Gastropod Seed Dispersal: An Invasive Slug Destroys Far More Seeds in Its Gut than Native Gastropods

Abstract

Seed dispersal is one of the most important mechanisms shaping biodiversity, and animals are one of the key dispersal vectors. Animal seed dispersal can directly or indirectly be altered by invasive organisms through the establishment of new or the disruption of existing seed dispersal interactions. So far it is known for a few gastropod species that they ingest and defecate viable plant seeds and consequently act as seed dispersers, referred to as gastropodochory. In a multi-species experiment, consisting of five different plant species and four different gastropod species, we tested with a fully crossed design whether gastropodochory is a general mechanism across native gastropod species, and whether it is altered by the invasive alien slug species Arion lusitanicus. Specifically, we hypothesized that a) native gastropod species consume the seeds from all tested plant species in equal numbers (have no preference), b) the voracious invasive alien slug A. lusitanicus – similarly to its herbivore behaviour – consumes a higher amount of seeds than native gastropods, and that c) seed viability is equal among different gastropod species after gut passage. As expected all tested gastropod species consumed all tested plant species. Against our expectation there was a difference in the amount of consumed seeds, with the largest and native mollusk Helix pomatia consuming most seeds, followed by the invasive slug and the other gastropods. Seed damage and germination rates did not differ after gut passage through different native species, but seed damage was significantly higher after gut passage through the invasive slug A. lusitanicus, and their germination rates were significantly reduced.

Misperceived invasion: theLusitanian slug (Arion lusitanicusauct. non‐Mabille orArion vulgarisMoquin‐Tandon 1855) is native toCentralEurope

“…Blattmann et al. ), which is questionable given the presented results. We thus argue that our approach should be applied as cautionary measure in cases where the a priori evidence for anthropogenic introduction is poor or nonexistent before attributing the status of invasiveness with the above‐mentioned consequences for biodiversity management and applied research.…”

Floral herbivory of an invasive slug on a native weed

“…Slugs influence weed populations in several aspects -as seed, seedling, and mature plant consumers (Kozlowski & Kozlowska 2000;Honek et al 2009) and vectors of seed dispersal (Calvino-Cancela & Rubido-Barrá 2012, Blattmann et al 2013;Türke & Weisser 2013). The food preferred by slugs are seedlings (Fenner et al 1999).…”

Towards the unravelling of the slug <i>A. ater–A. rufus</i> complex (Gastropoda Arionidae): new genetic approaches

“…Hatteland et al, 2015;Noble and Jones, 1996;Rowson et al, 2014). This problem probably comes from their very similar external morphology and their distinct internal morphology, as well as life history and ecological traits (Blattmann et al, 2013). For example, A. ater is in general black coloured and A. rufus is orange, while another species of the genus (A. vulgaris) is brown; thus specimens of dark brown can be misidentified (Roth et al, 2012), although the morphology of their genitalia separates clearly these species (Hatteland et al, 2015).…”