Syrphidae-Of-Pollardstown-Fen-2002
Total Page：16
File Type：pdf, Size：1020Kb
_196_ Bull. Ir. biogeog. Soc. No. 26 em2) AN ANNOTATED LIST OF TIIE SYRPIIIDAE (DIPTERA) OF POLLARDSTOWN FEN, CO. KII,DARE, IRELAND Martin C. D. Speight ResearchBranch, Naional Park and WiAW, 7 Ety Place, Dublin 2, Irelnd. Introduction PollardstownFen, in Co. Kildare, may be known as a site of scientific interest, but little has beenpublished on its fauna and flora. This is inevitably particularly true of its invertebrate fauna. The presenttext provides a list of the speciesof one family of flies, the Syrphidae,or hoverflies, known from PollardstownFen, togetherwith somecomment on that list. The hoverfliescollected from PollardstownFen tota;l77 species,as comparedwith 94 for Co. Kildare in general(Speight, 2000). The Irish list for this fly family now comprises178 species. Very few of the syrphid recordsfrom the fen have beenpublished previously. One exceptionis the occurrence of Platycheirus amplus Curran, which was, at the time, the frst published record for this speciesin Europe (Speightand Vockeroth, 1988). Detailed information on the Irish syrphid speciesis availableelsewhere, and has beenbrought togetherby Speight(2000), so the commentspresented here are more concernedwith what the hoverfly faunaof the Fen may tell us about the Fen, than with the speciesthemselves. Essentially,the text is focussedon the questionof whether the speciesobserved reflect the habitas observed.The potential contribution of PollardstownFen habitatsto maintenanceof syqphiddiversity, within the local landscape,is also considered.These processes are mediated by the data coded into the Syrph the Net (StN) databasespreadsheets. Examples of the use of the StN databasein interpretationof specieslists are provided by Speightand Castella(2001a). Methods Collection of hoverflies from PollardstownFen has beencarried out by direct methodsi.e. use of a hand net to collect the adult insectsfrom flowers etc, and a sweepnet to collect them from low-growing vegetation.These processes have beenaugmented latterly by use of Malaise traps and, to a minor extent, emergencetraps. The recordsspan the period 1975-2001and -t97- Bull. Ir. biogeog.Soc. No.26 determinationshave been carried out by the author. The product of this collecting activity is a list of the syrphid speciesobserved on the Fen, which can be usedfor comparisonwith the list of speciespredicted to occur on the Fen. The nomenclatureused follows Speightand Castella (2001b), updatedas necessary. Given that habitatassociations of the Irish speciesare known and the Pollardstownsyrphid fauna can be regardedas a subsetof the Irish syrphid fauna, the Irish speciesassociated with the habitatspresent on the Fen togethercomprise a list of the syrphidsthat would be predicted to occur on the Fen. This list of predictedspecies can then be comparedwith the list of species observed,following the basic proceduredescribed in Speightet al. (2000\. Using the methodologyemployed here, productionof a list of the speciespredicted to occur on a site involves the use of a list of the habitatcategories present on that site. And, in order to use the StN databasefor predicting the fauna, the habitatcategories referred !o require to be thoseemployed in the database.All habitatcategories referred to in the databaseare defined in is Macrohabitatsglossary (see Speight a al.,200la) and habitatsurvey ofthe Fen has been carried out (during 2000 anri 2001) using thosedefinitions. Results The list of syrphid speciesobserved is given in Appendix 1. The syrphid macro-habitat categoriesobserved are as follows:- forest categories: - Fraxinus, overmature/mature/saplings,with springs,drainage ditches, flushesand streams. - conifer plantation, with drainagedirches. - isolatedmature/sapling Fraxinus and Salix. - Atlantic scrub: Ulex thickets. wetland categories: - transitionmire, with springsand flushes. - acid fen, with flushes, pools and drainageditches. - rich fen, with springs, flushes, streams,pools and drainageditches. - reed beds, with springs, flushes, streamsand drainageditches. - tall sedgebeds, with springs, flushes, streamsand drainageditches. _198_ Bull. Ir. biogeog.Soc. No.26 - tall herb communities. openground categories: - unimproved,humid/flooded oligotrophic Molinia grassland,with springs, streams,flushes, temporarypools and drainageditches, lightly-grazedby horsesand cattle. - improvedgrassland, grazed by cattle, with drainageditches. - intensivegrassland. other categories: - hedges. Using the habitat associationdata coded into tle Macrohabitatsfite of the StN databasethe numberof observedspecies associated with eachof thesehabitat categories can be totalled. The number of specieson the Irish and Co. Kildare lists associatedwith eachof thesehabitat categoriescan similarly be