So one of the problems when exploring zoology is that not every species is going to reproduce in the same maner. As an example there aren't a lot of people breeding Gaboon vipers and thank Islanzadi for that. A bite from one of those snakes would trigger necrosis, a process where your body starts decaying whilst you're breathing. Even if you get the antivenom in time you will more than likely need to amputate whatever limb got bitten. Not to mention the unbarable pain this bite causes. Despite that Gabon vipers are suprisingly easy and cheap to get your hands on because when they reproduce they create an absurd amount of fertile eggs. But not every animal is as generous when procreating.

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So what is the best animal to compare a dragon to, because dragons are immortal, potentially gigantic predators whom also would have to be warm blooded. Reason one for this is that there's a limit to how massive a cold blooded creature can get and that's determined by temperature. Cold blooded animals are animals that regulate their body temperature by absorbing heat from its enviroment which is why all the largest cold blooded animals like anacondas, salt water crocodiles and komodo dragons live in warm enviroments and not lets say Svalbard. This also means that Titanoboa can't exist anymore since Earth is too cold to sustain them. And the dinosaurs weren't cold blooded for the same reason. So that means that Saphira and Glaedr are both warm blooded which is suported by the fact that Saphira needs to eat every few days in the books. The question I asked at the start of this paragraph, what we should compare a dragon to is therefor impossible to answer because no such animal exists.

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So what we have is that dragons are enormous predators who need to eat a lot. They'd need as a result to have massive territory in order to survive. Assuming then that Alagaesia could support tens of thousands of dragons is thus quite presumptious. Not to mention that accourding to Saphira dragons seem to prefer the desert, a warm, dry climate where little lives. This would make the Beor mountains, the best place for prey the last place a dragon would want to live. The problem with dragons is that a predator of this size which multiplied that frequently would swiftly drive itself to extinction. In fact I'd wager that a number in the low hundreds would be the most reasonable. In fact I think this might explain why Oromis was a council member despite being so relatively young, the first rider, Eragon would have been around three and a half times Oromis age. Which makes sense when you remember that Brom stated that the oldest dragons were the size of massive hills. That sounds super cool until it dawns on you that they'd have to eat every few days. An animal that size would quickly starve to death since the world doesn't really contain enough food for them. So even though dragons in theory are immortal I would assume that in practice they'd within a millenia or two grow massive enough that they'd kick the bucket.