J. Zoo/., Land. (1989) 217, 177-201
The biology of Schizomus vine; (Chelicerata: Schizomida) in the caves of Cape Range, Western Australia
W. F. HUMPHREYS Department of Biogeography and Ecology, Western Australian Museum, Francis Streef, Perth, Western Australia 6000
M. ADAMS Evolutionary Biology Unit, South Australian Museum, North Terrace, Adelaide, South Australia 5000
AND B. VINE 86 Schruth Street, Kelmscolf, Wesrem Australia 6111
(Accepled 25 May /988)
(With 6 figures in the text)
The chelicerate order Schizomida is represented in Western Australia by a single species, Schi:umus vinei Harvey. from caves in the semi-arid Cape Range 011 the North West Cape peninsula. Schizomus vinci occurs in eight of 170 caves known from the range but is found only in areas where the relative humidity exceeds 92°/,.. The sehizomids are associated with a rich fauna (at least II species) mostly ofdetritivores, some ofwhich show troglobitic adaptations. They prey on the cave animals that feed on detritus and are known 10 eat oniscoid isopods. millipedes. cockroaches, worms and S. rinei. The size class structure of the population in cave C 118 was strongly skewed negatively suggesting that the smaller size classes occupy interstices of the infill ofsumps. Schizomids in this cave were found to be distributed at random up to the third nearest neighbour. The minimum population size. with gyX, confidence. was estimated to be 1323 individuals. Schizo/1/lis vinei grew very slowly in vivaria. One female produced nine eggs which did not survive. Schi:olllu$ rim'i has II high mean rate of water loss (470,4 rng g-I h- I) and a low resistance to water loss (15·2 em sec-I); their resistance is about 10 x grellter than that ofa free water surface, but is ahout two orders of magnitude lower than that of some spiders and scorpions. Schizolllus villei excretes a clear fluid and may be ammonotelic. • Al10zyme electrophoresis strongly suggests that individuals from the different caves are of the same species. Consideration ofdimate. age of separation of the caves and the general biology of the schizomids suggests that those caves containing schizomids may be linked.
Contents Page Introduction 178 Methods 178 Field 178 Laboratory 179 Population analysis 179 Electrophoresis 179 Husbandry .. 179 177 0952-8369/89/002177 +25 $03·00 © 1989 The Zoological Society of London 178 W. F. HUMPHREYS, M. ADAMS AND B. VINE
Water loss [80 Statistics 180 Description of the area 180 CaveCI18 181 Associated fauna [81 Results and discussion 181 Physical environment 181 Size. 184 Breeding. 185 Length/weight 185 Allometry 185 Growth 186 Dispersion 186 Numbers. 187 Food, fceding and habits 188 Genetics. 190 Excretion 191 Water loss 191 General discussion 193 Obligate troglobite? 193 Distribution 193 Population estimates 194 Rainfall necessary for nooding [95 Age of separation of caves as determined by aridity [96 Persistence of the populations 196 Constancy 196 Community relations [97 Connections of the caves 197 References . [98 Appendix I. 201
Introduction Many troglobites occur in exceedingly low numbers (Milchell, 1970), except for those associated with guano deposits where the large and predictable nulrient input sustains high population densities (Mazanov & Harris, 1971). This paper examines a relict population of Schizomus vinei Harvey (Arachnida: Schizomida) reported to occur in low numbers in two caves in Cape Range, Western Australia. The populations are supported indirectly by organic debris thai is washed into the caves by run-otT from intermittent and unpredictable heavy rainfall. Vine, Knott & Humphreys (1988) commented on the conservation of the populations in two caves. This paper examines the population status and degree of genetic isolation of S. vinei populations from four caves in Cape Range, and considers at length the conservation of the populations.
Methods
Field
Cave C 118 (not named) was surveyed to Grade 5·3 using standard speleological methods (Ellis, 1976). Temperature and relative humidity were measured with both a whirling hygrometer (Brannan, England) and an electric hygrometer (KM 8004, Kane May, England) calibrated using saturated standard saIL solutions (Winston & Bates, 1960). Six replicate soil samples were collected from 5 areas within the cave where varying THE BIOLOGY OF SCHIZOMUS IN CAPE RANGE 179 numbers of schizomids occur. The water contcnt of the soil was determined gravimetrically after drying al 70 C. The organic carbon content was determined by the Walkley-Black dichromate oxidation method with glucose as a standard: the presence ofCaC03 up to 50% orthc sample volume gives no interference (Allison. 1965). Schizomid numbers were estimated by direct searching. by nearest neighbour analysis and by mark and recapture methods. Direct searching was conducted under torch-light by various numbers of people searching the same areas on different occasions; the schizomids found were trapped beneath inverted vials to await further examination. On 3 days, the distance to the 3 nearest neighbours (vials) was estimated, to within I em. with a tape measure. The schizomids were measured (total length) and marked with fluorescent powders (Daylight Pigments; Abel Lemon Company, Adelaide). Different colours were used for the north and south side of the cave on the first day, and a third colour on subsequem occasions throughout the cave. After the first day of sampling. all schizomids caught were ex.amined for powder marks under an ultraviolet lamp (Model MS-47: Ultra-violet Products Inc. San Gabriel. California).
Laboratory Population analysis: this is considered at length because the status of the population must be known for conservation implications to be assessed. As the number of recaptures from the mark-recapture experiment was small, it is inappropriate to use the traditional algorithms to estimate the population (Otis. Burnham. White & Anderson. 1978) on account of the inherent and pronounced negative bias of their confidence intcrvals (Chapman. 1951: Robson & Regier. 1964: Ricker, 1975). The estimation was therefore conducted using the sequential Bayes algorithm as recently used by Gazey & Staley (1986). This algorithm is being actively developed to deal with the more intractable problems of population estimation (Raftery, Turet & Zeh, 1988). For comparison, the more familiar Bailey's (1951) modification of the Lincoln-Petersen Index 2 census method was used for each day of recapture, assuming that no marked individual was recaplUred on sequential days; the probability of this, determined by simulation, is 0·037 at the minimum population size with 95% confidence (by Bayes algorithm) of 1323. In addition, the dispersion and density were estimated from the first 3 nearest neighbours following the methods of Thompson (1956) and Morisita (1954), respectively.
Electrophoresis: cellulose acetate gel electrophoresis was conducted using standard methods (Richardson, Baverstock & Adams. 1986). Homogenates were made from whole frozen S. villei and used to examine the allozyme variation between populations. For systematic purposes, the null hypothesis under test was that all populations were sampled from the same gene pool ofa single species. Four individuals were examined from each ofcaves C 18 (Dry Swallett), C 106 (Shot Pot) and C 118 and 2 individuals from C 126. Such sample sizes are entirely adequate for systematic studies on allopatric populations (Richardson et al.. 1986). Interpretable gels were found for 20 enzymes and one non-enzymic protein, encoded by a presumptive 24 loci. The enzymes (and protein) used were: Aconitate hydratase (ACO . E.c. 4.2.1.3), Adenosine deaminase (ADA. E.C. 3.5.4.4), Aldolase (ALD, E.C. 4.1.2.13), Enolase (ENOL. E.C. 4.2.1.11), Esterase (EST, E.C. 3.1.1.1), Glyceraldehyde-phosphate dehydrogenase (GAPD, E.c. 1.2.1.2), Aspartate aminotransferase (GOT. E.C. 2.6.1.1), General protein (GP), Glyeerol-3-phosphate dehydrogenase (GPD, E.C. 1.1.1.8), Glucose-phosphate isomerase (GPI, E.C. 5.3.1.9), Hexosaminidase (HEX, E.C. 3.2.1.30), Hexokinase (HK, E.C. 2.7.1.1), Isoeitrate dehydrogenase (IDH, E.C. 1.1.1.42), Lactate dehydrogenase (LDH, E.C. 1.1.1.27), Malate dehydrogenase (MDH, E.C. 1.1.1.37), Peptidases (PEP, E.C. 3.4.11 or 13.*), Phosphoglycerate mutase (PGAM, E.C. 2.7.5.3), Phosphoglycerate kinase (PGK, E.C. 2.7.2.3), Phosphoglucomutase (PGM, E.C. 2.7.5.1), Pyruvate kinase (PK, E.C. 2.7.1.40), and Triose-phosphate isomerase (TPI. E.C. 5.3.1.1). The nomenclature and conventions for referring to alleles and loci follow Richardson el al. (1986).
Husbandry: Schizomus vinei was maintained in the laboratory in either 50 ml vials or 50 x 10 x 10 em vivaria: in both cases the ftoorcomprised 1cm or more ofsoil from C 118. The soil was kept moist with distilled watcr 180 W. F. HUMPHREYS. M. ADAMS AND B. VINE
TAULf. J The predictability ofvarious rainJall SIll/is/ies' 0/1 North West Cape from /965-/986 inclusive. Tlll'indices/olloll' Colwell ( 1974). The raif!fllll .\·/{IIi.~lic.\' (Ire (A) mOIl/hly raillj{t1I, (il) maximum rainfall ('lIl'11l per mOlllh, lind (ej lIumber v/rain day.5 (> 0·/ 111m) per mOl/til. All analyses ll'ere based Ofl logz chuses ill order 10 eliminate Ille correlal;oll betll'een rhe mea" und t"ariallce in Ihe dara
Index A B C
Predictability (P) 0·325 0·488 0·344 Constancy (C) 0·131 0·229 0·154 Contingency (M) 0·193 0·258 0·189 CfP 0·404 0·470 0·449 MIP 0·595 0·529 0·550
I Sources of rainfall dala: For Exmouth (Vlaming Head) [965-[967. Exmouth composite 1967-1975 and Lcarmonth 1975-1986 (Microfiche Climatic Averages. Australia and TABS Elements May [986. Bureau of Meteorology. Canberra)
to maintain ncar saturated humidity. An incandescent light bulb maintained the temperature above 18 C but the temperature otherwise varied with the ambient weather. They were fed weekly on live oniscoid isopods.
