108
0. R. POTTS AND 0. P. VICKERMAN
F. cOb30ph’8
.
1. Introduction
.
2. Percentege Composition end Trophic Structure
3. The Reletionship Between the Numbers of Mecroscopic Collembole
.
and Predatory Coleoptera .
V. Partridges .
A. Introduction .
B. Methods .
C. Predation
.
1. Fox .
2. Carrion Crow and Magpie
4. Mustelidae .
6. Other Predetors .
6. Predetor-Prey Reletionships
.
7. Conclusions
.
.
3. R8t .
VI. Conclusions .
Acknowledgements
.
References .
166
166
167
161
162
162
164
173
176
176
177
177
179
180
183
184
188
189
I. INTRODUCTION
Notwithstanding various political and economic considerations the
overall concern of agriculture is to intensify the production of food and
each step in the development of agriculture has further removed the
crop ecosystems from their parent non-agricultural ecosystems. Until
recently, however, fairly obvious ecological constraints have determined
much of the progress in the development of agriculture. For example, in
Britain the natural nitrogen cycle and pest and weed situation had
resulted in a fairly fixed system of alternate cropping or rotation until
the 1950’s. Since that time, however, the general availability of manufactured nutrients and pesticides has freed the agricultural systems
of their old straitjacket. The overall energy cost of these changes can
be calculated (Odum, 1971) but the ecological costs of this freedom
are not known, although most ecologists are aware of the various
environmental hazards which have followed the recent changes
(0.g. Coulson et al., 1972). We do not know which, if any, of the costs
are the result of flaunting ecological principles-these principles are
in any case not well established even from the study of natural ecosystems. We therefore do not know which costs are an inevitable
result of the need for increased crop hygiene to maintain increased
yields, and which could probably have been avoided.
Our recent experience has suggested that research is needed to
detect and thus avoid those increases in crop hygiene which are likely
to be, in the long run, counterproductive. We must also avoid temporary
practices which are likely to incur long-term environmental costs.
0. R. POTTS AND 0. P. VICKERMAN
F. cOb30ph’8
.
1. Introduction
.
2. Percentege Composition end Trophic Structure
3. The Reletionship Between the Numbers of Mecroscopic Collembole
.
and Predatory Coleoptera .
V. Partridges .
A. Introduction .
B. Methods .
C. Predation
.
1. Fox .
2. Carrion Crow and Magpie
4. Mustelidae .
6. Other Predetors .
6. Predetor-Prey Reletionships
.
7. Conclusions
.
.
3. R8t .
VI. Conclusions .
Acknowledgements
.
References .
166
166
167
161
162
162
164
173
176
176
177
177
179
180
183
184
188
189
I. INTRODUCTION
Notwithstanding various political and economic considerations the
overall concern of agriculture is to intensify the production of food and
each step in the development of agriculture has further removed the
crop ecosystems from their parent non-agricultural ecosystems. Until
recently, however, fairly obvious ecological constraints have determined
much of the progress in the development of agriculture. For example, in
Britain the natural nitrogen cycle and pest and weed situation had
resulted in a fairly fixed system of alternate cropping or rotation until
the 1950’s. Since that time, however, the general availability of manufactured nutrients and pesticides has freed the agricultural systems
of their old straitjacket. The overall energy cost of these changes can
be calculated (Odum, 1971) but the ecological costs of this freedom
are not known, although most ecologists are aware of the various
environmental hazards which have followed the recent changes
(0.g. Coulson et al., 1972). We do not know which, if any, of the costs
are the result of flaunting ecological principles-these principles are
in any case not well established even from the study of natural ecosystems. We therefore do not know which costs are an inevitable
result of the need for increased crop hygiene to maintain increased
yields, and which could probably have been avoided.
Our recent experience has suggested that research is needed to
detect and thus avoid those increases in crop hygiene which are likely
to be, in the long run, counterproductive. We must also avoid temporary
practices which are likely to incur long-term environmental costs.