In my economics book*, in the lesson explaining what price elasticity of supply is, it's written:
In reality, supply curves are likely to be non-linear, so will have a different PES value at different points. Supply is more elastic at lower prices and more inelastic at higher prices.
Why supply is more elastic at lower prices and more inelastic at higher prices? Doesn't an increase in price mean more suppliers will be able to join the market?
So not only supply will increase when demand gets higher— due to old suppliers increasing their supply— but because of the new supply added by new suppliers too.
Please note that the cases shown in this picture are said by the author to be theoretical. The more likely cases where shown in another page as straight inclined lines