Persistently warmer temperatures lead to life history changes in bluegill sunfish (Lepomis macrochirus)

Abstract

Life history strategies shape many aspects of species’ ecological importance and population demographics. For ectotherms, life history strategies are highly dependent on temperature, among other environmental conditions. With projected increases in global temperatures, understanding the success of organisms under warmer conditions is critical. Due to the difficulty of establishing long-term heating studies on whole lake systems, there is little empirical evidence addressing the potential changes in life history strategies of fish in situ in response to future climate warming predictions. Here, we study early growth rates, size-at-maturation, maximum adult size, and lifespan of bluegill sunfish in three lakes in Illinois from 2013 to 2017 that experience above-ambient temperatures year-round due to artificial heating by electrical power plant cooling systems and compare these to populations in three nearby ambient lakes. Temperature changes in the heated lakes are within the range of temperature increases predicted by the year 2100. We find evidence that life history strategies and population demographics are substantially affected by warmer environments. Heated populations showed 22% faster first-year growth, 23% shorter lifespans, greater rates of maturation at small body sizes, and over a 4-fold reduction in the relative number of individuals that reach large sizes. Changes in life history strategies, including lifespan and maximum sizes, will be evident across many fish species under warmer conditions in the future and further research should aim to address how these changes will affect trophic interactions.