View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Horizon / Pleins textes Ecological observations on the caddisflies (Insecta : Trichoptera) from Trinidad and Tobago (W. Indies) Lazare BOTOSANEANU (1) and Dexter SAKAL (2) ABSTRACT The paper presents the ecological results of a campaign of intensive sampling of Trichoptera in a number of localities in Trinidad and Tobago (taxonomie, faunisfic, and biogeographic resulls are published elsewhere [BOTOSA- NEANU and ALKINS-KOO, in press]). A general review is given of the sampling localities? most of these being in the Northern Range of Trinidad (the ” vertebral column” of fhis study being sampling and observations in the successive stream orders in the catchment of Rio Guanapo), with other sampling localities in Central and South Trinidad, and in Tobago. Autecological notes - but also observations on ethology and.trophic guilds - are presented for 42 species (slightly more than 50 species being presently known from the two islands). These redis are condensed in a Table in which lhe succession of species corresponds 10 a gradient - from species caught only or mainly in Springs and in Isl order streams, 10 those inhabiting Vih order waler courses or calm streams of the lowlands. In fhe final par1 of ihe paper are firstly discussed aspects concerning the longitudinal succession (zonation) essentially in the water courses of the Northern Range of Trinidad, the conclusions being thaf there is a clear-tuf limit befween Rhithron and Polarnon, that diversity and biomasses are highest in IIId order and in Upper reaches of IVth order streams of densely forested amas? that an association of rafher few species inhabits the Crenal and the Epirhifhral, and that the fauna is suddenly impoverished starting with the inferior reach of streams of the IVth order; suppositions are advanced concerning the factors responsible for this longitudinal succession; the results are in agreement- with the “ intermediate - disturbance hypothesis” as applied 10 lotit ecosystems. Certain regularities have been observed in the distribution of species of Chimarra, Smicridea, and Helicopsyche. Finally, are tackled aspects relative 10 the distribution of species belonging 10 Ihe various trophic guilds; our knowledge of trophic peculiarities of caddisfly larvae is often far from Perfect, and, in the bibliography, the limits between guilds were too often ioo rigidly drawn, many species being - or being able 10 become in certain circumstances - generalists able 10 exploit several types of resources. A11 trophic guilds are represented in a11 stream orders in a Northern Range bassin (there are, nevertheless, also peculiar situations). A conclusion _ based on observation of ihe balance beiween trophic resources and caddisfly populations development - is that the importance of Ihe trophic facfor for the distribution of populations along water courses has probably often been exaggeraied. On several points throughout the paper, comparisons are made with the relafively fez results already obtained in the West Indies and in Central America. KEY WORDS : Trichoptera - Autecology - Zonation - Trophic factor - Trinidad and Tobago - Caribbean - Tropical. (1) Insfituut uoor Taxonomische Zoologie, Uniuersifeit uan Amsterdam, Plantage Middenlaan 64, 1018 DH Amsterdam, The Nether- lands. (2) Department of Zoology, Uniuersity of the West Indies, St. Augustine, Trinidad and Tobago (IV. 1.). Rev. hydrohiol. trop. 25 (3): 197-207 (1992). 198 l.. BOTOSANEANU, D. SAKAL RÉSUMÉ ORZ~ER~~ATI~NS ÉCOLOGIQUES SUR LES TRICHOPTÈRES (INSECTA : TRICHOPTERA) DE TRINIDAD ET TOBAGO Le travail présente les résultats écologiques d’une campagne de récoltes intensives de trichoptères dans un nombre dP localités à Trinidad et Tobago (les résultats taxonomiques, faunisliques et biogèographiques son1 publiés ailleurs [BOTOSANEANU and ALKINS-KOO, sous presse]). Un aperçu général est donné des localités où les récoltes ont été r@alisées, surtout dans les bassins du Northern Range de Trinidad (la «colonne vertébrale» de cette étude étant représentée par les récoltes ef observations dans les ((stream orders >isuccessifs du bassin du rio Guanapo), mais aussi au Trinidad central et méridional, et à Tobago. Des noies autécologiques, mais aussi éthologiques et se rapporfanf à l’appartenance aux <<trophic guilds» sont présentées pour 42 espèces (un peu plus de 50 espèces étant actuellement connues pour les deux iles). Ces résultats sont condensés dans un tableau dans lequel la succession des espèces correspond à un gradient - depuis celles capfurées uniquement dans des sources ou dans des ruisselets du Ier ordre, jusqu’ù celles caractérisant les cours d’eau du T/e ordre ou bien les ruisseaux calmes des basses altitudes. Dans le chapifre final sont d’abord discutés des aspects ayant trait ù la succession longitudinale (zonation) essentiellement dans les cours d’eau du Northern Range de Trlnidad, avec la conclusion de l’existence d’yne nette limite entre Rhithron ef Potamon, d’une diversité et de biomasses maximales dans les ruisseaux du IlIe ordre et dans le cours supérieur