In a second analysis the different biogeographic histories of the continents were taken into account; thus, the test was repeated independently with localities grouped by their respective biogeographic realms. Conceptually, this forced us to remove from the study those localities that belong to biomes represented by only one community in a biogeographic realm.
However, our results were significantly improved when the analyses were repeated separating communities by biogeographic realms (Table 3), indicating a noteworthy influence of the evolutionary history on prey community structure based on their body size distributions.
While for cenogram global analysis are the slope variables (P5, P5-P1, G, W1 and WG) the principal ones that contribute to discriminate biomes, for the biogeographic realms analyses different variables contribute to separate biomes in every region.
The mayfly genus Heptagenia Walsh, 1863, (Insecta: Ephemeroptera: Heptageniidae) is distributed throughout the Holarctic biogeographic realm
and part of the Oriental realm, with twelve species currently recognized from North America (Webb et al.
It is also possible for trade-off surfaces to shift toward greater competitive ability, on average, when species enter a new biogeographic realm. This would occur if most invading species left behind some of their predators, parasites, or pathogens [ILLUSTRATION FOR FIGURE 9C OMITTED].
The opposite case, that all realms are difficult to invade and that invaders have little impact on native species, would require that trade-off surfaces shift away from the origin when species were introduced into a new biogeographic realm. Might this occur, initially, when some plant species are introduced to a new realm?
In comparisons of most biogeographic realms, the phylogenetic origins of species are different.
Mexico is the only country in the world where clear boundaries of two biogeographic realms
are found: Nearctic and Neotropic.
Situated, as it is, at the meeting place of the three Old World biogeographic realms
, the Arabian Peninsula has a wide species diversity, with representatives of all three realms breeding in the area.
Longitudinal and latitudinal barriers represented by the arrangement of land masses and oceans, by temperature gradients, and by hydrodynamic patterns and water properties divide the oceans into a series of biogeographic realms
with their own characteristic species assemblages (Briggs, 1995; Longhurst, 1998).