Local populations can show different reproductive phenology because their habitats have different environmental conditions. Reproductive phenology may also diverge among populations as a result of demographic stochasticity in individual phenology if population sizes are small. Such small population sometimes observed at a small spatial scale, where individuals can disperse, and phenological variation in reproductive phenology at this scale can affect metapopulations dynamics. Here we studied Rhacophorus arboreus metapopulations to explore whether environmental heterogeneity and/or demographic stochasticity affects their population-level variation in reproductive phenology. Moreover, we examine how spatiotemporal variation in phenology affects metapopulation dynamics using matrix population models.
Results/Conclusions
We surveyed the breeding phenology of R. arboreus at 23 ponds in warm−temperate forest in Japan (<10km2) for 5 years. It was found that migration is common in this scale based on population genetic analysis using multiplexed ISSR genotyping by sequencing (MIG-seq). The maximum spatial difference in peak phenology between sites ranged from 16 days in 2014 to 34 days in 2018. Even in 2018, when large spatial variation was observed, there was no clear relationship between environmental factors (temperature and water depth) and phenological peak. The maximum annual variation in phenology peaks in each site across 5 years ranged from 3 days to 23 days. The annual variation in phenology of smaller populations tended to be larger than that of larger populations. Randomization tests revealed that much of the observed spatiotemporal variation in phenology was not necessarily explained by site-specific factors such as environment and imply the effects of population sizes. These results imply demographic stochasticity driven by population sizes might determine phenological peaks. The matrix population models showed that spatial variation in phenology influence metapopulation stability. Interestingly, it depends on the driver of spatial variation in phenology, which is environmental heterogeneity or the stochastic effects of the local population size.