Thomas Malthus was the economist that influenced that idea.
—Evidence—
•]Thomas Malthus reasoned that if the human population grew unchecked, there wouldn't be enough living space and food for everyone.
•]Darwin realized that Malthus's reasoning applied to even more organisms than it did to humans. So it applied to more than just humans
Thomas malthus also discovered the idea of economy and the idea of competition for resources especially during times of population growth.