How are species related to the concept of biodiversity？
Your question is a bit unclear, but I think you are asking for how the two concepts relate. An ecosystem is the environment and the species that live in it. Ecosystems can be large or small (see attached link). The health of the biological part of the ecosystem is directly related to the number of species of different organisms that live in it. The more diverse, the more likely it is to be able to survive some sort of stress. For example, if an ecosystem is dependent on only one type of producer (plant), it is at risk if something happens to that producer; the entire food web would be destroyed if, say, a bacterial infection destroys the plant. If there is only one, or a few, types of producers, one bacteria/virus/fungus can spread rapidly because the plant is next to another of the same kind--which is also susceptible to that threat. I've used plants as an example, but the same is true for animals within an ecosystem. The more variety, the more likely the system is to survive.