Effect of population size on the prospect of species survival

Abstract

Abstract:Many recent studies have demonstrated a negative effect of small population size on single plant traits. However, not much is known about the actual consequences of reduced plant performance on the long-term prospect of species survival.I studied the effect of population size on population growth rate and survival probability in the rare perennial herb Scorzonera hispanica occurring in fragmented grasslands. Its performance was measured using several traits related to reproduction in 21 populations ranging in size from 3 to 2475 plants. These data were then connected with data on full demography of the species from three of the studied populations. Two different matrix models differing in the number of transitions based on measurements in the populations differing in size were used to explore the relationship between population size and population growth rate.Both matrix models showed that despite the decline in seed production in small populations, population growth rate is never significantly different from one, and the populations could thus be expected to survive in the long run. Calculations of extinction probabilities that take into account demographic and environmental stochasticity, however, showed that populations below 100 flowering individuals have a high probability to become extinct. This demonstrates that demographic and environmental stochasticity is an important driver of the fate of small populations in this system. This study demonstrates that estimation of population growth rate can provide new insights into the effect of population size on population growth and survival. It also shows how matrix models enable the combination various pieces of information about the single populations into one overall measure, and may provide a useful tool for the standardization of studies on the effects of population size on population performance.

Seed mass and population characteristics interact to determine performance of Scorzonera hispanica under common garden conditions

“…Because many of the environmental characteristics were correlated with each other, we selected only a subset of those that were only weakly correlated and had significant effect in previous studies in the system (Münzbergová , 2004(Münzbergová , , 2006a. This resulted in the following independent variables: aboveground biomass, Beals index, logarithm of population size, Nei's genetic diversity, and allelic richness.…”

“…For this study, we used 20 populations that were found in a previous field survey of the landscape, ranging from 10 to 2475 flowering individuals ( Table 1). The same populations were the subjects of a previous study examining performance of the species in the field (Münzbergová , 2006a).…”

“…Environmental variables were selected to capture the expected most important differences between the populations; these factors correspond to those recorded in the previous study (Münzbergová , 2006a). They include site inclination, potential direct solar radiation (PDSI) in January and June, and the mean of PDSI from the period between January and July, soil water holding capacity, bulk density (mass of dry soil per volume) and aboveground biomass (see Münzbergová , 2006a, for details on collection of these data).…”

“…They include site inclination, potential direct solar radiation (PDSI) in January and June, and the mean of PDSI from the period between January and July, soil water holding capacity, bulk density (mass of dry soil per volume) and aboveground biomass (see Münzbergová , 2006a, for details on collection of these data).…”

Dynamics of isolatedSaponaria bellidifoliaSm. populations at northern range periphery

“…This is not an unusual result: 598 small populations of Scorzonera hispanica in a fragmented 599 landscape of Cehia (Münzbergová 2006), the rupicolous 600 endemic Petrocoptis pseudoviscosa (García 2008) or the 601 peripheral Cypripedium calceolus populations (García 602 et al 2010) also had growth rates not significantly different 603 from unity or not declining, and good chances to persist in 604 the long run. Similarly, the dynamics of Silene regia 605 populations in American prairies were primarily affected 606 by management and only secondarily by size, isolation and 607 genetic diversity (Menges and Dolan 1998).…”