Predicting the persistence of species under climate change is an increasingly important objective in ecological research and resource management. However, variation in climate change responses among populations can greatly impact species-level predictions, especially in species that exhibit large biological differences at small spatial scales. Such microgeographic variation can significantly enhance the stability and resilience of species through portfolio effects, but it is rarely monitored or built into conservation and management plans. For species such as brook trout (Salvelinus fontinalis) that are widely distributed and consist of many populations, understanding drivers of asynchrony in population dynamics can help improve predictions of climate change impacts for the species. In this study, we use time-series of census population size (Nc) from mark-recapture surveys of eleven natural brook trout populations in Cape Race (Newfoundland, Canada) to examine the impact of population variation in demographic responses to a changing climate. The focal populations are strongly differentiated, occupy a small area (~150km2) with few human impacts, and experience similar climate conditions. Nc time-series from 2010-2021 were analyzed via dynamic factor analysis (DFA) to quantify patterns and drivers of population asynchrony, while variation in key demographic relationships were explored using generalized linear mixed models (GLMM).
Results/Conclusions
Preliminary results from DFA revealed significant population asynchrony in Nc patterns and the effect of incubation temperature on age-1 cohorts. Population-specific DFA loadings and covariate effects were not explained by five hypothesized drivers of population differences: average Nc, somatic growth rate, reproductive success, groundwater inputs (correlation analysis; p > 0.05) and neutral genomic divergence (Mantel test; p > 0.05). Similarly, variance partitioning from GLMMs (all coded with population as a random effect) suggested that a significant percentage of stock-recruitment, recruit-adult, and density-dependent growth relationships were driven by population variation in intercepts and slopes. Analysis of pairwise correlations and coefficients of variation in Nc supported the notion that population asynchrony drives portfolio effects in Cape Race brook trout, ultimately yielding more stable regional abundance patterns. Taken together, these results imply that population diversity can play a significant role in underpinning species responses climate change and other human impacts, even at microgeographic scales. We argue that increased monitoring of population variation in suitable taxa has the potential to reveal undiscovered mechanisms shaping the resilience of species in a changing world – mechanisms that could tip the balance between extirpation and persistence.
