ABSTRACT
The evolution of populations has always been a central theme in mathematical modelling and in we have already mentioned that after the pioneering efforts by mathematical modelling of populations, viewed as the central players in the ecosystem, has become a mainstay in ecology. The chapter starts with simple single-species models and then move on to multispecies models. It is considered as a primary bio-indicator species to assess the levels of nutrients or toxic substances in freshwater environments. The chapter examines the basics of population dynamical models, starting with single-species modelling, and then expanding the analysis to include the interactions between competing species, eventually culminating in the modelling of the entire food web. It considers several species, which might range from the flea to the elephant, simply counting individuals could become impossible, particularly when it describe the interactions among them and with the environment.
