According to a new study, excess nutrient input - or nutrient pollution -creates an imbalance in the interactions between partner - also known as mutualistic - species across a variety of ecosystems. The culprit: nitrogen fertilizers and fossil-fuel combustion. In a very short period of time, humans have short-circuited the tight recycling of nutrients between mutualistic species, and this in turn has changed the balance of how such partners interact. [Source: University of California, Santa Barbara]