 Southwest Airlines, already under pressure from a hedge fund for disappointing financial results, said Wednesday that a key revenue ratio will be weaker than expected because of changes in how consumers book travel. The airline said it still expects second quarter revenue to hit a record. However, it said revenue for each seat flown one mile, a closely watched measure of pricing power, will fall four to four and a half percent compared with the same quarter last year. Cost per mile will rise, too, and the airline's dealing with rising labor costs.