steeper slope here indicates the area is very much as compared to the population of species.

steeper slope means that the number of species found increases faster with the area explode for example given in the NCERT mammals and birds the number of species of mammals and bird will keep on increasing at higher rate upon increasing the area explored also from physics we know that if why is proportional to X raise to the power sum number which is greater than 1 then we get a parabola and if you see a parabola the number of species or species richness on y axis will keep on increasing with x-axis which is area