Monitoring Demography of Resurrected Populations of Locally Extinct and Extant Species to Investigate Drivers of Species Loss.

AbstractExtinctions are predicted to rise by an order of magnitude over the next century. Although contemporary documented extinctions are uncommon, local extirpations likely provide hints about global extinction risks. Comparing responses to global change of locally extinct versus extant species pairs in a phylogenetic framework could highlight why certain species are more vulnerable to extinction than others and which anthropogenic changes are most relevant to their decline. As anthropogenic changes likely interact to affect population declines, demographic studies partitioning the effects of multifactorial stressors are needed but remain rare. I examine demographic responses to nitrogen addition and deer herbivory, two major drivers of species losses in grasslands, in experimental reintroductions of 14 locally extinct and extant confamilial native plants from Michigan prairies. Nitrogen consistently reduces survival, especially in locally extinct species, and growth of locally extinct species benefits less from nitrogen than growth of extant species. Nitrogen reduces population growth rates, largely via reductions in survival. Deer herbivory, meanwhile, had inconsistent effects on vital rates among species and did not affect population growth. Nitrogen and herbivory rarely interacted to affect vital rates. These results link community-level patterns of species loss under nitrogen addition to the population-level processes underlying those losses.