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