Water!oss: evaporative water loss (EWL) was measurcd in a dry air stream (90 ml min I; c. 1·5 em sec I) and the water content of the downstream air determined by means ofan electrolytic water detector (CEC 26-303 moisture monitor). The current output of the electrolytic cell was monitored with a Thurlby digital muhimeter with an RS·232 interface to a Commodore 128 microcomputer. The computer logged the data at 30 sec intervals. and calculated EWL (mg min-I). surface area specific EWL (mg cm- 2 sec-I) and resistance (sec em-I). The surface area was estimated from 57 measurements of the body and limb diameters ofS. vinei from the drawings of Harvey (1988) assuming cylindrical cross·scctional shape. Resistance to water loss (R) was calculated after Nobel (1974) as R =C"",./E\VL, where C..... is the water vapour concentration deficit (mg em J) and EWL is the surface-area-specific evaporative water loss (mg cm- 2 sec -I).
Statistics: least squares regression, one-way ANOYA with GT2 multiple comparisons at a:=0·05, the comparison of the slopes and displacement of regression lines (ANCOYA), correlation and partial correlation follow the algorithms ofSokal & Rohlf(1981). Geometric mean regression follows Ricker (1973) and the non-parametric procedures arc after Daniel (1978). Analysis of the genetical data follows Richardson. Baverstock & Adams (1986). Analysis of the first 3 nearest neighbours followed the method of Thompson (1956); probabilities were determined from Xl values with from 18 to 618 df. and P>0·95 and P<0'05 indicate significant over dispersion (regularity) and under dispersion (clumping). respectively.
Description of the area The climate ofthe North West Cape peninsula is hOI (mean daily lemperature c. 27°C) and dry, with the annual evapotranspiration being II-fold greater than preeipitation (Vine e1 al., 1988). Rainfall in the region of Cape Range results from at least four proeesses (Gentilli, 1972; Beard, 1975) and so is highly unpredietable in all its aspeels (Table I). The low predictability is partitioned THE BIOLOGY OF SCHIZOMUS IN CAPE RANGE 181 fairly evenly between the contingency and constancy components. This means that the low level of overall predictability is due to considerable variation both among months and years as well as irregular seasonality. Synopses of the geomorphology and geology of the Cape Range, together with climatic summary of the North West cape peninsula, have been presented elsewhere (Vine el al., 1988). Of the 170 caves known in Cape Range, eight are now known to contain S. vinei. Only about 12% ofthe outcropping Miocene strata likely to be caverniferous has been examined for caves and even in this area about 50 new caves have been found since the previous publication was prepared (Vine el al., 1988). In addition to the IwO caves previously described (C 18 [089 544 Sheet 1653 Cape Range] and C 106 [915 562 Sheet 1753 Learmonth] [Vine el at., 1988]), the presence ofS. vinei was confirmed in C 103 (Trionomo; 077 504 Sheet 1653 Cape Range), C 118 (083 468 Sheet 1653 Cape Range), and C 126 (093 479 Sheet 1653 Cape Range) in July 1987, and up to November 1987 schizomids have also been found in the newly discovered caves C 162 (Rock Bench; 092 475 Sheet 1653 Cape Range), C 163 (Wanderers' Delight; 912480 Sheet 1753 Learmonth) and C 167 (not named; 089 473 Sheet 1653 Cape Range: R. Wood and M. East, pers. comm., 1987). The C prefix denotes caves from Cape Range (Matthews, 1985). The caves containing schizomids are up to 9· 7 km apart and cover about 16·9 km' of Cape Range.
Cave C 118 This cave is entered from a doline via a narrow passage to a pilCh of 18·5 m into the cave (Fig. I). A dry steam bed containing water-smoothed pebbles runs between mud banks on the cave floor before bifurcating to a lateral exit and two sump holes.
Associmedfauna
In addition to S. vine;, C 118 contains large populations of earthworms, oniscoid isopods and white millipedes. At least II invertebrate species are present in the cave, of which four have clear troglobitic adaptations (Appendix I). Small mammals have been seen in the cave and a recent skeleton collected was of Ral/liS ral/lis L. (Rodentia: Muridae).
Results and discussion
Physical environment Temperatures of the caves examined were from 17·0°C to 25·2°C with relative humidities ranging from 63 to 100% (Table II). Schizomids were found in areas of caves covering the full range oftemperature but were found only in those parts ofcaves exceeding 92% relative humidity (Fig. 2). The saturation humidity did not differ between parts of caves with and without schizomids (Fsl.I2 = 0·18; P= 0·68) but the vapour concentration deficit, which is a measure of the evaporation power of the air, did differ [Fsl.I' = 28·57; P < 0·00 I, based on log (X + I) dalal, with means, respectively, of 0·71 (S.D. = 0·416, /I = 6) and 3·29 (S.D. = 1-471, /I = 8). Soil samples from C 118 had a mean water content of 16-4% oflhe dry soil weight (Table 111) but the water content of soil from different areas in the cave was not Ihe same (FS4.25 = 17·91, P < 0·00 I); S. vi/lei was more abundant in those parts of the cave with the greatest soil waler content (Table III). Soil samples from C 118 had a mcan organic carbon content of 1·51 % ofthe dry soil weight (Table III) but the MN 06 \ ""N
A- A
Deline and Entrance :;: :n J: C ;:: "C Main chamber 25 J: 16 23 22 26,<> m '"-< ~ !" ;:: > /15 o A > ;:: V> G;-'---'- ~ ,.';.~ > " Z " " o 13 '\, , _.- _.--_. -' '"< Z m cz::, Vertical hole down 01 09 '.¢: Vertical hole up 1,,"" Direction of slope Extended elevation A-A ~ Rockfall, talus ;.. ~.~.:: Pebbles, gravel :::~ .::..-:Mud, 50;1
• 10 m •
FIG. I. Plan and latcnll projccted views ofcavcC 118 in which the population studies were made. The sc.tlc bar denotes 10 m and the letters denoleareas mentioned in the lext and Table V. The cave was surveyed by Brian Vine. Ray Wood. Malcolm East. Eva Hart and Rae Young in July 1987. THE BIOLOGY OF SCHIZOMUS IN CAPE RANGE 183
(a)
(b) 10
2
60 80 90 100 Relative humidity (%)
FIG. 2. The frequency distribution of (a) temperature and (b) relative humidity from six caves in Cape Range. The records arc separated into those areas where S. lIim'" was present (0) and absent (0) and indicate the dependence of the schizomids on humidity but not temperature.
TA8LEII The relalive humidity and lemperatllre ofI"OriO/IS parts ofsome cOl:es alld Ihe presence oj.fclri:omids. II is lhe lIumber 0/sill's (ill C J/8 the number ofoccasions) the temperature aflll "umidil)' were recorded and S.D. ;s 'he slandard dedo/iOfl
Cave Temp. R.H. status Location Schizomid (-C) ('Vo) " C 18 Entrance chamber absent 17 83 I C 18 Fringe twilight present 18 94 I C 103 Level I absent 23·5 89 3 C 103 Level 2 absent 23·3 91 2 C 103 Level 3 present 23-5 98 2 C 106 Halfway mudbank 19 87 1 C 106 Bottom entrance absent 19·8 63 3 C 106 South chamber absent 19·1 72 2 C 106 Bottom chamber many 18·8 93 3 C 113 Boltom absent 23·3 83 1 C 118 Upper entrance present 23-0 95 2 C 118 Top ofside chamber present 25·0 100 I C 118 Bottom many 23·3 95-4 14 S.D. 0·21 1·87 C 140 Bottom absent 25·2 80 3 184 W. F. HUMPHREYS. M. ADAMS A DB. VINE
TABLE 111 n", 1l'1Iler (0/" dry weight) and organic carbon (o/" dry weighr) conti'lll ofsoil.~ in C 1/8. MNII/S (11=6) followed hy a common !l'tler 111rlli1l (j co/ullin do /lol diffel" signijical/l(I' (olle-II'ay ANO VA ll'illl GT2 11/ullip/c ('olltporiso/l /(!.I")
Water conlent ('r.,) Organic carbon (0;,,) Area in Schizomid cave numbers Mean S.D. Mean S.D.
