1. species. Meaning SEVERAL kinds or varieties of bat, but not all kinds.
2. those. Refering to the 'coronaviruses',
Here we report that several kinds of bat are a natural host of coronaviruses closely related to those (coronavirus) responsible for the SARS outbreak.
"Those" does not refer to bats, as bats were not responsible for the SARS outbreak, the viruses however were found in many of the victims. (90% Hong Kong)