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
Scientists on the road to discovering impact of urban road dust
18.01.2018 | University of Alberta
Gran Chaco: Biodiversity at High Risk
17.01.2018 | Humboldt-Universität zu Berlin
On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.
We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
19.01.2018 | Materials Sciences
19.01.2018 | Health and Medicine
19.01.2018 | Physics and Astronomy