Which statement about density-independent factors is true?
A) Davidson and Andrewartha's studies of thrips (Thrips imaginis) showed that density-independent factors play a major role in the annual fluctuations of abundance of this species. B) Density-independent factors increase the size of populations when population size is low. C) Density-independent factors decrease the size of populations when population size is high. D) Food and habitat availability are density-independent factors that influence population size.