Download
1 / 19
190 likes | 400 Vues
Biology Review Darwin’s Finches : Natural S election and Adaptation Energy Flow through an Ecosystem : Food chains, webs, and pyramids. Bio review: Natural Selection and Ecosystems. Bio Review : Natural Selection and Ecosystems.
E N D
Biology Review Darwin’s Finches: Natural Selection and Adaptation Energy Flow through an Ecosystem: Food chains, webs, and pyramids Bio review: Natural Selection and Ecosystems
Bio Review: Natural Selection and Ecosystems • All of Earth’s inhabitants are woven together into a complex web of relationships. Removing one species from an environment can have affects on the whole system. Ecologyis the study of the interactions of living organisms with one another and with their physical environment (soil, water, climate, etc.) • Anecosystem, or ecological system, consists of a community and all the physical aspects of it’s habitat; the living and nonliving parts (such as soil, water, and weather).
Bio Review: Natural Selection and Ecosystems • The flow of energy is the most important factor that controls what kind of organisms live in an ecosystem and how many organisms the ecosystem can support. • Organisms that first capture and convert the energy from sunlight into usable food are called producers and include plants, some kinds of bacteria, and algae. • All other organisms in an ecosystem are consumers. Consumersare those organisms that consume plants or other organisms to obtain their energy. • Animals that eat plants or other animals are consumers.
Bio Review: Natural Selection and Ecosystems • Ecologists study how energy moves through an ecosystem by assigning organisms in that ecosystem to a specific level called a trophic level. • In the chart at right, energy moves from one trophic level to the next; from sunlight to producer to primary consumer and on down the chain. • The lowest trophic level of an ecosystem is occupied by the producers (plants, algae, bacteria) which take sunlight and convert it to food energy by photosynthesis. • Producersuse the energy of the sun to build energy rich carbohydrates, the food the plants subsists on.
Bio Review: Natural Selection and Ecosystems • At the second trophic level we have herbivores. Herbivores are animals that eat plants or other primary producers. • These organisms that consume producers are called primary consumers. Cows and horses, as well as caterpillars and ducks, field mice and moose; are all examples of primary consumers. • .At the third trophic level we have secondary consumers. Secondary consumersare animals that eat other animals. • These animals are called carnivoresbecause they consume other animals. • In the diagram at right, the mouse is a primary consumer because it feeds off the producer. The snake is a secondary consumer because it feeds off the mouse.
Bio Review: Natural Selection and Ecosystems • At the third trophic level in our food chain we have secondary consumers;animals such as tigers, wolves, and snakes who are carnivores; consuming other animals. • Some animals, such as bears, eat both plants and other animals. They are both herbivores and carnivores together, called an omnivore.
Bio Review: Natural Selection and Ecosystems • In every ecosystem there is a special class of consumers called detritivores. • Detritivoresare organisms which obtain their energy from organic wastes and dead bodies produced at all trophic levels. • They are the decomposers of the food chain; assisting in breaking down dead organisms and helping return their nutrients to the Earth. • These decomposers include worms, bacteria, fungi and some insects. Their niche in the ecosystem is to return the nutrients from decaying dead organisms back to the soil to provide nutrients for the producers.
Bio Review: Natural Selection and Ecosystems • Many ecosystems contain a fourth trophic level made up of carnivores that consume other carnivores called tertiary consumers. • The hawk that eats a snake is a tertiary consumer unless a larger bird of prey eats the hawk. The tertiary consumer is the topmost point of the food chain. Nothing consumes a tertiary consumer except for decomposers after the organism dies. The decomposers complete the cycle returning the food energy back to nutrients for the producer level. • Very rarely do ecosystems contain more than 4 trophic levels.
In most ecosystems, energy does not simply follow one path on one level because organisms often feed at many different levels of a food chain. • This creates a complicated interconnected group of food chains called a food web. • In the diagram at right, the producers are the grass and plants and the rabbits, squirrels, mice birds and insects. The fox, hawk and snake are secondary consumers, eating the rabbits and squirrels. • The fox, hawks and snakes are all also examples of tertiary consumers because they are the final stop on the food web. Only with their death and decay does their energy return to the system.
Darwin and Natural Selection Darwin and Natural Selection
Darwin and Natural Selection • In 1859, in London, an English naturalist named Charles Darwin proposed a reasonable theory that explained that species evolved over time. • During Darwin’s voyage around the globe, he found evidence that challenged the traditional beliefs that species were unchanging. As Darwin travelled and collected evidence, he found fossils that suggested that creatures were slowly changing over time. • Darwin’s key breakthroughs came when he visited the Galapagos islands off the coast of South America. Darwin noticed that many animals and plants resembled those from the South American coast 1000 miles away.
Darwin and Natural Selection Darwin came to a key conclusion: • Individuals that have physical or behavioral traits that better suit their environment • are more likely to survive • will reproduce more successfully than those without the traits. • Darwin called this differing rate of survival-reproduction natural selection. ____________________________________________ • Natural selection is the process by which individuals that have favorable variations and are better adapted to their environmentsurvive and reproduce more successfully than less well adapted individuals do. _________________________________________ • In time, the number of individuals that carry favorable characteristics that are inherited (passed along to them) will increase in population because of this adaptation.This process is called evolution. • An adaptation is an inherited trait that has become common in a population because the trait provides a selective advantage.
Darwin and Natural Selection The process of natural selection is driven by 4 important factors: 1: All populations have genetic variation: In any population, there is an array of individuals that differ slightly from one another in genetic makeup. 2: The environment presents challenges to successful reproduction. Naturally, an organism that does not survive to reproduce or whose offspring die before the offspring can reproduce does not pass on it’s genes to future generations. 3: Individuals tend to produce more offspring than the environment can support. Thus individuals of a population often compete with each other for food, shelter, and breeding partners. Those best suited to attract a mate, have a better chance to breed and pass on genes. 4: Individuals that are better able to cope with the challenges presented by their environment tend to leave more offspring.
Darwin and Natural Selection • Darwin collected 31 specimens of finches from three islands when he visited the Galapagos Islands. In all, he collected 9 distinct species, all very similar to one another except for their bills. • Two ground finches with large bills feed on seeds that crush in their beaks, • while two with narrower bills eat insects. • One finch is a fruit eater, • one picks insects out of cactus, • while yet another creeps up on seabirds and uses it’s sharp beak to drink their blood.
Darwin and Natural Selection • Darwin suggested the nine species of finches all developed from an original ancestral species. Changes occurred as different populations adapted to different food sources. • In years when food was not as plentiful, those finches that had adaptations that aided them to get food in their immediate location survived and bred where their counterparts perished.
Darwin and Natural Selection • The formation of species occurs in stages. Natural selection favors changes that increase reproductive success. • Therefore, a species molded by natural selection has an improved “fit” to it’s environment. • The accumulation of differences between groups is called divergence. Divergence leads to the formation of new species. • Biologists call the process by which new species form speciation.
Darwin and Natural Selection • Separate populations of a single species often live in several different kinds of environments. • In each environment, natural selection acts upon the population. • Natural selection results in offspring that are better suited to that environment. • If the environments differ enough, separate populations of the same species can become very dissimilar
Darwin and Natural Selection • Over time, populations of the same species that differ genetically because of adaptations to different living conditions become what scientists call a subspecies. • The members of a newly formed subspecies have taken the first step toward speciation. • Eventually the subspecies become so different that they can nolonger interbreed successfully. • When these subspecies get to this point where they can not interbreed; Biologists than consider them a new separate species.
