Final answer:
Reduction of a population often leads to decreased geographic range because smaller populations are less likely to disperse into and occupy marginal habitats. Clumped population distributions provide protection for individuals but do not directly relate to geographic range.
Step-by-step explanation:
Reduction of a population can lead to a decreased geographic range due to a number of factors. The key reason is that smaller populations contribute to a lower rate of dispersal into marginal habitats. These habitats are considered 'marginal' because they are less optimal for the species' survival, and often support smaller numbers of individuals. When there are fewer individuals in a population, it is less likely that some will disperse into these less favorable areas, as there may not be enough individuals to 'spare' from the main population. This results in a decreased geographic range.
A clumped population distribution can also be beneficial for prey animals. Being part of a larger group provides better protection against predators, although this is not the direct cause of a decreased geographic range. Population distribution itself is influenced by numerous factors, including the availability of resources, such as water in arid environments, which can lead to an evenly spaced population, or patchy resource distribution, which can lead to clumping.
Population isolation is another important aspect that is a result of habitat fragmentation. Isolation restricts movement and, consequently, immigration and emigration, affecting the population's range and distribution. It is more pronounced in landscapes altered by human activity where barriers like highways and urban areas prevent the free movement of individuals or the dispersal of seeds and spores, leading to even further decreased geographic ranges for certain species.