PATTERN AND PROCESS IN COMPETITION
15
and chemical conditioning by nonvolatile substances were not limiting
factors in these populations, and suggested that lack of oxygen or
repeated physical contact might depress the feeding rate, or that food
quality might be a limiting factor (P. W. Frank, personal communication), but there was no evidence of interference with access to a resource.
Ullyett (1950) found no evidence of aggressive activity in competition
among larvae of the sheep blowflies Lucilia sericata and Chrysomyia
chlorophyga. They feed on the same food and compete only through
exploitation of the same resource. Ullyett regards competition in these
species in terms of “the provisions of nature rather than in the light of
a specific ‘struggle’. The phenomenon which really acts as the controlling agent is basically sheer starvation.” It is in this sense that Nicholson
used the term “scramble” to distinguish between this and a form of
competition in which “each successful individual lays claim to a supply
of requisites sufficient to maintain it and to enable it to produce offspring. The unsuccessful individuals are denied access to the critical
requisites by their successful competitors” (Nicholson, 1955).
In each of these examples the populations were directly limited by
absolute amounts of food, food quality, or by a factor which affected
their abilities to exploit their food resources. There is the suggestion, in
other words, that food becomes limiting unless (1) some form of interference acts as a regulating mechanism relative to the space that
contains a supply of resources, or (2) extrinsic factors such as climate
prevent the level of population from reaching a critical value. The
crowded populations and variations in body size that are commonly
observed in natural populations of some dung, carrion and log-dwelling
insects may reflect events similar to those observed in laboratory
studies, in which exploitation is the principal form of competition. But
there remains the question of how often natural populations are in fact
directly limited by a resource such as food, or how frequently they are
forced into a competitive interaction dominated by exploitation.
111. THE ECOLOGICAL NICHE
A. HISTORICAL DEVELOPMENT O F THE NICHE CONCEPT
Elton and Miller (1954) have noted that the “ecological niche” is a
far more elusive concept than was supposed by either Elton or Grinnell
when they introduced the term into the literature. Elton (1927) observed that although there may be a difference in species composition
between one community and another, there is usually an obvious
similarity in their “ground plans”. We can expect to find groups of
herbivores, predators, parasites and scavengers in every animal community, even though these roles may be filled by different species.
15
and chemical conditioning by nonvolatile substances were not limiting
factors in these populations, and suggested that lack of oxygen or
repeated physical contact might depress the feeding rate, or that food
quality might be a limiting factor (P. W. Frank, personal communication), but there was no evidence of interference with access to a resource.
Ullyett (1950) found no evidence of aggressive activity in competition
among larvae of the sheep blowflies Lucilia sericata and Chrysomyia
chlorophyga. They feed on the same food and compete only through
exploitation of the same resource. Ullyett regards competition in these
species in terms of “the provisions of nature rather than in the light of
a specific ‘struggle’. The phenomenon which really acts as the controlling agent is basically sheer starvation.” It is in this sense that Nicholson
used the term “scramble” to distinguish between this and a form of
competition in which “each successful individual lays claim to a supply
of requisites sufficient to maintain it and to enable it to produce offspring. The unsuccessful individuals are denied access to the critical
requisites by their successful competitors” (Nicholson, 1955).
In each of these examples the populations were directly limited by
absolute amounts of food, food quality, or by a factor which affected
their abilities to exploit their food resources. There is the suggestion, in
other words, that food becomes limiting unless (1) some form of interference acts as a regulating mechanism relative to the space that
contains a supply of resources, or (2) extrinsic factors such as climate
prevent the level of population from reaching a critical value. The
crowded populations and variations in body size that are commonly
observed in natural populations of some dung, carrion and log-dwelling
insects may reflect events similar to those observed in laboratory
studies, in which exploitation is the principal form of competition. But
there remains the question of how often natural populations are in fact
directly limited by a resource such as food, or how frequently they are
forced into a competitive interaction dominated by exploitation.
111. THE ECOLOGICAL NICHE
A. HISTORICAL DEVELOPMENT O F THE NICHE CONCEPT
Elton and Miller (1954) have noted that the “ecological niche” is a
far more elusive concept than was supposed by either Elton or Grinnell
when they introduced the term into the literature. Elton (1927) observed that although there may be a difference in species composition
between one community and another, there is usually an obvious
similarity in their “ground plans”. We can expect to find groups of
herbivores, predators, parasites and scavengers in every animal community, even though these roles may be filled by different species.