nutrition affecting reproduction even under 

 relatively mild conditions." 



Similarly, Teer et al. (1965:56) stated: "Changes in 

 carrying capacity occur rapidly and frequently, and are often 

 independent of density of grazing herbivores." Du Plessis 

 (1972) noted that "Blesbok lose condition during the dry 

 season." Rogers (1987) reported that reproduction in black 

 bears was controlled mainly in a density-independent manner by 

 fruit and mast supplies that fluctuate in abundance from year 

 to year. 



Although the influence of various factors on population 

 dynamics sometimes varied with density, density was not a 

 consistently regulating factor nor did it function 

 deterministically . Often, density was only a coincident 

 factor, thus regression analyses and correlations can result 

 in false conclusions about cause and effect. Population 

 growth and decline were both limited by the length of time 

 that extrinsic factors (especially weather) remained either 

 favorable or unfavorable. This, together with the behavioral 

 and biological capabilities of the animals, determined the 

 "distribution and abundance" of the deer. 



It is clear that application of regulation or limitation 

 theory must take variable exogenous factors into account. 

 These factors, for many populations, tend to hold them below 

 densities where density-dependent processes might operate. To 

 date, with rare exceptions, too little emphasis has been 

 placed on variable environmental conditions and heterogenous 

 habitat. The natural tendency of man is to lump, type, or 

 categorize, thus variability has been considered the 

 exception. We maintain that variability and heterogeneity are 

 more pervasive and applicable than stable equilibria. 



The importance to population dynamics of heterogeneity of 

 the environment in both space and time interacting with 

 characteristics of the animal species will perhaps be more 

 clearly portrayed by use of illustrations. Heterogeneity of 

 habitat quality and quantity in space is illustrated by Figure 

 12.1. The relative mix and juxtaposition of types of habitat 

 quality and quantity will vary from area to area, by species, 

 and by ecological amplitude of the species. Despite and 

 because of this variability, the major point of Figure 12.1 

 remains; habitat is heterogeneous in space, not all space is 

 equal in habitat quality and quantity. The performance and 

 fates of individual animals occupying individual home ranges 

 will vary as individuals, not as l/N. 



Habitat quality and quantity are also heterogeneous in 

 time (Fig. 12.2). Habitat quality and quantity in the 3 

 different time periods illustrated (Fig. 12.2 A, B, and C) do 



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