Question

a new species of fish was released into a lake. state two unwanted outcomes that could arise from the introduction of this new species.

Answer 1

The overall outcome of new species of fish actually released in the lake, the first outcome will be, competition with the original species and the second is going to be predation of the new species itself. Now let me shed some details about the latter two.

1) Competition: It is a Original or newly developed rivalry for obtaining the "same" resources for a biotic community and a succession in the overall environment. It is generally of two types, a) Intraspecific competition and b) Interspecific competition. Actually the overall outcome will depend on these two but, a third outcome is also present, that is, predation. Also, you have clearly stated different species so, it will be Intraspecific.

a) Intraspecific competition: This rivalry is amongst the members of different species. The severity of competition will hugely depend on the similarity of the environment and the requirement of food and shelter. Every type of organism has a particular niche or a role in the environment to play. No two types of organisms can have exactly same niche. One of the two is "eliminated". The phenomenon is called as Gause hypothesis or principle of competitive exclusion (removal of one species of the two species), Gause gave this hypothesis in 1934. Gause found that inoculation of Paramecium aurelia and P. caudatum in the same culture resulted in the elimination or complete elimination of P. caudatum (as the culture was suitable for inoculated individuals). Balanus similarly found that it nearly excludes smaller barnacle Chthamalus from the intertidal area. Connell (in 1961) found that Balanus population was reduced to a very small extent or eliminated, Chthamalus continued to flourish. The phenomenon is called as competitive release. In nature organisms undertake resource partitioning or sharing of resources without the knowledge of other species in order to avoid competitive exclusion. For example, 14 finches in Galápagos Islands or 20 species of Antelopes in Serengeti plain, roots to different depths.

2) Predation: A small topic which is also an unwanted outcome; One organism called as predator captures, kills and eats another organism called prey. Predators are carnivorous but some are herbivores which destroy whole plants/seeds are also called predators (plants do have life :). Carnivorous plants are also predators, for an example, Nepenthes, Drosera, Utricularia. A predator might become a prey for another higher species. Therefore, predation is a mechanism of biological control that assists in keeping the population of various organisms in check. A rise in predator population will reduce prey population, which in turn will cause reduction in the population of predators due to starvation and emigration. A rise in herbivore population will result in the overgrazing, shortage of herbage or herbs species and ultimately reduction in herbivore population. So, the population of everything should be balanced.

Now, the introduction of new species will face those two outcomes with hypothesis and phenomena taking in place.