E Sparse 11·4a 2·42 0·42 0·078 B Few 15·0a 1·30 1·85a 0·221 D Few IS'5ab 2·98 1·50a 0-450 A Many 19·2bc 0·79 1·78a 0·269 C Many 20·4c 1·53 2·04a 0·489
9·26 7·47
{/j 5·43 ~ "0 4·75 ~ 3·80 3·04 2·44 ~
FIG. 3. The size class (body length, mm) distribution ofS. vine; taken from caves C t 18 and C 126, The data (11= 131) arc plotted in cquallogarilhmic size chl~scs. with the lower limits (shown) having a multiplication factor of \·25.
organic carbon content ofsail from the lower parts ofthe cave was greater than in soil from upper areas (Fs4.2s = 58· 36. P< 0·00 I); S. villei was present in numbers only in those parts ofthe cave with greater than 1·5% organic carbon and more Ihan 14% soil water (Table Ill). Soil water content (x) and organic carbon content (y) were strongly correialed (rxy" = O' 724, P < 0·00 I) and Ihe relalive density (z) of S. villei was correlated significanlly with both soil variables (rxz,,=0'874 and ryz2R=0·692). Only the first order partial corrclation between relative dcnsity and soil water content was significant (rxz.y = O' 754, I" = 7·90, P < 0·00 I). Areas of the cave with low flooding potential (> 2 m above cave floor), where worm casts were absent, had lower levels of organic carbon (0'82%) than areas with high flooding potential (1·6 u/ll) where worm casts were present.
Si:e The size class distribution of the individuals caplured in C 118 and three individuals from C 126 (Fig. 3) show a considerable excess ofindividuals in the larger size classes. lfit is a true reflection of the size class structure. then it suggests either that S. villei breed periodically and synchronously. or that they grow fast relative to the longevity oflhe adults. II is possible Ihat periodic breeding could be entrained to flushes of organic detritus being washed into the cave. However, the presence of some small individuals suggests that this is not the case. There arc indications in the literature that schizomids take several years to mature (Rowland. 1972) and it is shown below that S. villei grow THE BIOLOGY OF SCHIZOMUS I CAPE RA 'GE 185 slowly. Extreme longevity ofadults could result in the top heavy population structure seen in Fig. 3 but this thesis is rejected as most of the large S. villei in C 118 were not adults. It is probable that the smaller size classes were sampled less efficiently than the larger size classes. This bias is unlikely to be due to small individuals escaping notice because young schizomids are white and are clearly visible on the bare deep-red mud banks. Small individuals probably occupy a different microhabitat from those sampled. Consequently, the population estimates represent predominantly sub-adults and adults and therefore considerably underestimate the true size ofthe population.
Breeding One female kept in a vivarium for 28 weeks and housed only with another female, which she ate, laid nine eggs each 0·9 mm in diameter. She abandoned the eggs within seven days. The eggs were attached to the ventral side of the abdomen which was held nearly vertical as has been illustrated for some schizomids (Gravely 1915, plate XXIV; Rowland, 1972, fig. I): S.floridalllls does not hold the abdomen erect while carrying eggs (Brach, 1976). However. the schizomids wandered freely and did not construct and remain in a brood chamber as do the other species in which breeding has been observed [Rowland, 1972; Gravely, 1915: respectively, Trithyrells pellwpe/tis (Cook) and S. crassicalldatlls (Chamberlin)]. Some other cave (Rowland. 1972) and non cave dwelling species (Brach, 1976) have also been caught at large carrying their eggs, implying the absence of brood chambers. The clutch size is in accord with that for other Schi:omus (seven eggs in S. crassicalldatlls [Gravely, 1915] and three to eight embryos in S.flaridal/lls (Brach, 1976), but substantially smaller than in T. pel/tape/tis which produced 30 eggs (Rowland 1972). Rowland (1972) considered that, after dispersal from the mother, schizomids have four moults and five instars, as in S.floridal/lls (Brach, 1976). From the illustration of T. pentape/tis with young (Rowland, 1972, figs I and 2), we calculated a mean growth increment in length of c. 1·6 per stadium. On the assumption that young in the eggs are folded at Ihe petiole, newly hatched S. villei would be about 1·8 mm long. The first moult occurs before the young disperse (Rowland, 1972; Brach, 1976) so that the expected length of the smallest free living S. villei is c. 2·9 mm compared with the smallest S. vinei, length 2·5 rom, seen in the caves. Hence it is thought that the entire size range of free living S. vinei is represented in Fig. 3.
Length/weight Schizomids are slightly built animals and this is reflected in the relationship between length (L mm) and weight (W mg) of S. vinei, which is described by the equation log (L') = 1'03710g(W) + 1·656 (11 ~ 23, r' = 0,947, P = < 0'001). To place this in the context of a more familiar arachnid, comparison with the same relationship for a wolf spider, Geolycosa godeffroyi [Koch] (Humphreys, 1973), shows that the lines are parallel but displaced (FsI.24=244·8; P Allometry Three linear measurements were made on 17 S. villei; total length (T), carapace length (c) and carapace width (w) to analyse the allometry of growth. The slopes of the double logarithmic regressions were bCT = 0,55, bWT = 0·71 and bwc = 1·15 (P < 0·0I in each case) and the slopes differ 186 W. F. HUMPHREYS. M. ADAMS AND B. VINE 3 M .sE -& 2 c ~ 3' 1'---~4-----~---_----~ -0·4 0 004 0·8 1·2 Log weight (mg) FIG. 4. The relationship between length and weighl in S. dIll'; compared with thai (lower line) for the burrow inhabiting wolf spider. G. godeffroy; (data from Humphreys. 1973). from each other (Fs,... ~ 4'17; P=0·022). However. only ber differs significantly from a slope of 1·0 (P < 0,01). Hence, during development the total length increases 41 % faster than the carapace length. Growth In vivaria the growth rate (mg mg- I d -I) ofS. vi/lei, over 59 days, was inversely related to initial weight (X mg: Y =0·015- 0'0121og X, r=O·72,/I = 14. P=0·004), with the mean rate being 0·0064 mg mg- I d- I at a mean weight of6'0 mg. While the growth rate ofS. vinei may seem low, it is at a rate 0·21 (S.D. =0,14, /I = 14) that of a wolf spider (G. godeffroyi) during periods of the latter's active growth and at a rate similar to the winter growth ofthe spider (calculated from Humphreys, I 1976, tables 6 and 7). Over 139 days, S.vinei grew 0·0044 mg mg- d -I (S.D. = 0·0023; n = 6) at a mean weight of 6·0 mg. Slow growth rates have been reported for other schizomids (Briggs & Hom, 1966; Rowland, 1972; Brach, 1976). As with the other schizomids maintained in the laboratory (Rowland, 1972; Brach, 1976), ecdysis has not been observed in S. vinei and the number of instars is unknown; other schizomids, however, have five postembryonic moults (Rowland, 1972; Brach, 1976). Only one schizomid moulted in the laboratory, 30 weeks aner its removal from C 118. This compares with the first moult 75 days after oviposition and 40 days aner hatching in Tri/hyrells pen/ope/tis (Rowland, 1972). The dispersion of the schizomids on three sampling days was analysed separately using the distances to the first three nearest neighbours. The results show that, at the smaller scales considered (first and second neighbours), the individuals were distributed at random (0·22 < P Ti\RUIV The 1/WI/bers of Sch;:omuJ l';ne; cough' by direct searching of ,he mud banks of (:urt! C 1/8. logether Wilh the /llimber marked and recaptured ollfil'e days 10 . people Search time umber Number! umber Number Dale searching (h)(STl' found ST marked recaptured 7.7.87 3 0·6 13 22 9.7.87 4 2·3 47 20 43 12.7.87 6 4·5 57 13 53 I 13.7.87 I 1·8 40 22 0 3 15.7.87 6 4·0 49 12 0 5 1 person-hours TARLE V The dellsity of s. I';ne; extima/ell by nearl'Sl neighbour ollalysis (Morisiru. /954) 011 tllree occa.~ioll5 ill can> C 1/8. The mild bunks, main chamber alld whole COL'i' fwd areas ofahow 100. 388 ulI(/544 III}, respec/h:ely Day and Density area " (m-'j All da13 103 0·68 Day I all 23 1·5) area I 12 6·06 Day2all 59 0·57 area v 9 0·46 area a II 0·99 area p II )·89 Day) 21 0·60 group nor repel each other, a statistical result which is in accord with observations made in the cave and in the laboratory. On a larger scale (third neighbour), there is significant clumping in the distribution of the schizomids (P<0·02) which reflects the concentration of individuals in localized regions of the cave, especially along the borders of sumps. Within these local areas (sumps) and on the mud banks themselves, individuals were randomly dispersed. Numbers The crude direct searching ofabout 18% of the total area of the cave resulted in hourly capture rates varying by about two-fold (Table IV). The animals were not spread throughout the cave and some areas were favoured, in particular the mud banks and sumps where organic detritus accumulated and where the population estimates were made. Organic debris washes into the rock filled drainage holes which cannot be searched, and the highest densities of S. vinei were found adjacent to these areas (Table V: areas I and pl. On the first day of marking, many of these schizomids were marked but only one individual was recaptured; this suggests that the population extends at high density into these inaccessible areas where organic maller accumulates. In addition, S. ville; are often found under rocks (three individuals were found under a stone ofc. 300 188 w. F. HUMPHREYS. M. ADAMS AND B. VINE TAUUVI The de/lsity ofSc:hizomus I';n/.'; eSlima/(>(/ from fhe mark-rt'w!Jlure tiara ([lid variOllS mbsers ojrite data alier 500 iteratiollS ofrhe Bayes algorithm (Ga=('y & Staley. /986) al/d hy Bailey',\' ( 195/) modifica- tiO/1 of the Linco/II-Peler.