How strongly do interactions with closely‐related native species influence plant invasions? Darwin's naturalization hypothesis assessed on Mediterranean islands

Abstract

Aim Recent works have found the presence of native congeners to have a small effect on the naturalization rates of introduced plants, some suggesting a negative interaction (as proposed by Charles Darwin in The Origin of Species), and others a positive association. We assessed this question for a new biogeographic region, and discuss some of the problems associated with data base analyses of this type. Location Islands of the Mediterranean basin. Methods Presence or absence of congeners was assessed for all naturalized alien plants species at regional, local and habitat scales. Using general linear models, we attempted to explain the abundance of the species (as measured by the number of islands where recorded) from their congeneric status, and assessed whether the patterns could be alternatively accounted for by a range of biological, geographical and anthropogenic factors. A simulation model was also used to investigate the impact of a simple bias on a comparable but hypothetical data set. Results Data base analyses addressing Darwin's hypothesis are prone to bias from a number of sources. Interaction between invaders and congenerics may be overestimated, as they often do not co‐occur in the same habitats. Furthermore, intercorrelations between naturalization success and associated factors such as introduction frequency, which are also not independent from relatedness with the native flora, may generate an apparent influence of congenerics without implying a biological interaction. We detected no true influence from related natives on the successful establishment of alien species of the Mediterranean. Rarely‐introduced species tended to fare better in the presence of congeners, but it appears that this effect was generated because species introduced accidentally into highly invasible agricultural and ruderal habitats have many relatives in the region, due to common evolutionary origins. Main conclusions Relatedness to the native flora has no more than a marginal influence on the invasion success of alien plants in the Mediterranean, although apparent trends can easily be generated through artefacts of the data base.

Plant extinctions and introductions lead to phylogenetic and taxonomic homogenization of the European flora

“…Moreover, the perception of taxonomic homogenization is dependent on the spatial scale at which samples are gathered and increases with increasing sample area (46). Similarly, phylogenetic homogenization may also be scale dependent because closely related alien and native species may not cooccur in the same plant communities (47,48). Thus using regions may overestimate the degree of homogenization experienced by local plant communities.…”

Darwin's naturalization hypothesis: scale matters in coastal plant communities

“…This has generated a growing interest in assessing the role that functional similarity and phylogenetic relationships play in biological invasions (Daehler 2001, Duncan and Williams 2002, Lambdon and Hulme 2006, Strauss et al 2006, Winter et al 2009). However, most studies have provided only partial or even diverging conclusions.…”

Establishment of introduced reptiles increases with the presence and richness of native congeners

“…In the "pre-adaptation hypothesis", Darwin (1859, p. 86) proposed that invaders are more likely to be successful in areas where native congeners are present because in these areas non-native species are likely to contain traits that pre-adapt them to the new environment (Daehler, 2001;Duncan and Williams, 2002 To date, plants have been the focus of most studies testing these hypotheses, but these studies have produced mixed results. Some studies supported Darwin's naturalization hypothesis (Mack, 1996;Rejmanek, 1996;Rejmanek, 1998), while others supported the preadaptation hypothesis (Daehler, 2001;Duncan and Williams, 2002), and still others supported neither hypothesis (Lambdon and Hulme, 2006). We are aware of only two studies that have tested these hypotheses with animals at a global scale.…”