ANIMAL ECOLOGY OF JOHNSON COUNTY 19 
Even the two remaining strips of typical prairie cited (indi- 
cated by x-shaped marks upon the county map, Plate III*) are 
so limited in extent that the animal life is no longer truly repre- 
sentative in character. An apparent exception to this statement 
may be presented, viz., that the invertebrate forms, chiefly the 
insects, remain as they were originally, owing to the fact that the 
same plants are present in species and numbers comparable to 
former conditions. Yet changes have been brought about in the 
vertebrate fauna, and even in the insect fauna, due to the estab- 
lishment of introduced forms from the adjacent cultivated fields, 
so that the present conditions are not identical with those of 
previous times. However, these bits of prairie are the most rep- 
resentative of any in the county, and careful intensive studies of 
the animal associations now occupying them should contribute 
something of value toward an interpretation of the groupings of 
animals that once held place. 
The rolling prairies. This type of prairie was the one which 
originally covered the greater part of the county and is still 
represented by the strip of land along the Chicago, Rock Island 
and Pacific railroad east of Iowa City. This is directly upon the 
loess deposits, which accounts for the rolling topography. It 
was established over all the loess deposits in the county except 
those areas which were forested. Its topography makes for 
rapid drainage after rainfall. This, together with the fact that 
it is fully exposed to all the evaporating effects of wind and sun 
and all changes of temperature, has made it impossible for any 
but plants xerophytically adapted to maintain themselves. The 
soil is loose and fertile, permitting a great abundance of plants 
fitted to cope with the conditions. Thus the great majority of 
plants making up its vegetation are composites and grasses. 
This multiplicity of plant species has made possible the existence 
of a great variety of insects; and the occurrence of the flowering, 
highly specialized composites accounts for the great abundance 
and variety of the insects of the more highly specialized orders— 
the Hymenoptera, Diptera, Lepidoptera, and Coleoptera, many, 
indeed, of which are nectar-feeding or pollen-carrying forms. 
These prairie plants, while all are modified in some way to meet 
*Adapted from the Good roads map of Johnson County, copyright by M. Huebinger, 
1913. 
