Nepenthes don't just EAT ants, they also FEED them. Therefore the
relationship is not purely carnivorous, but MUTUALISTIC....
Ants are a big item on wild Nepenthes menus. The important thing about
ants being colonial is that once they find food they hurry home to let the
rest of the family know about it. Consequently you don't want to eat the
first ant that comes along, and sure enough this is just what you find with
Nepenthes in the wild - they are pretty hopeless at their theoretically
efficient task. Ants can often be seen running all over the inner wall of
the pitcher, under and over the peristome and under the lid, and off again
down the tendril and home. BUT .. and this is the important point - if you
give the pitcher the merest touch, even a little puff of breath, down go the
ants, and they don't survive. So it seems they've made the pitcher just SO
efficient, but not TOO efficient - i.e. the elderly ladies loose their
slipping often enough, but the young girls generally scamper home without
loss. By eating just a tiny percent of an ant-colony per day, they go on
turning up. By Game Theory one can predict that for the ants the occasional
loss of the elderly ant, for which in return the plant prospers and hands
out more free nectar, is a good evolutionary deal, likewise by not eating up
all the scouts straightaway, the pitcher plant gains a more regular long
term supply. With Sarracenia and Darlingtonia likewise, very large numbers
of flies are seen to visist, feed and fly away - in this case it is probably
not so much a case of recruiting more flies, but that the plants are not TOO
efficient, because they want to set up a relationship with ants, in some
respects these flying visitors are parasitic on the nectar handout.
For those interested the full details of this story, they have been spelt
out by Dan Joel in The Biological Journal of the Linnean Society (1988)
Volume 35, pages 185-197.
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Matthew Jebb,
School of Botany,
Trinity College Dublin, E-mail:mjebb@mail.tcd.ie
Dublin 2, Tel: +353-1-702 1421
IRELAND. Fax: +353-1-702 1147
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