Demographic effects of global change on range shifts in a perennial plant

Background/Question/Methods

Range shifts are expected to be one of the more common responses of organisms to global change. Changes in demographic parameters can modify both range shift success as well as response to global change. Understanding demographic traits that might be related to successful range shifts can therefore be useful for making predictions about species’ response to global change. I introduced Pityopsis aspera into plots at different life cycle stages and tested how increasing temperature and soil nitrogen affected this species across life stages using a life table response experiment. I also determined whether increasing temperature and soil nitrogen affected P. aspera directly or indirectly through the responses of other species. To do this, I compared transition matrices of P. aspera created from plots in the presence of native species in their natural and reduced abundances.

Results/Conclusions

The estimated population growth rate (λ) was reduced by nitrogen addition, and increased by warming, warming x native reduction, and nitrogen x native reduction. Fecundity was important in modifying differences in λ between warming and nitrogen addition treatments. Growth of young individuals also contributed to changes in λ, but only when warming and nitrogen addition were crossed with the native reduction treatment. This work shows that population level responses to factors associated with global change are mediated by different life history traits and may occur via indirect effects through established species.  This study highlights how demographic investigations of global change effects should include direct and indirect effects of multiple life stages.