While Bitcoin is still the most popular of cryptocurrencies, it has ceded share considerably over the past three years, mostly to Ether.
In 2015, Bitcoin had an 86% share of market cap value for cryptocurrencies. In 2017, this had dropped to 72%. Correspondingly, Ether increased its market cap share from less than 1% in 2015 to 16% in 2017.
Much of this growth comes not just from crypto traders hedging their investments across multiple currencies, but the significant growth in ICO activity between 2015 and 2017.
According to Coindesk, there were three ICOs in October 2016 which cumulatively raised $13.4 million. In September 2017, there were 35 ICOs that raised a total of $534 million. The majority of these ICO sales were based on Ether.