PATTERN A N D PROCESS IN COMPETITION
67
causes and especially the mechanisms of species interactions. Attempts
to derive general theories of population control have been seriously
hampered by the indiscriminate application of results from studies of
one taxonomic group t o observations of relationships in another, and
the same can be said of competition theory. There is no reason to
assume that all animals respond in the same way to the same factors
and are, therefore, subject to the same laws of population growth or
competition. Gammarus duebeni has a large amplitude with respect to
abiotic factors but low productivity, while its competitors G. salinus
and G. zaddachi have high productivities, faster development rates,
higher growth rates and higher reproductive potentials within a narrower range of conditions (Kinne, 1954). On the basis of research with
these and other marine organisms Kinne (1956) suggests that animals
with a narrow range of tolerance to abiotic factors tend to have a high
biotic potential. However, it would obviously be a mistake to assume
that a high replacement rate is a universal criterion of biological
success. I n species with ill-defined space requirements, competing mainly
through exploitation rather than interference, replacement rate may
have high value; but in species with strong interference elements in
their competitive relationships and rather rigid dispersion mechanisms,
it may be more advantageous to have a relatively low replacement rate
and greater population stability. I n other words, animals living in
restricted niches may be successful in maintaining their populations
either through high biotic potential and exploitation or by competitive
interference.
This article suggests a t least two major sources of species diversity.
When competition is primarily through exploitation and the system
is under strong environmental control, it is likely that fluctuations in
factors affecting reproduction and survival will continually alter the
outcome of the competitive interaction, allowing coexistence of mixedspecies populations. If there is no interference, the more similar the
species the more likely that their interaction values will be equal and
correspondingly less environmental change will be required in order to
allow coexistence. If there is a strong element of interference resulting
in competitive exclusion, species diversity may still be increased if one
of the species becomes specialized and, in so doing, reduces its niche
size in such a way that both species are able to exist in the same biotope,
e.g. when the more specialized competitor occupies an included niche
which is small enough to allow the other species to survive in the
difference subset of their niches. -4s noted earlier, coexistence is a,
relative term depending on the size of area one chooses to measure. If
there is a strong element of interference and the critical habitat features
are uniformly distributed, competitive exclusion may operate over
67
causes and especially the mechanisms of species interactions. Attempts
to derive general theories of population control have been seriously
hampered by the indiscriminate application of results from studies of
one taxonomic group t o observations of relationships in another, and
the same can be said of competition theory. There is no reason to
assume that all animals respond in the same way to the same factors
and are, therefore, subject to the same laws of population growth or
competition. Gammarus duebeni has a large amplitude with respect to
abiotic factors but low productivity, while its competitors G. salinus
and G. zaddachi have high productivities, faster development rates,
higher growth rates and higher reproductive potentials within a narrower range of conditions (Kinne, 1954). On the basis of research with
these and other marine organisms Kinne (1956) suggests that animals
with a narrow range of tolerance to abiotic factors tend to have a high
biotic potential. However, it would obviously be a mistake to assume
that a high replacement rate is a universal criterion of biological
success. I n species with ill-defined space requirements, competing mainly
through exploitation rather than interference, replacement rate may
have high value; but in species with strong interference elements in
their competitive relationships and rather rigid dispersion mechanisms,
it may be more advantageous to have a relatively low replacement rate
and greater population stability. I n other words, animals living in
restricted niches may be successful in maintaining their populations
either through high biotic potential and exploitation or by competitive
interference.
This article suggests a t least two major sources of species diversity.
When competition is primarily through exploitation and the system
is under strong environmental control, it is likely that fluctuations in
factors affecting reproduction and survival will continually alter the
outcome of the competitive interaction, allowing coexistence of mixedspecies populations. If there is no interference, the more similar the
species the more likely that their interaction values will be equal and
correspondingly less environmental change will be required in order to
allow coexistence. If there is a strong element of interference resulting
in competitive exclusion, species diversity may still be increased if one
of the species becomes specialized and, in so doing, reduces its niche
size in such a way that both species are able to exist in the same biotope,
e.g. when the more specialized competitor occupies an included niche
which is small enough to allow the other species to survive in the
difference subset of their niches. -4s noted earlier, coexistence is a,
relative term depending on the size of area one chooses to measure. If
there is a strong element of interference and the critical habitat features
are uniformly distributed, competitive exclusion may operate over