Spatiotemporal patterns of emergence phenology reveal complex species-specific responses to temperature in aquatic insects

Abstract

Aim: Climate change is broadly affecting phenology, but species-specific phenological response to temperature is not well understood. In streams, insect emergence has important ecosystem-level consequences because emergent adults link aquatic and terrestrial food webs. We quantified emergence timing and duration (within-population synchronicity) of insects among streams along a spatiotemporal gradient of mean water temperature in a montane basin to assess the sensitivity of these phenological traits to heat accumulation from mid-winter through spring emergence periods. Location: Six headwater streams in the Lookout Creek basin, H.J. Andrews Experimental Forest, Oregon, USA. Methods: We collected emerging adults of four abundant insect species twice weekly throughout spring for 6 consecutive years. We fit Gaussian models to the empirical temporal distributions to characterize peak emergence timing (mean) and duration (days between 5th and 95th percentiles) for each species/stream/year combination. We then quantified relationships between degree-day accumulation and phenological response. Results: Only one of the four species (a caddisfly) showed a simple response of earlier emergence timing in both warmer streams and years. One stonefly had lengthy emergence periods resulting in substantial phenological overlap between warmer and cooler streams/years. Interestingly, two species (a mayfly and a stonefly) responded strongly to temporal (interannual) temperature differences but minimally to spatial differences, indicating that emergence was nearly synchronous among streams, within years. These two species had among-stream differences approaching 500 degree-days from mid-winter to peak emergence. Conversely, duration of emergence was more strongly associated with spatial than temporal differences, with longer duration in lower-elevation (warmer) streams. Main conclusions: Emergence phenology has species-specific responses to temperature likely driven by complex cues for diapause or quiescence periods during preceding life cycle stages. We hypothesize a trade-off between complex phenological response that synchronizes emergence among heterogeneous sites and other traits such as adult longevity and dispersal capacity.

Department(s)

Biology

Document Type

Article

DOI

10.1111/ddi.13472

Keywords

aquatic insects, headwater streams, life history traits, phenology, temperature

Publication Date

8-1-2022

Journal Title

Diversity and Distributions

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