noun
natural increase
Used in demographics and statistics for population growth excluding migration, i.e., births minus deaths.
日本の人口は自然増加がマイナスに転じた。
Japan's natural population increase has turned negative.
社会増加 refers to population change from migration (social increase), while 自然増加 is the change from births and deaths.
Compound of 自然 (natural) and 増加 (increase).