Bijdragen tot de Dierkunde, 52 (2): 191-199 — 1982
Amsterdam Expeditions to the West Indian Islands, Report 18.
Stygobiont Crustacea Malacostraca from geologically older
and younger Antillean Islands: a biogeographic analysis
by
Jan H. Stock
Institute of Taxonomie Zoology, University of Amsterdam,
P.O. Box 20125, 1000 HC Amsterdam, The Netherlands
Summary close coherence with geological and palaeogeo-
data. Area-species graphs for stygobiont Crustacea Malacostraca of graphic
seven islands in the southern Caribbean have been In is made compared. the present paper an attempt to It that the “constants” C and of these appears z graphs are of of islands evaluate the impact age certain on influenced by the geological time elapsed since the island’s stygofaunal diversity (the "age" being the time emergence. In older islands the values for C and z are higher
than in islands. The values for z of and that island's younger younger elapsed since the emergence above sea
older islands are much higher (0.79-0.97) than usually level). To this end, seven islands of similar obtained in literature for terrestrial animals (0.20-0.40). This and with similar climates in the be the limited faculties may explained by very dispersal of morphology K-strategists, such as stygobiont Malacostraca. southern Caribbean have been compared.
Résumé
On des des METHODS compare graphiques aréal-espèces pour Crustacés
Malacostracés stygobiontes provenant de sept îles de la Mer des Caraïbes. have been taken in three Les «constantes» C et z dans ces graphiques Stygofaunal samples
semblent influencées le écoulé être par temps géologique ways: depuis l’émergence de l’île respective. Dans le cas des îles The method. A hole is plus anciennes les valeurs aussi bien (1) Karaman-Chappuis sont plus élevées, pour
C dans le des îles récentes. Les valeurs in loose alluvia. The que pour z, que cas dug inflowing groundwater des îles, trouvées pour z anciennes ou récentes, sont de and fine is ladled out passed through a net (mesh élevées beaucoup plus (0,79-0,97) en comparaison avec celles 0.05 mm). mentionnées dans la littérature pour des animaux terrestres
Ceci The Bou-Rouch method. A hollow iron (0,20-0,40). s’explique probablement par les facultés (2)
de très limitées des tels les dispersion stratégistes-K, que probe is driven in the substrate until it reaches the Malacostracés stygobiontes. groundwater table and the groundwater is then
means of a Norton INTRODUCTION pumped up by hand-pump. (3) The Cvetkov method. A vertical plankton net the of During past 10 years (1973-1982) a team (mesh 0.05 mm) provided with a back-stroke biologists of the University of Amsterdam, occa- piston is lowered and lifted in drill holes, shafts, sionally assisted by scientists of other universities, and wells. have studied the fauna of groundwater biotas Methods (2) and (3) have been described in (cave waters, wells, springs, hyporheic and inter- more detail by Bou (1975). stitial environments) in the West Indies. Over 50 The samples are preserved in 4% neutralized islands have been sampled in a more or less formalin, sorted later in the laboratory, and trans- and uniformous systematic way. ferred to 70% ethanol. The project aims at an analysis of the of validity Taxonomie of the animal analyses groups en- a number of biogeographic models, explaining the countered in the samples taken have been, and origin of the West Indian nonmarine in fauna, will in be, published the present series of Reports
the Amsterdam on Expeditions to the West Indian *) Report 17 appeared in Bijdr. Dierk., 52 (1): 13-42 (1982). islands.
