Microclimatic variation affects developmental phenology, synchrony and voltinism in an insect population

Abstract

Temperature influences the rate of most biological processes. Nonlinearities in the thermal reaction norms of such processes complicate intuitive predictions of how ectothermic organisms respond to naturally fluctuating temperatures, and by extension, to climate warming. Additionally, organisms developing close to the ground experience a highly variable microclimate landscape that often is poorly captured by coarse standard climate data. Using a butterfly population in central Sweden as a model, we quantified the consequences of small‐scale temperature variation on phenology, emergence synchrony and number of annual reproductive cycles (voltinism). By combining empirical microclimate and thermal performance data, we project development of individual green‐veined white butterflies (Pieris napi) across 110 sites in an exceptionally high‐resolved natural microclimate landscape. We demonstrate that differences among microclimates just meters apart can have large impacts on the rate of development and emergence synchrony of neighbouring butterflies. However, when considering the full development from egg to adult, these temporal differences were reduced in some scenarios, due to negative correlations in development times among life stages. The negative correlations were caused by temperatures at some sites beginning to exceed the optimum for development as the season progressed. Indeed, which sites were optimal for fast development could change across the lifetimes of individual butterflies, that is, ‘fast’ sites could become ‘slow’ sites. Thus, from a thermal point of view, there seem to be no consistently optimal microsites. Importantly, the fast sites were not always the warmest sites. We showed that such unintuitive effects could play an important role in the regulation of phenological synchrony and voltinism in insects, as most sites consistently favoured two generations. The results were generally robust across years and three different egg‐laying dates. Using high‐resolved empirical climate data on organism‐relevant temporal and spatial scales and considering nonlinear responses to temperature, we demonstrated the large and unintuitive population‐level consequences of locally and temporarily high temperatures. We suggest to—whenever possible—incorporate species‐ and life stage‐specific nonlinear responses to temperature when studying the effects of natural microclimate variation and climate change on organisms. Read the free Plain Language Summary for this article on the Journal blog.

Interspecific differences in microhabitat use expose insects to contrasting thermal mortality

“…Microclimatic exposure during the development of insects will simultaneously affect other physiological and demographical rates besides larval survival (Braschler et al, 2021; Diamond et al, 2013; Kingsolver et al, 2011; von Schmalensee et al, 2021), which can influence the patterns of larval mortality described here. For example, different microclimatic regimes can lead to shorter or longer larval development times due to nonlinear changes in development rates with temperature (thermal performance curves; Greiser et al, 2022; von Schmalensee et al, 2021; Appendix S1: Figure S16). These variations in the development time would in turn modulate the time of exposure to microclimatic lethal stresses.…”

Seasonal specialization drives divergent population dynamics in two closely related butterflies

“…Points represent individual eggs and the band shows the 90% credible interval, colored by species probability. Microclimate data are previously published 135 . …”

“…In 2019, rapeseed plants ( Brassica napus napus ) were grown in a common greenhouse and subsequently translocated to 36 microhabitats across a field site in Södermanland, Sweden (58°58′23.2″N, 17°09′19.7″E) 135 . Sites were selected manually from a total 110 sites 135 to ensure accessibility during the experiment, while capturing as much as possible of the variation in mean temperatures, and variation around those mean temperatures (based on temperatures the previous summer). All plants were translocated simultaneously (within an hour), two days after the cotyledons had sprouted, to standardize the quality of the plants ( B. napus napus cotyledons are attractive to ovipositing females 56 , 136 ).…”

Microclimate, an important part of ecology and biogeography

“…There is a need for identifying general patterns of microclimate‐organism relationships across and within ecosystems (Kemppinen et al., 2021). For example, what makes microclimates act as microrefugia varies by site, by species and potentially by life stage, each depending on different spatiotemporal factors and scales (Caron et al., 2021; Greiser et al., 2022). Thus, not all microrefugia are equally valuable for protecting biodiversity (Hylander et al., 2015).…”