In order to properly speculate the existence of wildlife in Destiny, we must first take a look back at Bungie's previous game before Destiny. When you look at Halo: Reach, you can see evidence of all sorts of mechanics that Bungie was experimenting with. One of those was Armor Abilities. These can easily be translated as tests for how Supers in Destiny will work. That is just one example, but guess what else Bungie experimented with in Reach. That's right, wildlife. Destiny was the first time we saw the series attempt to introduce sentient life into the game that just sort of existed as apart of the planet's ecosystem, and took no part in the greater conflict or story arc. One example is theexistence of the passive [url=http://halo.wikia.com/wiki/Moa]Moa[/url]. These harmless bird-like creatures did nothing but stand around, and attempt to flee at the sight of impending danger. Killing them even landed you an achievement in one case. Another example is the [url=http://halo.wikia.com/wiki/G%C3%BAta]Gúta[/url]. These ferocious creatures were very agressive and would attack anything that got in it's way. Aside from those two species, there are various moments in Reach where you will see birds and even rats. So what does this tell us about Destiny? Well I believe that Destiny will have not only it's primary alien factions, but all sorts of wildlife in between. Perhaps even different creatures on each planet. Some passive, and some you might want to avoid if your health is low. Keep in mind this is all my own speculation, and none of this is set in stone. It is an educated guess based on a developer I have been following for over a decade.

Destiny is a ever-changing world what do you think...

Not really sure about the wildlife or the weather change. But bungie said there would be night missions so I'm guessing there will be time change. Hopefully there is wildlife. It'd make the whole exploring experience a little more cooler. And the weather change would be sweet as well. Like having to take shelter due to storms or having to change you're battle strategy because it's snowing.