totalled. Taking the Co. Kildare list as the speciespool from which the PollardstownFen syrphid fauna is derived, the numberof Kildare speciesassociated with eachof the Pollardstownhabiats is taken as the number of speciespredicted to occur with each of thosehabitats on any fen in the Co. Kildare region. Similarly, taking the Irish syrphid list as the speciespool from which the PollardstownFen syrphid fauna is derived, the number of Irish speciesassociated with eachof the Pollardstownhabitas is taken as the numberof species predictedto occur with each of thosehabitats on any fen nationally. Of the 7'l syrphid speciesrecorded from the Fen, the occurrenceof only three (i.e. lessthan 5% of the species)would not be predictedthere from their habitatassociations. The three exceptions are: Cheilosia bergenstanuniBecker, C. variabilis (Panzer) and Paragas haemorrhousMeigen. They are excludedfrom further analysisof the PollardstownFen fauna but are consideredbriefly in Appendix 2. Basingprediction on all of the habitaS representedthere, PollardstownFen would be expected to support 85 of the speciesrecorded from Co. Kildare and fully 133 of the speciesknown from lreland in general.This would meanthat 85% of the expectedKildare speciesare recordedfrom the Fen (including its periphery), as comparedwith 557oof the expectedIrish speciesin general.But some of the habitatcategories observed on the Fen and at its periphery cannotrealistically be regardedas either natural/semi-naturalor wetland-related.Conifer plantation, Ulex thickeu, hedges,improved grasslandand intensivegrassland would fall into -r99- BULL.Ir. biogeog.Soc. No.26 this ca@goryand have, for thesereasons, been excludedfrom further analysis.Suffice it to say that noneof the syrphidspecies recorded from PollardstownFen would be predictedto disappearfrom the Fen if the coniferplantation habitat were lost from the Fen. Similarly, loss of improved grasslandand intensivegrassland from the Fen's periphery would be predictedto causeloss of only one species,Eupeodes corollae (Fabr.), from the existingspecies list. The contributionof thesehabitats to maintainingthe presentfauna of the site could thusbe regarded as negligible. Loss of hedgesand lJlex scrub from the Fen periphery might be expectedto causeloss of four species:Baccha elongata (Fabr.), Dasysyrphus albostriatus (Fall6n), MelangynaLasiophthalnn (Zetterstedt) and Meliscaevacinctell,a (Zetterstedt). The proportionof the predicredsyrphid fauna that hasbeen observed at PollardstownFen tbr habitasother thanconifer plantation, improved and intensivegrassland, ULex scrub and hedges, is shownin Table 1, at both levelsof prediction- regional(i.e. Co. Kildare)and national.The habitatsrepresented by the more-or-lessisolated trees of Fraxinus and Salix found scattered aroundthe Fen are also omitted,since they are predictedto havevery few associatedspecies, all of which would be predictedto occuron the Fen in associationwith other habitatscovered by Table I. Table 1. Numberof syrphidspecies in the observedand predictedlists for PollardstownFen, associatedwith eachof varioushabitats occurrinq on the fen. Habitat number of species 7o of predicted spp observed observed predicted predicted Kildare IRL Kildare IRL Fraxinus forest 25 28 35 89 1l transition mire l-) 14 15 93 87 acid fen 35 38 44 92 '19 rich fen 44 48 54 92 82 reed beds l9 22 26 86 '73 tall sedgebeds JJ 36 40 92 83 tall herb communities r6 19 2I 84 76 unimproved Mo linia gr assland 42 48 63 88 <1 -200- Bull. Ir. biogeog. Soc. No.26 In Table 2, microhabitatdata are summarised,for the observedand predictedsyrphid faunasof PollardstownFen, using the information coded into the Microsite Featuresfile of the StN database(see Speight et al.,200lb). The speciescovered are thoseassociated with the habitats coveredby Table I, but taken all together,rather than habitatby habitat. The categories recognisedare not true micro-habitats,but physical featuresof sites (micrositefeatures) that are usedas proxies for micro-habitats.The array of categoriesshown is a selectionof those coveredby the StN database,in which speciesassociations for more than 80 micro-sitefeature categoriesare coded. Table 2. Number of syrphid speciesin the observedand predictedlists for Pollardstownfen, associatedwith eachof various micro-habitatsimicrositefeatures. Microsite feature Nurnber of species olp as io observed (o) predlcted (p) terrestrial timber 2 3 67 overmature uees 4 JI tree foliage t4 23 6r understorey trees 5 8 63 shrubs/bushes/saplings l0 r6 63 lianas 4 5 80 tall herbJayer plants (on) 20 )R 11 low-growing herb-layer plants (on) 11 1< t5 within herb-layer plant tissues 8 t6 50 ground-surfacedebris I7 18 94 nests of social insects 2 50 grass-rootzone 10 13 77 aqualrc on emergent plants l3 20 65 on submerged plants 4 t2 33 submerged