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INTRODUCTION TO THE REGRESSION oped endemic taxa (subspecies, species, and even
MODEL of marine genera) stygobionts. In several cases,
still in relatives (not necessarily ancestors) are In I a number of previous papers, have advanced existence. Elsewhere (Stock, 1981a) I have called the theory that sea-level fluctuations have been attention to the fact that such stygobionts are scenario of great significance for the evolutionary restricted to islands in which regression of the of biotas of many members groundwater (the relative sea level predominated over transgressive so-called stygobionts) of the West Indian islands Most islands of the Leeward movements. group, (Stock, 1977b, 1980a). In particular negative of the Windward and of the Greater An- group due relative changes of the sea level, either to tilles belong to this category. In the Bahamas, in- eustatic of local geological uplifting, or to drops cluding the Turks and Caicos islands, transgres- of intertidal or the water level, caused stranding than sion has been much more important regres- For ele- shallow-water communities. many faunal sion. These islands strikingly lack regression model such strandings will have been catastrophic, ments, but be at elements, may invaded, presumably a such in particular of course for sessile organisms, rather recent (post-Pleistocene) geological epoch, A of events as reef corals. testimony catastrophic by marine species, penetrating karst features that be found on by negative sea-level movements can drowned during a marine transgression. islands of the Calcareous Antilles and many **) In the West Indies, for instance, regression of the Leeward group***), in terraces of fossil evolution is demonstrated by an abundance of level. Other coral reefs above the actual sea orga- hadziid taxa of Gammaridae (Amphipoda) on stand chance nisms kind of to a were pre-adapted islands of the Antillean whereas many arc, no In of sea-level regressions. partic- surviving during hadziids have been found in the Bahamian archi-
ular those animals that (a) have a burrowing or pelago, where stygobionts are much more rare but interstitial and lack pelagic stages, life, (b) in the Antilles. anyway than the have instead brood care or pass greater part Limiting ourselves to rising islands, it would of their larval life inside the eggshell, belong to be the of their interesting to compare diversity this During the slow process of regressive group. stygofauna with palaeogeographic data. If the animals could movements of the sea level, these major factor influencing the evolution of stygo- survive in the humid macro- and micro-interstitia bionts in the Antilles would be the repeated trans- of coral rubble, gravel or coarse sand, and evolve and regressions of the sea level during the Pleisto- vicariant into groundwater in- through processes number of cene, one would expect a comparable habitants. In the interstitial biotope, a very gradual in islands of different taxa geological age. marine shift in can be observed, from fully salinity If the other hand the Plio-Miocene on regres- brackish near the waterline, through higher up sions are the most important factor in the evolu- In of the shore, to almost fresh more inland. many tion of the West Indian stygofauna, the older arid the Antillean islands, having (nowadays) an islands must have a significantly more diverse inland — most climate, the salinity even of the than islands. groundwater biota the younger mesohaline groundwaters — stays at oligo- or
do not levels, so that real fresh groundwaters
THE ISLANDS exist. The scenario in which vicariant evolution of stranded (uplifted) populations plays an im- For testing the two alternatives brought forward in the colonization of portant role groundwaters, in the last lines of the preceding paragraph, we is called the model references, see regression (for in the have selected 7 islands (6 Leeward group Stock, 1980a). plus Barbados) from a total of some 50 islands islands in the West Indies have devel- Many in sampled during our fieldwork program 1973-
The islands with each other 1982. selected agree
in that they have been subject to tectonic uplift **) Used in the sense of Weyl, 1966. and have calcareous More- of 8. important deposits. ***) Used in the sense Wagenaar Hummelinck, 1981:
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the over, islands are their THE AGE OF THE comparable by geo- ISLANDS of the graphic position, altitude, area same mag- The Netherlands islands nitude, and semi-arid climate. Leeward (Aruba, Bo-
called The six islands of the Leeward north Curaçao, often the A-B-C group, naire, islands)
as shallow shoals on a volcanic basement of the South American mainland, are Aruba, Cu- emerged the late Miocene the Los La during (De Buisonjé, raçao, Bonaire, Roques group, Tor- 1974). and in tuga, La Blanquilla. The seventh island, Bar- Geotectonic uplifts the post-Miocene periods raised abrasion bados, is selected because it is the southernmost are evidenced by terraces, ex-
raised coral calcareous island of the north-south branch of cavated surf lines, and reefs, presently
found altitudes to 150 m above level. the Antillean arc (this branch consists mainly of at up sea from each volcanic, non-calcareous, islands ). The position of The islands are separated other by very
the islands in this and water to 900 waters occur seven compared paper, deep (700 fms). Deep
certain other localities mentioned in the text, is also between Curaçao and Bonaire and the main-
shown in fig. 1. land. Aruba, however, is separated from the South
American a much shal- Every single island, or group of coherent keys, Paraguana peninsula by
the and from the lower straits over 100 is isolated from next group con- (slightly fms).
