Abstract
Abstract. Plantations of Eucalyptus globulus Labill. have been expanding rapidly worldwide. The species is considered invasive in several regions. While in the native range, post-dispersal seed predation is known to severely limit eucalypt recruitment, there is no experimental evidence of seed predation in the introduced range. We hypothesised that E. globulus seeds largely escape predation in Portugal, which may explain its prolific recruitment in some locations. We tested this hypothesis in central Portugal by exposing E. globulus seeds to the local fauna. For comparison purposes, we also used seeds from locally common species: Acacia dealbata Link (alien, larger, elaiosome-bearing seeds) and Cistus salviifolius L. (native, similarly sized seeds). We installed 30 feeding stations across three study sites, each one dominated by one study species. Each feeding station featured four feeders with different animal-access treatments: invertebrates; vertebrates; full access; no access (control). We placed five seeds of each plant species every day in each feeder and registered the number of seeds missing, eaten and elaiosome detached over 9 summer days. Eucalyptus globulus seeds were highly attractive to fauna in the three sites. Nearly half of E. globulus seeds were predated or removed, thus contradicting our hypothesis. Surprisingly, E. globulus and A. dealbata seeds were used by animals in similar proportions and C. salviifolius seeds were the least preferred. Vertebrates were the predominant seed predators and preferred the alien seeds. Invertebrates used all seed species in similar proportions. We found spatial variation regarding the predominant type of seed predators and the levels of seed predation according to the following patterns: predominance of vertebrates; predominance of invertebrates; negligible seed predator activity. Locations with negligible seed predation were abundant and scattered across the study area. Such spatial variation may help to explain the heterogeneous recruitment patterns of E. globulus seedlings found in previous studies.
Highlights
Eucalyptus globulus Labill. is an evergreen tree native to southern Victoria (Australia), Tasmania and the Bass Strait Islands (Jordan et al, 1994)
We modelled the effect of explanatory variables: feeder type, seed species and their interaction, on the proportion of seeds used using generalised linear mixed models (GLMMs) with a binomial error distribution, following the procedures described in Zuur et al (2009)
The number of seeds used increased daily over the experiment until the seventh day, when a maximum was reached (484 seeds; 35.9 %), practically stabilising afterwards. This temporal dynamic was similar for all seed species and feeder types, but not for the three study sites, since the daily total of seeds used stabilised around the fourth day in the E. globulus plantation (Fig. 1)
Summary
Eucalyptus globulus Labill. is an evergreen tree native to southern Victoria (Australia), Tasmania and the Bass Strait Islands (Jordan et al, 1994). Plantations of E. globulus have expanded rapidly worldwide since the mid-20th century, becoming one of the most popular exotic plantation trees (Potts, 2004; Rejmánek and Richardson, 2011). In Portugal, where E. globulus plantations are widespread, it was found that the recruitment of E. globulus seedlings is several times higher than in the native range (Catry et al, 2015; Águas et al, 2017; Deus et al, 2016). E. Deus et al.: Seed predation in Eucalyptus globulus et al, 2014; Becerra and Bustamante, 2008; Fernandes et al, 2017; Calviño-Cancela and Rubido-Bará, 2013), but the impact of predators on post-dispersed seeds has been poorly studied
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