Research & Innovation 2015-16 - Page 119



Feature
at the University of KwaZulu-Natal (UKZN) who did the
chemical analyses for this study, was amazed at both
the complexity of the scents emitted by Ceratocaryum
seeds, and their similarities to antelope dung. “It still
remains to be seen exactly which chemical is the most
attractive to the dung beetles,” says Johnson.
“I have long had an interest in seed burial by certain
Cape rodent species, and was convinced that the
enormous size of Ceratocaryum seeds would make
them attractive to rodents – either to eat immediately,
or to bury,” says Midgley. Together with MSc student,
Joseph White and small-mammal expert, Dr Gary
Bronner, both in the Department of Biological Sciences,
he began investigating whether free-ranging small
mammals were interested in Ceratocaryum nuts.
“We used motion-sensing trail cameras to observe
small-mammal interactions with the nuts under field
conditions, and it seemed that they were disinterested
or even repelled by the seeds. When small mammals did
crack seeds open, it was clear they were interested in
the nutritious inner parts of the seeds,” says White.
The beetle
The seed
The most surprising result from their field experiments
was the discovery of dung beetles dispersing
Ceratocaryum nuts. “Through both camera trapping and
direct observation, we saw dung beetles being attracted
to the nuts, rolling them away and then burying them,
by pulling them down from below,” comments Bronner.
“Previously, we had observed the same behaviour by
another dung beetle species in the Cederberg, where
Ceratocaryum plants do not occur; suggesting that this
phenomenon may be quite general and widespread in
fynbos.”
“I wonder what would happen if we put these nuts out
in the savanna?” ponders Midgley. “Would they fool
savanna dung beetles?” Dung beetles do inadvertently
disperse some seeds – for instance, those already
in the dung of fruit-eating mammals, which the
beetles bury to nourish their offspring. But this is
not deception, as the beetles gain a reward. With
Ceratocaryum nuts, however, dung beetles are duped
into dispersing and burying nuts with no reward, but
with an energy cost.
“This type of dispersal is probably quite rare, because
it depends on the right ratio of dung to dung beetles.
Too much dung, and the nuts will not be buried –
because beetles have too much of a choice; too
little dung, and there will be a similar lack of burial,
owing to too few dung beetles. We still have much
to learn about the dynamics of such faecal mimicry,”
concludes Midgley.
By Carolyn Newton. Images by Joseph Douglas,
Mandla White.
The dung dupe
VIDEO: Watch camera-trap footage of the small
mammal R pumilio dehusking Ceratocaryum nuts.
VIDEO: Watch camera-trap footage of a dung
beetle burying a Ceratocaryum nut.
Life below water and life on land 114

Watch the videoWatch the video





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