tinent by deep water (400 fms and more), with To the A-B-C islands of the Netherlands Lee-
the exception of Aruba (vide infra). ward group belong, in addition to the three larger
the small A number of islands of Leeward group are islands, two very ones, Klein Curaçao, to
do not the of and Klein excluded from our analysis because they east Curacao, Bonaire, to the
fulfill all is not west of Bonaire. Of Klein Bonaire is requirements: Margarita mainly these, sepa-
and is water from rated shallow and straits from calcareous not separated by deep by a very narrow
American Los and the South continent; Testigos are Bonaire, forms a biogeographical unit with it.
Aves and La Orchila On other not calcareous; the group the hand, Klein Curaçao is surrounded
have not been sampled by our team. by deep waters (300-800 fms), and constitutes
in size the In general, and relation to the of a separate unit. We have not sampled Klein Cu-
island table 10 to 100 island its remains (cf. I), samples per raçao, so stygofauna unknown. Thus,
have been considered sufficient for a more detailed for practical purposes, our data pertain to three of from Zoogeographie analysis; only La Tortuga a the five islands only: Aruba, Curaçao, and Bo-
smaller number of 7 was available. naire. The fact samples ( ) that Aruba lies on the South
American continental shelf, does not seem to have T ableI
influenced its which Island size. stygofauna, has close rela-
to that of Curaçao and lacks South Amer- 2 tionships area (km ) maximum altitude (m) ican elements.
Aruba 1901) 1891) According to Weyl (1966: 273) the A-B-C Curaçao 472 1) 375 l) islands form with the Venezuelan islands Bonaire 281 l) 241 l) (Aves,
2 Los Roques «<1000 ) 1163) Los Roques, La Orchila, La Tortuga, La Blan-
La Blanquilla 52.5 *) «;60 5) and Los quilla Hermanos) an "independent part La Tortuga 171 4 ) 30 ®)-40 4) of the Antillean 7 8 (in translation). Barbados 430 ) 340 ) orogenesis" The igneous-metamorphic basement of La Blan- *) Hoetink, 1969. is often similar 2 quilla compared with rocks in the ) Méndez, 1978.
s U.S. Defence A-B-C islands ) Mapping Agency, Hydrographie Center, (Rutten, 1931, 1940; Schubert & Washington, Chart 24444, revised ed., 1974. Moticska, 1972, 1973). The igneous-metamorphic *) Williams, 1980. s complex, consisting of a ) Hummelinck, 1940. trondhjemite batholith,
8 ) U.S. Defence Mapping Center, is at the island's Agency, Hydrographie nowadays exposed western part. Chart revised Washington, 24441, ed., 1973. It is of possibly upper-Cretaceous (Schubert 7 age ) Weyl, 1966. & Moticska, in 8 Directorate of Colonial 1972, 1973). Mainly the eastern ) Surveys (D.C.S.), 955, London, Barbados 2nd 1965. of the island, map 5, ed., part two uplifted coral terraces are
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of localities mentioned in the text. Fig. 1. The West Indies, with the names the
40 exposed (7 and 30 m above actual sea level; Although the archipelago consists of over
and these Maloney, 1971), of Pleistocene-Recent age (Zu- islands keys, are situated on a single
the loanga, 1950). Although geological history common, very shallow submerged platform (water
of La Blanquilla is less completely known than depths of at most 20 fms, usually much less),
that of the A-B-C is from the islands Aves islands, my interpretation separated next (the group
that the extent and altitudinal uplift of the fossil in the west and La Orchila in the east) by waters
small in terraces shows that a portion of the island, of over 500 fms depth. Similar depths are
the and the South Amer- comprising the highest top (ca. 60 m above sea found between Roques
remained the ican the level), emerged during Pleistocene- continent. So, for purpose of this study
Recent sea-level rise. the entire Roques group is considered a single
La is oceanic without internal Blanquilla separated by very deep waters isolated, island, geo-
(100 to >2000 fms) from La Orchila in the graphical barriers.
