| Summary: | Thesis (MSc)--Stellenbosch University, 2003. === ENGLISH ABSTRACT: The geometric tortoise, Psammobates geometricus, found in the Western Cape, South
Africa, is one of the world's rarest tortoises. At present, it is only known from five
isolated geographical areas, one being the Worcester-Tulbagh Valley. The primary
aims of my study were to determine the status of geometric tortoise subpopulations
along the Nl highway in the Worcester Valley, to determine the population structure
of these subpopulations and, if necessary, to provide recommendations for the
mitigation ofNI highway-induced impacts on geometric tortoise subpopulations
along the road. All Renosterveld remnants along the Nl between Du Toitskloof and
Worcester were surveyed for the presence of geometric tortoises, and tortoise density
and population structure were determined for each remnant that supports tortoises.
Two geometric tortoise subpopulations on opposite sides of the Nl were identified. In
the larger remnant of the two, females dominated both the subadult and adult classes,
whereas in the other remnant male frequency was slightly higher than female
frequency for the adult class only. In both remnants, adult females were significantly
larger than adult males in mean carapace length. Mean body mass for adult females
and males also differed significantly in both remnants. Analysis of habitat quality
showed that both remnants supporting the geometric tortoise are seriously infested by
encroaching indigenous and alien plants. The barrier effect of the Nl highway can be
mitigated by constructing underpasses, linking the two remnants on opposite sides of
the road. Furthermore, road mortality of tortoises can be avoided by erecting tortoise
proof fencing along appropriate sections of the highway in the Worcester Valley. By linking the remnants, the largest single area available to the geometric tortoise in the
Worcester Valley will also be formed. An additional aim of my study was to
investigate the correspondence of geometric tortoise density in individual habitat
remnants to the West-to-East change in vegetation composition/characteristics
occurring along the Nl in the Worcester Valley. Vegetation
composition/characteristics were thus determined in all remnants also surveyed for
tortoises. The West-to-East change in vegetation composition/characteristics of the
study area indicates that there is a transition from Renosterveld in the West to karroid
veld in the East. === AFRIKAANSE OPSOMMING: Die geometriese skilpad, Psammobates geometrieus, wat in die Wes-Kaap, Suid-
Afrika, voorkom, is een van die wêreld se skaarste skilpaaie. Vandag word hierdie
skilpad net nog in vyf geïsoleerde geografiese streke gekry, een van hulle die
Worcester-Tulbagh Vallei. Die primêre doel van my studie was om die status van
geometriese skilpad subpopulasies langs die Nl snelweg in die Worcester Vallei te
ondersoek en om die populasiestruktuur van hierdie subpopulasies te bepaal. Verder
was die doelook, om aanbevelings te maak oor hoe die impakte van die pad op die
geometriese skilpad subpopulasies langs die Nl verminder kan word. Al die
Renosterveld oorblyfsels langs die Nl tussen Du Toitskloof en Worcester, en binne
die bekende gebied van die geometriese skilpad, is deursoek vir geometriese
skilpaaie. Populasiedigtheid en populasiestruktuur van die skilpaaie is bepaal vir elke
oorblyfsel wat skilpaaie bevat. Twee geometriese skilpad subpopulasies is gekryaan
teenoorgestelde kante van die Nl. In die groter oorblyfsel, het wyfies albei die
onvolwasse en volwasse klasse gedomineer. In die ander oorblyfsel is gevind dat die
frekwensie van mannetjies ietwat hoër was as die frekwensie van wyfies, maar vir
slegs die volwasse kategorie. Binne albei oorblyfsels is gevind dat volwassse wyfies
betekenisvol groter in gemiddelde doplengte is as volwasse mannetjies. Gemiddelde
liggaamsgewig het ook betekenisvol verskil tussen volwasse wyfies en mannetjies in
albei oorblyfsels. 'n Analise van habitatkwaliteit het gewys dat beide oorblyfsels wat
die geometriese skilpad ondersteun grootliks ingeneem is deur inheemse indringers,
sowel as uitheemse plante. Die versperrings effek van die Nl snelweg kan verminder
word deur duikwege te skep wat die twee ooblyfsels, op teenoorgestelde kante van die pad, verbind. Bowendien, deur 'n ondeurdringbare heining langs passende dele
van die snelweg in die Worcester Vallei op te rig, sal skilpadmortaliteit vermy word.
Deur oorblyfsels te verbind, salook die grootste enkele area, beskibaar aan die
geometriese skilpad in die Worcester Vallei, gevorm word. 'n Addisionele doel van
hierdie studie was om veranderinge in vegetasie langs 'n wes-na-oos gradient binne
die studie area te korreleer met die teenwoordigheid van skilpaaie langs hierdie
gradient. Vegetasie samestelling/eienskappe is dus bepaal vir elke oorblyfsel wat
deursoek is vir skilpaaie. Die wes-na-oos verandering in vegetasie
samestelling/eienskappe binne die studie area wys dat daar 'n oorgang van
Renosterveld in die weste na 'n karooagtige veld in die ooste is.
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