25 — Poop.

While waste from wildlife is actually beneficial for the ecosystem — as it is comprised of resources from the ecosystem, which are continuously cycled through — dog waste is made up of high levels of nitrogen, phosphorous, and other nutrients coming from their commercial foods. When an ecosystem is not used to increased nutrient levels, invasive plant species have a better chance of growing and harmful diseases are more easily spread. This is especially the case with dogs, as they tend to carry harmful diseases that can spread to humans through contact with their waste.