and Grenada in the and is west, east, by deep waters La Tortuga "geologically new; it belongs to
in south. (>800 fms) from Margarita the It the Quaternary period" (Williams, 1980: 117,
must therefore be in It considered an oceanic island. translation). has undergone a double uplift, The Roques archipelago is much younger. It resulting in two elevated coral terraces (Ernst,
probably emerged as late as the early Quaternary 1886, as quoted by Williams, 1980).
(viz., the igneous-metamorphic rocks of Gran Barbados is one of the islands with actually
whereas the rest of the the tectonic 3 Roque ), archipelago, more greatest uplift (4.3 cm 10 years, than 40 islands and keys, emerged even later see Matthews, 1973). In the Pleistocene, it was
1978: This makes the covered (Méndez, 41-46). A-B-C still by the sea (Weyl, 1966: 270), thus
and also La its is to that of the islands, possibly Blanquilla, some age comparable Roques group
6 than 14-10 years older the Roques archipelago. and La Tortuga.
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mentioned THE STYGOFAUNAL MALACOSTRACA The stygofauna of Aruba, as before,
is devoid of South American elements (such as The composition of the malacostracan stygofauna Bathynellacea or limnic Bogidiellidae ), notwith- of the seven islands under consideration is standing the fact that Aruba has been connected enumerated in table II. These records are based with Paraguana (Venezuela) during the Pleis- on the of Stock 1976b, 1977a, papers (1976a, tocene. and the 1977b, 1977c, 1979, 1980b, 1981b) on
Gammaridae, Ingolfiellidae, Microparasellidae, RESULTS AND DISCUSSION Bogidiellidae, and Thermosbaenacea, of Kensley
The that been examined from the (1981) on the Paranthuridae, of Botosaneanu & samples have
islands in in Stock the Cirolanidae and seven are enumerated (1979, 1982) on cya- question
and data. table III. thurids, on unpublished The latter
data the in Bar- from certain category comprises on occurrence Although the number of samples
less bados of a blind, undescribed species of Quadrivi- islands is smaller than that from others, the sio (Amphipoda, Gammaridae). Oculate, epigean diverse stygofaunal composition of the Roques,
of this several islands La and Barbados does not seem to be species genus occur on (in- Tortuga, cluding Aruba, Bonaire, and Barbados), but do accidental. not need to be considered in the present context. The very high incidence of stygobiont Mala-
The islands limited number of in is also and be Roques have a costraca Curaçao striking, may
Malacostraca of which the of the rather stygiobiont (4 species), consequence complex paleoge- at least 3 belong to genera that contain both marine ography of the island, which is composed of two and limnic species. So far, no taxonomie descrip- nuclei melted into one island during the Pleisto- tions of the Roques stygofauna have been pub- Holocene (Stock, 1977b). In general, the in-
cidence A-B-C islands lished. of occurrence is high on the
From the island La La Tortuga, a single unde- and Tortuga, low on the Roques and Barbados, scribed of Gammaridae has and La species been collected, intermediate on Blanquilla. The reason for which is locally quite abundant. these obvious differences remains uncertain.
