Not only am I not certain about this, I am not certain about what evidence you could gather to go about examining it. A general good rule of thumb when thinking about the distant past is "how would we know this". With literary evidence you would need a general familiarity with the corpus of surviving texts, and I suppose in this case you will have to trust me that we do not have anything that would illuminate this question (literary evidence for Roman Britain in genera is pretty sparse, and that sort of ecological analysis is pretty rare in ancient texts). With archaeology you can be a bit more theoretical: what evidence for this question would have a reasonable chance of 1) surviving 2) be recovered, and 3) present some sort of data set for analysis (there is also the 4) match some sort of research interest and funding opportunity). I this case it is very difficult to meet these criteria, theoretically maybe something with strontium isotopes in deer teeth but these sorts of data sets are rare for humans let along animals (I am also not sure if deer range widely enough).

So I think the answer is that while we can be certain the wall did have an ecological effect--hard to imagine a wall like that not having an impact--but actually describing that impact is well beyond our evidence set.

That said, there is a question somewhat to the side of yours that we can answer--what impact did the wall have on the human environment? And in that case there is pretty striking evidence of disruption, and in certain cases catastrophe. For example, in the coastal areas of Northumberland, exploration has revealed a dense and stable settlement pattern developing around 200 BCE and proceeding up until a rapid collapse in the early/mid second century, roughly when the wall was constructed. There may have been a deliberate policy of depopulation, the creation of a defensive "no man's land" north of the wall, but the impact of the physical barrier severing relations that had bound communities for generations, and perhaps even a psychological impact of seeing the wall built up, cannot be discounted.

Of course, the wall brought benefits, as a security system it was blunt but seemingly effective, but its nature was a stark line dividing what had been a tightly interconnected human environment.

This analysis owes much to Symonds, Protecting the Roman Empire.

Are there existing similar discussions of ecological impact for other walls? The one that immediately comes to mind is, pretty obviously, the Great Wall of China, but the one I'd be most interested in is the Iron Curtain (inasmuch as it was an actual wall), given that it spanned a continent.