Chiral molecules or ions are particles which cannot be made congruent to one another via flipping one or rotating one. For example, the same property applies to your hands, assuming that you were born without a genetic abnormality; if both are facing down, the thumb will be on the right side of the left hand and the left side of the right hand, as opposed to both being on the same side of their respective hand.
Mirror life refers to hypothetical life-forms whose component building blocks - proteins, amino acids, et cetera - have a different chirality than those of Earth-based life. In this case, that means right-handed amino acids and left-handed sugars, rather than Earth's left-handed amino acids and right-handed sugars.
Let's say that you have an entire ecosystem of mirror life, completely identical to Earth's in every way except for that their amino acids are right-handed and their sugars are left-handed. Let's also say that this ecosystem evolved alongside Earth's more conventional one since the beginning of life on the planet, meaning that there are plenty of right-handed amino acids and left-handed sugars to go around so that these hypothetical organisms aren't deprived of their building blocks.
How this happened is irrelevant to the scope of this question. Just assume that, somehow, it did.
How much biological overlap would there between this mirror life ecosystem and a normal Earthly one?
For the sake of this argument, assume that this is a 50-50 split; that is, one out of every two organisms has one type of chirality, and the other one out of two has the other type of chirality.
Also, please note that all organisms in this question use either right-handed amino acids and left-handed sugars (anything that's part of the mirror life ecosystem) or left-handed amino acids and right-handed sugars (anything that's part of the Earth-standard ecosystem). There are no right-handed-amino-acid-and-right-handed-sugar organisms, nor any left-handed-amino-acid-and-left-handed-sugar organisms.
Good answers will list a way that an ecosystem of mirror life (see above for reference) is capable of interacting with Earth's opposite-handed-acids-and-sugars-based biology; for instance, interconnections between their food webs, competition for nutrients/energy, territorial conflicts, etc.