Sustainable Footprint

Secrets of Successful Ecosystems

Secrets of Successful Ecosystems
This study used a lab-based artificial ecosystem of communities of bacteria to examine what happens when the bacteria move around and evolve to live in different parts of the ecosystem over the course of hundreds of generations. The scientists measured the effect this dispersal of species has on the productivity and biodiversity of the ecosystem.
'Productive' ecosystems are defined as those that support a large total amount of living matter, from tiny microbes up to plants and animals.
Studies in the last decade have shown that ecosystems that have a high biodiversity are also highly productive over short time scales, but until now the underlying processes creating this link between high levels of biodiversity and productivity over evolutionary time scales have not been understood.
The scientists found that both the biodiversity and productivity of an ecosystem are at a peak when there is an intermediate rate of dispersal of species - not too little and not too much - between different parts of the ecosystem.
When there is little or no dispersal, populations of species that remain in harsh areas are unable to adapt to their environment due to a low population size and lack of genetic variation. But when there is too much dispersal in an ecosystem, species evolve to be 'generalists' that can survive in many habitats, but fail to thrive in any given one.
An intermediate rate of dispersal creates a 'happy medium' wherein species move around enough to ensure that harsh environments are adapted to, but not so much that they become generalists.
Dispersal constantly brings new individuals and new genes into harsh environments, which is essential for evolutionary adaptation to difficult environments. When species adapt to new environments it increases the productivity of the ecosystem and it can increase the biodiversity, as movement between different parts of an ecosystem provides more 'niches' for species to exploit.

The researchers created an artificial ecosystem for the bacterium Pseudomonas fluorescens. The ecosystem consisted of 95 different areas, each one containing a different food source. The scientists introduced the bacteria - which could eat approximately half of the 95 food sources - to the ecosystem, and then began to manipulate the rate at which the bacteria dispersed between the 95 different areas.

Every day the team measured the biomass in the ecosystem as an indicator of the ecosystem's productivity, and found that the levels of biomass were highest when there was an intermediate dispersal rate.
After 400 generations, bacteria were isolated from the ecosystem and the ability of the bacteria to grow on each of the food sources was measured. Using this data, the team were able to measure the diversity of the ecosystem, as it indicated how many different species had evolved from the bacteria which were originally introduced to the experiment, which could only eat half of the food sources available.
Adapted from: Imperial College London
March 14, 2008

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Sustainable Footprint

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