Effects of density and fire on the vital rates and population growth of a perennial goldenaster

Abstract

Intraspecific density effects are generally associated with other factors, like disturbance. Therefore, the ways inwhich density effects might interact with disturbance to modify the relationships between vital rates and population growth must be understood. I quantified the effects of density on the life-history stages of the perennial composite Pityopsis aspera over 3 years, the span of which included years in which fire did and did not occur. In an experimental study, I estimated the survival, growth and reproduction for shoots in plots established across a natural range of densities in Florida,USA. Inanovel analysis, a regression-design life-table response experimentwas usedto determinewhich transitions were associated with density, how they contributed to differences in estimated population growth rates and how this relationship differed as a result of fire. The shape of the relationship between population growth rate (l) and density was modified by fire, primarily as a result of contributions from adult flowering stasis and survival, and firstyear survival probabilities. Fire modified and even reversed the effect of extreme densities on adult flowering stasis and survival and of first-year survival, resulting in more positive contributions from these transitions to l at the lowest and highest density values. These results demonstrate the first application of a regression-design life-table response experiment to elucidating the interactive effects of density and fire. They highlight the utility of this approach for both capturing the complex dynamics of populations and establishing ameans of determining howvital rates might contribute to differences in demography across densities. © The Authors 2013.