The coyote was orginally a marginal desert predator. They operated in the area were the wolf was not present.
When we eliminated the wolf they moved in to fill the void. For years the Miss. River served as a barrier to their expansion. When they learned to use the bridges, expanded dramatically.
To understand the impact on the deer population one must look at the effect they have had on the antelope population in AZ and Idaho.
Their hunting technique is to identify a Doe who is ready to drop her calf. They follow her and have been video taped by Idaho game management biologist literally pulling the calf out of the Doe. This hunting practice is devastating on the Antelope population.
The Antelope herd in the area were I live is about 50 animals. My neighbors and I counted only 2 fawns from the 2011 crop. AZ Fish and game has opened coyotes to night hunting in certain Antelope Management areas in order to increase the Antelope population.
Additionally, they are scavangers and have learned to live in close quarters with humans. In addition to the garbage and handouts generated by humans, they found that domestic animals, cats and dogs, are tasty.
I apologize if I used improper terms for Antelope. I still have not learned the correct terminology.