Re-analysis of data from Collin (2003 ) describing sizes and distributions of
planktotrophically dispersing calyptraeid gastropods, shows a weak relationship
between adult body size and both eggs and hatching larvae (Fig.10.5 ), although
there is no evidence for an effect of adult size upon range. A similar pattern
linking egg size to adult (i.e. test) size is evident in re-analysis of data describ-
ing regular echinoids (composite data from Emlet,1995; Levitan,2000 ; Moyse &
Tyler,1990; Meinkoth,1981 ) (Fig.10.6a). However, there is again no apparent
trend in either of these cases for an effect of egg or adult size upon
overall geographic range (Figs.10.6b& c), although Emlet (1995 ) does demon-
strate a clear effect of reproductive/dispersive strategy upon range size, with
planktotrophs having significantly greater geographic ranges than non-feeding
planktonic dispersers.
Foggoet al. (unpublished) summarize trends in abundance, distribution and
body size for British marine macroinvertebrates (see Foggoet al., 2003for
methods and data sources). These data were examined for evidence of patterns
linking adult body size to a measure of range (proportion of sampled sites
occupied). Polychaetes represent a group with a range of reproductive/disper-
sive strategies and, although there was no evidence of linear trends in range size
with increasing body size, there were clear differences between non-planktonic,
lecithotrophic and planktotrophic developers in terms of both the mean pro-
portion of sites they occupied (Fig.10.7a) or their mean body lengths (Fig.10.7b).
Thus, there appears to be a general trend for smaller passively dispersed marine
invertebrates to be less widespread, echoing the trends encountered in some
freshwater passive dispersers (see above).
The comparison between passive dispersal in marine and freshwater systems
seems at the outset to be somewhat contrived. Freshwaters are highly disjunct01002003004005006000 2040 6080
Adult shell length (mm)Egg/larval size (μm)Figure 10.5Relationships
between adult shell length
and egg size (open circles,
dashed line) and hatching
larvae (closed circles, solid
line) for a set of
planktotrophically
dispersing calyptraeid
gastropods: eggs
R^2 ¼0.342, F1,28¼14.58,
P¼0.001; larvae
R^2 ¼0.328, F1,19¼9.28,
P¼0.007. Data from
Collin (2003 ).200 S. D. RUNDLEET AL.