Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Soft, serene insect songs add an intrinsic aesthetic value to the landscape. Yet these songs also
have an important biological relevance. Acoustic signals across the landscape carry a multitude
of localized information allowing organisms to communicate invisibly within their
environment. Ensifera are cryptic participants of nocturnal soundscapes, contributing to
ambient acoustics through their diverse range of proclamation songs. Although not without
inherent risks and constraints, the single most important function of signalling is sexual
advertising and pair formation. In order for acoustic communication to be effective, signals
must maintain their encoded information so as to lead to positive phonotaxis in the receiver
towards the emitter. In any given environment, communication is constrained by various local
abiotic and biotic factors, resulting in Ensifera utilizing acoustic niches, shifting species songs
spectrally, spatially and temporally for their optimal propagation in the environment. Besides the importance of Ensifera songs from an ethological point of view, the
multitude of species-specific signals provide an acoustic tapestry representing species diversity
across ecological gradients and over time. Acoustic inventorying and monitoring of the
landscape can reflect the environmental status of ecological systems, from natural to disturbed
by human influence. In contrast to traditional survey techniques, sound recording and
interpretation is a non-invasive method that allows for the detection and classification of highly
cryptic, yet insightful indicators of ecosystem change. Here, acoustic monitoring was used
across diverse ecological gradients to improve understanding of species diversity patterns, and
how they change in response to both natural gradients and in response to the human dominated
landscape mosaic.
This study was undertaken in three geographic locations from tropical rain forest of
Brunei, Borneo, to the landscapemosaic of plantation forestry in KwaZulu-Natal, South Africa, and to the botanically rich, mountain fynbos region of the Cape Floristic Region, also in South
Africa. Each region provided a diverse and particular landscape to test the value of acoustic
surveys for determining local diversity patterns across natural gradients and to assess the value
of the technique for assessing the impact human influence across landscapes.
In tropical rainforests, an entire acoustic guild was investigated to determine how
acoustic species partition their acoustic communication channels spectrally, temporally and
spatially, to avoid acoustic interference. The overall assemblage showed considerable spectral
partitioning. Diurnally active species showed low temporal niche overlap, whereas nocturnal
species did not utilize temporal partitioning. Lack of nocturnal temporal partitioning suggests
other mechanisms of acoustic avoidance are sufficient to avoid acoustic overlap, or that there
are insufficient cues to partition nocturnal acoustic environments. Acoustic species also utilized
spatial partitioning, with distinct acoustic assemblages at vertical heights and with elevation.
Utilization of a range of different strategies allow many species to communicate with
conspecifics with little or no interference from other species in a signal rich environment. Acoustic profiling was also undertaken in KwaZulu-Natal, South Africa, across a
plantation forestry landscape mosaic with diverse ecological gradients containing both alien
and indigenous vegetation, as well as boarding large natural protected areas. Areas covered in
alien timber or non-endemic grass were devoid of acoustic signals. Managed areas that were
mowed and heavily grazed were not effective in maintaining the natural complement of
nocturnal acoustic species. Within natural vegetation patches inside plantations, acoustic
species richness increased with plant heterogeneity and patch size. Patches of indigenous
vegetation within the plantation matrix effectively reduced the contrast of transformed
landscapes with surrounding natural areas, with indigenous forest patches containing a highly
characteristic acoustic species assemblage. Within the botanically rich, mountain fynbos region of the Cape Floristic Region,
acoustic profiling was conducted across gradients of elevation, season and vegetation. Across
these gradients, katydid acoustic signals were identified and characterized for the first time.
This resulted in the discovery of two new katydid species and a novel sound producing structure
in a carabid beetle, a species previously unknown to produce sound. Acoustic diversity across
seasonal and elevational gradients increased with increasing temperatures. Climatic variability
along the elevational gradient produced variation in seasonal phenology. Katydids also utilized
high frequency acoustic signals, which is probably an adaptation to overcome background
noise from wind, so prevalent in this area. Furthermore, despite producing conspicuous signals
for mate attraction and pair formation, katydids were found not to be part of bat-eared fox diet,
an insectivorous, nocturnal predator that uses its characteristic large ears to detect sounds made
by invertebrate prey. This study shows the value of using acoustic emissions from katydids to identify
acoustic diversity patterns across ecological gradients and in response to human impacts on the
landscape. / AFRIKAANSE OPSOMMING: Sagte, rustige insekliedjies voeg ‘n intrinsieke estetiese waarde aan die landskap. Tog is hierdie
liedjies ook van belangrike biologiese waarde. Akoestiese seine oor die landskap dra ‘n
magdom plaaslike inligting wat organismes in staat stel om onsigbaar te kommunikeer binne
hul omgewing. Langhoringsprinkane is kriptiese deelnemers van die nagtelike klankomgewing
en dra by tot die omringende akoestiek deur hul verskeidenheid van proklamasieliedjies.
