualism Competitive Interactions Effects of Competition Resource Partitioning Predator-Prey Interactions Models for Predator-Prey Interactions Cyclid Changes in Abundance An Evolutionary Arms Race Coevolution of Predators and Prey Coevolution of Herbivores and Plants Parasites and parasitoids Parasitism: Strangers in the Nest Parasitoids Biological Pest Controls Ecological Succession Successional Change Factors That Influence Succession Species introduction, loss, and other disturbances The Role of Keystone Species Adapting to Disturbance Species Introductions Biogeographic Patterns in Community Structure Latitudinal Patterns Island Patterns FIGHTING FOREIGN FIRE ANTS (REVISITED) SUMMARY DATA ANALYSIS EXERCISE SELF-QUIZ CRITICAL THINKING Objectives 1. Learn some basic ecological terms: habitat, niche, commensalisms, mutualism, and symbiosis. 2. Know how mutualism can be beneficial to both species involved. 3. Understand the complex relationships between competitive species. 4. Describe the different types of predator responses to increases in prey densities. 5. Know how predators and prey adapt to be more successful. 6. Learn the lifestyle of parasites and parasitoids. 7. Know how cowbirds have adapted to changes over time. 8. Be able to characterize the steps of both primary and secondary succession. 9. Learn what is meant by a keystone species and how species introduction can change a community. 10. Through the use of examples, see how an introduced species may devastate a community. 11. Know which factors play a role in where species are located worldwide. Key Terms habitat community niche commensalism mutualism interspecific competition predation prey parasitism symbiosis character displacement ecological niche competitive exclusion resource partitioning camouflage herbivory warning coloration mimicry parasitoids brood parasitism social parasites pioneer species primary succession secondary succession intermediate disturbance hypothesis keystone species jump dispersal exotic species indicator species biogeography area effect distance effect equilibrium model of island biogeography Lecture Outline 45.1 Fighting Foreign Fire Ants A. The accidental introduction of fire ants in the United States disrupted the natural community. 1. Invasive species, such as the fire ant, are finding new habitats due to increased global trading. 2. The introduction of fire ants proves detrimental to the native ant populations. 3. The fire ants have even impacted the number of some bird species, because they devour their eggs. 4. In addition, the fire ants can disrupt normal pollination activities, and therefore damage plant species. B. A community is defined as all of the species that live in a region. 1. The introduction of fire ants to regions of the U.S. has dramatically influenced the communities that have been invaded. 45.2 Which Factors Shape Community Structure? A. Where a species resides is its habitat, whereas a niche is its role in the community. 1. Factors influencing the niche of a plant would be soil, water, light, etc. B. There are many types of relationships that exist between species. 1. Commensalism is when one species in the relationship is benefited and the other is unaffected. 2. Symbiosis refers to the close relationship between two species that benefits at least one of them. a. Commensalism, mutualism, and parasitism can be symbiotic relationships. 45.3 Mutualism A. Mutualistic relationships are those in which both organisms are benefited. 1. Insects serve as pollinators, while plants provide nectar for the insect. a. Scientists designed a plant that made little nectar. b. The plant eventually disappeared, because insect pollinators avoided it. 2. Legumes change nitrogen into a usable form and the plants provide nutrition. 3. In a lichen, the fungi serves to soak up water while the plant again provides nutrition. 4. The E. coli in your digestive tract provide the host with vitamin K, while the bacteria benefits from the food in the host’s colon. 5. The anemone fish protects the anemone, and the anemone provide defense for the fish in the form of nematocysts. 45.4 Competitive Interactions A. Competition between species is usually not as intense as competition within a species. 1. Each species must establish its own ecological niche. a. The niche of each species includes both biotic and abiotic factors. B. Interference competition is when one species prevents another from accessing a resource. 1. For example, a scavenger may chase another animal away from the prey. 2. Also, some plants release substances that prevent other plants from establishing near them. C. In exploitative competition, each species reduces the amount of a resource by consuming it. 1. For example, deer and blue jays both feed on acorns, so they both decrease the amount of available food for the other. D. Effects of Competition 1. Competitive exclusion is when one species out-competes the other and drives it to extinction. When two species of paramecium were in the same environment, one thrived and one died. E. Resource Partitioning 1. Species may be able to survive together if they partition the resources. a. When two species of salamander coexist, they partition the resources unequally and one species becomes larger than the other. 45.5 Predator-Prey Interactions A. Models for Predator-Prey Interactions 1. The number of prey can influence the quantity and type of predators. a. In a type I response, a fairly constant number of prey are killed. 1) The amount of prey killed depends on their density. 