270 



POPULATIONS 



tions, utilizes elaborate and repeated assays 

 of population size. These techniques were 

 used: 



1. Records of furs taken by trappers 



2. Statements in the literature 



3. Questionnaires concerning hare abundance 



4. Field work (conducted at nine stations) 



(a) Trapping (both live and dead traps) 



( b ) Censuses of various sorts 



( c ) Observations on hares seen 



(d) Information derived from scatology 



This ends the treatment of the determina- 

 tion of population size. The reader will 

 recognize that, while this problem is tech- 

 nically the central one in population re- 

 search, it is often a difficult one to put into 

 actual, accurate operation. He will recog- 

 nize also that some of the applications in 

 the literature are inadequate for one reason 

 or another and that in planning any popu- 

 lation venture this whole matter demands 

 prior thoughtful attention. 



Scope* 



Something is gained by examining briefly 

 the practical categories into which modem 

 population studies fall. While these are not 

 necessarily the most logical ones, they show 

 how the entire field is developing. There are 

 at least six of these categories. 



1. Studies of natural populations (both 

 intraspecies and interspecies) 



2. Studies of experimental laboratory 

 populations (both intraspecies and in- 

 terspecies) 



3. Studies of human populations (intra- 

 species) 



4. Epidemiological studies (interspecies) 



5. The approach through theory 



6. The approach through experimenta- 

 tion based on theory 



A brief discussion of each of these categories 

 is relevant. 



1. Natural Population Studies. By and 

 large, these studies deal with the distribu- 

 tion, total size, density, territory relations, 

 equilibrium and departures from it, preda- 

 tion and other interspecies competition ef- 

 fects, intraspecies feeding activities, and the 

 relation of the population to its immediate 

 physical environment. Animals that have 

 been most studied as natural populations 

 include insects, fishes and plankton, birds, 



• Before reading this section the reader is 

 encou»aged to re-examine the historical chap- 

 ters, particularly pages 60 and 61. 



and mammals. Each of these groupings may 

 be broken down more specifically (although 

 by no means completely) as follows: 



(o) Insects: coUembola; locusts; chinch 

 bugs; gall midges and other midges; 

 tsetse flies; mosquitoes; Drosophila spp.; 

 Mediterranean fruit fly; boll weevil; 

 Japanese beetle; European corn borer; 

 cutvvorms; codling moth; thrips; bees 

 and ants 



( b ) Fishes and Plankton: * 



(1) Marine fishes: salmon; European 

 plaice; cod; haddock; herring; 

 mackerel; hake; halibut 



(2) Fresh-water fishes: some game 

 fishes; trout; whitefish; carp; 

 Ameiurus; Gambusia 



(3) Plankton: studied relative to (a) 

 composition, density, and distri- 

 bution; (b) food for the fish 

 population 



(c) Birds: pheasants; snowy owl; bobwhite; 

 song sparrow; ringdove; mourning dove; 

 house wren; red-winged blackbird; great 

 horned owl; ducks and geese; gulls and 

 terns; sparrow hawk; starlings; finches; 

 titmice; English robin; swifts 



Id) Mammals: voles; mice; lemmings; rats; 

 hares and rabbits; chipmunks; squirrels; 

 muskrats; skunks; weasels; shrews; 

 Arctic fox; red fox; lynx; sheep; elk and 

 deer; monkeys and apes 



(e) Miscellaneous: soil protozoa and bac- 

 teria; triclad worms; snails (particularly 

 Lymnaea and Goniohasis); oysters 



2. Experimental Populations. The back- 

 groimd and development of experimental 

 population studies were discussed in some 

 detail in the historical section. These studies 

 make their prime contribution by a control 

 of the physical and biotic environment not 

 possible in the field. The laboratory studies 

 attempt to analvze a specific group relation- 

 ship that would be technically difficult, if 

 not impossible, in many natural popula- 

 tions. Thus they are viewed as comple- 

 mentary and supplementary to field work. 

 The general problems most studied in the 

 laboratory are: 



(a) Intraspecies 



( 1 ) Population growth-form 



( 2 ) The nature of population density 



(3) The eff"ect of density on re- 

 production and mortality 



" This is a logical association. The plankton 

 are often studied as populations purely because, 

 in furnishing food for the fish populations, they 

 occupy a unique place in the food chain of 

 the community. 



