The Paradox of Enrichment: Introduction

The namesake of this blog is a fairly counterintuitive idea. For years and years, biologists believed that enriching an ecological system would increase its stability and its diversity. This idea is very intuitive. If you have twenty predators, one hundred herbivores and one thousand plants with a certain nutrient amount in an ecosystem (normally called the carrying capacity or K) then one could logically expect that if you double the nutrients in the system, you could double the biomass, and double the population sizes for each group, making it less likely that the populations would go extinct and perhaps even providing enough nutrients/energy for a top predator to successfully enter the ecosystem. Initial theoretical work using the Lokta-Volterra equations for predation (simple linear differential equations) seemed to justify these predictions.

However, in the 1960s, M.L. Rosenzweig and Robert MacArthur replaced the simple linear differential equations with a nonlinear equation. The results completely contradicted the prevailing logic: the more nutrients you add to the system, the more unstable it became and could push the populations to extinction. This result became known as the paradox of enrichment. Why it occurs is relatively simple, but understanding it required a different kind of thinking from ecologists. At first, ecologists were just looking at the static state of the system and their predictions flowed from that view of ecology. What Rosenzweig and MacArthur did was put the emphasis on the dynamics of the system as well as the various interactions between the different actors in the system.

When looking at the problem from this perspective, one can see that if one enriched the soil with a great deal of nutrients, there would be a dramatic increase in the number of plants. With so many plants around, the number of herbivores would increase as well, causing a large drop in the number of plants. With the increase in herbivores, the predators would increase in their numbers, driving down the number of herbivores greatly and perhaps giving a chance for the plants to regrow. When the herbivores become scarce, then the predator population will experience a crash, perhaps even resulting in their extinction. If not, the cycles of high and low population levels would continue, as the enrichment has led to the destabilization of the stable state.

What I am trying to get at from this theory is the following: a lot of the intuitive ideas we have about the world can be erronous as we tend to focus only on certain aspects. By having such narrow perceptions of the world around us, there is a great possibility that many of our "good" actions end up being disastrous as we did not look at the problem from all the angles. What this blog is going to try to do is expose people to very important ideas in ecology and biology and how these ideas can reshape our views about the world around us in profound ways. I hope you enjoy it.