A Guide to the Natural World David Krogh © 2011 Pearson Education, Inc. Chapter 35 Lecture Outline An Interactive Living World 2: Communities in Ecology Biology Fifth Edition

© 2011 Pearson Education, Inc 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 Figure 35.1

© 2011 Pearson Education, Inc. 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 Figure 35.2

© 2011 Pearson Education, Inc. 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 biodiversityLow biodiversity many different species few species broad distribution of speciesnarrow distribution of species high genetic diversity within population low genetic diversity within population (a) Species diversity (b) Geographic diversity (c) Genetic diversity Figure 35.3

© 2011 Pearson Education, Inc. Biodiversity Recent research indicates that species diversity tends to enhance a community’s productivity and stability.

© 2011 Pearson Education, Inc 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 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 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. (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 P. aurelia P. caudatum P. aurelia P. bursaria Time (days) Population size X Figure 35.4

© 2011 Pearson Education, Inc. 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 Figure 35.6 Resource Partitioning Cape May warbler Bay-breasted warbler Myrtle warbler

© 2011 Pearson Education, Inc 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 Figure 35.7

© 2011 Pearson Education, Inc. 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. Predator–Prey Dynamics Figure 35.8 Lemmings per 2.5 acres Lemming population Stoat population Lemmings’ winter nests occupied by stoats per 2.5 acres Year

© 2011 Pearson Education, Inc. 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 Figure 35.10

© 2011 Pearson Education, Inc. 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 Figure 35.11

© 2011 Pearson Education, Inc. Mimicry Müllerian mimicry occurs when several species that have protection against predators come to resemble each other.

© 2011 Pearson Education, Inc. Müllerian Mimicry Figure 35.12

© 2011 Pearson Education, Inc 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 Figure 35.13

© 2011 Pearson Education, Inc. 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 Figure 35.15

© 2011 Pearson Education, Inc. Community Interactions Table 35.1 Community Interactions One organism... While the other... In this type of interaction... Competition Predation and parasitism Mutualism Commensalism Is harmed Gains Is harmed Gains Is unaffected

© 2011 Pearson Education, Inc 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. exposed till pioneer species: lichens, bacteria, horsetails, and liverworts Dryas shrub alder bush spruce spruce-hemlock ponds and bogs eventually? Primary Succession Figure 35.17

© 2011 Pearson Education, Inc. 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 Figure 35.16

© 2011 Pearson Education, Inc. 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 Figure 35.18