It would be the oasis and aquifers provide water to the people. In the arid places people tend to supply by travelling around the desert and stopping in areas that has oasis and aquifers in order to replenish their water supplies. Also oasis and aquifers become stopping posts if it is a trade route for merchants and travelers in the arid regions.
True, if the number of prey decreases, the predators will have nothing left to eat and will slowly starve.
His bed is 2/5 of his room, which is 1/8th of the house. In order to know how much of the entire houre the bed takes we have to multiply this: (2/5)*(1/8). When we multiply fractions, we can multiply "independently" the numerator and denominator, like this:
(2*1)/(5*8)
That's 2/40, or 1/20. So his bed takes up 1/20 of his house.