Between these two extremes, most species exist as constellations of subpopulations where most individuals interact within their small group, with the rare individual dispersing over greater distances. These species are structured as a meta-population, or a population of sub-populations. These sub-populations are distributed across a landscape (or a military installation) as many “occurrences.” Each occurrence has a low probability of persisting over the long term, in isolation from other occurrences. Most sub-populations are simply too small to be resilient to environmental variation, or demographic or genetic bottlenecks. Neighboring occurrences are constantly providing, at some low but critical rate, “new blood” into a given sub-population. These neighboring occurrences also provide sets of “founder” genes that will re-colonize a vacant area.
Meta-populations can be envisioned, then, as a galaxy where each “star” is a subpopulation. These “stars” are winking off and on as sub-populations disappear, and then reappear as the vacant areas are re-colonized. The space between these stars—the voids—is not suitable habitat for these creatures, and so is simply not available for colonization by this species.
Next Page: Sources and sinks and their importance
Bob Unnasch, Ph.D.
Sound Science LLC