Invasion pathways and lag times in the spread of Callosciurus erythraeus introduced into Argentina

Abstract

Invasion pathways and invasion-related lags are critical to understand the invasion process and to manage invasive species. The challenge of dealing with introduced populations increases when charismatic species are involved, such as the case of invasive squirrels. In this study, we integrate previous information into a comprehensive description of the invasion process of Callosciurus erythraeus in Argentina, and we synthesise a framework of invasion pathways and associated lag times for introduced squirrel species. One of the main invasion pathways for introduced squirrels involves the trade of pets and ornamental wildlife, i.e. deliberate transportation by humans as vectors using routes of pet/ornamental trade. This was the case of the importation of C. erythraeus into Argentina in 1970 that originated an invasion focus, which firstly spread through squirrels dispersing into nearby habitat (unaided spread). Apart from this local spread, we have recorded a total of 31 translocations within the country of squirrels taken 33−933 km from the source site (aided spread). Most of these translocations-releases occurred close to the invasion foci that functioned as a source of squirrels. Therefore, a key pathway for the invasion of C. erythraeus in Argentina is the illegal and intentional transport of individuals within country boundaries. Time lags can be found throughout the invasion process. We have previously described a lag in population growth and range expansion in the main invasion focus, and also a lag in vector activity (i.e. a lag in the onset of translocations). We now report a lag in the time between the detection by residents of C. erythraeus in a new area and when they report its observation. This time lag shows a decreasing trend, i.e. recent releases are reported sooner, that could respond to a changing lag in the perception of the problem due to communication activities. We propose a general conceptual framework for invasive squirrels that integrates two invasion pathways (A: aided spread that determines the number of invasion foci, and B: unaided spread that determines the size of each invasion focus) and three types of time lags (1: lag in population growth and spread, 2: lag in vector activity, and 3: lag in perception of the problem (human dimension)). Communication and education activities can be a powerful tool to change perceptions and gain support and active engagement of the local community to deal with invasive, charismatic species. Long-term communication programmes should be implemented along with strict and coordinated government policies.