| Abstract: |
In traditional ecology, emphasis is usually placed on the "vertical" exchange of energy between different trophic or energy levels and on the problem of defining the different links in this food chain. Biogeographers, on the other hand, concentrate on a complementary yet more "horizontal" view of the world. Their central concern is the distribution of species in time and space. pg 263 Author presents a stability-time hypothesis. Stability is the concept that: with all else held constant, the more stable and unchanging an environment, the greater the number of species it will contain. Notes that his hypothesis says nothing about total biomass, only about number of different species. pg 264 Three consequences arising from this hypothesis: 1) More stable environments are conducive to biological accomodation and hence large numbers of species
when flucuation is limited, it pays for a species to concentrate on utilizing a limited range of resources as effectively as possible and to adapt tightly to a specific and relatively small habitat niche from whihc it may be able to exlcude other species successfully. 2) Elements or species in resilient systems persist, although their numbers and distributions may alter dramatically over time. Their more finely-tuned, stable counterparts are inherently more fragile and less tenacious. 3) Stenotrophy Species with low maximum intrinsic rates of increase, narrow physiological tolerance limits and a high ability to resist competition from other species Eurytopy Species attuned to a biologically-controlled environments broad. Physiological toleration, a high intrinsic rate of increase and a failure to specialize on the consumption of narrow energy sources. pg 265 As a general rule, the greater the variability of an environment, the greater the advantage of behavioral plasticity. Studies on temperate, tropical and desert bird species indicate that when resources are abundant, constant and reliable, the maintenance of discrete, intraspecifically defended territories is the rule. As the temporal and spatial patchiness and unpredictability of habitat circumstances increase, however, looser forms of territoriality are to be found, as well as inter- and intraspecific flocking. While mor ethan one factor may be responsible, he has demonstrated that the degree of patchiness and unpredictability of food resources is highly correlated with different tpes of territorial behavior. The likelihood that the \ipredictability\i of resources, rahter than abundance of variability, may play a central and determining role in adaptation. reliable but locally unpredictable food resources in the tropical froest. In the tropical grasslands food is predictable at all season, but not available throughout the year. Hence birds defend terriotories to assure themselves of food during the reliable time and leave the habitat when food will be predictably scarce. In the forest food is more orless reliable throughout the year, but locally unpredictable. In this situation territories are not maintained by many species.... Food resources probably exert the greatest influence on spacing system. pg 267 While the band-territory concept is acceptabl from one point of view, it predicts very little about the movement of individuals and families over time. pg 268 Aggregationinto larger social groupings to place time of plenty when resources in a local area could support a greater number of people. During other times of the year, smaller, highly mobile groups were the rule. From ethnographic examples, from a normative point of view, social organization can be described as circumscribed and rigidly defined. From the historical or observer's point of view, group structure and composition is depicted as extremely loose and fluid. pg 270 In relatively severe, variable environments of low predictablity, populations exhibit resilience and the ability to persist over time. pg 271 The fluidity of movement with H-G society, while variable in degree partly because of external circumstances, has the effect over the long run of keeping internal barriers to a minimum.
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