APES Chapter 8 Notes Community Ecology: Structure, Species Interactions, Succession, and Sustainability General Types of Species Native species—species that normally live and thrive in a particular ecosystem Non-native, exotic or alien species— species that migrate into an ecosystem or are deliberately or accidentally introduced into an ecosystem humans. ◦ Ex: Africanized Bees, Zebra Mussels, Cane Toad, Kudzo. General Types of Species Indicator species—species that serve as early warnings that a community or ecosystem is being damaged. ◦ Birds are excellent indicators because they are found almost everywhere and respond very quickly to environmental change. ◦ Some amphibians are also classified as indicator species. General Types of Species Keystone species—species whose roles in an ecosystem are much more important than their abundance or biomass would suggest. They play pivotal roles in the structure, function, and integrity of an ecosystem. ◦ Ex: sea otters, wolves, elephants, great white shark, all pollinators. Species Interactions: Competition and Predation Members of species may be harmed by, benefit from , or by unaffected by the interaction. Competition Competition—Two organisms compete to obtain the same limited resource. ◦ Intraspecific—Members of same species competing for resources. ◦ Interspecific—Members of different species competing for resources. The more similar the competing species, the more intense the competition. Species compete in two ways: Interference—one species limits another’s access to some resource by direct contact, such as establishing a territory and defending it. Exploitation—occurs indirectly. Competing species have equal access to a specific resource but differ in how fast or efficiently they exploit it. Competition Competitive Exclusion Principle—No two species can occupy the same ecological niche in the same place at the same time. ◦ Less fit species may die out or evolve into a slightly different niche. Resource Partitioning Adaptations evolved to reduce or avoid competition. In Resource Partitioning species with similar needs use similar resources: ◦ 1. at different times (hunting: hawks-day, owls-night) ◦ 2. in different ways ◦ 3. in different places Resource Partitioning Overlapping Niche of 2 species creates competition Over time, species evolve and become specialized Fig. 8-9 p. 175; Refer to Fig. 7-13 p. 152 & Fig. 8-10 p. 175 Resource Partitioning Predation One species (predator) feeds directly on another species (prey). Predation Predators increase their chances by: ◦ ◦ ◦ ◦ ◦ Running fast Keen eyesight Hunting in packs Camouflage Humans have invented tools (weapons and traps) Predation Prey defend themselves against predators by: ◦ ◦ ◦ ◦ ◦ ◦ ◦ Run, swim or fly fast Keen eyesight or sense of smell Live in herds Protective shells or spines Camouflage Thick bark Thorns Predation ◦ Chemicals-poisonous, irritating, foul smelling, bad tasting ◦ Warning coloration-so predators know they are poisonous or bad tasting ◦ Mimicry-taking on the appearance of another organism that may be very poisonous Symbiotic Relationships Symbiosis—Close, physical relationship between two different species. At least one species derives benefit from the interaction. ◦ Parasitism—One organism (parasite) living in or on another organism (host), from which it derives nourishment. Parasite benefits and host is harmed. Ectoparasites—Live on host’s surface. Fleas Endoparasites—Live inside host. Tapeworms Symbiotic Relationships Commensalism—One organism benefits, while the other is unaffected. ◦ Remoras and Sharks Mutualism—Both species benefit. Obligatory in many cases as neither can exist without the other. ◦ Mycorrhizae Parasitism Mutualism Commensilism Community Structure 4 Characteristics: ◦ 1. Physical appearance: size, stratification, and distribution of populations. ◦ 2. Species diversity or richness: number of different species. ◦ 3. Species abundance: number of individuals of each species. ◦ 4. Niche structure: number of ecological niches. Community Structure: Appearance and Species Diversity Fig. 8-2 p. 166 Stratification Species diversity Niche structure Edge effects Three Factors Affecting Biodiversity Latitude(terrestial)- the closer to the equator, the higher the biodiversity ◦ Highest species diversity in tropics; lowest in polar regions Ants Depth(aquatic)- biodiversity increases with depth to about 2000 m then begins its decrease Pollution- as levels increase, biodiversity decreases Birds 25 20 20 15 15 10 10 5 5 Coast 0 0 Fig. 8-3 p. 167 25 Snails Species diversity 2,000 Deep Sea 4,000 Depth (meters) 0 6,000 0 Tube worms Coast 2,000 Deep Sea 4,000 Depth (meters) 6,000 Island Biodiversity © 2004 Brooks/Cole – Thomson Learning Rate of immigration or extinction High Theory of Island Biodiversity-the number of species found on an island is determined by: 1. Species immigration Low Equilibrium number Number of species on island Immigration (a) and extinction rates Immigration- movement of organisms into a place Emigration- movement of organisms out of a place 2. Species extinction Communities in Transition Ecological Succession—the gradual and fairly predictable change in species composition of a given area over a period of time. Climax community—Stable, longlasting community, primarily determined by climate. Succession Primary Succession—Begins with bare mineral surfaces or water and total lack of organisms. Secondary Succession—Begins with disturbance of an existing ecosystem. ◦ Much more commonly observed. Primary Succession Terrestrial Primary Succession ◦ Pioneer Community: Collection of organisms able to colonize bare rock (i.e. lichens, mosses). ◦ Lichens help break down rock, and accumulate debris helping to form a thin soil layer. ◦ Soil layer begins to support small life forms. Terrestrial Primary Succession Aquatic Primary Succession Except for oceans, most aquatic systems are considered temporary. All aquatic systems receive inputs of soil particles and organic matter from surrounding land. ◦ Gradual filling of shallow bodies of water. Roots and stems below water accumulate more material. Wet soil established. Aquatic Primary Succession Secondary Succession Occurs when an existing community is disturbed or destroyed. With most disturbances, most of the soil remains, and many nutrients necessary for plant growth may be available for reestablishment of the previous ecosystem. ◦ Nearby undamaged communities can serve as sources of seeds and animals. Tends to be more rapid than primary growth. Terrestrial Secondary Succession Secondary Succession of a Beaver Pond Modern Concepts of Succession and Climax As settlers changed “original” ecosystems to agriculture, climax communities were destroyed. ◦ Many farms were abandoned, and land began to experience succession. Ecologists began to recognize there was not a fixed, pre-determined community. ◦ Only thing differentiating climax community from successional community is time scale.