2) Examples include spiders and filter feeders. In a type II response, the number of prey killed depends on the skill level of the predator. Initially, there are many more kills, but eventually it slows down since predators can only eat so much. 2) Examples include large animals like tigers, wolves, etc. In a type III response, the number of prey killed increases at a slow rate, and then quickly and finally levels off. 1) This could be due to the predator switching to a different type of prey. 2) The predator could be learning more effective ways of hunting prey. 3) The rapid rise in kills could involve the prey running out of hiding places. B. Cyclic Changes in Abundance 1. Often there are situations in which an increase or decrease in number of prey organisms is followed by a similar change in the amount of predator organisms. a. This cycle of change occurs approximately every 10 years in the Canadian lynx and snowshoe rabbit populations. 1) When rabbit populations flourished, so did the lynx populations. 2) When the rabbit population decreased due to predation, so did the lynx population. b. Researchers discovered that the one-predator-one-prey model was not entirely accurate. 1) Other factors that contribute to the cyclic changes in the rabbit population are multiple predators and the availability of different food sources. 2. It is important that scientists understand the cyclical nature of predator-prey relationships so that endangered animal species can be saved. 45.6 An Evolutionary Arms Race A. Coevolution of Predators and Prey 1. Prey develop various defenses for survival. a. Some have a natural camouflage to hide them from predators. 1) Examples include bittern birds, caterpillars, and lithop plants. b. Some have warning coloration to alert a predator to a bad taste or possible sting. 1) An example is the yellow jacket. c. Some illustrate mimicry, where an organism appears like another organism that is dangerous or distasteful. 1) Examples include the viceroy butterfly mimicking the monarch and other insects resembling yellow jackets. 2. Predators develop various adaptations. a. Some develop better hunting methods. 1) An example is the swift cheetah. b. Some utilize camouflage to ambush prey. 1) Examples include the undetectable scorpion fish and the polar bear. B. Coevolution of Herbivores and Plants 1. Plants have developed two types of defenses to deter herbivory (animals eating plants). a. Some plants can re-grow quickly after being eaten. b. Other plants have defense mechanisms like spines and ill-tasting substances. 45.7 Parasites and Parasitoids A. Parasitism 1. A parasitic lifestyle benefits the parasite and usually harms the host. a. Parasites may weaken the host or cause sterility. b. A successful parasite should not destroy the host. c. Often parasites utilize a vector to deliver the parasite to a suitable host organism. 1) Vectors include insects and other arthropods. 2. Hosts can minimize the effects of parasites. a. Carriers of the sickle-cell trait are resistant to malaria. b. Other hosts perform grooming activities that enable them to discover and remove parasites. c. Some hosts produce chemicals to repel parasites. B. Strangers in the Nest 1. Social parasites are those that take advantage of another animal’s behavior. a. An example is the cowbird who lays its eggs in another bird’s nest so that the other bird serves as a foster parent. b. This practice is known as brood parasitism. C. Parasitoids 1. A parasitoid is a parasite that lays eggs in an insect’s body and destroys it. D. Biological Pest Controls 1. Parasites and parasitoids can be used as biological controls in an attempt to eliminate an undesirable organism. These biological controls should not harm other non-harmful species. 45.8 Ecological Succession A. Successional Change 1. A pioneer species is one that settles in a vacant habitat. 2. A primary succession is when an area lacking soil is originally colonized. a. Lichens and mosses settle first because they can inhabit an area with little or no soil. b. Soil is developed from plant litter and other species settle. 3. A secondary succession relates to an area’s recovery from a fire or natural disaster. B. Factors that Influence Succession 1. The factors that relate to the organisms that occur during succession are sometimes unpredictable. a. Factors that determine the species populations during succession are soil composition, climate, and often chance events. 2. The intermediate disturbance hypothesis states that the number of species inhabiting an area is highest when the disturbances are less drastic. 45.9 Species Introduction, Loss, and Other Disturbances A. The Role of a Keystone Species 1. A keystone species is one that has an overwhelming effect on the environment. a. Examples include periwinkle snails and beavers. B. Adapting to Disturbance 1. Some species have a selective advantage because they can withstand or benefit from a disturbance. a. For example, some plants can germinate only after a fire has occurred. 2. Indicator species are those that are particularly sensitive to environmental changes. a. When the trout population in a stream declines rapidly, it may indicate a low oxygen level. C. Species Introductions 1. An exotic species is one that is dispersed from its home habitat. 2. Some exotic imported species may upset the natural balance in the new environment. a. A common algae present in fish tanks can dominate natural waterways. b. The kudzu plant from Japan is extremely fast-growing and difficult to control in the United States. c. Australia attempts to control a rabbit infestation. d. Hearty gray squirrels introduced into Europe out-survive the native red squirrels. 