Ecological Change - AP Environmental Science

Today, 99.9% of all species that have ever existed on Earth are extinct. We are currently in the middle of the 6th mass extinction. The dinosaurs went extinct during the 5th, the Cretaceous, about 65 million years ago.

The correct response is Milankovitch cycles. This theory describes how the orbit, tilt, and axis of the Earth operate on a 100,000 year cycle that cause the Earth to be further from the sun. As the Earth gets farther from the sun, it can trigger an ice age. The theory is aptly named after the man who discovered it. The El Nino and La Nina events occur on a much shorter time scale and have nothing to do with ice ages.

The Wallace Line, named for Alfred Russel Wallace, is a boundary that separates Asia and Australia. Wallace noticed that the some of the islands in this region contained species common to Australia and some contained species common to Asia, none of which would have crossed the open water in between the continents. Wallace correctly reasoned that this meant that sea levels were once much lower, an artifact of the last glacial maximum.

Primary succession commonly occurs after a volcanic eruption or a glacier recedes, because these areas have been stripped of organic matter. Primary succession is the process by which pioneer species colonize an area otherwise uninhabitable for plant life and generate nitrogen for other plant communities.

Primary succession is characterized by a total loss of biomass and soil from the ecosystem or a beginning lack thereof. Land that has been covered by a glacier or under the seabed will be devoid of soil, much like the exposed bedrock seen after the Dust Bowl or the Mount St. Helens eruption. By contrast, a forest fire can typically be characterized as secondary succession because the soil remains intact and the ecosystem can typically recover much quicker because of that fact.

Primary succession is characterized by plants establishing themselves in areas that were initially devoid of soil (usually bedrock). Grasses establishing themselves on a newly-formed island that is mostly bedrock is the best fit for this definition.

Primary succession is characterized by pioneer species establishing themselves in areas that are predominantly bedrock and devoid of organic material. The formation of organic material in these areas typically occurs with the accumulation of wind-carried soil erosion, nutrients deposited by flowing bodies of water, and erosion of bedrock. Wildlife populations are also a significant contributor of soil nutrients, with feces being rich in both nitrogen and phosphorus. In contrast, pre-existing nitrogen-fixing plants (or any pre-existing plant communities) are uncommon to nonexistent in an area with no established soil system.

Succession is a structural change in a community and its nonliving environment over time. Community changes alter the ecosystem in ways that favor competitors, and species replace one another in a somewhat predictable manner until a stable community is reached. Examples are the changes that occur after volcanos erupt and forest fires. Adaptation is a characteristic of an organism that helps it survive and reproduce in a particular environment. The differential survival and reproduction on the basis of genetic differences among individuals is termed natural selection. Evolution is any change in the proportions of different genotpyes in a population from one generation to the next. Mutation is a change in the base sequence of DNA in a gene that is usually significant enough to alter the appearance or function of the organism.

Primary succession begins with no soil. Eventually, lichens and mosses grow and die, which creates some soil. Small plants such as grasses and some ferns use this soil and grow. It would be very unlikely for a tree to grow in this environment.

Primary succession is, by definition, the establishment of living communities in areas where life had not previously existed. A waterfront that is barren rock does not initially have the potential to support life until mineral and soil deposits allow new plant communities to establish themselves. The other answers are not correct because plant communities already exist in these examples, which is not characteristic of primary succession.

The correct response is primary succession. This represents the initial growth following a disturbance, such as a volcanic eruption. While pioneering succession involves the colonization of a location that has been affected by ecological damage, primary succession is a better answer since it refers specifically to vegetation colonizing a location in which soil is absent (such as after a volcanic eruption). Climax succession is not a term used to describe species succession over time, rather, a climax community is one that, over time, has reached a steady state.

Grasses are also early successional species because they reproduce quickly and require minimal diversity of resources to survive. Their quick reproduction and growth also categorizes them as R-selected species.

The correct response is secondary succession. This process occurs following some disturbance when the seedbank is still intact. For example, after an earthquake or fire all the vegetation is removed but there are still seeds in the ground. This would be an example of secondary succession because the vegetation can still recover. This is different from primary succession - primary succession occurs when there is no prior vegetation on the landscape and there is no seedbank. Tertiary and quaternary succession are made up terms.

Ecological succession is the change of the structure of an environment overtime. The environment can be changed due to a sudden disruption or small changes overtime. These changes can take place over a few decades or millions of years.

Lichens are able to survive on bare rocks, with very few nutrients available. As a result, they are one of the first organisms to colonize an area of primary succession, where they usually break down rocks over time to form the base of soil in the new habitat.

Prokaryotes are simple, single-celled organisms which lack membrane bound nuclei. They developed before any of the other listed answer choices, as all of the other listed answer choices are multi-celled organisms that developed from prokaryotes.

Sharks and dolphins are not closely related and evolved their streamlined shapes separately from one another. This is an example of convergent evolution, in which two species that are not closely related evolve similar characteristics. Divergent evolution is the opposite.

Evolution is a process of orderly and gradual change or development. The theory that all living species have developed as a result of changes in their genetic material over time. Evolution is a change in the proportions of different genotypes in a population from one generation to the next. The characteristic of an organism that helps it survive and reproduce in a particular environment is adaptation. Variability is the range of alterations present in a genome, such as the number of diverse alleles of a specific gene. The differences in reproductive output among individuals of a population, normally as a result of genetic differences is differential reporduction. Gene flow is the movement of alleles from one population to another owing to the migration of individual organisms.

Coevolution occurs when one species evolves at the same time as another related species. Often one of these species is a prey-animal that adapts or develops traits that increase survival and reproductive rates. The predator that hunts the prey is required to adapt, increasing favorable traits that allow them, once again, to be able to hunt the prey. Coevolution is a type of evolution, but is not a cause of evolution.

Speciation is a general term referring to evolutionary processes leading to the creation of a new species. This occurs when a parent species is divided into at least two groups that are isolated from each other. These isolated groups adapt and mutate separately until they are no longer compatible for breeding.

Evolution caused by geographic isolation takes place when a species is separated into multiple groups due to a physical barrier of some kind (like a rock fall blocking a previously open canyon).

Evolution due to reproductive isolation occurs when members of two species that were previously able to produce viable offspring cannot due to changes in physical characteristics or behaviors. These species can procreate, but their offspring are not viable (able to reproduce).