7. Pollution, Overharvesting, Invasive Species, and Disease

Many threats to biodiversity do not lead to immediate and/or direct mortality, but instead have sublethal impacts that compromise organisms’ fitness over time. But responding to these silent, insidious, and easily-overlooked threats is often delayed, especially when the negative effects are felt only years after exposure. Environmental pollution leaves ecosystems uninhabitable for native wildlife, and cause sickness and death in wildlife and people. Common causes of this include pesticides, heavy metals, plastic, fossil fuels, fertilisers, light, heat, and noise, leading to pollution of water, groundwater, air, and soil. Furthermore, overharvesting is becoming an increasingly damaging threat to biodiversity because people have better access to previously unexploited areas and are adopting increasingly efficient methods for harvesting wildlife products. Persecution, which has its roots in human-wildlife conflict, is also becoming an important threat because a growing human population is increasingly encroaching on the shrinking remaining natural habitats. As a result, invasive species outcompete local species and change the structure and composition of their native ecosystems. Needless to say, human activity is responsible for these invasions, by accidentally or deliberately moving wildlife to new regions of the world. Disease transmission and spread increase when wildlife is confined to small areas and/or crowded conditions. Therefore, managing for diseases is also important in zoos and other ex situ facilities, because diseases spreading from one individual to another can prevent those individuals from being released into the wild. These diseases are not only transmitted between wildlife, domesticated species, but also humans.