45.10 Biogeographic Patterns in Community Structure A. Latitudinal Patterns 1. Biogeography studies the natural locations of species. 2. The greatest number of species settles close to the equator. a. This is due to the amount of rainfall, temperature, and the fact that tropical environments are well-established communities. B. Island Patterns 1. Newly formed islands are an excellent habitat for studying speciation. a. The equilibrium model of island biogeography attempts to predict the amount of speciation on an island. b. The distance effect says that the amount of speciation can be estimated by its distance from the mainland. c. The area effect indicates that islands with a greater area will support more species, and these populations are usually large and less likely to become extinct. 45.11 Fighting Foreign Fire Ants (Revisited) Phorid flies, parasitoids, have been imported from Brazil to try to reduce the fire ant populations. The female fly lays her eggs in the ant and the larva becomes larger and eventually causes the fire ant’s head to fall off. Other organisms, such as fungi and protists, are being investigated to see if they can help control the number of invasive fire ants. Suggestions for Presenting the Material • Explain the philosophy behind each of the types of species interactions. For example, how does a parasite derive the maximum amount of benefit from the host without causing its death? How can it maintain its lifestyle without being detected by the host? • The elaborate species interactions described in the chapter offer an opportunity to discuss coevolution. Examples such as the array of yucca species in Colorado, each pollinated exclusively by one kind of yucca moth species, emphasize the point that individuals don’t evolve, populations do. Students will be able to see many good examples of adaptive traits in this chapter. • The coevolution of predator and prey is another good example of the impact of one species on the evolution of another. After reading and discussing this chapter, students should understand that communities are shaped by a complex web of many different factors. • Show some slides of animals in nature exhibiting camouflage, mimicry, and warning coloration. Can the students always spot the organism in the photo? • Use a “Jeopardy” or “Who Wants To Be a Millionaire” format to quiz students on key terms. The templates for both of these quiz formats can be found at: _http://teach.fcps.net/trt2/links/powerpointgames.htm_ Discuss the introduction of Japanese beetles into the U.S. How did they enter the country? What control methods have been initiated? Some beetle traps utilize pheromones, but some researchers worry that many crops are destroyed by insects traveling to these traps. How can the use of pheromones be used effectively? Is this a safer method of insect control than the use of pesticides? Classroom and Laboratory Enrichment • Look into the chemical relationship between the nodules on legumes and their ability to alter nitrogen. When was this discovered? What particular chemical reactions are involved? Can you envision any way to artificially induce these changes in atmospheric nitrogen? • Look at some preserved samples of human parasites. How do they enter the host’s body? What can be done to prevent their introduction into the body? • Choose a community, list its species, and categorize them as producers, consumers, decomposers, of detritivores. • Examine construction sites, flooded river banks, plowed fields, and other places that have been recently disturbed. Can you find several plant species that you would describe as pioneer species? • Look at any natural setting. Describe the habitat and niche for every organism observed. • Show the graphs (Figure 45.6) of the classic experiments of Paramecium growth that Gause performed. Why did Paramecium caudatum decrease to near extinction in the containers but thrive in nature? • Have the students name other examples of camouflage in nature. After they name a few, show examples such as the phasmids (walking sticks). • Select any environment and take a look at the predator-prey relationships within it. Draw a Venn diagram to see what food sources may overlap between two predators. How does this overlapping affect those particular prey populations? • Examine a vegetated area on campus or in an area nearby. How are the plants in the area competing for resources? Suggest some ways in which competition has shaped the plant community. • Describe patterns of succession at edges of stream beds, rivers, or coastlines. • Look in your own backyard or in areas that surround your school for examples of resource partitioning. • Using the observation that grass quickly establishes itself in cracks in the pavement of a highway on which traffic has been blocked for some time, describe what is happening using terms from the chapter. Refer to Table 45.1 on page 810. Go around the room and see how many examples of the various types of two-species interactions the students can name. Discuss the biological control system that is used to combat infestation by gypsy moths. Classroom Discussion Ideas • Have the class voice their opinions on the ideas of instilling parasitoids in the environment to eliminate fire ants. What else should be considered when introducing a species such as the Phorid flies? • Do the Phorid flies have a deleterious effect on native ant populations or any other naturally occurring insects? • Why do insects introduced into the United States become such pests when they were not so in their native country? • Do the Phorid flies serve as a vector for any diseases in other species such as man or livestock? • Do the students have