r/K Strategists concept
Alan Soffan
In nature insect makes adaptation known as adaptive stategy as a result of selective
environment factor acting in a population (Horn, 1976). They need to have certain
strategies for efficiently utilizing the available time and energy to maximize their own
survival (Atkins, 1980).There are two extreme strategist applied by insect in adapting
theirself in certain environment.
1. R-stretegies
R-strategies principally operates to maximize reproductive rates in harsh,
unstable environment or during habitat disturbance (Atkins, 1980;
Matthews&Matthews, 1978), while there are only a little competition exist
(Elzinga, 1997). This R-strategies favor a “gambling” strategies (Price,1984).
Some characters for r-strategist listed in table below.
2. K-strategy
Principally, these insect tend to maintain their populations at a more or less
constant level, close to the carrying capacity of environment (Atkins, 1980),
They prefer not to increase a number of young, but they apply their high
survival ability (Matthews&Matthews, 1978), Some characters for r-strategist
listed in table below..
Table: Characteristics of extremes of r-K strategist
R-Strategist
Body size small
K-Strategist
Body size large
Short generation time
Long generation time
High level of dispersal
Low level of dispersal
The mortality is densityindependent
High reproductive rate
and often reach
overshoot
The mortality is density
dependent
Low reproductive rate and
rarely reach overshoot
Population density
fluctuative “boom and
bust”
Tend to be poor
competitors
Good colonization ability
Population density relative
constant from generation to
generation
Good competitors or keen
No food spezialitation
Usually they restrict just to
The population only contains
a few of individuals
Reference
Matthews& Kitching,
1984; Horn, 1976
Matthews&Matthews,
1978; Matthews&
Kitching, 1984; Horn,
1976
Matthews& Kitching,
1984
Matthews& Kitching,
1984; Horn, 1976
Matthews&Matthews,
1978; Matthews&
Kitching, 1984; Horn,
1976
Matthews&Matthews,
1978; Matthews&
Kitching, 1984
Matthews&Matthews,
1978; Horn, 1976
Matthews&Matthews,
1978; Matthews&
Kitching, 1984
Matthews& Kitching,
They lives in
unpredictable
environment
Rarely able to persist
successfully for long
period in certain habitat
Able to quickly discover
new habitats or
nomadens
Examples: grasshoppers
(Chortoicetes
terminifera), wasp scelio
fulgidus, Bushfly Musca
vestustissima,
few of plant
They usually lives in a stable
environment
High survival rate, especially
reproductive stages
Examples : Morabine
grasshoppers (Geckomima
sp.)
1984
Matthews&Matthews,
1978; Matthews&
Kitching, 1984; Horn,
1976
Matthews& Kitching,
1984
Matthews&Matthews,
1978; Matthews&
Kitching, 1984
(Matthews& Kitching,
1984)
Reference
Atkins, Michael D.1980. Introduction to Insect Behavior.Mac Millan Publishing
Co.New York.237p
Elzinga, Richard J. 1997. Fundamentals of Entomology. Prentice Hall. New
Jersey.475p.
Horn, David J. 1976. Insect Biology.W.B.Saunders.Philladelphia.439p
Matthews, Robert W., &Matthews, J.R. 1978. Insect Behaviour. John Wiley & Sons.
Canada.507p.
Matthews, E.G.& Kitching, R.L. 1984. Insect Ecology. University Quesland
Press.Asutralia.211p.
Price, Peter W.1984. Insect Ecology.John Wiley&Sons. New York.607p.
By Arya
Insects commonly have two type of strategy applied in its life. These strategies are r
and K-strategy. Some of insect may be flexible in applying r-K strategy. Locust and
aphids are example for r selected insect and tsetse flies and carpenter bees are
example for k selected insect (Matthew and Kitching 1984).Flour beetles, Tribolium
castaneum and Tribolium confusum, are best-studied example for insect that are
flexible in applying r-K strategy.(Matthew, 1976)
r-strategist occupy to environment which has high food density and low population
density of insect (Speight et al 1999). Such situation may occur when there are
changes in weather, or through human activity such as the planting of food crop. r
strategists are likely to be unpredictable in their ecologies, to produce large number
of offspring in relatively brief period of time, and essentially to over exploit their
habitats (Matthews and Kitchin 1984, Robinson 1987). r strategist has high mobility
and polyphagy (Matthew, 1976). They are very efficient at exploiting a seasonal food
supply that is available for only short period of time (Robinson 1987).
