Population Demography of Primula farinosa subsp. modesta and Its Implications for Responses to Changing Environments in Subalpine Plant Species

Abstract

Because global climate change has a massive impact on plant ecosystems, including rising temperatures, the movement to higher altitudes, and phenological shifts, significant differences in the distribution of plant species are being observed. These effects of climate change are projected to cause huge changes in plant distribution. Although many studies have been conducted to predict species distribution to changing environments, the different demographic responses of populations make predictions difficult. Plant populations in alpine ecosystems sensitive to climate change can show various responses to environmental factors due to geographical isolation. Therefore, demographic analyses by sites are needed to predict alpine plant species distribution accurately. We conducted a study using a demographic model to understand changes in the species distribution of subalpine plants in response to environmental changes. On the other hand, despite the emphasis on the effects of biotic factors on species distribution, an understanding of biotic interactions in demographics is lacking. In particular, competition under climate change can be a major driver limiting species distribution. Alpine plants are known to be vulnerable to competition intensified by climate change.Therefore, we aimed to evaluate the effect of biotic factors on the demographic response of subalpine plants. In this study, we studied the demographics of a subalpine plant species, Primula farinosa subsp. modesta, and evaluated the effects of interspecific competition on population demography. In Chapter 2, we built population models by sites to investigate temporal variations in demographic responses. We conducted a demographic survey from 2016 to 2021 and analyzed the temporal demographic variation of P. farinosa populations on four distant sites in Korea (CH, Chenhwangsan; GY, Gayasan; JR, Jirisan; HL, Hallasan). The life cycle of P. farinosa was divided into four life stages, and stage-structured transition matrices were constructed for each site and year. We employed a life table response experiment (LTRE) to decompose the variation of λ into site and year effects and further decomposed into the LTRE effects of vital rates. We assessed the correlation between the LTRE effect of the vital rates and the temporal variation of λ. A negative correlation indicates that the variation in these vital rates buffers the annual variation in λ. Next, the effects of demographic compensation on the temporal variation of λ were examined by evaluating the negative correlations between the LTRE effects of vital rates. This study shows that P. farinosa exhibited site-specific yearly variation in the population growth rate (𝛌𝛌), implying that high mountain populations might not decline simultaneously. The contribution of vital rates to the yearly variation and patterns of demographic compensation also differed among the sites, which likely induced the site-specific temporal variation of λ. As a result of Chapter 2, we suggested that it is necessary to consider temporal variation within each site to preserve alpine plants under climate change. In Chapter 3, we hypothesized that the increase in surrounding vegetation due to climate change would lead to changes in the distribution of P. farinosa through biotic interactions. We conducted an annual census to verify this hypothesis by expanding the survey plots from 2018 to 2021 in four sites. The survey plots were set according to the coverage gradient of surrounding vegetation, and demographic analyses were performed by creating an integral projection model for each plot. We focused on whether the high coverage of herbaceous plants significantly affects the population growth rate and vital rates of P. farinosa. Results of this study showed that the high coverage level caused a low population growth rate of P. farinosa, which was predicted to be smaller than the current population size. Coverage of surrounding vegetation affected survival rates, especially juvenile stage, and elasticities of survival. Finally, the attenuated survival rate of P. farinosa contributed to the reduced population growth rate. We predicted that the interspecific competition with Sanguisorba hakusanensis, which mainly constitutes the surrounding vegetation, had a negative effect on P. farinosa in Chapter 3. Therefore, in the study of Chapter 4, we conducted a competition experiment between P. farinosa and S. hakusanensis and included two temperature conditions (18'C and 20'C) in the experimental design to evaluate the effect of warming on the competition. The survival rate, rosette size, number of leaves, flowering probability, and number of flowers in 236 pots were measured after P. farinosa had grown for 7 months, including 2 months of vernalization. In the results of Chapter 4, the survival rate and flowering rate of P. farinosa were reduced under competition with S. hakusanensis. Rosette size was reduced by competition before vernalization, but rosette size after vernalization was not affected by competition. There was also a decrease in survival rate due to temperature conditions, but there was no difference in the competitive effect due to warming. As a result, it was experimentally verified that P. farinosa could be affected by interspecies competition and cause negative demographic responses. These studies presented comprehensive results from demographic models and growth experiments to understand the population dynamics of P. farinosa and its conservation with consideration of climate change. Furthermore, we quantitatively evaluated demographic responses against a gradient of biotic factors. This thesis suggested that these processes apply to various plants that should be conserved, ultimately contributing to accurate distribution prediction and biodiversity with climatic changes.