System of differential equations

Hello

say I have a system of diff. equations describing an ecosystem on an island.

dP/dt = a1*P+a2*P^2*R

dR/dt = b1*P*R + b2*R

where P(t) is the number of plants as a function of time

and R(t) is the number of rodents as a function of time

t is the time in years

a1, a2, b1, b2 are constants

Say the islanders start to spray the island with pesticide so that 70% of the rodents die each year and 20% of the plants die each year. How will this change the differential equations?

/Alex