February 1, 2016

Diversity of nature formulated

Specific food web formed by plants, plant eaters and top predators and their feeding
connections. Plants are capable of using basic chemical or physical nutrients to live and
reproduce, this means there is a flow of energy from the nutrients to the plants. Plant-eating
animals may live exclusively on the available plants while top predators feed on other animals.
(Credit: Jan Härter, Niels Bohr Institute)

(February 1, 2016) We humans are affecting nature to a greater and greater degree and this is contributing to the reduction of biodiversity globally. To better assess the consequences requires a better understanding of the environmental conditions that the species in an ecosystem live under. A group of biophysicists from the Niels Bohr Institute have therefore analysed data and calculated how the species in an area affect each other and how an ecosystem can be in balance or out of balance. The results are published in the scientific journal, PLoS Computational Biology.

 Mathematically, coexistence means that a path through the interaction matrix, formed by all
species in the food web, can be found. The figure visualizes an example interaction matrix,
with white boxes connecting neighbor trophic levels contain non-zero elements.
The path consists of using the combination of a given row and column only once,
as shown by blue boxes. The connections to the nutrient source, shown by yellow, which
feeds all species at the bottom layer, can - but need not – be used as a part of the path.
In the given case, there are 4 basal species, e.g. plants, 5 plant eaters, and 2 top predators.
(Credit: Jan Härter, Niels Bohr Institute)

In nature, animals move around and encroach into new areas where other animals have their habitat.   Here they might be prey for some of the original animals and they can also be eaten themselves. They are all part of the food chain. This pattern of eating and being eaten can be in balance or it can lead to disturbances in the environment, for example when rabbits were introduced in Australia and the rabbits multiplied dramatically, as they had no natural enemies.

But how do you know if an ecosystem is in balance? Can you even formulate it? Yes, a group of biophysicists from the Niels Bohr Institute has done it. The formula is called Lotka-Volterra and it is used to calculate the mutual influence, which is a key factor in a sustainable coexistence.

journal reference (Open Access) >>