Academic literature on the topic 'Desert locust swarm'

Organisms move, and their movement can take place by walking, swimming, or flying; via transport by another organism (phoresy); or by a vehicle such as wind or current (Dingle 1996). The functions of movement include finding food or mates, escaping from predators or deteriorating habitats, the avoidance of inbreeding, and the invasion and colonization of new areas. Virtually all life functions require at least some movement, so it is hardly surprising that organisms have evolved a number of structures, devices, and behaviors to facilitate it. The behavior of individuals while moving and the way this behavior is incorporated into life histories form one part of this chapter. This discussion focuses on the action of selection on the evolution of individual behavior, on how specific kinds of movement can be identified from the underlying behavior and physiology, and on the functions of the various movement behaviors. The other major part of our discussion focuses on the consequences of movement behaviors for the ecology and dynamics of populations. The pathways of the moving individuals within it can result in quite different outcomes for a population. First, movements may disperse the members of the population and increase the mean distances among them. The separation may be a result of paths more-or- less randomly chosen by organisms as they seek resources, or it may be a consequence of organisms avoiding one another. In contrast to dispersing them, movement may also bring individuals together either because they clump or congregate in the same habitat patch or because they actively aggregate through mutual attraction. Clumping can also lead to aggregation and mutually attracting social interactions. A classic example is the gregarious (aggregating) phase of the desert locust (Schistocerca gregaria), in which huge swarms of many millions of individuals first congregate in suitable habitats and then develop and retain cohesion based on mutual attraction. The foraging swarms make the locust a devastating agricultural pest over much of Africa and the Middle East (Farrow 1990; Dingle 1996). It is the aggregation of locusts that makes them such destructive pests; they would be far less harmful if the populations dispersed.

Viewed from space by human eyes, the predominant colours of our planet are the blue of the oceans and the white of the clouds. The blue of the oceans forms the subject of another of our chapters. However, if one focuses on the land masses other colours dominate. On land the white colour still features prominently in the polar areas covered with snow and ice, but zoom in on lower latitudes and much of the land is a mix of the green of vegetation and the brown of more arid areas. Green dominates large areas of land, so unless you are reading this in a desert, during the high-latitude winter, or in a highly urban area, then green will probably feature prominently in your surrounding landscape. One answer to the question that heads this chapter is that the climate (often rainfall) allows some parts of the land to be green with plant life, while making other areas arid and brown. However, this green of extensive plant life is still a puzzle—plants are food for a wide range of animals, so why is so much food left unused? Swarms of locusts, destroying most plants in their path (be they biblical plagues or modern day outbreaks), are the exception not the rule. But why is this so? Why are so many parts of our world green in the face of this threat from herbivores? As we will see, if herbivores are the key to our question, then what starts as a question in plant ecology ends up being a question about factors that limit the size of herbivore populations. In effect, we need to understand why herbivore populations do not increase in density to such a level that they destroy all the available plants, giving a land that is brown rather than green. Until the middle of the twentieth century if you had put the green world question to biologists, many of them would probably have suggested that it was not in the interests of a species to consume all of its food reserves.