Table II
Crustacea Malacostraca Leeward and Barbados. Stygofaunal in the group
= D = (A Amphipoda; I = Isopoda; T = Thermosbaenacea; Decapoda).
taxa with "continental" taxa in which also marine species are known
species only
(A) (A) (A) (I) (A) (I) (I) group (A) (1) (T) (D) (I) (D) (A) Quadrivisio la iel Metaniphargus Arubolana Psammogammarus lf Curassanthura Microparasellidae Microcerberus Typhlatya Saliweckelia blind Actogidiella Ingo Anthuridae Haloshaena Alpheopsis Total
Aruba 111 00001100000 5
Curaçao 301 11012110110 13
Bonaire 001 01002002100 7
Los Roques 000 10000101001 4
La Blanquilla 000 00001000100 2
La Tortuga 000 01000000000 1
Barbados 001 00100000000 2
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Table III on a logarithmic scale (in which A is the area
Number of number of in km2 of each island and of samples per island, and samples S the number stygo- containing Crustacea Malacostraca. stygobiont biont function species or subspecies). This power
model usually is significantly better than other No. of No. of % of alternatives The samples samples samples (Sugihara, 1981). resulting plots containing with lie approximately on a straight line, according to Malacostraca Malacostraca the equation S = CA*. In fact, two lines ( 1 and 2
in Aruba- fig. 2) one for La Blanquilla- Aruba 56 27 48 emerge, another for La Curaçao 111 75 68 Bonaire-Curaçao, Tortuga-Barba-
Bonaire 93 28 30 dos-Los Roques. The first line slopes slightly Los Roques 24 2 8 value for and steeper (has a higher z) runs at a La Blanquilla 10 2 20 level value for La Tortuga 7 3 43 higher (has a higher C) than the
Barbados 32 3 9 second line.
The area-species graphs confirm in general the
results obtained for other and by previous authors, As to the number of taxa on specific sub-
of and on other in that each the groups animals, islands, specific level on of islands (table II) we the plots lie approximately on a straight line. reach the following conclusions: Although the meaning of differences in value of For Aruba, Curaçao, Bonaire and La Blanquilla, the C and is still controversial number of taxa to be parameters z highly the total proves directly Connor (see & 1979, for an elegant related to the size of each island. The number of McCoy, of deserve further La is review), a couple points taxa on Barbados, Tortuga, and the Roques may
or if wishes. the first consideration, speculation one lower than expected (fig. 2). Of group,
~ and C ~ — are both 2 (1) Cj —30, 2 58 the smallest island (La Blanquilla, 52.5 km ) nega-
tive. As well known, the value for C, a constant, has the lowest number of taxa (2), followed by
varies taxa and to the the next smallest island km2 5 greatly among according (Aruba, 190 , taxa), unit of measurement. The fact that the values and Bonaire (281 km 2 7 taxa), whereas the area ,
2 largest, Curaçao (472 km ) has the highest num- ber of taxa (13). Thus, a good correlation exists
Bo- between the area of La Blanquilla, Aruba,
and 12.4 and the naire, Curaçao (1.4 : 5 : : 7.4)
malacostracan number of stygobiont taxa (2 : 5 :
13 : 7).
of Although the Roques group consists many
Lee- more islands and keys than the Netherlands
and is about ward group (>40 versus 5), 1
times larger (1500 km 2 ) than the A-B-C islands
together (943 km 2 ), its stygobiont Crustacean
fauna is clearly less diverse. The figures for the
Roques compare well with the low diversity ob-
served in the stygofauna of Barbados, with its
km2 430 and 336 m of elevation of about the
km2 same size as Curaçao (472 and 372 m), but
with only 2 stygobiont species of Crustacea, versus
13 in Curaçao.
Fig. 2. The area-species curves (logarithmic scale) for
One in accordance the method stygobiont Crustacea Malacostraca of seven West Indian may plot, to islands: B1 = La Blanquilla; A = Aruba; B = Bonaire; elaborated by Darlington (1957) and later C = Curaçao; T = La Tortuga; Ba = Barbados; R = MacArthur Wilson A S by & (1967), against Los Roques.
