Past and present climates : owl pellet composition as an indicator of local climatic change

Van Niekerk, Christiaan Hermanus (2001-03)

Thesis (MScAgric)--University of Stellenbosch, 2001.

Thesis

ENGLISH ABSTRACT: During Holocene times a considerable deposit of barn owl pellet material accumulated in the Hot Pot Cave at De Hoop Nature Reserve on the southern coast of the Western Cape Province, South Africa. An excavation of this accumulation has yielded information on barn owl prey species over the past some two millennia. Four distinct layers were excavated and radiocarbon-dated to AD 381, AD 615, AD 991 and AD 1417. The micromammalian cranial contents of these layers were compared to material from two pellet collections that represent modem bam owl predation at De Hoop (AD 2000). Comparisons were made from three perspectives: (1) physical size measurements of certain cranial parameters, (2) micromammal community species composition and (3) community structure indices, such as the Shannon-Wiener diversity index, Simpson's diversity index and the species equitability index. By extrapolating from known ecological distribution information of the relevant prey species, these data were used to recreate the local climate at the time of the accumulation of the layers. The results were compared to other palaeoclimate models for the region as a test of validity. It was found that the lower two layers of the sequence represented mild conditions with possibly more grass than in recent times, while the upper layers represented cool weather with a possible increase in scrub. AD 381 was found to be somewhat dry and mild, AD 615 to be the wettest level and possibly milder than AD 381, AD 991 to be the coolest of all the levels and dryest of the ancient levels, AD 1417 to be somewhat cool and probably drier than AD 615, but wetter than AD 381, and AD 2000 to be the mildest and dryest of all levels, with the artificial influence of nearby agricultural activities evident.

AFRIKAANSE OPSOMMING: Tydens die Holoseen tydperk het 'n relatief groot hoeveelheid nonnietjie-uil bolusmateriaal versamel in Hot Pot Grot in die De Hoop Natuurreservaat aan die Wes-Kaapse suidkus, Suid- Afrika. Opgrawings van hierdie bolusversameling het waardevolle en insiggewende inligting aandie lig gebring rakende nonnetjie-uil prooi tydens ongeveer die afgelope tweeduisend jaar. Vier defnitiewe lae is opgegrawe en deur radiodatering is die lae se datums vasgestelop 381, 615, 991 en 1417 n.e. Deur gebruik te maak van kraniale kriteria. is die mikrosoogdier inhoud van die opgrawings vergelyk met dié van twee bolusversamelings wat die huidige uilprooi (2000 n.Ci) in De Hoop verteenwoordig. Die vergelykings is op drie maniere getref: (1) fisiese grootternates van sekere kraniale parameters, (2) species-samestelling van die mikrosoogdiergemeenskap en (3) gemeenskap-struktuur indekse nl. die Shannon-Wiener diversiteitsindeks, Simpson se diversiteitsindeks en die species-gelykheid indeks. Deur ekstrapolasie vanaf bekende ekologiese verspreidingsinligting rakende die betrokke species, is hierdie data gebruik om die klimaat van daardie tydperke te herskep op 'n streeksbasis en vergelyk met ander paleoklimaat-modelle om die geldigheid daarvan te beproef. Die resultate het getoon dat die onderste (oudste) twee lae warmer toestande met moontlik meer gras verteenwoordig, terwyl die boonste twee lae koeler weer met moontlik meer bosse verteenwoordig. Daar is verder gevind dat 381 n.e. redelik droog en warm was, 615 n.e. die natste laag en moontlik warmer as 381 n.e., 991 n.e. die koudste van al die lae en droogste van die grot-lae, 1417 n.e. redelik koel en moontlik droëer as 615 n.e., maar natter as 381 n.e., en 2000 n.C. die warmste en droogste van al die lae, met kunsmatige invloed van nabygeleë landbou aktiwiteite.

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