In his WSJ opinion piece, Wilson gives a blunt answer by way of a "professional secret": "Many of the most successful scientists in the world today are mathematically no more than semiliterate." He does make the rather unexceptionable point that "if your level of mathematical competence is low, plan to raise it," but also adds that "you can do outstanding scientific work with what you have." Of course, if your level of math is not all that high, he also suggests you avoid "most of physics and chemistry, as well as a few specialties in molecular biology."
His article has led to tons of responses: Paul Krugman agrees, but with a caveat: "at least in the areas I work in, you do need some mathematical intuition, even if you don’t necessarily need to know a lot of formal theorems."
A couple of other responses. In Science's Cult of Calculation, Jag Bhalla talks about the rivalry in science between "math-monks" vs. "pluralist reasoners". Terry McGlynn places Wilson's piece within the context of Tribalism in the sciences: empiricists vs. theoreticians.
The tribe of theoretical ecologists appears to have got very upset with Wilson's piece for reasons that lie within the internal politics of that field -- this post explains some of it, and has tons of links.