Drawing and interpretation graphs, as key mathematical skills, are widely used in teaching various subjects within science education. Population ecology, a topic in the environmental education course within the elementary education curriculum of Türkiye, is one such subject. In the context of this environmental education course, graphs are employed to teach and interpret the factors influencing the growth and decline of populations. This qualitative study aimed to examine the graph drawing and interpretation skills of preservice elementary school teachers in relation to population size. Fifty-seven preservice elementary school teachers from the elementary education department of a university in the Central Anatolia region of Türkiye participated in the study. These preservice teachers were provided with growth rate vs. time graphs of different populations and were asked to draw and interpret graphs representing change numbers of individuals vs. time. The findings revealed that many preservice teachers struggled with both drawing and interpreting population graphs. Specifically, most participants encountered difficulties while drawing and interpreting linear and particularly curvilinear graphs, as they failed to account for the simultaneous changes in two variables. The study’s findings are expected to raise awareness about the importance of mathematical skills and the need for interdisciplinary collaboration in environmental education, as well as providing direction for future research.