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Chapter 6 Testing Your Comprehension 1 Both interspecific and intraspecific competition can restrict the ecological role played by an individual, leaving it to fill just a portion of its full potential role, the so-called fundamental niche. This more limited role is the so-called realized niche. Species adapt to competition by evolving to use different resources, or to use shared resources in different ways. 2 Predation is the relationship in which one organism, a predator, consumes another, its prey. Parasitism is a relationship in which one organism, the parasite, depends on another, the host, for nourishment or some other benefit while simultaneously harming the host (but generally not killing it). Herbivory is the consumption of a plant or a portion of a plant by an animal, the herbivore. 3 Fungi and plant roots that form associations called mycorrhizae are symbiotic mutualisms. Bees pollinating plants while ingesting nectar exemplify a non-symbiotic mutualism. Many agriculturally important plant species require insect pollination. Moreover, each one of us depends on symbiotic bacteria in our digestive tracts to continue living. 4 A trophic level is a rank in the feeding hierarchy of a community, with plants and/or chemoautotrophic producers occupying the first trophic level, and various consumers occupying the second trophic level. If this list of who eats whom is extended, you have a food chain. In reality, it is common for one species to consume and be consumed by multiple species, resulting in a network of feeding relationships called a food web. 5 A species might be considered a keystone species if its removal from the ecosystem causes pervasive ripple effects throughout the food web. Removal of predators at high trophic levels can result in increased prey abundance, which may cause decreased abundance of their food as they overgraze. Other species that have major effects because they physically modify the environment shared by community members (as beavers and their dams do) are more often considered “ecosystem engineers.” 6 Primary succession involves the establishment of an ecological community in an area that has never before been colonized by life (e.g., on fresh lava flows or land that has been uncovered by melting glaciers). Secondary succession begins with the recolonization of an area following a significant disturbance, such as the regrowth of natural vegetation on an abandoned farm field. In each case, the community alters the physical environment over time and responds to that changing environment. 7 Clements viewed communities as cohesive entities, much like superorganisms. Gleason viewed them as temporary associations of species. 8 Changes to the Great Lakes include increased numbers of zebra mussels, decreased smaller zooplankton and plankton-eating fish, decreased numbers of native molluscs that compete with zebra mussels, increased cyanobacterial populations, increased numbers of benthic organisms that make use of zebra mussel waste nutrients, and increased food for organisms that eat zebra mussels (e.g., ducks, crayfish, muskrats, etc.). See Fig 6.16a. 9 Terrestrial biomes’ distributions are most strongly influenced by climate, which can be summarized in a climatograph of average monthly temperature and precipitation. Water temperature, depth, salinity, dissolved nutrients, wave action, currents, and type of substrate shape aquatic ecosystems’ distributions. 10 See Figure 6.23b and Figure 6.26b. These diagrams indicate the range and timing of temperature and moisture stresses likely to be faced by organisms in those biomes. Interpreting Graphs and Data 1 The 2007 population estimate is about 230–240% greater than that of 1983. 2 The recent increase in the sea otter population should be helping to keep sea urchin numbers down, which should allow lush underwater forests of kelp to grow and provide habitat for many other species. 3 Each graph should have years along the x axis and numbers of individuals along the y axis. The sea urchin graph (a) should show decreasing numbers of sea urchins—that is, a trend line going in the opposite direction as that of sea otters. The kelp graph (b) should show increasing amounts of kelp. The fish graph (c) should show increasing amounts of fish, because they benefit from increasing amounts of kelp as habitat. Calculating Ecological Footprints Table 1. Introduced Species Taxon Percentage of total introduced 50 Number of species introduced 25,000 Mammals 0.04 2,000 Birds 0.19 9,500 Molluscs 0.18 9,000 Arthropods 9 45,000 Microbes 40 20,000 Percentage of total costs 60 Economic cost Plants Table 2. Aquatic Invaders Invader Fish species $5.4 billion Zebra/quagga mussels 11 $0.99 billion Asiatic clam 11 $0.99 billion West Nile virus 11 $0.99 billion Aquatic plant species 5 $0.45 billion Shipworm 2 $0.18 billion Green crab 1 $0.09 billion 1 Plant species that happen to do well in soils and conditions where they have been introduced, or those that have been freed from their herbivores and parasites, may spread quickly, often with seeds that disperse long distances. Invasive plant species can overrun vast regions, competing with and displacing native vegetation. 2 Answers will vary. Judging by the aquatic data, animals and microbes seem to have greater impacts than plants in aquatic environments. However, half of all terrestrial introduced species are plants, so perhaps they would have large impacts overall. 3 In gardening, you might plant exotic species that could proliferate. You might accidentally spread aquatic invasives through boating activity. You might release exotic fish from an aquarium into the wild. You might spread seeds of invasive weeds from place to place when they get stuck on your shoes. To address such risks, you could carefully research the source and potential impacts of anything you plant in the ground. You could check boat propellers for aquatic plants and dispose of bilge water in upland waters before entering sensitive waters. You could refrain from disposing of home aquarium water into any area that could enter or run off into a public waterway. You could check your socks and shoes for weed seeds, especially after a hike. You could help monitor your environment for invasive species, and assist with invasive species removal projects in your community.