248780621 Elements of Ecology 8e Smith Smith Test Bank Chapter 18

Elements of Ecology, 8e (Smith/Smith) Chapter 18 Factors Influencing the Structure of Communities 18.1 Short Answer Questions 1) The ________ is a group of plant and animal species that inhabits a given area. Answer: community Topic: Introduction to Chapter 18 2) A(n) ________ model of community structure assumes that the presence and absence of individual species in a community result from independent responses to the physical environment, and interactions among species have no impact on community structure. Answer: null Topic: Section 18.1 3) When interspecific interactions involve more than just two species, they are said to be ________. Answer: diffuse Topic: Section 18.2 4) ________ predation is a type of indirect interaction in which a predator enhances the success of one or more inferior competitors by reducing the abundance of a superior competitor. Answer: Keystone Topic: Section 18.3 5) ________ competition is a type of indirect interaction that occurs when a single species of predator feeds on two prey species. Answer: Apparent Topic: Section 18.3 6) When an indirect interaction is beneficial to one of two interacting species and neutral to the other, the indirect interaction is termed indirect ________. Answer: commensalism Topic: Section 18.3 7) ________ or functional groups are groups of species in a community that are thought to have similar roles in the community. Answer: Guilds Topic: Section 18.4 8) When prey populations are controlled by predators in a trophic level above them, they are said to be under ________ control. Answer: top-down Topic: Section 18.4

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9) Patterns of temperature and ________ resulting from regional variations in climate are the major determinant of regional and global patterns of vegetation distribution. Answer: moisture Topic: Section 18.5 10) Variation in environmental conditions within a community is referred to as environmental ________. Answer: heterogeneity Topic: Section 18.6 11) In all experimental studies to date, the effect of increasing nutrient availability to plants has been to ________ plant diversity. Answer: decrease Topic: Section 18.7 12) ________ describes the number of trophic links in a food web. Answer: Connectance Topic: Quantifying Ecology 18.1: Quantifying the Structure of Food Webs: Connectance 18.2 Multiple-Choice Questions 1) Considerable evidence indicates that the null model of community structure is incorrect because A) each species responds independently of other species to the prevailing physical environment. B) interactions among species have no significant influence on community structure. C) when one species is removed, the populations of the other species are unaffected. D) species interactions modify the fundamental niche of the species involved, influencing their relative abundance and, in some cases, their distribution. Answer: D Topic: Section 18.1 2) Experiments on competition among species within a community reveal that A) removing a single species or a group of species has relatively little effect on a community. B) removing a single species has a stronger effect than removing a group of species from a community. C) removing a group of species has a stronger effect than removing a single species from a community. Answer: C Topic: Section 18.2

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3) When apparent competition occurs, the A) populations of predator and prey species are smaller. B) population of the predator species is larger and the populations of the prey species are smaller. C) population of the predator species is smaller and the populations of the prey species are larger. D) populations of predator and prey species are larger. Answer: B Topic: Section 18.3 4) Food webs are typically arranged into trophic levels with A) primary producers at the bottom, herbivores in the middle, and carnivores at the top. B) herbivores at the bottom, carnivores in the middle, and primary producers at the top. C) carnivores at the bottom, herbivores in the middle, and primary producers at the top. D) primary producers at the bottom, carnivores in the middle, and herbivores at the top. Answer: A Topic: Section 18.4 5) When top-down control occurs within an intertidal zone along the rocky coastline of the Pacific Ocean, which of the following species controls the abundance of other species? A) kelp B) mussels C) barnacles D) starfish Answer: D Topic: Sections 18.1 and 18.4 6) Plant community structure along an environmental gradient can often be explained by A) differences among species in their competitive abilities. B) differences among species in their abilities to tolerate stress. C) differences among species in their resistance to herbivores. D) a trade-off among species with respect to competitive ability and stress tolerance. Answer: D Topic: Section 18.5 7) In aquatic environments, the three major environmental gradients of water that directly influence the distribution and dynamics of communities include A) temperature, depth, and oxygen content. B) depth, flow rate, and salinity. C) pressure, temperature, and depth. D) flow rate, salinity, and oxygen content. Answer: B Topic: Section 18.5

