Habitats of the British amphibians (4): Agricultural lowlands and a general discussion of requirements

BiologicalConservation21 (1981) 127 139

HABITATS OF THE BRITISH AMPHIBIANS (4): AGRICULTURAL LOWLANDS A N D A GENERAL DISCUSSION OF REQUIREMENTS

TREVOR J. C. BEEBEE

School o f Biology, University o f Sussex, Falmer, Brighton BN1 9QG, Great Britain

ABSTRACT

Ponds on about 8 0 k m 2 o f farmland in Sussex were investigated with regard to breeding amphibians. The survey coveredfive different geological strata and included 60 ponds (out of a total o f more than 200) marked on 1.'25000 ordnance maps. Eighteen o f these ponds were f o u n d on inspection not to exist," the remainder were characterised with respect to surface area, depth, pH, ionic score, aquatic vegetation, fish fauna and surrounding terrestrial habitats as well as f o r amphibian species. 14 pools contained amphibians," Triturus vulgaris was the most widespread (9 ponds) closely followed by T. helveticus (8 ponds). T. cristatus occurred at 5 sites, Rana temporaria at 2 and Bufo bufo not at all. The 2 f r o g sites were very shallow pools on pasture~woodland interfaces," the ideal newt pond had no fish, was 0"5 1"0 m deep and < 200 m 2 in surface area with 5-50% aquatic vegetation cover and a low ionic score ( < 400parts/106). Callitriche-containing ponds were particularly favoured, and with terrestrial habitat there was a requirement.for a scrub or woodland component.

INTRODUCTION

This paper describes the final part of an investigation into amphibian habitats in a defined region of Sussex. The area included in this section of the work is outlined elsewhere (Beebee, 1977) as a zone 2.5-3-0 km in breadth running 22 km east-west below (north of) the scarp face of the South Downs between the rivers Adur and Ouse. It lies between 25 100m above sea level and is comprised mainly of fairly small fields bounded by hedgerows and predominantly pastural with occasional woodland copses. 127 Biol. Conserv. 0006-3207/81/0021-0127/$02"50 ~ Printed in Great Britain

Applied Science Publishers Ltd, England 1981

128

TREVOR J. C. BEEBEE METHODS

These were essentially as o u t l i n e d elsewhere (Beebee, 1977; 1979). All p o n d s within the confines o f the s t u d y a r e a a n d m a r k e d on a 1:25000 o r d n a n c e m a p were n u m b e r e d a n d a s a m p l e c h o s e n for study. A l t h o u g h essentially r a n d o m , it was e n s u r e d t h a t there were at least 10 f r o m each o f the 5 geological regions within the z o n e a n d an a d d i t i o n a l 10 i n d e p e n d e n t o f g e o l o g y were also a d d e d to m a k e 60 a l t o g e t h e r . T h e p o n d s were n e t t e d as t h o r o u g h l y as possible to a s c e r t a i n w h i c h b r e e d i n g a m p h i b i a n s o r their spawn o r t a d p o l e s were present d u r i n g M a r c h . E a c h was also visited later, in A p r i l , using t o r c h l i g h t at night as a p a r t i c u l a r l y v a l u a b l e check on the d i s t r i b u t i o n o f newts. W a t e r samples were t a k e n for p H a n d c o n d u c t i v i t y m e a s u r e m e n t s a n d v a r i o u s o t h e r aspects o f the h a b i t a t s r e c o r d e d .

RESULTS

Characteristics of the ponds N o r t h o f a n d parallel to the D o w n s run four successive s t r a t a : u p p e r g r e e n s a n d , g a u l t clay, lower g r e e n s a n d a n d w e a l d e n clay. T h e relative a m o u n t s o f these soils a n d the o c c u r r e n c e o f p o n d s on t h e m are s u m m a r i s e d in T a b l e 1. L o w e r c h a l k TABLE 1 DISTRIBUTION AND SAMPLING OF PONDS

A r e a of h a b i t a t (km 2) No. p o n d s e x a m i n e d

No. ponds still extant No. exhibiting flow Extrapolated total no. ponds extant Extrapolated total no. ponds extant per km 2

