A model of egg bank dynamics in ephemeral ponds

Resting life stages (e.g. dormant seeds and resting eggs) have important implications for ecological and evolutionary processes. In this study, we simulated the impact of different environmental scenarios on the dynamics of resting eggs that make up an “egg bank” of a common fresh water ostracod, Heterocypris incongruens (Crustacea). Our goal was to investigate how the persistence and the wind-mediated spatial distribution of the species in vernal temporary ponds on Lampedusa Island (Southern Italy) were affected. A general model for selection on seed germination in unpredictable environments was used to simulate within pond egg bank dynamics. Metapopulation dynamics were simulated using Levin's and Hanski's models assuming three generalized spatial patterns of pond distribution (random, aggregated along the main wind direction, evenly spaced along the main wind direction) and two dispersion processes (random walk and wind shear). We applied global sensitivity and uncertainty analysis (GSUA) to the models. We estimated the egg bank growth rate based on 30-year simulations under present climatic conditions, and assuming a 2°C rise in winter temperature under global climate change. Hatching rate and deterioration rate were the most important input factors for the dynamics of the egg bank. In warmer winter conditions, the probability that a pond water balance is positive, a reliable hydroperiod estimation, was the most important factor in the egg bank simulation dynamics. Regular distribution of ponds along the wind gradient and wind shear, had the highest dispersal and colonizing potential, considering the percentage of empty ponds reached (60 %). Levins’ model predicted that the equilibrium varied between 0 and 8 % of colonized ponds while Hanski's model predicted values between 0 and 20 %. In Hanski's model the rescue effect increased the probability of occupied ponds. Potential colonizing resting eggs and extinction rate were positively and negatively correlated to the percentage of colonized ponds, respectively. Our simulations can be generalized to aquatic invertebrate taxa that inhabit temporary ponds, have egg banks, colonize habitats using few propagules and disperse passively by wind.