Evolutionary rescue from antagonistic invaders: Birth-limiting competition among residents can aid rescue

From invasive predators displacing wildlife to medically deployed bacteriophages eliminating pathogens, biological invasions by antagonists are a fundamental driver of extinction, with implications for both conservation and medicine. Resident populations facing such invasions can sometimes avoid extinction through adaptation, a process known as evolutionary rescue. Here, an analytical approximation is derived for the probability of evolutionary rescue from antagonistic invaders, focusing on how rescue depends on a key antagonist trait--victim specificity. Rescue is shown to be most likely either when invaders are slow-spreading, resident-dependent specialists whose failure to encounter suitable victims buys time for mutation, or when invaders are fast-spreading generalists that rapidly relieve standing genetic variation of intraspecific competition. The central result is that, whether invaders are generalists or specialists, a lower resident birth rate can facilitate rescue relative to a higher one by diminishing the effect of demographic stochasticity on mutant establishment. If the lower birth rate is density-independent, it primarily promotes rescue from generalists, whereas if it arises from birth-limiting competition it can also appreciably aid rescue from specialists. Overall, the results suggest that invader victim specificity can reshape evolutionary rescue by dynamically coupling the rate of resident decline to the growth rate of the stressor driving the decline, with resident life history mediating the outcome.