All organisms affect the ecosystem in which they live. why do human activities have a greater impact than those of other organisms?

Hello!

Although all organisms have an effect on their ecosystem, not all are as strong. Humans have a large impact on the ecosystem because of several things that we find to be entirely normal today. Some of these include: the establishment of buildings, several inventions (both environmentally harmful and harmless), deforestation, etc. 
Human activities also are not restricted to one ecosystem. Human wastes and pollution can enter other ecosystems, causing them to function differently. 

I hope this helps answer your question! Feel free to comment or PM me if you have any additional questions!