Demographic and functional determinants of large-scale population dynamics and ecological niches of 26 serotinous Proteaceae

[摘要] ENGLISH ABSTRACT: Understanding how organisms respond to the environment at large spatial scales is central toecology, biodiversity research and conservation. Environmental variation affects the fitness (orperformance), population dynamics and geographical distributions of species viamorphological traits. Quantifying how demographic rates and functional traits vary acrossenvironmental gradients may thus yield insights into the underlying determinants of ecologicalperformance and geographical distribution. However, studies of demographic and trait variationwidely rely on observations from a few species, at small spatial scales and seldom includemultiple abiotic and biotic drivers. A basic understanding of the drivers of large-scaledemographic variation and how functional traits relate to population dynamics and species'niches remains limited.Using the Hutchinsonian niche concept (i.e. the set of environmental conditions in whichpopulations can grow), I investigated how environmental conditions and functional traits affectthe demography, population dynamics and ecological niches of 26 serotinous Proteaceaespecies with fire-dependent life cycles from the Cape Floristic Region (South Africa). Myobjectives were to: (i) identify the environmental drivers of large-scale demographic variation,(ii) investigate whether plant functional traits explain demographic performance andHutchinsonian niches, and (iii) study geographical variation in population sensitivity towildflower harvesting. I addressed these objectives using data on key demographic rates andplant functional traits sampled across species' entire geographical ranges.Environmental drivers (climate, fire disturbance, soil nutrient status and population density)explained variation in key demographic rates of reproduction and survival across species'geographical distributions. The relative importance of these drivers varied throughout the lifecycle of the study species: fecundity was mostly driven by fire interval whereas recruitmentdepended more on climate. A trade-off between survival and reproduction was also found where species with fire-protected buds (resprouters) had substantially higher fire survival comparedto species without fire-protected buds (nonsprouters). Overall, intraspecific variation infecundity and recruitment was greater than that of fire survival.I also investigated whether variation in functional traits (leaf, plant-architectural and seed traits)explains the Hutchinsonian niches of species. Results showed that interspecific trait variationexplained considerable variation in global maximum population growth rates (rmax), as well asniche optima and widths along different environmental gradients. Intraspecific trait variationhad positive effects on niche widths. Overall, relatively few individual traits stood out aspredictors of species' demographic niches.Finally, I integrated range-wide demographic data and dynamic population models to assessspatial variation in sensitivity to harvesting across species' geographical distributions. Idetected considerable variation in sensitivity to harvesting across species and populations.Range-wide intraspecific variation in sensitivity to harvesting showed distinct geographical andenvironmental relationships. Notably, sensitivity to harvesting was highest at the environmentallimits of species' ranges.Combined, these range-wide demographic and functional approaches on species niches providefundamental and applied perspectives in ecology and conservation biogeography. These arenecessary steps to understand how range dynamics emerge from variation in demography andfunctional traits, and how species may be affected by ongoing global change.

[发布机构] Stellenbosch University