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for C and C x are lower than in most of colonized marine invaders is 2 cases being by equal
recorded in Anglo-Saxon literature, depends partly for each island, irrespective of the distance to the
km 2 instead mi2 The 2 on the use of of use of km next and the of the . landmass, thereby major part
causes a shift of the graphs towards the abscissa aquatic colonizers differs from terrestrial animal
in invaders. (£mi + 2 log 1.609), but no change
C is it is La z. However, not merely smaller, The different values of C for the Blan-
in and the negative our two graphs. In general, nega- quilla-Curaçao line La Tortuga-Los Roques
in values do tell much in curves on line be tive not us very can, my opinion, explained only by a
but the values for different related distance a logarithmic scale, negative striking-chance, not to
least inland to the but to the time of existence of C seem to permit at one supposition: source, the
islands islands: islands have waters of isolated (non-continental) can geologically older had a
when the island has — hit develop a stygofauna only a greater (longer) striking-chance, and once
certain minimum size. If below the supposed — a longer time for adaptation to subterranean
devel- in than critical size, no inland stygofauna comes to conditions, resulting a higher diversity,
Based the data in the critical islands of opment. on fig. 2, a younger age.
2 size (A at S = 1) is approximately 34 km for (3) For both the La Blanquilla-Curaçao line
2 in the La graph 1, and 180 km for graph 2. (line 1 fig. 2) and Tortuga-Los Roques line the (2) The value for C for graph 2 is lower than for (line 2), value for z is much larger than
usual ~ to MacArthur & Wilson [ z ~ 0.79, calculated as graph 1. According Zj 0.97, 2 (log
5 A' 1 (1967: 17) C depends largely on the popula- + log C) log "]. Empirically determined
the innate diver- values for often 0.20-0.40 tion density as well as on species z range from (gener-
whereas its value in alized to a sity in a given taxon, decreases 2 0.25). Darlington (1957) obtained
value those regions where the quality of the environ- arithmetically a z of 0.301, while Preston
is When these broad showed that the value ment poorer. generalizations (1962) z resulting from a
the the West Indian should are adapted to situation for lognormal distribution be 0.26. According
islands under that to MacArthur Wilson consideration, one might put & (1967: 18), an increase
the lower the of z above 0.26 "can number of niches or habitats on an be explained as the outcome
island the C will of the of biotas of islands ("monotonous islands") lower breaking up large into
be. At least the climate and the elevation of the semi-isolated communities due to the increase
in islands cannot be of great influence, since these topographic barriers and environmental varia-
such It feasible tion on islands". This formulation are largely comparable. seems however, appears that geologically spoken older islands have devel- to apply only marginally to the situation in the
a finer web of niches, than rela- seven Antillean islands studied in the oped ecological present
recent rise to value First of of the studied tively islands, giving a higher paper. all, none islands can
be of C in the older islands. called "large islands". Secondly, "environ- mental variation" Still another factor influencing C is the degree is expected to be low for ground-
water each island. This — of isolation of factor amongst inhabitants, one of the characteristics of others related the distance the centre its Of to to nearest groundwaters being stability. course, it
of — must be added that least dispersal or source population may be impor- at the factor salinity in tant for, terrestrial animals that have to be the of the islands say, groundwaters may widely
to islands. For fluctuate. The transported (dispersed) emerging presence, on certain islands such as the Antillean stygofauna, this factor is considered Curaçao of "semi-isolated communities" has been of since it is assumed that this demonstrated in no importance, by Stock, 1977b, a microgeo- fauna has marine evolved predominantly from graphic distribution analysis of hadziid Gamma-
that have lived in the ridae ancestors surrounding sea, (Amphipoda). in accordance with the model. The The fact that is much regression 2 so very higher for both distance to the the is and line 1 and in source (i.e. sea) zero, line 2 the present analysis, than in the is The striking-chance very large. potential most previous studies, must be related to biological
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ACKNOWLEDGEMENTS peculiarities of most stygofaunal Malacostraca.
