Appendix: What is the difference between "r-selected" and "k-selected" species?
The main differences between the two groups are size of animal, population density and the time-frame of birth, life and death. R-selected species are relatively small and for them life is short but productive. Everything is speeded up and there is more of everything: more young per litter; more litters per female per year; the young are reared more quickly; offspring mortality is high; the age of sexual maturity is measured in weeks rather than pears; and both reproductive life-span and actual life-span are short. Population density and its absolute size are great but there are often sharp swings in numbers -cycles of population explosions and crashes that are linked to food supply and predator numbers. As far as mammals are concerned, rats, rabbits and voles are examples of extreme r-strategists. Such species can usually easily weather the storms of a rapidly changing environment, both short-term and long-term, as the quick population turnover aids recovery of numbers and genetic adaptation.
K-selected species are relatively big and approach life at a more sedate pace. They produce a litter, at most, every year or two and the number of young per litter is limited to about one to three, but their survival rate is higher. The young are dependent on their mother (or both parents) for a relatively long period and sexual maturity is reached after several years. Population densities are close to maximum and do not swing between highs and lows, and while life-spans are longer, this does not compensate for the slower turnover. Consequently, population numbers are measured in thousands or tens of thousands rather than the millions or billions of most r-selected species. Elephants, lions, otters and giant pandas are all examples of K-selected species.
In giant panda society, members of the opposite sex must be compatible in order to commit themselves to mating. In the wild, males compulsively follow a females scent marks, but the female does not submit to the male until she has been accustomed to him. She may climb a tree, swat him, or bite him his nose if shes not ready to mate. In a captive environment, putting a female and male together during the females receptive period does not automatically make for a successful liaison. Very often, the male will either be aggressive or indifferent to the female's solicitations and so the relationship never gets off the ground. In order to hit it off, would-be partners have to go through a series of lengthy olfactory and vocal exchanges. Only when they have both passed these tests the pair will engage in the close-contact interaction of courtship, and even then there can be a change of heart at the last minute on the part of the female if she has been courting more than one male.