zooplankton species to disperse rapidly over local scales (Ca ́ceres & Soluk,2002 ;
Cohen & Shurin,2003 ; Largier,2003 ; Louette & De Meester,2005 ).
Since the nineteenth century, many authors have considered the biogeog-
raphy of selected passively-dispersing freshwater taxa – see for example
accounts in Rundle, Robertson and Schmid-Araya, (2002a) for various meiofauna.
Some of these studies have attempted to search for general macroecological
patterns. Gillooly and Dodson (2000 ), for example, demonstrated that, for New
World Cladocera, there was a peak in body size at around 60 degrees latitude in
both the Northern and Southern Hemispheres and suggested that within these
temperate regions body size was also maximal at intermediate temperatures
during the year. However, there have been relatively few studies that attempt to
assess macroecological patterns across taxa.
Rundle, Bilton and Shiozawa ( 2000 ) and Rundleet al.(2002b) presented an
analysis of distribution patterns at a variety of spatial scales (local-regional)
employing parsimony analysis of endemicity to assess whether there were
species assemblages characteristic of different areas of the globe. Analysis of
the copepod family Canthocamptidae demonstrated that only 4% of described
species were widespread (i.e. occurred in more than one biogeographical region –
sensuWallace,1876 ). Galassiet al.(2002 ) suggest that even this may be an
over-estimate, since recent taxonomic studies of microcrustacea (e.g. Galassi,
Dole-Olivier & De Laurentiis,1999 ;Stoch,2001 ) tend to favour the splitting of
species considered to be cosmopolitan on the basis of morphology alone, with
genetic studies (e.g. Hebert & Finston,1996 ) typically revealing additional pheno-
typically cryptic taxa. Despite the low number of widespread species, relation-
shipsbetweenregions revealed fromtheseanalysesmadebiogeographicsense.At
a global scale there was evidence of vicariant links, such as that between western
Palaearctic and eastern Nearctic faunas, whereas within western Europe, there
was a suggested role for post-glacial dispersal in shaping northern faunas.
In relation to body size, it is worth noting that all species of Canthocamptidae
are relatively small (lengths< 1000 mm), and that freshwater copepods are
believed to disperse between water bodies largely via eggs, which are typically
< 50 mm in length. Such a size range is well below the transition to cosmopoli-
tanism proposed by Finlay (2002) and Wilkinson (2001) (Fig.10.1). Despite this,
however, the vast majority of canthocamptids do indeed have a biogeography,
and such a statement is true of most other meiofauna (Rundleet al., 2002a).
Obviously, small dispersing propagules alone do not result in cosmopolitan
distributions in freshwater taxa, and other factors such as population size,
dispersal vector and the resistance of propagules must play an important role,
as will the distribution of resulting dispersal distances themselves (Levinet al.,
2003 ). Unfortunately, comparative data on such traits are lacking for freshwater
copepods and, indeed, it is unclear how life-history features such as resting
egg duration influence dispersal and range size. Many species of zooplankton
BODY SIZE, DISPERSAL AND RANGE SIZE IN AQUATIC INVERTEBRATES 197