Investigations of the ecology of earthworms (Lumbricidae) in arable soil
Undersøgelser af regnormenes (Lumbricidae) økologi i dansk landbrugsjord
Niels Caspar Andersen
Royal Veterinary and Agricultural University Copenhagen
AARHUS UNIVERSITET Det Jo rd b ru g s v id e n s k a b e lig e Fakultet
Biblioteket Forsøg s vej 1 D K-4200 Slagelse
Tidsskrift for Planteavls Specialserie
Copenhagen 1987
Planteavlsforsøg
Beretning nr. S 1871
Investigations of the ecology of earthworms (Lumbricidae) in arable soil
Undersøgelser af regnormenes (Lumbricidae) økologi i dansk landbrugsjord
Niels Caspar Andersen
Royal Veterinary and Agricultural University Copenhagen
AARHUS UNIVERSITET Det Jordbrugsvidenskabelige Fakultet
Biblioteket Forsøgsvej 1 D K-4200 Slagelse
Tidsskrift for Planteavls Specialserie
Copenhagen 1987
INVESTIGATIONS OF THE ECOLOGY OF EARTHWORMS (Lumbricidae) IN ARABLE SOIL
by NIELS CASPAR ANDERSEN
CONTENTS page:
PREFACE 7
ACKNOWLEDGEMENTS 9
PART I. G E N E RA L E C O L O G Y 10
CHAPTER I EA R T H W O R M S A N D TEMPERATURE REGIME 10
INTRODUCTION 10
MATERIAL A N D ME TH ODS 14
ANALYSIS OP TE M P ERATURE REGIME 16
Winte r 20
Spring 21
Summer 22
Temperature i n d ex 23
TEMPERATURE I N D E X A N D AUTU M N D E N S IT Y OF DIFFERENT SPECIES 26
A . longa 26
L . terrestris 28
A. rosea 29
A . caliginosa an d A . chlorotica 29
DENSITY AT D I F F ER ENT LEVELS OF MANUR E A ND TEMP. INDEX 30
A.longa 3 1
A . ca l iginosa 34
A . chlorotica 37
A.ro s e a 38
L . terrestris 40
G ENERAL REMARKS 40
C O MBI N ED INFLUENCE OF TEMPERATURE REGIME AN D PRECI PITAT ION 45
P r e c i p i t a t i o n duri ng summer 46
Pr e c i p i t a t i o n during sprin g 53
C ONCLUSIONS 54
APPENDIX: Temperature and p r e c i p i t ati o n 1975 - 1 981 55 CHAP T ER II RES P I R A T I O N OF E AR THWORMS 60
I N T R O D U C TI O N 60
MA TER I A L A N D METHODS 61
OXYGEN C O N S U MPTION OF DIFFERENT SPECIES 63
D I S C U S S I O N 72
CHAPTER III E C O L O G Y OF Ap orrectodea t u b e rc u lat a (Eisen) 79
I N T R O D U C T IO N 79
METHODS 81
C LIMATIC CONDITIONS, AUGUST I98O - DE C EMB E R 1 9 8I 82
Temperature 82
Pr e c i p i t a t i o n 83
V ER T I CA L M IG R A T I O N 84
N ewly ha t ch e d 84
Juveniles, subadults and adults 88
P O P U L A T I O N DEVELOPMENT 89
Eme r ge n c e of n ewly ha tc he d 89
Development time of cocoons 91
N u mb e r of cocoons p rod u ced 91
Juveniles 92
Subadults and adults 95
General p o p ulation development 97
D I S C U S S I O N 98
CHAPTER IV F I EL D R E S P I RA TI ON OF A . tub e rcu l ata 104
INTRODUCTION 104
METHODS 105
RESULTS AND D I S C U S S I O N 106
Annual oxyge n co n sumption 106
Oxygen c o n s u mp t io n and. vertical m i g r a t i o n 109 CHAPTER V P I LO T STUDIES O N THE GROWTH OF A . caliginosa 112
A . t u b e r c u l a t a , A.longa and 0 .cyaneum
INTRODUCTION 112
MATERIAL A N D M ETHODS 113
A . longa e x p eriment 115
A . tuberculata experiment 115
A. caliginosa experiment 115
0. cyaneum experiment 117
TREATMENT OF GROW TH DATA 117
RESULTS 120
A.longa 120
A. caliginosa 121
A. tuberculata 123
0 .cyaneum 123
RELATIVE S PE C I F IC GROWTH RATE 125
RESPIRATION / P R O D U C T I O N RATIO 129
DISCUSSION 131
PART II E AR T H W O R M S A N D AGRIC UL TU RA L PRACTIC E 136 CHAPTER I D I F F E RE NT MECHA N ICA L TREATMENTS A N D 136
C A T C H CR OP OF W HI TE M U ST A R D (Sinapis alba L.)
EXPERIMENT A. R O T A V A T I O N W I T H - AND PL OU G H I N G 138 WITHOUT CATCH CROP
EXPERIMENT B. FIVE DIFFERENT SOIL TREATMENTS AND CATCH CROP 140 CHAPTER II CONTINUOUS BARLEY WI TH CATCH CROP, 144
P L O U G H I N G AND ROTA V ATI O N
CHAPTER III SPRING BARLE Y W I T H U N D E R S O W N 149 GRASS A N D LEGUMES
TO TAL N U M B E R OF EARTH WOR M S 1 9 8 3 - 1 9 8 4 150
SPECIES COM PO SI TI ON 152
E F F ECT S OF CATCH CROPS AND FER TIL I ZER 15 2
C HAPTER IV DIRECT D R ILL I NG 155
B A L L U M 155
H E IN I N G E 156
DIRECT DR I LLING A N D OTHER SYSTEMS 156
C HAPTER V EFFECT OF FA RM YA RD MANURE A N D S L U R R Y 159 IN TR AD IT IO NA L SYSTEMS
EFFE C T S OF MANURE A N D Y E A R ON D ENSITY A N D BIOM A SS 159 C O MBI N ED E FF E C T O F MANU R E,D O SE AN D Y E A R ON D E N S I T Y 161
T U RNO V E R OF ORGANIC M A T T E R 165
SUMM A R Y 167
I NFLUENCE OF TEMPERATURE 168
R E S P I R A T I O N 169
E C O L O G Y OF A . tuberculata 171
FIELD R E S P I R A T I O N 172
GROWTH OF EARTHWORMS 173
AG R I C U L T U R A L PRACTI CE 175
D A N S K RESU M E (Danish summary) 178
U N D E R S Ø G E L S E R AF REGN O RMENES (Lumbricidae) 178 Ø KOLOGI I D ANSK L A N D B R U GS JO RD
T EM P ER A T U RF O RHOLDENE S BET Y D N I N G 179
R E S P I R A T I O N l8l
ØKOLOGI HOS A . tu be rc ul at a 182
P O PUL A TI O N S R E S P I R A T I O N 183
V Æ K S T F O R H O L D HOS R EG N O R M E 183
I N D V I R K N IN G AF DY RK NI NG SP RA KS IS 186
REFE RE N C E S 188
PREFACE
In the p resent thesis are treated a number of aspects of lum- bricid ec o lo g y in r el ation to agricul t u ral systems, emerging from ten y ears work at the Zoological Department of the Royal Veterinary a n d Agricultural University, Copenhagen. The thesis falls in two parts. In part I, are treated some of the more general a s p ec t s of lumb r ici d ecology, with reference mai n l y to arable land. These results h av e not been p u bli s hed p r e v i ously, a n d h a ve been gathered from a large bo d y of mat erial and experiments, which have a c c u mu la te d and been p erfo rme d du
ring the years. These are data on temperature effects on field populations, respiration and growth, includ i ng field surveys of seasonal dynamics with respect to reprod uct i on and general biology.
