Relationships between living things

State whether the following relationships are intraspecific or interspecific: a shoal 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.

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.

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

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

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

Along a river stretch, the European mink (native) and the American mink (invasive alien) coexist. A municipal plan proposes: "To stop the decline of the European mink, we will periodically introduce tons of fish and crayfish so there is plenty of food and both species can coexist without problems."

1. a) Relying on the concepts of ecological niche (the set of resources and conditions —food, space, shelter— that a species needs and the role it plays in the ecosystem) and competitive exclusion (two species with the same niche cannot coexist indefinitely in the same place), argue why the municipal proposal will not prevent the disappearance of the European mink.
2. b) Propose a reasoned hypothesis about the direct and indirect consequences that the simultaneous presence of both species may have on native amphibian populations while competition lasts.

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

In the food chain holm oak → caterpillar → great tit → sparrowhawk, state which trophic level each organism occupies (producer, primary consumer, secondary consumer, or tertiary consumer).

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.

An investor states the following: "We can set up a commercial lion farm fed exclusively on beef from calves raised on our pastures, and we will get almost the same amount of lion meat to sell as if we sold the calves directly."

1. a) Numerically demonstrate, applying the 10% ecological efficiency rule and starting from 100 000 kJ of solar energy fixed by the pasture, how much energy reaches the calves and how much would reach the lions.
2. b) Using your calculations, refute the investor's claim and justify why in natural terrestrial ecosystems there are almost never predators in a fifth or sixth trophic level.

Analyze the following biomass data from two different ecosystems:

• Terrestrial ecosystem (meadow): Producers (grass) = 10 000 kg; Herbivores (grasshoppers) = 1 000 kg; Primary carnivores (frogs) = 100 kg; Secondary carnivores (snakes) = 10 kg.

• Marine ecosystem (open sea): Phytoplankton = 20 kg; Herbivorous zooplankton = 120 kg; Small fish = 15 kg.

1. a) Knowing that an adult snake in that meadow weighs about 0,5 kg, calculate the maximum number of snakes that ecosystem can support and justify why it would be unfeasible to maintain a stable population of 60 adult snakes.
2. b) A student claims that the marine ecosystem data are incorrect because "a biomass pyramid can never have less biomass at the base than at the level above it." Refute their statement by explaining how it is possible for that mass of phytoplankton to sustain a biomass six times larger of zooplankton.