A Comparison of the Recruitment Success of Introduced and Native Species Under Natural Conditions

Habacuc Flores-Moreno,Angela T Moles,Hans Henrik Bruun

doi:10.1371/journal.pone.0072509

Abstract

It is commonly accepted that introduced species have recruitment advantages over native species. However, this idea has not been widely tested, and those studies that have compared survival of introduced and native species have produced mixed results. We compiled data from the literature on survival through germination (seed to seedling survival), early seedling survival (survival through one week from seedling emergence) and survival to adulthood (survival from germination to first reproduction) under natural conditions for 285 native and 63 introduced species. Contrary to expectations, we found that introduced and native species do not significantly differ in survival through germination, early seedling survival, or survival from germination to first reproduction. These comparisons remained non-significant after accounting for seed mass, longevity and when including a random effect for site. Results remained consistent after excluding naturalized species from the introduced species data set, after performing phylogenetic independent contrasts, and after accounting for the effect of life form (woody/non-woody). Although introduced species sometimes do have advantages over native species (for example, through enemy release, or greater phenotypic plasticity), our findings suggest that the overall advantage conferred by these factors is either counterbalanced by advantages of native species (such as superior adaptation to local conditions) or is simply too small to be detected at a broad scale.

Highlights

Seeds and seedlings are exposed to many risks during establishment, such as predation, loss of viability in the soil, drought, herbivory, pathogen attack, shading, nutrient deprivation and competition [1]
The fourth aim of our study is to ask whether introduced species have higher survival from germination to first reproduction than do native species at a broad scale, under natural conditions
When we compared the continuous longevity of introduced and native species we found that, on average, introduced species had significantly shorter lifespans (~9.6 years, P = 0.0005) than did native species (~53.6 years; Table S6)

Summary

Introduction

Seeds and seedlings are exposed to many risks during establishment, such as predation, loss of viability in the soil, drought, herbivory, pathogen attack, shading, nutrient deprivation and competition [1]. The idea that introduced species might have higher recruitment success is based on both theoretical arguments and empirical observations of three main mechanisms: enemy release, higher plasticity, and faster growth rates. Greater plasticity of introduced species could allow them to germinate under a wider range of environmental conditions and promote their higher tolerance to environmental stress in the early stages of life. Faster growth rates could shorten the time introduced species spend in early vulnerable stages of the life cycle and/or reduce the time to reproduction, reducing a species’ exposure to mortality [4,15]. Some theories and data suggest that introduced species should have advantages over native species, the evidence has been inconsistent. Our main objective is to provide a large scale test of the idea that introduced species have superior recruitment success than do native species

Objectives

Methods

Results

Conclusion