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
BIOLOGY A GUIDE TO THE NATURAL WORLD FOURTH EDITION DAVID KROGH An Interactive Living World 2: Communities in Ecology Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. 34.1 Structure in Communities Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Structure in Communities • An ecological community is all the populations of all species that inhabit a given area. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Structure in Communities • Many communities are dominated by only a few species. • The few species that are abundant in a given area are called ecological dominants. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Ecological Dominants Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.1 Keystone Species • A keystone species is a species whose absence from a community would bring about significant change in that community. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Keystone Species • Some keystone species are top predators in a community, meaning species that prey on other species but that are not preyed on themselves. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Keystone Species Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.2 Keystone Species • Keystone species need not be top predators, however, and every community does not have a keystone species. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Biodiversity • Biodiversity, defined as variety among living things, takes three primary forms: – A diversity of species in a given area. – A geographic distribution of species populations. – Genetic diversity within species populations. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Biodiversity High biodiversity Low biodiversity many different species few species broad distribution of species narrow distribution of species high genetic diversity within population low genetic diversity within population Species diversity Geographic diversity Genetic diversity Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.3 Biodiversity • Recent research indicates that species diversity tends to enhance a community’s productivity. • Productivity is defined as the amount of solar energy that photosynthesizing organisms are able to capture and transform into living material or biomass. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Biodiversity • There is disagreement about whether species diversity also enhances community stability, meaning the ability of a community to retain its characteristics in the face of environmental disruption. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 34.2 Types of Interaction Among Community Members Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Modes of Interaction • There are four primary types of interaction among community members: – – – – competition predation (and a special variety of it, parasitism) mutualism commensalism Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Habitat • Habitat can be thought of as the physical surroundings in which a species normally can be found. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Niche • Niche can be defined metaphorically as an organism’s occupation, meaning what the organism does to obtain the resources it needs to live. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Competition for Resources Among Species • The competitive exclusion principle states that when two populations compete for the same limited, vital resource, one always outcompetes the other and thus brings about the latter’s local extinction. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Competition for Resources Among Species • There are numerous instances in nature in which two related species use the same kinds of resources from the same habitat over an extended period of time but will divide the resources up such that neither of the species undergoes local extinction. • This phenomenon is called coexistence through resource partitioning. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Competition for Resources Among Species Competitive exclusion When two species compete for the same limited, vital resource, one will always drive the other to local extinction—as the paramecium P. aurelia did to the paramecium P. caudatum. This is the competitive exclusion principle at work. Resource partitioning Conversely, when Gause put P. aurelia together with another paramecium, P. bursaria, the two species divided up the habitat, and both survived. This is a demonstration of resource partitioning. P. aurelia P. caudatum P. aurelia P. bursaria Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.4 Resource Partitioning Cape May warbler Bay-breasted warbler Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Myrtle warbler Figure 34.6 Predation • Predation is defined as one free-standing organism feeding on parts or all of a second organism. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Parasitism • Parasitism is a variety of predation in which the predator feeds on prey but does not kill it immediately and may not kill it ever. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Parasitism • The prey of a parasite is known as the host. • A parasite can use a host not only as a food source but as a vehicle to facilitate its reproduction. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Plants Parasitizing Plants Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.7 Predator-Prey Dynamics • Predator and prey population sizes can move up and down together in a fairly tight linkage, but predator-prey interaction generally is only one of several factors that control the population level of either predators or prey. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Predator-Prey Dynamics Lemming population Stoat population Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.8 Predator-Prey Dynamics • Over evolutionary time, predator-prey interactions have spurred physical modifications in both predator and prey species. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Avoiding Predation Through Camouflage Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.10 Mimicry • One form that such modifications take is mimicry: a phenomenon in which one species has evolved to assume the appearance of another. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Mimicry • One form of mimicry, Batesian mimicry, occurs when one species evolves to resemble a species that has superior protective capability. • Batesian mimicry always includes three players: a mimic, a model, and a dupe. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Mimicry • The mimic species evolves to match the appearance of the model species, which has superior protective ability. • The dupe species is then deceived into believing the mimic species is the model species. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Batesian Mimicry Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.11 Mimicry • In a second form of mimicry, Müllerian mimicry, several species that have protection against predators come to resemble each other. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Müllerian Mimicry Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.12 Mutualism • Mutualism is an interaction between individuals of two species that is beneficial to both individuals. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Mutualism Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.13 Commensalism • Commensalism is an interaction in which an individual from one species benefits while an individual from another species is neither harmed nor helped. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Coevolution • Coevolution is the interdependent evolution of two or more species. • Flowers have evolved colors and fragrances that attract bees, for example, while bees have evolved vision that is most sensitive to the colors of the flowers they pollinate. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Coevolution Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.14 Community Interactions Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Table 34.1 34.3 Succession in Communities Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Succession • Parcels of land or water that have been abandoned by humans or devastated by physical forces will almost always be reclaimed by nature to some degree. • This process is called succession: a series of replacements of community members at a given location until a relatively stable final state is reached. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Succession • Primary succession proceeds from an original state of little or no life and soil that lacks nutrients. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Primary Succession ponds and bogs eventually? spruce exposed till pioneer species: lichens, bacteria, horsetails, and liverworts Dryas shrub spruce-hemlock alder bush Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.16 Succession • Secondary succession occurs when a final state of habitat is first disturbed by some outside force, but life remains, and the soil has nutrients. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Succession • The final community in any process of succession is known as the climax community. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Succession • A common set of developments occurs in most instances of primary succession. • These include the arrival of “pioneer” photosynthesizers, facilitation of the growth of some later species through the actions of earlier species, and the competitive driving out of some earlier species by the actions of later species. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Succession • As succession proceeds, species diversity tends to increase within communities and smaller, shorter-lived species tend to be replaced by larger, longer-lived species. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Succession • The rejuvenation of the Mount St. Helens area that has occurred since 1980 has provided ecologists with a wealth of information regarding both primary and secondary succession. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Mount St. Helens Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.15 Succession • One of the chief lessons learned concerns the degree to which succession can be facilitated by biological legacies, defined as living things, or products of living things, that survive a major ecological disturbance. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Survivor on Mount St. Helens Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Figure 34.17