In part II, are summarized and up da t e d the results from i n v e s t i gations ca rr i ed out in different agricul t ura l systems, some of which have b e en presen ted in the publications l) - 4), listed at the end of the preface. As part of the thesis are enclosed two papers, 5) and 6), dealing with the effects of sewage slud
ge and u p t a k e of h ea vy metals.
1. Andersen, C. (1 9 8O): The influence of far m yar d manure and slurry on the earthwo r m popu la t ion (Lumbricidae) in ar ab l e soil. In: "Soil Bi ol og y as related to L a n d Use Practices", (ed. D.L. Lindal). pp. 148-156. P r o c e edi n gs of the Vllth International C o ll o q u i u m on Soil Zoology, Syracuse USA, 1979. US E P A 560/13-60-038.
2. Andersen, C. (1 9 8I): Regnorme, (in Danish). In: Report No.l.
Reduceret jordbehandling, Ø r r i t slevgård, 1972-1980. Statens Jord b ru gstekni s ke Porsøg. pp. 75-80.
3. Andersen, C. (1 9 8 3): Nitro g en turnover by earthworms in a r a ble plots treated with farmyard manure an d slurry. C h a p t e r 11 in : "Earthworm Ecology" (ed. J.E. Satchell), pp. 1 3 9 - 150. C hapman and Hall.
4. Andersen, C., Eiland, P. and Vinther P.P. (1-983): Ecological investigations of the soil m icr o f l o r a an d fauna in a g r i cultural systems with reduced cultivation, spring ba rl e y an d catch crop (In Danish with English summary). Danish Journal of Plant and Soil Science 87 (3): 257-296.
5. Andersen, C. (1979): Cadmium, lead and c a l c i u m content, n u m be r an d biomass in earthworms from sewage sludge treated soil. P edo b i o l o g i a 19. 309-319.
6. Andersen, C. and Laursen, J. (1982): Dis t r i b u t i o n of h e a v y meta l s in Lumb ric u s t e r r e s t r i s , A p o r r e c t o d e a longa and A.
rosea m ea su re d by atomic a bs o r p t i o n and X - ray fluores
cence spectrometry. P e d o bi ol ogia 24, 247-256
ACKNOWLEDGEMENTS
The author wants to express his gratitude to the Zoological Department for p r o v i d i n g excellent w o r k i n g conditions duri ng the study period. Special thanks are given to Dr. A. Dam Ko- foed, A skov R es earch Station, for support duri n g the i n i t i a tion of studies on earthworm ecology in agricultural soils in Denmark and to prof. Niels H a a r l ø v for encouraging and i n s pir i n g comments throughout the study period. Further I want to thank the staff of the different research stations for technical assistance, K. Dalbro, Biometric Section, D a nish Research Service for Plant and Soil Science, Lyngby, for advice and performance of some of the statistical a n a l y ses, and A. Olsen, M.B. S ø ren s en and H. Rawat for assistance during the extensive field work. Further is thanked the Royal V e ter inary- and A gricultural Univ er si ty and the Danish R e search Council, SJVF, for financial support.
PART I GENERAL ECOLOGY
CHAPTER I
EARTHWORMS AND TEMPERATURE REGIME
INTRODUCTION
It is well k nown that earthworm populations (density and spe
cies composition) m ay v a r y considerably fro m one year to a n o ther (Andersen 1 9 8O; Barnes and Ellis 1979) as well as th rou gh
out the year (Hopp 1948; K r u g er 1952; V a n Rhe e 1967), with marked seasonality in m orta l ity rates and emergence of new individuals (Nordstrom 1975). There is general agreement on the s ignifican
ce of climatic conditions for the development of earthworm p o pulations, especially of moisture conditions (Satchell 1 9 8 0b).
However, it is less well documented to w h i c h extend the te mp e r a ture regime of different years may influence population density, as well as how temperature and soil m o ist u re conditions may in
teract. This stems most ly from the lack of continuous field da
ta, c o v ering several years in sufficient detail to undertake an analysis of this type. It m a y also be a sked if there is a short t er m response to varia t ion s in temperature regime, or if a res
ponse is more easy to r ecognize if a general trend in t e m p e r a t u re regime is observable, e.g., in rel a tio n to season or whole y e a r s .
R e cently the influe nc e of different climatic regimes on the evolutionary strategies (r- and K- selection) has been evalua
ted by Satchell (1 9 8Ob), inspired by Bouchés (1977) ecological classification of earthworms intö the three m a i n groups of life forms, the epigeic, endogeic and anecique. The epigeic, e.g., Eisenia fetida, Lumbricus castaneus and Dendrodrilus rubidus are typically red- pigmented surface and lit ter dwellers. The endogeic, e.g., A p o r r e c t o d e a , A l l o l o b o pho r a and Octol a sio n s p p . are in contrast to these strongly as sociated with the mineral soil. They are generally non- p ig m ent e d and survive adverse se a
sons by ret r e a t i n g deeper in the soil profile, where they may enter a r e s t in g or aestiv a tin g state. Some species not found in Denmark possess an obligate diapause. The anecique, e.g., L u m bri cus terrestris and L .rubellus are intermediate be t ween the epigeic and endogeic and feed in the surface layers, but m a y a l so retreat to deep er horizons d u ri ng adverse climatic conditions.
Both endogeic and anecique species may survive for more than one season.
Adverse seasons ma y be represented by cold winters as well as hot and dry s u m m e r s , and in fact (Satchell 1980b), selection pressures ex e r t ed by the two extremes, seem to have favoured the evolution of both life forms, epigeic and endogeic. E p i g e ic species are said to be r- selected (high re productive rate and m e t a b o l i s m ) , w hich ensures p r o du ct io n of enough cocoons to maintain the population. Epigeic life is v e ry r isky in terms of predation, an d most of the p op u l a t i o n may die out during dry spells a nd d u ri ng winter. The endogeic, which are said to be
X - 'selected are more prote c ted from p r ed a t i o n i n the subsurface layers than the epigeic and tend to conserve energy (lower m e t a boli s m and reproduction, la r g e r body size, ut ili s ati on of more low gra:de food and greater l o n g e v i t y ) . The aneciqu e s are i n t e r mediate bet w een these two extremes a long the r- K- gradient.
The terms r- and K- are derived from the V erh u l s t - Pearl equation: dN/dt = r (1 - N/K) N, where r is the intrinsic r a te of natural increase, K, the carrying ca p a c i t y of the envi
ronment and N, po pulation density.
