40 Years of Climate-Induced Shifts in the Reproductive Phenology of Keystone Species Across a Biogeographic GradientLong-term Temporal Trends

Bruno Salonen¹, Antony Knights², Louise Firth², David Bilton¹

¹University of Plymouth, UK - ²University College Cork, Ireland

Environmental temperature fundamentally shapes species distributions, metabolism, and reproductive phenology, making it critical for understanding ecological responses to climate change. This study examines how long-term climate variability has influenced the reproductive phenology of the keystone limpet Patella vulgata and its congeners across a latitudinal gradient from northeast England to southern Portugal. Using datasets from cold (1972–1986) and warm (2011–2016) periods, we analysed changes in peak reproductive readiness, seasonal reproductive engagement, the timing of seasonal peaks, and failure years. Results reveal distinct species- and region-specific responses to warming. For P. vulgata, northern populations (NE England) exhibited resilience, with a 6.3% increase in peak readiness, a 20.3% rise in seasonal peak magnitude, and earlier, extended reproductive activity. In contrast, southern populations (S England and N Portugal) showed shortened reproductive seasons and reduced engagement despite modest readiness increases (2.1% and 7.8%, respectively), reflecting thermal stress. P. depressa populations in S England and N Portugal showed stable readiness and earlier peaks, supported by trickle-spawning, buffering against moderate warming. However, southern populations (C and S Portugal) experienced delayed peaks, reduced readiness, and significant declines in engagement (AUC drops of 45.7% and 60.9%), indicating thermal constraints near range edges. For P. ulyssiponensis, reproduction remained stable in S England but declined sharply in S Portugal, with reduced readiness (12.3%), AUC decline (68.4%), and delayed peaks, highlighting vulnerability at thermal limits. Additionally, in S Portugal, this species shifted from synchronous to trickle-spawning. Failure years were rare, observed only in P. ulyssiponensis during the cold period in S England, reflecting its sensitivity to thermal variability. These findings highlight how warming exacerbates vulnerabilities at thermal limits but may extend reproductive windows in cooler regions, providing insights into species’ adaptive potential and resilience under ongoing climate change.