Evol Ecol Res 1: 719-729 (1999) Full PDF if your library subscribes.
Optimal population harvesting in a source–sink environment
Per Lundberg * and Niclas Jonzén
Department of Theoretical Ecology, Ecology Building, Lund University, S-223 62 Lund, Sweden
Author to whom all correspondence should be addressed.
We derive optimal harvesting strategies for a single population in a simple two-habitat environment. We let one of the habitats function as a source with logistic population growth and the other habitat as a sink that cannot have positive equilibrium population density without immigration from the source. The dispersal between habitats is assumed to be density-independent and cost-free. The total yield function for simultaneous harvesting in the two habitats has no interior extreme point. Given that maximum sustainable yield is the management goal (not necessarily a very wise one), two possible harvesting policies emerge. Either the sink should be harvested at its optimal rate (provided that the yield function has a maximum), or the sink should be harvested at a maximal rate and the source at its optimal rate. In the former case, the yield from the sink always exceeds the yield from the source; in the latter case, the reverse is often, but not always, true. The relationship between maximum per capita growth rate in the source and the dispersal parameters determine which of the above two cases applies. Regardless of harvesting strategy, or if we harvest at all, the sink often has the highest population density. Harvesting the sink will always result in the highest yield. Both source and sink harvesting generally destabilize the dynamics of the total population. Although sources and sinks are real, it may be impossible to distinguish between them in the field. Our results are, therefore, not directly or easily applied to real harvesting situations. Given that there are habitat quality differences of the source–sink kind, however, harvesting decisions may result in unexpected and unwanted outcomes that population management should take into account.
Keywords: dispersal, harvesting theory, population harvesting, population management, population stability, source–sink dynamics.
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