Disturbance frequency and vertical distribution of seeds affect long-term population dynamics: A mechanistic seed bank model

Background/Question/Methods

Seed banks are critically important for disturbance specialist plants because they germinate only in disturbed soil and, as a consequence in years without a disturbance, the population often relies solely on its seed bank to persist.  Disturbances, as well as a seed’s depth in the soil, affect the survival and germination probability of seeds in the seed bank, which in turn also affect population dynamics.  We developed a density-dependent stochastic integral projection model to evaluate the effect of stochastic soil disturbances on plant population dynamics with specific emphasis on mimicking how disturbances vertically redistribute seeds within the seed bank.  We performed a simulation analysis of the effect of the frequency and mean depth (intensity) of disturbances on the population’s quasi-extinction probability as well as the long-term mean and variance of the total number of seeds in the seed bank.

Results/Conclusions

We show that increasing the frequency of disturbances increases the long-term viability of the population but the relationship between the mean depth of disturbance and the long-term viability of the population is not necessarily monotone for all parameter combinations.  Specifically, an increase in the probability of disturbance increases the long-term mean of the total seed-bank population and decreases the probability of quasi-extinction.  However, if the probability of disturbance is too low, a larger mean depth of disturbance can actually yield a smaller mean total seed-bank population and a larger quasi-extinction probability, a relationship that switches as the probability of disturbance increases.