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Ecological Knowledge and Environmental Problem-Solving Concepts and Case Studies (1986) / Chapter Skim
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5. Scales in Space and Time
Pages 68-74

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From page 68...
... Focusing on the consequences of single perturbations can lead to a failure to perceive the patterns and cumulative effects of those perturbations over time and space. If a population or community is repeatedly disturbed for long enough, changes qualitatively different from and more serious than the effects of single perturbations often occur.
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From page 69...
... In addition, greater homozygosity for the population as a whole might be associated with reduced genetic variability and lead to reduced ability of the population to adapt to environmental change (Soule, 19801. Mating with near relatives also increases the likelihood of producing individuals homozygous for recessive traits that are lethal or severely deleterious.
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From page 70...
... In general, the minimal number of individuals nec essary to support a population for a long period increases as average population density decreases. The average area necessary to support an individual animal is greater for predators than herbivores, and in general it increases with body size within groups of similar species (McNab, 1963; Schoener, 19681.
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From page 71...
... Spatial (::onsiderations Population dynamics in patchy environments are determined primarily by the rates of individual movements between patches and rates of local population extinction. The properties that enable populations to maintain themselves in patchy environments include high dispersal rates, tendencies to cross unsuitable habitats, high growth rates, early reproduction, and high reproductive rates (Baker and Stebbins, 1965; MacArthur and Wilson, 1967~.
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From page 72...
... However, current rates of human-caused disturbance are so high in most areas of the world that species requiring late stages of succession, such as old-growth forests, are in the most precarious positions (Chapter 171. In addition, many organisms have complex life histories in which different stages require distinct habitats.
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From page 73...
... CONCLUSIONS The great importance of size and spatial relationships in the working of ecological processes points to the importance of dealing explicitly with scales in space and time in all efforts to solve environmental problems. The major changes in processes and products that accompany changes in spatial and temporal scales can escape attention, if efforts are not directed
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From page 74...
... Individual trees could be especially susceptible to attack by herbivores, and the maintenance of large populations of trees could depend critically on patches. Similarly, patches of high concentrations of nutrients resulting from defecation of zooplankton might be essential to survival of algae, and patches of high concentrations of plankton might be important to the survival of marine fish larvae (Sissenwine, 19841.
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Key Terms

  • species adapted
  • late stages
  • near relatives
  • direct sunlight
  • lake washington

  • physical disturbance
  • genetic variability
  • severely deleterious
  • patch size
  • viable population

  • animal species
  • population dynamics
  • patchy environments
  • local populations
  • successional stages

  • ecological processes
  • physical environment
  • minimal viable
  • single perturbations
  • maintain themselves

  • patches increases
  • reduced genetic
  • habitat type
  • spatial relationships
  • increased homozygosity

  • size varies
  • striking increase
  • cause effects
  • habitat patches
  • southern indian


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