Browsing by Author "Kruger, L M"

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    Elephant fruit :The dispersal attributes of Balanites maughamii / Storme Viljoen
    (2013) Viljoen, Storme; Midgley, Jeremy J; Kruger, L M
    Endozoochorous plant species that have obligate dispersal mutualisms with megafauna are at risk of extinction because of the unique conservation threats associated with large animals. This study examines Balanites maughamii which appears to have similar dispersal attributes to Sclerocarya birrea and Balanites wilsoniana, both of which are considered to be obligate elephant fruits. Here, I emphasize the traits that make B. maughamii suitable for elephant dispersal and examine the cues required for seed germination. Large, fleshy fruits with a single, exceptionally hard seed which requires a crushing force of > 2.0 kN to promote germination are characteristic of this species. Using scent analysis of ripe fruits, the range of volatile that are responsible for the pungent odour were identified as being those which should function in mammal-attraction. Finally I examine the potential for long-distance dispersal by elephants using a gut passage time experiment, which revealed that elephants retain seed for approximately 48 hours, equating to a 4-8 km dispersal distance. Using fruit and seed bait stations to determine which other animals interact with B. maughamii, I found that small mammals may play a significant role in seed predation and that there is little evidence to suggest extensive secondary dispersal by rodents. These finding allude to the vulnerability of the long-term maintenance of B. maughamii in the absence of elephants, who appear to be their only legitimate disperser.
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    How do fires kill plants? The hydraulic death hypothesis and Cape Proteaceae "fire-resisters"
    (Elsevier, 2011) Midgley, J J; Kruger, L M; Skelton, R
    The actual mechanism which causes plant death after having been burned has been poorly studied. One possibility is that fire causes direct, or indirect, fatal damage to plant hydraulic systems. If true, this suggests that burned plants ultimately die of drought. This hypothesis was tested on the post-fire response of a "fire-resister" species of the Cape Proteaceae, as well as by analysing its morphology. Fire-resisters are plants which are incapable of resprouting, but nevertheless survive some fires. Mortality of the studied fire-resister appears to be compatible with a hydraulic death hypothesis because i) most post-fire mortality occurred within days, ii) it occurred from the base-upwards and iii) correlated negatively with stem diameter rather than plant height. Higher levels of survival of the fire-resister is probably due to absolutely thicker bark than co-occurring re-seeder species of the same age. Since this bark has not evolved to protect buds, it has probably evolved to protect stem hydraulic systems.