Chapter 27 Community Interactions

Learning Goals for Ch. 27 27.1 Why Are Community Interactions Important? 27.2 What Is the Relationship Between the Ecological Niche and Competition? 27.3 What Are the Results of Interactions Between Predators and Their Prey? 27.4 What Is Parasitism? 27.5 What is Mutualism? 27.6 How Do Keystone Species Influence Community Structure? 27.7 Succession: How Do Community Interactions Cause Change Over Time?

27.1 Why Are Community Interactions Important? An ecological community consists of all the interacting populations within an ecosystem A community can encompass the entire biotic, or living, portion of an ecosystem Interactions between populations in a community help limit their size

Type of Interaction Effect on Species A Effect on Species B Competition between A and B Harms Harms Predation by A on B Benefits Harms Parasitism by A on B Benefits Harms Mutualism between A and B Benefits Benefits Table 27-1

27.1 Why Are Community Interactions Important? An ecological community consists of all the interacting populations within an ecosystem (continued) The process by which two interacting species act as agents of natural selection on one another is called coevolution

Co-Evolution Bull Thorn Acacia and Ants

27.1 Why Are Community Interactions Important? The most important community interactions are: Competition, which harms both species Predation, which benefits the predator but harms the prey Parasitism, which benefits parasite but harms the host Mutualism, which benefits both species

27.2 What Is the Relationship Between the Ecological Niche and Competition? Each species occupies a unique ecological niche that encompasses all aspects of its way of life These include: Its physical home or habitat The physical and chemical environmental factors necessary for its survival, such as nesting sites, climate, and the type of nutrients it needs The role that the species performs within an ecosystem, such as what it eats and the other species with which it competes Although different species share aspects of their niche with others, no two species ever occupy exactly the same ecological niche within a community

27.2 What Is the Relationship Between the Ecological Niche and Competition? Competition occurs whenever two organism attempt to use the same, limited resources Interspecific competition occurs between members of different species, if they feed on the same things or require similar breeding areas Ex. Cattle and deer Ex.Wild horses and Elk Ex. Zebra mussels and native mussels

27.2 What Is the Relationship Between the Ecological Niche and Competition? Adaptations reduce the overlap of ecological niches among coexisting species The competitive exclusion principle states that if two species occupy exactly the same niche with limited resources, one will outcompete the other

27.2 What Is the Relationship Between the Ecological Niche and Competition? The competitive exclusion principle was formulated by microbiologist G. F. Gause, who performed laboratory experiments using two species of protists, Paramecium aurelia and P. caudatum Both species thrived on the same bacteria and fed in the same region of their laboratory flasks When put into the same flask, P. aurelia always eliminated P. caudatum Gause repeated the experiment, replacing P. caudatum with P. bursaria, which fed in a different part of the flask In that case, both species could coexist because they occupied different niches

Competitive Exclusion P. aurelia P. caudatum (a) Grown in separate flasks (b) Grown in the same flask Fig. 27-1

Resource Partitioning Adaptations reduce the overlap of ecological niches among coexisting species (continued) When species with largely similar ecological niches coexist and compete, each species occupies a smaller niche than it would by itself, a phenomenon called resource partitioning

Resource Partitioning Ecologist Robert MacArthur explored the competitive exclusion principle by carefully observing five species of North American warbler These birds all hunt for insects and nest in the same type of eastern spruce tree MacArthur found that each species concentrates its search for food in specific regions within spruce trees, employs different hunting tactics, and nests at a slightly different time

Resource Partitioning Yellow-rumped warbler Bay-breasted warbler Cape May warbler Black-throated green warbler Blackburnian warbler Fig. 27-2

27.2 What Is the Relationship Between the Ecological Niche and Competition? Interspecific competition may reduce the population size and distribution of each species Although natural selection can reduce niche overlap, interspecific competition may still restrict the size and distribution of competing populations

Intraspecific Competition Competition within a species is a major factor controlling population size Intraspecific competition, competition between individuals of the same species, is the most intense form of competition If resources are limited, this is a major factor controlling population size

27.3 What Are the Results of Interactions Between Predators and Their Prey? Predator prey interactions shape evolutionary adaptations Predators eat other organisms; these include herbivores (animals that eat plants) as well as carnivores (animals that eat other animals) Predators include a grass-eating pika, a bat hunting a moth, and the more familiar example of a hawk eating a bird Predators tend to be less abundant than their prey

Forms of Predation Fig. 27-3

27.3 What Are the Results of Interactions Between Predators and Their Prey? Predator prey interactions shape evolutionary adaptations (continued) Predator and prey populations exert intense selective pressure on one another, resulting in coevolution As prey become more difficult to catch, predators must become more adept at hunting

27.3 What Are the Results of Interactions Between Predators and Their Prey? Some predators and prey have evolved counteracting behaviors Bat and moth adaptations provide excellent examples of how body structures and behaviors are molded by competition Bats emit high-pitch sound pulses that bounce off their surroundings, allowing them to navigate and detect prey Moths (their prey) have evolved ears sensitive to the pitch of sounds the bats emit, and they take evasive actions in response The bats, in turn, counter by switching the frequency of their sound pulses away from the moth s sensitivity range