As to the endogeic, K- selected species, w hich ar e most common in ag r icultural soils, it might be suspected that a general p o sitive increase in temperature regime m a y y i e l d a positive r e s ponse in p o p ulation d ensity (and vice versa, neg ative trends a negative o n e ) , so lon g as soil moisture levels do not become limiting. Lumbricids require a relative h u m i d i t y of close to 100 io in their environment for optimal performance, and the p o p ulation size is therefore believed to be gr eat l y dependent on the amount of precipitation. Species which are closely a sso c i a t ed with the mineral soil a n d possess good b u r r o w i n g capabilities retreat to deeper horizons during periods wi t h low precipitation, where they m a y aestivate until environmental conditions again b e come favourable. At extreme drought both epigeic and endogeic species ma y be seriously affected. During per i ods with excess amounts of precipitation, w a t e r l ogg i ng and anaer obic conditions m ay develop, also in c r e a s i n g mortality. Under such conditions also incre a se d m ig r a t i o n m a y be induced, r e s u l t i n g in morta lity from p r ed a t i o n and exposure to sunlight.
Extremes of this kind occur from time to time also u nder the Danish climatic regime. In wo od l a n d extremes tend to be dampened b y the ins ul a t i ng effect of canopy (summer)and litter l a y er (winter), but in agricultural soils, which will be u nder consi
deration in the f ollowing account, earthworms are generally more exposed to the impact of climatic extremes. Other important factors in f l u e n c i n g earthworm density in ag r icultural soils are availability of food, mec h ani c al treatment, pesticide treat
ment and soil type.
F r o m a study of the influence of different levels of farmyard- manure and s l u r r y at A sk ov E xperimental Station, Jutland (Ander
sen 1 9 8 0) a continuous 6 years record (1976-1981) of a u tumn den
sities of e a rthworms is available for an attempt to evaluate the response of 5 d ifferent species to changes in yearly temperature regime. Because the project was run as two separate ones, are the records of s p r i n g populations (for financial reasons), u n f o r t u nately not complete. The reason for l o ok i n g at temperature reg i
me at all, was that the v a ri a t i o n between years of the different species (autumn populations), a pp arently did not follow the same pattern. Some species following a similar pattern, A.l o n g a , A.
rosea and L .t e r re st ri s might be suspected of b e ing somewhat de
pendent of t e m p e ra tu re regime, with A . caliginosa and A . c hloroti- ca perhaps b e i n g more dependent of soil m oisture (p.18). In the following account, it has be en tried to derive a temperature in
dex for the i n d i v i d u a l years, in a m a nn e r which attempts to p e r fo rm a w e i g h t i n g of periods (seasonal), with positive, respe c
tively negative deviations from normal temperatures.
MATERIAL AND METHODS
S amp l in g programme for the Askov study can be seen in A n d e r s e n (1 9 8 0). Temperature and p r ec ip it at io n data for the station w e re obtained ..from the Danish Meteorol ogi c al Institute.
In the attempt to look for an effect of te mpe r atu r e regime, it was chosen to keep so ma ny environmental v a r i a b l e s constant as possible. Organic m a t t e r input m a y be c o n si d ere d constant f r o m y ear to year, at a n input of 100 tons manure / h a / year. Only data from farmyard manure treatment (FYM) w ere used, because slurry depresses the deep b urr o w i n g species A . l o n g a and L.te r - restris (Andersen I98O ) . This amount of m a nu r e (100 tons) is most likely in excess, and therefore the effect of crop r o t a t i o n (barley, ryegrass, sugar beets), which other wis e may be s i g n i f i cant (Lofs-Holmin 1983a), has b ee n ignored. Soil tillage was t raditional (ploughing), however, with m i n o r differences in r e l a ti o n to establishment of the different crops. The effect of t h e se, however, cannot be analysed, because there was only one crop p er year. The i n t r o du cti o n of add itional o rganic matter, e.g., catch crops (Andersen et al. 1983) seems able to compensate for n e gative effects of soil tillage. The p osi t ive effect of F Y M o n earthworms is, however, much more dramatic (p. 159), which p r o bably renders these m i n or differences insignificant.
A ft e r c a l c ulation of a general temperature index, this can be set in relat i on to different species, p r e c i p i t a t i o n and diffe
rent amounts of organic ma tt e r input. However, it must be n o t e d that a temperature index of the type derived i n the following
has a number of limitations, as well as different approaches to a n evaluation of v arious climatic effects may be discussed.
Tab l e 1.
As ko v, L - field. Total no. 2
of e a r t h w o r m s / m , 1976 - 1981.
Year A. lonqa A. calig. A. rosea A. chlor. L. t er restr.
Fert. 1976 20.0 38.2 19.0 18.3 4 .5
90 N 1977 2 7.4 76.4 15.8 29.9 7.1
1978 16.0 74.8 16.3 24.5 3.3
1979 6.5 27.0 3.8 4.2 2.8
1980 26 .8 103.2 7.2 18.8 3.0
1981 16.0 83.3 3.2 11.2 4 .2
50 t FYM 1976 43 .8 51.5 18.3 15.3 16.0
1977 4 7.0 142.0 14.8 22.5 16.5
1978 29.8 133.8 29.0 28.0 12.3
1979 - - - - -
1980 39.2 149.2 6.4 21.5 7.5
1981 29.2 188.5 5.2 17.5 9.8
100 t FYM 1976 98.8 46.0 37.5 16.8 17.8
1977 5 1.8 157.5 14.3 40.5 19.5
1978 22.0 142.0 15.9 24.0 10.0
1979 19.0 61.0 1.5 9.0 7.0
1980 58.2 199.8 10.2 29.2 12.0
1981 39.5 251.5 6 .8 27.2 7.2
50 t SLU 1976 14.0 76.5 21.0 11.0 3.3
1977 9.5 233.0 17.8 25.5 5.8
1978 13.0 188.0 24.5 20.2 3.0
1979 - - - - -
1980 15.8 208.2 7.5 10.8 6 . 8
1981 10.5 202.2 6.2 11.5 1.2
100 t SL U 1976 18.5 98.8 23.0 11.0 3.3
1977 15.3 275.3 19.0 43.3 7.8
1978 9.8 227 .8 17.5 16.3 1.5
1979 12.8 121.8 7.5 7.5 2.8
1980 12.5 257.2 9.5 16.8 2.0
1981 14.5 307.0 5.9 16.2 ro o
F e r t i l ize r : kg N / ha / year. Man ure s: tons / ha / year.
ANALYSIS OF TEMPERATURE REGIME
Fig. 1A, shows the air temperatures at A sko v Experimental S t a tion f r om 1 9 7 5-1 9 8 1, i.e., m e a n wee kly air temperature, a b s o l u te wee k l y m a x imum and abs olute minimum. To m ake it more easy to
recognize relatively hot and colder periods, different colours have b e e n assigned to the f o ll ow in g intervals of mean air t e m perature. Above 1 7 °C - red. 15-17 °C - orange. 14-15 °C - y e l low. 1 0 - 1 4 °C - blue. 7-10 °C - green (April - May only). In Fig. 1A, is also given the m e a n week l y precipitation, likewi se with a colour code. 0-30 m m - blank. 30-50 m m - green. Above 50 m m - blue.
