Background: Energy is passed up a food chain or web from lower to higher trophic levels. However, only about 10 percent of the energy at one level is passed up the next level. This is represented by the ecological pyramid in Figure below . The other 90 percent of energy at each trophic level is used for metabolic processes or given off to the environment as heat. This loss of energy explains why there are rarely more than four trophic levels in a food chain or web. There isn’t enough energy left to support additional levels. It also explains why ecosystems need a constant input of energy.

Situation: An island in the Pacific ocean has a strange an compact ecosystem. There are only 4 species of living organism on it. There are plants, Insects, birds, cats. Because of this there is a very specific food chain on this island. Any new species added to it has cause the population of all other species to decrease. This is because when a new species is added it causes the others to not have enough food as they all feed on each other. The insects eat the plants, the birds eat the insects and the cats eat the birds. When a species of wolf that eats the cats was added the plants began to die off because the wolves outlived the cats so the plants could not get the energy in time to regrow before the insects would eat them. Because of this the insects would die, then the birds then the cats. because the energy source for each species was being consumed faster than it could be produced.

Question: Will adding a new species to the island cause the available energy to increase or decrease?
Answer: decrease

Situation: An island in the Pacific ocean has a strange an compact ecosystem. There are only 4 species of living organism on it. There are plants, Insects, birds, cats. Because of this there is a very specific food chain on this island. Any new species added to it has cause the population of all other species to decrease. This is because when a new species is added it causes the others to not have enough food as they all feed on each other. The insects eat the plants, the birds eat the insects and the cats eat the birds. When a species of wolf that eats the cats was added the plants began to die off because the wolves outlived the cats so the plants could not get the energy in time to regrow before the insects would eat them. Because of this the insects would die, then the birds then the cats. because the energy source for each species was being consumed faster than it could be produced.

Question: Will the insect population decreasing cause the available energy to the bird population to increase or decrease?
Answer: decrease

Situation: An island in the Pacific ocean has a strange an compact ecosystem. There are only 4 species of living organism on it. There are plants, Insects, birds, cats. Because of this there is a very specific food chain on this island. Any new species added to it has cause the population of all other species to decrease. This is because when a new species is added it causes the others to not have enough food as they all feed on each other. The insects eat the plants, the birds eat the insects and the cats eat the birds. When a species of wolf that eats the cats was added the plants began to die off because the wolves outlived the cats so the plants could not get the energy in time to regrow before the insects would eat them. Because of this the insects would die, then the birds then the cats. because the energy source for each species was being consumed faster than it could be produced.

Question: which part of the food chain will be hurt first if a new species is added that eats insects, the bird population or the plants?
Answer: birds