\'(!11 Illdex tlVo·ceflSIl.~ fllClhod Bayes algorithm: Bailey's method: Day Minimum l Mean Median Mean 95% limits All 1323 1987 3495 3505 2 1711 3478 2979 3020 1247 -140-2634 3 1069 2343 2979-3020 2352 333-4371 4 1004 1757 2979-3020 2352 646-4058 3+4 1000 1576 2+3+4 1118 1984 2979 3020 max.jmin. 1·71 2·21 1·16 1·89 I This is the minimum population size cslimalcd With 95%, confidence (sec Gazey & Staley, 1986) em2); the upper banks of the mud flats arc strewn with immovable stones which cannol be examined for schizomids. Nearest neighbour analysis (Table V) gives an overall density orS. villei orO·68 m -2 and shows 2 clearly the variation in density in different regions of the cave, from 0-46 to 6·06 m- . The analyses of the mark-recapture data (see Methods) estimate population size independent of any assumptions concerning the area occupied by the schizomids. The estimated mean population orS. villei in C I 18 ranges rrom 1000 to 2352 individuals (Table VI). Bayes algorithm, however, is Ihe only method which uses the complete data set 10 estimate the population and puts the minimum population size. estimated with 95% confidence, as 1323 (Fig. 5a. Table VI). and the mean and median populations about 2000 and 3500 individuals. respectively. not dissimilar to the estimates using Bailey's method (Table VI). The lenward mobility or the sequential curves (Fig. 5b) suggests that, despite the closed population, it declined during the sampling period oreight days. That this is due to mortality by trampling is considered improbable since no dead schizomids were seen, even after repeated searching orthe mud banks, twice under ultraviolet lighl (for dead marked sehizomids) and rour times under white light. Animal avoidance movement due to disturbance caused by the work in the cave may possibly account for the reduction. In Bayes algorithm, the posterior distribution (Fig. 5b) is much more sensitive in location for an increasing than for a decreasing population, since only the unmarked population is affected in the rormer case (Gazey & Staley, 1986). Hence the apparent decrease in the population size (Fig. 5b) has much less effect on the minimum (P~0·95) estimated population size (Table VI) than on the estimated mean population. FoodJeedillg olld hobits One S. villei was observed in C 118 carrying a rreshly killed isopod in its jaws. Some species or schizomids (Rowland, 1972), but not others (Brach, 1976), arc considered dilficult to reed in captivity. Most newly captured S. vine; fed within a few days of being offered prey. bUL after some THE BIOLOGY OF SCHIZOMUS IN CAPE RANGE 189 (a) § '5 1·0 .0 'C ~ 0·8 B ".: 0·6 w '"o 0. 0-4 ~ iii "5 0·2 E => o aL.__----,- -,-__--=:::;:::===~- 1 2 3 4 5 L::::::~~:-s:~~~==~====; 2 3 4 5 Population estimate (x 10-1 FIG. 5. Statistics derived to estimate the population size of S. vinei in C 118 from the mark-recapture data using the Bayes algorithm. (a) The cumulative probability of the posterior distribution of the estimated population size. The dotted line shows thc minimum population size estimated with 95% confidence. (b) The sequential posterior distributions plotted against the population size. Numbers all the lines refer to thc sequence of analysis (sec Gazey & Staley, 1986). weeks in the vivaria they usually fed immediately and numerous observations were made of their feeding behaviour. Captive S. vinei ate all species from the caves that were offered to them, namely isopods, small worms, schizomids (females inadvertently ate the smaller males), cockroaches and millipedes; S.jioridanlls also ate a wide range ofprey (Brach, 1976). Schizomlls vinei captured prey between 10% and 100% of their own body length and macerated it, usually leaving only the dislocated sclerites. However, schizomids may often run away from potential prey of all sizes. Observations made on S. vinei in caves and vivaria and from video tapes of captive animals, indicate the same general patterns ofmovement described for S.jioridanlls (Muma) (Brach, 1976) and Trithyrells stllrmi Kraus (Sturm, 1973). They groom themselves frequently, especially the amenniform front legs and the flagellar region which is reached by folding the opisthosoma over the prosoma. Their usual progression appears jerky because they move forward for a body length at a time and then stop and feel around the new unknown area, using their long and highly mobile front legs (L1). The area is searched thoroughly with LI by probing every crack and hole in the substratum. If prey is encountered, and the schizomid does not retreat, the prey is stroked by both L1, especially at the extremities, seemingly to assess its size. The schizomid then either retreats or the prey is seized by the pedipalps after a sudden forward lunge of the whole body. The prey is either held or quickly (within two seconds) thrown some distance away after which it may be ignored or t90 w. F. HUMPHREYS. M. ADAMS A '0 B. VINE TABLE VI) AIlt.>lefreqllt'lIdt'sfor lite 111'0 of24 en=ymes scored wlrieh hadpo~rmo,phicloci. The lIumber ofitrdir'id/lols sampled is inc/icmet! in brackc/s C 18 C 106 C 118 C 126 Locus Allele (4) (4) (4) (2) Esl-2 100 loo 62 100 "b 38 Pgm 50 "b 50 loo loo loo' I 11= I. 2 Caves C 18 and C 106 arc separated from C 118 and C 126 by a deep gorge (sec text) recovered. Feeding starts immediately the prey is subdued although, apparently whilst the schizomid is still feeding, the prey is sometimes carried around. This usual pattern of movement belies the locomotory ability of the schizomids. Stronger stimuli cause them to run at great speed for short distances, either forwards or backwards with equal facility. They could complete a movement ofat least 1·2 body lengths within one video frame (0·04 sec; 30 body lengths sec-I), giving a mean velocity ofat least O· 33 m sec-I. This is well above the maximum running speed of0·13 m seC I predicted for a body mass of 10 mg from the general equations in Peters (1983, fig. 6.4). They also have the ability during these escape reactions to jump forwards and backwards, with or without turning movements, due to their saltatorial rear legs (Harvey, 1988, fig. I). While catching schizomids in C 118 a pungent odour (possibly acetic or formic acid) was noticed. This also has been observed in closed tubes containing Schi:omus spp. (Gravely, 1915). On handling S. vinei in the laboratory, a similar odour was noticed associated with the abdomen being arched forwards over the prosoma, possibly to squirt an irritating substance for defence. Genetics All populations were fixed for the same allele at 22 ofthe 24 loci examined (two loci were evident for the enzymes EST, MDH and PEP). This left two polymorphic loci (Est-2 and Pgm), both of which exhibited two alleles but with the rarer allele confined to a single (different) cave (Table VII). The allele frequency data therefore strongly support the idea that all populations sampled are from a single species (Richardson el al., 1986). Given the small sample size, there is no statistical support to reject a null hypothesis that the samples were drawn from a single gene pool. Note, however, that the two polymorphic loci are confined to different caves separated from each other by a deep gorge which bisects the Tulki Limestone, clltting into the Mandu Calcarenite beneath. Ifmore comprehensive sampling ofthese two caves indicates that the preliminary allele frequencies shown in Table VII are substantially correct, then this will provide evidence that C 18 and C 118 are not genetically isolated. The limited genetical data currently do not refute the interpretation, for reasons suggested elsewhere in this paper and from the faunal composition of the caves, that the cave faunas form THE BIOLOGY OF SCHIZOMUS IN CAPE RANGE 191 TABLE VIII The re{tI/;lI(' loss of carbon (Inti hydrogen for e{lch nitrogell arom excreted by l"(1riOIiS ('xcrelO,y produclJ. Dow mo.