Mate retention, harassment, and the evolution of ungulate leks

Current models of lek breeding mostly suggest that males defendclustered mating territories because females show a preferencefor mating on leks. Here we argue that, in lek-breeding ungulates,males may also gain benefits from holding clustered mating territoriesbecause clusters retain does in estrus. We show that in fallowdeer (Dama dama) harems are commonly disrupted by young males.Bucks that hold territories on the lek that lose their haremsquickly regain does as other harems are disrupted, whereas bucksdefending isolated, single territories rarely regain does thesame day. The risk of harassment may also help to explain whydoes in estrus leave the large, unstable herds that they usuallylive in. Does in estrus are frequently chased by young maleswhen outside male mating territories. Benefits of moving tothe lek (versus moving to single territories) include reducedrisks of long chases. Though intrusions by young bucks are thecommonest cause of does leaving male territories in our studypopulation, other factors that cause does to move between neighboringharems (including disturbance by predators and persistent courtshipby males) may generate benefits to males holding clustered matingterritories. Once clustered mating territories have developed,the additional costs of mate choice are likely to be low, andfemale preferences for particular male characteristics may belikely to develop.