The importance of r versus K selection, comes in and out of favour in ecology, but I have always been intrigued by it. K selection has always interested me as a measure of the parental investment per offspring. I would have always assumed that humans would rank highest by this scale, and they almost do, but a few challenge their top position. It may not be the best direct measure for intelligence, but it should be a very good a gauge of the potential for learning. I would love to see an attempt to rank the top ten, but I will start with one claim that orangutans would top the list, and that elephants are the classic example.
Elephant females take 12-14 years to reach maturity, and bulls about 20. The interval between calves is about 5 years. twining rate 1%.
Orangatung females reach maturity at 14-16 years old and males at 18-20. The interval between births is 6-7 years
Note how neither elephants nor orangutans are much more K selected than humans. In humans the twinning rate is around 1%
In sperm whales the females reach maturity at about 9-10, but the males only get there around 39. Weaning is at 2. The twinning rate is 1%.
I notice that, if we restrict our analysis to land animals (on whom the data is better than aquatic ones), a list of top half dozen K selected land animals would be almost identical to the half dozen most intelligent ones. I must return to this topic some time, and do it justice.