The point on the graph that represents the outbreak of moose ticks and a drastic decline in the moose population is Point C The abiotic factors that might cause a rapid change in population size for moose or wolves includes; flood; earthquake, rising temperatures/climate change, ice bridge formation, etc, while the biotic factors include; loss of food source (vegetation for moose, moose for wolves), parasites, shortages of mates, genetic deformities due to inbreeding.
The large-scale ocean-atmosphere climate interaction linked to a periodic warming in sea surface temperatures across the central and east-central Equatorial Pacific is what is used to describe an El Niño, so I’m guessing this is what is associated with it.