07_Invasive impact on islands
Invasive species impacting the functioning and services of island protected areas through losses of endemic species.
Lead Author: Carl Beierkuhnlein (UBT)
Contributors: Carl Beierkuhnlein (UBT), Severin Irl (UBT), Samuel Hofmann (UBT), Andreas Schweiger (UBT), Yrneh Ulloa (UBT) Frank Weiser (UBT), Anna Walentowitz (UBT)
Islands are of outstanding importance for speciation and for the development of species diversity. They host a high number and a high proportion of endemic species (Fig. 2). However, these species are highly threatened by global extinction because they are not adapted to the pressures by introduced species like goats and rabbits. In consequence, biodiversity loss and subsequent loss of ecosystem functioning and services are likely to occur if no counteractive measures are implemented in order to avoid threats and restrictions for humans on islands that are directly dependent on the services provided by nature.
Figure 1: One of the last remaining members of the only remnant population of Lotus eremiticus, a species that is highly threatened by global extinction because it is intensely browsed by invasive herbivores (rabbits, goats).
Furthermore, the loss of endemic species would also mean a loss of aesthetic values (Fig. 1) and potential economic profit from ornamental plants. The Canary Islands hosts a high number of taxa that have become enormously important in gardening worldwide (e.g. Argyranthemum spec., Aeonium spec. Echium spec.).
The conservation value, however, and the targets of protected areas are difficult to define, because the patterns of total species richness, richness of endemic species and of the proportion of endemic species differ. Areas that are of high value for these protection targets are not the same (Fig. 2). Priorities must be defined.
Figure 2: Spatial interpolation maps of (a) species richness, (b) number of single-island endemics (nSIE), (c) number of archipelago endemics (nAE), (d) percentage of single-island endemics (pSIE) and (e) percentage of archipelago endemics (pAE) (Irl et al. 2015).
Particularly, island ecosystems are under threat by introduced species such as herbivores (rabbits, goats) and invasive plant species (Fig. 3). One reason is that island plants did not evolve (or loose) protective traits against herbivory such as thorns or poisonous compounds (Irl et al. 2014). Often they are also less competitive than non-native plant species, increasing the invasibility of island systems. 
Figure 3: Browsing of rabbits on the leaves and juvenile branches of the single-island endemic subalpine species Genista benehoavensis that was close to extinction in the summit region of the La Palma Biosphere Reserve. The loss of sensitive species is leading to species poor subalpine scrubs that are expected to have low resilience towards climatic extremes. 
Figure 4: Fenced population of the shrub species Chamaecytisus proliferus (Fabaceae) in pine forest ecosystems on La Palma. This endemic species is completely browsed by rabbits outside the fences where the field layer consists almost only of pine needle litter and open soil.
On the one hand, introduced herbivores pose a threat to endemics by preferentially browsing them, thereby increasing the extinction risk of already range-restricted species. Non-native plant species often possess mechanical and chemical defence mechanisms deterring introduced herbivores, while endemic species often have lost these traits because of the speciation processes that occurred in the absence of mammalian herbivores. On the other hand, invasive plant species can outcompete native island species, especially at low elevations. Often non-native plant species are highly competitive owing to their wide ecological amplitude, fast reproduction, high anthropogenic disturbance tolerance, efficient resource use and effective defence mechanisms against herbivores.
Papers (published, accepted, submitted, in preparation):
Eibes, P., Eisenbacher, J., Chiarucci, A., Field, R., Irl, S.D.H., Köhler, T., Veetas, O., Beierkuhnlein, C. (in prep.) Lone fighters or team players? How co-occurrence patterns shape the patchy vegetation in arid volcanic environments.
Hanz, D., Beloiu, M., Wipfler, R., Beierkuhnlein, C., Field, R., Vetaas, O., Irl, S.D.H. (in prep.) From coast to coast How environment drives functional diversity in an insular system.
Weigel, R., Irl, S.D.H., Treydte, K., Beierkuhnlein, C., Berels, J., Field, R., Miranda, J.C., Steinbauer, A., Steinbauer, M.J., Jentsch, A. (2018). A novel dendroecological method finds a non-linear relationship between elevation and seasonal growth continuity on an island with trade wind-influenced water availability. AoB Plants, 10(6), ply070
Ecopotential References
Hoffmann, F., von Jeetze, P.J., Schepers, J., Chiarucci, A., Irl, S., Jentsch, A., Kienle, D., Vetaas, O., Beierkuhnlein, C., Estimating plant richness and productivity using a new ground-based digital imaging method for (nearly) vertical habitats (in prep).