de ceux du IT7e ordre des zones densément boisées, d’une association peu riche en espèces peuplant le Crénal et I’Épirhilhral, et d’une faune brusquement appauvrie à partir du cours inférieur des ruisseaux du IV? ordre; des suppositions sont avancées concernant les facteurs impliqués dans cette succession longitudinale; les résultats sont en accord avec la (( intermediate - disturbance hypothesis » appliquée aux systèmes lotiques. Une certaine régularité a été observée dans la distribution d’espéces appartenant aux genres Chimarra, Smicridea, et Helic.opsyche. Sont enfin abordas des aspects concernant la distribution des espèces appartenant à divers «guildes trophiques»; on aifire l’altention sur le fait que notre connaissance des pariicularités trophiques des larves de Trichoptères est souvent imparfaite, et que, dans la bibliographie, les limites entre «guildes~~ ont été trop souvent trop rigidement tracées, de nombreuses espèces élan1 - ou pouvant devenir - des généralistes capables d’exploiter plusieurs types de ressources. Tous les guildes trophiques sont représentés dans tous les stream orders dans un bassin du Northern Range, mais cependanf des cas particuliers existent. On aboutit à la conclusion - basée sur l’observation des relations entre ressources trophiques et développement de populations de trichopfères - que l’importance du facteur trophique dans la distribution des populations le long des cours d’eau a probablement souvent été exagérée. Sur plusieurs aspecis? des comparaisons sonf faites avec les résultats peu nombreux obtenus ailleurs aux Antilles ou en Amérique centrale. MOTS CLÉS : Trichopteres - -4utécologie - Zonation - Fac.teur trophique - Trinidad et Tobago - Caraïbes - Tropical. INTRODUCTION In every locality also the aquatic inst.ars were sear- ched for, picked by hand or wit.h a forceps, observa- tions were made on the populations in their habitats, In April 1991 the authors (sometimes with others : and t.he necessary effort was done for obtaining as see Acknowledgements) have intensively sampled many as possible correct associations. About 40 spe- Trichoptera in a number of carefully selected locali- cies were named in the above mentioned publication ties in Trinidad and Tobago. The results of this (the fauna of Trinidad and Tobago slightly exceeds mainly taxonomie, faunistic., and biogeographic 50 species in the present, state of our knowledge). study - for which also Trinidad and Tobago mate- Some 5 000 “ Perfect ” adult specimens were exami- rial m t-he USNM (Washingt.on) and in the Depart- ned, as well as large numbers of larvae, pupae, ment of Zoology, University of the W. Indies at St. “ metamorphotypes ” and pharate adults. Augustine was examined - are published in BOTO- The Northern Range of Trinidad is ‘an excellent SANEANU and ALKINS-1<00'(in press) and the reader area for study of running water insects. These low may find there also a complete list of localities. mount.ains (maximum elevations slightly above Adults were sampled mainly during t.he night. with 900 m, length of the chain ca 75 km) represent the a portable UV-lamp, but in some localities, also direct Cont>inuation of the Coast Range of eastern during the day. It is clear t,hat sampling adults, espe- Venezuela and thus stand as the extreme outpost of cially by light, gives a much more accurate idea on the eastern branch of the Andean mountain system ; the caddisfly fauna of a locality than bottom sam- we have here a deeply dissected mountain range pling, enabling also accurate specific identifications. with a marked East -West trend, composed of meta- Rev. hydrobiol. frop. 25 (.3) : 397-207 (1992). ECOLOGY OF THE CADDISFLIES FROM TRINIDAD AND TOBAGO 199 morphic rocks (BARR et SAUNDERS, 1965). A rather growth of filament.ous algae; the flow regime is very large number of streams arise - sometimes, maybe, astat.ic, frequent spates having visible effects on t.he at altitudes as high as c.a 700-800 m - from the sou- fauna which may be flushed away in large propor- thern slopes of the Range ; the length of t,heir catch- tions : our observations in April and *July 1991 ; the n1ent.s is of the order of 10-20 km. Their water is temperature varied bet.ween 23 and 25 OC during an collected in most cases by River Caroni, the main April day. In an order V river t,he change is, again, water course of t.he island, Bowing from E to W at important : about 12 m wide, fairly deep, the very the Range’s foot. Shorter or much shorter are the turbid (brownish) wat,er flowing smoothly on a sub- streams arising from the N face of the Range, the strate represented mainly by silt, without apparent mountain sloping here directly down to the Coast.. aquatic veget.ation, and between banks covered by Most of our sampling locahtles are in the Nort.hern grass with sparse trees; the river has here certainly Range, the “ vertebral column ” of this study being highly astat.ic thermie and flow regimes; during an sampling and observations in t.he watershed of River April day the water temperature varied between 24 Guanapo, located in the central part of t,he Range.