Omission deeds are infinite - such as failing to save all sapient species/individuals. As such, saving all of them cannot be, realistically, an obligatory requirement for one's morals. But saving the ones you can save is morally salutary. And saving the ones you can easily/relatively easily save (with little risk to yourself, with relatively little resource expenditure) IS morally obligatory. Also - in detemining such actions, you must consider the individuals/species that exist NOW, not that may or may not exist in some ambiguous future. And yes, sapience is the criterion - or, at least, one of the main criteria - for choosing whom to save. As Belz said, Sentient beings > non-sentient beigns.