New Zealand Journal of Botany abstracts
Why is mast seeding in Chionochloa rubra (Poaceae) most extreme where
seed predation is lowest?
JON J. SULLIVAN*
DAVE KELLY+
Department of Plant and Microbial Sciences
University of Canterbury
Private Bag 4800
Christchurch 1, New Zealand
email: d.kelly@botn.canterbury.ac.nz
*Present address: Department of Biology, University of
Pennsylvania, Philadelphia, PA 19104-6018, USA.
Abstract Mast seeding (highly variable population seed crops
among years) is common in the New Zealand flora, and is especially evident in
high elevation populations of Chionochloa (snow tussocks). However, mast
seeding is less pronounced at low elevations in New Zealand plants, including
C. rubra. Past studies of high elevation Chionochloa
populations showed that the main benefit of mast seeding is the
satiation of pre-dispersal insect seed predators. We therefore predicted that,
to be able to set seed regularly, either C. rubra should suffer less
predation than other Chionochloa species, or low elevation populations
of C. rubra should experience lower seed predation than higher elevation
populations. To test these predictions we surveyed seed predation in C.
rubra and neighbouring C. pallens and C. flavescens at 22 New
Zealand sites spanning over 1000 m in altitude. Total seed predation was
not significantly lower in C. rubra (48%) than in C. pallens
(22%) and C. flavescens (54%). Seed predation significantly
increased with decreasing altitude, in direct contradiction to our prediction.
This reveals a reproductive paradox: why do low elevation populations of C.
rubra not show more pronounced mast seeding? We discuss three possible
answers: (1) C. rubra has not formed altitudinal ecotypes with different
critical temperatures for heavy floral induction; (2) the seed predators at low
elevation are harder to satiate; or (3) low elevation populations suffer
stronger disadvantages from masting through high intraspecific competition
and/or density dependent seedling mortality. We suggest that this paradox may
also occur in many other masting plants with wide altitudinal ranges, that
predator satiation will often break down at the lower altitudinal limit of the
plant, and that seed predation may limit the lower elevational range of some
masting plant species.
Keywords Chionochloa; Poaceae; mast seeding; seed
predator satiation; effects of altitude; climate; site favourability;
ecotypes
+Author for correspondence.
B99037
Received 29 July
1999; accepted 11 November 1999
PDF file of entire paper: medium quality (1128K); (scanned from paper original: notes about this process)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
