The phrase "abundant source" means there is a large amount or plenty of something available. It suggests that there is a plentiful supply or a lot of the thing being referred to. Full definition
Meat is the most abundant source of protein for most people. (healingedge.net)
That niche, he says, offered more abundant sources of nutrition, so a habit of fighting over meals became less important to survival. (discovermagazine.com)
Although collagen is the most abundant source of protein in your body, normal production declines as you age. (primalkitchen.com)