W h e n the temperature trends during the study per iod are s umma rized, it becomes evident that f r om 1975/76 to 1 9 7 9, there was a general cooling trend, fr om relative mi l d wint e rs and hot summers, towards colder winters and summers. Temperatures d u ring the summ er 1 9 8O were much higher, an d a g a i n somewhat
lower in 1 9 8I. With respect to p r e c i p i t ati o n there was no clear trend, a nd a number of different combinations of temperature and p r e c i p i ta ti on occ urr e d dur i ng the study period. Details of temperature and pre c i p i t a t i o n for i nd ividual y e a rs are given at the end of chapter I (Appendix, p. 55).
In Fig. IB, po pulation de n sit y of the d ifferent species in O c t o ber has b e e n plotted a gainst the different y ears (1976-1981).
Also the summer p r e c i p it at io n for the period, June - August, is shown. The p r ec ip it at io n d u r i n g spring, March - May, was much
J F M « M J J A S O N D
Pig. 1A. W e e k l y mean, ab solute m a x i m u m and. m i n i m u m te mpe
ratures a n d w e e k l y pr e c i p i t a t i o n at A s kov Research Station.
J F M A M J J A S O N D
Pig. 1A. Continued.
less v ar i a b le (Table 4 B ) . V a riations in p r e c i p i t a t i o n during winter, No v ember - February, were not considered.
The most abundant species w as A . caliginosa (Fig. IB). The v a r i a tions in density betw e e n y e ars of A . c a l i g i n o s a , seem somehow to f oll o w the summer precipitation. Also A . c h l o r o t i c a seem to fol
low this pattern. The other species, A.l o n g a , A , rosea and L.ter-
Fig. IB. A u t u m n densities of different species of earth
worms at Askov. 100 tons F Y M / ha / year, 1976 - 1981.
■A.longa. aA. c a l i g i n o s a . A A . rosea.. □ A. c b l o r o t i c a . O L . t e r - r e s t r i s . ---- m m precipitation, June - August, 1976-1981.
restris, o f which A . l onga was the most abundant, follow a d if fe
rent pattern. The response of these species, by comparison b e tween Figs. 1 A and IB, seems to follow the general temperature regime of the d ifferent years, e s pecially summer condtions.
The response of earthworms to the amount of p r eci p ita tion is well documented, whereas, as menti on e d before, a temperature response in field populations has been paid less attention. In the following, however, it is shown that a te m p e r a t u r e index m a y be derived, summariz ing positive and neg ative effects of the t e m perature regime experienced.
It must here be n ot e d that the present exp e rim e nt (p. 14) was not o r i ginally d es igned towards analysis of c lim a tic factors, yet a significant effect of "year" has be e n e s t ab l ish ed (Table 20) for part of the data (1976 - 1978), t hrough a general analy
sis of variance (p. 159).
P o p u l a t i o n density in October m ay be c o nsidered a cumulative r esponse to the p r e c e d i n g year. Therefore it m a y be possible to analyse, how positive and ne g ative deviations f r o m the normal a i r temperature dur in g different periods (Table 2), winter, s pri n g an d summer), m a y be correlated with the Oct obe r p o p u l a t i o n data.
This has been done on a week ly (cumulative) b asi s for winter (November - March), spring (April - May) an d s u m m e r (June - A u gust). The analysis was b ased on the most a b u n d a n t of the three species app ar ently f ol l o w i n g the temperature regime: A.longa (Table 3 A ) .
Winter
D u ri n g most of the winter, the worms are g e n e r a l l y quiescent deep in the soil, i.e., 30-60 cm below the su r f a c e (p. 87 ), and
Ta bl e 2.
As k ov Resear c h Station. T e m p e r a t u r e data, 1975 - 1981.
Nu m be r of weeks: N o v e m b e r - Mar c h, w i t h A p r i l - J u n e - A u g u s t mean air t e m p e r a t u r e s or a b s o l u t e m i n i m u m ___________ May
t <0°C t < - 5 C t <-10°C t <-12°Ca t >7° C t <14° C t >15° C t >17° C
1974/75 1 2 0 0 1975 6 1 11 5
1975/76 7 11 3 1 1976 5 2 8 7
1976/77 9 9 2 1 1977 5 4 4 2
1977/78 5 8 4 2 1978 4 7 4 3
1978/79 13 13 7 3 1979 4 7 3 1
1979/80 10 10 2 1 1980 7 6 6 2
1980/81 7 11 2 1 1981 5 7 4 2
t , a b s o l u t e m i n i m u m t e m p e r a t u r e , w e e k l y t, w e e k l y me an a i r t e m p e r a t u r e
therefore perhaps only exposure to very low temperatures m a y be significant. The f ol lo wi ng temperatures were analysed. Number of weeks (November - March), with m e a n air temperatures below 0 °C and -5 °C, and numb er of weeks with absolute m i n i m u m air temperatures < -10 and -12 °C. Analyses w e re done by l i n e a r r e gression, and the most significant relationship was f ound for -12 °C abs. min. after a log / l o g t r a ns fo r mat i on (p < 0.01, Ta
ble 3 A ) . Below -12 °C there were too few data for analysis.
There were no significant relationships for 0 and -5 °C.
Spring
The normal m e a n a i r temperature for April - Ma y is close to 7
°C. Positive deviations from this temperature were an a l y s e d in the same m a n n e r as above, show i ng a s ignificance of p < 0.05 (Table 3A), w h e n 1976 was excluded. This points towards some po
sitive effect of higher sprin g temperatures.
Summer
M e a n normal air temperature for the period June - August is clo
se to 15 °C, and in the same man n e r as above for winter and spring, the number of weeks with positive deviations from 15 °C (Table 2) were analysed, i.e., m e a n a ir temperatures > 15 °C and 17 °C. Simila rl y negative deviations, i.e., m e a n air te mpe
ratures < 14 °C w er e analysed. Significant relationships were found for deviations > 15 °C and < 14 °C, p < 0.01 and p < 0 . 0 5 ,
Table 3-______________________________________________________
A. Correlation between number of weeks with different temperature characteristics, during different seasons, and October densities of A.longa, 1976-1981 at Askov.
t °c Corr. r= Sign, p <
Win t e r t < 0 _ -
t < -5 - -
ta < -10 - -
"fca < -10 1) -0.9310 0.01
"ta < -12 -0.7789 0.05 ta < -12 2) -0.9036 0.01
Spring t > 7 0.4700 _
t > 7 3) 0.8879 0.05
Summer t > 17 -
t > 15 0.9380 0.01
t < 14 -0.7950 0.05
B. Temperature index, C, , of the different years
1975 1 . 8 2
1976 1.30
1977 0.70
1978 0.06
1979 -0..24
1980 0.84
1981 0.15
Winter: N o v e m b e r - M a r c h . Spring: April-May. Summer: June- August. t, Mean weekly air temperature, t , Weekly abso
lute m i n imum air temperature. 1) log/log transformed, excl.
