Quantifying the Hydroregime of a Temporary Pool Habitat: A Modelling Approach for Ephemeral Rock Pools in SE Botswana

Abstract

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 interannual 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.

Hatching phenology, life history and egg bank size of fairy shrimp Branchipodopsis spp. (Branchiopoda, Crustacea) in relation to the ephemerality of their rock pool habitat

“…Due to erratic rainfall and high evaporation rates, wet phases often do not allow sufficient time for maturation and reproduction of aquatic organisms (Hulsmans et al 2008). Model reconstructions indicate that in the Korannaberg pool cluster on average 45% of inundations are too short (\7 days) for fairy shrimp to reach maturity and allow for reproduction (Seaman et al 1995;Vanschoenwinkel et al 2009a).…”

“…Temporary aquatic habitats are typically characterised by variation in timing, frequency and duration of inundations; a number of variables that together shape the disturbance regime (i.e., hydroregime) of the habitat (Hulsmans et al 2008). Permanent inhabitants of these systems, such as fairy shrimps (Anostraca), survive the dry habitat phases by means of dormant life stages in the sediment.…”

Salinity and depth as structuring factors of cryptic divergence in Moina brachiata (Crustacea: Cladocera)

“…Human made changes in hydrologic regimes, levee building for river flood prevention and agricultural expansion have had drastic effects on temporary waters during the last centuries worldwide. In addition, the effects of climate change threaten these aquatic habitats (Hulsmans et al 2008). The severe decline of biodiversity in freshwater systems during the past decades (Dudgeon et al 2006, Balian et al 2008, Naiman 2008, Heino et al 2009) underscores the importance of research and conservation efforts for these unique temporary habitats.…”

Hatching phenology and voltinism of Heterocypris barbara (Crustacea: Ostracoda) from Lampedusa (Sicily, Italy)

“…Organisms must take advantage of pond filling when it occurs and hedge their bets for the possibility of favourable long lasting hydroperiod so that more than one life cycle may be completed and a larger amount of dormant stages produced. In ephemeral pools hydroperiod predictability varies accordingly to latitude and season (Brendonck et al, 1998; N o n -c o m m e r c i a l u s e o n l y Hulsmans et al, 2008). Earlier onset of development and increased voltinism may promote faster population growth and have major implication for egg bank accumulation.…”