Variation in life-cycle between three rare and endangered floodplain violets in two regions: implications for population viability and conservation

We studied the demography of Viola elatior, V. pumila, and V. stagnina, three rare and endangered Central European floodplain species, to (i) analyse variation in life-cycles among congeners and between regions (Dyje-Morava floodplains, Czech Republic; Upper Rhine, Germany), (ii) to define sensitive stages in the life-cycles, and (iii) to identify possible threats for population viability and species conservation. Matrix models were based on the fate of marked individuals from a total of 27 populations over two years. We analysed population growth rate (λ), stage distribution, net reproductive rate (R ₀), generation time, age at first reproduction, and elasticity and calculated a life table response experiment (LTRE). Most populations were declining and λ did not differ between species or regions during the observed interval. Despite higher probabilities for survival and flowering in the Dyje populations, R ₀ was higher in the Rhine populations. Also other demographic traits showed consistent differences between regions and/or species. Complex life-cycles and large variation in λ precluded unequivocal identification of sensitive stages or vital rates for conservation. Variation between regions may be a consequence of differences in habitat quality. Our results suggest that deterministic processes such as reduced management, succession, habitat destruction, and lack of disturbance through reduced or eliminated flooding present the strongest threat for the viability and persistence of populations of the three floodplain violets as compared with stochastic processes. However, the persistent seed bank of the species may buffer populations against environmental variation and represents a reservoir for recovery after resumption of suitable land-use management.