Answer each question, using it as an opportunity to illustrate the depth of your knowledge in this area. 1. One of the fundamental controls which ecosystems exert over individual species is limits on population size. This is done by a combination of predatory, competitive, parasitic and mutualistic relationships within the ecosystem. Never the less, the human population has increased well beyond what is healthy for those systems. How did we manage to grow beyond these limitations?
2. Natural variations in weather patterns have effects on certain populations. A warm damp spring for example, is ideal for small rodent species and certain insects, who benefit from the lush vegetation produced by this pattern. As a result, their populations swell to high levels. In the end however, this doesn't result in population growth at the higher tropic levels. You don't end up with more predators, just fatter predators. What limits the ability of the higher tropic levels to grow in response to the increased availability of food?
3. An unfortunate series of events finds you stranded on a remote uninhabited south Pacific island, with little chance of being rescued. It is a modest-sized island with adequate resources to support you, if you are careful to minimize your impact on it. You know that inserting yourself into this ecosystem will almost certainly mean the loss of members in some populations, so your goal is to minimize your impact on the overall biodiversity of the system. With this in mind, from which tropic level(s) should you obtain your food?

1. Humans are an “invasive species” because human populations have eliminated many ecological relationships, dramatically changing the dynamic of their ecosystems

2. continued loss of energy due to metabolic activities

3. lower trophic levels

Explanation:

1. An invasive species is any organism that is not native to an ecosystem and may negatively alter its new environment. Invasive species don't interact with native species when they are introduced into an ecosystem (for example, invasive species usually don't have any natural predators). Humans are an 'invasive species' that occupy a wide range of habitats and whose presence has caused the extinction of many native plants and animals. Human populations have drastically reduced the biodiversity of different ecosystems by competing with native species for limited resources, and we also have altered their habitats (global human population growth is also due to medicine and farming techniques, reducing hunger and diseases). In this regard, it is important to highlight that the human population can also grow in an ecologically sustainable manner by taking care of the ecosystems we live in.

2. Animals (predators) are consumers, thereby they depend on lower trophic levels for their food supply. The Second Law of Thermodynamics indicates that the continual loss of energy due to metabolic activities at lower trophic levels leads to a decrease in the amount of available energy at higher trophic levels. In consequence, the population size decreases at higher levels due to the amount of energy available from one lower level to the next higher level has to decrease when it is used for metabolic activities (i.e., growth, development, etc).  

3. In the food chain, the primary producers are found at the lower trophic level (e.g., plants). Primary producers are followed by consumers (e.g., herbivores), they are followed by secondary consumers (i.e., carnivores that eat herbivores), and so on. When an invasive species at higher trophic levels is introduced into a new ecosystem (in this case, human species), it is imperative to preserve the biodiversity (and consequently also the productivity) at lower trophic levels because they are fundamental for the survival of higher trophic levels (i.e., consumers).