We are encroaching into habitats that previously we as humans did not really know those ecological niches were occupied by other species. But we are invading them.”
This pressure was probably a consequence of competition to fill the new ecological niches opened up by an ability to recognise sweet things as both edible and nutritious.
For example, some plants may be relying on a certain amount of rainfall, or an animal may feed exclusively on one species, they have a specialized ecological niche.
These larger sizes allowed pterosaurs to conquer ecological niches that weren't available to birds, like flying long distances over the open ocean in search of food.
In the aftermath of the extinction at the end of the Cretaceous, diving predators like small mosasaurs and plesiosaurs were gone, so their ecological niches were suddenly open.
During the Triassic as dinosaurs were evolving to fill large bodied ecological niches on land the other amniote groups were evolving to fill the sea and the air.
And what adaptive radiation is is: an evolutionary process by which a parent species rapidly undergoes changes resulting in various new speciesin order to fill multiple ecological niches.