CHARACTERISTICS OF THE NATURALIZED FLORA OF SOUTHERN AFRICA LARGELY
REFLECT THE NON-RANDOM INTRODUCTION OF ALIEN SPECIES FOR CULTIVATION
- Ali Omer,
- Qaing Yang,
- Trevor Fristoe,
- Noëlie Maurel,
- Patrick Weigelt,
- Holger Kreft,
- Jonas Bleilevens,
- Wayne Dawson,
- Franz Essl,
- Jan Pergl,
- Petr Pysek,
- Mark van Kleunen
Abstract
Most studies on biological invasions focus on the later stages of the
invasion process, i.e. after species have already become naturalized. It
is frequently overlooked, however, that patterns in origin, phylogeny,
and traits of naturalized alien species might largely reflect which
species have been introduced in the first place. Here, we quantify and
account for such introduction biases by analyzing 5,317 plant species
introduced for cultivation in Southern Africa. We show that this
cultivated alien flora represents a non-random subset of the global
flora, and that this bias at the introduction stage largely drives
patterns in origin, growth form and phylogenetic composition of the
naturalized flora. For example, while species from Australasia are,
compared to the global flora, disproportionally overrepresented in the
naturalized cultivated flora of Southern Africa, this pattern is solely
driven by their higher likelihood of having been introduced for
cultivation. We also show that among cultivated aliens, naturalization
success was correlated with intermediate seed mass and height, as well
as high specific leaf area. Our quantification of introduction biases
demonstrates that they are huge, and that accounting for it is essential
to avoid over- or under-estimation of the characteristics of
successfully naturalized alien plants.