1975/76. 2) log/log transformed all years. 3) E xcl.1976.
respectively (Table 3A). Deviations > 17 °C were not signi fi
cant .
Temperature index
A temperature i ndex was calculated for each of the different years (1975-1981) b a s ed on the n u m ber of weeks e x h i biti ng the positive a n d ne gative deviations (spring, summer, winter), for which a s ignificant relationship with A . longa (October densiti
es) could be established. The temperature index, (analogy with calories), was calculated as log a coefficient, perfo rmi ng a weighting of positive and negative deviations respectively:
E i - H i
4 J
With i = n u m b e r of weeks for the periods 1 - 4 showing the significant te mp er at ur e deviations:
1. Spring: M e a n air temp. > 7°C, r= 0.8879 ; P < 0.05 2. Summer: - - - > 15 - r= 0.9380 ; p < 0.01 3. Summer: - - - < 14 - r =-0.7950 ; p < 0.05 4. Winter; A b s . min. air < - 1 2 - r=-0.9036 ; p < 0.01
Thus the n u m b e r of weeks with positive correlation coefficients are put into the numerator, and those with a negative into the denominator, where they are multiplicated. The calculated values for the different years are given in Table 3B. After this, it w a s possible to plot the index values (C^) of the r e s pective y e a r s against the autumn p o p ul ati o n densities of the
different species (log- transformed) and to p e r f o r m a linear r e gre ssion (Table 4A). It is here n oted that t he r e was an extr eme
ly good fit of with the A.longa data (Table 4A), both total density and n ew ly hatched worms. The five different species are treated separately below.
The temperature effect m a y also be a nal y sed by other approaches, i.e., by means of the slope of the r e g res s ion lines for the dis c r im i n a t i n g temperature characteristics of the respective p e riods, or it could be attempted to pe r f o r m a w e ig h t i n g of the individual contributions H i ^ . . . £ i ^ of the temperature index.
This procedure, however, w ou l d probably not increase the a c c u r a cy of the index, taking the limited n u m b e r of years into account.
An o the r method of an a l y s i n g the data, could h a ve been a d e t a i l ed statistical analysis of all species and environmental data.
This however, w ould have required that the r e sponse of the worms had been recorded with shorter intervals, e.g., monthly or b i w eek l y determinations of density, biomass, ve r t i c a l distributi
on, soil temperatures and soil moisture content. If this had b een possible, also for a greater n u m b e r of years, 10-15, a more gene r alized model could have been developed, p erhaps also t a king into account, the type and amount of organic m a t t e r introduced into the system. However, as already mentioned, there were not resources for a survey of this order of m a g n i t u d e at the i n i t i a tion of the study.
Thus the temperature index, as derived here, has a number of l i mitations. It applies specifically to the Askov site (sandy lo am
soil), and a si t u a t i o n with more or less u n li m i t e d food a v ai la
bility, a specific species composition, traditional soil tillage and a specific crop rotation (barley, ryegrass, sugar beets), all of which factors m a y influence the response of the worms. When these limitations are taken into consideration, however, it may still be reasonable, also from a statistical point of view (I. Skovgård pers. comm.), to consider an index of the present type as a good a p pr ox im at io n to an idea of a gen e ral i zed te mpe
rature response of field populations.
In the f o l l ow i ng the response of the different species is trea
ted separately. W h e n the amount of organic m a t t e r is reduced, the relationship with temperature m a y be somewhat modified.
This has also b e e n treated separately (p. 30 ). As to the combi
n e d effect of temperature, as v i s u a l i z e d by the temperature in
dex, and precipitation, this has been d iscussed (p. 45 ), by means of three d imensional plots of , pr e c i p i t a t i o n (June - August, and Ma rch - May, respectively) and density in October.
This has been done for A . longa and A . c a l i g i n o s a , re p r e s e n t i n g a deep burrowing and a shallow w o r k i n g species, respectively, both belonging to the endogeic type (p. 11). In this context the same set of limitations must be taken into consi d era t ion as applied to the derivation of the temperature index.
A. longa
It is seen from Figs. 2 and 3, that a p p a r e n t l y there is a v e r y good fit b e t w een l o g A . l ong a density and the temperature index,
. The co rr el at io n coefficients for the total popualation and newly h a t c h e d wo rms were 0.9645 and 0.9281, respectively, p <
0.001 an d 0.01 (Table 4 A ) . The slope of the reg r essi on line for the newly h a t c h e d was more steep than for that of the whole p o pulation, 1.123 vs. 0.455 (Table 4A), w hi c h m a y seem to i n d i c a te that r e p r o du ct io n is most sensitive to i n c r e a s i n g values.
In Fig. 3, C]_g^5 has b e e n onto the r e gre s sion line. = 1.82 is v e ry high and results from a m i l d w i n t e r 1974/75, b e i n g follo w ed by a v e r y war m summer. The e s ti m ate d population size at this value is arou nd 160 individuals m . F r o m Fig.lA-B, it is_2 seen that p r e c i p it at io n d uri n g July a n d A u g ust 1975 was m o d e r a t e in spite of the hot weather. Therefore p r o b a b l y no depression of the p o p u l a t i o n size is likely to have occurred. However, it mu st be n o t e d that the manure experiment was i n i t i a t e d in 1973, and that therefore , o wing to the relatively l o n g development time of A.l on g a (p. 73), some time may have ela pse d before the full beneficial effect of the farmyard man u re was achieved. This a g a in m eans that the e stimated 160 indi v idu a ls m _2 may be s o m e what too high. The summer of 1976 was also v e r y hot, but here severe drought occurred d u r in g August a n d September. Nev ertheless the highest p o p ul at io n of A . longa was recorded, during O cto b e r the same year. This is fur t her disc uss e d p. 23, when the com bi-
Log newJyhatched p>Log newlyhatchedA Log new
Figs. 2 - 7 - Relati on sh ip between e arthworm den sity and the t em p e r a t u r e index, .
Table 4.
A. Correlation betw e e n C. and autumn density of different species (O c t o b e r ) , at Askov, 1976-1981. 100 tons FYM / h a / year.
Corr. r= Sign. p< Slope
A.longa Total 0.9645 0.001 0.4554
Newly hatched 0.9281 0.01 1.1230
L.terrestris Total 0.8456 0.02 0.2799
Newly hatched 0.8277 0.05 0.8971
A . rosea Total 0.7946 0.05 0.6447
Newly hatched 0.6622 0.10 0.7250
A . caliginosa Total -0.0195 -
Newly hatched 0.2735 - -
A.chlorotica Total 0.3655 _ _
Newly hatched 0.2538 - -
B. Seasonal precipitation mm at Askov, 1976-1981
March-May June-August September-Oct.
