REGULATION BY PLUNDERING OF RESOURCES - HOW ORGANISMS SHAPE THEIR ENVIRONMENTS

How do organisms and environments interact, and how influential has the outcome of their interactions been in modifying the world over geologic time? A new theory (biotic plunder) will be described which suggests that the most universal and important form of interaction is the ubiquitous propensity of biological populations to expand, depleting essential resources in the process, and halted only by eventual running out of those resources. Illustrations of this principle come from the population trajectories of introduced herbivores onto predator-free remote islands (e.g. St. Matthew, Isle Royale, South Georgia), and the damage they inflict on vegetation as their numbers increase exponentially.

This same dynamic is also at work in complete natural ecosystems containing a full complement of predators and trophic levels, but is most significant there in the interactions between primary producers and the nutrients they require for growth. Biotic plunder of nutrients in the ocean is apparent in (1) the spring blooms then subsequent summer declines (upon nutrient depletion) of phytoplankton populations in temperate lakes, seas and oceans, and (2) the dramatic proliferations of phytoplankton following upwelling events in non-polar oceans, until nutrients are once more virtually exhausted and steady-state is re-attained. Biotic plunder of nutrients on land is apparent in (1) the increase in nutrients in run-off following clear-cutting of watersheds in Hubbard Brook, and (2) the near absence of nutrients in water draining from tropical rain forests.

This mechanism can account for oligotrophic ocean 'deserts', and may be implicated in the low CO2 content of the Earth's atmosphere.