DOI: 10.5061/dryad.msbcc2fww
title: Selection on individuals of introduced species starts before introduction

description: Biological invasion is a global problem with large negative impacts on
 ecosystems and human societies. When a species is introduced, individuals
 will first have to pass through the invasion stages of uptake and
 transport, before actual introduction in a non-native range. Selection is
 predicted to act during these earliest stages of biological invasion,
 potentially influencing the invasiveness and/or impact of introduced
 populations. Despite this potential impact of pre-introduction selection,
 empirical tests are virtually lacking. To test the hypothesis of
 pre-introduction selection, we followed the fate of individuals during
 capture, initial acclimation, and captivity in two bird species with
 several invasive populations originating from the international trade in
 wild-caught pets (the weavers Ploceus melanocephalus and Euplectes afer).
 We confirm that pre-introduction selection acts on a wide range of
 physiological, morphological, behavioral and demographic traits (incl.
 sex, age, size of body/brain/bill, bill shape, body mass, corticosterone
 levels, and escape behavior); these are all traits which likely affect
 invasion success. Our study thus comprehensively demonstrates the
 existence of hitherto ignored selection acting before the actual
 introduction into non-native ranges. This could ultimately change the
 composition and functioning of introduced populations, and therefore
 warrants greater attention. More knowledge on pre-introduction selection
 also might provide novel targets for the management of invasive species,
 if pre-introduction filters can be adjusted to change the quality and/or
 quantity of individuals passing through such that invasion probability
 and/or impacts are reduced.
description: We tested whether pre-introduction selection occurs, when it
 acts, and on which phenotypic traits, by following the fate of a set of
 individuals previously characterized for various traits (that we
 <i>a priori</i> thought to be potentially important for
 invasion success and to be exposed to pre-introduction selection) across a
 number of potentially selective events: capture, initial acclimation, and
 captivity. Native individuals of <i>P. melanocephalus</i> and
 <i>E. afer</i> were caught by us using mist nets . We
 collected data for the phenotypic characterization of individuals (sex,
 age, morphometric and behavioral measures, and a feather to measure
 corticosterone levels). We also accompanied professional local bird
 trappers. They caught individuals using a traditional clap net lying on
 the ground baited with seeds and stuffed decoys to attract birds We
 characterized the phenotype of all these individuals in the same way as
 for the individuals caught by us and marked them with uniquely numbered
 plastic rings, after which they were handed back to the trappers. The
 first invasion filter of selective uptake was assessed by statistically
 comparing the traditionally caught birds with those caught by us using
 mist nets. We then monitored the survival of the marked individuals
 captured by local trappers and in their care, and tested statistically if
 survival was associated with any phenotypic characteristics.