Chapter 4Ecosystems and Living Organisms

Overview of Chapter 4EvolutionNatural SelectionDomains and KingdomsBiological CommunitiesPrimary & Secondary SuccessionSymbiosisMutualism, Commensalism, ParasitismPredation & CompetitionResource PartitioningKeystone SpeciesSpecies Richness & Community Stability

EvolutionThe cumulative genetic changes that occur in a population of organisms over timeCurrent theories were proposed by Charles Darwin, a 19th century naturalistEvolution occurs through natural selectionNatural SelectionIndividuals with more favorable genetic traits are more likely to survive and reproduceFrequency of favorable traits increase in subsequent generations

Natural SelectionBased on four observations about the natural worldOverproductionEach species produces more offspring than will survive to maturityVariationIndividuals in a population exhibit variationLimits on Population GrowthResource limitations will keep population in checkDifferential Reproductive SuccessIndividuals with most favorable traits are more likely to reproduce

Natural SelectionDarwins finches exemplified the variation associated with natural selection

Domains and Kingdoms of Life

Biological CommunitiesCommunities vary greatly in size and lack precise boundariesThey are often nestled within each other

SuccessionThe process where a community develops slowly through a series of speciesEarlier species alter the environment in some way to make it more habitable by other speciesAs more species arrive, the earlier species are outcompeted and replacedTwo types of successionPrimary successionSecondary succession

Primary SuccessionSuccession that begins in a previously uninhabited environmentNo soil is present!Ex: bare rocks, cooled lava fields, etc.General Succession PatternLichen secrete acids that crumble the rock (soil begins to form)

Lichen mosses grasses shrubs forests

Primary SuccessionBare rock with lichenGrasses and shrubsForest community123

Secondary SuccessionSuccession that begins in an environment following destruction of all or part of the earlier communityEx: abandoned farmland, open area after fireDoes NOT follow primary succession!Even though name may imply this Generally occurs more rapidly than primary succession

Secondary Succession of an abandoned farm field in North Carolina

Interactions Among OrganismsSymbiosisAn intimate relationship between members of 2 or more speciesParticipants may be benefited, harmed or unaffected by the relationshipResults of coevolution is the interdependent evolution of two interacting species. Flowering plants and their animal pollinators have a symbiotic relationship that is an excellent example of coevolution. Three types of symbiosisMutualismCommensalismParasitism

MutualismSymbiotic relationship in which both members benefitEx: Mycorrihzal fungi and plant rootsFungus grows around and into roots providing roots with otherwise unavailable nitrogen from soilRoots provide fungi with food produced by photosynthesis in the plantLeft: root growth without fungiRight: root growth with fungi

CommensalismSymbiotic relationship where one species benefits and the other is neither harmed nor helpedEx: epiphytes and tropical treesEpiphytes anchors itself to the tree, but does not take nutrients from the treeEpiphyte benefits from getting closer to sunlight, tropical tree is not affected

ParasitismSymbiotic relationship in which one species is benefited and the other is harmedParasites rarely kill their hostsEx: Varroa mites and honeybeesMites live in the breathing tubes of the bees, sucking their blood and weakening them

PredationThe consumption of one species by anotherMany predator-prey interactionsMost common is pursuit and ambushPlants and animals have established specific defenses against predation through evolution

Pursuit and AmbushPursuing prey simply means chasing it down and catching itEx: Day gecko and spider (see picture)Ambush is when predators catch prey unawareCamouflageAttract prey with colors or light

Plant Defenses Against PredationPlants cannot flee predatorsAdaptationsSpikes, thorns, leathery leaves, thick waxProtective chemicals that are poisonous or unpalatable

Animal Defenses Against PredationFleeing or runningMechanical defensesEx: quills of porcupines, shell of turtlesLiving in groupsCamouflageChemical defenses- poisonsEx: brightly colored poison arrow frog

CompetitionInteraction among organisms that vie for the same resource in an ecosystemIntraspecificCompetition between individuals in a populationInterspecific Competition between individuals in 2 different species

Ecological NicheThe totality of an organisms adaptations, its use of resources, and the lifestyle to which it is fittedTakes into account all aspect of an organisms existencePhysical, chemical, biological factors needed to surviveHabitatAbiotic components of the environmentEx: Light, temperature, moisture

Ecological NicheFundamental nichePotential idealized ecological niche Realized nicheThe actual niche the organism occupiesEx: Green Anole and Brown Anole