Geological substratum GC LGS

LC

UGS

11 10

9 10

15 13

5 1 5

7 4 22

12 2 43

0.45

2.44

2-87

WC

Total

23 14

18 13

76 60

9 4 44

9 0 45

42 11 159

1.91

2.50

2.10

L C = lower c h a l k ; U G S = u p p e r g r e e n s a n d ; G C = gault clay; L G S = lower g r e e n s a n d ; W C = wealden clay. E x t r a p o l a t i o n s are based on the t o t a l n u m b e r s of p o n d s m a r k e d on the o r d n a n c e m a p s a d j u s t e d for

the proportions found not to exist in the samples. constitutes the foothills o f the Downs, and wealden clay extends to much larger areas b e y o n d the edge o f the s t u d y zone. T h e b o u n d a r i e s between the s t r a t a are n o t o b v i o u s to the casual observer a n d l a n d use a p p e a r s h o m o g e n e o u s over the whole district. T h e s a m p l e o f p o n d s e x a m i n e d represents a b o u t 27 % o f the t o t a l m a r k e d on the m a p . O f the 60, 18 (33%o) no longer existed; this was m a i n l y due to n a t u r a l succession t h o u g h a few h a d been d e l i b e r a t e l y d r a i n e d . A s s u m i n g this p r o p o r t i o n was typical o f the entire p o n d p o p u l a t i o n in the area, there m u s t be a b o u t one p o n d

129

BRITISH AMPHIBIANS IN AGRICULTURAL LOWLANDS

every 50 ha in this part of the Weald. N o significant evidence of the existence of pools other than those marked was found and it was surprising to record that in what is generally regarded as a wet area of Britain there was at most only about half the density of ponds indicated as the national average on pasture by Ratcliffe (1977). Apart from the small numbers on the lower chalk there was little difference in pond density between the various strata. Geological effects are complicated by the occurrence of spring-line ponds fed by water from the chalk (Downland) aquifer and manifest in the greensand belts especially by the high proportion of pools exhibiting flow, and this has to be borne in mind when considering the chemical characteristics oflthese freshwaters. Table 2 summarises some physical and chemical features of the ponds. Most were quite small but there was no single normal distribution of sizes and some could more accurately be described as lakes, p H average values were similar on all the geological TABLE 2 GENERAL CHARACTERISTICSOF THE PONDS

Surface area (m 2)

No. ponds

Depth (m)

No. ponds

pH

No. ponds

Ionic score (parts/lO 6)

No. ponds

0-80 80-180 180-300 300-500 500-700 700-1000 1000-5000 > 5000

4 13 7 5 2 3 6 2

0-0-5 0-5-1-0 1.0 1.5 > 1.5

18 13 7 4

6-7 7-7.5 7.5 8 > 8-0

6 24 8 4

< 300 301-600 601 1000 > 1000

6 28 5 3

Range: 15-36000 Mean: (1) 217 (167) (2) 5616 (10271)

0.1-2.0 0.76(0.53)

6.1 9.0 7.41(0.58)

175-2025 554(361)

Means for pond surface areas were divided into pools 700 m 2 (1) and those above 700 m 2 (2). Standard deviations are given in brackets.

strata though the range of pHs observed did increase with distance away from the Downs (i.e. moving northwards across the various soils). The lack of acid ponds even on lower greensand reflected the lack of podsolisation in this area, quite unlike the situation elsewhere in the Weald where broader belts of this substratum are associated with heathland conditions. Ionic scores were somewhat higher than those of garden ponds but lower than those in marsh dykes (Beebee, 1979; 1980); average values tended to drop in the various strata moving away from the Downs but the differences were small. Amounts and types of aquatic vegetation in the pools in relation to geology, surrounding land use and pond depths are summarised in Table 3. Nearly half the ponds had less than 10}o vegetation cover but this was not related to any of the features described in the table. There was, as might be expected, a tendency for the

