Interspecific and temporal variation of condensed tannins and cyanide concentrations in potential dietary sources of extralimital giraffes (Giraffa camelopardalis) in the Karoo

Marais, Eugene (2019-04)

Thesis (MSc)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: During 2016 and 2018 four giraffe (Giraffa camelopardalis) mortalities occurred in the Karoo potentially caused by acute hydrogen cyanide poisoning. Plants have various defence mechanisms to protect themselves against herbivory, including the production of secondary metabolites such as condensed tannins and hydrogen cyanide. This study quantified condensed tannin and hydrogen cyanide production in selected Karoo plant species that giraffe may browse, to assess the possibility of acute hydrogen cyanide poisoning and condensed tannin intoxification. Condensed tannins and hydrogen cyanide concentrations were explored in both spatial and temporal scales. The spatial assessment was performed at macro-scales (different locations within the Karoo), whereas temporal assessment was performed at seasonal scale. The effect of water availability and herbivory on condensed tannin production in Vachellia karroo trees was also investigated. Condensed tannin concentrations were high throughout seasons and did not differ significantly among the study sites in plant species giraffe primarily browse. In winter, V. karroo leaves were unavailable and secondary plant species increased in dietary importance. The most preferred plant species in the giraffes’ diet, V. karroo, contained high levels of condensed tannins in mature leaves as well as in new-growth plant tissue. Condensed tannin concentrations increased significantly in several evergreen tree species during winter, including Schotia afra var. afra and species of the Rhus genus, which may indicate an increase in dietary importance during winter season. Schotia afra var. afra contained lower condensed tannin concentrations than V. karroo throughout the study. Condensed tannin production increased significantly in three of the four treatment groups of V. karroo trees that received simulated herbivory regardless of the browsing intensity. Both treatment groups which received water, increased in nitrogen contentment, whereas trees from the browsed and not watered treatment decreased in nitrogen content value and palatability. The high condensed tannin concentrations seem to be a fixed defence response by Karoo plants to browsing, or a response when sufficient water is available. The high condensed tannin concentrations may reduce the available browse as giraffe and other herbivores may reject leaves high in condensed tannins. However, giraffe have the ability to partially degrade condensed tannins and will therefore not be as susceptible to tannin intoxification than other herbivores. The higher browsing pressure caused by giraffe may therefore be detrimental to other herbivores utilising the same plant species in the Karoo, that do not have the ability to degrade condensed tannins. Therefore, careful considerations should be taken when introducing large game species into the Karoo. Only focusing on vegetation composition and abundance may be insufficient in predicting carrying capacities in semi-arid environments such as the Karoo without taking chemical composition into account. None of the plant species, except for one Eucalyptus cladocalyx tree, contained any measurable hydrogen cyanide, therefore making the probability of acute hydrogen cyanide poisoning highly unlikely. However, various other poisonous plants occur in the Karoo, these plants need to be investigated to determine whether they form part of the giraffe diet during times of limited browse, and how these plants may respond to browsing.

AFRIKAANSE OPSOMMING: Plante het verskeie verdedigingsmeganismes om hulself teen herbivore te beskerm, insluitende die produksie van sekondêre metaboliete soos gekondenseerde tanniene en waterstofsianied. In hierdie studie is gekondenseerde tannien- en waterstofsianied produksie in geselekteerde Karoo-plantspesies wat kameelperde (Giraffa camelopardalis) kan ineem/eet gekwantifiseer, om die moontlikheid van akute waterstofsianied vergiftiging en gekondenseerde tannien vergiftiging te bepaal. Gekondenseerde tanniene en waterstofsianied is ondersoek in beide ruimtelike en temporale skale. Die ruimtelike assessering is op makro-skaal (verskillende lokaliteite binne die Karoo) uitgevoer, terwyl tydelike assessering op seisoenale skaal uitgevoer is. Gekondenseerde tannienproduksie is ook ondersoek as 'n reaksie op verskillende omgewingstoestande en blaar verlies as gevolg van herbivore. Gekondenseerde tannien konsentrasies was hoog gedurende al die seisoene en het nie beduidend verskil tussen die studie areas nie. Plantspesies uit die Rhus-genus het gedurende die winter toegeneem in benutting en het aansienlik toegeneem in gekondenseerde tannienproduksie by al die studie areas. Die belangrikste plantspesie in die kameelperde se dieet, V. karroo het hoë vlakke van gekondenseerde tannienkonsentrasies in volwasse blare asook in nuwe groei plantweefsel bevat. Gedurende die winter was V. karroo blare onbeskikbaar en het sekondêre plant spesies toegeneem in benutting. Die gunsteling plant spesies in die kameelperd se dieet, V. karroo, het hoë vlakke gekondenseerde tanniene bevat in beide ou en nuwe blare. Immergroen plante soos Schotia afra var. afra en spesies van die Rhus genus was dus meer benut tydens die winter, en het hoër gekondenseerde tannien konsentrasies bevat tydens winter. Gekondenseerde tannienproduksie het toegeneem in drie uit die vier behandelingsgroepe van V. karroo bome wat gestimuleerde beweiding ontvang het, ongeag van die beweidingsintensiteit, aangesien geen beduidende verskille tussen die behandelingsgroepe geidentifiseer kon word nie. Beide behandelingsgroepe wat water ontvang het, het egter toegeneem in voedingswaarde, terwyl bome in die behandelingsgroep wat hoë beweiding ontvang het, maar geen water nie, verminder het in voedingswaarde en smaaklikheid. Die hoë gekondenseerde tannienkonsentrasies blyk om ̒n stabiele verdediging meganisme te wees in Karoo plante teen beweiding, maar ook tydens fases wanneer water beskikbaar is. Daarom wanneer dit oorweeg word on groot-wildspesies in die Karoo aan te hou, moet verskeie aspekte rakende chemiese verdediging deur plante in ag geneem word, en moet daar nie slegs net gefokus word op plantegroei samestelling en voorkeur nie. Dit kan onvoldoende wees om drakragte in semi-ariede omgewings soos die Karoo te voorspel sonder om chemiese samestelling in ag te neem. Geen van die plantspesies wat in hierdie studie ingesluit was, behalwe vir een Eucalyptus cladocalyx boom, het enige meetbare waterstofsianied geproduseer nie, dus is die waarskynlikheid van akute waterstofsianied vergiftiging hoogs onwaarskynlik. Daar is egter verskeie ander giftige plante in die Karoo, wat ondersoek moet word om te bepaal of hulle deel vorm van die kameelperde se dieet gedurende tye van beperkte plantegroei, en hoe hierdie plante potensieël kan reageer ten opsigte van chemiese produksie teen beweiding.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105981
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