I would think that power lines are a minimal impact. What probably really hurts is some species have roam areas of dozens to hundreds of square miles. With the introduction of roads and urban areas to break up some of the ecosystems that spanned multiple states, for example, had to have a much more dramatic effect. Fencing, road barriers, etc. Create choke points and make it harder especially for large predators to thrive. The Florida panther was not even an especially large feline but it did occupy a central place at the top of the food chain in Florida and now its population has been decimated due to fractured ecosystems and each one needing about 75-150 square miles of roam area.