An experimental test of food limitation and trophic interaction hypotheses on demographic parameters in a cyclic population of red-backed voles

Determining the factors that limit and regulate population density is a key problem in population ecology, but often difficult to test in practice. The northern red-backed vole ( Clethrionomys rutilis Pallas, 1779 sec. Kryštufek et al. 2020) occurs throughout the boreal forests of the northern hemisphere and the factors influencing their populations are still being elucidated. A large-scale experiment was conducted in the Yukon from 1986 to 1996 in which food availability, nutrient availability, predation, and interspecific competition were experimentally manipulated. Paradoxically, there was no evidence that these experimental treatments altered vole population density. Here, we apply a capture–mark–recapture modeling framework to test for experimental treatment effects on recruitment and apparent survival. Experimental manipulations resulted in opposing effects on recruitment and apparent survival. These contrasting demographic effects meant that the population growth rate and density remained unaffected by experimental treatments, upholding the original results. We suggest that as some experimental areas became more saturated with voles, this forced higher levels of vole dispersal or attracted mustelid or avian predators, either of which could result in the contrasting effect on apparent survival. Our results highlight that manipulation of environmental factors can alter demographic parameters without substantially affecting overall abundance.