greatly i)rclcrrf(l tlu- liranclies of (kriduous trcfs 

 (I'almgren 1930). 



Tlircc s])fcii\s of garter snakes are fouiul together 

 in Michigan, but TUamnophis biitleri is restricted to 

 grasses and sedges near water, T. saitritiis prefers 

 bushy areas near water and is a fret|uent climber, 

 while T. sirtalis occupies a variety of habitats regard- 

 less of proximity to water (Carpenter 1952). 



The evidence indicates that if the type of cover 

 recjuired by a species is missing, that species will not 

 occur even if all other conditions are favorable. This 

 is of particular concern to the wildlife manager. He 

 must learn to control succession, either by accelerat- 

 ing or retarding it, to give species of game the cover 

 that they need (Leopold 1933, Elton 1939). 



Food and predators 



Since most organisms select their food from 

 that most easily available to them, it is usually more 

 important in characterizing their niches to indicate 

 the type of food consumed and the stratum or exact 

 microhabitat from which it is obtained than merely 

 to give a list of species that are taken. Thus, fresh- 

 water fishes are best classified as mud-eaters, plant- 

 eaters, plankton-eaters, mollusk-eaters, insect-eaters, 

 fish-eaters, detritus-eaters, or omnivora ( Forbes 

 1914). In a similar manner birds have been cate- 

 gorized into aerial-soaring, or perching insect-eaters ; 

 those which feed on foliage insects, seeds, or nectar : 

 timber-searchers or drillers ; feeders on ground in- 

 sects, or seeds, and predators (Salt 195F). 



The accurate description of feeding niches re- 

 quires careful attention to details. Two or more spe- 

 cies may feed together in the same community but be 

 segregated from each other because they search for 

 their food from dififerent plant species, from different 

 parts of the same plant,- or they take dififerent foods 

 from the same parts of the same plants. Furthermore, 

 species may overlap broadly in their feeding habits 

 during most of the year but be clearly segregated dur- 

 ing periods when food is scarce (Gibb 1954, Belts 

 1955). 



The difl^erence in type of vegetation inhabited by 

 each of the three species of Michigan garter snakes 

 mentioned a moment ago correlates with differences 

 in kinds of food each consumes : Thamnophis hutleri 

 feeds almost entirely on earthworms and leeches ; 

 T. saurilus. on amphibians, fish, and caterpillars ; and 

 T. sirtalis, on both earthworms and amphibians, as 

 well as a few mammals, birds, fish, caterpillars, and 

 leeches (Carpenter 1952). Several species of Dro- 

 sophila flies may occur in a single region, especially in 

 the tropics, but each species feeds preferentially on a 

 different species of yeast (Dobzhansky ef al. 1956, 

 Cunha ct al. 1957). The spider- wasps Anophits 



scmirujus and .-/. apicidatiis have many very similar 

 behavior patterns, but they avoid competition at a 

 critical ])oint. A. apiciilatiis hunts for its food in the 

 sandy areas where Iioth s])ecies nest, while A. semi- 

 nijiis moves to woods or shrubby areas to feed and 

 feeds on a different group of organisms at that 

 (I'.vans 1953). 



Differences of food habits between related species 

 often correlate with ditTerences in size. Thus the 

 large-billed parrot crossbill of Europe feeds on pine 

 cones, the smaller-billed red crossbill on spruce cones, 

 and the still smaller-billed white-winged crossbill 

 on larch cones (Lack 1944). Two species of fish hav- 

 ing very similar re(|uirements occur in the same type 

 of habitat in British Columbia, but Coitus rhotheus 

 has a larger mouth than C. asper, and feeds on larger 

 kinds of food (Northcote 1954). Size differences 

 even occur commonly between related species of cope- 

 pods that live together in the same body of water 

 (Hutchinson 1951). Male and female differences 

 of size, structural adaptations, and habits may occa- 

 sion distinctive preferences in kinds of food taken 

 and feeding location which make it possible for the 

 two sexes to live together more comfortably within a 

 small area than were their requirements absolutely 

 identical (Rand 1952). 



For describing the position a species occupies in 

 the food chains of a community, it is necessary to 

 indicate not only the kinds of food eaten but also 

 what species prey on it and the manner in which they 

 do so. Some parasitoids are quite specific as to the 

 kinds of animals in which they deposit their eggs. 

 If a parasitoid that is specific to a prey species is 

 present in a niche, the simple presence of that para- 

 sitoid may determine the success with which the prey 

 species will compete for and fully occupy the niche. 



BEHAVIOR ADJUSTMENTS 



Somehow an animal must get into a hos- 

 pitable niche out of the multitude of niches avail- 

 able to it. Doubtless, some animals accomplish this 

 passively by the instrument of random dispersal of 

 spores, eggs, or larval stages, some of which by 

 chance reach favorable locations, there to mature and 

 survive. But higher animals have more complex ner- 

 vous systems, greater intelligence, and their sense 

 organs are more highly evolved. They are equipped 

 to search actively for and recognize niches hospi- 

 table to them either by sight, smell, contact, or other 

 means. For instance, the intricate migratory behavior 

 of birds and other animals is such that they seek out 

 nearly constant climatic environments throughout the 

 year. 



The apparent ease and speed with which a new 

 generation of individuals discriminates a hospitable 



Niche segregation 249 



