Resources and Biodiversity

What is the relationship between the diversity of resources (e.g., space, sunlight, water, nutrients) and biodiversity? In most cases it is direct and positive—that is, the greater the diversity of resources the greater the biodiversity.  The relationship is also often mutually reinforcing—that is, byproducts, detritus, and the organisms themselves increase the diversity of the resource base. Of course, ultimately both resource and biodiversity are limited by both abiotic and biotic controls. The relationships look something like this:

I analyzed a model of this same type, involving geomorphic systems, here. The upshot is that when the mutually reinforcing interactions between resource and  biodiversity are stronger than the abiotic and biotic limits on diversity, the system is dynamically unstable. This indicates that changes are likely to persist and grow over time, rather than to be offset. From the diversity perspective, this can be good—a small, local rise or surge in resource or biotic diversity would disproportionately increase overall diversity (e.g., gap dynamics in forests). However, it can also be bad—a decline in either can trigger an overall spiral of decline (e.g., effects of surface mining).

The resource diversity-biodiversity feedbacks will indeed be dominant, for good or ill, when an environmental system is well shy of its biotic or abiotic limits. As those limits are approached however, those negative arrows in the figure become dominant and the system is dynamically stable. That means that the effects of not-too-large changes or disturbances are offset or damped, returning the system toward its original state. Thus neither resource diversity nor biodiversity can increase indefinitely. Assuming the limits also work on the lower end—that is, there are always a minimum variety of resources available for some biota, even if only microbes, and a minimum variety of biota to exploit them—this also prevents extinction of biodiversity or complete vanishing of resources.

The implications of these dynamics for geomorphic systems are discussed in the article I referred to earlier. With respect to biodiversity, the restrictions on development in one direction or another are likely more variable and arguably less well known than for geomorphology, where factors such as base level and sedimentary accommodation space provide clear limits. Biodiversity involves different biota, of course, with different needs, tolerances, and sensitivities to various resources. Other than some obvious outer limits such as finite space and solar input (and photosynthetic efficiency), what are the bounds to diversity at the community level?

Studies of ecosystem engineering and niche construction may be extremely helpful in this regard. Introduced (invasive) species that are ecosystem engineers may provide opportunistic experiments where interrelated changes in resource and biodiversity may be observed.  

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