FEATHER LICE I3I 



Ecological Niches. If the louse population of any individual bird is 

 examined it is evident that this comprises a number of quite different 

 types of Hoe. Each of these is distinguished by habits and general body 

 form and most birds are found to harbour five or six, some even up to 

 twelve of these different genera. This diversity of lice can be explained 

 by the theory of ecological niches. 



It is a truism that no place which can support life is without Hfe. 

 Every possible habitat and source of food — that is, every ecological 

 niche — will be utilised by some form of organism. It can be stated 

 broadly that all the higher categories of classification, such as the orders, 

 are based on the original divergence of the ancestral stock to fill 

 available ecological niches. The order Anseriformes (ducks, geese and 

 swans) is descended from a line which became adapted to life in the 

 water, and the Ciconiiformes (storks and herons) from one that became 

 adapted to life in swamps and marshes. 



We have seen that the reptile-like ancestors of the birds developed 

 feathers and thus produced a new type of environment— an empty 

 ecological niche. This was occupied by a primitive free-living insect 

 which gave rise to the parasitic bird-lice of to-day. 



The invasion of any new territory, where food is unlimited and 

 competition absent, seems to act as a great stimulus to evolution. ^ The 

 primitive, unspecialised, ancestral Mallophaga finding such a territory, 

 must have rapidly filled the ecological niches then available on the 

 body of the host, and also those formed subsequently through the 

 differentiation of the plumage during the evolution of the birds. The 

 occupants of each ecological niche diverged from one another as they 

 became specialised and adapted to the particular environment in 

 question — whether of the head and neck or wings and back. In the 

 same way the marsh dwelling birds with their long legs, long necks and 

 long pointed bills which adapt them for life in that particular ecological 

 niche, differ from the birds of the ponds and lakes, with their short legs, 

 webbed feet and flattened beaks. 



Looking at the louse population of most birds it is a simple matter 

 to pick out the lice adapted to two of the ecological niches, namely, 

 those of the head and of the wings and back. The Mallophaga living 

 on the head and neck, where they are out of reach of the bird's beak, 

 have less need for rapid movement and have become adapted to a 

 comparatively sedentary life on the feathers. The abdomen is short 

 and round and not particularly flattened, the legs are short with strong 



FFC— K 



