First principles predict negative frequency-dependent sex allocation, but it is unproven in field studies and seldom considered, despite far-reaching consequences for theory and practice in population genetics and dynamics as well as animal ecology and behaviour. Twenty-four years of rhinoceros calving after 45 reintroductions across southern Africa provide the first in situ experimental evidence that unbalanced operational sex ratios predicted offspring sex and offspring sex ratios. Our understanding of population dynamics, especially reintroduction and invasion biology, will be significantly impacted by these findings.
This work was supported by granted funds from the US Fish & Wildlife Service administered Rhinoceros and Tiger Conservation Act of 1994 (grant agreement numbers 98210-2-G363, 98210-4-G920 and 98210-6-G102), International Rhino Foundation, Victoria University of Wellington, and Nelson Mandela Metropolitan University. Our thanks to K. Adcock, G. Kerley and M. Knight.
Supplementary Tables 1 and 2