I think that none of equations has an infinite range of validity. As soon as something reaches critical level, the laws of functioning of the system change. Still we can get reasonable description of complex systems by deriving and using systems of differential equations. But we need to know laws of different sciences along with ranges of validity to do that. You can have a look at my exercise dealing with logistic equations (both for population and nature) but also adding interaction with economy. It is more model 1 with simulation results in the end; see https://www.researchgate.net/publication/278110040_Low-Dimensional_Nonlinear_Dynamical_Systems_as_a_Tool_for_Socio-Economic_Modelling

Conference Paper Low-Dimensional Nonlinear Dynamical Systems as a Tool for So...

Thanks for your interest. Ecological phenomena have intrinsic relationships between ecological variables across scale and this could be seen and contemplated in Allometric Scaling Theory, Allometric Cascades and Metabolic Theory of Ecology. For example, there's two ecological laws described from r and K parameters: Fenchel's Law (1974) and Damuth's  Law (1981). All Ontogenetic Theory is derived from Bertalanffy's arguments (1938) and the empirical Kleiber's Law (1975). These three examples of ecological laws describe bio-ecological variables which scale with body mass in two different ecological scales (individuals and populations). Metabolic Theory of Ecology (2004) connected the relationships between these variables across ecological compartments because the evidence accumulations of different cause-effect relationships between ecological compartments, from biochemical shfits (driven by metabolism) in individuals impacting in population and community, or even in ecosystem (there're empirical evidence for this). Also ecosystems is studied anothers ecological field, the Ecological Networks (Bascompt et al, 2010) and Macroecology (1989) and there are some effort to consider effects from smaller scales.  So we could devise some well-establishing arguments to encourage news advances to understand the interface between ecological scales and find news allometric laws. 

Thanks for your interest. Looking the problem I placed with systemic (complex) lens your suggestion really need to be take account. But also biologists have an intrinsic interest to understand (like physicist) the cause-effect relationships between variables even though they are occuring in a open (complex) system, with a multitude of variables occuring togheter. So we've a problem that exist em bio-ecological phenomena: we can't isolate variables, because we can't desing experiments that occur in nature (unviable experimentally and time-expansive). What we can do is speculate something reasonable and wait for a special empirical situation with well-delimited conditions to validate this. 

This is better explained here

Article Making some advances in Ontogenetic GrowthTheory based on Po...