4 l 0

2 3 1 3 L 10

3 5 4

GC 5 3 1

LGS

2 1 5 3 5 16

1 1 5 3 4 15

3 2 8 6 8 27 1

1

4 4 1

1 I 2

A

1 1 5 1 3 11

Callitriche

WC

Grasses Phragmites Total Elodea or Iris

Marginal vegetation

4 3 0

UGS

Geology

6 7 1

P 8 3 1

W/S

l 3

2 2 2

8 5 5

0-0.5 m

1

1

6 7 1

0.5-1.0 m

Depth

6 4 0

> 1m 20 16 6

Total

1

I 1 1

3

1

1 1

1 3

1 1

2 3 6 2 6 19

Potamageton P. Rorippa N u p h a r Total natans crispus

Submerged aquatics

4 I 2

W/P/S

Ranunculus Lemna L. minor trisulca

1 4 0

AlP

Land use

Geological abbreviations are as in Table 1 ; A = arable, P = pasture, W -- woodland; S = scrub. Figures given are numbers of ponds in each category. Plants in most cases are identified to genus only, and marginal and aquatics totalled separately. Totals are now always simple additions because several ponds had more than one species. One further pool on upper greensand had extensive growths of filamentous algae (only).

LC UGS GC LGS WC Total

Geology Plants absent

(B): PLANTS PRESENT

1 0 ~ cover 10-90 °/. cover 90 o~ cover

LC

(A): EXTENT OF COVER

TABLE 3 AQUATIC VEGETATION IN THE PONDS

¢3

< O

U,

131

BRITISH A M P H I B I A N S IN A G R I C U L T U R A L L O W L A N D S

most densely vegetated pools also to be the shallowest ones. Thirteen types of aquatic plants were noted in the pools but a large proportion of ponds (nearly 20~°~,) had no vegetation of any kind. Weed-free pools were especially c o m m o n on greensands. Mats of terrestrial grasses and reeds (Phragmites) were frequently found around the shallow edges, but of true aquatics Callitriche was the most widespread especially on clay strata. Nevertheless it is worth noting that only 20 of the pools, less than half, contained any truly aquatic plants at all. Clay-based ponds were generally the better vegetated. These data also indicate (Table 3A) the preponderance of livestock farming in the area; whereas 9 ponds were partly or wholly surrounded by arable fields, 26 were at least partly in pasture and 19 in pasture with scrub or woodland.

Amphibians in the ponds" Table 4 summarises the overall picture of amphibian occurrence in the study pools. A number of points may be made. (1)

(2) (3)

Of the 5 widespread British species, one type was absent altogether: BuJo bu[b, the c o m m o n toad. If it occurs at all in this part of Sussex it must be extremely rare and only 1 breeding site in this general area of the Weald (outside private gardens) is known to me, about 1.5 km north of the study area perimeter. O f t h e 4 2 k n o w n p o n d s w h i c h h e l d w a t e r , 14 (exactly one third) contained at least one species of amphibian. Of the 15 possible combinations of the 4 species found only 7 were actually encountered. Although the numbers are too low for statistical analysis, some aspects of this distribution appear to be non-random. In particular all 3 newt species occurred alone less often than might be expected by chance and together much more often. A similar situation was observed in dewponds (Beebee, 1977). TABLE 4 OCCURRENCE OF AMPHIBIANS IN THE PONDS C o m b i n a t i o n s o f species f o u n d

Frequency Expected frequency Relative a b u n d a n c e s

RT

TV

TH

TC

2 2

2 6

2 6

1 3

TV+TH

TV+TC

TV+TH+TC

3 2

1 1

3 0

TV < TH = 1 TV=TH=I TV > TH = 1

TV = TC

TV = TC = TH = 1 TV=TC TH = 1

F r e q u e n c y refers to the n u m b e r of p o n d s in w h i c h each species was found, a n d expected frequency to t h a t c a l c u l a t e d o n the basis of overall o c c u r r e n c e o f each species in 42 ponds. Relative a b u n d a n c e s are based on n u m b e r s c a u g h t a n d seen of each newt species. R T = R a n a t e m p o r a r i a ; T V = T r i t u r u s vulgaris; T H = T. helveticus; T C = T. c r i s t a t u s .

