Age-specific, density-dependent and environment-based mortality of a short-lived perennial herb

Abstract

Density-independent and density-dependent processes affect plant mortality. Although less well understood, age-specific mortality can also play an important role in plant mortality. The goal of this study was to analyse sev- eral factors accounting for mortality in the Mediterranean short-lived peren- nial herb Lobularia maritima. We followed three cohorts of plants (from emergence to death) during 4 years in field conditions. We collected data on plant mortality of the effect of biotic agents (moth larvae and mycoplasma- like organisms, MLOs) and environmental variables. We also estimated den- sity-dependent relationships affecting the fate of seedlings and adults. Results show that cohorts differed in their survival curves and ageing signif- icantly increased mortality risk. Seedling mortality was density-dependent whereas adult mortality was not affected by density. MLO infection led to higher plant mortality whereas moth larvae attack did not affect plant mor- tality. In general, seedlings and adult plants experienced the highest mortal- ity events in summer. We found, however, weak relationships between weather records and plant mortality. Age and size structures were not corre- lated. Overall, this study provides a comprehensive review of age-specific, density-dependent and density-independent factors that account for mortal- ity of L. maritima plants throughout their life cycle in field conditions, highlighting the fact that age is an important factor in determining plant population dynamics