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Transcript
Community Structure and Biodiversity Chapter 40 Ecosystems Ecosystems vary in size. They can be as small as a puddle or as large as the Universe itself. Any group of living and nonliving things interacting with each other can be considered as an ecosystem. Within each ecosystem, there are habitats which may also vary in size. A habitat is the place where a population lives. A population is a group of living organisms of the same kind living in the same place at the same time. All of the populations interact and form a community. The community of living things interacts with the non-living world around it to form the ecosystem. The habitat must supply the needs of organisms, such as food, water, temperature, oxygen, and minerals. If the population's needs are not met, it will move to a better habitat. Two different populations can not occupy the same niche at the same time, however. Community All the populations that live together in a habitat Habitat is the type of place where individuals of a species typically live Type of habitat shapes a community’s structure Factors Shaping Community Structure Climate and topography Available foods and resources Adaptations of species in community Species interactions Arrival and disappearance of species Physical disturbances Niche Sum of activities and relationships in which a species engages to secure and use resources necessary for survival and reproduction Realized & Fundamental Niches Fundamental niche Theoretical niche occupied in the absence of any competing species Realized niche Niche a species actually occupies Realized niche is some fraction of the fundamental niche Species Interactions Most interactions are neutral; have no effect on either species Commensalism helps one species and has no effect on the other Mutualism helps both species Species Interactions Interspecific competition has a negative effect on both species Predation and parasitism both benefit one species at a cost to another Symbiosis Living together for at least some part of the life cycle Commensalism, mutualism, and parasitism are forms of symbiosis Mutualism Both species benefit Many examples in nature Some mutualisms are obligatory; partners depend upon each other Mycorrhizae Obligatory mutualism between fungus and plant root Fungus supplies mineral ions to root Root supplies sugars to fungus Yucca and Yucca Moth Example of an obligatory mutualism Each species of yucca is pollinated only by one species of moth Moth larvae can grow only in that one species of yucca Competition Interspecific - between species Intraspecific - between members of the same species Intraspecific competition is most intense Forms of Competition Competitors may have equal access to a resource; compete to exploit resource more effectively One competitor may be able to control access to a resource, to exclude others Competitive Exclusion Principle When two species compete for identical resources, one will be more successful and will eventually eliminate the other Competitive Exclusion Expt Paramecium caudatum Paramecium aurelia Resource Partitioning Apparent competitors may actually have slightly different niches Species may use resources in a different way or time Minimizes competition and allows coexistence Predation Predators are animals that feed on other living organisms Predators are free-living; they do not take up residence on their prey Coevolution Natural selection promotes traits that help prey escape predation It also promotes traits that make predators more successful at capturing prey Predators and Prey Density • I represents abundant prey; II represents a leveling off as predators consume their fill; III shows prey levels dropping off and predator response slowing Variation in Cycles An association in predator and prey abundance does not always indicate a cause and effect relationship Variations in food supply and additional predators may also influence changes in prey abundance Species Interactions • Canadian lynx (dashed lines) versus snowshoe hares (solid line) Prey Defenses Camouflage Warning coloration Mimicry Predator Responses Any adaptation that protects prey may select for predators that can overcome that adaptation Prey adaptations include stealth, camouflage, and ways to avoid chemical repellents Parasitism Parasites drain nutrients from their hosts and live on or in their bodies Natural selection favors parasites that do not kill their host too quickly Types of Parasites Microparasites Macroparasites Social parasites Parasitoids Biological Controls Parasites and parasitoids are commercially raised and release in target areas as biological controls An alternative to pesticides Must be carefully managed to not upset natural balances Study: Cowbirds Brown-headed cowbirds evolved in the Great Plains region of the U.S., living as commensalists with bison As they migrated along with the bison, the cowbirds learned to lay eggs in the nests of other birds Cowbird hatchlings push the “host” bird eggs out of the nest Today, cowbirds parasitize some 15 species of birds End for now! The exam will cover material to this point! 80% on material since the last exam 20% will include material from the beginning of the class - general principles which you should know Succession Change in the composition of different species over time Pioneer Species Species that colonize barren habitats - first come, first served! Lichens, small plants with brief life cycles Improve conditions for other species who then replace them lose out to better adapted species who themselves lost out to even better adapted species. Types of Succession Primary succession new environments Secondary succession communities were destroyed or displaced Following hurricanes After the tsunami Climax Community Eventually we arrive at the climax community Stable array of species that persists relatively unchanged over time Succession does not always move predictably toward a specific climax community; other stable communities may persist Multiple outcomes. Cyclic Changes DYNAMIC and STABLE Cyclic, nondirectional changes also shape community structure Tree falls cause local patchiness in tropical forests Fires periodically destroy underbrush in sequoia forests Community Instability REMEMBER Disturbances can cause a community to change in ways that persist even if the change is reversed Keystone Species A species that can dictate community structure Removal of a keystone species can cause drastic changes in a community; can increase or decrease diversity… Lubchenco Experiment QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Periwinkles promote or limit diversity in different habitats Tidepools Rocks exposed at high tide Species Introductions Introduction of a nonindigenous species can decimate a community Just recently Hawaii has introduces Sea Stars to control sea weed WHY? There are; No natural enemies or controls Can outcompete native species Exotic Species Species that has left its home natural range and become established elsewhere Becomes part of its new community Can have beneficial, neutral, or harmful effects on a community… Kudzu in Georgia QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Kudzu in Georgia Quic kTime™ and a TIFF (Unc ompres sed) decompress or are needed to see this picture. Imported for erosion control No natural herbivores, pathogens, or competitors Grows over landscapes and cannot be dug up or burned out May turn out to have some commercial use for humans Caulerpa taxifolia QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Caulerpa taxifolia Researchers developed a hybrid, sterile strain of this green alga - for fish tanks. Somehow it was released into the wild, where it reproduces asexually - down the drain!!! Thrives in varying conditions and emits a toxin that poisons invertebrates and fishes Illegal to import the “aquarium” strain into the U.S. Rabbits in Australia QuickTi me™ and a TIFF ( Uncompressed) decompressor are needed to see thi s pi ctur e. Rabbits were introduced for food and hunting Without predators, their numbers soared Attempts at control using fences or viruses have thus far been unsuccessful QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Biodiversity The sum of all species occupying a specified area during a specified interval, past and present Diversity by Latitude Diversity of most groups is greatest in tropics; declines toward poles a) ant species b) breeding birds Why Are Tropical Species Rich? Resources are plentiful and reliable Species diversity is self-reinforcing Rates of speciation are highest in the tropics Surtsey: Volcanic Island Primary succession Distance Effect The farther an island is from a mainland, the fewer species. WHY? Closer islands receive more immigrants Species that reach islands far from mainland are adapted for long-distance dispersal and can move on Distance Effect Endangered Species A species that is extremely vulnerable to extinction Habitat loss is putting major pressure on more than 90 percent of the endemic species that now face extinction Conservation Biology Is a systematic survey of the full range of biological diversity Entails efforts to decipher biodiversity’s evolutionary and ecological origins Attempt to identify methods of maintaining and using biodiversity in ways that can benefit the human population Only real way to save the local ecosystem Sampling of Current Species Diversity Areas at Risk Preserving Biodiversity Requires identifying and protecting regions that support the highest levels of biodiversity It is possible to protect a habitat and still withdraw resources in a sustainable fashion - but based on human nature it is a risky practice!