any alternative suggestions for controlling the fire ant population? How would one go about creating a pesticide that would only affect the fire ant population? • Is there any possibility that insect pheromones could be used to remove the harmful fire ants from the environment? Why are biological controls not used more commonly by the average homeowner? Have there been any previous examples of foreign insect infestation that could be studied? Were there any methods that proved effective against the invading insects? Additional Ideas for Classroom Discussion • Are certain plants “born” to be weeds? Or do they achieve that status by human condemnation? • Investigate some of the adaptations that parasites have undergone to survive in the caustic environment of the host’s digestive tract. • What is the difference between true parasitism and social parasitism? Can the students give examples of both types of lifestyles? • Re-examine the graph on page 821. Would you expect a major disturbance such as tsunami to result in a rapid variety of speciation? Why or why not? • Why is resource partitioning essential for groups of functionally similar species living together? • In some areas of the country, wildfires are a natural phenomenon. Should they be allowed to proceed without human intervention? • Relating to environmental issues, voters tend to vote with their wallets rather than with scientific concerns. How can we stop this dangerous trend? • What characteristics distinguish a pioneer species? Are pioneer species good competitors against later successional species? Why are pioneer species dependent on the frequent advent of open, disturbed places? • Discuss predator-prey interactions. Why are the cycles of predator and prey abundance, shown in Figure 45.10, described as idealized? What do you think a predator would do if deprived of its primary prey item? Examine the actual diets of several predatory species; how do these diets change from one month to the next throughout the year? How can environmental disturbances such as fires, floods, climate fluctuations, and insect outbreaks influence the predator-prey cycle? What are some of the other variables that may be overlooked in predator-prey interactions? • Would you expect competition between two finches of different species to be less intense or more intense than competition between two finches of the same species? Explain your answer. • The monarch butterfly is orange and black and tastes bad (birds eating them spit them out immediately); viceroy butterflies are almost indistinguishable from monarchs but taste good. Which of these is the model and which is the mimic? • Why should so-called “good ideas” like kudzu get more scrutiny before being released into a habitat? • According to your text, “In primary succession changes begin when pioneer species colonize a barren habitat.” Are there any uninhabited places left on Earth for pioneer plants and animals to colonize? What would create such a setting? There are different types of mutualism. Investigate each of these types and the following examples: Trophic mutualism (derive benefit from resources) – zooanthellae algae and coral polyps Dispersive mutualism (help in distribution of pollen) – plant and insect pollinator Defensive pollinator (protective advantage) – acacia tree and ants Review the three types of responses seen in predator-prey interactions. Can the students name examples for each of these models? Discuss the methods that plants utilize to deter herbivory. How many examples can the students name? How Would You Vote? Classroom Discussion Ideas • Monitor the voting for the online question. Students may become most engaged in a discussion if they break off into groups to discuss their opinions on a question. If the class is divided into two groups, they could discuss the effectiveness of the process of inspecting imported goods. They should examine the possible effectiveness of the process and also its financial implications. For example, is it more economical to undertake the tedious process of inspecting foreign goods or to attempt to eradicate a species once they are established? Most individuals would probably vote for the most economical choice (unless they are ecologists!). Investigate foreign species that have entered our country accidentally via imported goods. Are they still a big problem or were attempts to eradicate them successful? Term Paper Topics, Library Activities, and Special Projects • A student could pick an organism and investigate how that particular introduced species disrupted the natural environment. What effect did it have on other native species? What steps are being initiated to control the population of the foreign species? Do you have any alternative methods to reduce the influence of that species? • Examine several articles that discuss the method by which a bacterial form of mitochondria became incorporated into cells as an organelle. When did scientists develop this theory? Are there any other potential explanations for this feature? • Look into the excellent example of mimicry between the scarlet king snake and coral snake. They both exhibit the same coloration, but only the coral snake is poisonous. The old adage says, “Red next to yellow can kill a fellow, red next to black—venom lack.” Do you think most predators take the time to look at the order of the colors? Therefore, the scarlet king snake’s coloration is effective to deter predators. • Research the parasite Schistosoma. Even though this organism infests millions of people annually, most people have not even heard its name. Why do you think this organism is not well-known? How