Phenological responsiveness and fecundity differ in range edge vs range interior populations of Lysimachia borealis

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Emily Dangremond and Christopher H Hill, Biological, Physical and Health Sciences, Roosevelt University, Chicago, IL, Christopher H Hill, Southern Illinois University

Background/Question/Methods
In boreal species, populations at a southern range edge are at risk of being extirpated due to rising temperatures from climate change and potentially from demographic factors that affect small populations. The ability to track climate through phenological responsiveness can affect survival and reproductive success, with implications for long-term population persistence. This study examines phenological responsiveness and fecundity in populations of an understory plant species, Lysimachia borealis in the Midwestern United States. We collected flowering data from herbarium records and observations from 1877-2020. We used regression models to examine how flowering date has changed over time and the relationship between flowering date and spring temperature. We conducted field surveys to quantify fecundity in range-edge and range-interior populations spanning from Illinois to Minnesota.
Results/Conclusions
Range-edge populations have not shown a shift in average flowering date over time, though some range-interior populations have. We found that range-interior populations show phenological responsiveness to spring temperature, flowering approximately 3 days earlier for every 1°C increase in spring temperature. Range-edge populations did not change flowering dates in response to temperature. Range-edge populations have lower rates of flowering and fecundity than range-interior populations. Range-edge populations have fewer and smaller individuals than range-interior populations. These results suggest that southern-range edge populations of L. borealis are not performing well and are expected to continue to decrease in abundance.