Sudden collapses in many ecological systems are the rule rather than exceptions to the rule.
This is shown by Professor Lennart Persson of Umeå University, Sweden, in the latest issue of the scientific journal Proceedings of the National Academy of Sciences. Among other things, the article provides an explanation for the collapses in cod stocks in different parts of the world. Several models have shown that ecological systems can experience catastrophic collapses. On the other hand, these models have not been able to say how common they are.
Lennart Persson and co-author André M. De Roos of the University of Amsterdam have now shown in a model that two fundamental traits of individuals in many organisms promote the occurrence of catastrophic behaviors in ecological systems. The two traits that the authors have examined are the correlation between growth and the amount of ingested food and the correlation between mortality and body size. In simple terms, animals grow more the more they eat, and the smaller an animal is, the greater the risk that it will be eaten. On this basis, Persson and De Roos have been able to show that collapses in ecological systems are rather the rule than exceptions to the rule.
"The mechanism is actually quite simple, but that`s also what makes it so general," says Lennart Persson. "Considering that more than 85 percent of all species on earth exhibit populations with variations in size, these results should be extremely generalizable.
Paradoxically, the number of available prey can increase with the number of predators. This happens because the competition among the remaining prey diminishes, and these prey also grow more quickly. Increased growth yields greater reproduction, and that in turn leads to increased numbers of the small-sized prey that predators thrive on. If, on the other hand, mortality among predators increases, say as a result of high pressures from fishing, it is a natural consequence for mortality to rise among the prey these predators live on. This in turn means that competition increases among the prey, thereby checking their growth. This leads to a decline in the number of prey of the sizes preferred by predators. This can bring about a collapse in the number of predators.
When a collapse occurs, it comes extremely rapidly, and it is difficult to discover changes in advance. The species that professional fishers capture in their nets, such as cod and full-grown herring, provide no clues to what is under way. On the other hand, the small-sized, sexually immature individuals of the species of prey that are nevertheless too large to be eaten by the predators (sexually immature herring, for instance) and the food that the former live on exhibit differences.
"It is actually these small-sized individuals of the species of prey that need to be monitored, because it is here that you can get a measure of when collapse is imminent," explains Lennart Persson.
These small-sized individuals of the species of prey increase in number when the fishing of predators increases. This occurs since the competition for food increases among the small-sized individuals. They have no possibility of growing larger, so their growth is stunted, and the number of small-sized individuals grows. This means that we must be extremely vigilant.
"If fishing is increased, very little change will be noticed until there is a collapse. In order to promote growth at this juncture, fishing must be cut to extremely low levels. Halving quotas, for example, will not help; total bans on fishing are the only answer then," says Lennart Persson.
This line of reasoning is supported by developments in North Atlantic cod stocks, which have not recovered despite drastically reduced fishing.
Karin Wikman | AlphaGalileo
Dune ecosystem modelling
23.06.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau
Understanding animal social networks can aid wildlife conservation
23.06.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology