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7 Biogeography 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. | 7 Biogeography 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 A. Fragmentation B. Disturbances to Aquatic Ecosystems C. Species Introductions IV. Conservation Biology V. Models of Spatial Dynamics VI. Summary 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 .