1976 130 52 196
1977 174 194 123
1978 169 256 196
1979 231 165 132
1980 83 443 271
1981 226 334 227
C. October densities of A.longa and A . caliginosa at Askov, 1976-81.
100 tons FY M / h a / year.
p p
Newly h. no/m Newly h. $ of tot. Total no/m A.longa A . c a l . A.longa A. cal. A. 1 onga A . cal,
1976 80.8 28.0 82 37 98.8 46.0
1977 27.0 125.0 52 79 51.0 157.5
1978 8.8 76.8 41 54 22.0 142.0
1979 0.8 8.0 4 13 1 9 . 0 61.0
1980 17. 2 87.2 30 44 58.2 199.8
1981 4.8 107.2 12 43 39.5 251.5
L. terrestris
This species is the other large sized species i n Danish a g r i cultural soils. However, because L . te rrestris exhibits the ane cique m od e of life, in contrast to the e n dog e ic A.l o n g a , it n e v e r b ecomes v er y abundant (Table l). Also L . terrestris p o p u l a tio n development showe d a good cor r ela t ion w i t h C^. For the
whole p o pu l a ti o n (Fig. 5), the co r rel a tio n coefficient was 0.8456 (p < 0.02) and 0.8277 (p < 0.05) for newly h a t c h e d indi
viduals (Pig. 4). Also here the slope of the r e gr e s s i o n line for the n e w l y h a t c h e d individuals was st e e per than fo r the whole p o pu l a ti o n (Table 4A).
A.CALIGINOSA A.CALIGINOSA
C;
- > • 7 8 -/
* 7 9
C;
A.CHLOROTICA A.CHLOROTICA
i C; l c <
Pigs. 8 - 1 1 . Relation s hip b et w e e n earthworm de nsi ty and the te mp e ra t ure index, .
A. rosea
A . rosea exhibits the endogeic mode of life, but never becomes very nu m erous (Table l). This species also shows a reasonably good correlation with . For the whole p o p u l a t i o n (Pig. 7), the correlation coefficient was 0.7946 (p < 0.05). The corre
lati o n for the n e w l y ha tc he d individuals (Pig. 6) was less good, r = 0.662 (p < 0.10). There was only litt le difference be twe e n the slope of the regression lines for the whole p o p u l a ti o n an d newly h a t ch ed individuals (Table 4A).
A .caligin osa and A. chlorotica
There was no correlation b etween the n u m b e r of A . caliginosa and ; n e i ther for the whole pop ulat i on n o r n e w l y hatched individuals (Pigs. 9 and 8). The same is true f o r Allolobopho- ra chlorotica (Pigs 10 and 11). On the co n tra r y it appears that there is an optimum v alue of around 0.40 - 0.60, which is f urther d iscussed p. 34-
DENSITY AT DIFFERENT LEVELS OF MANURE AND TEMPERATURE INDEX
A vailable food resources and the qu ali t y of f o od are some of the m o st important factors governing p o p u l a t i o n density of earthworms. In the f oll o win g it has b e e n a t t e m p t e d to see h o w the t e m pe rature regime of the different years, exemplified b y
m a y interact with different levels of manure. This has
been done for 50 and 100 tons h a ^ y e a r - "1" of F Y M and slurry, including fertilizer, 80 k g N h a ^ y e a r - 1 . In Figs. 12 - 19, population d e n s i t y in October of the different species has been pl ott e d a gainst .
W h e n temper at u r e s increase from solar heating, standard m e tabolism of p o i k i l o t h e r m s , together with a ctivity level, will increase and t y p ically result in increased constraints on available food resources. This generalized type of response has of course b e e n m od if ie d in different groups of poikilo
therms to fit specific ecological niches and climatic stres
ses by means of different behavioural patterns and physiolo gical adaptations, as mentioned in the intro duc t ion p. 11.
for earthworms.
A. longa
Being a deep b u r r o w i n g species (although not m a k i n g burrows as deep as t hose of L . t e r r e s t r i s ), A.lo nga seems well prot ec
ted against the effects of high temperatures and desiccation It must here be n o t e d that although is calculated from temperature data, it has an inherent soil m o ist u re component at high temperatures, because l o w soil moisture tend to fol
low high t e m p e r at ur es during summer. This is a general rule, which of course is not without exceptions as is clearly de
m onstrated p. 51 , where precip i tat i on is set in relation to temperature. E v a n s and Guild (1947) considered A . longa to possess a p e r i o d of obligate diapause duri ng summer, which,
h owever has not been confirmed by other authors. During an i n v e s ti g at i o n of vertical distribution at the study site, A . l o n ga was found to be fully active in the m i dd l e of July 1978 (Andersen 1981b). Most likel y A . longa is only a esti vating u nd er severe drought. Dur i n g the present study (1976 - 1 9 8 1 ), severe drought was only en cou ntered in 1976, w hich h o w e v e r did not reduce the numb er of A . l o ng a found in October. On the contra
ry, the highest density of A . longa for the w h o le study period was found in October 1976. However, at that time 8o $ of the po p ulation of A . longa consisted of n ewly h a t c h e d individuals.
This indicates that the drought period re s ul t e d in a signifi
cant m o r t a l i t y a m on g adult and juvenile worms, whereas cocoons a pp arently were less affected. Contribu t ing to the high n u m ber of n ewly ha t ched A . l onga was probably a r e l a t i v e l y high i n i t i al popu la t io n size as a result of favourable climatic conditi
ons during 1975 until the onset of drought i n Ju ly 1976. H i g h er soil temperatures pr ob ab ly also reduced the incubation time of cocoons.
From Fig. 12 it can be seen that u n l i m i t e d a c c e s s to food, i.e.
100 tons F Y M ha "'“y e a r ^ and high temperatures i n general fa
vour e d A . l o n g a . At the l owe r dose, 5o tons, it is seen that density, as C^ increases, is l e v ell i ng off, w h e r e a s density in 100 tons F Y M was still increasing. In fertilizer, 80 N, m a x i m u m density of A.lo n g a was reached at a C^ v a lue of 0.75, a f ter which d ensity decr eas e d at higher C^ values. From this it follows that food resources in the fe r t i l i z e r plots were r e l a tively more quickly exhausted than in the m a n u r e d plots. Phil-
lipso n et al. (1976) showed a significant correlation between the di s t ri b u t io n of A . longa and M e r c u r i alis p e r e n n i s , and a less significant correlation to drying out patterns of the soil during J u l y - August. N or ds tr om and Run dgren (1974) found a significant correlation to soil organic mat t er content be- w e e n 2o an d 6o cm depth, and Lindquist (1941), that A . longa is able to distinguish be tw ee n different kinds of litter.
1 2.
13.
Figs. 12 and 13. R elationship b e t we en earthworm density and the temperature index, , at different levels of farmyard manure (FYM). * 1 0 0 tons / ha / year. A 5 0 tons / ha / year. DFerti li ze r, 80 kg N / ha / year. Fig. 12,
•••• 50 and 100 tons slurry / ha / year.
