ECOLOGY OP ISLE ROYALE. 161 



the upper beach, as Pterostichus. Under such conditions were found 

 P. femoraUs and Harpalus megacephalus (1, 2; V, 2). The flower 

 feeders also continue to maintain their position, but the BernbiMums 

 have largely been eliminated. 



These open sunny spots, surrounded by dense shady forests, in their 

 attractiveness for insects, remind one of electric lights where insects 

 congregate in such vast numbers. As representative of these condi- 

 tions the great variety of beetles found about the camps should be 

 recalled. 



S. Lake, Pond and Bog Hahitats and Associations. 



From the park-like rock openings let us turn to another series of 

 open habitats: those which are initiated by inland water bodies. The 

 water beetles to be found in the open lakes were not given special at- 

 tention but there can be no doubt as to their existence in such places, but 

 in general we may say that water beetles increase in number and kind 

 nearer the margins and in shallow water. Here the Gyrlnids (V, 63), 

 Donacia (III, 5), and Gulerucella (VI, 3) abound, while farther in- 

 land at the bog margins and in the bogs occur Haliplids and Hydro- 

 philids, Ealiplus, Hydroporus, Agabus and Scutopterus (I, 4, 6; V, 5). 

 Even this brief series outlines the main features seen in the transition 

 from the strictly open water conditions and species to those of the bog. 

 But this succession may even be safely carried a step farther, as i* 

 clearly shown by an important observation by Wickham ('97, p. 126;) at 

 Bayfield, Wisconsin. He states that "The Water Beetles were not 

 found in such abundance as I had hoped from a perusal of lists from 

 northern localities, and of those named in the present report a great 

 part were taken not in water but under moss in damp spots — a pecu- 

 liarity which I have noted in some species of Agabus collected on a 

 previous trip to Alaska." Under such conditions as this the bog asso- 

 ciation of water beetles may even be able to spread beyond the bogs- 

 and invade the forest, a change of haMtat which ha® been recognized 

 among plants but has been lai'gely overlooked by students of animals.. 

 It is only by the detailed study of habitg,ts that the significance of suchi 

 facts can be understood and the peculiarities of succession determined 

 for different regions. 



There is thus seen to be a very perfect transition from the bog 

 forest into that of the balsam and spruce, and the dominance of coni- 

 fer trees clearly shows that the beetles frequenting such forests will be 

 on the increase as the aquatic association of beetles declines in domin- 

 ance. The methods and detailed order of this succession awaits in- 

 vestigation, but it is clearly dominated by the forest succession. 



4. The Forests and Their Beetle Associations. 



The gradual and perfect character of the transition from the bog 

 to the balsam-spruce forest has just been indicated. This is paralleled 

 by a corresponding transition from the park-like openings and the bare 

 ridges to the forest. These habitats change as rapidly as soil, humus, 

 and shade increase at the margins of the openings; and as shrubs and 

 young trees encroach upon the open. Thus as the bogs fill up, and as the 

 soil increases on the rock surfaces, both habitats tend to become trans- 



