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Biology A Guide to the Natural World Chapter 35 • Lecture Outline An Interactive Living World 2: Communities in Ecology Fifth Edition David Krogh © 2011 Pearson Education, Inc. 35.1 Structure in Communities © 2011 Pearson Education, Inc. Structure in Communities • An ecological community is all the populations of all species that inhabit a given area. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Ecological Dominants © 2011 Pearson Education, Inc. Figure 35.1 Keystone Species • A keystone species is a species whose absence from a community would bring about significant change in that community. © 2011 Pearson Education, Inc. Keystone Species © 2011 Pearson Education, Inc. Figure 35.2 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. © 2011 Pearson Education, Inc. 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 (a) Species diversity (b) Geographic diversity (c) Genetic diversity © 2011 Pearson Education, Inc. Figure 35.3 Biodiversity • Recent research indicates that species diversity tends to enhance a community’s productivity and stability. © 2011 Pearson Education, Inc. 35.2 Types of Interaction Among Community Members © 2011 Pearson Education, Inc. Modes of Interaction • There are four primary types of interaction among community members: • competition • predation (and a special variety of it, parasitism) • mutualism • commensalism © 2011 Pearson Education, Inc. Habitat • Habitat can be thought of as the physical surroundings in which a species normally can be found. © 2011 Pearson Education, Inc. Niche • Niche can be defined metaphorically as an organism’s occupation, meaning what the organism does to obtain the resources it needs to live. © 2011 Pearson Education, Inc. 35.3 Interaction through Competition © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. (a) Competitive exclusion P. aurelia Population size 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. P. caudatum (b) 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. Population size Time (days) X P. aurelia P. bursaria Time (days) © 2011 Pearson Education, Inc. Figure 35.4 Competition for Resources Among Species • Coexistance through resource partitioning refers to instances in which two similar 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. © 2011 Pearson Education, Inc. Resource Partitioning Resource Partitioning Cape May warbler Bay-breasted warbler © 2011 Pearson Education, Inc. Myrtle warbler Figure 35.6 35.4 Interaction through Predation and Parasitism © 2011 Pearson Education, Inc. Predation • Predation is defined as one free-standing organism feeding on parts or all of a second organism. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Plants Parasitizing Plants © 2011 Pearson Education, Inc. Figure 35.7 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. © 2011 Pearson Education, Inc. 10 10 Lemming population 0.1 1 0.001 0.1 Stoat population 0.01 1988 Lemmings’ winter nests occupied by stoats per 2.5 acres Lemmings per 2.5 acres Predator–Prey Dynamics 1990 1992 0.00001 1994 1996 1998 2000 2002 Year © 2011 Pearson Education, Inc. Figure 35.8 Predator–Prey Dynamics • Predator–prey interactions have spurred the evolution of physical modifications in both predator and prey species. © 2011 Pearson Education, Inc. Avoiding Predation Through Camouflage © 2011 Pearson Education, Inc. Figure 35.10 Mimicry • One form that such modifications take is mimicry: a phenomenon in which one species has evolved to assume the appearance of another. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Batesian Mimicry © 2011 Pearson Education, Inc. Figure 35.11 Mimicry • Müllerian mimicry occurs when several species that have protection against predators come to resemble each other. © 2011 Pearson Education, Inc. Müllerian Mimicry © 2011 Pearson Education, Inc. Figure 35.12 35.5 Interaction through Mutualism and Commensalism © 2011 Pearson Education, Inc. Mutualism • Mutualism is an interaction between individuals of two species that is beneficial to both individuals. © 2011 Pearson Education, Inc. Mutualism © 2011 Pearson Education, Inc. Figure 35.13 Commensalism • Commensalism is an interaction in which an individual from one species benefits while an individual from another species is neither harmed nor helped. © 2011 Pearson Education, Inc. Coevolution • Coevolution is the interdependent evolution of two or more species. © 2011 Pearson Education, Inc. Coevolution © 2011 Pearson Education, Inc. Figure 35.15 Community Interactions Table 35.1 Community Interactions In this type of interaction . . . One organism . . . While the other . . . Competition Is harmed Is harmed Predation and parasitism Gains Is harmed Mutualism Gains Gains Commensalism Gains Is unaffected © 2011 Pearson Education, Inc. Table 35.1 35.6 Succession in Communities © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Succession • Primary succession proceeds from an original state of little or no life and soil that lacks nutrients. © 2011 Pearson Education, Inc. Primary Succession ponds and bogs eventually? spruce spruce-hemlock alder bush exposed till pioneer species: lichens, bacteria, horsetails, and liverworts Dryas shrub © 2011 Pearson Education, Inc. Figure 35.17 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. © 2011 Pearson Education, Inc. Succession • The final community in any process of succession is known as the climax community. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Mount St. Helens © 2011 Pearson Education, Inc. Figure 35.16 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. © 2011 Pearson Education, Inc. Survivor on Mount St. Helens © 2011 Pearson Education, Inc. Figure 35.18