~lIv from Edney ( /977) H,CN H/N ' C/N' Main excretory product in: Ammonia 3,0,1 ) 0 Aquatic invertebrates Uric acid 4:5:4 I 1·25 Insects. birds and reptiles Guanine3 5S5 I I Spiders Urea 4:1:2 2 05 Mammals 1 A low H(N ratio is an advantage if water is scarce 2 An low C/N ratio is an advantage if energy is scarce 3 Note that spiders. which have other adaptations consistent with general scarcity of food, and which are exposed to water stress, excrete guanine which is optimal for these constraints part ofa continuous community which must link through the cave systems. The genetical data are from schizomids in caves up to 9·7 km apart covering aboul 16·9 km' of Cape Range. Excretion Schizonws vinei was observed, from video tape, to secrete droplets of clear fluid from the posterior end (c. 1·2 III and 10% of body weight) and deposit it on the soil into which it soaked immediately (the drop formed and was deposited in 0·92 sec). This raises questions about the nitrogenous excretion of schizomids and suggests that they may be ammonotelic, a condition found in many terrestrial arthropods with access to surplus water but which is unknown in arachnids (Edney, 1977). The excretory product has not been characterized. The excreta of most arachnids are characteristic white spots due to the excretion of guanine (Horne, 1969; Hamdy, 1972) and uric acid. No evidence of such excretion was observed in the schizomids. The excretion of ammonia would seem advantageous in low energy and humid caves where water conservation is not important, as ammonotely involves no loss ofcarbon (Table VIII) and avoids the high energetic cost of synthesizing uric acid (Bursell, 1964b, 1970) or guanine. Water loss Schizomus vineilose water at a rate of 39·5% (S.D. 11-0%) body weight h-I in dry air moving at a mean velocity ofc. 0·02 m sec-I. Water loss (y mg individual-I min -I) scales to the 0·71 power of body weight (x mg: log y=0·71 log x -1·94; n=8, P=O·OOI). The weight-specific and the area specific water losses are presented in Table rx, together with the resistance to water loss. The resistance ofS. vinei is about 10 times more than a free water surface, but it is more than two orders ofmagnitude lower than that ofa burrow-inhabiting, temperate zone spider, G. godeffroyi (Table IX; Humphreys, 1975). The latter has a resistance similar to a burrow-inhabiting arid zone scorpion, Urodocus yoshellkoi [Birula] (Shorthouse. 1971), although neither species is especially resistant to desiccation. The assertion that schizomids require high levels of humidity (Rowland, 1972; table II, fig. 2), is supported by these data. Free-living species, however, have been maintained in the laboratory without particular attention to water (Gravely, 1915). Resistance to water loss from S. vinei is extremely low, similar to that ofa free water surface and to most humid-adapted frogs (Withers, Hillman, Drewes & Sokol, 1982). In consequence, the 192 w. F. HUMPHREYS. M. ADAMS AND B. VI E TARLE IX Ralesofemporotive 1I'(ller lou (EWL)from eight S. vineiprese1/fed as mass (lnd are(l-Speeijic roles logether lI'ith lilt' II"I/Ole body rl'sistance (R). Also KiI'ell is Ihe rOlio ofImler lo.~.~ (mg h- I) from S. ";nei 10 Ihall?stima/(·djfJr a 1I'0ljspider, G.xodeffro),;, ofthe .mme mass under eqlliralc'/II phy.~ical conditions (f{lImphreys, 1975). The error .Wl/i.Hie i.~ lite coc1]icielll ofvarialion (c./I.). The rt'laiiOll.5ltips belll'eeflll'eiKltt (W mR), lellRrh (L !11m) 01/(/ est;m(1/ed surfacl' area (A I1m/!) for s. I'mel are: A=(1'180Lj! (;//{I L= (52'J7W-15'33)u-w Water loss relative to: mass area Resistance (mgg-lh- l) (mgcm-2h- l) (em sec 1) Ratiol Mean Mean 470·4 4·71 13·2 146 c.v. 37·1 23·8 25·2 30 Minimum Mean 394·4 3·99 15·2 123 c.v. 28·1 16·3 17·4 21 I Schizomid-spider ratio 1·0 Cl. 0.5 "" oL-!;--~----!;,----!-----!~--:-'=-----::l:------;:l:===:,::::--::c: o 2 4 8 16 32 64 128 256 Rainfall class (mm) FIG. 6. The cumulative probabilities (P) ofa single rainfall event in any month exceeding a given range on North West Cape. Thc data are plollcd as an octave plol wilh the upper limit shown to the right ofeach bar. The data (n =227) were extracted from the available data for Exmouth. Lcarmonth and Exmouth (Navy) (Microfiche Climatic Averages. Australia and TABS Elements May 1986, Bureau of Meteorology. Canberra). schizomids could only survive for a few hours at the humidity recorded above-ground on North Wesl Cape (see below). Schizomids placed in contact with liquid water should absorb waler rapidly and so nol survive flooding of the caves. Survival of flooding as eggs (for which no information is available concerning their water resistance) is also unlikely because schizomids attach their eggs to the abdomen and carry their first instar young (Gravely, 1915; Rowland, 1972). Vapour concentration deficil (Cw.) is loweS! in the morning (09:00 h recording). Examination of the maximum and mean 09:00 h relative humidities and temperatures for stations on orth West 3 3 Cape shows thai mean Cw• ranges from 4·8 g m- in July (minimum recorded being c. 2·1 g m- ) THE BIOLOGY OF SCHIZOMUS IN CAPE RA GE 193 and 15·8 g m -3 in December. Taking 15% as the maximum tolerable water loss (Bursell, 1964a), S. l:inc; could be expected to survive in a meteorological screen for only OA to I·3 h over this range of CM • dropping to c. 0·2 h during the day in summer. While moving on or in the soil would increase the survival time, it is clear that the ability of S. vinei to move between caves other than through cave systems is limited. General discussion ObligaTe Trog/obiTe' Schi:omus vinei has been considered to be a facultative troglobitc (Vine et al., 1988), but schizomid species found only in caves often lack both cuticular pigmentation and eyespols, as does S. ,·illei. Rowland & Redgell (1979a, b, 1980, 198 I) provide details onI species of New World SchizOIllIlS. Of those with eyespots, 18 are troglobites (four specified as obligate and eight as facultative troglobites) and 37 are non-troglobites, whereas all eight species lacking eyespots (none with unknown habits) are troglobites. The habits of a further eight species are unknown. Hence, S. villci has the characteristics of other obligate troglobitic Sclzi:omus. The other two genera of New World schizomids both lack eyespots; ProlOsc!,izOIllIlS spp. (2) being non-troglobites and Agasioschizollllls spp. (2) being troglobites (Rowland & Reddell, 1979a). Distribution As in Cape Range, schizomids occur elsewhere in caves surrounded by arid lands (S. harrolo Rowland in Mexico; Rowland & Reddell, 1980). In a temperate part of USA, Trilhyrells shoshollellsis (Briggs & Hom) occurs in a cave warmed by a thermal spring and separated by more than 200 km of desert from the nearest other schizomid known (Briggs & Hom. 1972). Briggs & Hom (1972) suggested that the distribution of schizomids may be limited by low temperature. However, the northern-most New World schizomid, S. briggs; (Rowland), is commonly found in winter, even beneath snow-covered rocks. and in early spring: early spring activity occurs also in S.jos/lI/ellsis (Rowland) and S. be/kill; (McDonald & Hogue) (Rowland & Reddell, 1981). Our data show a clear relationship between the distribution ofS. vine; and water, both soil water and relative humidity (Fig. 2, Tables II and III). The animals were sparse in dry areas ofC I 18; one was seen in the twilight zone on rock in the entrance and one in the upper part ofthe side chamber which had dry soil (I I% soil water: e in Fig. I). However, these areas had relative humidities, respectively, of 95% and 100% (Table II). Together with the data on relative abundance (Table II), this suggests that relative humidity is an important factor determining the range of S. vine; within the caves, but that their abundance is related to soil water content (Table III). The schizomids depend on the detritivores (woodlice, millipedes, worms) and omnivores (cockroaches) that fced on the organic matter washed into the caves by the intermittent influx of surface water. Such matter is mostly trapped in the bottom of the caves but may also settle on the mud banks if the cave is deeply flooded. The breakdown of detritus depends on microbial action, which requires soil moisture, and on the action of the detritivores (including the abundant worms in the mud banks ofC 103, C 106 and CI 18). SchizOlllllS villei concentrates in damp. detritus-rich areas where its prey are to be found. The schizomids wander widely, even into the twilight zone of caves, as long as the relative humidity is above 92%. 194 W. F. HUMPHREYS. M. ADAMS AND B. VINE Sclz;:omus cine; digs networks of burrows which are not, as has been suggested elsewhere (Brach. 1976), associated with breeding, for even the smallest immature S. vine; maintained in the laboratory dug burrows; prey added 10 containers orten entered the burrows but it is not known whether prey are caught there. As with other Sdli:omus spp. (Gravely, 1915), the burrows arc not a focus of the activities of S. vinei. It is, however. possible that S. ville; may forage within worm burrows as they atc small worms in laboratory cultures; schizomids have been found associated with termite colonies (McDonald & Hogue, 1957; Briggs & Hom, 1966; Kaestner. 