This article presents research concerning the way in which primary school pupils in southern Spain interpret the concepts of population and species. The results show that, for the concept of population, there was an intense anthropocentrism in pupils' responses, while for the concept of species, only animals were considered as living creatures. These interpretations influence the vision that the students will develop of ecosystems and biodiversity, as well as their respect and care for living beings. We propose some suggestions in order to improve the teaching of these concepts in primary education.