76
N. W. MOORE
to kill any living organism which is free-living or has a free-living stage
in its life history.
The term ecology raises important questions of methodology. One
branch of ecology deals with the relationship between individual organisms and t,heir physical environment. Population ecology on the other
hand is the study of groups of individuals rather than of separate
organisms. I take the view that there is a fundamental difference between these two types of ecology. The h s t is an adjunct of other
disciplines, e.g. of physiology, but population ecology is a scientific
discipline in its own right. Unfortunately the terms autecology and
synecology do not coincide completely with the two divisions of the
subject; for population ecology includes the population aspects of
autecology, as well as the synecological subjects of population ecology
of groups of species, of community ecology and ecosystem ecology.
Accordingly the term population ecology is used throughout the paper
when reference is made to the study of groups of organisms, and the
term ecology is retained as a general inclusive term, covering all
relationships between organisms and their environment.
I should state briefly my personal views on population control since
they underlie some of the arguments in this paper but are not discussed
in it. I believe a useful distinction can be made between density-independent and density-dependent factors (Howard and Fiske, 191 1, etc.).
Experimental evidence is lacking to show which type of factor usually
controls animal populations. Density-independent factors operate continuously and one or more of them may keep a population at a relatively
low level for a long period of time, but in the long run it seems unlikely
that they could produce the stability in populations which is observed
in nature. Therefore I favour the thesis that ultimately populations are
controlled by those factors in the total complex which are densitydependent. I believe that behaviour mechanisms control population
density more often than is usually supposed.
B. THE S T U D Y O F PESTICIDES AS AN ECOLOGICAL PROBLEM
The widescale use of chemicals to control plants and animals is a
recent development: within the space of about twenty years a new type
of ecological factor has come into prominence, which is likely to affect
all the ecosystems of the world. The situation is potentially of extraordinary interest to biologists. Yet, while great interest has been shown
in the use and abuse of pesticides, the fundamental and theoretical
aspects of the problem have been given less attention. It is possible to
guess some of the reasons. The chemical revolution of agriculture has
developed gradually from small beginnings and there has been no particular moment when it could be said that a qualitative difference in
N. W. MOORE
to kill any living organism which is free-living or has a free-living stage
in its life history.
The term ecology raises important questions of methodology. One
branch of ecology deals with the relationship between individual organisms and t,heir physical environment. Population ecology on the other
hand is the study of groups of individuals rather than of separate
organisms. I take the view that there is a fundamental difference between these two types of ecology. The h s t is an adjunct of other
disciplines, e.g. of physiology, but population ecology is a scientific
discipline in its own right. Unfortunately the terms autecology and
synecology do not coincide completely with the two divisions of the
subject; for population ecology includes the population aspects of
autecology, as well as the synecological subjects of population ecology
of groups of species, of community ecology and ecosystem ecology.
Accordingly the term population ecology is used throughout the paper
when reference is made to the study of groups of organisms, and the
term ecology is retained as a general inclusive term, covering all
relationships between organisms and their environment.
I should state briefly my personal views on population control since
they underlie some of the arguments in this paper but are not discussed
in it. I believe a useful distinction can be made between density-independent and density-dependent factors (Howard and Fiske, 191 1, etc.).
Experimental evidence is lacking to show which type of factor usually
controls animal populations. Density-independent factors operate continuously and one or more of them may keep a population at a relatively
low level for a long period of time, but in the long run it seems unlikely
that they could produce the stability in populations which is observed
in nature. Therefore I favour the thesis that ultimately populations are
controlled by those factors in the total complex which are densitydependent. I believe that behaviour mechanisms control population
density more often than is usually supposed.
B. THE S T U D Y O F PESTICIDES AS AN ECOLOGICAL PROBLEM
The widescale use of chemicals to control plants and animals is a
recent development: within the space of about twenty years a new type
of ecological factor has come into prominence, which is likely to affect
all the ecosystems of the world. The situation is potentially of extraordinary interest to biologists. Yet, while great interest has been shown
in the use and abuse of pesticides, the fundamental and theoretical
aspects of the problem have been given less attention. It is possible to
guess some of the reasons. The chemical revolution of agriculture has
developed gradually from small beginnings and there has been no particular moment when it could be said that a qualitative difference in