• Energy Research

Summary Future moderate changes in evaporation and precipitation regimes could have pronounced effects on zooplankton populations in small and temporary aquatic habitats, by causing higher salinity and a shorter wet phase and by reducing passive dispersal via hydrological connections between pools and increasing it by exposing propagules to the wind. Using a hydrological model, we simulated various climate change scenarios in a natural cluster of temporary rock pools in South Africa. In our simulations, a shift towards a drier climate was associated with reduced permanence and increased conductivity, resulting in a lower percentage of inundations sufficient for the hatching, growth and reproduction of aquatic organisms (up to a 21% decline for a fairy shrimp). Connections between pools by overflowing occurred less frequently (by up to 28%). However, more frequent desiccation events (by up to 15%) led to increased exposure of dormant propagules to wind, possibly promoting dispersal within the pool cluster but also leading to losses from the propagule bank. Our results suggest that environmental change might not only affect local (within‐pool) selection pressures but also regional dynamics in rock pool metapopulations and communities.

Higher temperatures and increased environmental variability under climate change could jeopardize the persistence of species. Organisms that rely on short windows of rainfall to complete their life-cycles, like desert annual plants or temporary pool animals, may be particularly at risk. Although some could tolerate environmental changes by building-up banks of propagules (seeds or eggs) that buffer against catastrophes, climate change will threaten this resilience mechanism if higher temperatures reduce propagule survival. Using a crustacean model species from temporary waters, we quantified experimentally the survival and dormancy of propagules under anticipated climate change and used these demographic parameters to simulate long term population dynamics.By exposing propagules to present-day and projected daily temperature cycles in an 8 month laboratory experiment, we showed how increased temperatures reduce survival rates in the propagule bank. Integrating these reduced survival rates into population models demonstrated the inability of the bank to maintain populations; thereby exacerbating extinction risk caused by shortened growing seasons.Overall, our study demonstrates that climate change could threaten the persistence of populations by both reducing habitat suitability and eroding life-history strategies that support demographic resilience.

Climate change does affect not only average rainfall and temperature but also their variation, which can reduce the predictability of suitable conditions for growth and reproduction. This situation is problematic for inhabitants of temporary waters whose reproductive success depends on rainfall and evaporation that determine the length of the aquatic phase. For organisms with long-lived dormant life stages, bet hedging models suggest that a fraction of these should stay dormant during each growing season to buffer against the probability of total reproductive failure in variable environments. Thus far, however, little empirical evidence supports this prediction in aquatic organisms. We study geographic variation in delayed hatching of dormant eggs in natural populations of two crustaceans, Branchinella longirostris and Paralimnadia badia, that occur in temporary rock pools along a 725 km latitudinal aridity gradient in Western Australia. Consistent with bet hedging theory, populations of both species were characterised by delayed hatching under common garden conditions and hatching fractions decreased towards the drier end of the gradient where the probability of reproductive success was shown to be lower. This decrease was most pronounced in the species with the longer maturation time, presumably because it is more sensitive to the higher prevalence of short inundations. Overall, these findings illustrate that regional variation in climate can be reflected in differential investment in bet hedging and hints at a higher importance of delayed hatching to persist when the climate becomes harsher. Such strategies could become exceedingly relevant as determinants of vulnerability under climate change.

SummaryOver the past 65 my, theAustralian continent experienced a pronounced shift from predominantly wet, tropical, conditions to a much drier climate. Little is known, however, about the effect of this important continent‐wide event on freshwater organisms and ecosystems. Fairy shrimps (Crustacea;Anostraca) are ancient and specialist inhabitants of temporary and saline aquatic habitats that typically prevail under semiarid conditions. Therefore, they present suitable evolutionary models to study scenarios of historic environmental change and the impact of a drying climate on aquatic ecosystems in particular.Focussing on both macro‐ and micro‐evolution in the fairy shrimp genusBranchinellaand using mitochondrialDNAdata (16SandCOI), we evaluated whether patterns of contemporary genetic variation reflect historic climate change.There is a close match between episodes ofCenozoic climate change and macro‐evolutionary diversification inAustralian fairy shrimps, presumably mediated by a progressive increase in the abundance and diversity of temporary aquatic habitats on the continent. Micro‐evolutionary patterns reflect both range expansion and recent contraction, linked to extreme drying events during the Pleistocene glacial periods.This study effectively illustrates the potential long‐term effects of environmental change on the diversity and the evolutionary trajectories of the fauna of temporary waters. Moreover, it demonstrates the importance of adaptation to new environments and non‐adaptive processes, such as divergence in isolation, for explaining extant diversity patterns in this particular environment.