animals These are fieldwork based has been typically having The on which the present study is for limited of low number of financially supported by the Netherlands Foundation the very means dispersal (a Advancement of Tropical Research (WOTRO), The Hague; As large eggs, absence of pelagic stages). repeat- the Treub Maatschappij, Utrecht; the Beijerinck-Popping of edly shown by various authors, a high degree Fonds, Amsterdam; the Amsterdamse Universiteits Vereni-
Amsterdam; and the Fonds Landbouw Hogeschool, endemism, or formation of isolated and morpho- ging, Wageningen. in logically distinct populations limited geo- The has carried with the sampling program been out
is in this of members of team: Dr. Lazare graphical areas, very pronounced group assistance the following our
Botosaneanu, Drs. Nico Mrs. Sylvia van Lies- of animals. I have no doubt that this factor is Broodbakker, hout, Mr. Jos Notenboom, Dr. Steven Weinberg, and Mrs. for chiefly responsible the high value of z for Francisca Weinberg. the Malacostraca the southern Carib- stygobiont on The organization of the fieldwork in Venezuela has greatly
rendered of The bean islands. benefited from support by H.M. Embassy
Netherlands, Caracas, in particular by Dr. Ir. Th. P. M. have value (4) Finally we to consider the lower de Wit, Agricultural Attaché.
for in the La of Fundación Cientifica z Tortuga-Barbados-Los Roques The hospitality and support the
line. for the Los Roques, Caracas (Drs. Roger Laughlin and Ernesto In general, the value z conforms to Weil), and of the Fundación La Salle de Ciencias Naturales, rule "The better the geographic isolation, the Campus de Margarita (Drs. J. J. Bocaranda, J. Otaola, formulated from higher z". This rule, typically a H. Villegas), is gratefully acknowledged. The captain and
of de be crew R.V. Dona Teresa (Punta Piedras, Margarita) dispersionalist's viewpoint, can modified, I of the have been great assistance on out-islands. to include also historical factors into this think, made The fieldwork on the A-B-C islands has been formulation: "The older the island in (and, con- possible through the kind cooperation of the Caribbean
the niches Marine Biological Institute, Curaçao (Dr. Ingvar Kristensen), sequence, more or ecological subregions of of and on Barbados, the Bellairs Research Institute are developed), the higher z". McGill University (Dr. Finn Sander). in This is agreement with the data obtained
Line in from our present analysis. 1 fig. 2,
representing the older islands La Blanquilla- REFERENCES
Aruba-Bonaire-Curaçao, has a higher value for z BOTOSANEANU, L. & J. H. STOCK, 1979. Amsterdam Expedi- than (0.97), line 2 (La Tortuga-Barbados-Los tions to the West Indian Islands, Report 6. Arubolana imula first cirolanid n. gen., n. sp., the hypogean isopod Roques; z ~ 0.79). crustacean found in the Lesser Antilles. Bijdr. Dierk.,
49 (2): 227-233.
& 1982. Amsterdam the West , Expeditions to CONCLUSION Indian Islands, Report 17. Les Cyathura stygobies (Iso-
poda, Anthuridea) et surtout celles des Grandes et des The difference in the value for C in the two Petites Antilles. Bijdr. Dierk., 52 (1): 13-42. of islands lines 1 and 2 groups represented by Bou, C, 1975. Les méthodes de récolte dans les eaux sou-
29 in fig. 2, as well as the higher value for z of terraines interstitielles. Annls. Spéléol., (4): 611-619.
BUISONJÉ, P. H. DE, 1974. Neogene and Quaternary geology line 1, both point in the direction that area-species of Aruba, Curaçao and Bonaire. Uitg. natuurwet. Studie- curves give a good indication for the relative kring Suriname Ned. Ant., 78: 1-293, maps 1-4.
time since the island CONNOR, E. F. & E. D. MCCOY, 1979. The statistics and geological age (the elapsed biology of the species-area relationship. Am. Nat., 113 emerged above sea level) of Caribbean islands. (6): 791-833. The of the Netherlands Leeward emergence DARLINGTON, P. J., 1957. Zoogeography: the geographical
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Received: 30 June 1982
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