Population resistance and recovery after an extreme heat event are explained by thermal effects on life-history traits

Extreme heat events lower the fitness of organisms by inducing physiological stress and increasing metabolic costs. Yet, little is known about the role of life-history traits in elucidating population responses to extreme heat events. Here, we used a trait-based approach to understand population resistance and recovery using four closely related species of soil-dwelling Collembola. We measured thermal reaction norms of life-history traits (survival and reproductive traits) and used this information to identify ecological mechanisms linked to population responses after an extreme heat event (i.e. one week at 26–30°C, representing + 10°C above ambient conditions). Furthermore, we investigated potential shifts in the body size distribution of recovering populations to better understand if extreme heat events can restructure body size spectra within populations. While resistance remained unaltered across species in our study, the recovery response of the most heat-sensitive species (Protaphorura pseudovanderdrifti, predominantly a boreal species) was strongly affected by the extreme heat event (−54% population change compared to ambient conditions). Given that the fecundity (linked to recovery) of P. pseudovanderdrifti was more sensitive to heat than their survival (linked to resistance), we detected a decoupling between population resistance and recovery to an extreme heat event in this species. In addition, the detrimental effects of heat on fecundity were largely responsible for a drop in the proportion of small-sized (juvenile) individuals in the recovering populations of P. pseudovanderdrifti. Thermally insensitive resistance and recovery in the other three species (P. armata, P. fimata, P. tricampata; predominantly temperate species) can be explained by their high survival and fecundity at warmer temperatures. We highlight that life-history trait responses to warming can help explain population resistance and recovery after extreme heat events

Temperature-dependent trade-offs in maternal investments: An experimental test with two closely related soil microarthropods

Organisms face trade-offs in their reproductive investment due to energetic constraints. Yet, little is known about how such investments may change at different temperatures, and particularly so in soil invertebrate organisms. Here, we studied two Collembola species (Folsomia candida and Proisotoma minuta) using a long term (several generations) temperature incubation experiment (separately at 15 and 20 ◦C) to investigate how egg size and egg numbers and the trade-off between the two are affected in two temperature regimes. Both species are known to grow at these temperatures, but the variation in their reproductive strategies are little known. Our results show that egg sizes of F. candida were larger in colder temperature whereas no such patterns were found in P. minuta. By contrast, we found no effect of the two temperatures on egg numbers (per clutch) in any of the species. Moreover, we observed a negative correlation (indication of a potential trade-off) between egg size and egg numbers (per clutch) at colder temperature in F. candida, which disappeared in warmer temperature in the same species. No such trade-offs were found in P. minuta. Our results highlight that temperature effects on maternal investments are both trait- and species-specific, particularly when Collembola species are within their optimal thermal niches

Dealing with moving spatialities in disaster governance: the case of locust swarms

International audienceLocusts, albeit considered a biological hazard and one of the most destructive migratory pests in the world by the United Nations, are almost absent from risk governance studies. Yet their natural dynamic that alternates between recessions and periods of large-scale expansions imposes great spatio-temporal variabilities and discontinuities, and brings into sharp relief societies’ capacities to collaborate to face this transboundary and erratic bio-hazard. While natural sciences have largely contributed to building efficient preventive strategies around the world, invasions still occur and other approaches are needed to understand locust outbreaks and implement effective and sustainable responses. In this context, social sciences and geography are essential to address the social factors that shape preventive strategies and their articulation from local to international levels. Using multiple sources of data including interviews, literature review, and participatory workshops in three different case studies - the desert locust, the Australian plague locust, and the South American locust - we analyze the main challenges in the multi-level and nested governance systems required for locusts. In particular, we discuss the consequences of the extended, uncertain and discontinuous spatial structure imposed by locusts on the distribution of responsibility among multiple players with diverging values, interests, and/or capacity to act. We identify the responses implemented by locust managers around the world to face this variability, and analyze their inherent fragilities. We conclude that in a context of global change that imposes renewed conditions of interconnectedness, hazards, and vulnerabilities, locusts are a textbook case that can inform collaborative governance for managing and responding to large-scale disasters

Governing in the face of extreme variance and the inherent fragilities of adaptiveness: Insights from locusts

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