Patterns of population dynamics are scale-dependent.  Populations exhibit different levels of variability at different temporal scales.  Animal populations may resonate with varying environments at the same frequency (harmonically) or at different frequencies (e.g., sub-harmonically), depending on life history strategies of the animals.  We hypothesize that populations of small-sized insectivorous mammals and omnivorous rodents that rely on insects as winter food undergo regular seasonal variations owing to predictable shortages of winter food and short breeding seasons, whereas populations of small-sized folivorous mammals may exhibit long-term or multi-year fluctuations, owing to food-induced variability in the length of the breeding period among years.  We analyzed 10-25 years of monthly population time series of Blarina brevicauda, Peromyscus leucopus, Microtus pennsylvanicus, and Microtus ochrogaster to test our hypotheses, using continuous wavelet coherence, discrete wavelet cross-correlation, and wavelet-based analysis of variance. 

Results/Conclusions Populations of B. brevicauda and P. leucopus fluctuated at an annual scale, whereas populations of two species of Microtus exhibited the greatest variability at a scale of 16-32 months. The populations of B. brevicauda and P. leucopus resonated with climate change at an annual scale.  Cross-scale regressions showed that the mult-annual dynamics of the M. pennsylvanicus population were related to annual climatic dynamics at a scale of 8-16 months, suggesting sub-harmonic resonance.  Therefore, small mammal populations form a continuum of slow-fast or annual- multiyear dynamics.  Future studies of demographic mechanisms for slow or fast population dynamics are needed for better understanding temporal variability of mammal populations.