The odonates are ideally suited for investigating macroecological patterns
and the potential role of body size and dispersal in influencing these patterns.
First, they are used as models for exploring the biomechanics of flight (see
above) and, hence, there is the potential for future studies to make robust
macroecological predictions based on scaling relationships between body size
and key traits related to dispersal ability (e.g. wing size and shape, mass of
thoracic muscles, and ratios within muscle-lever systems). Second, the vivid
markings and relatively large size of dragonflies and damselflies means that
they are one of the groups of invertebrates that attract the most attention.
Hence, they are well-known taxonomically and ecologically, and extensive
distributional data exist for dragonflies and damselflies in many areas of the
world, particularly the Holarctic.
Data for North American damselflies and dragonflies have recently been
made available electronically on the OdontataCentral database (Abbott,2005)
and these data were used to explore how range size related to patterns in
relation to body size and wing size (see Fig.10.2for details). Based on some of
the evidence presented above, significant positive relationships between size
measures and distribution extent might have been expected. Although dragon-
flies were, on average, significantly larger than damselflies, they did not have
significantly larger ranges (Fig.10.2). However, within the dragonflies, there was
some evidence for positive relationships between wing size and both range size
and occupancy (Figs.10.2c& d), no such relationships being evident for dam-
selflies. Although these findings should be viewed with some caution, given the
very high scatter around the derived regressions, they do suggest that the
further exploration of such macroecological patterns, perhaps using more
sophisticated regression techniques (e.g. McClain & Rex, 2001 ) may be instruc-
tive in revealing the potential role for traits linked to dispersal in macroecology.
There have been a few previous attempts to relate dispersal potential to range
size in freshwater invertebrates, with mixed findings. Ribera and Vogler (2000)
consistently found that range size was significantly smaller in lotic versus lentic
taxa in a comparison of clades of aquatic beetle differing in habitat preference. It
was suggested that this macroecological pattern resulted from differing disper-
sal abilities in lentic versus lotic taxa, these differences being driven by differ-
ences in the duration of running (relatively long persistence) and standing
waters (short persistence) over evolutionary timescales. Malmqvist (2000) exam-
ined the relationship of wing and body size with range size measures in mayflies
and stoneflies in Sweden. He showed that there was no relationship between
body size and range size, but that the ratio of wing length to body length was
positively related to range extents in both groups. Hence, for at least two groups
of freshwater taxa, there was evidence that a size-related trait might be related
to distribution patterns. These results should be viewed with some caution,
however, as the analysis was only partial (for most taxa studied, Sweden194 S. D. RUNDLEET AL.