In an ecosystem, the factors that affect the organisms in that ecosystem can either be BIOTIC OR ABIOTIC. Biotic factors refers to the living components of an ecosystem while the ABIOTIC factors refer to the non-living components of the ecosystem.
According to this question, the abiotic (nonliving) factors that can affect a deer population includes WATER AND WEATHER. Note that the other options including flies and other organisms are both biotic factors.
