Exercises: Relationships between living things

State whether the following relationships are intraspecific or interspecific: a school of fish swimming together, a bee feeding on nectar from a flower, two stags fighting over a female, and a tick feeding on a dog.

In the food chain grass → grasshopper → frog → snake, identify the producer and name the primary, secondary, and tertiary consumers.

Explain what predation is and give an example from a marine ecosystem, stating which is the predator and which is the prey.

Classify the following relationships as intraspecific or interspecific: a pack of wolves hunting together, a tapeworm living in a wolf's intestine, two wolves fighting over prey, and a raven following the pack to take advantage of the leftovers.

Define what mutualism is and give an example, stating what each species gains from the relationship.

In the food chain live oak → caterpillar → black-capped chickadee → Cooper's hawk, state which trophic level each organism occupies (producer, primary consumer, secondary consumer, or tertiary consumer).

Explain what commensalism is and give an example from a marine ecosystem, stating what each organism gains.

State whether the following organisms are producers, consumers, or decomposers: a mushroom, a lettuce, a cow, a bacterium, an earthworm, and an eagle.

The diagram represents a food web; the arrows point from the organism that serves as food to the organism that eats it.

1. a) Which organism is hidden behind the "?" symbol, knowing that it feeds on frogs and mice?
2. b) Name the primary consumers in the food web.
3. c) Predict what would happen to the rabbit and plant populations if foxes disappeared.

Distinguish between mutualism, commensalism, and parasitism, and classify these cases: a lichen (an alga and a fungus benefiting each other), a remora traveling attached to a shark without harming it, and a tapeworm living in a person's intestine.

Explain the difference between a food chain and a food web, and explain why a food web better describes what happens in a real ecosystem.

Cattle egrets accompany livestock and eat the insects the animals stir up as they walk, without harming them. State what type of relationship they have with the livestock and compare it with that of a tick attached to the same cow.

Draw with arrows the food web formed by these organisms: phytoplankton, sardine, tuna, and seagull. The sardine feeds on phytoplankton, and the tuna and the seagull feed on sardines. Then state which trophic level each one occupies.

Explain the difference between a parasite and a predator, and explain why it is not in the parasite's interest to cause the death of its host.

Some ants protect aphids from their enemies and, in return, feed on the sugary liquid the aphids excrete. Classify the relationship and explain what each species gains.

Two species of mice in the same forest feed on the same seeds. State what type of interspecific relationship they have and explain what may happen to their populations if food becomes scarce one year.

Following an epidemic that reduces the fox population in an oak forest by 90%, a team of ecologists records these changes over three years:

• Year 1: The rabbit population doubles and the herbaceous plant cover barely changes.

• Year 2: Grass cover drops by 70% and the soil begins to erode severely.

• Year 3: The rabbit population suffers a sudden collapse and falls to levels well below the initial ones, even though foxes are still absent.

1. a) Explain the trophic cascade that connects the disappearance of the foxes with the degradation of the vegetation in Year 2.
2. b) Formulate an ecological hypothesis that justifies why the rabbit population collapsed in Year 3 if there were no predators hunting it.

To halt the spread of the Asian hornet (Vespa velutina), which preys on honey bees at beehives, an association proposes placing bottles containing sugar water and beer throughout the woodland as an attractant to drown them.

1. a) Analyze the indirect impact that the loss of bees caused by the hornet has on two different trophic levels: wild plant producers and the ecosystem's frugivorous birds.
2. b) Critically evaluate the association's proposal: justify why this non-selective trapping method using sweet liquids can be counterproductive and further harm the ecosystem's biodiversity.

In a restoration project on a hillside scorched by a wildfire, holm oak saplings are planted in two plots with poor, degraded soil:

• Plot 1: Heat-sterilized soil supplemented with abundant soluble chemical fertilizer (nitrogen and phosphorus).

• Plot 2: Non-sterilized soil inoculated with mycorrhiza-forming fungi, without added chemical fertilizer.

During the first summer, marked by an extreme drought, 85% of the saplings in Plot 1 die from dehydration, while 90% of those in Plot 2 survive and grow vigorously.

1. a) Identify and describe the interspecific relationship responsible for the success of the saplings in Plot 2.
2. b) Explain why the chemical fertilizer in Plot 1 was not enough to guarantee the survival of the holm oaks under arid conditions.