Might be a silly question, but it is an important topic to discuss, if we want to be responsible dog owners/guardians and visit the outdoors in line with the “leave no trace” principle.
The main difference: their diet.
Wild animals consume foods and nutrients directly from the ecosystem, where they reside, and the same nutrients and resources are “returned” into the same environment with their excrements. For example:
“Researchers in Colorado’s Rocky Mountain National Park were greeted with exciting findings earlier this year when samples of bear scat mixed with soil in the Park’s greenhouse yielded more than 1,200 Oregon-grape and Chokecherry seedlings. The astounding number of seedlings that germinated from the fertile mixture of bear scat and soil provided even greater evidence for the interdependence of species living in the Rocky Mountain ecosystem. According to researchers, the seedlings are much more likely to germinate after passing through a bear’s internal system compared to simply dropping off the plant. This is because seeds from plants like Chokecherry have a thick, durable seed coat that needs to be broken down for the seed to germinate – a service the bear’s stomach performs remarkably well.” (lnt.org)
So, the entire feeding cycle of wild animals actually benefits the natural environment (ecosystem), since it is a closed loop.
In case of our dogs or other pet animals, the ecosystem gets thrown out of its equilibrium balance. Our dogs usually eat foods (either raw or processed food) that are packed with added nutrients that are not found in wildlife ecosystems.
Excrements of our dogs add excess nutrients into the environment, such as nitrogen and phosphorus. These nutrients in excess amounts create unstable conditions in the ecosystems. For example, this allows for algae blooms inhabit and cloud the rivers, lakes and streams, and create an easy habitat for invasive weeds to grow. Invasive species are usually more aggressive than endemic species, which are then not able to grow. This again causes an imbalance in the ecosystem, which effects every species (including humans). Also, not all nutrients from your dog´s poop can be easily decomposed, which means that they affect the soil, water sources, plants, other animals, etc.
One gram of dog poop contains 23 million bacteria, like E.coli, salmonella, Campylobacteriosis, and tapeworms.
You might think “It´s just one poop, it´s just once” .. but if we all though this way, you can imagine that our natural environment would be covered with poop soon enough. We owe it to our natural environment to be responsible dog owners/guardians and pick up their poop, also in the natural environment.