Biodiversity: Animal immigrants benefit from size variability

Mammals whose body size can vary within one species are especially good at adapting to new environmental conditions. Such animal immigrants have a clear competitive advantage in the battle for new habitats. This is the conclusion that scientists at the University of Fribourg came to as a result of their participation in an international research project.

Body size can vary greatly within many mammalian species: the top row shows skulls of the rabbit Oryctolagus cuniculus, the bottom row those of the hare Lepus europaeus. This variability is exactly what makes them successful in new habitats. © Héctor Garrido (Estación Biológica de Doñana, CSIC)

Animals and plants following global trade and travel routes frequently end up in parts of the world they are actually not native to. While many of these species disappear again, some of them succeed in establishing independent populations. Some invasive species even multiply so rapidly that they cause considerable economic and ecological damage. The extent of such damage can be demonstrated by an example from Australia: rabbits which were introduced to the continent by the first European settlers regularly devastate large areas of agricultural land. This results in annual crop losses running into millions. At the same time, these animals force out native species. Europe is also a popular destination for animal immigrants. Here there are about 13,000 known invasive species which cause damage costing more than 12 billion Euros a year.

Variability increases the chance of survival

For a long time scientists have looked for traits which characterise successful intruders by comparing the average traits of invasive and non-invasive species. “But this is too limiting”, explains Jonathan Jeschke of the Free University of Berlin. “It also depends on the differences within a species.” The greater the variation, the better are the chances of survival when the animals are faced with a new environment. Intra-species differences enable the animals to establish themselves more easily in new locations. “But not every kind of variability necessarily leads to success”, concedes Sven Bacher of the University of Fribourg. “Variations which reduce an animal’s fitness consequently have the opposite effect”.

The key to success

In the course of their investigations the scientists analysed global datasets of mammals which are found outside their native areas. In doing so, they discovered that species exhibiting a large variation in body size were able to establish themselves especially often. “It is above all the body size variations in adult animals which appear to have a positive effect”, says Bacher.

The researchers are hoping that this knowledge will help better predict or even prevent invasions and they recommend the introduction of control measures for particularly variable species. On the one hand, this would allow better control of pest species, and on the other, it would support measures for the reintroduction of endangered species.

The present study by the institute Estación Biológica de Doñana (Spain), the University of Fribourg, the Technical University of Munich, the Free University of Berlin and the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) was published recently in the scientific journal “The American Naturalist“.

Manuela González-Suárez, Sven Bacher, Jonathan M. Jeschke (2015): Intraspecific trait variation is correlated with establishment success of alien mammals. The American Naturalist, DOI: 10.1086/681105.

Contact details:

Privatdozent Dr. Sven Bacher, Department of Geoscience, University of Fribourg, +41 026 300 88 22, sven.bacher@unifr.ch

Prof. Dr. Jonathan Jeschke, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) und Free University of Berlin, +49 30 83871046, jeschke@igb-berlin.de