K strategist, on the other hand, are more often regulated by density-dependent factors,
such as intraspecific competition and natural enemies, they have relatively few
offspring and avoid over exploiting their habitats. Some species are characterized by
having giant eggs, low fecundity, and prolonged life spans (Maeta et al.1992). they
are also food specialization, individual defence, and lack of mobility (Matthew,
1976).
R or k strategist have each own advantages. R strategist relies on number of
individuals, while a K strategist relies on the quality of individuals. R strategist has a
great flexibility at the system level of the population. This means that the species can
survive major catastrophes, even if only at the expense of very large number of
individuals. For example, in the presence of the insecticide DDT, a new DDT resistant
strain can be selected, bur this can only happen at the cost of very high mortality
(Robinson 1987).
On the other hand, K strategist have great flexibility at the level of individual. They
depend on the survival ability of a complex and resilient individual which is able to
cope with all but the worst of natural catastrophes (Robinson 1987).
In the nature, r strategist are controlled by density independent control. Study on the
population of Euphydryas editha, shows that interspecific competition and predation
play relatively small roles in controlling many (but not all) of its populations (Daly
1978). In contrast, a butterfly of humid tropics such as Heliconius ethilla, which said
to be K selected, (Ehrlich and Gilbert 1973) is not subject to catastrophic weatherrelated mortality, but it faces heavy loses in the larval stage from predatory ants (Daly
1978).
The best studied of flexible r-K strategy are Tribolium castaneum and Tribolium
confusum (King and Dawson 1972). These beetles have intrinsic density-regulating
mechanism, including egg and pupal cannibalism by larvae and adult, reduced
fecundity and fertility in aged population, and the secretion of an inhibitory quinone
gas in crowded situation (Matthew 1976). Cannibalism is not only a regulatory
mechanism but also improves the fitness of surviving individuals (Mertz and Robert
1970).
References
1. Daly, H.V. 1978. Introduction to insect biology and diversity. London:
McGraw-Hill. 
2. Matthews, E.G. 1976. Insect ecology. St Lucia: University of Queensland
Press.
3. Matthews, E.G. and R.L. Kitching. 1987. Insect ecology 2nd edition. St Lucia:
University of Queensland Press.
4. Robinson, R.A. 1987. Host management in crop pathosystems. New York:
MacMillan Publishing Company.
5. Speight, M.R., M.D. Hunter, and A.D. Watt. 1999. Ecology of insect: concept
and application. Oxford: Blackwell Science.
r/K Strategists concept
Boy
r/k strategist is a life history theory proposed by Mac Arthur and Wilson
(1967) for classifying species based on their population growth which has correlation
with their life strategies to survive in the environment (Denno and Dingle, 1981;
Robinson, 1987). In this concept, species are classified as r-strategists and Kstrategists (Zadoks and Schein, 1979; Pedigo, 1989).
Insects (species) which have high reproductive rates but with low survival
rates are called
r-strategists, named after the statistical parameter “r”; the
symbol for the growth rate coefficient (Pedigo, 1989). Many pests of crops are rstrategists, they are small in size, have high reproductive rate, have short-lived
individuals in a relatively brief period of time, have high level of dispersal (
Robinson, 1987; Matthews and Kitching, 1984), have low investment in defence and
other interspecific competitive mechanisms (Matthews and Kitching, 1984), and they
have capacity to escape from severe enemy impact through the interaction of excellent
colonizing ability and a high population growth (Metcalf and Luckmann, 1982). For
instance, their colonizing ability can be seen from the explosion of the pest population
in early season (after germination of the host plant) or after the application of
insecticides, where the big number of new resistant population will be present for
replacing the susceptible population (Metcalf and Luckmann, 1982). Migratory locust
is an example of r-strategists. It was so difficult to control this pest which has ability
to reproduce new generation rapidly (Matthews and Kitching, 1984) and has ability to
disperse or migrate in a great distances (Metcalf and Luckmann, 1982). Water beetle
(Eretes australis), ghost moths (Trictena argentata) and some of dragonflies are other
examples of r-strategists species (Matthews and Kitching, 1984)
In contrast, insects which have low reproductive rates but with high survival
rates are called
K-strategists, named after the symbol for flattened portion of a
population growth curve “K”, the abbreviation means the carrying capacity of the
environment (Pedigo, 1989; Robinson, 1987).