Thus all observations tend to confirm that A.l o nga pref er a- bundant organic m at t e r of high quality and as a deep b u rro wing species is relatively well protected against d esi ccation and high temperatures, unless u nder extreme conditions as experi
enced d u r i ng 1976. In plots with slurry application, 50 and 1 0 0 tons h a ^ y e a r \ density of A . longa was v e r y low (Pig. 12), because of the toxic effects of slurry (Curry 1976; An dersen 1980). F o r a species requir i ng a rich supply of organic m a
terial for food, like A . l o n g a , the amount of energy spent in search for food m a y soon become critical, relative to what is n ece s s a r y to ma in t a i n normal growth and reproduction, wh en the total supply of organic ma tt e r becomes less. If temperature in
creases in a system like this, the stress on available r e sou r
ces becomes still more serious for a species like A , l o n g a , at least so lo n g as the temperature is not high enough and m o i s t ure content has not become low enough to induce aestivation.
In 100 tons F Y M no decrease in popul a tio n size was seen when increased; but the sparser the food, e.g., 50 tons F Y M and fertilizer, the sooner, i.e. at still lower v a l u e s , a dec rea se in p o p u l at io n density did occur. The absolute level of p o pul a t i o n density over the whole range of C* v a l u es from 1976- 1 9 8 1 is clearly determined by the level of organic mat t e r s u p ply. Likewise the negative effect of low values is clearly demonstrated.
A.caliginosa
In A . caliginosa p o p u l ati o n m axi m u m in 100 tons FYM, seemed to be reached at a rela ti ve ly low Ci value = 0 . 4 (Fig. 14). In
50 tons F Y M a n d fertilizer, m a x i m u m occurred at the same value.
The question is, whether or not, the decline in popula tion de n
sity at h i g h e r values was due to a direct effect of t e m p e r a ture on behaviour, or food was be co m i n g a l i mit i n g factor.
Probably b o th mecha ni sm s were operating. In the most fa -
14.
15.
A .c a lig in o s a (Slurry)
Figs. 14 an d 15. Relationship be tw ee n earthworm density and the te m p e rature index, , at different levels of farmyard man ur e (FYM). Fig. 14 and slurry, Fig. 15.
A 100 t on s / ha / year. A5 0 tons / ha / year. □ F e rti
lizer, 80 k g N / ha / year.
v ou rable r a n g e , it seems obvious that food l i m i tati on must be important, but at both ends of the range it is likely that climatic conditions are mor e important. In 1979 growth and r e p r o du c ti o n were inhibi te d by low temperatures, a n d in 1976 hot an d dry conditions were the causes. A shallow w o r ki ng species like A . caliginosa will soon begin to aestivate u n d e r conditions like in 1976, and u n d e r the prolonged drought morta lit y was p r o ba bly greatly increased, d esi c cation a f f e c t i n g all developmental stages, i n cl uding cocoons. The relative significance of food l i mi t at i o n and climatic conditions are difficult to study u nd er field conditions, and ther ef or e the offered explanations m a y be somewhat tentative. However, loo ki ng at A . l o n ga at 50 tons FYM, food limi t at i on seemed to become significant at a value of a ppr o x im a te l y 1.0 (Pig. 12), whereas in A . calig i nosa (Fig. 14), m a x i m u m p o p u lation density occurred at = 0.40, i n both 50 and 100 tons FYM. F r o m this it m a y be suggested that there was no serious competition bet w e e n the two species for food, either b e cause of different fee d ing behaviour, and or i n conjunction with this, because the climatic optimum for the two species is not the same. That climatic factors are stron gly influencing the performance of A . calig i nos a ma y be seen f r o m the fact that m a x i m u m p o pu l ation dens i ty in this species o c c u r r e d at the same
value in the three different treatments, fertilizer, 50 and 100 tons FY M (Fig. 14). In slurry (Fig. 15), m a x i m u m populat ion de nsi t y in A . c al iginosa was 300 and 2 33 i n d iv i dua ls m _2 for 100 and 50 tons slurry respectively. This is s o mewhat higher than fo r the same levels of FYM. But slurry treatment greatly redu-
ced the n u m b e r of the two deep b ur r o w i n g species A . l ong a and L.
terrestris (Pigs. 12 and 13), because of the tox icity of slur
ry, which easily i nf iltrate the burrows of these species.
(Andersen 1980; Curry 1976). Therefore the higher m a x i m u m p o p u lation d ensity in slurr y may reflect that some c omp e tition for food between A . l o nga a nd A . caliginosa does exist, however, n e v e r becoming significant for the reasons just mentioned. It is interesting to notice that m a xi m u m popu lat i on density of A . cali
ginosa in slur r y occurred at the same C^ value as in FYM. This again stresses the importance of temperature regime for the de
velopment of A . c a l i g i n o s a , irrespective of food supply, the level of which of course in the end sets the limit.
A. c h lo ro tic a
This species (Figs. 16 a n d 17) showed a response somewhat similar to that of A . c a l i g i n o s a , but with a p o pul a tio n m a x i m u m occurring at a somewhat h i g her C^ value, close to 0.60. This was seen in all treatments, except in 50 tons FYM, where it was close to 0.40, as in A . c a l i g i n o s a . In fert il iz er (Fig. 16), p o p ul ati on m aximum was the same as in 50 tons FYM, but in 50 tons slurry
(Fig. 17), it was lower. In other f e rtilizer experiments (Barnes an d Ellis 1979) there has been a positive effect of inc r e a s i n g a- mounts of f e r t i l i z e r on the n u m b e r of A . chlorotica in comparison with A . c a l i g i n o s a . This was a t t ri bu te d to a bet t er performance of A . chlorotica at the slightly l ow e r soil temperatures, b eing caused by the i n cr e a s e d foliage coverage at high levels of ferti
lizer. This m ig h t as well have be e n a climatic effect, or have
be e n caused by a negative influence of high fe r tilizer doses on A . caliginosa
16.
17.
Pigs. 16 and 17- Re lationship b e t w e e n earthwo rm density an d the temperature index, , at diff e ren t levels of farmyard manure (FYM), Fig. 16 and slurry, Fig. 17.
A 100 tons / ha / year. A50 tons / ha / year. DFerti- lizer, 80 kg N / ha / year.
A. r o s e a
In A . r osea (Figs 18 and 19) there were i ndi c a t i o n s of a p o p u l a t i - cnjnaximum at = 0.20, and another at > 1.00. In the range
of = 0 . 2 0 - 1.00, the n u m b e r of A . rosea was pr o bably reduced, by competition f r o m A . caliginosa and A . c h l o r o t i c a . A . rosea seems to utilize rou g h ly the same food resources as A . caliginosa and A.
c h lorotica, but b ecause of its slow growth rate and rep roduction (Phillipson a n d B o lton 1977), it appears to be sensitive to com
petition f r o m these two species in their most favourable ran ge.
1 8.
19.
Figs. 18 a nd 19. Re lationship be twe e n earthworm density and the t em perature index, C^, at different levels of farmyard m a nure (FYM), Fig. 18 and slurry, Fig. 19.
A 100 tons / ha / year. A5 0 tons / ha / year. Q F e r t i l i - zer, 80 k g N / h a / year.
L. t e r r e s t r is
L . terrestris (Fig. 13), which is deep b u r r o w i n g and forages on the soil surface (anecique), never became v e r y numerous.
Like A . l onga and A . rosea it seems to tolerate relatively high values, and apparently there was no great competition for food b e tw e e n L . terrestris and the other species. But because the m anures were ploughed into the soil, the endogeic species were favoured.
