  The competitive exclusion principle (CEP) is a fundamental concept in the
niche theory, which posits that the number of available resources constrains
the coexistence of species. While the CEP offers an intuitive explanation on
coexistence, it has been challenged by counterexamples observed in nature. One
prominent counterexample is the phytoplankton community, known as the paradox
of the plankton. Diverse phytoplankton species coexist in the ocean even though
they demand a limited number of resources. To shed light on this remarkable
biodiversity in large ecosystems quantitatively, we consider
\textit{intraspecific suppression} into the generalized MacArthur's
consumer-resource model and study the relative diversity, the number ratio
between coexisting consumers and resource kinds. By employing the cavity method
and generating functional analysis, we demonstrate that, under intraspecific
suppression, the number of consumer species can surpass the available
resources. This phenomenon stems from the fact that intraspecific suppression
prevents the emergence of dominant species, thereby fostering high
biodiversity. Furthermore, our study highlights that the impact of this
competition on biodiversity is contingent upon environmental conditions. Our
work presents a comprehensive framework that encompasses the CEP and its
counterexamples by introducing intraspecific suppression.