K-strategists has characteristics
such as large in size, low level of dispersal organisms, long-lived individuals over
relative long periods of time (Robinson, 1987). K-strategists live in harsh
environment by producing few offspring which have ability to defense from predation
(Metcalf and Luckmann, 1982; Zadoks and Schein). Morabines grasshopper is an
example of K-strategists. A Population of this species may contain only a few of
individuals (low reproduction rate) but with the ability to survive in the environment
by using mimicry/ camouflage on the plants where they are life (Matthews and
Kitching, 1984). Tsetse flies, carpenter bees, and some forest lepidoptera are
examples of K-strategists species (Speight et.al, 1999).
We may find many intermediate species (between r and K strategiests) in the
real world, and some species may show traits of both r- and K-strategists at different
times or in different locations (Speight et.al, 1999). A single species may exhibit r- or
K-strategists depending on its population density. Low population densities of the
bean weevil (Acanthoscelides obtectus) showed r -strategists characteristics when
compared with high-density populations, which appeared to be more K-strategists
(Aleksic et al, 1993 in Speight et.al, 1999).
REFERENCES
Denno, R.F and Dingle, H. 1981. Insect Life History Patterns: Habitat and Geographic
Variation. Springer-Verlag: New York.
Matthews, E.G and Kitching, R.L. 1984. Insect Ecology. Second Edition. University of
Queensland Press: Australia.
Metcalf, R.L and Luckmann, W.H. 1982. Introduction to Insect Pest Management. Second
Edition. John Wiley and Sons: New York.
Pedigo, L.P. 1989. Entomology and Pest Management. MacMillan Publishing Company: New
York
Robinson, R.A. 1987. Host Management in Crop Pathosystems. MacMillan Publishing
Company: New York
Speight, M.R; Hunter, M.D; Watt, A.D. 1999. Ecology of Insects. Blackwell Science:
London.
Zadoks, J.C. and Schein, R.D. 1979. Epidemiology and Plant Disease Management. Oxford
University Press: New York.
By Haris
Insects as another animals, has behavior to response the habitat or
environment changes. Response to environment change and environmental changes
produced the dynamical of insect it’s self. The dynamical population of insect known
as r-/K- selection (another scientist called r-/K- strategist). r is symbol of rate of
population growth and K is symbol population density. The number of individuals of
species per unit area of space is referred to as population density, and growth of
population is the number of individuals added minus the number lost during a unit of
time □ (Elzinga, 1981). Generally insect population had two distinctive characteristic.
First many populations were extremely stable in size, generation after generation,
second others could be extremely variable in size, with number rising rapidly in one
or two generation to extremely high levels and then falling just as rapidly to very low
numbers. □ (Ross, et.al. 1982).
The two principal tactic of the r-strategy, nomadism and rapid population
build up, clearly seen in plague locust, which are associated with areas all over the
world □ (Matthews, 1984). K-strategic depend on many factor like availability of
food and extent of predation □ ( Romoser, 1981), it’s happened in Morabine
grasshopper in arid and semi-arid region of Australia. Basicly the r-/K- strategic based
on assumption, that r- strategic have exponential population growth, stable age
distributions, repeated colonization or fluctuations in population density and Kstrategy had logistic population growth environmental stable, population near
equilibrium density, competition important Δ ( Stearns, 1977)
Kind of insect which belongs to r- and K-strategy can be characterized below:
r- strategy
K-strategy
Climate
Uncertain variable, unpredictable
Fairly
consistent,
reasonably certain.
predictable,
Life cycle
Short, a few weeks
Rapid development and growth rate
Early reproduction and single
reproduction
Small body size
Potentially many offspring
Mortality catastrophic, usually
Longer, usually several months
Slower development and growth rate
Delayed or extended reproduction
period
Large body size
Fewer and large offspring
Mortality more evenly distributed,
density independent
density dependent
Population size
Variable in time, non equilibrium, Fairly constant, equilibrium, at or near
usually significantly below carrying carrying capacity, no need for
capacity periodic recolonization
recolonization
Competition
Variable commonly low
Usually high.
