Ecosystem engineering of public and private goods

We draw an analogy between public and private goods, and the effects of ecosystem engineering, in order to understand the difference between species which modify environmental conditions, and those which create new abiotic resources. A public environmental good, in our sense, refers to something that does not get ``used up" (e.g. alteration of temperature), while a private environmental good can be consumed by members of the population (e.g. refugia or specific environmental states). We discuss the results of a population dynamics model of an ecosystem engineer that affects its abiotic environment, and, in turn, the abiotic environment affects the engineer's density-dependent and density-independent population growth rates. Our model smoothly bridges separate models for these two different types of environmental "good". Results of the model demonstrate that the environmental feedback to the engineer can lead to bistability or runaway population growth, but that population oscillations can be produced where private goods are created.