Generally it doesn't make sense to talk about rape outside of a human context. Can bacteria rape each other? What the fuck would that even mean?
Sexual reproduction happens in a lot of different ways, many of which make it impossible to define any kind of analogue of rape. For lots of animals fertilisation is external, often simply involving eggs and sperm being released into the water to float around.
External fertilisation does sometimes involve mate choice, however, where the male will induce the female to release eggs through some kind of mating ritual, or will construct a nest in which a female will choose to lay her eggs. In both cases, there are sometimes sneak matings, in which a second, uninvolved male will attempt to fertilise some of the eggs. In some cases this can lead to two completely different male mating strategies, either carried out at different life stages (juveniles sneak and older makes build nests) or two wholly different male development patterns.
This isn't really what we would think about as rape in humans, though. Among animals which do copulate, it's sometimes only possible with the active cooperation of the female, for anatomical reasons. In most animals, the female is larger, which limits the ability of the male to use force. In species where the female is orders of magnitude larger than the male, like with many spiders, they can attempt to sneakily mate while the female is distracted, which if you going to insist on anthropomorphising I could guess you could call rape.
Animals which offer the best analogues for what we would generally think of as rape are typically going to be ones with some kind of intromittent organ (ie. a dick), and certain types of social structure. Probably the most notorious animal rapists are ducks. Ducks do not reproduce solely by rape as sometimes implied. Mallards form monogamous pairs which cooperate to raise young.... (Tbc)
