Resource limitation of nesting: Chance favors the prepared dung beetle

Abstract

Over a period of 2 yr, physiological and morphological traits related with nesting in two dominant dung beetle species in the Guadix-Baza Basin (Onitis ion [Ol.] and Onthophagus merdarius Chevr., Coleoptera: Scarabaeidae) were analyzed. The role of physiological conditions and resource availability for nesting as factors determining reproductive output in these species is discussed. Our results show that food does not seem to constrain sexual maturation. Both species reached sexual maturation and stored large amounts of reserves after a short period of nourishment. In addition, females were inseminated shortly after emergence, so they were ready to lay eggs only a few days after emergence. Although both species reached sexual maturation quickly, the number of nests dug by the females and the number of eggs laid were low, as indicated by the very low tibial wear and the low proportion of yellow bodies found. Although the rate of dung colonization was high, the number of beetles per dung pat was generally low. Therefore, aggregation of beetles does not seem to explain the low proportion of eggs laid by females of these species. Most dung pats in the study site were small, and only a small proportion (10.4%) was large enough to be suitable for nesting. In conclusion, both species were ready to reproduce soon after emergence, allowing beetles to increase their chances of reproductive success in a harsh environment in which high dung desiccation rates cause a low availability of suitable dung for nesting.