Habitat describes the space where a species is found and traditionally in ecology, it was thought of as a set of external environmental factors that an organism would seek out to meet their needs in an energy efficient manner. More and more, we have seen that species can also alter the environment to meet their needs by controlling the availability of resources, thus creating habitat for themselves and other organisms. Autogenic ecosystem engineers represent the extreme end of this spectrum, self-assembling structures and selecting for other community members that can benefit from these structures such as coral reefs or tree canopies.
While there is certainly a spectrum of environmental conditions that all organisms must operate within such as temperature and moisture gradients particular to a species, ecosystem engineers can alter the abiotic and biotic conditions that surround them to create habitat. They also indirectly alter their surroundings by creating habitat for other organisms that continue to create habitat in increasingly smaller nested networks moving from large to small, vertebrates to viruses, further controlling the movement and availability of resources on smaller spatial scales. From this perspective, habitability is not found but assembled organically through the interactions of many living things.
Jones and colleagues published the first paper in ecology to define and discuss the ecosystem engineer concept in 1994. Their paper highlights the pervasiveness of engineering organisms in virtually every environment on earth. There are the intuitive cases such as the beaver that redistributes resources by creating a pond and the less intuitive cases such as grasses that redistribute resources by creating above ground biomass that fuels periodic fires. At first read, engineers seem so pervasive that it would be easier to identify organisms that do not control the availability of resources for other organisms- a fact that would lead to considerable criticism of the term after its introduction. Yet, the authors emphasize that while prevalent, the impact of engineers on their environment and other organisms is highly variable and scale dependent in both space and time. They argue that the engineers with the greatest impact are those “species with large per capita effects, living at high densities, over large areas for a long time, giving rise to structures that persist for millennia and which affect many resource flows”. Jones and colleagues are also quick to implicate us as “human analogues” for the ecosystem engineer concept.
I argue that humans have easily become the most successful environment altering species and that ecological habitability has lost meaning for us. We can live in and exploit environments that far exceed our physiological limits and in high densities over large areas. We so precisely control the availability of resources that we are depleting global supplies. In effect, we stopped seeking habitability and we started manufacturing it. In doing so, we have redistributed and constrained the availability of our resources to the extent that we affect habitability for many other organisms. Looking now at how Jones and colleagues originally described the type of ecosystem engineer that would give rise to the greatest impact, it reads as though they are specifically describing us.