A high species diversity suggests relatively few successful species in the habitat. Hence the correct option is d.
A high species diversity indicates that there is a variety of different species present in a particular habitat. In a diverse ecosystem, various species coexist, contributing to a complex web of interactions and relationships. However, the statement "relatively few successful species in the habitat" contradicts the concept of high species diversity.
In a biodiverse ecosystem, the presence of numerous species suggests that many different organisms have successfully adapted to and found niches within the environment. Therefore, the idea of "relatively few successful species" is inconsistent with the understanding of biodiversity. Instead, high species diversity implies that a multitude of species are thriving, leading to a more resilient and adaptable ecosystem. The other options, such as complex food webs and the availability of ecological niches, align with the positive aspects associated with high species diversity in an ecosystem. Hence the correct option is d.