□ (Ross, et.al,1982 and Horn, 1976)
References :
- Ross, Herbert et.al. 1982. A textbook of entomology. John Wiley and Sons,
Inc. USA.
-
Horn , David J.1976. Biology of insect. W.B. Saunders Company.
Philadelphia, USA.
-
Matthews, E.G.1984. Insect ecology. University of Queensland Press.
Australia
-
Elzinga, Richard J. 1978. Fundamentals of Entomology. Prentice Hall Inc.
New Jersey.
-
Romoser, Wiliam S. 1981.Science of Entomology, second ed. Macmillan
Publishing Co.Inc. New York
-
Stearn, Stephen C.1977. Annu.Rev.Ecol. Sys. 8:145-71
By Koko
r-selection operates to maximize reproductive rate in harsh, unstable environments
where population remain well below the carrying capacity of the environment are
resources are not limiting except for time to reproduce successfully ( Peter, 1984).at
the other extreme of the continuum, in predictable, stable environment populations
will frequently reach the carrying capacity of the environment and selection will
operate by improving adaptations for living in these crowded, competitive condition,
where enemies such as predators and parasites will be very effective – k selection.
The bare essentials of this theory of r- and k- selection therefore involve five
characteristics that must be integrated there are:
1. Relatif stability of environmental conditions adn population size
2. Reproductive rate of species
3. Carrying capacity of the environment relative to mean population size.
4. The frequency of intraspecific and interspectif competition
5. The importance of enemy attack.
In here can be explained the concept of r and k strategist and their
development during the evolution of organism is certainly not new, although these
particular terms to describe the process have been used for only a short period of time.
There is presently a great deal of uncertainty as to how important these stratagems are
in the functioning of organism within ecological communities. Dobzhansky, 1950 in
Peter, 1974. He described that the differences between temperate or arctic
environments and those of tropical regions.
In tropical environment, organism are more constantly crowded and selection is
influenced more by biotic factor. Competition then become a primary selective force
because the populations are more constantly at or near the carrying capacity of the
environment.
MacArthur and Wison, (1967 in peter 1974) they said that the stage of the population
there are two posible situations: (1) An environment in which a population is
expanding, and (2) an environment in which a population is crowded. They assumed
relatively stable condition in both cases, no great physical changes occurring to
radically change the environment. Under this condition, organisms should evolve
toward productivity and large families since there is no shortage of resourr-/KStrategy of insect
Insects as another animals, has behavior to response the habitat or
environment changes. Response to environment change and environmental changes
produced the dynamical of insect it’s self. The dynamical population of insect known
as r-/K- selection (another scientist called r-/K- strategist). r is symbol of rate of
population growth and K is symbol population density. The number of individuals of
species per unit area of space is referred to as population density, and growth of
population is the number of individuals added minus the number lost during a unit of
time □ (Elzinga, 1981). Generally insect population had two distinctive characteristic.
First many populations were extremely stable in size, generation after generation,
second others could be extremely variable in size, with number rising rapidly in one
or two generation to extremely high levels and then falling just as rapidly to very low
numbers. □ (Ross, et.al. 1982).
The two principal tactic of the r-strategy, nomadism and rapid population
build up, clearly seen in plague locust, which are associated with areas all over the
world □ (Matthews, 1984). K-strategic depend on many factor like availability of
food and extent of predation □ ( Romoser, 1981), it’s happened in Morabine
grasshopper in arid and semi-arid region of Australia. Basicly the r-/K- strategic based
on assumption, that r- strategic have exponential population growth, stable age
distributions, repeated colonization or fluctuations in population density and Kstrategy had logistic population growth environmental stable, population near
equilibrium density, competition important Δ ( Stearns, 1977)
Kind of insect which belongs to r- and K-strategy can be characterized below:
r- strategy
K-strategy
Climate
Uncertain variable, unpredictable
Fairly
consistent,
reasonably certain.
predictable,
Life cycle
Short, a few weeks
Rapid development and growth rate
Early reproduction and single
reproduction
Small body size
Potentially many offspring
Mortality catastrophic, usually
density independent
Longer, usually several months
Slower development and growth rate
Delayed or extended reproduction
period
Large body size
Fewer and large offspring
Mortality more evenly distributed,
density dependent
Population size
Variable in time, non equilibrium, Fairly constant, equilibrium, at or near
usually significantly below carrying carrying capacity, no need for
capacity periodic recolonization
recolonization
Competition
Variable commonly low
Usually high.