1968). The population estimates by nUlrk and recapture suggest that much of the S. dne; population is not available to visual search. High densities ofS. vinei are associated with the outflow areas from the accessible parts orthe cave (areas Iand p: Table V), which act as a sink ror the smaller pieces or detritus. We suggest that much or the schizomid and detritivore populations inhabit the rubble and rock-filled drains. and extend downwards for an unknown dist.ance into the finer leads of the cave. Although not contradicted by the genetics data, a more comprehensive study is needed to test for panmixis of S. vinei in the cave systems of Cape Range. Populatioll estimates Mitchell (1970) used both quadrat and crude mark and recapture methods to estimate populations in the 650 m long Fern Cave, Texas. and had difficulty reconciling his estimates. Population estimates of three insect species from quadrats were 1·3,6 and 13 times greater than those obtained by the mark and recapture method. For various reasons, he accepted the quadrat estimates and emphasized the problems inherent in estimating populations under the difficult conditions found in caves. Four classes of assumptions are inherent in mark-recapture experiments: (a) the population is closed over the sampling period; (b) there is an equal probability orrecapture; (c) there is no loss or marks and (d) all marks are reported on recapture (ror a rull discussion see Gazey & Staley, 1986 and rererences therein). The preliminary electrophoreticevidence presented here can neither reject nor support panmixis for S. villei. However, sampling is on a short time scale relative to panmixis, and because of the limited mobility and slow rate of normal locomotion of S. villei, assumption (a) is probably not violated. Assumption (b) is probably satisfied because, as will be shown below, individual S. vinei do not interact on a small scale and their habits are consistent with random wandering within the reeding areas where they concentrate and where the sampling was conducted. Assumption (c) is probably met due to the long period between moults (none or about 20 S. villei moulted in the laboratory in a two-month period) and the longevity orthe marks applied (six marks applied were present arter 21 to 25 days and 50% arter 48 days during which time there was no unexplained mortality). Assumption (d) is satisfied because no naturally occurring fluorescence, similar to that used for marking, was found in the cave. The known population or S. villei is 140 individuals, namely the number marked plus the maximum number of unmarked individuals caught on either of the last two days. The estimated population varies with the method of analysis and its accuracy is dependent on the assumptions made. The lack orcorrelation between the number orpeople searching (x), total search time (y) and number or schizomids round (z: maximum partial correlation is ryz.x ~0'91; t, ~ 3,04, P=0·09; Table IV) suggests that the population was not seriously depleted by the containment or up to 57 individuals, as would be expected ir say 41 % (57/140) or the population had been round. THE BtOLOGY OF SCHIZOMUS tN CAPE RANGE t95 The nearest neighbour analysis (Table V) for all the data suggests a population on the mud banks, where the captures were made, of 49% of the known population. Crude mark-recapture analysis (single mark and recapture) suggests populations in excess of 1000 individuals for each period analysed (Table VI). This is in accord with the analysis using Bayes algorithm which is the only method applicable utilizing all the data in a single analysis. Furthermore, despite the leftward drift in the successive sequential curves (Fig. 5b), the crucial estimate, namely the minimum population with 95% confidence, is robus!. We accept this minimum population ofc. 1300 S. vinei in C 118; this is a conservative estimate as it underestimates the population of small individuals assumed to be present (see above). Populations oftroglobitic schizomids are usually sparse (see Vine el al., 1988). Hence the large population in C 118 and the suitability of the cave for research makes C 118 an important natural laboratory for work on this little known order. Following deep flooding of the caves. the population of S. vinei was severely depleted (Vine ef 0/.,1988). This observation is in accord with the low resistance to water loss and probable uptake ofwater in S. vinei, a factor which would also make them and their eggs (see above) vulnerable to flooding. After populations are reduced by flooding. the caves are probably repopulated from non-flooded areas of the cave system. As schizomids are slow to mature (Rowland, 1972), the frequency of rainfall sufficient to flood the caves to some depth has implications for conservation. In addition, the frequency of rainfall sufficient to cause run-off into the caves is of consequence because the run-off brings with it the organic debris that fuels the cave ecosystem. The following section examines these factors. Rainj{i1/llecessary lor jloading In semi-arid Mulga Zone rangelands of Western Australia the red sandy-loam soils with a hardpan at 20 cm require 15 mm and 25 mm of rainfall in a single wet period (rainfall separated by less than two dry days) for first- and third-order water courses, respectively, to flow (Davies. 1986). About 25 mm of rain is required to make minor water courses flow on sand and loam soils of the eastern wheatbeli of Western Australia (W. Young, pers. comm.. 1987) and other arid and semi arid areas (Slatyer, 1961; Davies, 1973; MOll, 1973). Although the rangeland soils differ from those ofCape Range. which overlie rock, the presence ora shallow hardpan makes comparison between the sites reasonable and provides the basis from which to calculate the probability of water flow into the caves on Cape Range. The probability ofa single rainfall exceeding 25 mm in any month is 0·185 (Fig. 6). Hence, on average. the caves should receive a pulse oforganic maller once every 5-4 months, and should flood deeply once every 56 months (rainfall> 150 mm); both measures have low predictability (Table I). Do schizomids, which are considered to be a circum-tropical group, possess the characteristics which would permit them to survive and respond to pulsed food input or does the cave environment buffer them from this pulse? There seems little doubt that schizomid populalions are unable to track numerically a pulsed food supply ofthe type being considered. Schi::omus vinei grows slowly and Scllizomus spp. mature slowly, are long lived (Rowland, 1972) and produce few eggs (Gravely, 1915; Rowland, 1972). Some arachnids (Araneae) have very low metabolic rates (Anderson. 1970) and these are reduced substantially during starvation (Miyashita, 1969); both these allributes have been considered to be adaptations to food scarcity (Riechen & Lockley. 1984). It would seem that schizomids may be 196 w. F. HUMPHREYS. M. ADAMS AND B. VINE similarly adapted for ·S. peradelli)'ellis [a litter dwelling schizomid] lived in a eorked tube ... with out food or water for about three months' (Gravely. 1915: 524). Age o/separation ofcaves as determined by aridity As S. villei oceupy only areas ofhigh relative humidity, it is unlikely that they can at the present time move between caves over land. Furthermore, we suggest that the area has been as arid as at present for at least 25000 years. The genesis ofthe cave systems in Cape Range has not been studied but the Tulki Limestone, in which the caves containing schizomids occur, is of Middle Miocene age (Condon. 1968; Playford e/ 01., 1975). Marine erosion terraces (? Quarternary interglacial) on Cape Range are warped, and this indicates significant Quaternary tectonism (van de Graafr, Denman & Hocking, 1975). There is no reliable dating ofthe start ofthe present arid eonditions in the region. A roek shelter at the foot of Cape Range was occupied by aboriginal people with a maritime economy from 25000-20000 BP (carbon dates). The shore line receded as the sea level fcllto - 150 m about 18000 BP. during which time the climate was less temperate and drier than at present (Bowler & Wasson. 1984). The sea level rose again and the site was occupied from 2500-430 BP (Morse, In press). The occupation site contains bones of rnurid rodents (2yzomys pedunculatus (Waite), Noromys alexis Thomas and N. IOllgicauda/us (Gould) (Morse, In press) which are now inhabitants of arid and semi-arid Australia. 2Y=0111Y5 peduIJcularus, now an inhabitant of rocky outcrops in arid Central Australia, was prescnt during both periods of human occupancy. The evidence points to Cape Range having been arid for al least 25000 years and hence the schizomid populations will have been isolated in the caves for at least that period; the area may not have been substantially wetter since the Tulki Limestone was laid down (G. Kendriek, pers. comm., 1987). Persistence of the populations Vine e/ 01. (1988) discussed some of the factors which might impinge on the populations of schizomids in Cape Range; these included pollution and changes in the catchments of the caves and hence the influx of the organic matter necessary to maintain the cave ecosystems. Cave faunas generally, and schizomids in particular, are vulnerable to changes to the water table. Schizomus wes.ml1i (Chamberlin) was eliminated from its type locally as a result oflong-term drying of the Santa Cruz River due to agricultural activities, and oases were made unsuitable for S.joshuellsis by draining (Rowland & Reddell. 