Conclusions about niche expansion in introduced Impatiens walleriana populations depend on method of analysis.

Lisa Mandle,Eric J Von Wettberg,Johanna Schmitt,Matthias H Hoffmann,Dan L Warren,A Townsend Peterson,Jane Catherine Stout

doi:10.1371/journal.pone.0015297

Abstract

Determining the degree to which climate niches are conserved across plant species' native and introduced ranges is valuable to developing successful strategies to limit the introduction and spread of invasive plants, and also has important ecological and evolutionary implications. Here, we test whether climate niches differ between native and introduced populations of Impatiens walleriana, globally one of the most popular horticultural species. We use approaches based on both raw climate data associated with occurrence points and ecological niche models (ENMs) developed with Maxent. We include comparisons of climate niche breadth in both geographic and environmental spaces, taking into account differences in available habitats between the distributional areas. We find significant differences in climate envelopes between native and introduced populations when comparing raw climate variables, with introduced populations appearing to expand into wetter and cooler climates. However, analyses controlling for differences in available habitat in each region do not indicate expansion of climate niches. We therefore cannot reject the hypothesis that observed differences in climate envelopes reflect only the limited environments available within the species' native range in East Africa. Our results suggest that models built from only native range occurrence data will not provide an accurate prediction of the potential for invasiveness if applied to areas containing a greater range of environmental combinations, and that tests of niche expansion may overestimate shifts in climate niches if they do not control carefully for environmental differences between distributional areas.

Highlights

The capacity to predict where a species is likely to become invasive could provide valuable insight into population and community ecology, as well as inform efforts towards remediation of the effects of introduced species
Both of these niches can be modified further by the potentially more limited suite of environments represented on the landscape of the distributional areas, leading us to recognize two further concepts: the ‘‘existing fundamental niche’’ and the ‘‘existing realized niche,’’ as the portions of the two niches that are manifested on relevant landscapes [12]
Interpretation of results Analysis of raw climatic variables associated with occurrence points suggested that naturalized populations of I. walleriana occupy climates wetter than are found in the native range, while more controlled comparisons based on ecological niche models did not support the idea of a niche expansion in introduced populations

Summary

Introduction

The capacity to predict where a species is likely to become invasive could provide valuable insight into population and community ecology, as well as inform efforts towards remediation of the effects of introduced species. The degree of climate match between native and introduced ranges has been shown to be significant in determining potential distributions of introduced plants [8,9,10] This climate-matching approach to understanding and predicting potential geographic ranges of invasive species is generally addressed via ecological niche models (ENMs) built by integrating occurrence data with climate data [2]. The realized niche – the environmental conditions under which a species is found to occur – is the subset of the species’ fundamental niche from which it is not excluded by biotic interactions Both of these niches can be modified further by the potentially more limited suite of environments represented on the landscape of the distributional areas, leading us to recognize two further concepts: the ‘‘existing fundamental niche’’ and the ‘‘existing realized niche,’’ as the portions of the two niches that are manifested on relevant landscapes [12]. Species may fail to occupy locations with suitable conditions owing to limited dispersal ability

Methods

Results

Conclusion