The growth of the moose population can be attributed to growing food availability or reduced predation, which in turn allows wolf populations to rise due to more food sources being available.
The best explanation for growth in the moose population in the year prior is that there was more food available or the degree of predation decreased, allowing wolf populations to increase. This interplay between moose and wolves demonstrates the complexity of predator-prey dynamics in ecosystems such as Yellowstone National Park.
As the moose population grows, it provides an ample food source for wolves, which can then also increase in numbers. However, this simplified explanation must consider environmental factors as well, such as the availability of resources and the degree of predation, which are influence points for the carrying capacity of a species within an ecosystem.
From the additional reference, wolves in Yellowstone act as a keystone species, where their presence has a disproportionate effect on the ecosystem. And changing elk behavior, they promote vegetation regrowth, which benefits various species, including beavers, and improves habitat quality, affecting the ecosystem's carrying capacity for the wolf population adversely.