Dependence on and Competition for Resources

Predict: During an investigation of an ecosystem during a drought, you observe that the decrease in water has negatively affected the growth of prairie grass. What do you predict will happen to the deer population that feed on the grass?

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How does competition for biotic and abiotic factors affect the size of populations?

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Jenn and Murphy are studying data from a small forest ecosystem in a city park. The data indicates that the deer population in the forest has grown significantly over the last several years. Why will the size of the deer population most likely decrease in the next few years?

• The deer are competing for oxygen.

• The deer are competing for soil.

• The deer are competing for space.

• The deer are competing for sunlight.

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Environmental factors, such as temperature, can significantly affect the populations in an ecosystem. A group of scientists studied the sycamore lace bug (Corythucha ciliata) to determine how it is affected by the temperature of its environment. The scientists allowed batches of eggs to hatch and the larvae to grow to adulthood at five different temperatures. The survival rates of the lace bug at each temperature are on the graph.

• 19–22°C

• 22–26°C

• 26–30°C

• 30–33°C

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Which is an example of an effect an abiotic factor could have on a population in an ecosystem?

• An insect invasion kills a population of trees.

• An increase in rainfall causes an increase in the population of many plants.

• A fungus infects a population of bats, and many of the bats die.

• An increase in fruit flies leads to an increase in a population of spiders.

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Nutria are large semiaquatic rodents that were imported from South America to the United States by fur traders. In the late 1940s, a hurricane dispersed nutria throughout southeast Texas. They feed on native seedlings and saplings—native organisms that are naturally found in the ecosystem—and have cleared wide areas of floodplains and marshland along the Gulf Coast.

 Which is most likely the effect of the introduction of nutria into southeast Texas ecosystems?

• The nutria depend on native herbivores for food.

• The nutria compete with native organisms for abiotic factors.

• The nutria compete with native herbivores for food.

• The nutria compete with native carnivores for food.

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Pink salmon return to the same waters in which they were born to mate. Researchers collected data on the pink salmon returning to Auke Creek and the average water temperature. Table 1 shows the calendar dates of the highest percentage of pink salmon returning to Auke Creek in Juneau, Alaska, to mate in six years spanning from 1971–2010. Table 2 shows changes in the creek during the same time period.

The data in Table 1 and Table 2 show the relationship between salmon and which abiotic factor?

• water availability

• atmosphere

• temperature range

• light availability

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Observe the food web below. Which populations directly compete with owls for food?

• Snake, Hawks, and Fox

• Rabbit, Frog, and Mouse

• Bird, Snake, and Hawk

• Rabbit, Fox, and Hawk

• Grasses, Grasshopper, and Frog

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Eutrophication occurs when algae grow rapidly and then die and decompose. The process of decomposing uses lots of oxygen. Fish in the water depend on oxygen to survive. What is the most likely effect of eutrophication on fish?

• Competition for oxygen will increase, and fish population sizes will decrease.

• Competition for oxygen will decrease, and fish population sizes will decrease.

• Competition for oxygen will increase, and fish population sizes will remain the same.

• Competition for oxygen will decrease, and fish population sizes will remain the same.

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A scientist observes the plants in a forest ecosystem. In the spring, she notices that the wildflowers on the forest floor sprout and grow leaves before leaves grow on the trees. What is the best explanation for this observation?

• The soil is better-suited to the needs of the wildflowers than the trees.

• Wildflowers require warmer temperatures than trees for optimal growth.

• Wildflowers compete more effectively for water than trees, so they can grow leaves sooner.

• Growing leaves before the trees helps wildflowers compete with the taller trees for light.

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