Success of invasive mammals depends on their reproduction rate, study finds

Invasive mammals which reproduce at a high rate are more likely to survive and become widespread, new research by the University of Hull and University of Reading suggests.

Invasive mammals live in areas that they are not normally found in, having either been deliberately or accidentally introduced by humans.

The research, led by Dr Isabella Capellini at the University of Hull, shows that invasive mammal species, such as grey squirrels in Europe and rabbits in Australia, have very high reproductive rates compared to those that fail to become widespread.

The study tested whether the most reproductive species succeed, or whether it is species that live longer that can better cope with new environmental conditions, despite being less reproductive.

Implications for conservation

Dr Capellini’s team compiled the largest dataset ever collected of mammals that have been introduced to non-native regions throughout history.

The team tracked the success of over 500 different mammal species, from their introduction through to how much they spread.

The more productive mammals were found to succeed at every stage throughout the process of invasion, from establishing in their new region to spreading over large areas.

The research also shows that humans have preferentially introduced over centuries, accidentally or intentionally, mammals that are already more productive.

Dr Capellini said: “Animals are typically introduced in small numbers outside their native range, but small founder populations face high risk of extinction. This is due, for example, to environmental unpredictability or inbreeding.”

“We show that being able to reproduce at a high rate gives an advantage to mammals that face new habitats in which they did not evolve.”

“This leads to rapid population growths and large population sizes that escape the risk of extinction.”

Why some species become widespread when introduced into new regions, while others fail to even establish viable populations, is one of the most urgent questions in ecology with important implications for conservation.

Dr Capellini continued: “Invasive mammals appear to have specific traits or combinations of traits that allow them to become widespread.”

“The ways these creatures interact with the native wildlife are very complex. A minority of non-native species are considered to be invasive when they have a negative impact on wildlife, habitat or the economy.”

The study, published today in Ecology Letters, was funded by the Natural Environment Research Council (NERC) and the University of Hull.