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

RICHARD B. PRIMACK 855
35
-
1976-77
30 -
20~~~~~~~~~~~
-
10 _
11 16 18 21 24 26 28 30 1 3 5 7 9 I'l 1'3 15 I? 17 9 21 2J3 25 2'7 31 4
December
Jonuory
35 - 1977-78
20 __
11 16 18 21 24 26 28 30 4 7 9 1 13 15 17 1 21 2 25 37
1
70 5 21 2
-4.>~~~~~~~~~~~4
December
Jonuary
FIG. 3. Flowering dates of thirty-five plants of Dracophylluim spp. in 2 yr in New Zealand. See Fig. 1
for an explanation of symbols.
in a population, occurs primarily during the shorter period of abundant flowering. When
a plant flowers strongly, only a portion of the other plants in the population are similarly
flowering strongly and capable of exchanging genes. The degree of overlap in flowering
among individuals can be quantified by calculating for all possible pairs of n individuals,
c = a/b
where a is the number of census dates on which plants are flowering strongly, and b is
the number of census dates for whichever individual flowered strongly for the fewest
census dates. An index of overlap in flowering, Z, for the individuals in a population
would be
where the number of comparisons will be
N = n(n - 1)/2.
The index of overlap would be 1.0 with complete overlap and 0.0 with no overlap.
The indices of flowering overlap for the two successive seasons are 0.68 and 0.74 for
Leptospermum, 0.42 and 0.74 for Discaria, and 0*34 and 0.41 for Dracophyllum. Each