[svenrufus]

Greys don't strictly speaking fill the same niche as reds. They do a more or less similar job, but in subtly different ways which can have big impacts. Eg. taking hazelnuts before they are fully ripe, and when burying them if they are forgotten they have much less chance of germinating. If Reds had done this the nuts would have been more mature and so more likely to germinate. There are apparently less new hazels in grey squirrel areas than might be expected under other circumstances - I think I got that from Rackham.

In terms of what benefit the Greys provide, well, any action which looks destructive is constructive for something else. If they damage trees, it opens up niches for fungi and invertebrates. If they damage them enough and they kill a tree, it adds complexity to the structure of the woodland environment. In a similar vein to the debate about killing crows elsewhere on this site, we have a very human perspective of the things going on in the natural world - we may not like what we see, but other wildlife may see things entirely differently.

Given a magic wand, I would eradicate Greys from the UK, but if your assignment is to consider wiping them off the face of the entire earth, then no, they have a place - it's just that that place is about 6000 miles to the west.