\articletype Original Articles Intraspecific variation in phenotypic plasticity can affect the ability of populations, and thus species, to respond to environmental changes. However, the prevalence and drivers of such variation are not well known. It is often assumed that intraspecific variation in phenotypic plasticity is driven by mechanisms associated with the position of a population within the species’ geographic range and the environmental heterogeneity experienced by the population. To test the effect of these two drivers, we use a combination of germination and greenhouse experiments to measure thermal phenotypic plasticity in traits ranging from germination to flower abundance in populations of three Hypericum species sampled across their European ranges. We then relate thermal plasticity to each population’s position within the species’ range and to the environmental heterogeneity of the sampling site. Our results revealed that while average thermal plasticity in several traits was similar among the three tested Hypericum species, it varied among the conspecific populations. Specifically, populations from closer to the range edge tended to be more plastic in germination probability and plant height, while populations from more heterogeneous environments tended to be more plastic in flowering phenology, plant height, and flower abundance. Interestingly, for plasticity in germination phenology, plant height, and flower abundance, we found a substantial interactive effect with accentuated plasticity in heterogeneous sites near the range edge. This suggests that populations in heterogeneous environments at range edges may adjust to environmental change via phenotypic plasticity more effectively than are other conspecific populations. These results support both tested drivers and reveal important interactive patterns for some of the tested traits. Furthermore, they encourage further research on plasticity to consider both range position and environmental heterogeneity.

Nature conservation has shifted towards a climate change adaptation approach, in which expected species range shifts are increasingly considered. Facilitating species movements requires improving ecological connectivity across landscapes, and for these assessments, new and powerful approaches are emerging. One such approach is the use of geodiversity information as a proxy for biodiverse, resilient, and dispersal-enhancing areas. Although data on abiotic nature are routinely used in many connectivity assessments, geodiversity is not necessarily recognized by researcher due to non-explicit application of variables combined with vague definitions of terms. Here, we present a systematic literature review examining the role of geodiversity in ecological connectivity. We used the PRISMA method to review 89 research articles on the topic. Of these, 34% explicitly modeled connectivity and included geodiversity variables, while the remaining studies discussed or explored the potential effects of geodiversity on species movement and broader biodiversity patterns, without directly modeling connectivity. Our findings highlight the value of integrating geodiversity and the Conserving Nature’s Stage approach in both research and the management of connectivity and climate resilience. We identified that the key challenges hindering the widespread use of geodiversity information in biodiversity conservation stem from the limited adoption of the term outside geosciences and the lack of established quantitative metrics to explore the geodiversity-biodiversity relationship. Addressing these gaps could greatly enhance ecological connectivity assessments, thereby improving conservation outcomes. After all, geodiversity is the abiotic counterpart to biodiversity, and together these two components form the dynamics of nature that we aim to conserve.

Temperature plays a pivotal role in defining the distribution of species and the fitness of individuals within species’ ranges. Phenotypic plasticity can allow individuals to cope with varying environmental conditions, including rapid climate change. Populations at range edges experience more variable conditions than core populations and thus are hypothesized to exhibit higher thermal plasticity. However, as the strength of plasticity often varies between individuals, it can also differ among local populations at range edges. We studied the extent of and variation in thermal plasticity for several traits within and between populations of the perennial herb Plantago lanceolata L. (Plantaginaceae) at its northern range edge. We sampled seeds from nine sites within a 50 x 50 km region and grew them under three temperature regimes in a greenhouse. We measured traits related to size, flowering, pathogen responses, and inflorescence pigmentation. We expected to find higher plasticity in traits less strongly connected to fitness and that differences between individuals would outweigh differences between populations in underpinning this variation in plasticity. Our results show thermal plasticity in leaf size and abundance, flowering probability and abundance, and pigmentation. Notably, we also found increased pathogen symptoms and higher infection rates of one of two viruses screened, highlighting the potential for changes in pathogen sensitivity and exposure under climate change. Importantly, in all traits but flower abundance, more variation in plasticity was attributable to differences within populations than between populations. Although this contribution was small in magnitude compared to thermal effects on traits, the higher intra- versus interpopulation variation in plasticity suggests that differences between individuals provide most of the variation in thermal plasticity, which may be driven by small-scale variations in habitat conditions; highlighting the need for conservation strategies that consider microhabitat variation to support short-term adaptive responses to thermal variability.

1. Introduction Ongoing climate change poses an increasing threat to biodiversity. To avoid decline or extinction, species need to either adjust or adapt to new environmental conditions or track their climatic niches across space. In sessile organisms such as plants, phenotypic plasticity can help maintain fitness in variable and even novel environmental conditions and is therefore likely to play an important role in allowing them to survive climate change, particularly in the short term. Understanding a species’ response to rising temperature is crucial for planning well-targeted and cost-effective conservation measures. 2. Methods We sampled seeds of three Hypericum species (H. maculatum, H. montanum, and H. perforatum), from a total of 23 populations originating from different parts of their native distribution areas in Europe. We grew them under four different temperature regimes in a greenhouse to simulate current and predicted future climatic conditions in the distribution areas. We measured flowering start, flower count, and subsequent seed weight, allowing us to study variations in the thermal plasticity of flowering phenology and its relation to fitness. 3. Results Our results show that individuals flowered earlier with increasing temperature, while the degree of phenological plasticity varied among species. More specifically, the plasticity of H. maculatum varied depending on population origin, with individuals from the leading range edge being less plastic. Importantly, we show a positive relationship between higher plasticity and increased flower production, indicating adaptive phenological plasticity. 4. Synthesis The observed connection between plasticity and fitness supports the idea that plasticity itself may be adaptive. This study underlines the need for information on plasticity for predicting species’ potential to thrive under global change and the need for studies on whether higher phenotypic plasticity is currently being selected for as natural populations experience a rapidly changing climate.