Bat-Moth Coevolution

27.3 What Are the Results of Interactions Between Predators and Their Prey? Camouflage conceals both predators and their prey Camouflage renders animals inconspicuous even when in plain sight Predators and prey have evolved colors, patterns, and shapes that resemble their surroundings

Camouflage by Blending In Fig. 27-4

Camouflage

27.3 What Are the Results of Interactions Between Predators and Their Prey? Camouflage conceals both predators and their prey (continued) To avoid detection by predators, some animals have evolved to resemble objects, such as leaves, twigs, seaweed, thorns, or even bird droppings Some plants have evolved to resemble rocks to avoid detection by herbivores

Camouflage by Resembling Specific Objects Fig. 27-5a, b

Camouflage by Resembling Specific Objects Fig. 27-5c, d

27.3 What Are the Results of Interactions Between Predators and Their Prey? Camouflage conceals both predators and their prey (continued) Camouflage also helps predators ambush their prey Examples include the cheetah blending with tall grass and the frogfish resembling a rock

Camouflage Assists Predators Fig. 27-6

27.3 What Are the Results of Interactions Between Predators and Their Prey? Bright colors often warn of danger Some animals have evolved bright warning coloration that attracts the attention of potential predators Warning coloration advertises that the animal is bad-tasting or poisonous before the predator attacks Examples include poison arrow frogs, coral snakes, and honey bees

Warning Coloration Fig. 27-7

27.3 What Are the Results of Interactions Between Predators and Their Prey? Some prey organisms gain protection through mimicry Mimicry refers to when members of one species have evolved to resemble another species Two or more distasteful species may each benefit from a shared warning coloration pattern (Müllerian mimicry) Predators need only experience one distasteful species to learn to avoid all with that color pattern For example, toxic monarch and viceroy butterflies have similar wing patterns; if a predator becomes ill from eating one species, it will avoid the other

Mullerian Mimicry Fig. 27-8

Some prey organisms gain protection through mimicry (continued) Some harmless organisms can gain a selective advantage by resembling poisonous species (Batesian mimicry) For example, the harmless hoverfly avoids predation by resembling a bee The harmless mountain king snake is protected by a warning coloration that resembles the venomous coral snake

Batesian Mimicry Fig. 27-9a, b

Batesian Mimicry Fig. 27-9c, d

27.3 What Are the Results of Interactions Between Predators and Their Prey? Some prey organisms gain protection through mimicry (continued) Some animals deter predators by employing startle coloration These animals may have spots that resemble the eyes of a larger animal If a predator gets close, the prey will flash its eyespots, startling the predator and allowing the prey to escape Examples include the peacock moth and the swallowtail caterpillar

Startle Coloration Fig. 27-10

27.3 What Are the Results of Interactions Between Predators and Their Prey? Predators may use mimicry to attract prey In aggressive mimicry, a predator resembles a harmless animal or part of the environment, to lure prey within striking distance For example, a frogfish dangles a wriggling lure that attracts a curious fish that is then eaten

Aggressive Mimicry Fig. 27-6b

Predators and prey may engage in chemical warfare Predators and prey use toxins for attack and defense The bombardier beetle sprays boiling-hot chemicals from its abdomen onto its attacker

Chemical Warfare Fig. 27-12a

Predators and prey may engage in chemical warfare for attack and defense (continued) Many plants have evolved chemical adaptations that deter their herbivore predators, such as the milkweed In the case of the milkweed, however, monarch butterfly caterpillars have evolved to tolerate the toxins and store them in their tissues as a defense against predation

Chemical Warfare Fig. 27-12b

Parasites live in or on their prey, which are called hosts, usually harming or weakening them but not immediately killing them Parasites are generally much smaller and more numerous than their hosts Examples include tapeworms, fleas, ticks, and many types of disease-causing protists, bacteria, and viruses

Social parasites! Animals that take advantage of the social behavior of a host to complete their life cycle.

What Is Parasitism? Parasites and their hosts act as agents of natural selection on one another (continued) Nagana, a disease in cattle caused by a parasitic protist, kills cattle imported into areas of Africa, but some African breeds of cattle have evolved an immunity to it and survive

27.5 What Is Mutualism? Mutualism refers to interactions between species in which both benefit For example, lichens form a mutualistic relationship between a fungus and an algae The fungus provides support and protection while obtaining food from the photosynthetic alga

Mutualism Fig. 27-13a

27.5 What Is Mutualism? Mutualism refers to interactions between species in which both benefit (continued) Another example of mutualism is the clownfish and sea anemones The clownfish takes shelter from predators among the venomous tentacles of an anemone, while in turn cleaning it, providing it with scraps of food, and defending it from predators

Mutualism Fig. 27-13b

Mutualisms Obligatory: Yucca plants and Yucca moths

27.6 How Do Keystone Species Influence Community Structure? In some communities, a keystone species plays a major role in determining community structure A keystone species role is out of proportion to its abundance in the community If a keystone species is removed from the community, normal community interactions are significantly altered and the relative abundance of other species changes dramatically Keystone species need to be identified and protected so that human activities do not lead to the collapse of entire communities and ecosystems

