Data from: Niche shifts over spread of a biological invasion: unveiling the role of changing habitat preference and density-dependence

Aim: Anticipating the ultimate fraction of a landscape that might be
susceptible to invasion is challenging as several species are able to
expand the range of environmental conditions used over invasion. Despite
its relevance, the more proximate processes underlying observed shifts are
not sufficiently understood. Habitat selection theory predicts that as
population density increases, individuals start using sub-optimal
resources to compensate for the limitation of the preferred ones. However,
niche shifts might also occur as a result of changes in habitat
preferences over time. Here we tested these alternative hypotheses by
investigating nesting resource use and selection over a biological
invasion and the relative effect of density dependence on such patterns.
Location: Barcelona, Spain. Methods: We take advantage of a large dataset
recording the occurrence of the invasive Monk Parakeet, Myiopsitta
monachus, in Barcelona in the period 1975–2015. We apply generalized
linear models to analyse changes in nesting habitat preferences and their
interactive effect with conspecific presence.   
Results: Temporal changes in nesting habitat use occurred. Palm species
were the most commonly used nesting substrate since the beginning of the
invasion, but the diversity and frequency of use of other nesting
substrates increased over time. Changes in nesting substrate use were
consistent with a change in habitat preferences, that mostly involved the
less-frequently used resources. Although a general role of conspecific
aggregation on occupation patterns was found, it was mostly additive. That
is, shifts in nesting substrate did not structure in relation to
conspecific distribution. Conclusions: Shifts in nesting resource
selection can occur during the spread stage of biological invasions,
probably related to innovation and learning, rather than to optimal
habitat selection. These shifts present a significant challenge for
forecasting efforts and management. However, changes do not happen rapidly
over time, highlighting that there is a management opportunity window
before significant shifts occur.