Acoustic profiling of the landscape

[摘要] ENGLISH ABSTRACT: Soft, serene insect songs add an intrinsic aesthetic value to the landscape. Yet these songs alsohave an important biological relevance. Acoustic signals across the landscape carry a multitudeof localized information allowing organisms to communicate invisibly within theirenvironment. Ensifera are cryptic participants of nocturnal soundscapes, contributing toambient acoustics through their diverse range of proclamation songs. Although not withoutinherent risks and constraints, the single most important function of signalling is sexualadvertising and pair formation. In order for acoustic communication to be effective, signalsmust maintain their encoded information so as to lead to positive phonotaxis in the receivertowards the emitter. In any given environment, communication is constrained by various localabiotic and biotic factors, resulting in Ensifera utilizing acoustic niches, shifting species songsspectrally, spatially and temporally for their optimal propagation in the environment.Besides the importance of Ensifera songs from an ethological point of view, themultitude of species-specific signals provide an acoustic tapestry representing species diversityacross ecological gradients and over time. Acoustic inventorying and monitoring of thelandscape can reflect the environmental status of ecological systems, from natural to disturbedby human influence. In contrast to traditional survey techniques, sound recording andinterpretation is a non-invasive method that allows for the detection and classification of highlycryptic, yet insightful indicators of ecosystem change. Here, acoustic monitoring was usedacross diverse ecological gradients to improve understanding of species diversity patterns, andhow they change in response to both natural gradients and in response to the human dominatedlandscape mosaic.This study was undertaken in three geographic locations from tropical rain forest ofBrunei, 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 SouthAfrica. Each region provided a diverse and particular landscape to test the value of acousticsurveys for determining local diversity patterns across natural gradients and to assess the valueof the technique for assessing the impact human influence across landscapes.In tropical rainforests, an entire acoustic guild was investigated to determine howacoustic species partition their acoustic communication channels spectrally, temporally andspatially, to avoid acoustic interference. The overall assemblage showed considerable spectralpartitioning. Diurnally active species showed low temporal niche overlap, whereas nocturnalspecies did not utilize temporal partitioning. Lack of nocturnal temporal partitioning suggestsother mechanisms of acoustic avoidance are sufficient to avoid acoustic overlap, or that thereare insufficient cues to partition nocturnal acoustic environments. Acoustic species also utilizedspatial partitioning, with distinct acoustic assemblages at vertical heights and with elevation.Utilization of a range of different strategies allow many species to communicate withconspecifics with little or no interference from other species in a signal rich environment.Acoustic profiling was also undertaken in KwaZulu-Natal, South Africa, across aplantation forestry landscape mosaic with diverse ecological gradients containing both alienand indigenous vegetation, as well as boarding large natural protected areas. Areas covered inalien timber or non-endemic grass were devoid of acoustic signals. Managed areas that weremowed and heavily grazed were not effective in maintaining the natural complement ofnocturnal acoustic species. Within natural vegetation patches inside plantations, acousticspecies richness increased with plant heterogeneity and patch size. Patches of indigenousvegetation within the plantation matrix effectively reduced the contrast of transformedlandscapes with surrounding natural areas, with indigenous forest patches containing a highlycharacteristic 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. Acrossthese 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 structurein a carabid beetle, a species previously unknown to produce sound. Acoustic diversity acrossseasonal and elevational gradients increased with increasing temperatures. Climatic variabilityalong the elevational gradient produced variation in seasonal phenology. Katydids also utilizedhigh frequency acoustic signals, which is probably an adaptation to overcome backgroundnoise from wind, so prevalent in this area. Furthermore, despite producing conspicuous signalsfor 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 madeby invertebrate prey.This study shows the value of using acoustic emissions from katydids to identifyacoustic diversity patterns across ecological gradients and in response to human impacts on thelandscape.

[发布机构] Stellenbosch University