Intelligence works in some places, speed works in others, and strength in yet others. Species have evolved to find a happy medium between the three that yields optimum survival for them.
Did their niches change? Or did man upset the evolutionary processes by his mere existence?..............
Yes to both. Hunman evolution has upset many niches, although the same is true for the evolution of other predators. Species either evolve to find new niches or they go extinct. I think humans are somewhat unusual because they have had unique evolutionary pressures over the last few hundred thousand years pushing ever-greater intelligence. But there are costs and limites to increased human intelligence as well -- brain size is limited by the width of the female pelvis. If the brain is too large, humans can't be born vaginally. If female pelvises were wider, women wouldn't be able to walk bipedally.
The evolutionary solution would be to grow larger, taller and more wider in order to accomodate the larger brain mass, but since we do not use anywhere near the maximum capacity of the human brain, such a change is not necessary. The de-evolution of man wil be brought about by the lack of use of the brain mass capacity and is evident in many animalistic behavioral traits of humans in gangs, prisons, Democrat conventions etc.......