□ (Ross, et.al,1982 and Horn, 1976)
References :
- Ross, Herbert et.al. 1982. A textbook of entomology. John Wiley and Sons,
Inc. USA.
-
Horn , David J.1976. Biology of insect. W.B. Saunders Company.
Philadelphia, USA.
-
Matthews, E.G.1984. Insect ecology. University of Queensland Press.
Australia
-
Elzinga, Richard J. 1978. Fundamentals of Entomology. Prentice Hall Inc.
New Jersey.
-
Romoser, Wiliam S. 1981.Science of Entomology, second ed. Macmillan
Publishing Co.Inc. New York
-
Stearn, Stephen C.1977. Annu.Rev.Ecol. Sys. 8:145-71
This kind of evolution is called r- selection.
On the other hand, under condition of crowding, selection should evolve toward
feeding efficiency since resources are in short supply. The organism that can replace
itself with the least waste of resources in the most fit in this environment, evolution
here is called k selection.
Pianka, (1970 in peter 1974) thoroughly treated the subject listed some of the
correlates of both r and k selection. He propos that terestrial vertebrates and perennial
plants are predominately k- selected. Whereas terrestrial invertebrates and annual
plants are more r- selected. Gadgil and solbrig, (1972 in peter 1974) discussed r and
k selection, objected to the assumption that increased or decreased birth brate by itself
is evidence of increased r or k selection respectively.
There are characteristics associated with both with both r and k strategists.
Certain characteristic of r and k startegists is:
R STRATEGISTS
K STRATEGISTS
Found most abudantly where density
Found most abudantly where density
independent factors predominate:
dependent factors predominate:
- temperate and arctic climate
- tropical climate
- edges population range
- center population range
- disturbed situation
- undisturbed situation
Have a high fecundity and short
generation time
Have a low fecundity and long generation
time
Usually reproduce early and rapidly, and
died early.
Usually reproduce early and rapidly, and
died early.
To be small in size
To be large in size
Dependent upon abudant food resources.
Can exist with limited food resources
highly competitive for resources.
Poor competitors- opportunists
good competitors- specialists
May have greater tolerances to harsh
environment conditions.
May have restricted tolerances to harsh
environment conditions.
The concept of r and K strategies can act only as a mechanism for relative
comparisons of biotic components of a community since there are no absolute criteria
by which an organism can be designated as an r or K strategist. These comparisons
may vary, depending on the species In www.springerlink.com
r-strategist and k strategist can be classified according to their population growth
curves ( MacArthur and Wilson, 1967 in Robinson). At one are the opportunists, the
quantity breeders, that reproduce very large numbers of small-sized, biologically
cheap, short-lived in individual. Each population explosion is followed by a
population axtinction in which all active individuals normally perish and the species
survives only in a dormant push as seeds, eggs, pupae, or spores. These quantity
breeders is called r-strategist. Plant parasites, such as aphids are typical r-stategists.
K-strategists depend on the survival ability of a complex individual.
As the species subjected to r selection build up its numbers, and competitors and
predators, the environment become crowded with species and the condition of r
selection no longer prevail. These are the short of selectionpressures that operate in
environment of the second kind, those that are predictably favourable and stable, the k
environment ( k represents carrying capacity). Southwood, 1977a in Martin et all,
elaborates on this set of evolutionary interactions with the environment. He associates
the r-k spectrum with so called ‘’durational stability’’.
Daly and howell, 1978 can describe the two principal tactict of the r-strategy,
nomadism adn rapid population build up, on the locusts. The locust need condition
favourable. These favourable condition are largely dependent on soil type.
REFFERENCE
Daly., howell.V. 1978. Introduction to Insect and Diversity. America.
Martin, R. S., Mark, D.H, Allan, D.W. 1999. Ecology of insects concepts and
applications. Department of zoology, university of Oxford. Oxford.
Matthews, E. G., R.L. Kitching. 1976. Insect ecology. University of Queensland
Press. Queensland.
Peter, W.P. 1974. Evolutionary Strategies of Parasitic Insect. Department of
Entomology University of Illinois Urbana, Illinois.
Robinson, R. A. Host Management in Crop Pathosystem. University of California.
Barkeley.
www.springerlink.com