120 
FIFTEENTH REPORT. 
THE FACTORS THAT DETERMINE THE DISTRIBUTION OF 
BOLEOSOMA NIGRUM IN DOUGLAS LAKE, 
CHEBOYGAN COUNTY, MICHIGAN. 
IIY II. V. HEIMBURGER. 
This paper is a brief account of a piece of work done during July 
and August, 1912, at the University of Michigan Biological Station. 
By means of a careful survey of the lake, it was found that Boleosoma 
nigrum was confined 1o water less than thirty inches in depth. Thir- 
teen localities were found, in eight of which both young and adult of 
the species were aboundant. In five habitats only immature specimens 
were found. 
It is known that the breeding habits and the food habits of animals 
play an important part in the determination of the local habitat. The 
breeding habits of Boleosoma nigrum have been described by Hankin- 
son and by Forbes. These authors state that the eggs of Boleosoma 
are attached to stones, mussel shells and sticks which lie loosely on 
the bottom. Spawning occurs in April and May. 
I have found by examination of the contents of twenty-one stomachs 
that the food of adult Boleosoma consists, as was found by Hankinson 
at Walnut Lake, almost wholly of the larvae of Chironomidae; Chir- 
onomus prevailing. The young Boleosoma subsist very largely upon 
Entomostraca, but eat correspondingly larger proportions of Chironomus 
as they themselves grow larger. 
The larvae of Chironomus and other midges occur plentifully wher- 
ever there is an abundance of decayed vegetable matter on the bottom. 
The eggs of midges are deposited on the floating leaves of such plants 
as Potomageton, Nymphaea, etc., whence the larvae find their way to 
the muck of the bottom. 
An analysis of the habitats in Douglas Lake shows them to have the 
following features in common: 
(1) Mussel shells, small stones and sticks on the bottom. 
(2) Quiet water, protected from violent wave action, allowing a 
thin deposit of muck to accumulate in patches over the sand. 
(3) Absence of thick muck deposit in the shallow water. There are 
always patches of sand, stones, etc., not covered by the muck. A deep 
deposit of muck is usually found in the deeper water near by. 
(41 Masses of Potomageton or other aquatic plants with floating 
leaves, are found in the immediate vicinity. 
These characters of the habitat are shown to be directly connected 
with the food habits or the spawning habits of Boleosoma and may 
be regarded as physical features that determine the distribution of the 
species. , 