Alhoewel dit nie sonder inherente risiko’s en beperkings is nie, is die belangrikste funksie van
seine seksuele advertering en paarvorming. Vir akoestiese kommunikasie om effektief te wees,
moet seine hul geënkodeerde inligting handhaaf, sodat dit sal lei tot positiewe fonotaksis in die
ontvanger teenoor die emittor. In enige gegewe omgewing, word kommunikasie beperk deur
verskeie plaaslike abiotiese en biotiese faktore. Dit lei tot die gebruik van akoestiese nisse deur
langhoringsprinkane, wat hulle liedjies spektraal, ruimtelik en temporeel aanpas vir optimale
verspreiding in die omgewing. Benewens die belang van die langhoringsprinkaan liedjies uit ʼn etologiese oogpunt,
bied die menigte spesie-spesifieke seine ʼn akoestiese tapisserie wat spesiesdiversiteit
verteenwoordig oor ekologiese gradiënte en oor tyd. Akoestiese opname en monitering van die
landskap kan die omgewingstoestand van ekologiese stelsels weerspieël, van natuurlike tot
menslik versteurde stelsels. In teenstelling met tradisionele opnametegnieke, is klankopname
en interpretasie ʼn nie-indringende metode wat dit moontlik maak om hoogs kriptiese, nog
insiggewende indikators van ekosisteemverandering op te spoor en te klassifiseer. In hierdie
studie is akoestiese monitering gebruik oor diverse ekologiese gradiënte om ons begrip te
verbeter van spesies diversiteitspatrone, en hoe dit verander in reaksie op beide natuurlike
gradiënte en in reaksie op die menslik gedomineerde landskapmosaïek. Hierdie studie is onderneem in drie geografiese liggings: tropiese reënwoud in Brunei,
Borneo, die landskapmosaïek van plantasiebosbou in KwaZulu-Natal, Suid-Afrika, en die
plantryke, bergfynbos-streek van die Kaap Floristiese Streek, ook in Suid-Afrika. Elke streek
het 'n diverse en besondere landskap verskaf om die waarde van akoestiese opnames te toets
vir die bepaling van plaaslike diversiteitspatrone in natuurlike gradiënte, asook om die waarde
van die tegniek te bepaal vir die beoordeling van die impak van menslike invloed oor
landskappe. In tropiese reënwoude, is 'n hele akoestiese gilde ondersoek om te bepaal hoe akoestiese
spesies hul akoestiese kommunikasiekanale spektraal, ruimtelik en temporeel verdeel om
akoestiese inmenging te vermy. Die algehele groep het aansienlike spektrale verdeling getoon.
Dagaktiewe spesies het lae temporele nisoorvleueling getoon, terwyl nagtelike spesie nie
temporele verdeling benut het nie. Gebrek aan nagtelike temporele verdeling dui daarop dat
ander meganismes van akoestiese vermyding voldoende is om akoestiese oorvleueling te
vermy, of dat daar onvoldoende seine is om nagtelike akoestiese omgewings te verdeel.
Akoestiese spesies het ook ruimtelike verdeling benut, met verskillende akoestiese
spesiesversamelings op vertikale hoogtes en met hoogte bo seevlak. Die gebruik van 'n
verskeidenheid van strategieë maak dit moontlik vir spesies om te kommunikeer met min of
geen inmenging van ander spesies in 'n seinryke omgewing. Akoestiese profielsamestelling is ook onderneem in KwaZulu-Natal, Suid-Afrika, oor
'n plantasiebosbou landskapmosaïek met diverse ekologiese gradiënte wat beide uitheemse en
inheemse plantegroei, sowel as groot, natuurlike, beskermde gebiede ingesluit het. Gebiede
wat bestaan het uit uitheemse timmerhoutbome of nie-endemiese gras, was heeltemal sonder
akoestiese seine. Bestuursgebiede wat gesny en swaar bewei was, het nie doeltreffend die
natuurlike komplement van nagtelike akoestiese spesies gehandhaaf nie. In natuurlike plantegroei fragmente binne plantasies, het akoestiese spesiesrykheid toegeneem met
plantverskeidenheid en fragmentgrootte. Fragmente van inheemse plantegroei binne die
plantasiematriks het effektief die kontras van getransformeerde landskappe met omliggende
natuurlike gebiede verminder, en inheemse woudefragmente het hoogs kenmerkende
akoestiese spesiesversamelings gehad. Binne die plantryke bergfynbosstreek van die Kaap Floristiese Streek, was akoestiese
profielsamestelling gedoen oor gradiënte van hoogte bo seevlak, seisoen en plantegroei. Oor
hierdie gradiënte, is langhoringsprinkaan akoestiese seine geïdentifiseer en gekenmerk vir die
eerste keer. Dit het gelei tot die ontdekking van twee nuwe langhoringsprinkaan spesies en 'n
nuwe klankvervaardiging struktuur in 'n Carabid kewer, 'n spesie wat nie voorheen bekend was
om klank te produseer nie. Akoestiese diversiteit oor gradiënte van seisoen en hoogte bo
seevlak het toegeneem met toenemende temperature. Variasie in klimaatstoestande oor die
gradiënt van hoogte bo seevlak het variasie in seisoenale fenologie veroorsaak.
Langhoringsprinkane het ook hoë frekwensie akoestiese seine benut, wat waarskynlik 'n
aanpassing is om agtergrondgeraas van die wind, wat so algemeen is in hierdie gebied, te bowe
te kom. Verder, ten spyte van die vervaardiging van opvallende seine vir maataantrekking en
paarvorming, het langhoringsprinkane nie deel gevorm van die bakoorjakkals se dieet nie.
Hierdie is 'n insekvretende, nagtelike roofdier wat gebruik maak van sy kenmerkende groot ore
om klanke op te spoor wat gemaak word deur invertebraatprooi. Hierdie studie toon die waarde van die gebruik van akoestiese seine van
langhoringsprinkane om akoestiese diversiteitspatrone te identifiseer oor ekologiese gradiënte
en in reaksie op menslike impakte op die landskap.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86463 |
| Date | 04 1900 |
| Creators | Grant, Paul Brian Charles |
| Contributors | Samways, M. J., Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 271 p. : ill. |
| Rights | Stellenbosch University |
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