Temporal Change in Community Composition, Ecological Niche, and Phenotypic Selection in Minnesota’s Rare Arctic Relict Plants

Abstract

Rare, arctic relict plant populations of Minnesota, found in the cool and moist microclimate produced along the cold waters of Lake Superior, face an uncertain future due to anthropogenic climate change. In this study, we used a variety of approaches to examine the contemporary impacts of climate change and to predict how populations will respond in coming decades. To investigate how these arctic relict communities have already changed, we surveyed population occurrence based on historical herbarium records, and compared community composition after nearly 20 years of climate change across a latitudinal gradient that mimics a range of different degrees of warming. Large temporal dissimilarity in community composition occurred across all sites surveyed, and southern sites showed an overall mean decrease in species richness. Ecological niche modeling based on Minnesota populations of Primula mistassinica, Pinguicula vulgaris, and Euphrasia hudsoniana show a high probability of drastic reduction in suitable habitat under a conservative climate model forecast. To understand the current patterns of selection in Minnesota arctic relict populations, we conducted a phenotypic selection analysis on the same three species across the latitudinal gradient. All species sampled showed reduced flowering in the most southern populations, where average summer temperatures were nearly +2 °C warmer than the northernmost plots. Phenotypic selection analysis of Pinguicula vulgaris, the species estimated to be most vulnerable to climactic changes according to ecological niche models, revealed differences in the direction of selection on flowering date between northern and southern populations. Preliminary estimates of population viability yielded mixed results and additional data is needed to forecast the future of these arctic relict communities in Minnesota.