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n Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie - Verspreiding en habitats van , tussengasheerslak van die peervormige bot , in Suid-Afrika : research and review article

Volume 21, Issue 4
  • ISSN : 0254-3486
  • E-ISSN: 2222-4173

Abstract

<b>Distribution and habitats of <i>Bulinus tropicus</i>, snail intermediate host of the conical fluke <i>Calicophoron microbothrium</i>, in South Africa</b> <br>This paper focuses on the geographical distribution and the habitats of <i>Bulinus tropicus</i>, the snail intermediate host of the conical fluke, <i>Calicophoron microbothrium</i>. <i>Bulinus tropicus&lt;/i&gt; is the freshwater snail species with the most extensive geographical distribution, as reflected by the collection sites of the 7 992 samples currently on record in the database of the National Freshwater Snail Collection (NFSC) of South Africa. The presence of this species was noted by collectors in a total of 14 different types of waterbodies, however, the largest number of samples was collected in dams and brooks and in habitats of which the water was described as standing, clear and fresh. The effect size was calculated for each variable separately to determine its importance in governing the distribution of this species. The data in the database were further processed and adapted to construct an integrated decision tree. This is a statistical model allowing the selection of those variables which can maximally discriminate between the frequency of occurrence of a given species and all other species in the database under specific conditions. The success of <i>B. tropicus</i>, as reflected by its extensive geographical distribution, can most probably be ascribed to the circumstance that population dynamic studies by various authors have shown, without any doubt, that it is highly <i>r</i>-selected and that it additionally has the ability to survive conditions of drought for relatively long periods. It does however, appear as if its limited tolerance to water with a relatively low conductivity could possibly be a limiting factor for its colonisation of specific areas in South Africa. As intermediate host of <i>C. microbothrium&lt;/i&gt; which causes paramphistomosis in domestic stock and sometimes can lead to great losses, the wide distribution of <i>B. tropicus&lt;/i&gt; has economic implications, especially for residents of informal, rural settlements whose livestock traditionally forms an integral part of their daily existence.

Hierdie artikel fokus op die geografiese verspreiding en habitats van <i>Bulinus tropicus</i>, die slaktussengasheer van die peervormige bot, <i>Calicophoron microbothrium</i>. <i>Bulinus tropicus&lt;/i&gt; is die varswaterslakspesie met verreweg die wydste geografiese verspreiding, soos gereflekteer deur die vindplekke van die 7 992 monsters wat tans in die databasis van die Nasionale Varswaterslakversameling (NVV) van Suid-Afrika op rekord is. Die voorkoms van hierdie spesie is deur versamelaars in 'n totaal van 14 waterliggaamtipes opgeteken, maar die grootste getal monsters is in damme en spruite en in habitats waarvan die water as staande, helder en vars beskryf is, versamel. Die effekgrootte van elke veranderlike is afsonderlik bereken om die rol daarvan in die bepaling van die verspreiding van hierdie spesie vas te stel. Die data in die databasis is verder verwerk en aangepas om 'n geïntegreerde besluitnemingsboom saam te stel. Dit is 'n statistiese model waarvolgens 'n seleksie van veranderlikes gemaak kan word wat maksimaal kan diskrimineer tussen die voorkomsfrekwensie van 'n gegewe spesie en die res van die spesies in die databasis. Die sukses van <i>B. tropicus&lt;/i&gt; soos gereflekteer deur sy omvangryke geografiese verspreiding, is waarskynlik toe te skryf aan die omstandigheid dat hierdie spesie grootliks <i>r</i>-geselekteerd is soos onteenseglik in bevolkingsdinamikastudies deur verskeie outeurs bevind is. Daarbenewens beskik die spesie oor'n besondere vermoë om opdroging van 'n habitat vir relatief lang tydperke te kan oorleef. Dit kom egter voor asof sy beperkte verdraagsaamheid ten opsigte van water met 'n relatief lae geleidingsvermoë, moontlik as 'n beperkende faktor vir sy besetting van bepaalde gebiede in Suid-Afrika mag optree. As tussengasheer vir <i>C. microbothrium</i>, wat paramphistomose by vee veroorsaak en soms tot groot verliese kan lei, het die wye verspreiding van <i>B. tropicus&lt;/i&gt; in Suid-Afrika egter ook ekonomiese implikasies, veral vir inwoners van informele, landelike nedersettings wie se vee tradisioneel 'n integrale deel van hul daaglikse bestaan uitmaak.

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/content/aknat/21/4/EJC20319
2002-12-01
2019-08-24

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