Global climate is changing rapidly, and the degree to which natural populations respond genetically to these changes is key to predicting ecological responses (1-3). So far, no study has documented evolutionary changes in thermal tolerance of natural populations as a response to recent temperature increase. Here, we demonstrate genetic change in the capacity of the water flea Daphnia to tolerate higher temperatures using both a selection experiment and the reconstruction of evolution over a period of forty years derived from a layered dormant egg bank. We observed a genetic increase in thermal tolerance in response to a two-year ambient +4 deg C selection treatment and in the genotypes of natural populations from the 1960s and 2000s hatched from lake sediments. This demonstrates that natural populations have evolved increased tolerance to higher temperatures, probably associated with the increased frequency of heat waves over the past decades, and possess the capacity to evolve increased tolerance to future warming.

Most temporary pond zooplankton species produce drought-resistant eggs that accumulate in the sediment and form an egg bank. When a pond dries and the egg bank is exposed, wind erodes eggs and wind action has been suggested as an important determinant of population demographics. While field observations suggest that egg bank erosion may be highest shortly after pond drying and physical disturbance of the sediment crust, this remains to be tested empirically. We performed a laboratory wind tunnel experiment to assess the effects of wind speed and sediment characteristics on egg pickup rates over time in a controlled environment. We used sediment samples in which an egg bank of the fairy shrimp Branchipodopsis wolfi was embedded and compared the number of eggs that blew away from dry, drying and disturbed egg banks as a function of time. Few eggs were picked up when the egg bank was dry prior to exposure, even at winds of 70 km h−1. Most eggs were eroded when the egg bank was exposed to wind before it dried out, after the last water evaporated. Likewise, physical disturbance resulted in strong erosion fluxes. Overall, our results suggest that the state of the egg bank may be more important for egg bank erosion rates than the prevailing wind speed or the wind exposure time. Also, our findings are worrying in the context of climate change since they imply that predicted increases in drying events and reduced inundation lengths may compromise egg bank persistence in temporary ponds.

Ecological and evolutionary processes in temporary rock pools operate within constraints imposed by their hydrologic regimes. These shallow pools flood when seasonal rains accumulate on impermeable substrates. Despite the ecological importance of hydrologic conditions for these ecosystems, we typically lack tools and empirical data required to understand the implications of hydrologic variability and climate change for biotic populations and communities in these habitats. In this study, we developed a hydrologic model to simulate rock pool hydrologic regimes based on rainfall, evapotranspiration, and basin geometry. The model was used to investigate long-term patterns of seasonal and inter-annual variation in hydroregime. In addition, hydrologic conditions associated with potential climate change scenarios were simulated and evaluated with respect to the biological requirements of the anostracan Branchipodopsis wolfi. The model’s output for daily inundation matched with field observations with an overall accuracy of 85% and correctly estimated complete hydroperiods with an overall accuracy of 70%. Simulations indicate large variation in individual hydroperiods (76–115%) as well as in the number of hydroperiods per year (19–23%). Furthermore, this study suggests that climate change may significantly alter the rock pool hydroregime. These findings confirm the hydrologic sensitivity of these ephemeral habitats to precipitation patterns, and their potential sensitivity to future climate change. Modelling indicates that the suitability of average inundation conditions for B. wolfi deteriorates significantly under future climate predictions. High levels of spatial and temporal variation in hydrologic conditions are dominant features of these habitats and an essential consideration for understanding population and community-level ecological processes.