Diversity of terrestrial isopod species in the Chambi National Park (Kasserine, Tunisia)

Diversity of terrestrial isopods across habitats and altitude was studied in the National Park of Chambi (central Tunisia). Samples were collected over five years in seven sites (S1-S7), within an altitudinal range from 750 to 1,500m a.s.l. Twelve species belonging to five families were identified, with one endemic species (Porcellio djahizi) to this area, and three species were present in all sites (P.djahizi, Leptotrichus panzerii and Armadillidium tunisiense). Agnaridae represented by Hemilepistus reaumurii species was the most abundant family (58.77%) and found in only one site. Our results showed differences in species richness between sites. Indeed, S2 and S3 (900 and 1,050m) showed the highest species richness with 11 species each. This result validates the hypothesis of mid-elevational richness peak and contradicts the theory of large sampling regimes in determining the relationship between species richness and elevation. Terrestrial isopod species richness in the Chambi Mountain tends to decrease with altitude: 11 species in S2 and S3 to four species in S7. The highest Shannon-Wiener diversity index value was observed in S2 (H=3.21 bits). Canonical correspondence analysis revealed that H.reaumurii was positively correlated with temperature whereas A.tunisiense and P.djahizi were the only species positively correlated with altitude. Resume Nous avons etudie la diversite des isopodes terrestres dans divers habitats et a differentes altitudes dans le Parc National de Chambi, au centre de la Tunisie. Les echantillons furent collectes pendant cinq ans sur sept sites (S1-S7), entre 750 et 1500m d'altitude. Nous avons identifie 12especes appartenant a 5familles, dont une espece endemique de la region (Porcellio djahizi) et trois especes qui etaient presentes sur tous les sites (Porcellio djahizi, Leptotrichus panzerii et A.tunisiense). Les Agnaridae, representes par Hemilepistus reaumurii, etaient la famille la plus abondante (58,77%) et ne se trouvaient que sur un site. Nos resultats ont montre des differences de richesse en especes entre les sites. En effet, S2 et S3 (900 et 1,050m) avaient la plus grande richesse avec 11especes chacun. Ce resultat valide l'hypothese d'un pic de richesse a moyenne altitude et contredit la theorie des grands echantillonnages pour determiner la relation entre richesse en especes etaltitude. La richesse en especes d'isopodes terrestres sur le mont Chambi tend a diminuer avec l'altitude, passant de 11especes en S2 et S3 a 4especes en S7. La plus grande valeur de l'Indice de diversite de Shannon-Wiener a ete observee en S2 (H=3,21). L'analyse canonique des correspondances a revele que H.reaumurii etait positivement lie a la temperature alors que A.tunisiense et P.djahizi etaient les seules especes positivement liees a l'altitude.