The graph shown represents the species-area relationship, which describes how species richness (S) increases with increasing area . The curve rises rapidly at first and then levels off, showing that larger areas tend to have more species, but the rate of increase slows down as area increases.
Mathematically, this relationship is commonly expressed as:-
Here:-
S = species richness
area
constant (dependent on the taxonomic group and region)
slope of the curve in a log-log plot, indicating how quickly species richness increases with area.