Cognitive abilities vary among humans, is the same true of other species?

This week's question comes to us from Anil Patni of Toronto. Here is his question:

The cognitive abilities of a human with an IQ of 80 compared to a human with an IQ of 140 are significantly different. Are there similar intelligence ranges withing other species?

Stanley Coren, professor emeritus of psychology at The University of British Columbia, says there are differences in the intelligence of any given species.

Dogs are a well-studied example. The brightest dogs have a mental age, or an equivalent intelligence, to that of a two-and-a-half to three-year-old human. The average dog has a mental age equivalent to that of a two to a two-and-a-half-year old human. This is measured by the number of words, signs and signals that the dog can understand.

Very smart dogs can learn up to about 250 commands. Border collies, poodles, German shepherds and golden retrievers are among the smartest dogs.

However, there is individual variability within any given breed of dog. For example, one Labrador retriever may not be as smart as the next. 

The same is true of other species. The average cat has a mental age equivalent to an 18-month-old human, but Maine Coon cats are slightly smarter. Among primates, the bonobo chimp is the smartest. It has a mental age equal to a four-year-old human being.