Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Storage effect wikipedia , lookup
Unified neutral theory of biodiversity wikipedia , lookup
Occupancy–abundance relationship wikipedia , lookup
Biodiversity action plan wikipedia , lookup
Habitat conservation wikipedia , lookup
Latitudinal gradients in species diversity wikipedia , lookup
Introduced species wikipedia , lookup
Coevolution wikipedia , lookup
Theoretical ecology wikipedia , lookup
Island restoration wikipedia , lookup
Anu Singh-Cundy • Gary Shin Discover Biology SIXTH EDITION CHAPTER 23 Ecological Communities © 2015 W. W. Norton & Company, Inc. CHAPTER 23 Ecological Communities, Part 1 FATAL FELINE ATTRACTION Mutualistic relationships benefit both species involved 23.1 Species Interactions Mutualistic relationships benefit both species involved Only one partner benefits in commensalism In exploitation, one member benefits while another is harmed In competition, both species are negatively affected 23.2 How Species Interactions Shape Communities Keystone species have profound effects on communities Invasive species can overtake communities 23.3 How Communities Change over Time Succession establishes new communities and replaces disturbed communities Communities change as climate changes CHAPTER 23 Ecological Communities, Part 2 23.4 Human Impacts on Community Structure Communities can reassemble after some human-caused disturbances People can cause long-term damage to communities BIOLOGY MATTERS: Introduced Species: Taking Island Communities by Stealth APPLYING WHAT WE LEARNED: HOW A PARASITE CAN HIJACK YOUR BRAIN Fatal Feline Attraction Imagine an alien that enters people’s brains and changes their behavior, sometimes even driving them crazy. • • Toxoplasma gondii is a single-celled parasite, most often contracted from raw meat, that alters the brain activity of rodents. The species that make up a community interact in all kinds of ways. An Association of Different Species • An ecological community is an association of different species that live in the same area. • Communities vary greatly in size and complexity and can be characterized by their species composition, or diversity. The Two Components of Community Diversity • Species richness refers to the total number of different species that live in the community. • Relative species abundance describes how common individuals of a species are compared with individuals of other species in the community. • Interactions among organisms have huge effects on natural communities. Species Interactions • Coevolution occurs when two species that interact trigger evolutionary change in each other as a consequence of their interactions. • Interactions among organisms can be divided into four categories: – Mutualism (+/+): interactions in which both species benefit – Commensalism (+/-): interactions in which one species benefits at no cost to the other – Exploitation (+/-): interactions in which one species benefits and the other is harmed – Competition (-/-): interactions in which both species may be harmed Species Interactions: Mutualism Mutualism evolves when the benefits of the interaction outweigh the costs for both species. • Mutualism is an association between two species in which both species benefit more than it costs them to interact with each other. • Two or more organisms of different species living together is symbiosis. • Although both species in a mutualism benefit from the relationship, what is good for one species may come at a cost to the other. For example, a species may use energy or increase its exposure to predators when it acts to benefit its mutualistic partner. • From an evolutionary perspective, mutualism evolves when the benefits of the interaction outweigh the costs for both species. There Are Many Types of Mutualism Gut inhabitant mutualism in deer gut: microbes that live in digestive tract receive food from their host and benefit the host by digesting foods that the host otherwise could not use. Examples of mutualisms include - Gut inhabitant mutualism - Protection mutualism - Behavioral mutualism - Seed dispersal mutualism - Pollinator mutualism An example of seed dispersal mutualism An Example of Behavioral Mutualism The goby acts as a “seeing eye” fish for the shrimp, which has poor vision. In return, the shrimp shares its burrow with the goby, thereby providing the fish with a safe haven in an environment with few options for sheltering from predators. Mutualism Can Determine the Distribution and Abundance of Species In this pollinator mutualism, the plant gets pollinated and the moth larvae eats some of its seeds. The plant and pollinator are completely interdependent: the yucca is the moth’s only source of food, and this moth is the only species that pollinates the yucca. • • • Mutualism can affect species distribution, the geographic area over which a species is found. Species abundance, the number of individuals of a species in a defined habitat, can also be affected by mutualism. Mutualism can have indirect effects on the distribution and abundance of species that are not part of the mutualism. Only One Partner Benefits in Commensalism • A relationship in which one partner benefits while the other is neither helped nor harmed is called commensalism. • Barnacles that attach themselves to whales are an example of commensalism. In Exploitation, One Member Benefits While Another Is Harmed • Exploitation encompasses a variety of interactions in which one species benefits and the other is harmed. • Exploiters are generally consumers falling into three main categories: – Herbivores are consumers that eat plants or plant parts – Predators are animals that kill other animals for food – Parasites are consumers that live in or on the organisms they eat A marine crustacean, Cymothoa exigua enters through fish gills and attaches to the base of the fish’s tongue to draw blood from it. Starved of oxygen, the tongue will eventually atrophy and die. The fish, however, will not. It will continue to live with C. exigua, still attached, acting as a surrogate tongue. Consumes Can Strongly Affect the Abundance