Abstract
Many threatened species in Europe have been expanding their distributions during recent decades owing to protection measures that overcome historical human activity that has limited their distributions. Range expansion has come about via two processes, natural expansion from existing range and reintroductions to new ranges. Reintroductions may prove to be a better way to establish populations because individuals are less subject to competitive relationships lowering breeding success than individuals expanding from existing populations. Whether this is true, however, remains uncertain. We compared success of breeding pairs of an expanding and a reintroduced population of spanish imperial eagles monitored for over 15 years in the south of Spain. We found significant differences in productivity between breeding pairs of each population. Newly established territories in reintroduction areas were almost three times more productive than new territories established as individuals expanded out from an existing population. We conclude that among these eagle populations reintroduced to new areas may fare as well or better than individuals expanding out form existing populations.
Highlights
Habitat loss and persecution has caused large predators to be largely confined to landscape locations that are subject to minimal human activity (Brown, McMorran, & Price, 2011; Chapron et al, 2014; Seddon, Griffiths, Soorae, & Armstrong, 2014)
That individuals undergoing natural range expansion are constrained by density-dependent reductions in mean productivity because they may be forced into poorer-quality habitat by individuals holding established territories (Ferrer & Bisson, 2003; Ferrer & Donazar, 1996; Ferrer, Newton, & Casado, 2006, 2008; Korpimaki, 1988; Newton, 1998; Sergio & Newton, 2003)
Nowadays most raptor species are increasing in both numbers and distributions (Ferrer et al, 2013; González et al, 2006; Horváth et al, 2014), and many species have been subject to reintroduction programs aimed to re-establish them in former range
Summary
Habitat loss and persecution has caused large predators to be largely confined to landscape locations that are subject to minimal human activity (Brown, McMorran, & Price, 2011; Chapron et al, 2014; Seddon, Griffiths, Soorae, & Armstrong, 2014). Reintroductions involve the release of individuals into suitable vacant habitat where the species may or may not have been extirpated (Seddon, Armstrong, & Maloney, 2007) It has been proposed, that individuals undergoing natural range expansion are constrained by density-dependent reductions in mean productivity because they may be forced into poorer-quality habitat by individuals holding established territories (Ferrer & Bisson, 2003; Ferrer & Donazar, 1996; Ferrer, Newton, & Casado, 2006, 2008; Korpimaki, 1988; Newton, 1998; Sergio & Newton, 2003). With empty high-quality habitat outside the old population boundaries, high productivity values are expected for young pairs These boundaries are promoted in philopatric species because of the tendency of individuals to return to the natal population to breed (Ferrer, 1993a). We compared two different means of colonization in the Spanish Imperial eagle in order to test potential demographic differences: a natural expansion of a past restricted breeding population into new territories that have not been occupied for at least 30 years and a reintroduced population reintroduced into a new distant area that has not been occupied for at least 30 years
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
