Presidential Address: Parasites on a Shrinking Planet

Abstract

Planet Earth is shrinking at an ever-accelerating pace. It is not shrinking geologically, of course, or even atmospherically, unless you refer to the growing ozone hole. It is not even shrinking biologically in terms of net biomass, though some might argue that biodiversity is shrinking. But for Homo sapiens as a species, the planet is definitely shrinking. Why is this? Because, at least for now and the foreseeable future, planet Earth is our sole living space. The effective size of the available living space for any species is determined by the ability of that species to disperse throughout potential habitats, to successfully colonize those habitats, and to effectively utilize the resources available to them in those habitats. In terms of terrestrial habitats, since we are essentially a terrestrial species, we have pretty much dispersed to and colonized the entire planet. But we are an ingenious species, highly adaptable, and thus likely to find even other Earthly habitats to colonize under the ocean, beneath the earth's surface, in areas such as Antarctica and desert landscapes where we can trade minerals, wind and geothermal energy, and other non-biological resources for food. Homo sapiens seem to be the ultimate invasive species. But, are we really? At first glance, no other species, throughout any of Earth's history, seems to come close to rivaling the capacity of Homo sapiens for dispersal and colonization of new habitats. The exceptions, of course, are the other species that we intentionally, or unintentionally, take with us as we disperse. These include the plants, animals, and microbes that we take with us as sources of food and fiber the livestock, the fish, the poultry, and so on. Also included are the parasites those that live on and in us, those that live on and in the species that we move around with us, and especially those that use both we and our food animals and companion animals as hosts. Since there are apparently more parasitic organisms than free living, these parasites must be actually the ultimate invasive species, using their lowly human and synanthropic animal hosts as vehicles for their own dispersal. Except for the pets or companion animals, we don't really want to take the other species with us. But we have no choice we have to eat. And we certainly don't want to take the parasites with us. But we seem to have no choice here either the parasites are just too adaptable, too ingenious, too good at staying with us despite our greatest efforts to leave them behind.