[1]Principia Cybernetica Web

                 r-K selection: the development-reproduction trade-off

   In order to maximize fitness in a predictable environment, it pays to invest
   resources in long-term development and long life (K selection); in a risky
   environment, it is better to produce as much offspring as quickly as possible (r
   selection).
     ____________________________________________________________________________

   [2]Fitness can fundamentally be achieved by two different strategies: long life
   (stability) or fast reproduction (multiplication, [3]replication). These
   strategies are to some degree dependent: since no organism is [4]immortal, a
   minimum amount of reproduction is needed to replace the organisms that have died;
   yet, in order to reproduce, the system must live long enough to reach the degree
   of development where it is able to reproduce. On the other hand, the two
   strategies cannot both be maximally pursued: the resources used for fast
   reproduction cannot be used for developing a system that will live long, and
   vice-versa. This means that all evolutionary systems are confronted with a
   development-reproduction trade-off: they must choose whether they invest more
   resources in the one or in the other.

   How much a given system will invest in one strategy at the expense of the other
   one depends on the selective environment. In biology, this is called r-K
   selection: in an r-situation, organisms will invest in quick reproduction, in a
   K-situation they will rather invest in prolonged development and long life.
   Typical examples of r-species are mice, rabbits, weeds and bacteria, which have a
   lot of offspring, but a short life expectancy. Examples of organisms undergoing
   K-selection are tortoises, elephants, people, and sequoia trees: their offspring
   are few but long-lived. In summary, r-selection is selection for quantity,
   K-selection for quality of offspring.

   [5]Selection for many offspring is most useful in an uncertain, dangerous
   environment, where most offspring will die anyway, whether the parents invest
   much resources in their development or not. The more offspring there is, the more
   chances that at least one of them will survive and continue the lineage.
   Selection for prolonged development is most useful when the environment provides
   a stable, predictable supply of resources, without great dangers. In that case,
   the one most likely to survive the competition with others will be the one that
   has had most time to develop its strength, experience or size.

   In a uncertain environment, reproduction is basically a a lottery: you cannot
   predict or influence which of your offspring will survive; the only way to
   increase your chances that at least one of them will survive is to produce as
   many as possible (like you can increase your chances of winning only by buying
   more lottery tickets). In a predictable environment, on the other hand,
   reproduction is more like a game of chess: the best way to win is to make few but
   well-prepared moves, rather than quickly making a lot of moves at random.
   K-selection, therefore, is selection for increasing [6]control over the
   environment, whereas r-selection is caused by an environment that is
   intrinsically difficult to control.

   The names r and K come from a mathematical model of population growth, which is
   typically a sigmoid curve. For small populations, growth is exponential as
   represented by the r parameter. When the population becomes larger, growth slows
   down as the population reaches the maximum carrying capacity (represented by the
   K parameter) of the environment. r-selected populations are typically far from
   their carrying capacity, and thus able to grow exponentially using an abundance
   of available resources. However, because of the dangers in the environments
   (diseases, predators, droughts, etc.) the population is regularly decimated so
   that it never actually reaches the carrying capacity. K-populations are
   well-protected against such disasters and therefore remain close to the carrying
   capacity. In that regime, resources are limited, and there is strong competition
   among the members of the population. This competition allows only the strongest,
   largest, most developed or most intelligent members of the species to survive and
   reproduce.

   It must be noted that the selective environment is not objectively given, but
   dependent on the specific system, whose organization and behavior determines its
   specific niche within the larger physical environment. Rabbits and tortoises may
   well share the same physical environment, but tortoises are shielded from dangers
   by their shell, and by their slow metabolism, which allows them to survive
   without food for a much longer time than a mouse would. Therefore, it pays for a
   tortoise to grow a large and strong shell and to have efficient repair mechanisms
   that allow it to live long, because this will increase its chances to produce
   offspring that will itself survive and reproduce. Rabbits, on the other hand, are
   easily killed by predators or temporary lack of food, and therefore do best to
   make sure they reproduce before such a calamity has struck, without investing too
   much energy in developing a body that is theoretically capable of living long,
   but that will in practice be killed long before this limit age (see the
   [7]Evolutionary causes of aging and death).