GENERAL REMARKS
In the b e g i n n i n g it might be thought that the influence of sea sonal temperature variations on field po p u l a t i o n s of earth
worms was relatively simple to describe, but w h e n different species are l i ving together, and different a m ou n t s of m anures and fertilizers have to be taken into consideration as well, the interactions become e xtremely complex. Another l i mi t a ti o n in studies of this kind, is the l a c k of relevant data, although in the present case a reco rd of 6 years have be en available. It might be suggested to incl u de all avail
able literature data in a similar anaüysis . This, however, will intro
duce still more variables, as different soil types, other crop rotations and a vari ety of mechanical treatments. In the p r e sent analysis extreme valu es were encountered, ranging from -0.24 to 1.30, which probably make the suggested res
ponse of the different species to t e mpe rature variations more convincing. For the reasons m e n t i o n e d ea r lie r it has not
b e en attempted to develop any sophisticated models for the b e h a v i our of the d ifferent species. To be able to do so, would have r e quired a continuous record of at least 10 - 15 years, with a f air
ly even d i s t r i b u t io n of values over the entire range, which in the present set of data is not quite fulfilled. Nevertheless, the results obtained in the present analysis seem to stress the sig
nificance of t e m pe rature regime for the development of field po pu
lations of earthworms. The findings presented here should be fur
ther tested b y d e ta il ed studies of the r e pro d uct i on of the re sp e c tive species at different temperatures.
As to the signifi c ance of temperature regime, it also appears that w h e n food is limited, there m a y be an important i n t e rac tion b e tween these two parameters, e.g., A . l o n g a . W h e n food is abundant, the general effect of temperature regime is more easy to recognize and species like A . l o n g a , L . terrestris and also A . rosea seem to perform well at high values, 1.30 or more, whereas A. caligino- sa and A . c h lorotica did best at intermediate values bet w e e n 0.30 an d 0.60. At e x tr e mely low values, e.g., -0.24 in 1979, with a v e r y cool Stimmer a fter a ve ry cold winter, the nu m b e r of all spe
cies was s e ri o us l y reduced. This effect persis t ed into the spring of 1980 (Pig. 52), but in the autumn, the p o pul a tio n h a d recovered
It could be su p po s ed that at least the E uro p e a n d i s t r i but ion (North A mer i c an d istributi o n is here left out of consideration), of the species t reated in this section, somehow reflects the different t e mp e rature range preferences, as exemplified by the temperature i n d e x . The E u r o p e a n distribu t ion of lumbricids
is considered to have been greatly i n fl u enc e d by the quaternary glaciations. This was treated in detail by Stop-Bowitz (1969).
Some species were able to recolonize North E u r o p a after the las ice age ( W u r m ) , presumably poss e ssi n g good spontaneous spreadir capabilities. These are generally re f erred to as "peregrine"
species. The species treated in the present section all b e l o n g to the peregrine species. South of the border line of maxim um glac i at i o n (Riss), in South-, South E a s t - and East Europa, the Middle East and into Asia, a vast array (incl. peregrine specie of other lumbr ic id species occur, referred to as endemic specie with presu m a bly lesser spreading capabilities and more strict requirements against environmental variables, e.g., general h a bitat, food, temperature range and p r e c i p i t a t i o n (steno bio nts).
A mong the perigrine species here u n d e r consideration, not all have penet r a ted equally far northwards. A p o r r ect o dea caliginosa has a v e r y wide distribution, from the Arctic Circle to North Africa, o ccupying a numbe r of ve ry different climates. A.l o n ga is much less common in Norway, only a few r ecords from South East Norw a y exist, which ma y be in agreement wi t h a higher opti m u m C^ value > 0.70 - 0.80, in this species, in comparison with A . caliginosa (optimum C^ value around 0.40). The distribution c A l l o bo p ho r a chlorotica is somewhat similar to that of A.l o n g a , and is considered occasionally to have be e n in troduced by m a n So u the r n Norw ay (Stop-Bowitz 1969). O p t im u m C^ value for A . chl(
rotica is around 0.60 - 0.70. A n o ptimum C^ v alue for A.rosea was hard to recognize because of com p etition interactions from other species (p. 39 ), hut w o u l d perhaps be w i t h i n the range o:
> 0.50. A . r o se a is common in South East Norway and goes also far eastwards into the USSR. L . terrestris with a n o ptimum v a lue presumably similar to A . rosea is di st r ibuted in both western and eastern S o u t h e r n Norway. Stöp-Bowitz (1969) r ecognized a number of d i s t ri b utional types, m a inl y with reference to Scandi navian lumbricids. A . c a l i g i n o s a , A . rosea and L . terrestris belon g to "The n o r t h e r l y a dv an ce d southern species". A.l onga and A . chlo- rotica were c on sidered to be "True South Scandina v ian species".
An interpret a ti o n of the temperature in dex C^, a l ong these lines must of course be v e r y cautious because of the ve r y v a r y i n g cli
mates occup i ed by the worms, from n orth to south and west to east, with respect to distributi o n of p re ci pi tati o n and annual t e m per a
ture range. It m a y here be suggested that perhaps species with an intermediate o ptimum like A . .c a l i g i n o s a , or less well defi
ne d towards the hig he r end, e.g., A . rosea and L . t e r r e s t r i s , will be among the more wide spread. This, however, m a y also be d e pen dent of o t h e r special requirements of the worms.
Other species with a v e r y widely d is tr ib ut i o n are L. rubellus and Dendrobaena o c t a e d r a . L . rubellus reaches very far north (North Cape). The same accounts for D . o c t a e d r a , which is also found in Greenland ( S töp-Bowitz 1969). Both species are a m o n g the most pH tolerant species (Satchell 1967; Piearce 1972a, 1972b), and D. octaedra is supposed (Stöp-Bowitz 1969) to have survived the last g l ac i at i o n ( W u r m ) , in r efuges in both W e s t e r n Norway and Greenland.
The v e r y variable values recorded in Denm a rk (1976 - 1981) are due to the fact that Denmark lies in a somewhat transitory region bet we en a we st e r n maritime and a more continental climate to the east. Thus it appears that the de nsi t y distribution of the different species a l o n g the Danish g r adi e nt (1976 - 1981) ma y indicate a general effect of temperature range (together with other environmental variables), also on the European d i s t r i b u t i o n of peregrine lumbricids. This subject, however, needs much further study, i.e., in other climates (South Europa, hot and dry summers, m i l d and wet winters, vs. East Europa, hot and r e latively dry summers and very cold winters), before a more comprehensive und e r s t a n d i n g of the distr i but i ona l ranges m a y be achieved.
Soil moisture levels are important with r espect to short term v e r ti c a l m ig rations (p. 84), as well as d u r i n g drought, occ u r r i n g from time to time. U nde r more normal conditions, it may turn out that temperature regime is not less important t h a n moisture c o n ditions, especially with respect to varia t ion s f r o m year to year.
In the follo wing se c tio n is looked upo n the combi,ned effect of temperature regime and p r ec ip ir at io n on p o p u l a t i o n development.