of Their Food Organisms • Sometimes a consumer exerts such a significant impact on a prey species that the population sizes of two species change together in a tightly linked cycle, known as a population cycle. Lynx populations increase when hare populations increase, but the increased number of lynx drive the hare populations down, which then turn drives down lynx populations. Consumers and Their Food Organisms Can Exert Strong Selection Pressure on Each Other • The presence of consumers in an environment has caused many species to evolve elaborate strategies to avoid being consumed. • An evolutionary arms race can develop as prey or host evolve a powerful defense and their consumers in turn experience strong selection pressure to overcome that defense. Avoiding Predation: Induced Defense • Induced defenses are responses from certain plants that are directly stimulated by an attack from herbivores. Avoiding Predation: Warning Coloration • Warning coloration is used by prey organisms to warn potential predators that they are heavily defended, for example, with toxins. Avoiding Predation: Mimicry • Mimicry is a type of adaptation arising from predator-prey interactions in which a species evolves to imitate the appearance of something unappealing to its would-be predator. In Competition, Both Species Are Negatively Affected • Interspecific (interspecies) competition is most likely when two species share an important resource that is limited. • An ecological niche is the sum total of the conditions and resources a species or population needs in order to survive and reproduce successfully in its particular habitat. • When two or more species compete, each has a negative effect on the other because each uses resources needed by its competitor. Competitors May Exclude Each Other from Their Own Special Niche • Competitive exclusion occurs when one species uses all the resources needed by another and that species becomes extinct. • There are two main types of competition: – Interference competition: one organism directly excludes another from the use of a resource – Exploitative competition Competition Can Limit the Distribution and Abundance of Species That Share Resources or Space • Exploitative competition: species compete indirectly for a shared resource, each reducing the amount of the resource available to the other Exploitative competition between an introduced and native wasp caused the extinction of the native in most localities. Both feed on the same insect, the citrus mealybug. Competition Is Reduced When Niches Are Used in Different Ways • Niche partitioning occurs when natural selection leads competing organisms to use their common niche in different ways as a method of reducing competition. These birds can coexist on the same shore because they dig for crustaceans in waters of different depths. Keystone Species Have Profound Effects on Communities • Keystone species have a disproportionately large effect, relative to their own abundance, on the types and abundances of the other species in a community. • Keystone species can include any producer or consumer of relatively low abundance that has a large influence on its community, and they are usually noticed only when they are removed or disappear from an ecosystem. Invasive Species Can Overtake Communities • Nonnative species introduced by people to new regions sometimes disrupt the ecological communities there. • Some species multiply rapidly when introduced to new areas due to lack of predation and fewer parasites than in their original home. How Species Interactions Shape Communities • Interactions among organisms can impact the communities and ecosystems in which those organisms live. • Human actions, such as urbanization and natural causes, such as fire, affect a species’ chances of survival. • Any changes in species diversity in a community will have a ripple effect throughout the community. How Communities Change over Time • The number of individuals of different species in a community often changes as the seasons or the years change. • Communities also undergo broad directional changes in species composition over longer periods of time. • The process by which species in a community are replaced over time is called succession. • Primary succession occurs in newly created habitat when a few species that are able to grow and reproduce under the challenging conditions begin to colonize the area. • Secondary succession is the process by which communities regain the successional state that existed before a disturbance. Succession Establishes New Communities • The first species to colonize the area may alter the habitat in ways that cause later-arriving species to thrive or fail. • The process of succession ends when the species composition of a community remains stable over a long period of time, resulting in a mature community. • Most ecological communities never reach maturity because of frequent disturbances such as fires or windstorms. Succession Replaces Disturbed Communities • Secondary succession is the process by which communities regain the successional state that existed before a disturbance. Communities Change as Climate Changes • The climate at a given location can change over time as a result of either global climate change or continental drift. • The change in the global climate causes slow but dramatic changes in the location and diversity of plant and animal species in an ecosystem. • Human activities are now accelerating the natural changes in the global climate. • As the continents move slowly over time, their climates change, causing large changes in their communities. People Can Cause Long-Term Damage to Communities • Some communities, such as cleared farmland, can recover from a human disturbance. • The sizes and abundances of species in a community are different after a disturbance, and there may be fewer species. • Ecological interactions brought about by humans, such as logging or overgrazing by cattle, can permanently affect natural communities for example by causing desertification. • Some communities may take hundreds to thousands of years to