Table 4.

Characteristics of snail communities in the three types of woodland ponds studied

Characteristics of snail communities	Type of water body
	P. acuta		F. fragilis		P. antipodarum
Number of species in type of ponds	17		16		16
Number of species in woodland ponds	4–12	$\overline{X}=8$	6–13	$\overline{X}=8$	3–12	$\overline{X}=7$
Density of snails (ind./m2)	79–388	$\overline{X}=182$	74–1,002	$\overline{X}=548$	117–948	$\overline{X}=429$
Density of an alien species (ind./m2)	7–97	$\overline{X}=32$	3–202	$\overline{X}=72$	3–536	$\overline{X}=196$
Other alien species	P. antipodarum F. fragilis				P. acuta