Latitudinal diversity patterns in estuarine tidal flats: indications of a global cline

Latitudinal diversity gradients are a general feature of the terrestrial re alm. Fewer studies have addressed marine habitats and those concerning soft sediments: have not reported such consistent trends. This study investigat es global patterns of macroinvertebrate alpha -diversity in estuarine tidal flats. A literature search was as conducted to collect data on species div ersity as well as various physical, chemical and biological factors that ma y prove useful in investigating the cause of trends. Regression analysis re vealed a significant association between latitude and diversity expressed a s Simpson's index of concentration (r(2) = 0.44), the index being lower (i. e. diversity higher) at low latitudes. There was no significant association between diversity and either available estuary area or annual rainfall. A significant, although weak. relationship between diversity and mean annual temperature was apparent (r(2) = 0.23). together with an increase in specie s to family ratio in the hottest areas. This could suggest greater evolutio nary speed in thr tropics (due to temperature increasing mutation rates and generation times) and may provide an explanation for the trend. However, a greater amount of variation is explained by latitude alone and it is sugge sted that a primary cause of the latitudinal dine in estuarine diversity ma y be the greater effective evolutionary time available fur communities in t he tropics, temperate estuaries bring regularly disturbed by glaciation dur ing the last 1.8 million years.