132

(4)

TREVOR J, C. BEEBEE

T h e r e w e r e c o n s i d e r a b l e d i f f e r e n c e s in a b u n d a n c e . F r o g s R a n a t e m p o r a r i a w e r e rare, o n l y 2 b r e e d i n g sites e a c h w i t h less t h a n 20 s p a w n c l u m p s b e i n g f o u n d . T h u s in this district a n u r a n s as a g r o u p w e r e v e r y m u c h s c a r c e r t h a n u r o d e l e s . T r i t u r u s vulgaris was the m o s t w i d e s p r e a d a n d a b u n d a n t a m p h i b i a n , o c c u r r i n g in 9 p o n d s a n d b e i n g t h e d o m i n a n t o r c o - d o m i n a n t species ( n u m e r i c a l l y ) in 7 o f t h e m . T. helveticus was also c o m m o n , b e i n g f o u n d in 8 p o o l s a n d d o m i n a n t o r c o - d o m i n a n t in 6. T. c r i s t a t u s w a s the least f r e q u e n t l y e n c o u n t e r e d n e w t , o c c u r r i n g n e v e r t h e l e s s in 5 p o o l s a n d b e i n g d o m i n a n t o r c o - d o m i n a n t in 4. It was o f s o m e i n t e r e s t t h a t o f the 4 p o n d s w h e r e T. cristatus c o e x i s t e d w i t h o t h e r n e w t species t h e f o r m e r s e e m e d to be at least as n u m e r i c a l l y a b u n d a n t as e i t h e r o f the o t h e r t y p e s in 3 o f t h e m .

T a b l e 5 o u t l i n e s t h e d i s t r i b u t i o n s o f the 4 species in r e l a t i o n to v a r i o u s p h y s i c a l a n d c h e m i c a l p r o p e r t i e s o f the p o n d s . D u e to the r e l a t i v e p a u c i t y o f a m p h i b i a n sites t h e n u m b e r s are t o o s m a l l for u n e q u i v o c a l c o n c l u s i o n s to be d r a w n b u t a few i n d i c a t i o n s m a y be o f i m p o r t a n c e . T h u s , b o t h t h e f r o g r e c o r d s w e r e f r o m g r e e n s a n d s a n d 3 o f the 5 T. cristatus r e c o r d s w e r e f r o m g a u l t clay, w h e r e a s T. vulgaris a n d T. helveticus g a v e n o i n d i c a t i o n s o f g e o l o g i c a l selectivity. B o t h o f the f r o g p o n d s TABLE5 ASSOCIATION OF A M P H I B I A N S W I T H P O N D F E A T U R E S

Feature

Species RT

Geology LC UGS GC LGS WC Area (m 2) 0-180 180-700 >700 Depth (m) <0.5 0-5 1.0 >1-0 pH 6-7 7-7-5 >7.5 Ionic score (parts/ lO6) < 300 301 600 > 600

TH

TV

TC

+

-

+

-

+

-

+

-

0 1 0 1 0

5 6 12 8 9

1 3 2 2 1

4 4 10 7 8

1 2 2 I 2

4 5 10 8 7

1 0 3 1 0

4 7 9 8 9

1 1 0

16 13 11

3 3 3

14 11 8

3 3 2

14 11 9

4 0 1

13 14 10

2 0 0

16 13 11

0 8 1

18 5 10

0 6 2

18 7 9

1 4 0

17 9 11

0 2 0

6 22 12

4 4 1

2 20 11

1 6 1

5 18 11

2 3 0

4 21 12

0 1

6 27

3 6

3 22

2 6

4 22

2 3

4 25

1

7

0

8

0

8

0

8

+, No. of sites with species; - , no. of sites without species.

