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Rodents and restios: rodents and the fates of Willdenowia incurvata (Restionaceae) seeds

Weighill, Benjamin (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH SUMMARY: The biodiversity hotspot of the fynbos offers a “natural laboratory” to study species diversification, particularly in flowering plants. Often it is the interactions with the surrounding biotic or abiotic environments that drive this diversification. Interactions between plants and seed dispersers are just one of these interactions. In Chapter 1 of this thesis, recent studies pertaining to rodent assisted seed dispersal as well as other biotic seed dispersers in the fynbos were reviewed. This review emphasized the need for more studies of biotic seed dispersal in the fynbos despite the recent discovery of the first dung beetle assisted seed dispersal in the fynbos and the first investigations into seed dispersal by the Cape spiny mouse (Acomys subspinosus) and the hairy-footed gerbil (Gerbilliscus paeba). In Chapter 2, the seed dispersing and consumption behaviour of the hairy-footed gerbil (Gerbilliscus paeba) and the four-striped mouse (Rhabdomys pumilio) was investigated. It was confirmed that G. paeba dispersed seeds of Willdenowia incurvata (Restionaceae) at night and only consumed a small percentage of seeds in situ. In contrast, R. pumilio, which was only active during the day, only consumed and never dispersed seeds. In Chapter 3, the final data chapter, the effect of added elaiosomes from the closely related Willdenowia glomerata on rodents’ reactions to W. incurvata seeds was investigated. It was found that the added elaiosomes deterred both G. paeba and R. pumilio from interacting with seeds of W. incurvata. Both rodent species preferred seeds without elaiosomes attached. Gerbilliscus paeba consumed and dispersed more seeds without elaiosomes attached than seeds that had elaiosomes attached when given a choice between seeds the two seed treatments. Rhabdomys pumilio, which does not disperse seeds, also consumed more seeds without elaiosomes attached than seeds with elaiosomes attached. In the fynbos, one of the prevailing views regarding myrmecochory (seed dispersal by ants) is that it evolved as a response to heavy seed predation by rodents as seeds are rapidly removed from the soil surface by ants. However, the findings of this thesis suggest that not all rodents are purely seed predators and that some species may play an important role in seed dispersal. Consequently, it is more likely that myrmecochory evolved primarily to protect seeds from fire, through seed burial. Seed dispersal by rodents also involves burial and so it is likely that some rodents may perform a similar role to ants in protecting seeds from fire. From a biodiversity perspective, the further study and identification of new interactions of this kind are key in understanding the processes that shaped the diversity seen in the fynbos today. In addition, such interactions are critical for maintaining ecosystem function. Protection of this biodiversity hotspot becomes extremely challenging when species interactions are unidentified or unstudied, emphasizing the importance of this study for conservation efforts. From an evolutionary ecology perspective, how scatter-hoarding in rodents evolved, as well as the evolution of plant strategies that enhance dispersal by rodents are highly contested. Evidence from fynbos studies could provide further insights for drawing conclusions regarding the evolution of this plant-animal interaction.

AFRIKAANSE OPSOMMING: Die fynbos is ʼn bioom ryk in biodiversiteit en bied ʼn “natuurlike laboratorium” voor waarin die diversifikasie van spesies beter bestudeer kan word, veral in blomplante of angiosperme. Een van die drywers van hierdie diversifisering is die interaksie tussen plante en hulle omgewing asook ander organismes. Een van hierdie interaksies kom voor tussen plante en saad verspreiders en een interessante saad verspreider is knaagdiere. In Hoofstuk 1 van hierdie tesis word onlangse studies van knaagdiere as saad verspreiders so wel as ander biotiese saad verspreiders in die fynbos opgesom. Alhoewel saad verpreiding deur miskruiers onlangs ontdek is en die eertse ondersokeing van saad versreiding deur twee knaagdiere, Acomys subspinosus (“Cape spiny mouse”) en Gerbilliscus paeba (“hairy-footed gerbil”), gedoen is, bly daar ʼn tekort aan studies van biotiese saad verspreiders in die fynbos. In Hoofstuk 2 word saad verspreiding deur Gerbilliscus paeba (Muridae) deuglik ondersoek. Daar word bevestig dat G. Paeba, wat slegs nagtelik aktief is, gereeld sade van Willdenowia incurvata (Restionaceae) versprei en vreet ook ʼn paar daarvan. Rhabdomys pumilio (“four-striped mouse”), wat slegs in die dag aktief is, vreet slegs sade en het geen sade versprei nie. In Hoofstuk 3, die finale data hoofstuk, word die effek van ʼn bygevoegde lipiede-ryk aanhangsel of “elaiosome” (wat gewoonlik miere lok) aan knaagdiere se reaksie tot sade ondersoek.. Hier, is dit gevind dat G. paeba sade sonder elaiosomes verkies bo die wat elaiosomes bygevoeg het deur om meer gereeld sade sonder elaiosomes te versprei en te vreet. Rhabdomys pumilio verkies ook sade sonder elaiosomes en vreet meer van hierdie sade as die wat elaiosomes bygevoeg het. Daar word gereken dat saad verspreiding deur miere as ʼn reaksie tot saad predasie deur knaagdiere ontwikkel het. Sodoende word sade vinnig van die grond verwyder, weg van knaagdiere wat daaraan so vreet. Hierdie tesis wys egter dat nie alle knaagdiere saad vreters is nie en dat sommige knaagdiere ook saad verspreiders is. Saam hiermee word daar ook voorgestel dat die elaiosome self knaagdiere so ontmoedig om die sade te versprei of te vreet. Van ʼn biodiversiteit oogpunt, is die identifikasie en beskrywing van hierdie interaksies krities om die evolusie van die fynbos se diversiteit beter te kan verstaan. In byvoeging, is die funksionering van ekostelsels afhanklik van die interaksies binne die stelsel. Sonder om hierdie interaksies te identifiseer en te verstaan is die bewaring van die fynbos byna ontmoontlik. Laastens hoe die evolusie van knaagdiere se neiging om sade ondergronds te stoor as ook hoe plante hierdie diere se gedrag bemoedig (en sodoende saad verspreiding aan te moedig) begin het, is debatteerbaar. Studies soos hierdie uit die fynbos, kan moontlik bydrae om wêreldwye gevolgtrekkings te maak rakend die evolusie van hierdie plant-dier interaksie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101425
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