15.1 Ecological Succession

Horatio is studying an abandoned farm in his community. The land of the farm once supported fields of corn, beans, and spinach, as well as pastures for cattle and sheep. Today, the farmland is covered in a variety of grasses, shrubs, and small trees, and is home to rabbits, gophers, and other small animals. The evidence most strongly supports which of the following conclusions?

• The farmland is undergoing primary succession, which eventually will restore the original climax community.

• The farmland is undergoing secondary succession, which eventually will restore the original climax community.

• The farmland is undergoing secondary succession, which may or may not restore the original climax community.

• The farmland has undergone primary succession, and is now a stable climax community.

Answer explanation

The farmland is undergoing secondary succession because it was previously cultivated and is now reverting to a natural state. This process may or may not lead to the restoration of the original climax community.

Tags

NGSS.MS-LS2-4

Julie is studying the clearing of tropical rainforests in Brazil. The land is being cleared for farming, but the poor quality of the soil limits the productivity of the farms. Julie is trying to evaluate the claim that if one of the new farms is abandoned, an ecosystem that is similar to the original rainforest will return to the land. Which statement is most useful for Julie to cite in her evaluation of this claim?

• Secondary succession always restores the original climax community.

• Primary succession always restores the original climax community.

• Secondary succession may not restore the original climax community when the soil structure and microbiome is damaged.

• Primary succession never restores the original climax community due to the local extinction of the original species.

Answer explanation

The correct choice highlights that secondary succession may not restore the original ecosystem if the soil and microbiome are damaged, which is relevant to Julie's evaluation of rainforest recovery after farming abandonment.

The diagram shows the communities of plants during a process of secondary succession. The process leads to a climax community of a forest of oaks, hickory, and other hardwood trees.

Which statement best describes the impact on animal communities during this process?

• The animal communities remain about the same, and do not undergo succession.

• The animal communities become smaller in population size and less diverse over time.

• The animal communities become larger in population size and more diverse over time.

• The animal communities become larger in population size and maintain the same diversity over time.

Answer explanation

During succession, animal communities typically increase in both population size and diversity as new species colonize and establish themselves, leading to a more complex ecosystem.

Tags

NGSS.MS-LS2-4

A wildfire burns a region of a healthy grassland ecosystem. Which climax community will most likely arrive in the burned region due to ecological succession?

• A grassland ecosystem that is very similar to the original ecosystem

• A community of pioneer species, such as lichens

• A grassland ecosystem of plants only that does not contain animals

• A patchwork of grasslands, hardwood forest, and other ecosystems

Answer explanation

After a wildfire, ecological succession typically leads to a recovery of the original ecosystem. Thus, a grassland ecosystem similar to the original will most likely develop, rather than pioneer species or a community lacking animals.

Tags

NGSS.MS-LS2-4

Ecological succession impacts populations and communities over time. When succession occurs, pioneer species move in and impact the ecosystem.

Which property distinguishes pioneer species from those that arrive later in ecological succession?

• Ability to grow very quickly

• Ability to grow and survive on hard, barren rock

• Ability to grow in loose, wet soil

• Defenses against herbivory

Answer explanation

Pioneer species are uniquely adapted to colonize harsh environments, such as hard, barren rock, where other species cannot survive initially. This ability allows them to establish ecosystems, unlike later species that require more developed soil.

Ecological succession impacts populations and communities over time. When succession occurs, pioneer species move in and impact the ecosystem.

If pioneer species are the first species to exist in an ecosystem that contains no life, what type of succession is occurring?

• Secondary succession, because the species is the first to arrive in the area

• Primary succession, because existing species will return to the ecosystem

• Secondary succession, because the previous ecosystem will populate rapidly

• Primary succession, because there are no traces of an older community

Answer explanation

Primary succession occurs when an ecosystem starts from bare rock or lifeless areas, with no traces of an older community. Pioneer species are the first to colonize these areas, establishing the foundation for future ecological development.