   This evolutionary principle, which states that organisms will determine their
   position on the development-reproduction trade-off according to the security of
   their environment, has many practical, observable applications. The main
   prediction that can be made is that organisms that are otherwise similar, but
   confronted with different environments, will put either more emphasis on
   development and survival or on reproduction. An example of such a prediction was
   recently confirmed: a [8]variety of opposum that lives on an island with no
   predators lives much longer than its cousins on the mainland, even when both are
   kept safely in a zoo: the island variant's genes have been selected for slow
   aging, a feature useless for the mainland variety, whose genes have been selected
   for quick reproduction.

   The development-reproduction or r-K trade-off is associated with an array of
   typical differences between types of organisms:

   r-organisms                      K-organisms
   short-lived                      long-lived
   small                            large
   weak                             strong or well-protected
   waste a lot of energy            energy efficient
   less intelligent, experienced... more intelligent, experienced...
   have large litters               have small litters
   reproduce at an early age        reproduce at a late age
   fast maturation                  slow maturation
   little care for offspring        much care for offspring
   strong sex drive                 weak sex drive
   small size at birth              large size at birth
     ____________________________________________________________________________

   [9]Copyright© 2000 Principia Cybernetica - [10]Referencing this page

   Author
   F. [11]Heylighen,

   Date
   Oct 2, 2000

                                       [12]Home
                                       [up.gif]
                           [13]Metasystem Transition Theory
                                       [up.gif]
                                [14]Evolutionary Theory
                                       [up.gif]
                                    [15]Replication

                                          Up
                           [16]Prev. [4arrows.gif] [17]Next
                                         Down
     ____________________________________________________________________________
   ____________________________________________________________________________

                                    [18]Discussion
     ____________________________________________________________________________

                                  [19]Add comment...

                                      [space.gif]

References

   1. LYNXIMGMAP:http://pespmc1.vub.ac.be/RKSELECT.html#PCP-header
   2. http://pespmc1.vub.ac.be/FITNESS.html
   3. http://pespmc1.vub.ac.be/REPLICAT.html
   4. http://pespmc1.vub.ac.be/BIOIMM.html
   5. http://pespmc1.vub.ac.be/SELECT.html
   6. http://pespmc1.vub.ac.be/CONTROL.html
   7. http://pespmc1.vub.ac.be/EVOLAGE.html
   8. http://pespmc1.vub.ac.be/VARIETY.html
   9. http://pespmc1.vub.ac.be/COPYR.html
  10. http://pespmc1.vub.ac.be/REFERPCP.html
  11. http://pespmc1.vub.ac.be/HEYL.html
  12. http://pespmc1.vub.ac.be/DEFAULT.html
  13. http://pespmc1.vub.ac.be/MSTT.html
  14. http://pespmc1.vub.ac.be/EVOLUT.html
  15. http://pespmc1.vub.ac.be/REPLICAT.html
  16. http://pespmc1.vub.ac.be/ORDNOISE.html
  17. http://pespmc1.vub.ac.be/MATHME.html
  18. http://pespmc1.vub.ac.be/MAKANNOT.html
  19. http://pespmc1.vub.ac.be/hypercard.acgi$annotform?

[USEMAP]
http://pespmc1.vub.ac.be/RKSELECT.html#PCP-header
   1. http://pespmc1.vub.ac.be/DEFAULT.html
   2. http://pespmc1.vub.ac.be/HOWWEB.html
   3. http://pcp.lanl.gov/RKSELECT.html
   4. http://pespmc1.vub.ac.be/RKSELECT.html
   5. http://pespmc1.vub.ac.be/SERVER.html
   6. http://pespmc1.vub.ac.be/hypercard.acgi$randomlink?searchstring=.html
   7. http://pespmc1.vub.ac.be/RECENT.html
   8. http://pespmc1.vub.ac.be/TOC.html#RKSELECT
   9. http://pespmc1.vub.ac.be/SEARCH.html