Variation in the Phenology of Natural Populations of Montane ...

Journal of Ecology (1980), 68, 849-862
VARIATION IN THE PHENOLOGY OF NATURAL
POPULATIONS OF MONTANE SHRUBS IN NEW ZEALAND
RICHARD B. PRIMACK*
Department of Botany, University of Canterbury, Chhristchurch 1, New Zealand
SUMMARY
(1) Variation in flowering time of individuals in one population of each of three
species of shrub was recorded over two growing seasons in montane scrub-grassland
in the South Island of New Zealand.
(2) There was considerable variation in flowering time within each popuLlation, but
the flowering rank-order of individuals in different years was positively correlated.
(3) Variation in flowering time was poorly correlated witlh the dLuration of
flowering and the number of flowers and fruits per plant, except that variation in
flowering time in Discaria toumatou (Rhamnaceae) was weakly positively correlated
with the percentage fruit set in 1976-77. If both earlier and later flowering plants
showed reduced fruit set this would suggest stabilizing selection, but there is no
indication of such a pattern. Weak and inconsistent directional phenotypic selection
for flowering time can be demonstrated for these two species however.
(4) In the warm, dry summer of 1977-78, Leptospermum scoparium (Myrtaceae)
and Dracophyllumn spp. (Epacridaceae) flowered on average 9 days and 5 days
earlier respectively and for 17 and 8 days shorter duration than in the cool, damp
summer of 1976-77. Further, L. scoparium plants had a lower production of flowers
and fruits in the second season in comparison with the first season. Plants of
Discaria toumatou also flowered earlier in 1977-78, but the duration of flowering
and flower and fruit production was greater in 1977-78 than in the 1976-77 season.
(5) Patterns of variation in flowering time are also apparent among adjacent
populations depending on altitude and on the major geographical units of the
range of species. Variation in flowering time both at the individual and the population
level may be an important adaptation by which selection and physiological
mechanisms increase reproductive success.
INTRODUCTION
Most species flower at a characteristic time during the year at a particular locality, but
many species show gradual changes in flowering time over geographical and environmental
gradients (Jackson 1966; Harris 1970; Hodgkin & Quinn 1978). Such differences
might be environmentally or genetically controlled (or both). The existence of genetic
variation for flowering time within populations is known for a large number of plant
species (for examples, see McMillan & Pagel 1958; McIntyre & Best 1978). Despite a
sustained interest in flowering phenology (Robertson 1924; Heinrich 1976; Schemske
1977; Schemske et al. 1978; Poole & Rathcke 1979), little is known about variation in
flowering time within natural populations, in particular with relation to the reproductive
success of those plants. The work reported here was an investigation of variation in
* Present address: Biology Department, Boston University, Boston, Massachusetts 02215, U.S.A.
0022-0477/80/1100-0849 $02.00?01980 Blackwell Scientific Publications
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