32 Ecology and Applied Environmental Science
3.4 intEractionS bEtwEEn two PoPulationS
The possibilities of interactions among populations are plenty and so are
their consequences, which can be classified according to the biological
interactions that take place. Yet considering the astonishing diversity in
the manner in which various plants and animals compete for space and
food, support each other, seek for or serve as food, it becomes obvious
that this classification is ineffective. Ultimately, each biological interaction constitutes a distinct situation. This difficulty can be overcome if
these inter actions are classified not simply on the basis of the processes
involved, but on the quantitative results they bring about. This approach
is the natural outcome of the populations’ mathematical description and
offers, besides simplicity, the advantage of its conclusions being translated
into quantitative relationships, and therefore into mathematical models.
The results of these interactions can be characterized as positive, negative
or neutral, depending on whether a population size increases, decreases or
is not affected by the other population’s presence. For example, from the
equation dN 1 /dt = α 11 N 1 + α 21 N 1 N 2 – β 31 N 1 N 3 we conclude that the change
of population N 1 is subjected to a positive effect by N 2 and a negative one
by N 3 , while the possible presence of a N 4 population has a neutral effect.
If we accept the fact that the interactions between two populations quantitatively influence the change of their size, we can classify them according
to the positive (+) or negative (–) or absence of impact by population A on
B or vice versa. Most interesting are the cases:
++, defined as symbiosis
– –, defined as competition
+–, defined as predation or predator-prey interaction
It must be noted that the interaction among populations constitutes one
of the main factors that shape natural selection; therefore it affects, to a
certain degree, the evolution of the respective species.
3.4.1 Symbiosis of two Populations
Symbiosis of two populations is an important biological function.
Nevertheless, its effects on population and ecosystem dynamics are rather
limited and have not been the object of extensive studies.
In a symbiotic relationship, the growth of each population is positively
affected by the presence of another population. This interaction tends to
lead the system of the two populations to a more rapid growth or to expand
the carrying capacity of the environment. If one of the populations disappears, then the second one, if it is completely dependent on the first, will
3.4 intEractionS bEtwEEn two PoPulationS
The possibilities of interactions among populations are plenty and so are
their consequences, which can be classified according to the biological
interactions that take place. Yet considering the astonishing diversity in
the manner in which various plants and animals compete for space and
food, support each other, seek for or serve as food, it becomes obvious
that this classification is ineffective. Ultimately, each biological interaction constitutes a distinct situation. This difficulty can be overcome if
these inter actions are classified not simply on the basis of the processes
involved, but on the quantitative results they bring about. This approach
is the natural outcome of the populations’ mathematical description and
offers, besides simplicity, the advantage of its conclusions being translated
into quantitative relationships, and therefore into mathematical models.
The results of these interactions can be characterized as positive, negative
or neutral, depending on whether a population size increases, decreases or
is not affected by the other population’s presence. For example, from the
equation dN 1 /dt = α 11 N 1 + α 21 N 1 N 2 – β 31 N 1 N 3 we conclude that the change
of population N 1 is subjected to a positive effect by N 2 and a negative one
by N 3 , while the possible presence of a N 4 population has a neutral effect.
If we accept the fact that the interactions between two populations quantitatively influence the change of their size, we can classify them according
to the positive (+) or negative (–) or absence of impact by population A on
B or vice versa. Most interesting are the cases:
++, defined as symbiosis
– –, defined as competition
+–, defined as predation or predator-prey interaction
It must be noted that the interaction among populations constitutes one
of the main factors that shape natural selection; therefore it affects, to a
certain degree, the evolution of the respective species.
3.4.1 Symbiosis of two Populations
Symbiosis of two populations is an important biological function.
Nevertheless, its effects on population and ecosystem dynamics are rather
limited and have not been the object of extensive studies.
In a symbiotic relationship, the growth of each population is positively
affected by the presence of another population. This interaction tends to
lead the system of the two populations to a more rapid growth or to expand
the carrying capacity of the environment. If one of the populations disappears, then the second one, if it is completely dependent on the first, will