This is a relevant part of the general spellcasting rules:
Before a spellcaster can use a spell, he or she must have the spell firmly fixed in mind, or must have access to the spell in a magic item. Members of a few classes, including bards and sorcerers, have a limited list of spells they know that are always fixed in mind. The same thing is true of many magic-using monsters. Other spellcasters, such as clerics and wizards, undergo a process of preparing spells. This process varies for different classes, as detailed in their descriptions.
In every case, the number of spells a caster can have fixed in mind at any given time depends on the character's level.
These features that let you use an ability without a spell slot are an exception to this general rule- they say you can cast the spell a limited number of times through the trait, but do not say that the spell counts as a specific class' spell/as prepared/as known for you, so you cannot expend spell slots on them. You can only cast them through the trait.