Hoffmann, S., Schmitt, T., Chiarucci, A, Irl, S.D.H., Rocchini, D., Vetaas, O.R., Tanase, M.A., Mermoz, S., Bouvet, A., Beierkuhnlein, C. (2018). Remote sensing of beta diversity: evidence from plant communities in a semi?natural system, Applied Vegetation Science, 22, 1326.
Hoffmann, S., Beierkuhnlein, C., Field, R., Provenzale, A., Chiarucci, A. (2018). Uniqueness of Protected Areas for Conservation Strategies in the European Union. Scientific Reports 8: 6445.
Irl, S.D.H, Schweiger, A.H., Medina, F., Fernández-Palacios, J.M., Harter, D.E.V., Jentsch, A., Provenzale, A., Steinbauer, M.J., Beierkuhnlein, C. (2017) An island view of endemic rarity Environmental drivers and consequences for nature conservation. Diversity and Distributions, 23, 1132-1142.
Irl, S.D.H., Beierkuhnlein, C., Threats of Climate Change to Single-Island Endemic Species in Protected Areas (2018) Symposium for Research in Protected Areas 6, 45-47.
Irl, S.D.H, Schweiger, A.H., Steinbauer, M.J., Dewenter, J., Fernández-Palacios, J.M., Hoffmann, S., Jentsch, A., Müller, C.L., Nuppenau, J.N., Beierkuhnlein, C. (under review). A test of the successional divergence hypothesis on lava flows of a subtropical oceanic island. Journal of Ecology
Irl, S.D.H, Schweiger, A.H., Steinbauer, M.J., Dewenter, J., Fernández-Palacios, J.M., Hoffmann, S., Jentsch, A., Müller, C.L., Nuppenau, J.N., Beierkuhnlein, C. (under review). How environment modulates primary succession dynamics - the successional divergence hypothesis. American Naturalist.
Irl, S.D.H., Schweiger, A.H., Steinbauer, M.J., Ah-Peng, C., Arévalo, J.R., Beierkuhnlein, C., Chiarucci, A., Daehler, C.C., Fernández-Palacios, J.M., Flores, O., Kueffer, C., Mad?ra, P., Otto, R., Strasberg, D., Jentsch, A. (in prep.). Hierarchical climatic filtering: towards a mechanistic concept of plant invasion on islands. Target journal: Global Change Biology.
Irl, S.D.H., Schweiger, A.H., Hoffmann, S., Beierkuhnlein, C., Hartmann, H., Pickel, T., Jentsch, A. (under review) Spatiotemporal dynamics of plant diversity and endemism during primary succession on an oceanic-volcanic island. Journal of Vegetation Sciences.
Kienle, D., Irl S.D.H., Hanz, D.M., Steinbauer, M.J., Beierkuhnlein, C. (in prep.) Treasure Island in peril? How climate change will affect island endemics in an oceanic biodiversity hotspot. Target journal: Journal of Biogeography.
Kienle, D., Sungur, L., Walentowitz, A., Chiarucci, A., Field, R., Irl, S.D.H., Vetaas, O.R., Beierkuhnlein, C. (in prep.). Phonolites rock: phonolites enhance plant diversity and growth on oceanic islands. Target journal: Biogeosciences.
Steinbauer, M. J., Irl, S.D.H., González?Mancebo, J.M., Breiner, F.T., Hernández?Hernández, R., Hopfenmüller, S., Kidane, Y., Jentsch, A., Beierkuhnlein, C. (2017). Plant invasion and speciation along elevational gradients on the oceanic island La Palma, Canary Islands. Ecology and Evolution, 7, 771779.
Walentowitz, A., Irl, S.D.H., Palomares-Martínez, A., Acevedo Rodriguez, A.J., Vetter, V., Zennaro, B., Beierkuhnlein, C. (in prep.). Projecting habitat suitability of an invasive grass species on island ecosystems, endemic plant species richness and protected areas.
Reports, meeting presentations (where, when, title):
Beierkuhnlein, C. at Research in Protected Areas Conference in Salzburg, Austria from 02 -03/11/2017. Threats of climate change to single island endemic species in protected areas.
Irl, S.D.H. at AK Biogeographie 2018 in Bonn, May 2018. Sukzessionsdivergenz entlang einer 6000-jährigen Chronosequenz von Lavaflüßen auf einer semi-ariden ozeanischen Insel.
Kienle, D. at IBS Climate Change Biogeography in Évora, Portugal from 20 24/03/2018. Precipitation changes on oceanic islands new insights to assess diversity and endemism.
You can click here to download a presentation of the storyline.
Last update: May, 2019.