Background

Populations, collections of interacting organisms of the same species, have a variety of interesting structures. For example, populations contain individuals of different ages (newborn, 1-, 2-year-old, and so on) and sexes (male and female), and thus have age-sex structures. Another universal and fascinating characteristic of populations, which will be the focus of this book, is that they have spatial structures, meaning that we can always find more or fewer individuals in some areas than in other areas, while sometimes we find none at all. On top of that, such spatial structures are dynamic, meaning that they change over time (e.g., an area with none of a species in a year may have a few individuals of that species in the next year). The processes underlying spatially structured population dynamics are called BIDE, which stands for birth, immigration, death, and emigration (Bartlett 1960; Pulliam 1988; Thomas and Kunin 1999). While birth and immigration make populations increase, death and emigration make them decrease. Furthermore, immigration and emigration are linked, in the sense that immigrants in an area must be emigrants from some other areas. The BIDE process is also called demography, while immigration and emigration combined can be called dispersal movement, or simply movement. Spatially structured population dynamics and underlying BIDE processes are driven by heterogeneity and dynamics of abiotic environment, along with intra- and inter-specific interactions.