(1) We investigated the influence of Microtus pennsylvanicus adults on young conspecifics by manipulating the density or sex ratio of the adult segment of several experimental populations. (2) Adults were removed from four experimental grids as follows: (i) all breeding males (female grid); (ii) all breeding females (male grid); (iii) most adults throughout the autumn, winter and spring (autumn-removal grid); and (iv) most adults throughout the spring (spring-removal grid). All manipulations were repeated the following year. (3) Survival, ages at sexual maturity, and reproductive rates were significantly improved in young individuals, especially young females, on all experimental grids except the female grid. The demography of young animals on the female grid was either similar to that on the control grid or intermediate between that on the control grid and that on the other experimental grids. For young females, there was a significant, negative relationship between adult density and each of these parameters; for young males, only survival rates of very young animals were negatively related to adult density. Individual growth rates were not influenced by any of the manipulations. (4) Therefore, adult animals, especially adult females, play a major role in limiting the density and fitness of young individuals.
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Rodd et al. (1988) studied this question.