Review Unit 7

Tropical rain forests have the greatest biodiversity of any type of land ecosystem .How does biodiversity contribute to the sustainability of an ecosystem?

• The presence of more species with different adaptations makes it more likely that some organisms will survive an ecological disaster

• Greater genetic variation within species makes it more likely that some individuals will survive a disease outbreak.

• The presence of a variety of herbivore species that can feed on a large number of different producer species helps ensure abundant prey for predators in the ecosystem.

• All of the above

An ecosystem that is not sustainable can break down when a natural disaster occurs. This can lead to organisms in the ecosystem either leaving the area or dying off. Increased biodiversity results in a more sustainable ecosystem because —

• a greater number of plant species means that there is less barren land

• a greater variety of species present allows more organisms to adapt after changes occur

• the transition area between two ecosystems is narrower

• there are fewer species to be affected by environmental stresses

Both primary and secondary succession begin with pioneer species that —

• change the area and make it safer from predatory organisms

• invade the area so that new organisms cannot be established

• modify the area and allow larger and more complex organisms to appear

• use up all the existing resources and prevent establishment of non-native

Some student stake care of a vegetable garden. When it is time to plant in the spring, the students leave part of the garden empty in order to observe ecological succession. Which of these will most likely occur first?

• Development of topsoil

• Growth of weeds and grasses

• Growth of trees and shrubs

• Development of a stream

With many varieties of plant and animal species, the most productive biomes on Earth that have the greatest biodiversity are —

• deserts

• temperate grasslands

• steppes

• tropical rainforest

Ecologists have shown that —

• higher animal to plants ratios provides the most stable environment

• having multiple keystone species is important to ecological stability

• higher biodiversity in an ecosystem provides better stability

• ocean ecosystems are far more stable than terrestrial ecosystems

The food webs below model relationships among the organisms in two ecosystems. Which ecosystem would be more likely to survive if a disease killed the grasses?

• The forest ecosystem, because most of the animals can eat other organisms

• The grassland ecosystem, because several predators compete for food

• The forest ecosystem, because it has three top predators

• The grassland ecosystem, because it has many herbivores

Students in a science class visited four local ecosystems. The students observed the species present in each ecosystem and recorded their observations in the table. Based on these observations, which ecosystem is likely to be the least sustainable?

• Ecosystem 1, because it has the fewest species

• Ecosystem 2, because it includes both aquatic and terrestrial species

• Ecosystem 3, because it has few predators

• Ecosystem 4, because it supports many animals

This picture shows a desert environment, which is home to many lizards, small mammals, and cacti and other plants with short roots. This environment allows some plants and animals to live there because the soil in the desert is

• dry and sandy, allowing small animals to burrow and hide from the Sun while allowing plants with short roots to reach and hold onto water.

• wet and hard, allowing small animals to rest and stay cool on the wet soil while allowing plants with short root systems to push through the hard soil to soak up water

• cold and wet, allowing small animals to remain cool when it rains while allowing plants with short root systems to easily push through sandy soil to soak up water.

• dry and hard, allowing small animals to lay on the hard soil to get sunlight while allowing plants with short roots to sit on top of the soil and hold onto water.

The picture below shows manatees, an herbaceous aquatic mammal, traveling along the saltwater estuary of Biscayne Bay in Florida. How does this saltwater estuary support populations of manatee?

• It provides shallow water for easy access to oxygen at the water's surface.

• It provides cold water to keep the manatees cool.

• It provides heavy currents for fast swimming.

• It provides several rocks for the manatees to hide from prey that they want to eat