The effects of an exotic palm on a native palm during the first demographic stages: contributions to ecological management

Ana Luisa T Mengardo,Vânia R Pivello

doi:10.1590/0102-33062014abb3326

Abstract

Biological invasions have negative impacts on native biota and consequently on biodiversity. In patches of Atlantic Forest in Brazil, the Australian palm tree Archontophoenix cunninghamiana has become invasive, whereas the endemic palm Euterpe edulis is threatened with extinction. The two species occupy parts of the same functional niche within the forests, which raises a question: Does the invasive species interfere with the recruitment of the native one when the two co-occur? We compared the initial demographic stages of these palms, and assumed that A. cunninghamiana would present better performance (higher rates of germination and seed viability) and would feature allelopathic properties that could influence the recruitment of the native species. We investigated indirect and direct allelopathic interference, respectively, by watering E. edulis seeds with aqueous leachate solutions of A. cunninghamiana fruits and leaves and by conducting combined germination experiments. The leachate solutions neither inhibited germination nor affected the size of E. edulis seedlings. In the direct interference experiments, depulped A. cunninghamiana seeds had higher viability and germination rates than did E. edulis seeds. In E. edulis, exposure to A. cunninghamiana seeds did not affect germination nor seedling development but slightly decreased germination speed. In conclusion, A. cunninghamiana presented no significant allelopathic impediment to E. edulis establishment. However, because A. cunninghamiana seeds are usually depulped when dispersed by birds, the potential of the species to establish itself in the community surpasses that of E. edulis. We propose management strategies to enhance E. edulis performance and to restrict the spread of A. cunninghamiana.

Highlights

The rapid disappearance of tropical forests worldwide is a result of direct and indirect human activities (Turner 1996)
In the control conditions of the direct interference experiment, the mean germination rate was much lower for the Euterpe edulis seeds than for the Archontophoenix cunninghamiana seeds (38.9% vs. 93.5%), the first being approximately half of and the latter being close to the initial seed viability, whereas seed germination of E. edulis was unaffected by the Gs or Gf treatments (H=2.7, p=0.3)
We found it surprising that the A. cunninghamiana germination rate was lower in the Gf condition than in the Gs condition (H=18.1, p

Summary

Introduction

The rapid disappearance of tropical forests worldwide is a result of direct and indirect human activities (Turner 1996). Intentional or accidental introduction of exotic species has become one of the greatest threats to the balance of ecosystems and the maintenance of native species in their habitats. When such introduction results in biological invasion, negative impacts may be observed at the individual, population, community or ecosystem level (Pyšek et al 1995; Lockwood et al 2007; Simberloff & Rejmánek 2011). The novel weapons hypothesis adds a new mechanism to explain the success of invasive species in the habitats into which they have been introduced (Hierro & Callaway 2003). The novel weapons hypothesis is based on the negative interaction with native organisms through the release of allelopathic substances in the environment (Callaway & Aschehoug 2000; Schaffner et al 2011). Hierro & Callaway (2003) argued that many invasive species are not dominant competitors in their natural habitats but can successfully outcompete their new neighbors by releasing phytotoxins that inhibit or eliminate the surrounding organisms, providing an alternative explanation for the ability of invaders to become more abundant and competitively dominant in the invaded sites (Inderjit et al 2008)

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