133

BRITISH AMPHIBIANS IN AGRICULTURAL LOWLANDS

were in the very shallow range whereas newts apparently preferred the intermediate (0.5-1.0m) depth pools. Ponds of small surface area seemed generally preferable (they seemed to contain the highest densities of newts, for example), though it should be added that thorough exploration of the larger areas of water is difficult and negative results correspondingly less certain. T. vulgaris was unexpectedly c o m m o n in the relatively few ponds in the pH 6.0-7.0 range, whereas the other species were not. One of the two frog ponds had the highest ionic score recorded ( > 2000 parts/106) but all 3 newts apparently chose ponds of lower than average ionic scores; thus the average of newt ponds = 381parts/106 (SD = 125) and the average of non-newt ponds =554parts/106 (SD = 361). These were significantly different by Mann-Whitney U-testing (p = < 0.01). There was however no special preference of T. helveticus for ponds of either low pH or low ionic score, a notable result in view of the work of Cooke & Frazer (1976), who sampled pools in the New Forest and recorded particular success of palmate newts in very ion-deficient waters. Table 6 lists the amphibian records in relation to pond vegetation. A slight preference of T. cristatus for pools with less cover than those favoured by the other newts is apparent here as it seemed to be in dewponds (Beebee, 1977). One of the frog ponds had no vegetation at all, whereas the other was furnished with extensive mats of terrestrial grasses. Newts, on the other hand, usually avoided pools without any form of vegetation but were not particular whether plant life was constituted by true aquatics or encroaching marginal or even terrestrial species (grasses). It was notable however that ponds containing Callitriche were particularly likely to have newts (6 out of 11 did so, whereas overall newts were found in 12 out of 42 pools) though by itself the presence of this plant was clearly insufficient to guarantee their occurrence. TABLE 6 ASSOCIATIONS

OF AMPHIBIANS

Feature of vegetation

AND

POND

VEGETATION

Species RT

TV

TH

TC

+

--

+

--

+

--

+

--

Extent of cover

< 10% 10-90 %

1

19

3

17

4

16

3

0

16

5

11

3

13

1

17 15

> 9 0 °j o

1

5

1

5

1

5

1

5

General types 0I" vegetation None Marginals present True aquatics present

Oceurrence m a l l ponds 1/2 1/2 0/2

1/9 7/9 8/9

1/8 6/8 6/8

1/5 4/5 3/5

1/4-2 1/16 1/2

+ , No. of sites with species; - , no. of sites without species. Fractions in the second part of the table represent the proportions of sites for each species which fall into the particular category.

134

T R E V O R J. C. BEEBEE

Fish of some sort were found in 9 out of the 42 ponds (i.e. about 21 ~ ) . Two of these 9 contained only three-spined sticklebacks Gasterosteus aculeatus whereas the others had larger species such as rudd Scardinius erythrophthahnus or carp Cyprinus carpo sometimes with sticklebacks as well. Table 7 shows that in relation to total numbers of amphibian records there was no selective avoidance of fishponds, but TABLE

7

AMPHIBIANS IN FISHPONDS

Amphibian

Absent

Occurrence t~f fish

Larger fish species present

Gasterosteus aculeatus only present RT TV TH TC TV + TH + TC None Total

2 4 6 5 3 22 33

0 1 1 0 0 1 2

0 2 1 0 0 5 7

Numbers are for pond sites in each category.

when individua! species are considered it is notable that the apparent tolerance of Triturus vulgaris and T. helw, ticus was counterbalanced by a complete lack of T. cristatus and Rana temporaria records from fishponds in the area. Terrestrial habitats Finally, Table 8 represents an attempt to relate amphibian distributions to the types of terrestrial habitats around or near the pools. Eleven types of surroundings are categorised and the difficulties of this kind of quantification are thus evident; no two pools were exactly alike with regard to their environs. Nevertheless, some useful deductions can be made. Ponds wholly surrounded by arable fields, pasture, arable and pasture mixtures or even dense woodland rarely produced amphibians. Indeed TABLE

8

TERRESTRIAL HABITAT ASSOCIATIONS

Amphibian

None Some present +RT + TV + TH + TC

Type o] terrestrial habitat around pond A

AS

P

PS

S

W

PU

AP

1

2

8 1

2 3

1 2

8

3 1

3

1

2 2 2

2 1 1

1 1

APS

WA

WP

1

I

1 1

1 1 1

5 2 1 2 1

Abbreviations as for Table 3, with U = urban area; combinations of letters reflect corresponding mixtures of habitats.

