4
RICHARD 5. MILLER
has been to reconfirm one case of the Volterra-Gause model, namely
that competitive exclusion can be demonstrated, and to ignore the more
interesting fact that coexistence for many generations has been repeatedly observed in highly simplified laboratory environments. After
showing that Drosophilafunebris and D . melanogaster were able to coexist in population cages where the only noticeable variable was a
periodic alteration in the freshness of the food medium, Merrell (1951)
stated that these results do not contradict the Gause hypothesis, because the two species were shown to have different responses to the
character of the medium. Merrell chose to devalue the important result
that, in an otherwise constant environment, a minor change in one
variable was sufficient to permit coexistence of the two species for
almost two years, after which the experiment was terminated. I n their
anxiety to “prove” the competitive exclusion principle, ecologists have
repeatedly ignored the important fact that many, if not most, laboratory studies of competition have provided better evidence of coexistence
than they have of competitive exclusion.
While competition between and within species has unquestionably
been an important force in the evolutionary history of natural communities and is presumed to be a major factor in the organization of
modern ecosystems, there is still no satisfactory explanation for the
tremendous diversity of species that is observed in natural systems.
When we consider the relatively low ecological efficiencies of animals,
and the fact that a classical food chain is limited for this reason to
about 4 or 5 direct links, we can understand why there is “room” for
a certain variety of forms. It is surprising, nevertheless, that discrete
biotopes such as small ponds or grasslands, with relatively uniform
structural characteristics, support the number of speciesl they do, especially large numbers of closely related species. During four years of
light trap collections at Rothampsted Experimental Station, 154 to
198 species of lepidoptera were recorded each year (Williams, 1964).
Kontkanen (1950) collected 4 288 individuals of 56 species of leafhopper in one day at a locality in North Karelia, Finland. In three
summers he never collected fewer than 37 species in any sample during
the months of July and August, and the mean per sample was 2 374
individuals representing 48 species. The H.M.S. Challenger expedition
collected 4 248 species of benthic animals, representing 1 438 genera,
from 70 stations less than 180 metres deep (Williams, 1964). -
Mitchell (1964) asks, “Why should several species share a common
energy source if one of the species could have become adapted to take
all of the energy?” Biotic communities are unquestionably the most
highly organized of natural systems. There is a high degree of interrelationship among different parts, self-regulation maintains a more or
RICHARD 5. MILLER
has been to reconfirm one case of the Volterra-Gause model, namely
that competitive exclusion can be demonstrated, and to ignore the more
interesting fact that coexistence for many generations has been repeatedly observed in highly simplified laboratory environments. After
showing that Drosophilafunebris and D . melanogaster were able to coexist in population cages where the only noticeable variable was a
periodic alteration in the freshness of the food medium, Merrell (1951)
stated that these results do not contradict the Gause hypothesis, because the two species were shown to have different responses to the
character of the medium. Merrell chose to devalue the important result
that, in an otherwise constant environment, a minor change in one
variable was sufficient to permit coexistence of the two species for
almost two years, after which the experiment was terminated. I n their
anxiety to “prove” the competitive exclusion principle, ecologists have
repeatedly ignored the important fact that many, if not most, laboratory studies of competition have provided better evidence of coexistence
than they have of competitive exclusion.
While competition between and within species has unquestionably
been an important force in the evolutionary history of natural communities and is presumed to be a major factor in the organization of
modern ecosystems, there is still no satisfactory explanation for the
tremendous diversity of species that is observed in natural systems.
When we consider the relatively low ecological efficiencies of animals,
and the fact that a classical food chain is limited for this reason to
about 4 or 5 direct links, we can understand why there is “room” for
a certain variety of forms. It is surprising, nevertheless, that discrete
biotopes such as small ponds or grasslands, with relatively uniform
structural characteristics, support the number of speciesl they do, especially large numbers of closely related species. During four years of
light trap collections at Rothampsted Experimental Station, 154 to
198 species of lepidoptera were recorded each year (Williams, 1964).
Kontkanen (1950) collected 4 288 individuals of 56 species of leafhopper in one day at a locality in North Karelia, Finland. In three
summers he never collected fewer than 37 species in any sample during
the months of July and August, and the mean per sample was 2 374
individuals representing 48 species. The H.M.S. Challenger expedition
collected 4 248 species of benthic animals, representing 1 438 genera,
from 70 stations less than 180 metres deep (Williams, 1964). -
Mitchell (1964) asks, “Why should several species share a common
energy source if one of the species could have become adapted to take
all of the energy?” Biotic communities are unquestionably the most
highly organized of natural systems. There is a high degree of interrelationship among different parts, self-regulation maintains a more or