Ecological NicheGreen Anole and Brown AnoleFundamental niches of 2 lizards initially overlappedBrown anole eventually out-competed the green anole- reduced the green anoles realized niche

Limiting ResourcesAny environmental resource that, because it is scarce or at unfavorable levels, restricts the ecological niche of an organism

Interspecific Competition

Competitive Exclusion & Resource PetitioningCompetitive ExclusionOne species excludes another from a portion of the same niche as a result of competition for resourcesResource PartitioningCoexisting species niche differ from each other in some way

Keystone SpeciesA species that exerts profound influence on a communityMore important to the community than what would be expected based on abundanceThe dependence of other species on the keystone species is apparent when the keystone species is removedProtecting keystone species is a goal to conservation biologists

Species RichnessThe number of species in a communityTropical rainforests = high species richnessIsolated island = low species richnessRelated to the abundance of potential ecological niches

Ecosystem ServicesImportant environmental benefits that ecosystems provide, such as:Clean air to breatheClean water to drinkFertile soil in which to grow crops

*Gray wolf. The reintroduction of gray wolves (Canis lupus) has caused many changes in plant and wildlife populations in Yellowstone National Park. **It occurred to Darwin that, from one generation to the next, inherited traits favorable to survival in a given environment would be preserved, whereas unfavorable ones would be eliminated. The result would be adaptation, evolutionary modification that improves the chances of survival and reproductive success of the population in its environment.**Figure4-1Darwin's finches. Note the various beak sizes and shapes, which are related to a species' diet. Since 1973 the long-term research of Peter and Rosemary Grant and others has verified and extended Darwin's observations on the evolution of Galpagos finches by natural selection. Beginning in the 1930s and 1940s, biologists combined the principles of genetics with Darwin's theory of natural selection. The result was a unified explanation of evolution known as the modern synthesis. (In this context, synthesis refers to combining parts of several previous theories to form a unified whole.) **The organisms in a community are interdependent in a variety of ways. Species compete with one another for food, water, living space, and other resources. (Used in this context, a resource is anything from the environment that meets a particular species' needs.) Some organisms kill and eat other organisms. Some species form intimate associations with one another, whereas other species seem only distantly connected.

there are communities within communities. A forest is a community, but so is a rotting log in that forest *Ecologists initially thought that succession inevitably led to a stable and persistent community, such as a forest, called a climax community. But more recently, the traditional view has fallen out of favor. The apparent stability of a climax forest is probably the result of how long trees live relative to the human life span. Mature climax communities are not in a state of permanent equilibrium but rather in a state of continual disturbance. Over time, a mature community changes in species composition and in the relative abundance of each species, despite its overall uniform appearance.*Although the details vary from one site to another, on bare rock, lichens are often the most important element in the pioneer communitythe initial community that develops during primary succession. *Figure4-4Primary succession on glacial moraine. During the past 200 years, glaciers have retreated in Glacier Bay, Alaska. Although these photos were not taken in the same location, they show some of the stages of primary succession on glacial moraine (rocks, gravel, and sand deposited by a glacier). (a)After the glacier's retreat, lichens initially colonize the barren landscape, then mosses and small shrubs. (Wolfgang Kaehler) (b)At a later time, dwarf trees and shrubs colonize the area. (Glenn N. Oliver/Visuals Unlimited) (c)Still later, spruces dominate the community. (Wolfgang Kaehler)**During the summer of 1988, wildfires burned approximately one-third of Yellowstone National Park. This natural disaster provided a chance for biologists to study secondary succession in areas that were once forests. After the conflagration, gray ash covered the forest floor, and most of the trees, though standing, were charred and dead. Secondary succession in Yellowstone has occurred rapidly. Less than one year later, in the spring of 1989, trout lily and other herbs had sprouted and covered much of the ground. Ten years after the fires, a young forest of knee-high to shoulder-high lodgepole pines had dominated the area, and Douglas fir seedlings were also present. Biologists continue to monitor the changes in Yellowstone as secondary succession proceeds.****Figure4-9Parasitism. Tiny tracheal mites live in the breathing tubes of honeybees and suck their blood, weakening and eventually killing them. These mites have devastated many of North America's wild and domestic honeybee populations.

