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 degreedays 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 | 1525 FINN et al.

Drivers of Odonata flight timing revealed by natural history collection data

“…But it emphasizes the limits of degree day estimates when calculated as annual sums, rather than incremental values that can be matched to specific Julian dates. Incremental or cumulative degree day values could be aligned directly with emergence dates, providing a mechanistic link to emergence (Cayton et al, 2015; Finn et al, 2022); this approach would be more powerful than the correlative one used here for DD18 and DOY. Similarly, degree days from the prior year may improve emergence timing models, particularly for semivoltine taxa (Richter et al, 2008).…”

Bucketloads of aquatic invertebrates in a dry intermittent stream

“…This caddisfly occurs in high densities during the flowing phase in Shelton Creek and has been documented to have egg diapause (Bowles & Allen, 1992). It is possible that caddisflies and other taxa underrepresented in our buckets have dormant stages that develop in response to additional cues beyond the presence of water (e.g., temperature; Finn et al, 2022).…”

Biological traits, geographic distributions, and species conservation in aquatic ecosystems

“…Our special issue contributes to the field by identifying key linkages between physiological and other traits. Finn et al (2022) assessed the sensitivity of phenological traits (emergence timing and duration) to heat accumulation (i.e. cumulative degree‐days) of the four most abundant, spring‐emerging species from the orders Ephemeroptera, Plecoptera, and Trichoptera during the emergence period in six headwater streams with different elevation in the Lookout Creek basin, Oregon.…”

“…The authors also observed highly variable phenological responses among different populations and species, indicating three clearly different phenological patterns with different thermal regimes among four aquatic insect species. Finn et al (2022) hypothesized a trade‐off between a complex phenological response that synchronizes emergence among heterogeneous sites and other traits such as adult longevity and dispersal capacity. This work sheds new light on the complexity of phenological responses of aquatic insects to water temperature and climate change and indicates key directions for future research.…”