Climate change has been identified as a threat to species persistence worldwide. However, population-level responses to changes in climatic factors may differ substantially between species or locations. While these differences are apparent at large spatial and taxonomic scales, differences in life history, and site-specific changes in biotic and abiotic drivers at smaller scales may have the ability to alter a population’s response to climate change as well. This study addresses the effects of climate in the current and previous year on 8 populations of closely related orchid species (genus Dactylorhiza and Gymnadenia) at two sites in central Norway. We used over 30 years of demographic and climatic data to construct matrix models parameterized by generalized linear mixed models (GLMMs). We examined the effects of current and previous year precipitation and temperature on standard vital rates (survival, transitions, and flower production). We compared the overall effect of these climatic variables by assessing growth rates in each population at differing combinations of climatic scenarios. We also used hierarchical clustering to compare the similarity of effects of the climatic variables on populations at the vital rate level.
Results/Conclusions
Population growth rates were more affected by temperature and precipitation in the previous year (maximum 20% change in population growth rate) than by spring temperature and precipitation in the current year (maximum 10% change). However, strong variance of similar magnitude between populations of differing species and conspecific populations at different sites was observed. Clustering analysis revealed certain vital rate responses were more differentiated by species (dormancy, flower production), while others were more differentiated by study area (probability of reproduction). Results demonstrate that the effects of climatic variation may strongly depend on the local environment and life history. Considering such small-scale heterogeneity may be key for developing successful conservation and management plans at the population level. Additionally the clear separation of species and site differences in the vital rates emphasize the importance of considering underlying vital rates as well as overall population dynamics in order to get a clearer view of the study system.