recover; others may never recover. Overgrazing can lead to desertification BIOLOGY MATTERS: Introduced Species: Taking Island Communities by Stealth • The Hawaiian Islands are the most isolated chain of islands on Earth. • Entire groups of organisms that live in most other communities have never reached these islands (no native ants or snakes; only one mammal, a bat). • The few species that did reach the islands evolved in isolation to form unique communities, without many types of predators and competitors found elsewhere. • As a result, these communities are ill equipped to cope with invasives, such as rats and beard grass, introduced by people. Hawaiian silverswords are found only in Hawaii. This diverse species evolved from a single ancestor (a tarweed from California). The three species in these photos have very different form because they’re adapted to live in very different habitats. APPLYING WHAT WE LEARNED: HOW A PARASITE CAN HIJACK YOUR BRAIN T. gondii improves its chances of spreading to cats by changing the behavior of infected rats. • Male rats infected with Toxoplasma gondii find the smell of cat urine irresistible; they’re eaten by the feline, the only host group in which T. gondii can sexually reproduce, which then excretes the parasite. • The parasite forms cysts in the brain and releases dopamine, a “feel good” neurotransmitter. • T. gondii infections in humans alters behavior differently in men versus women • The parasite is contracted from cleaning cat litter boxes, but also from handling raw meat or from consuming undercooked meat, unpasteurized milk, and unwashed fruits and vegetables. List of Key Terms: Chapter 23 character displacement (p. 534) coevolution (p. 527) commensalism (p. 529) community (p. 526) competition (p. 532) competitive exclusion (p. 533) desertification (p. 540) diversity (p. 526) exploitation (p. 530) exploitative competition (p. 533) herbivore (p. 530) host (p. 530) induced defense (p. 530) interference competition (p. 533) keystone species (p. 535) mimicry (p. 530) mutualism (p. 527) niche (p. 532) niche partitioning (p. 533) parasite (p. 530) pathogen (p. 530) pollinator (p. 528) population cycle (p. 531) predator (p. 530) prey (p. 530) primary succession (p. 537) relative species abundance (p. 526) secondary succession (p. 537) species richness (p. 526) succession (p. 537) symbiosis (p. 537) warning coloration (p. 530) Class Quiz, Part 1 Which of the following is not a major type of exploitation? A. herbivores B. parasites C. induced defenses Class Quiz, Part 2 Two species of bumblebees coexist in the same meadow, but one has a long feeding tube (proboscis) and sips nectar from columbines, and the other has a short proboscis and sips nectar from asters. This is an example of A. pollinator mutualism. B. behavioral mutualism. C. exploitative competition. D. niche partitioning. Class Quiz, Part 3 As this glacier retreats, the barren land that is exposed comes to be colonized by herbaceous plants, sedges, low shrubs, then alders, and finally, subalpine fir. This pattern of change is an example of A. primary succession. B. secondary succession. C. niche partitioning. D. commensalism. Relevant Art from Other Chapters All art files from the book are available in JPEG and PPT formats online Producers and Consumers 23.1 Concept Check, Part 1 1. The yucca moth pollinates the yucca plant and depends on it for food. How would you classify this type of interaction? Is it cost-free for both moth and plant? Explain. ANSWER: It is a mutualism. There are costs for both: the moth’s reproduction is limited because the plant restricts the number of eggs the moth can lay successfully, and the plant in turn loses some of its seeds to the moth larvae. 23.1 Concept Check, Part 2 2. Cattle egrets trail livestock—sometimes perching on their backs—to pick up insects stirred up by the grazing animals. How would you classify this type of interaction? Who benefits in this type of interaction? ANSWER: This is commensalism. The birds benefit because they get better access to their insect prey. The grazers are neither harmed nor benefited. 23.1 Concept Check, Part 3 3. Chthamalus (a barnacle that lives high on the shoreline) and Semibalanus (a barnacle that lives in the low intertidal zone) exhibit interference competition. How would the survival and reproduction of a Chthamalus colony be affected if it were relocated to the low intertidal zone either in the absence of Semibalanus or intermixed with Semibalanus? ANSWER: Chthamalus would thrive low on the shoreline as long as Semibalanus was absent. 23.2 Concept Check, Part 1 1. What is a keystone species? ANSWER: Any organism of relatively low abundance that has a disproportionately large influence on the diversity of a community is a keystone species. 23.2 Concept Check, Part 2 2. Why are invasive species such a significant problem? ANSWER: Because they lack biological controls on their population growth, such as predators or parasites, invasive species can potentially grow rapidly and displace, outcompete, or prey on native species. 23.3 Concept Check, Part 1 1. Describe the distinctive characteristics of species that tend to be the first to colonize a new habitat. ANSWER: They disperse more rapidly than other species, and/or they are better able to survive and reproduce in challenging environments. 23.3 Concept Check, Part 2 2. Compare primary succession with secondary succession. ANSWER: Primary succession is the order in which species replace others in a new habitat (one that contains no species). Secondary succession is the sequence of species that appear in a preexisting community disturbed by natural processes (such as fire) or human actions (such as deforestation). 23.4 Concept Check, Part 1 1. What kinds of human activities influence community structure? ANSWER: Logging, fire, agriculture, and grazing are among the many human activities that affect communities. 23.4 Concept Check, Part 2 2. Can human activity ever induce primary succession? ANSWER: Not likely. Human activity may damage or degrade communities, but it does not remove all species and soil.