does the parasite get into a human’s body? • Study the specific changes in the finch population on the Galapagos Islands in additional detail. Why did Darwin decide to study speciation in that particular location? Was his research very unique at that point in time? • Research Kettlewell’s study of the peppered moth in industrialized England. Although this study is primarily studied to discuss evolution, it can also be used in reference to camouflaged animals and their adaptability. • Find other examples of insect parasitoids. Do they infect their hosts in the same manner as the Phorid flies? Does this appear to be a successful lifestyle? • Write a report on the effects of interspecific competition on a native species whose populations have been adversely affected by an introduced species. • How did disturbance by human intervention help initiate secondary succession in American prairies? • Report on the successful control of the cottony-cushion scale by ladybugs in California. • When one thinks of a parasite-host interaction, one usually thinks of relationships between two animal species. Research the strangleweed mentioned on page 818. What species usually serve as its hosts? • The water hyacinth has become a severe problem in some waterways. How was it introduced into this country? How could it be controlled? • Describe succession as it has occurred following a specific major disaster such as a flood, mudslide, fire, or volcanic eruption. • The Pine Barrens are a unique habitat in New Jersey. The soil is quite acidic and fires are a normal occurrence. Research this environment and list the pioneer species that it supports during its frequent succession. • At what point will the growing number of plant species in a previously disturbed area stop increasing? What factors will halt the rise in species composition? Examine studies of island ecology that seek to answer this question. • One of the most recent U.S. invasive species is the northern snakehead fish. How was it introduced? Mark its current territory on a map. Why has it been so successful? • Select a group of related species for which distribution data are available and construct a graph of patterns of species diversity corresponding to latitude. • Discuss examples of mutualism among plants and animals. Zebra mussels are a species that was introduced in the Great Lakes. What problems are the zebra mussels causing? What is being done to eradicate them? Examine the relationship between whales and barnacles that attach to their side. What type of relationship does this depict? Pick one of the pairs of animals listed below and describe their symbiotic relationship. Zebra and ostrich Ratal (African mammal) and African honeyguide Hornbill and guenon monkeys Southern Rufous woodpecker and black tree ants Refer to the website http://invasivespeciesinfo.gov, which was mentioned in the chapter. Compile a report for the class on one of these introduced species and what efforts are being made to decrease its impact on the environment. Investigate the relationship between termites and intestinal flagellates. What type of species interaction does this represent? Perhaps one of the animals most adept at camouflage is the octopus. It is said that an octopus can even mimic the pattern of a checkerboard in an effort to be unseen. Scientists are uncertain whether the changes in coloration are controlled by hormones or by the nervous system. Look into the research—which theory do you support? Possible Responses to Critical Thinking Questions 1. The principal of competitive exclusion best explains the situation when cows are instilled with an increase of naturally occurring bacteria to discourage the growth of an undesirable strain. Since both species would inhabit the same niche, it is reasonable that the well-established species would not allow the other to effectively colonize. This seems much more desirable that feeding the cows antibiotic-laced food for several reasons. First, the antibiotics may destroy the natural flora of the cow’s digestive tract along with the harmful strain. This may make the digestive process in the cows more difficult. Secondly, the consumers of the milk or meat from the cow may ingest small amounts of antibiotics. Therefore, we may be creating an atmosphere for antibiotic-resistant organisms to develop in the consumer. 2. If flightless birds have existed for many generations in an island environment, it is not surprising that none develop the ability to fly. There would be no adult birds of that species to encourage that skill. Also, the current structure of the flightless birds is not designed for flight. Possible Responses to Data Analysis Exercise Questions Fire ants are an introduced species that causes discomfort in many southern states. This study was designed to test the effectiveness of ant-decapitating phorid flies and the microsporidian Thelohania solenopsae. The population size of the control fire ants increased over the first four months of the study. The fire ants in the two types of treated plots decreased over the same time period. If the study ended after one year, one would conclude that the biological controls had a major effect. At the end of the study at 28 months, one could still conclude that the efforts to eradicate the fire ants were somewhat successful. It appears, however, that some of the ants had become resistant to the pesticide by the study’s end.     452 Chapter Forty-Five 453 Community Ecology 452 Chapter Forty-Five 453 Community Ecology 452 Chapter Forty-Five 453 Community Ecology 452 Chapter Forty-Five 453 Community Ecology 452 Chapter Forty-Five 453 Community Ecology