Cappo et al. : Causes and consequences of a latitudinal cline in the demography Lut/anus johnii 
317 
Table 3 
Parameters of the functions that relate otolith weight (grams) to age (f years) for males (M), females (F), and 
all John’s Snapper ( Lutjanus johnii) sampled in northern Australia over the period of February 1989-April 
2002. Data were pooled from 3 regions with nonlinear least-squares estimation of otolith weight = a + b (t) 
+ c (t 2 ). Standard errors of parameters are shown in parentheses, and the range in ages (years), sample size 
(n), and coefficient of multiple determination (R 2 ) are also given. 
t range (years) 
n 
a 
b 
C 
R 2 
North Queensland (M) 
2.16-28.58 
84 
-0.31 (0.06) 
0.25 (0.02) 
-0.00 (0.00) 
0.95 
North Queensland (F) 
1.41-25.16 
80 
-0.34 (0.08) 
0.27 (0.02) 
-0.01 (0.00) 
0.90 
North Queensland 
1.41-28.58 
244 
-0.34 (0.05) 
0.26 (0.01) 
-0.00 
0.91 
Kimberley 
1.5-23.5 
563 
-0.16 (0.02) 
0.18 (0.01) 
-0.00 
0.89 
Cape York 
2.16-18.33 
99 
-0.07 (0.09) 
0.18 (0.02) 
-0.00 (0.00) 
0.77 
in theories of variation in body size of ectotherms 
in relation to geography (James’s rule; Blackburn et 
al., 1999) and temperature (temperature-size rule; 
Atkinson, 1994). However, our estimation of faster 
growth rates in cooler water farther from the equa- 
tor contradicts the temperature-size rule. Here, we 
discuss the major explanations for the patterns we 
observed through the use of prevailing ecological the- 
ories, and we consider the effects of our revised esti- 
mates of parameters for the VBGF on studies of life 
history. 
Explanations of James's rule for tropical fishes 
Similar dines in maximum size and growth have been 
documented for some sedentary coral reef species at 
much larger and smaller latitudinal scales, but, in the 
case of some lutjanids, the same trends have always 
been interpreted as an effect of fishing, regional dif- 
ferences in productivity of habitats, or the evolution 
of separate stocks. For example, Allman and Goetz 
(2009) and Burton (2001) reported that mean size at 
age in Gray Snapper ( Lutjanus griseus ) in Florida in- 
Table 4 
Summary of regional comparisons of otolith weight at age for John’s Snapper ( Lutjanus johnii ) from 
this study of a latitudinal cline in the demography of this species in Australia. Likelihood ratio 
tests, each with 3 degrees of freedom, were performed for coincidence of curves (Curves). Tests of 
differences among slopes ((1) and intercepts (a) were made by using 1-way analysis of covariance of 
otolith weight against log e (age). All tests were conducted over age ranges present at both levels of 
the pairwise comparisons. The number of samples (n, otolith weights) is shown in parentheses for 
each member of the pairs, with the common age range in years (yr). P=probability of null hypothesis 
being true. If the chi-squared goodness of fit statistic (% 2 ) is large, then the null model is a poor fit 
to the curve. The F statistic is the ratio of between-group mean square values to the within-group 
mean square values for slopes and intercepts. Inf=infinity. 
Region; age range 
Parameter 
Test statistic 
P 
North Queensland 
Male (80), Female (77); 2.16-25.16 yr 
Curves 
X 2 =Inf 
1 
P 
F=0.59 
0.44 
a 
F=0.33 
0.57 
North Queensland (227), Kimberley (563); 1.5-23.5 yr 
Curves 
X 2 =349.19 
<0.00 
P 
F=168.48 
<0.00 
a 
F=69.30 
<0.00 
North Queensland (221), Cape York (98); 2.16-18.3 yr 
Curves 
5C 2 =86.19 
<0.00 
P 
F=168.48 
<0.00 
a 
F=69.30 
<0.00 
Cape York (96), Kimberley (550); 2.16-18.3 yr 
Curves 
X-23.21 
<0.00 
P 
F=0.31 
0.58 
a 
F=1.59 
0.21 
