Lister - p. 2 
mediate with respect to this character, having scale sizes about twice as 
large as aeneus and trinitatis and half as large as griseus and richardi. 
Among sagrei populations there was no correlation between the coefficient 
of variation of dorsal scale count and measures of thermal niche width. 
On Abaco Island, where sagrei occurs in both open and closed habitats, 
dorsal scale counts were found to be significantly higher in a forest 
population than in a population occurring in an open habitat within a 
kilometer of the forest. Coastal forest populations of Cayman Brac sagrel 
also have a higher number of dorsal scales than populations inhabiting more 
open areas. Using starch gel electrophoresis, Preston Webster and Lister 
have found that forest and open populations on Abaco also differ as to gene 
frequencies at two polymorphic loci. These results suggest that a forest 
ecotype has evolved on Abaco. Thus Anolis species which have undergone 
habitat expansion in the absence of competitors should often be more variable, 
island wide, than on islands where competitors restrict their habitat range. 
(3) Among adult male sagrei populations, mean head length was positively 
correlated with mean prey size and prey size variance, The coefficient of 
variation of head length was found to increase with increasing niche width 
along the prey size axis. Populations taking a wider range of prey sizes 
also had a greater prey size specialization within the head size classes, 
i.e. a higher between-phenotype component to niche width, These results were 
consistent with Roughgarden's predictions for the evolution of niche width. 
However, a model of lizard growth developed by R. McMurtrie and Lister 
showed that the CV of head length should increase proportionately with an 
increase in mean head size. This relationship was found empirically both 
within and between species. Among 10 different populations of A. sagrei, 
mean head length alone accounted for 75% of the variation in the CVs of head 
length, and among 19 different Anolis species 77% of the variation in the 
CVs was explained by mean head length. Our model suggests that patterns of 
size variation in Anolis may not be the adaptive result of density dependent 
selection but a direct consequence of the way these lizards grow and mature. 
Thus the correlation between niche width and the CV of head length in sagrei 
populations probably results from the fact that both the CV of head length 
and niche width are positively correlated with mean head size. 
To date, the results of this study suggest that the evolution of eco- 
logically specialized phenotypes and adaptive increase in variation are not 
involved in niche expansion in anoline lizards. Rather, populations that 
have undergone ecological release have evolved a generalist phenotype capable 
of exploiting thermally diverse conditions, a variety of perch heights and 
an optimal range of food items. Indirect evidence indicates that the 
behavioral component of niche expansion is probably large, at least among 
good colonizers such as sagrei and carolinensis, and field experiments 
designed to determine the capacity for behavioral shift in several species 
are planned. 