1981). The North West Cape peninsula, from which Cape Range emerges, is undergoing major tourist developlnent which is dependent on water drawn from the northern part ofCape Range near the town of Exmouth. As the continuity of the water bodies in Cape Range is unknown. careful monitoring of the water table and its chemical characteristics needs to be considered with respect to the persistence of the cave faunas. Constancy Cave organisms are usually considered to live in a constant environment (Barr, 1967; Poulson & White, 1969) or one subject to regular occurrences such as spring flooding (Poulson & White, 1969). Relative constancy of temperature and humidity may be misleading, however, and caves may be highly periodic both in terms of energy input and physical environment. This periodicity may be regular (e.g. seasonal occupation by bats which raise the temperature and provide guano; THE BIOLOGY OF SCHIZOMUS IN CAPE RANGE 197 Harris, 1970; Mazanov & Harris, 1971), or irregular, as in the caves on Cape Range which receive organic matter as a result of highly unpredictable intermittent flooding. In these caves, the periodicity in both the energy input and the physical environment is limiting; the former by controlling population size and the latter by catastrophic reduction in the numbers ofschizomids (Vine et al., 1988). Community relations It is widely accepted that soil fauna, by comminution, exposes a large surface area ofdetritus to microbial attack and, by implication, accelerates decomposition (Satchell, 1974). Ifthis is the case in energy-limited caves then detritivores must reduce the energy available to themselves, reduce their production and, consequently, the energy available to the schizomids. There is, however, no firm evidence that the types of macrodecomposers present in the caves (Appendix I) accelerate significantly the subsequent decomposition oflitter. No such acceleration was found for millipedes (Nicholson, Bocock & Heal, 1976; Webb, 1977) or terrestrial isopods (Hassall, Turner & Rands, 1987); their most important role may be to transport litter down the profile to more humid locations (Hassall, Turner & Rands, 1987). Even this attribute will be of little consequence to S. vine; as they inhabit caves which are almost saturated with water. The comminution of organic matter by the detrilivores, however, may be of consequence in other ways. Gounot (1967) has shown that bacteria enrich cave muds by the production of complex nitrogenous compounds and growth factors and thus constitute an important source of food and vitamins for cavernicolous fauna. Calculating from Gounot (1967), a carbon/nitrogen ratio of 4·18 (S. D. = 0·13, II = 6) was found in the mud of six caves in France with carbon levels (0·2-0'66%) of similar order to those in Cape Range. There are reports which indicate that some troglobites cannot thrive or even survive without access to mud from the caves where they live (Poulson & White, 1969). Connec/ions of /he caves The high concentration ofcarbon dioxide and the lack ofair movement in a high proportion of caves in Cape Range would suggest that the caves generally are not connected. However, for the minority of caves which contain fauna, the biological indications are that the caves probably are connected. This is supported by the apparent similarity of the faunas in the few caves known to contain schizomids (the species have not been critically examined taxonomically; Appendix I), and by the lack of obvious genelic discontinuity between S. vinei in the different caves. In addition, three caves contain amphipods (Shot Hole Tunnel, C 103 and C 163 Wanderers' Delight). These appear to be the same cave-adapted species (B. Knott, pers. comm., 1987); the pool in C 103 from which the amphipods were collected in 1983 was dry in July 1987. Wide distributions are commonly found of small cave animals which can move through minorjoints and bedding planes in the limestone (Poulson & White, 1969). However, most of the caves known from Cape Range, including those containing schizomids and amphipods, are in an area comprising only about 12% of the potentially cavernicolous outcropping limestone (Vine ef al., 1988). The water supply for Exmouth is drawn from the northern part of the Range and the water is 2·3 times harder and 4·8 times more saline than that from C 163 (M. East & R. Wood, pers. comm., 1987). This suggests that the water body is not common throughout the range. The question will be resolved, however, only by sampling from a wider area for water, faunal and genetical analyses. 198 w. F.I-IUMPHREYS. M. ADAMS AND B. VINE This work was made possible through the assistance ofmany people who gave so generously oftheir time. I thank Malcolm East, Eva Hart. Ray Wood and Rae Young for finding schizomids and surveying C 118 and, for their help on various occasions finding caves and schizomids. Kurk Brandslatcr, Richard Curtis, Paul Medcraft, Mike Newlon, BTU Randall, Barbara Schomer and Hugh Tomlinson. Drs W. J. Gazey and V. Palermo (British Columbia) freely provided me with their programs to calculate the sequential Bayes algorithm. I am grateful for the determinations provided by Dr M. Malipatil (Museum ofArts and Sciences, Darwin; reduviids), Dr L. E. Koch (\V.A. Museum; centipedes), Dr H. Dalens (Universite Paul Sabatier, Toulouse; oniscoid isopods), Dr A. Baynes (W.A. Museum; mammal bones), Dr F. Hingston (Division of Forest Research, CSIRO, Perth; organic carbon) and Dr P. Withers (Department of Zoology, University of Western Australia; water loss). Dr B. Knott (Department of Zoology, University of Western Australia) was responsible for introducing WFH to the Cape Range schizomids and continually has been supportive of the enterprise. Kate Morse (W.A. Museum) discussed with me her archaeological data and permitted their citation. The figures were prepared by John Dell. Drs P. Withers and B. Knott and a referee suggested many improvements to a draft of this paper. REFERENCES Allison, L. E. (1965). Organic carbon. In MerllOt!.\· ill ~'oil (It/alysi.\·-Parf 2. Chemical alld microbiological prop('rlic'.~: 1367 1378. Black, CA., Evans, D. D.. Ensminger. L. E.. White. J. L. & Clark. F. E. (Eds). Madison. Wisconsin: American Society of Agronomy Inc. Anderson. J. F. (1970). Metabolic rates of spiders. Compo Biochem. Physiol. 33: 51 72. Bailey. N. T. J. (1951). On estimating the size of mobile populations from recapture data. Biometrica 38: 293 306. Barr. T. C (1967). Observations on the ecology of caves, Am. Nat. 101: 475--491. Beard. J. S. (1975). Pilbara: ,'egelaliollsun'l'y ofWe.\·remAllslralial:I.OOO.(XJOI.(.geullion.\·eril•.~.Explallatorynol(.s 10 sheer 5: rhe v('gewliofl of1"(' Pilbara area. Perth: University of Wcstcrn Australia Press. Bowler. J. M. & Wasson. R. J. (1984). Glacial age environments ofinland Australia. In L(l/l' Caillo=oic pal('odil1l(l/('s ofIhe solilherllhemispher£': [83 208. Vogel. J. C. (Ed.). Rotterdam: Balkema. Brach. V. (1976). Development ofthe whip scorpion Scilbmlll.\jlorid(JIII1.\.. with notes on behaviour and laboratory culture. Bull Slit Calif. Acad. Sci. 74: 97 lOll Briggs. T. S. & Hom. K. (1966). A new schizomid whipscorpion from California wilh nOles on Ihe others (Uropygi: Schizomidae). Pall-Pad/. £m. 42: 270-274. Briggs. T. S. & Hom. K. (1972). A cavcrnicolous whip-scorpion from thc northern Mojave Desert. California (Schizomida: Schizomidae). Occ. Pap. Calif. Amd, Sci. 0.98: I 7. Burcau of Meteorology. (1977). Raillfall stalistics. Alutralia 1977. Metric cdn. Department of Science. Burcau of Mcterology. Canberra. Bursell. E. (1964a). Environmental aspects: Humidity. III Tilt' phy.\'iology (~r If/saW I: 323-361. Rockstein. M. (Ed.). New York: Academic Press. Bursell. E. (1964b). Nitrogenous waste products of the tsetse fly. Proc. 1111. COllgr. EIIIOfllol. No. 12: 797. Bursell. E. (1970). All i"lrodliclion 10 itueci physiology. Ncw York: Academic Press. Chapman. D. G. (1951). Some properties ofthe hypergeometric distribution with applications to zoological samplecensus. U"i!". Calif. PubIs SUIlS I: 131 160. Colwell. R. K. (1974). Predictability. constancy. and contingency of periodic phenomena. EcoloJ!Y 55: 1148-1153. Condon. M. A. (1968). The gcology of the Carnarvon Basin. Westcrn Austnllia. Part III: Post-Permian stratigraphy: structurc; economic geology. Au.\·t. Bur. Min. Rl's. Bull. 77: I 68. Daniel. W. W. (1978). App!i('d 1I011-parall1elic stafi.Hics. Boston: Houghton Mimin Co. Davies. S. J. J. F. (1973). Environmental variables and the biology of native Australian anim.lls in the mulga lands. Trop. Grassland.. 7: 127-134. Davies. S. J. J. F. (1986). A biology of the desert fringe: Presidential address-I 984. J. R. Soc. Wesi. Ausi. 68: 37-50. Edney. E. B. (1977). Water balance in land arthropods. Zoophysiol. £col. No.9: 1-282. Ellis. B. M. (1976). Cave surveys. In The .fcienct' of~peleol()gy: 1-10. Ford. T. D. & Cullingford. C H. D. (Eds). London: Academic Press, Ga7..cy. W. J. & Staley. M. J. (1986). Population estimation from mark-recapture experiments using a sequential Bayes algorithm. Ecology 67: 941-951. THE BIOLOGY OF SCHIZOMUS IN CAPE RA GE 199 Gentilli, J. (1972). Au.~traliall c:Iimatic poltems. Melbourne: Nelson. Gaunal. A. (1967). La microflorc des limons argilcux soutcrrains: son activile productrice dans la biococnose cavernicolc. Anll. speleol. 