Effects of range position, inter-annual variation and density on demographic transition rates of Hornungia petraea populations

Abstract

The central-marginal model assumes unfavourable and more variable environmental conditions at the periphery of a species' distribution range to negatively affect demographic transition rates, finally resulting in reduced population sizes and densities. Previous studies on density-dependence as a crucial factor regulating plant population growth have mainly focussed on fecundity and survival. Our objective is to analyse density-dependence in combination with the effect of inter-annual variation and range position on all life stages of an annual plant species, Hornungia petraea, including germination and seed incorporation into the seed bank. As previous studies on H. petraea had revealed a pattern opposite to existing theory with lower population densities at the distribution centre in Italy than at the periphery in Germany, we hypothesised that (1) demographic transition rates are lower, (2) the inter-annual variation in demographic transition rates is higher and (3) the intensity of density-dependence is weaker in Italy than in Germany. To analyse demographic transition rates, we used an autoregressive covariance strategy for repeated measures including density and inter-annual variation. All the three hypotheses were confirmed, but the impact of range position, density-dependence and inter-annual variation differed among the transition steps. All transition rates except fecundity were higher in the German populations than in the Italian populations. Germination rate and incorporation rate into the seed bank were strongly density-dependent. Central populations showed a larger inter-annual variation in fecundity and winter survival rate. Winter survival rate was the only transition step with a stronger density-dependence in peripheral populations. In most cases, these differences between distribution centre and periphery would not have emerged without taking density-dependence and inter-annual variation into account. We conclude that including range position, inter-annual variation and density-dependence in one single statistical model is an important tool for the interpretation of demographic patterns regarding the central-marginal model.

The niche, limits to species' distributions, and spatiotemporal variation in demography across the elevation ranges of two monkeyflowers

“…Discussion Examination of detailed individual-level annual census data from natural populations has revealed marked differences in population dynamics between central and marginal areas of species' ranges. More studies have examined vital rate mean differences across the range than differences in temporal variability (33,35,36). Using a sequence of 7 annual transitions, this study shows that central and marginal populations differ not just in mean vital rates but in some cases also in the temporal variabilities of vital rates.…”

“…Paradoxically, populations at the M. cardinalis range center exhibit long-term growth rates that are below replacement levels, whereas marginal population growth rates encompass values consistent with population stability. Several other comparisons of central-marginal demographic patterns have found similarly ambiguous or unexpected results (35)(36)(37)(38)(39), which suggests that consideration of additional factors such as density dependence, source-sink dynamics, dispersal limitation, and disequilibrium between climate and current ranges will be necessary to fully understand the relationship between demography and distribution (39).…”

Linking N-driven biodiversity changes with soil N availability in a Mediterranean ecosystem

“…For a therophyte plant, the transition from seed in the seed bank to seedling or juvenile may depend on the initial seed density, while the transition from juvenile to reproductive adult and from adult plant to seed might depend on the corresponding density in the population (Kluth and Bruelheide 2005). Therefore, changes in the ratio of reduced to oxidized inorganic N may have prevented therophyte plants from using the increased N availability to complete their life cycle (van den Berg et al 2008) in the first and/or second years of N addition.…”

Plant performance in central and northern peripheral populations of the widespreadPlantago coronopus

“…Peripheral populations may occur in locally favourable conditions (Lennon et al 2002), such as high water availability, high soil organic matter content or low competition. While some studies have found lower fecundity (Garc í a et al 2000, Jump andWoodward 2003), recruitment (Tremblay et al 2002) or survival (Carey et al 1995) in peripheral populations, others have reported increased values in diff erent vital rates towards range edges (Kluth and Bruelheide 2005a, Angert 2009, Samis and Eckert 2009). While some studies have found lower fecundity (Garc í a et al 2000, Jump andWoodward 2003), recruitment (Tremblay et al 2002) or survival (Carey et al 1995) in peripheral populations, others have reported increased values in diff erent vital rates towards range edges (Kluth and Bruelheide 2005a, Angert 2009, Samis and Eckert 2009).…”

“…Demographic performance of populations seems to be indeed rather variable across many species ' ranges (Carey et al 1995, Nantel and Gagnon 1999, Garc í a et al 2000, Kluth and Bruelheide 2005a, Purves 2009), probably refl ecting specifi c local environmental conditions. In addition, populations at the range margin may or may not be considered marginal from an ecological point of view (Grant andAntonovics 1978, Herrera andBazaga 2008).…”