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Examples of natives facilitating exotic species

Posted by pbio on 07 May 2009 at 22:26 GMT

Author: Fabio Bulleri
Position: Post-doctoral researcher
Institution: Dipartimento di Biologia, Università di Pisa
Submitted Date: August 05, 2008
Published Date: August 7, 2008
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

I would like to thank Rob Miller for his interest in our Essay and to apologize for the delay in providing a response to his request for more observational examples. A number of cases of natives facilitating exotic species, other than those already presented in our Essay, has been reported for both marine and terrestrial habitats. To name a few, in the marine environment, Zabin and Altieri [1] have found that the native limpet, Siphonaria normalis, facilitates the settlement of the exotic barnacle, Chthamalus proteus, on intertidal rocky seashores; Ruesink [2] has reported that native neighbours (the mussel Mytilus californianus; the barnacles Pollicipes polymerus and Semibalanus cariosus; the anemone Anthopleura elegantissima) protect the introduced oyster Crassostrea gigas from predation at low tidal elevations on rocky shores, while Bulleri and Airoldi [3] have experimentally shown that the native mussel, Mytilus galloprovincialis, facilitates the persistence of thalli of the introduced green alga, Codium fragile ssp. tomentosoides, in intertidal artificial habitats, by preventing their dislodgement by waves. Also, Levin et al. [4] have shown that the native kelp, Laminaria saccharina, allows the establishment of the introduced epiphytic bryozoan Membranipora membranacea, on subtidal rocky reefs. In terrestrial environments, several invasive Ericales (Calluna vulgaris, Erica arborea, E. baccans, E. caffra, E. lusitanica), which are obligate mutualistic with ericoid mycorrhizal fungi, have successfully established taking advantage of indigenous mycorrhizal fungi [5]. In Hawaii, the native nitrogen-fixing legume, Chamaecrista nictitans, facilitates the invasion of native Heteropogon contortus grasslands by the exotic grass Pennisetum setaceum [6]. Finally, although the underlying mechanism was not identified, Parker [7] has observed that undisturbed prairie seemed to promote establishment of the exotic pest plant Cytisus scoparius (Scotch broom), suggesting that the presence of an intact resident assemblage of species could somehow foster the success of the invader. These examples provide some evidence about the importance of natives facilitating exotics in the real world. Given the disproportionate attention given to negative species interactions, in comparison to positive interactions, it would be not surprising if the study cases currently available in the literature would result only "the peak of the iceberg". This is why further research specifically focused on the role of positive species interactions on patterns of distribution of species and, even more important, on the functioning of ecosystems seems badly needed to improve the accuracy of predictions of current ecological theories.

1. Zabin CJ, Altieri A (2007) A Hawaiian limpet facilitates recruitment of a competitively dominant invasive barnacle. Mar Ecol Prog Ser 337: 175-185.
2. Ruesink JL (2007) Biotic resistance and facilitation of a non-native oyster on rocky shores. Mar Ecol Prog Ser 331: 1-9.
3. Bulleri F, Airoldi L (2005) Artificial marine structures facilitate the spread of a non-indigenous green alga, Codium fragile ssp. tomentosoides, in the north Adriatic Sea. J Appl Ecol 42: 1063-1072.
4. Levin PS, Coyer JA, Petrik R, Good TP (2002) Community-wide effects of nonidigenous species on temperate rocky reefs. Ecology 83:3182-3193.
5. Richardson DM, Allsopp N, D’Antonio CM, Milton SJ, Rejmánek M (2000) Plant invasions – the role of mutualisms. Biol Rev 75: 65-93.
6. Carino DA, Daehler CC (2002) Can inconspicuous legumes facilitate alien grass invasions? Partridge peas and fountain grass in Hawaii. Ecography 25: 33-41.
7. Parker IM (2001) Safe site and seed limitation in Cytisus scoparius (Scotch broom):
invasibility, disturbance, and the role of cryptogams in a glacial outwash prairie. Biol Inv 3: 323-332.

No competing interests declared.