B R I T I S H A M P H I B I A N S IN A G R I C U L T U R A L

LOWLANDS

135

there was only one Triturus vulgaris record out of the 23 pools in these combined categories. Two arable pools with small amounts of peripheral scrub also yielded no amphibians, but 1 pool with a mixture of arable, pasture and a little scrub did have smooth and palmate newts. The only other pond associated with arable land which held amphibians (all 3 species of newts) was close to an extensive area of open woodland. The best situations for newts were clearly those in which arable farming was absent and various combinations of woodland, pasture and scrub or scrub alone surrounded the pools. The woodland/pasture interface seemed particularly suitable, all 5 ponds in this category having amphibians and including both of the frog records. It was apparent that pasture alone was not a good habitat for any species.

DISCUSSION

A number of questions come to mind when considering the results of an investigation of this type. Perhaps the first might be: how stable is the situation as currently observed ? The area has not been systematically examined before and there are few previous records of any kind but my impression, gained from local naturalists, is that there have probably not been major changes at least over the last 20 years or so. In particular it would be interesting to know whether frogs and toads have always been as rare as they are now, and from my own knowledge of a small number of these sites over 10 years ago it is certain that frogs at least were once a little more widespread (Beebee, 1973). However, the consensus of local opinion seems to be that neither anuran has ever been particularly c o m m o n in the area and it may be that the habitat is fundamentally unsuitable for them. No other obvious reason, such as the use of pesticides or excessive predation, has presented itself especially in view of the fact that newts remain quite widespread. Another point relates to how amphibian distribution in the study area might be taken to reflect the likely situation in other parts of lowland England. I think that great caution should be exercised in any such extrapolation because although agricultural lowlands might seem superficially similar there will certainly be important differences in geology, land use and even climate across the country any or all of which could have major effects on the amphibians. Upland regions and minor habitats such as heathlands and coastal dunes might also be expected to differ in terms of herpetofauna, and what would be interesting is comparable information from systematic studies in some of these other regions. Table 9 is a summary of the data obtained in this and the 3 earlier sections of the work on other habitat types in Sussex. It is clear that there is considerable variation in the habitat preferences and overall success of the 5 species in this part of Britain. The smooth newt Triturus vulgaris emerges as the most adaptable type, not only being found in all 4 major habitats but also being the most abundant species in at

136

TREVOR J. C. BEEBEE

TABLE 9 O V E R A L L D I S T R I B U T I O N A N D A B U N D A N C E OF A M P H I B I A N B R E E D I N G SITES

Species RT BB TV TH TC

Chalk hills sites per km 2

2 2 14 5 5

0.014 0.014 O-1 0.04 0.04

Suburbia sites Marsh sites, dykes per km 2 per km 2

> 7000 ~ 100 >2000 ~30 > 3000 ~40 absent? nO absent? ~0

sparse absent? sparse very rare absent?

1? 0 1? 0.1 ?

Lowlands sites pekm z

5-10 absent? 35-40 30-35 ~20

O.1 0 0.5 0.4 0.25

Total sites

> 7000 >2000 > 3000 30-40 ~25

BB = Bufo bufo. Figures under each habitat are for numbers of sites.

