One would think that, outside of an ambush predator, such behavior would not be conducive to the long-term survival of a species.
Ditto actually has the best survival rate as a species compared to all other pokemon out there because they can imitate ANY object. Intimidation tactic? Mimic something far stronger than yourself. Stealth tactic? Mimic nearby rock. Infiltration tactic? Either mimic some Pokemon that lives in a herd, or mimic an egg inside that herd's nest.
The only problem being their reproduction, as they'd probably do with mitosis, since they're based on mimic slime after all.
I wasn't referring to shape-shifting in general, but mimicking delicious food in particular. Most animals try to be as unappetizing as possible.
Well, there's a reason we have 'if you want to hide a tree, hide it inside a forest' idiom. Let's picture this scenario: a Ditto was chased by, say, a Nidoking. The Ditto climbed into the nearest Berry Tree, which is Oran...
You can already see where this is going, right? Ditto morphs into Oran berry and rolls away unnoticed when the Nidoking topples said tree. There's always reason to mimic something if you have the metamorphosis ability.