Developmental trap or demographic bonanza? Opposing consequences of earlier phenology in a changing climate for a multivoltine butterfly

Abstract

A rapidly changing climate has the potential to interfere with the timing of environmental cues that ectothermic organisms rely on to initiate and regulate life history events. Short‐lived ectotherms that exhibit plasticity in their life history could increase the number of generations per year under warming climate. If many individuals successfully complete an additional generation, the population experiences an additional opportunity to grow, and a warming climate could lead to a demographic bonanza. However, these plastic responses could become maladaptive in temperate regions, where a warmer climate could trigger a developmental pathway that cannot be completed within the growing season, referred to as a developmental trap. Here we incorporated detailed demography into commonly used photothermal models to evaluate these demographic consequences of phenological shifts due to a warming climate on the formerly widespread, multivoltine butterfly (Pieris oleracea). Using species‐specific temperature‐ and photoperiod‐sensitive vital rates, we estimated the number of generations per year and population growth rate over the set of climate conditions experienced during the past 38 years. We predicted that populations in the southern portion of its range have added a fourth generation in recent years, resulting in higher annual population growth rates (demographic bonanzas). We predicted that populations in the Northeast United States have experienced developmental traps, where increases in the thermal window initially caused mortality of the final generation and reduced growth rates. These populations may recover if more growing degree days are added to the year. Our framework for incorporating detailed demography into commonly used photothermal models demonstrates the importance of using both demography and phenology to predict consequences of phenological shifts.

Changes in flight period predict trends in abundance of Massachusetts butterflies

“…1b) may be transitioning from univoltine to bivoltine in our region (Stichter, 2015). If additional generations are the causal mechanism between changes in flight period and increased abundance in multivoltine species, it would suggest that beneficial effects of higher population trends (Kerr et al ., 2020) and/or more rapid evolution (Chevin et al ., 2010) outweigh the potential costs of developmental traps (Van Dyck et al ., 2015; Levy et al ., 2015). List‐length analysis does not distinguish changes in per‐generation abundance from changes in the number of generations, so further investigation would be necessary to understand these mechanisms.…”

“…Our results highlight the potential for phenological changes to affect population dynamics, and the general importance of phenological flexibility for insect population dynamics in changing environments. Past studies of phenology rarely evaluated shifts at the end of the activity (Zipf et al ., 2017; Gallinat et al ., 2015), despite the demographic importance of late‐season events such as entry into diapause (Kerr et al ., 2020). We find little evidence in Massachusetts for the lost generation hypothesis (Van Dyck et al ., 2015); some multivoltine species did experience longer flight periods and decreased abundance (e.g.…”

“…Under a warming climate, populations that were formerly thermally restricted in parts of their range may be capable of producing an additional generation within the extended growing season since advanced emergence results in different experienced photoperiodic cues (Kozak et al ., 2019; Tobin et al ., 2008; Altermatt, 2010; Mitton and Ferrenberg, 2012; Grevstad and Coop, 2015). Species that can successfully add a generation in the extended growing season may benefit from another bout of reproduction, leading to higher overall population growth rates (Kerr et al ., 2020) and the potential for more rapid evolutionary responses to climate change (Chevin et al ., 2010). In spite of its potential benefits, an increase in voltinism can also be detrimental to insects.…”

Changes in Flight Period Predict Trends in Abundance of Massachusetts Butterflies

“…Under a warming climate, populations which were formerly thermally restricted in parts of their range may be capable of producing an additional generation within the extended growing season (Kozak et al, 2019;Grevstad & Coop, 2015;Mitton & Ferrenberg, 2012;Altermatt 2010;Tobin et al, 2008) which could be beneficial or detrimental for populations. Species that can successfully add a generation in the extended growing season may benefit from another bout of reproduction, leading to higher overall population growth rates (Kerr et al, 2020;Kerr et al, 2019), and the potential for more rapid evolutionary responses to climate change (Chevin et al, 2010). In spite of its potential benefits, an increase in voltinism can also be detrimental to insects.…”

Beyond thermal melanism: association of wing melanization with fitness and flight behaviour in a butterfly

“…For example, deviations from optimal thermal developmental conditions have negative consequences, as they can cause a mismatch in the timing of maturation (i.e. ‘developmental trap’, Boggs, 2016 ; Kerr et al., 2020 ; Van Dyck, Bonte, Puls, Gotthard, & Maes, 2015 ), affect final body size with cascading effects for adult life histories, and even impact survival ( Douhard et al., 2013 ; e.g. ; Jannot, 2009 ; Orizaola, Dahl, & Laurila, 2010 ; Pankhurst & Munday, 2011 ).…”