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8) As the degree of environmental heterogeneity of a community increases, the number of plant and animal species tends to A) decrease. B) remain the same. C) increase. D) increase initially and then decrease. Answer: C Topic: Sections 18.6 and 18.7 9) As the fertility of soil on the forest floor increases, the A) growth rate of plants increases. B) size of plants decreases. C) density of plants decreases. D) number of species of plants increases. Answer: A Topic: Section 18.7 10) In a food web, community complexity may be measured by the average number of feeding links per species, also referred to as A) trophic diversity. B) food web diversity. C) linkage density. D) interconnectedness. Answer: C Topic: Quantifying Ecology 18.1: Quantifying the Structure of Food Webs: Connectance 18.3 True/False Questions 1) Environmental conditions often vary spatially but do not tend to change over time in a given place. Answer: FALSE Topic: Section 18.1 2) There is considerable evidence that community structure is influenced by interactions between species. Answer: TRUE Topic: Section 18.1 3) Species interactions within a community rarely involve only two species. Answer: TRUE Topic: Section 18.2 4) Diffuse interactions often occur among competing species but never among predator-prey species. Answer: FALSE Topic: Section 18.2 4 Copyright © 2012 Pearson Education, Inc.

5) Competitive interactions are often diffuse, whereas mutualisms are not. Answer: FALSE Topic: Section 18.2 6) The populations of keystone predators are controlled by the populations of their prey species. Answer: FALSE Topic: Section 18.3 7) Indirect interactions can be either positive or negative for the affected species. Answer: TRUE Topic: Section 18.3 8) The removal of a single species from a community can have unpredictable consequences. Answer: TRUE Topic: Section 18.3 9) The control of an herbivore population by a parasitoid is an example of top-down control. Answer: TRUE Topic: Section 18.4 10) The "world is green" hypothesis suggests that herbivore populations limit the number of predators, allowing plant biomass to accumulate. Answer: FALSE Topic: Section 18.4 11) Within a community, most species have a similar range of environmental tolerances. Answer: FALSE Topic: Section 18.5 12) Competition among plant species rarely involves only a single resource. Answer: TRUE Topic: Section 18.5 13) Environmental heterogeneity tends to be positively correlated with species diversity. Answer: TRUE Topic: Section 18.6 14) The diversity of an animal community is unrelated to the physical structure of a plant community. Answer: FALSE Topic: Section 18.6 15) Competition for belowground resources is considered to be asymmetric because larger plants have a disproportionate advantage in competition for those resources. Answer: FALSE Topic: Section 18.7 5 Copyright © 2012 Pearson Education, Inc.

16) In aquatic communities, an increase in nutrients usually causes the number of autotrophic species to increase. Answer: TRUE Topic: Section 18.7 17) Recent studies suggest that as species richness in a food web increases, the number of trophic links increases but the connectance decreases. Answer: TRUE Topic: Quantifying Ecology 18.1: Quantifying the Structure of Food Webs: Connectance 18) The research of Sally Hacker has demonstrated that Juncus plants are strong antagonists, causing increases in conditions such as salinity that hinder the growth of other plants such as Iva. Answer: FALSE Topic: Field Studies: Sally D. Hacker 18.4 Essay Questions 1) Explain the differing roles of fundamental niches and species interactions in controlling community structure. Topic: Section 18.1 2) Explain how apparent competition may potentially affect the population sizes of predator and prey species. Topic: Section 18.3 3) Explain the difference between bottom-up and top-down control of community structure and discuss if one is more important than the other. Topic: Section 18.4 4) Summarize the "world is green" hypothesis of Nelson Hairston, Fred Smith, and Larry Slobodkin. Is this an example of bottom-up or top-down control? Topic: Section 18.4 5) Discuss the factors that may lead to zonation among plants along an environmental gradient. What factors tend to define the lower and upper boundaries along the environmental gradient of each species? Topic: Section 18.5 6) Discuss the impact of environmental heterogeneity on biological diversity within a community. Topic: Section 18.6 7) When nutrients are added to terrestrial and aquatic communities, what are the effects on the diversity of autotrophic species? Is there a difference between terrestrial and aquatic communities? Topic: Section 18.7 6 Copyright © 2012 Pearson Education, Inc.

8) What are the possible explanations for the paradox that diversity in terrestrial plant communities decreases when nutrient availability increases? Topic: Section 18.7

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