22: 23-146. Gravely, F. H. (1915). Notes on Ihe habits of Indian insects. myriapoda and arachnids. Ref. Ind. Mus. II: 495-504. Hamdy. B. H. (1972). Biochemical and physiological studies ofcertain ticks (Ixodoidea). Nitrogenous excretory products of Argas (Persicargas) arborefll.\' Kaiser. Hoogslral and Kohls. and other argassid and ixodid ticks. J, med. Em. HOl/olli/u 9: 346-350. Harris. J. A. (1970). Bat-guano cave environment. Science. Wash. 169: 1342-1343. Harvey, M. S. (1988). A new troglobitic schizomid from lorth West Cape. Western Australia (Chelicerala: Schizomida). Rec. W. Allst. MilS. 14: 15-20. Hassall. M.. Turner. J. G. & Rands. M. R. \Y. (1987). Effects of terrestrial isopods on the decomposition of leaf litter. Decologio 72: 597-604. Horne. F. R. (1969). Purine excretion in five scorpions. a uropygid and centipede. BioI. BIIJI. mar. bio/. Lab. Woods Hole 137, 155-160. Humphreys. W. F. (1973). The em'ironll/enl. biology andenergetic.·J of/he wolfspider Lycosa godeffroyi(L. Koch 1865). PhD thesis. Australian National University. Humphreys. W. F. (1975). The influence ofburrowingand thermoregulatory behaviour on the water relations ofGeolycosa godeffroyi (Araneae: Lycosidae). an Australian wolf spider. Oecologia 21: 291-311. Humphreys. W. F. (1976). The population dynamics of an Australian wolf spider. Geolycosa godeffro)'i (Koch 1865) (Araneae: Lycosidae). J. Anim. Eco/. 45: 59-80. Jamieson. B. G. M. (1971). Earthworms (Megascolccidae: Oligochaeta) from Western Australian and their zoogeography. J. Zool.. Lond. 165: 471-504. Kaestner. A. (1968). Im:ertebrate :oolog)' 2. (Trans. H. Levi). New York & London: Interscience Publishers. Mallhews. P. G. (1985). Australian karst index 1985. Australian Speleological Federation Inc.. Broadway. New South Wales. Mazanov. A. & Harris. J. A. (1971). Simulation ofa cave microcosm: A trip in eco-mathematical reality. Proc. ecol. Soc. AII.\·t. 6: 116-134. McDonald, W. A. & Hogue. C. L. (1957). A new Trithyreus from southern California (Pedipalpida. Sehizomidae). Am. MIl.\'. NOIlit. 1834: 1-7. Mitchell, R. W. (1970). Total number and density estimates of some species ofcavernicolcs inhabiting Fern Cave. Texas. Anllls Spilleol. 25: 73-90. Miyashita. K. (1969). The effccts of locomotory activity. temperature and hunger on the respiratory rate of Lycosa T imig"i/a Bacs. et Str. (Araneae: Lycosidae). Appl. En,. Zool. Tokyo 4: 105-113. Morgan. G. J. (1987). Catalogue of type specimens of worms (Phyla: Platyhelminthes. Nematoda.•md Annelida) in the Western Australian Museum. Perth. Rec. IV. AilS'. Mus. 13: 357-378. Morisita. M. (1954). Estimation ofpopulation density by spacing method. Kyushu Unit' .. Fac. Sci. Mem. ES. BioI. I: 187 197. Morse. K. (1989). Mandu Mandu Creek rockshelter: Pleistocene hum;.ln coastal occupation of North West Cape. Western Australia. Arc/weol. Oceania (In press). Mott. J. J. (1973). Temporal and spatial distribution of an annual nora in an arid region of Western Australia. Trop. Gra.\"II{mds 7: 89-98. Nicholson. P. B.. Bocock, K. L. & Heal. O. W. ([976). Studies on the decomposition of the faecal pellets of a millipede (Glomeris marginara (Villers»). J. Ecol. 54: 755-766. Nobel. P. S. (1974). II/troduction to biophysical plant p"y~·iology. San Francisco: W. H. Freeman & Co. Otis. D. L.. Burnham, K. P.. White. G. C. & Anderson. D. R. (1978). Statistical inference from capture data on closed populations. Wildl. Monogr. 62: 1-135. Peters. R. H. (1983). The ecological implicatiolls ofbody si:e. Cambridge: Cambridge University Press. Playford, P. E.. Cope. R. N .. Cockbarn. A. E.. Low. G. H. & Lowry. D. C. (1975). Phanerozoic: Carnarvon Basin. IV. AIlSl. Ceol. SIITl'. Mem. 2: 269-318. Poulson. T. L. & White. W. G. (1969). The cave environment. Scietlce. Wash. 165: 971-981. Raftery, A. E.. Turet, P. & Zeh. J. E. (1988). A Bayes empirical Bayes approach to interval estimation of bowhead whale. Balael/o my.uicelUs, population size. Rept. into Commn Whal. (In press). Richardson, B. J.• Baverstock, P. R. & Adams. M. (1986). AJlo:yme elec/ropJlOresis: a hant/bookfor animal.IT-Hematics and populatio/l studie.~. Sydney: Academic Press. Ricker. W. E. (1973). Linear regressions in fishery research. J. Fish. Re.\·. Bd Caflllda30: 409~434. 200 w. F. HUMPHREYS. M. ADAMS AND B. VINE Ricker, W. E. (1975). Computation and interpretation of biological statistics of fish populations. Bull. Fi.flJ. Re.f. Bd Can. 191: 1-382. Ricehcrt. S. E. & Lockley. T. (1984). Spiders as biological control agents. A. Rf'll. Em. 29: 299-320. Robson. D. S. & Regier. H. A. (I964}. Sample size in Petersen mark-recapture experiments. Trails. Am. Fish. Soc. 93: 215 226. Rowland. J. M. (1972). The brooding habits and early development of Trilhyreus {Jell/apeltis (Cook) (Arachnida. Schizomida). Em. Nl'W!)' 83: 69-74. Rowland, J. M. & Reddell. J. R. (1979(1). The order Schizomida (Arachnida) in the New World. I. Protoschizomidac and dllmitrescoae group (Schizomidac: Schi=omus). 1. Arlie/mol. 6: 161-196. Rowland. J. M. & Reddell. J. R. (1979b). The order Schizomida (Arachnida) in the lew World. 2. simollis and brasiliellsis groups (Schizomidae: Schizomus). J. Ame/mol. 7: 89-120. Rowland. J. M. & ReddelL J. R. (1980). The order Schizomida (Arachnida) in the New World. 3. mexicallllS and pecki groups (Schizomidae: SChi=O/1/1U). J. Ame/mol. 8: 1-34. Rowland. J. M. & Reddell. J. R. (1981). The order Schizomida (Arachnida) in the New World. 4. WW(/I/igh(ortllll and brigg.~i groups and unplaced species (Schizomidae: Schi=omus). J. Arad",ol. 9: 19-46. .' SatchelL J. E. (1974). Introduction. In Biology uJplam litler decompu.~i(ioll I: 13-44. Dickenson. C. H. & Pugh. G. J. F. (Eds). London: Academic Press. Shorlhousc. D. J. (1971). Sllldie~ 011 (he biology and('Iwrgelic.f oJUroducus )'Qshenkoi (Hirula 1904). PhD Ihesis. Australian National University. Canberra. Slatyer. R. O. (1961). Methodology ofa water balance study conducted on a deserl woodland (Acacia Of/eura F. M uell.) community in Central Australia. Arid Zone Res. 16: 15-25. Sakal. R. R. & Rohlf. F. J. (1981). Biometry: /he principles and prac/ia' oJ.\·wfis(ics ill hiological research. San Francisco: W. H. Freeman & Co. Sturm. H. (1973). Zur Elhologie von Trithyreu... stllrmi Kraus (Arachnida. Pedipalpi. Schizopcltidae). Z. Tierpsychol. 33: 113-140. Thompson, H. R. (1956). Distribution of distance to the Nth neighbour in a population of randomly distributed individuals. Ecology 37: 391-394. van de Graaff. W. J. E.. Denman, P. D. & Hocking. R. M. (1975). Emerged Pleistocene marine terraces on Cape Range. Westcrn Australia. Geol. Surv. of W. AII.I·t.: Alln. Rep.: 62-70. Vinc. B.. Knott. B. & Humphreys. W. F. (1988). Observations on the environment and biology of SChi=Ol1JllS vinei (Chelicerata: Schizomida) from Cape Range, Western Austnali;.t. Re£'. W. AIISI. Mus. 14: 21~34. Webb. D. P. (1977). Regulation ofdeciduous forcstlittercomposition by soil arthropod faeces. In T1ierole oJarthropod\' ill Jorest ecosystems: 57 69. Mallerson. W. J. (Ed.). Berlin: Springer-verlag. Winston. P. W. & Bates. D. H. (1960). Saturated solutions for the control ofhumidily in biological research. Ecology 41: 232-237. Withers. P. C.. Hillman. S. $.. Drews. R. C. & Sokol. O. M. (1982). W;.l1er loss and nitrogen excretion in sharp·nosed reed frogs (Iiypl'roJius 1I11.W(IIS: Anura. Hypcroliidac). J. expo Bioi. 97: 335-343. THE BIOLOGY OF SCHIZOMUS 1 CAPE RANGE 201 Appendix I Occurrellce ofcontemporary/aulla in tile caves 011 Cape Range known /0 cOl/rain S. vine;. The list is incomplete as fell' CO/;(;'S hm:e been examinedthoroughly. Those markedas present in boldtype or/! known to sholl' adaptarion~ 10 cave dwelling. Data/or C /62, C /63 and C /67 from 1"1. East and R. Wood (peTS. comm., /987)/1 Cave number (C] Taxon 18 103 106 113 118 126 162 163 167 Annelida Lumbricidsl + + + + Arthropoda 1yriapoda Millipedes1 + + + + + + Sculigeromorphs + +' Crustacea Amphipoda4 + + + Oniscoid isopod5 + + + + + + Arachnida Schizomids + + + + + + ++ Acarina + Araneae6 + 7 +' + + +' Collembola + Apterygota Thysanura + + Insecta Blattids + + + + Isoptcra + Psocids + Crickets + Rcduviids9 + + Coleoptera + + Diptera + + + Homoptera 10 + I The type locality of Aus"opholochaetella kendrick; Jamieson 1971. is cave C 6 in Cape Range (not WAPET No.4 dccp wcll as givcn in Jamieson (1971) and Morgan (1987); (G. Kendrick; pers. comm.. 1987»). Lumbricids from thc olher cavcs have nOI been J idenlified. J Blind and white. Allothereua lesuerii (Lucas). ;I Also in C 64 (Shot Hole Tunnel). the only cave known in the Mandu Calcarenitc. s 8eddelundia sp. (Armadillidae) from CI 18 and Aus mllophiloscia sp. (Philosciidae) from CIS and CI03. They show no morphological adaptations to cave dwelling (H. Dalcns. pcrs. comm.. 1987, 1988). 6 Filistatidae (loss of pigment and leg elonga tion; M. Gray (rers. eamm.. 1987]) in C 94 (not named). Pholcidae in dolincs orc 18 and C 118. 7 Pho1cidac. ~ Miturgidac (blind; M. Gray lpcrs. comm.• 1987]).9 Ploiaria sp. (Emersinae). 10 Vagrant in cavc. II C 169 has spiders. ants, crickcts and Hamoptcra.