When a parasite causes disease and sometimes the death of a host, it is known as a pathogen. **Figure4-10Predation. A Madagascar day gecko has just caught a spider. Unlike most geckos, the Madagascar day gecko is diurnal (active during the day). Native to Madagascar, the day gecko spends most of its time in trees, where it blends into the foliage*Plants cannot escape predators by fleeing, but they possess adaptations that protect them from being eaten. The presence of spines, thorns, tough leathery leaves, or even thick wax on leaves discourages foraging herbivores from grazing. Other plants produce an array of protective chemicals that are unpalatable or even toxic to herbivores.

How many of you have contracted poison ivy?**Competition occurs when two or more individuals attempt to use an essential common resource such as food, water, shelter, living space, or sunlight. Resources are often in limited supply in the environment, and their use by one individual decreases the amount available to others. *Because the ecological niche describes an organism's place and function within a complex system of biotic and abiotic factors, it is difficult to define precisely.

the niche includes the local environment in which an organism livesits habitat. *The ecological niche of an organism may be much broader potentially than it is in actuality. Put differently, an organism is potentially capable of using much more of its environment's resources or of living in a wider assortment of habitats than it actually does. The potential, idealized ecological niche of an organism is its fundamental niche, but various factors such as competition with other species usually exclude it from part of its fundamental niche. The lifestyle an organism actually pursues and the resources it actually uses make up its realized niche.*Figure4-13Effect of competition on an organism's realized niche. (a)The green anole (Anolis carolinensis) is native to Florida. (Ed Kanze/Dembinsky Photo Associates) (b)The brown anole (Anolis sagrei) was introduced in Florida. (Robert Clay/Visuals Unlimited) (c)The fundamental niches of the two lizards initially overlapped. Species 1 is the green anole, and species 2 is the brown anole (d)The brown anole out-competed the green anole, restricting its niche.*Figure4-14Limiting resource. An organism is limited by any environmental resource that exceeds its tolerance or is less than the required minimum.

*Figure4-15Interspecific competition. Data for graphs adapted from Gause, G. F. The Struggle for Existence. Baltimore: Williams & Wilkins (1934). (a)Gause studied competition between two species of Paramecium, a unicellular protist. (Michael Abbey/Photo Researchers, Inc.) (b)How a population of P. aurelia grows in separate culture (in a single-species environment). (c)How a population of P. caudatum grows in separate culture. (d)How these two species grow in a mixed culture, in competition with each other. P. aurelia outcompetes P. caudatum and drives it to extinction. (b, c, d, adapted from G. F. Gause)*Resource partitioning may include timing of feeding, location of feeding, nest sites, and other aspects of an organism's ecological niche.

Figure4-16Resource partitioning. Robert MacArthur's study of five North American warbler species is a classic example of resource partioning. Although it initially appeared that their niches were nearly identical, MacArthur determined that individuals of each species spend most of their feeding time in different parts (brown areas) of the spruces and other conifer trees they frequent. They also move in different directions through the canopy, consume different combinations of insects, and nest at slightly different times. (Adapted from R. H. MacArthur Population Ecology of Some Warblers of Northeastern Coniferous Forests. Ecology, vol. 39 (1958).) *One example of a keystone species is a top predator such as the gray wolf, which was discussed in the chapter introduction. Where wolves were hunted to extinction, the populations of deer, elk, and other herbivores increased explosively. As these herbivores overgrazed the vegetation, many plant species that could not tolerate such grazing pressure disappeared. Many smaller animals such as insects were lost from the ecosystem because the plants that they depended on for food were now less abundant. Thus, the disappearance of the wolf resulted in an ecosystem with considerably less biological diversity. *Species richness is usually greater at the margins of adjacent communities than in their centers. This is because an ecotonea transitional zone where two or more communities meetcontains all or most of the ecological niches of the adjacent communities as well as some niches unique to the ecotone. The change in species composition produced at ecotones is known as the edge effect.

Species richness is reduced when any one species enjoys a decided position of dominance within a community because it may appropriate a disproportionate share of available resources, thus crowding out other species. Ecologist James H. Brown and colleagues of the University of New Mexico have studied species competition and diversity in long-term experiments conducted since 1977 in the Chihuahuan desert of southeastern Arizona. In one experiment, the scientists enclosed their study areas with fencing and then cut holes in the fencing to allow smaller rodents to come and go but to exclude the larger kangaroo rats. The removal of three dominant species, all kangaroo rats, from several plots resulted in an increased diversity of other rodent species. This increase was attributed to less competition for food and to an altered habitat because the abundance of grass species increased dramatically after the removal of the kangaroo rats.*Conservationists maintain that ecosystems with greater species richness better supply such ecosystem services than ecosystems with lower species richness.

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