DISTRIBUTION BY ENVIRONMENTS 
103
II. DISTRIBUTION BY ENVIRONMENTS 
The nature of the spider fauna of different countries varies 
considerably. It we take the number of species belonging to each 
family as providing us with some rough idea of dominance after 
calculating the number in each case as a percentage of the total spider 
fauna, we find (
a
) that some, such as the Mygalomorphs, Salticids and 
Sparassids, flourish in the tropics and diminish progressively as we 
pass into cooler regions, (
b
) that others, including the Drassidae, 
Dysderidae, Agelenidae, Zodariidae and the Cribellate families, thrive 
most successfully in the warmer temperate or sub tropical areas, and 
(
c
) that others, including the Lycosidae and particularly the 
Linyphiidae, reach their greatest dominance in the Arctic or sub 
Arctic regions. An analysis of the known faunas of a representative 
selection of countries is given below in percentages (see p. 104). 
It cannot be doubted that the main cause of these differences in the 
constitution of the faunas is climatic. Even when we take such a small 
area as that covered by the British Isles we find marked differences 
between the north and the south, differences which demonstrate the 
same trends as those contained in the table given above. Scotland 
lacks Mygalomorphs, Oxyopids, Pholcids, Scytodids, Sparassids, 
Eresids and Uloborids, whilst the Linyphiids and Salticids represent 
50% and 4% of its fauna respectively, compared with 42% and 6% for 
England. 
Though I do not regard the average annual temperature of an area as 
being in itself a deciding factor in the potential distribution of a 
species, it is worthy of note 





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