I. Geographic Distribution
A. Global Patterns
B. Regional Patterns
C. Island Biogeography
D. Landscape and Stream Continuum Patterns
II. Spatial Dynamics of Populations
A. Expanding Populations
B. Metapopulation Dynamics
III. Anthropogenic Effects on Spatial Dynamics
B. Disturbances to Aquatic Ecosystems
C. Species Introductions
IV. Conservation Biology
GEOGRAPHIC RANGES OF SPECIES OCCURRENCE GENERALLY REFLECT THE tolerances of individual organisms to geographic gradients in physical conditions (see Chapter 2). However, most species do not occupy the entire area of potentially suitable environmental conditions. Discontinuity in geographic range reflects a number of factors, particularly geographic barriers and disturbance dynamics. By contrast, suitable habitats can be colonized over large distances from population sources, as a result of dispersal processes, often aided by anthropogenic movement. Factors determining the geographic distribution of organisms have been a particular subject of investigation for the past several centuries (e.g., Andrewartha and Birch 1954, Price 1997), spurred in large part by European and American exploration and floral and faunal collections in continental interiors during the 1800s.
The spatial distribution of populations changes with population size. Growing populations expand over a larger area as individuals in the high-density core disperse to the fringe of the population or colonize new patches. Declining populations shrink into refuges that maintain isolated demes of a metapopulation. Spatial distribution of populations is influenced to a considerable extent by anthropogenic activities that determine landscape structure and introduce (intentionally or unintentionally) commercial and "pest" species to new regions. Changes in insect presence or abundance may be useful biological indicators of ecosystem conditions across landscapes or regions, depending on the degree of habitat specialization of particular species (Rykken et al. 1997). Changes in the presence and abundance of particular species affect various ecosystem properties, encouraging efforts to predict changes in distributions of insect populations.
Geographic distribution of species populations can be described over a range of scales. At the largest scale, some species have population distributions that span large areas of the globe, including multiple continents. At smaller scales, individual species may occur in a suitable portion of a biome or in suitable patches scattered across a biome or landscape. At the same time, species often are absent from apparently suitable habitats. The geographic distribution of individual species can change as a result of changing conditions or dispersal.
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