Final answer:
No arrows point to producers because they are the energy producers at the base of the food web. An increase in the deer mouse population would directly deplete their food sources and indirectly affect predator populations and prey diversity.
Step-by-step explanation:
No arrows point to the producers in a food web because they are at the base of the ecosystem, producing energy through photosynthesis or chemosynthesis, which is then passed up the food web through consumption. Producers do not need to consume other organisms for energy as they make their own.
A direct effect of an increase in the deer mouse population could be a higher predation pressure on their food sources, such as seeds and fungi. An example of a direct effect is the depletion of pinyon nuts due to the increased consumption by a larger deer mouse population.
An example of an indirect effect of an increase in the deer mouse population could be a rise in populations of predators that feed on deer mice, like snakes and owls. This increase in predators could then lead to a decrease in other prey species that these predators consume, affecting the overall food web dynamics.