We would need a lot of resources to manipulate the Bitcoin price like other big whale speculators are doing at the moment and I don't think we here on Bitcointalk have the capital to do so.If some groups/companies have the capacity to hoard the supply of bitcoins, that would greatly affect the price of bitcoins because of the supply and demand rule.
Yeah I dont know if there are investors has a resource that could manipulate the whole market cap of bitcoin if seems that you will need enough resources to do that . Bitcoin prices I think is the reactions of natural of the masses when there are some Negative issues that would affect the price.