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. 2019 Apr 10;286(1900):20190136.
doi: 10.1098/rspb.2019.0136.

Endemic plant species are more palatable to introduced herbivores than non-endemics

Jonay Cubas  1 , Severin D H Irl  2 , Rafael Villafuerte  3 , Víctor Bello-Rodríguez  1 , Juan Luis Rodríguez-Luengo  4 , Marcelino Del Arco  1 , José Luís Martín-Esquivel  5 , Juana María González-Mancebo  1
Affiliations

Endemic plant species are more palatable to introduced herbivores than non-endemics

Jonay Cubas et al. Proc Biol Sci. .

Abstract

Islands harbour a spectacular diversity and unique species composition. This uniqueness is mainly a result of endemic species that have evolved in situ in the absence of mammal herbivores. However, island endemism is under severe threat by introduced herbivores. We test the assumption that endemic species are particularly vulnerable to generalist introduced herbivores (European rabbit) using an unprecedented dataset covering an entire island with enormous topographic, climatic and biological diversity (Tenerife, Canary Islands). With increasing endemism, plant species are more heavily browsed by rabbits than non-endemic species with up to 67% of endemics being negatively impacted by browsing, indicating a dramatic lack of adaptation to mammal herbivory in endemics. Ecosystems with high per cent endemism are most heavily browsed, suggesting ecosystem-specific vulnerability to introduced herbivores, even within islands. Protection of global biodiversity caused by disproportionally high endemism on oceanic islands via ecosystem-specific herbivore control and eradication measures is of utmost importance.

Keywords: European rabbit; conservation; endangered species; invasive species; island endemism; mammalian herbivory.

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Conflict of interest statement

We have no competing interests.

Figures

Figure 1.
Figure 1.
Rabbit browsing damage per level of endemism. (a) Endemic species (n = 150) are significantly more damaged by browsing than non-endemic native and non-native species (n = 169). Here, endemism is defined as all species endemic to Macaronesia. This includes single-island endemics as well as Canary endemics and Macaronesian endemics. (b) A tendency exists that with increasing endemism status browsing damage increases, indicating that palatability increases towards increasing range restriction of endemics. Here, endemism is explicit, i.e. Macaronesian endemics consist only of species endemic to Macaronesia but no Canary endemics nor single-island endemics. Endemism are single-island endemics only (n = 27), Canary endemics only (n = 98), Macaronesian endemics only (n = 27), non-endemic natives (n = 123) and non-natives and ruderals (n = 44). Asterisks indicate a high level of significance (*** = p < 0.001) in (a). Lowercase letters indicate significant groups in (b) (significance level: p < 0.05).
Figure 2.
Figure 2.
Spatial pattern and per-ecosystem rabbit browsing damage and rabbit density. (a) Spatial distribution of rabbit browsing and (b) rabbit density on Tenerife (n = 215 sites). Sample sites cover the entire island and all major ecosystems. Circle sizes are proportional to the values, which also increase from light to dark. Boxplots show (c) rabbit browsing damage per ecosystem and (d) rabbit density per ecosystem. Interestingly, rabbit browsing damage per ecosystem and rabbit density per ecosystem do not necessarily overlap. Colours as in (a) and (b), respectively. Boxplots in (c) and (d) are ordered from highest mean value to lowest. For more information on the ecosystems see electronic supplementary material, table S2.
Figure 3.
Figure 3.
Results of the structural equation model (SEM) for different levels of endemism explaining rabbit browsing damage. SEMs were constructed for (a) all species, (b) single-island endemics, (c) Canary endemics and (d) Macaronesian endemics. Blue arrows indicate positive, red arrows negative relationships. Values next to the arrows are standardized model estimates indicating the strength of the relationship. This strength is reflected in the proportional width of arrows. Only values greater than 0.2 or less than −0.2 are shown to increase readability of SEMs (for all values see electronic supplementary material, table S5). R2 values indicate the combined explanatory power of all dependent variables pointing at the respective variable. Note that some variables were log-transformed or quadratic-transformed.
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