Thesis (PhD)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: This study tested several hypotheses regarding various aspects of
habitat use by Cape clawless otters Aonyx capensis, in various
habitats. The hypotheses, namely that A. capensis do not select
any prey types, prey sizes or habitat type were tested. Habitat
type was investigated at a scale that enabled separating the
effects of types of riparian vegetation, geomorphology and
anthropogenic influences. Aspects of the resource dispersion
hypothesis (RDH) and optimal foraging theory were tested. This was
done in both the marine and freshwater environments.
The annual and seasonal diets of A. capensis in the Olifants
and Eerste Rivers, Western Cape Province, are described. Crabs
were found to be the main prey and fish the second most important
prey of A. capensis in both the rivers during all seasons. The
percentage occurrence of prey of A. capensis in both rivers,
showed an increase in the amount of crab in summer and a
corresponding decrease in the number of fish eaten. The seasonal
fluctuation in crabs and fish found in the spraints (faeces),
corresponded with the expected frequencies as determined from
trapping.
Seven A. capensis were caught in the two rivers and radiotracked
between 1993 and 1995. Total home range length varied from
4.9 to 54.1 km and core home range length from 0.2 to 9.8 km.
Total area of water used ranged from 4.9 to 1062.5 ha and core
area used from 1.1 to 138.9 ha. As predicted using the RDH total
home range length was correlated to mean reed bed nearest
neighbour distance. The otters were typically active from dawn for
2.6 h and moved a mean of 0.9 km. They were also typically active from sunset for a mean of 2.3 h moving a mean of 1.3 km. They
were found to select for areas with boulders and/or reed beds.
Aonyx capensis were found to be mainly solitary in all the
habitats. The pattern of female home ranges was suggestive of
territoriality. The males, however, had overlapping home ranges,
both with other males and females.
From spraint analysis and direct observations, the seasonal
diet and foraging behaviour of A. capensis feeding in the surf
zone in False Bay, Western Cape Province, were determined. The
most common prey species during all seasons was Cape rock crab
Plagusia chabrus. Diversity of prey was lowest in winter,
increasing through the seasons from spring to autumn. Foraging
behaviour data support the optimal breathing hypothesis, which
predicts that both surface and dive times should increase for
dives of greater depths. However, diving efficiency did not
decrease with increasing depth, nor did percentage time at the
surface increase with increasing depth. These results are
contrary to the optimal breathing hypothesis.
How A. capensis use their habitat in the presence of
potential competitors spotted-necked otters Lutra maculicollis
and water mongooses Atilax paludinosus was also determined by
investigating their trophic overlap during enforced cohabitation
in a relatively small range during drought conditions.
The analysis of trophic overlap showed that even during
enforced cohabitation in a relatively small range during drought
conditions, there was separation of diets of A. capensis, L.
maculicollis and A. paludinosus.
These results and their implications for conservation
management are discussed. / AFRIKAANSE OPSOMMING: Hierdie studie het 'n aantal hipoteses oor verskeie aspekte van
habitat gebruik deur die Groototter Aonyx capensis, in
verskillende habitatte, getoets. Die nul hipotese, nl. dat A.
capensis nie vir enige prooitipe, prooigrootte of habitat-tipe
selekteer nie, is getoets. Habitat tipe is ondersoek teen 'n
skaalgrootte wat dit moontlik gemaak het om die effekte van tipes
oewer plantegroei, geomorfologie en antropogeniese invloede van
mekaar te skei. Aspekte van die hulpbron verspreiding hipotese
(HVH) en optimale kossoek gedrag, is in beide die varswater en
seewater omgewing getoets.
Die jaarlikse en seiseonale diëte van A. capens~s in die
Olifants and Eerste Riviere in die Wes-Kaap Provinsie, word
beskryf. Daar is gevind dat krappe die hoof prooi en vis die
tweede mees belangrike prooi van A. capensis in beide riviere,
gedurende al die seisoene, was. Die persentasie A. capensis prooi
teenwoordig in beide riviere het 'n toename in krap getalle in die
somer en 'n ooreenstemmende afname in die hoeveelheid vis wat
geeet word getoon. Die seisoenale verandering van krap en vis wat
in die keutels (mis) voorkom, het ooreengestem met die verwagte
frekwensies soos bepaal deur fangste in fuike.
Sewe A. capensis is in die twee riviere gevang en tussen 1993
en 1995 d.m.v. radiosenders gevolg. Die totale tuisgebied lengte
het van 4.9 tot 54.1 km, en die kern tuisgebied lengte van 0.2 tot
9.8 km, gewissel. Die totale area water wat gebruik is het van 4.9
tot 1062.5 ha, en kerngebiede van 1.1 tot 138.9 ha gewissel. Soos
voorspel deur gebruik van die HVH, was die totale tuisgebied
lengte gekorreleer met die gemiddelde rietbedding naaste-buurman
analise afstand.
Die otters was tipies aktief vanaf sonsopkoms vir 2.6 ure en
het dan 'n gemiddeld van 0.9 km beweeg. Hulle was ook tipies
aktief vanaf sonsondergang vir 'n gemiddeld van 2.3 ure en het dan
gemiddeld 1.3 km beweeg. Daar is gevind dat hulle selekteer vir
areas met rotse en areas met rietbeddings. Dit is ook gevind dat A. capens~s in alle habitatte hoofsaaklik alleenlopend is. Die
wyfies se tuisgebied-patroon het op territorialiteit gedui, terwyl
die manlike diere se tuisgebiede oorvleuel het met beide dié van
wyfies, en met dié van ander mannetjies.
Die seisoenale dieet en kossoekgedrag van A. capensis wat in
die brander sone van Valsbaai, Wes-Kaap Provinsie, voed, is deur
keutel analise en direkte waarneming bepaal. Die mees algemene
prooi spesie gedurende al die seisoene was die Kaapse rotskrap
Plagusia chabrus. Prooi diversiteit was die laagste in winter en
het toegeneem vanaf lente tot herfs. Kossoekgedrag gegewens
ondersteun die optimale asemhalings hipotese, wat voorspel dat
beide oppervlak- en duik tye toeneem met dieper duike. Duik
effektiwiteit het egter nie afgeneem met toenemende diepte nie,
en persentasie tyd op die oppervlakte het ook nie toegeneem met
toenemende diepte nie. Dit is dus in teenstelling met die
optimale asemhalings hipotese.
Hoe A. capensis hul habitat in die teenwoordigheid van
potesieele kompiteerders nl. Klein otters Lutra maculicollis, en
Water muishonde Atilax paludinosus gebruik, is ook bepaal. Dit is
gedoen deur hul trofiese oorvleueling gedurende noodgedwonge
saamleef, veroorsaak deur droogte kondisies in 'n relatiewe klein
tuisgebied, te ondersoek.
Die resultate van die trofiese oorvleueling analise het getoon
dat selfs gedurende noodgedwonge saamleef gedurende droogte
toestande in 'n relatiewe klein gebied, daar 'n verskil was in die
diëte van A. capensis, L. maculicollis and A. paludinosus.
Hierdie resultate en hul implikasies vir bewaringsbestuur word
bespreek.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52293 |
| Date | 12 1900 |
| Creators | Somers, Michael John |
| Contributors | Nel, J. A. J., Kruuk, H., Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 224 p. : ill. |
| Rights | Stellenbosch University |
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