least 3 of them. It has successfully colonised garden ponds and become c o m m o n in suburbia; it remains relatively widespread in chalkland dew ponds and agricultural lowlands and may even be found in the apparently marginal amphibian habitat of river valley marshes. The other newts, however, have fared much less well and the patterns for T. helveticus and T. c r i s t a t u s are broadly similar though the former species is rather more widespread than the latter in the agricultural lowlands. Habitats occupied by the two species are mainly these lowlands and the upland dewponds; neither newt has colonised garden ponds and both are very rare or absent in the river valley marsh dykes. Frogs R a n a t e m p o r a r i a and toads B u f o bz4/b represent a converse situation to the latter two newts. Both anurans have colonised garden ponds very well indeed but are rare or absent in the 3 rural habitats. The reasons for this are still somewhat perplexing and the relationship between past and present abundance not always clear. From the data accrued by Cooke (1972) on a national basis we know that frogs and toads were once generally much more abundant in the countryside but whether the pattern of decline which he identified subsequent to the 1940s was manifest in all 3 of the habitats studied here, or whether some places never had many anurans, will probably never be known for certain. It does seem that there have been major reductions in at least the marsh dyke and dewpond habitats. The compensatory success of frogs and toads in gardens means that within the study area R a n a t e m p o r a r i a and T r i t u r u s vulgaris are the most abundant amphibians and T. c r i s l a t u s the rarest. The former are the only two species to occur in all 4 habitat divisions. It must also be reiterated that urban zones constitute a much higher proportion of the study area (23 '~'Jo)than they do of the country as a whole and this must be borne in mind in any attempt to extrapolate to the national situation, in which newts might be expected to increase and anurans decrease in relative abundances. It is of interest to compare these data with some recently available from Switzerland (Grossenbacher, 1980); in the northern plain of that country, about 80 ~o of wetlands constitute habitat for at least one species of amphibian and there is approximately one breeding site per 5 km 2. Excluding suburbia, the situation in Sussex varies from < l0 ~o of freshwaters being used (marsh dykes) through 33 ~o

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(lowlands) to about 45 p/ot(dewponds); numbers of breeding sites vary from about 0.5 per 5 km 2 (chalk hills) to perhaps 4-0 per 5 km 2 (lowlands). To what extent have these studies identified key factors in the habitat requirements of the 5 species ? This question is best considered by dealing with each amphibian in turn. (1) Rana temporaria. Very catholic in gardens pools, the presence offish being no deterrent. Few records outside gardens, but very shallow, fish-free pools seem to be preferred and the pasture/woodland interface may be important. Ionic scores and pHs probably not crucial over a large range (150-2000 parts/106 and pH 6-9 tolerable). (2) Bufo bufo. Not as abundant as frogs in gardens and though the reasons are uncertain it seems that larger, older pools of relatively high ionic score and with fish may be optimal. The virtual absence of this species from rural areas precludes further comment. (3) Triturus vulgaris. Widespread in garden ponds though success inversely proportional to the numbers of fish in them; nevertheless more frequently found with fish than are the other newt species in the countryside as well as in gardens. Small ponds ( < 2 0 0 m 2) of depth 0.5 1.0m and at least partly vegetated are probably ideal, pH uncritical between 6-9, but optimal ionic conditions may be around 380 parts/106 with declining abundance at higher values (though tolerant of < 150 1750 parts/106). Some scrub or woodland vegetation as terrestrial habitat in the vicinity of rural ponds is of great importance. (4) Triturus helveticus. Broadly similar to T. vulgaris within the study zone but since it is rarer on chalk formations (dewponds and most garden ponds fall within chalk-dominated areas) there may be some deleterious property of such freshwaters which disadvantage this species in comparison to others. Found across the pH range 6.~8-7 and at ionic scores < 30(~825 parts/106 but again with a probable optimum around 380 parts/106. The proposition of Cooke and Ferguson (1975) that the palmate newt is not a montane species but that its distribution is more likely related to chemical factors in freshwaters is exemplified in this study where the species was found to be much more abundant at low altitudes ( < 100m) than at higher ones on the chalk Downs. (5) Triturus cristatus. Absent from garden ponds, perhaps because it is more susceptible to fish predation of its larvae than is T. vulgaris (Dolmen, 1980). Shares much the same requirements as the other two species in terms of pond size and depth though rather less in the way of vegetation seems necessary. No selection of deeper ponds apparent. Found at pHs between 6.0 9.5 and ionic scores similar to T. helveticus, but not deterred by chalk strata. Sizeable areas of scrub or open woodland in the vicinity of the pool are important to this species even more than to the others. This is obviously less than a complete picture of the niches of the five species and it is easy to point out unanswered questions. What is the rare combination of factors

