Ecological Succession and Speciation

Grassland ecosystems in Texas have evolved to depend on periodic fires to return nutrients to the soil and

encourage plant reproduction. Humans have prevented fires in many of these grassland areas, resulting in plant

and animal communities with little diversity. Wildlife biologists often recommend purposefully starting fires called

prescribed burns, which are monitored and controlled, in grassland ecosystems every 3 to 4 years. These

biologists observe greater diversity in plant and animal life in the years following a prescribed burn.

What natural processes are the biologists attempting to imitate?

• Biomagnification

• Succession

• Population bottleneck

• Species Extinction

Which of the following biological processes would most likely increase species diversity in the ecosystem?

• Plants release a toxic substance into the soil to compete with other species in the area.

• The populations of herbivores increases exponentially while plant populations decreases.

• Bacteria present in the soil convert atmospheric nitrogen to nitrates used by plants.

• A species from a distant ecosystem establishes a population and outcompetes native species.

Why are ecosystems that undergo secondary succession more likely to reach equilibrium faster than ecosystems

that undergo primary succession?

• The beginning soil quality in an ecosystem undergoing secondary succession allows for pioneer species

  that generate more biomass.

• The lichens present during secondary succession break down hard rock material at a faster rate than

  primary succession.

• Secondary succession usually occurs in ecosystems with warmer climates which allows biological

  process to occur quickly.

• Ecosystems never reach equilibrium after primary succession because secondary succession always

  occurs after primary succession.

Hydrothermal vents form deep in the ocean when iron-rich magma is released from openings on the seafloor.

These vents spew extremely hot water (400°C) mixed with methane and sulfur. Bacteria that thrive in this hostile

environment form the base of a food chain that leads to colonization by tube worms, mussels, and many other life

-forms. When a hydrothermal vent becomes inactive and cold, the bacterial community that lives in the hot fluid

methane and sulfur dies out. Which organisms most likely succeed the original community in this ecosystem?

• Cold-tolerant bacteria that feed on sulfur and iron in the vents

• Giant kelp that use sulfur in photosynthesis

• Fish that do not need oxygen for cellular respiration

• Ocean mammals that tolerate cold and act as top predators in the food chain

During secondary succession, which of these best describes why decomposing pioneer plants give way to larger,

more complex plants species, such as hardwood trees?

• Increased amounts of sunlight are able to reach the ground while the pioneer species are decomposing.

• Increased soil temperatures from decomposing pioneer species help tree seeds germinate more quickly.

• Increased amounts of decomposing pioneer species remove nutrients that tree seedlings need to grow

  and mature.

• Increased amounts of soil nutrients from decomposing pioneer species allow plants with more extensive root

  systems to become established.

During ecological succession, how does the growth of young hardwoods affect the organisms living in an

ecosystem?

• Grasses and low shrubs are unable to obtain the amount of light they need to survive, so there are

  small numbers of them.

• The trees provide shelter and food for a variety of mammals, insects, and birds.

• In autumn, falling leaves provide a source of energy for decomposers such as fungi.

• All of the above

In 2011, fires in Bastrop County, Texas were the most destructive wildfires in Texas history. The fire spread

through the Loblolly pine trees and scorched nearly 5,700 acres of Bastrop State Park. The majority of the

Houston toad’s habitat was lost, and the Lost Pines Forest was heavily affected. The table below details

descriptions of changes in the population and diversity of species in the Lost Pines Forest. According to the information and table above, which of the following lists the correct order of the ecological succession in the Lost Pines Forest?

• I, II, III, IV

• II, III, I, IV

• IV, I, II, III

• III, II, IV, I

The diagram above shows the process of ecological succession after wild fire. Which

of the following is correct?

I. It usually takes more than 100 years to reach to a stable ecosystem after a natural

disaster such as wild fire and flood has occurred.

II. During the stage IV, many populations change, and each new population changes

the environment, making it more suitable for next coming species.

III. During the stage I, grasses and weeds are growing fast in the ecosystem because the species can grow better under the condition of little amount of sunlight than any tree plants.

IV. During stage V there is the least amount of Biodiversity

• I only

• I and II only

• II, III, and IV only

• I, II, and III only

Which statement best describes the differences in species diversity between an ecosystem beginning the process

of primary succession and one beginning the process of secondary succession?

• Species diversity is much greater in the ecosystem undergoing primary succession because that

  ecosystem is experiencing a longer period with a lack of competition for space.

• No differences in species diversity exist because both ecosystems initially lack living organisms.

• Species diversity is much greater in the ecosystem undergoing primary succession because the lack of

  soil provides a greater area for organisms to claim niches.

• Species diversity is greater in the ecosystem undergoing secondary succession because the soil already

  contains seeds and spores of various species.

The information shown in the graph suggests that the changes in the forest community were caused by

• tree-leaf replacement after a storm

• repeated habitat destruction due to human activity

• decreased species diversity after a fire

• one community of plants replacing the previous community