The following differential equations model a predictor/prey relationship between two species X and Y (the population sizes being given by x and y respectively):
ẋ = -x/30000 + xy/(3 × 10⁸)
ẏ = y/30000 - 2/(9 × 10⁸) y² - xy/(9 × 10⁷)
(i) Which species, X or Y, represents the predator? Explain so.
(ii) In the absence of species X (i.e. x = 0), find the populations for y at time t if y(0) = y₀ where y₀ > 0. Sketch the graph of y(t) against t for different values of y₀.
(iii) Find and classify the equilibrium points for the system.