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which makes a pond ideal for Bufo bufo? Why do newts thrive in m a n y areas where anurans do not? And what factors dictate the absence, presence or relative abundances of the 3 newt species in a pond ? The answers to some of these points may actually be implicit in the data already obtained, but to verify certain of the explanations suggested above and in the preceeding parts of this study will require more information from other areas. Furthermore it is clear that some aspects, such as relative newt abundances, are more likely to yield to detailed water analyses such as those carried out by Cooke & Frazer (1976). Nevertheless it remains true that examination of general habitat structure at the level described has pinpointed a number of important requirements and preferences of the various species. Finally, how might these data influence conservation measures for the British herpetofauna? A number of points are worth making in this context. (1)

(2)

(3)

Garden ponds should be encouraged and owners induced to omit fish from them. Species such as Rana temporaria, Triturus vulgaris and even Bufo bufo will often colonise such ponds quite rapidly without assistance, but deliberate introduction of Triturus cristatus and T. helveticus might be considered if there are viable local populations that can withstand the abstraction of a few adults. Both species usually colonise and do well under such circumstances. Local authorities should be encouraged to manage ponds in their jurisdiction (e.g. those in parks) to the benefit of the amphibians by keeping at least some free from fish and waterfowl, by not cleaning them out between February and September and by permitting the growth of dense vegetation (such as flowerbeds) rather than close-mown lawns around at least part of the pond perimeters. Most importantly, farmers should be induced not only to refrain from the infilling of ponds but to leave around them as large an area as possible of rough scrub or open woodland. Fencing off from livestock is also beneficial, though obviously successional changes which would lead to the total shading or silting up of the pool need to be prevented in some way. Management would have to be tailored to the individual situation to achieve this.

All of these approaches, which are largely educational, seem worth pursuing if the recent declines in wetlands and their amphibian (and other) wildlife communities are to be arrested. The magnitude of these declines is one thing that has come to light in these studies; 70 ~o of dewponds and 33 ~0 of farm ponds lost within a few decades, coincident with deleterious changes in river valley marsh dykes, are scarcely compensated by the current vogue for garden ponds. Welcome a reservoir as the latter may be, they have not proved beneficial to all species and it is in the infinitely larger expanses of open countryside that the main battle for wetland conservation must be fought if this part of our heritage is to survive the century.

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ACKNOWLEDGEMENTS I w o u l d like t o t h a n k K . C o r b e t t , B. P e r r y a n d J. B a r k e r f o r h i s t o r i c a l i n f o r m a t i o n a b o u t the study area. T h e w o r k was carried out on b e h a l f o f the C o n s e r v a t i o n Committee of the British Herpetological Society.

REFERENCES BEEBEE,T. J. C. (1973). Observations concerning the decline of the British Amphibia. Biol. Conserv., 5, 20-4. BEEBEE,T. J. C. (1977). Habitats of the British amphibians ( 1): chalk uplands. Biol. Conserv., 12,279 93. BEEBEE, T. J. C. (1979). Habitats of the British amphibians (2): suburban parks and gardens. Biol. Conserv., 15, 241 57. BEEBEE,T. J. C. (1980). Habitats of the British amphibians (3): river valley marshes. Biol. Conserv., 18, 281 7. COOKE,A. S. (1972). Indications of recent changes in status in the British Isles of the frog Rana temgoraria and the toad Bufo bujb. J. Zool. Lond., 167, 161 78. COOKE, A. S. & FERGUSON, P. F. (1975). ls the palmate newt a montane species? Brit. J. Herpetol., 5, 460-3. COOKE, A. S. & FRAZER, J. F. D. (1976). Characteristics of newt breeding sites. J. Zool. Lond., 178, 223 36. DOLMEN, D. (1980). Distribution and habitat of the common newt Triturus vulgaris and the warty newt Triturus cristatus in Norway. Proc. Eur. Herpetol. Syrup. GROSSENBACHER,K. (1980). A review of herpetological field research and conservation in Switzerland. Proc. Eur. Herpetol. Syrup. RATCHFFE, D. A. (ed.) (1977). A nature conservation review. Cambridge, Cambridge University Press.