27.6 How Do Keystone Species Influence Community Structure? In some communities, a keystone species plays a major role in determining community structure (continued) An example of a keystone species is the predatory sea star Pisaster ochraceous from Washington s rocky intertidal coast When removed from their ecosystem, their favored prey, native mussels, became so abundant that they outcompete other invertebrates and algae

Keystone Species Fig. 27-14a

27.7 Succession: How Do Community Interactions Cause Change Over Time? Most communities do not emerge fully formed from bare rock or naked soil Instead, they arise through succession, where the community and its nonliving environment change structurally over time Succession is usually preceded by a disturbance, an event that disrupts the ecosystem either by altering the community, its abiotic (nonliving) structure, or both

27.7 Succession: How Do Community Interactions Cause Change Over Time? During succession, most terrestrial communities go through stages Succession begins with arrival of a few hardy plants, called pioneers The pioneers alter the ecosystem in ways that favor competing plants, which eventually displace the pioneers

27.7 Succession: How Do Community Interactions Cause Change Over Time? During succession, most terrestrial communities go through stages (continued) Succession often progresses to a relatively stable and diverse climax community Recurring disturbances can set back the progress of succession The continuous disturbances maintain communities in earlier, or subclimax, stages of succession

Ecological Succession Change in the composition of species over time Classical model describes a predictable sequence with a stable climax community Pioneer Species Other Species Climax Community

Succession in Progress Fig. 27-15b

27.7 Succession: How Do Community Interactions Cause Change Over Time? There are two major forms of succession Primary succession Secondary succession

Primary succession Changes an area lacking any community (no plants, animals, seeds, soil) to one with a functioning community of plants, animals, fungi etc. Pioneer plants: lichen and mosses

Secondary Succession Follows disturbance of an existing community that removes or damages the vegetation, but does not remove, destroy, or cover the soil.

Secondary Succession Pioneer plants of secondary succession start from roots or seeds remaining in the soil or from seeds carried in by wind or animals from surrounding communities.

27.7 Succession: How Do Community Interactions Cause Change Over Time? Primary succession occurs from scratch, where there is no trace of a previous community This process may take thousands or even tens of thousands of years The disturbance that sets the stage for primary succession may be a glacier scouring the landscape to bare rock, or a volcano

27.7 Succession: How Do Community Interactions Cause Change Over Time? Secondary succession occurs after a disturbance changes, but does not obliterate, an existing community, leaving remnants such as soil and seeds This type of succession often takes just hundreds of years An example is Mount St. Helens, which erupted in 1980 and left a thick layer of nutrient-rich ash that encouraged new growth Another example is fire, which also produces nutrientrich ash and spares some trees and many healthy roots

Succession in Progress Fig. 27-15a

27.7 Succession: How Do Community Interactions Cause Change Over Time? Primary succession can begin on bare rock Isle Royal, Michigan, is an example of primary succession This island in Lake Superior was scraped down to bare rock by glaciers The bare rock provided a place for pioneer species, such as lichen and mosses

Primary Succession rock scraped bare by a glacier lichens and moss on bare rock bluebell, yarrow blueberry, juniper jack pine, black spruce, aspen spruce-fir climax forest: white spruce, balsam fir, paper birch 1,000 0 Fig. 27-16

Secondary Succession plowed field ragweed, crabgrass, Johnson grass blackberry, aster, smooth sumac goldenrod, Queen Anne's lace, broom sedge grass Virginia pine, eastern red cedar oak-hickory climax forest: white and black oak, bitternut and shagbark hickory 100 0 Fig. 27-17

Succession in a Small Freshwater Pond Fig. 27-18

27.7 Succession: How Do Community Interactions Cause Change Over Time? Succession culminates in a climax community Succession ends with a relatively stable climax community, which perpetuates itself if not disturbed by outside forces, such as fire

27.7 Succession: How Do Community Interactions Cause Change Over Time? Succession culminates in a climax community (continued) Climax species tend to be larger and longer-lived than pioneer species The exact nature of the climax community at a site reflects the local geological and climatic conditions, such as temperature, rainfall, and elevation

27.7 Succession: How Do Community Interactions Cause Change Over Time? Some ecosystems are maintained in a subclimax stage Frequent disturbances maintain subclimax communities in some ecosystems A subclimax community example is the tallgrass prairies that once covered northern Missouri and Illinois Periodic fires maintained the grasses and prevented forests from encroaching

27.7 Succession: How Do Community Interactions Cause Change Over Time? Some ecosystems are maintained in a subclimax stage (continued) Another example of a subclimax community is suburban lawns Mowing and use of herbicides keep weeds and woody species in check A further example of a subclimax community is agriculture Plowing and pesticides keep competing weeds and shrubs from replacing grains

27.7 Succession: How Do Community Interactions Cause Change Over Time? Climax communities create Earth s biomes The climax communities that form during succession are strongly influenced by climate and geography Extensive areas of characteristic climax plant communities are called biomes, and include deserts, grasslands, and forests