The latest environmental “crisis” is the floating garbage polluting the world’s oceans, which is said to be killing “more than a million seabirds and 100,000 mammals and sea turtles each year.” But does this number really mean anything? The number of animals killed alone is meaningless without context. Understanding why requires a little ecological intuition.
Suppose that a hunter goes into an isolated forest once a month to kill a deer. What is the hunter’s impact on the deer population? In the short term, after each deer is killed, the population decreases by one deer. In the long term however, the forest is only capable of sustaining a fixed number of grazing animals, and each deer that dies makes room for additional animals. Each dead adult means that there is more food available for the next generation. Whether the deer population remains stable or decreases depends on the adaptive capacity of the species to reproduce fast enough to compensate for the missing deer. If only a small percentage of the population is killed each year, then there will probably not be any change in the population.
Given that there are colonies of sea birds which number over a million and a single sea turtle lays 150-200 eggs, it is far from obvious whether the number of animals killed by garbage has any impact on their population. Animals that survive due to decreased competition may balance the animals killed by plastics. Furthermore, the more drastic the impact on animal populations, the higher the evolutionary pressure for the surviving animals to adapt to their new plastic-rich environment.
It is conceivable that plastic waste has a beneficial impact on the oceans, as it is well known for attracting schools of fish, perhaps because it forms a base for microorganisms. It certainly wouldn’t be the first time that environmentalists were dramatically wrong about the impact of a deadly pollutant. In any case, the evolutionary process will certainly maximize the potential of marine species to take advantage of their new environment.