Over population is subjective to definition and a general terminology relative to opinion and perception. One can argue if resources are strained that is over population of the resource consuming species, or hyberbole to Armageddon scenario of an extinction event due to over population, or environment and resource is depleted due to over populating species. Either way its not limited or constrained to just resources, therefore impossible. Without checks and balances and predator prey scenarios, overpopulation is not only possible but probable as it has been proven time and time again in nature and human populations.