Fire ant dispersal along Texas highways

All organisms require specific resources for growth and reproduction. Favorable environments lead to positive population growth and, eventually, to depletion of limited resources. This depletion creates the need for dispersal to relieve crowding and to provide access to new resources. Dispersal can, therefore, be for the purpose of locating necessary resources; e.g., food, mates, shelter, or oviposition sites. Price (1984) described populations as not just increasing or decreasing in numbers, but also moving from place to place and expanding and contracting. Dispersal is adaptive, permitting individuals to escape crowding and colonize new habitats.

Organisms must be capable of dispersal to new habitats, and active dispersal requires energy to walk, swim, or fly to a new habitat Passive dispersal does not require energy but does require favorable environmental conditions (wind, water, host). Available habitats require that organisms have access to the habitats, and space or other resources must be available to the immigrant organism. However, the overall geographic range of an organism is seldom one continuum of habitat. Organisms tend to avoid unfavorable habitats; therefore, populations of some organisms may be found in clumps of favorable habitat but may be absent from the vast majority of its habitable range. Haas (1995) found that robins and tlirasbes, for example, traveled along wooded draws connecting planted windbrealcs as if the draws were stepping stones b>etween the windbreaks. The likelihood was greater that birds would disperse between habitats when habitats were connected by a wooded draw.