Context-dependent acquisition of territories by male collared lizards: the role of mortality

We recorded the behavior of free-ranging collared lizards for 11 consecutive seasons to test the hypotheses that natural mortality of territorial males that were 2 years and older (2y+) allows first-year males to switch to territorial tactics and that such events increase opportunities for courtship. Because neighboring 2y+ males sometimes expanded and sometimes did not expand into the areas made vacant by mortality, we also compared first-year male behavior under these 2 conditions. In response to 2y+ male mortality, first-year males increased rates of travel, distant display, courtship frequency, and number of different females courted. Newly territorial first-year males did not significantly increase aggression with rival males. Travel and both courtship frequency and number of females courted were higher when neighboring males did not expand. First-year males that acquired territories during the breeding season had lower values for all variables than 2y+ males, whereas first-year males acquiring territories after over-winter mortality courted less frequently than 2y+ males. First-year males acquiring territories after over-winter mortality traveled at higher rates and were more aggressive with rivals than those that gained territories after mortality during the breeding season and established 2y+ males. Our results indicate that mortality of territorial males both during the reproductive season and over winter prompts first-year males to adopt territorial tactics that promote increased opportunities to court females. Acquisition of territories during the first-year as a consequence of territory owner mortality potentially increases the lifetime mating success of these males markedly. Copyright 2010, Oxford University Press.