© 2015 Pearson Education, Inc. CH 37: COMMUNITY STRUCTURE AND DYNAMICS

© 2015 Pearson Education, Inc Community Ecology The next step up is a biological community, an assemblage of all the populations of organisms living close enough together for potential interaction. A community can be described by its species composition.

© 2015 Pearson Education, Inc Community Ecology Community ecology is necessary for the conservation of endangered species and the management of wildlife, game, and fisheries, is vital for controlling diseases, such as malaria, bird flu, and Lyme disease, that are carried by animals, and has applications in agriculture, where people attempt to control the species composition of communities they have established.

© 2015 Pearson Education, Inc Interspecific Interactions Interspecific interactions are relationships with individuals of other species in the community greatly affect population structure and dynamics. Competition: populations of two different species compete for the same limited resource. Mutualism: both populations benefit. Predation: one species (the predator) kills and eats another (the prey). Herbivory: an animal consumes plant parts or algae. Parasitism: the host plants or animals are victimized by parasites or pathogens.

© 2015 Pearson Education, Inc Competition An ecological niche is the sum of an organism’s use of the biotic and abiotic resources in its environment. Interspecific competition occurs when the niches of two populations overlap and both populations need a resource that is in short supply. In general, competition lowers the carrying capacity of competing populations the resources used by one population are not available to the other population.

© 2015 Pearson Education, Inc. Mutualism Video: Clownfish and Anemone

© 2015 Pearson Education, Inc EVOLUTION CONNECTION: Predation Predation benefits the predator but kills the prey. Prey adapt using protective strategies that include camouflage, mechanical defenses, and chemical defenses.

© 2015 Pearson Education, Inc EVOLUTION CONNECTION: Herbivory A plant whose body parts have been eaten by an animal must expend energy to replace the loss. This has lead to the evolution of many defenses. Plant defenses include: spines and thorns and chemical toxins Toxins have bad tastes or can cause abnormal growth in the organisms that eat them.

© 2015 Pearson Education, Inc Parasites and pathogens A parasite lives on or in a host from which it obtains nourishment. Internal parasites include nematodes and tapeworms. External parasites include mosquitoes, ticks, and aphids. Pathogens are disease-causing microscopic parasites that include bacteria, viruses, fungi, or protists. Parasitic aphids

© 2015 Pearson Education, Inc Trophic structure Every community has a trophic structure, a pattern of feeding relationships consisting of several different levels. The sequence of food transfer up the trophic levels is known as a food chain. This transfer of food moves chemical nutrients (matter) and energy from producers up through the trophic levels in a community.

© 2015 Pearson Education, Inc. Producers are autotrophs that support all other trophic levels. Consumers are heterotrophs. Herbivores are primary consumers. Secondary consumers on land typically eat herbivores and in aquatic ecosystems typically eat zooplankton. Tertiary consumers typically eat secondary consumers. Quaternary consumers typically eat tertiary consumers Trophic structure

© 2015 Pearson Education, Inc Trophic structure Detritivores derive their energy from detritus, the dead material produced at all the trophic levels. Decomposers are mainly prokaryotes (bacteria) and fungi and secrete enzymes that digest molecules in organic materials and convert them into inorganic forms in the process called decomposition.

© 2015 Pearson Education, Inc Food chains interconnect, forming food webs A more realistic view of the trophic structure of a community is a food web, a network of interconnecting food chains. A consumer may eat more than one type of producer, and several species of primary consumers may feed on the same species of producer. Some animals weave into the food web at more than one trophic level.

© 2015 Pearson Education, Inc Species diversity includes relative abundance and species richness Species diversity is defined by two components: 1.species richness, the number of species in a community, and 2.relative abundance, the proportional representation of a species in a community. A B

© 2015 Pearson Education, Inc Species diversity includes relative abundance and species richness Plant species diversity in a community often has consequences for the species diversity of animals. Species diversity also impacts pathogens. Diverse communities will be less impacted by host- specific pathogens. Low species diversity is characteristic of most modern agricultural ecosystems.

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37.11 SCIENTIFIC THINKING: Some species have a disproportionate impact on diversity Keystone species, defined as a species whose impact on its community is larger than its biomass or abundance indicates and that occupies a niche that holds the rest of its community in place. For example, in the tropics, figs bear fruit year around. In the dry season, this is the only food available for many species. If figs were removed from the forest, many fruit-eating animals would disappear; and this in turn would affect many other plants that depend upon these frugivores for pollination. So, the fig is key to the survival of the community.

© 2015 Pearson Education, Inc Disturbance Disturbances are events that damage biological communities and include storms, fires, floods, drought, and human activity. The disturbed area may be colonized by a variety of species, which gradually replace other species over time, in a process called ecological succession.

© 2015 Pearson Education, Inc Disturbance Primary succession begins in a virtually lifeless area with no soil. Examples: rubble left by a retreating glacier or fresh volcanic lava flows.

© 2015 Pearson Education, Inc Disturbance Secondary succession occurs when a disturbance destroys an existing community but leaves the soil intact. Examples: Wildfires Whenever human intervention (farming, logging, etc.) stops, secondary succession begins.

© 2015 Pearson Education, Inc CONNECTION: Invasive species Invasive species are organisms that have been introduced into non- native habitats by human actions and have established themselves at the expense of native communities. The absence of natural enemies often allows rapid population growth of invasive species /the-threat-of-invasive- species/?tag=contentBody;cbsCarouselhttp:// /the-threat-of-invasive- species/?tag=contentBody;cbsCarousel

© 2015 Pearson Education, Inc CONNECTION: Invasive species Examples of invasive species include the deliberate introduction of rabbits into Australia and cane toads into Australia.