Unit 8 Ecology

Both primary and secondary begin with pioneer species that ___*

• change the area and make it safer from predatory organisms

• invade the area so that the 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 organisms.

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Some students take 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

Students in a science class visit four local ecosystems. The students observed the species present in each ecosystem and recorded their observations in the table. *

Ecosystem 1: Grassy lawn on school property Observation: The grass is mowed often and kept short. Two sparrows foraged for food in the grass. No other animals were observed.

Ecosystem 2: Small pond with cattails growing around the edge Observations: Two types of fish were seen in the pond. Tadpoles were swimming in the shallow areas. Large wading birds were seen feeding on tadpoles and crayfish.

Ecosystem 3: Agricultural field Observations: Wheat plants are the only plants growing in the field. There were many insects. No predators were observed except for a single circling hawk.

Ecosystem 4: Wooded area along a stream Observation: Fish, frogs, crayfish, insect larvae, and turtles were seen in the stream, and wading birds were eating small fish. Raccoon tracks were seen in the mud. Deer were moving through the trees. Many birds were seen feeding in the canopy of the woods.

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 plants.

• Ecosystem 3, because it has few predators

• Ecosystem 4, because it supports many animals.

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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.

• 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

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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.

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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.

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The picture shows a mangrove estuary environment. Which of the following is a quality of the mangrove estuary environment that allows small fish and crustaceans to live there?

• It provides shelter and protection from predators for small animals.

• it has lower-than-normal oxygen levels because of the mangrove trees.

• it has a higher salt content than ocean water.

• it has a fast-moving current and waves running through it.

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In the rain forest ecosystem, some plants are able to grow attached to the sides of the tallest trees. This adaptation benefits these plants by allowing them to better compete for what resource that is limited on the forest floor?

• Water

• Sunlight

• Nutrients

• Air

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A large area of forest is cleared of trees that usually provide shade. In response to this change, plants in the environment would be expected to?

• attract insect pollinators

• develop deep root systems

• produce wind-blown seeds

• withstand direct sunlight

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The picture below shows a desert environment, on the left, and desert iguana, on the right. How does this desert environment support populations of desert iguana?

• It has a lush landscape of plats for the iguana to eat

• It has a lot of water to drink

• It has sandy soil for burrowing shelters

• it is extremely hot during the day

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