The Distribution and Abundance of
Lake-Dwelling Triclads - towards a Hypothesis
T. B . R E Y N O L D S O N
Department of Zoology, University College of North Wales,
Bangor, Ca,erns., Wales
I. Introduction.. .........
................. 1
4
111. The Pattern of Distribution and Abundance.. ............................
6
A. Introduction and Field Methods.. .... .............................
6
B. Results ...........................................................
12
IV. Historical Aspects of Distribution and Abundance.. .......................
20
V. Determinants of Distribution and Abundance.. ...........................
28
A. Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
B. A Place to Live.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
C. Food ...........................................
. . . . . . . . . . . . . 34
D. Organisms of the Same Species.. .....................................
40
E. Organisms of Different Species.. .............................
. . . . 43
VI. The Explanation of Distribution and Abundance - a Hypothr5is. . . . . . . . . . . 63
A. The Total Triclad Population.. . . . . . . . .
. . . . . . . . . . . . 63
B. The Individual Species.. ............................................
56
VII. Conclusions and Summary.. ............................................
62
Acknowledgments .......................................................... 63
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11. The Taxonomy of the Triclads.. ........................................
I. INTRODUCTION
One of the main objectives of the ecologist is the study of factors
underlying the distribution and abundance of animals. These factors are
numerous, often subtle in operation and interact in complex ways so
that in practice research is usually restricted to include only those which
experience or a priori reasoning suggests may be important. Many inconclusive studies may stem from examples in which the wrong factors
have been selected for study. There is much to be said for tackling such
projects with resources of manpower equivalent to those which have
been successfully employed in t,he study of the spruce-budworm (Morris,
1963) but it remains important to avoid stifling the initiative and ideas
of the individual worker (Lund, 1!)64). Andrewqrtha and Birch (1954)
provided a great stimulus in this field of ecology and interest has been
maintained in recent texts by Odum (1953) and Macfadyen (1963). But
1
Lake-Dwelling Triclads - towards a Hypothesis
T. B . R E Y N O L D S O N
Department of Zoology, University College of North Wales,
Bangor, Ca,erns., Wales
I. Introduction.. .........
................. 1
4
111. The Pattern of Distribution and Abundance.. ............................
6
A. Introduction and Field Methods.. .... .............................
6
B. Results ...........................................................
12
IV. Historical Aspects of Distribution and Abundance.. .......................
20
V. Determinants of Distribution and Abundance.. ...........................
28
A. Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
B. A Place to Live.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
C. Food ...........................................
. . . . . . . . . . . . . 34
D. Organisms of the Same Species.. .....................................
40
E. Organisms of Different Species.. .............................
. . . . 43
VI. The Explanation of Distribution and Abundance - a Hypothr5is. . . . . . . . . . . 63
A. The Total Triclad Population.. . . . . . . . .
. . . . . . . . . . . . 63
B. The Individual Species.. ............................................
56
VII. Conclusions and Summary.. ............................................
62
Acknowledgments .......................................................... 63
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11. The Taxonomy of the Triclads.. ........................................
I. INTRODUCTION
One of the main objectives of the ecologist is the study of factors
underlying the distribution and abundance of animals. These factors are
numerous, often subtle in operation and interact in complex ways so
that in practice research is usually restricted to include only those which
experience or a priori reasoning suggests may be important. Many inconclusive studies may stem from examples in which the wrong factors
have been selected for study. There is much to be said for tackling such
projects with resources of manpower equivalent to those which have
been successfully employed in t,he study of the spruce-budworm (Morris,
1963) but it remains important to avoid stifling the initiative and ideas
of the individual worker (Lund, 1!)64). Andrewqrtha and Birch (1954)
provided a great stimulus in this field of ecology and interest has been
maintained in recent texts by Odum (1953) and Macfadyen (1963). But
1