Enemy damage of exotic plant species is similar to that of natives and increases with productivity

Abstract

Summary1. In their colonized ranges, exotic plants may be released from some of the herbivores or pathogens of their home ranges but these can be replaced by novel enemies. It is of basic and practical interest to understand which characteristics of invaded communities control accumulation of the new pests. Key questions are whether enemy load on exotic species is smaller than on native competitors as suggested by the enemy release hypothesis (ERH) and whether this difference is most pronounced in resource-rich habitats as predicted by the resource-enemy release hypothesis (R-ERH). 2. In 72 populations of 12 exotic invasive species, we scored all visible above-ground damage morphotypes caused by herbivores and fungal pathogens. In addition, we quantified levels of leaf herbivory and fruit damage. We then assessed whether variation in damage diversity and levels was explained by habitat fertility, by relatedness between exotic species and the native community or rather by native species diversity. 3. In a second part of the study, we also tested the ERH and the R-ERH by comparing damage of plants in 28 pairs of co-occurring native and exotic populations, representing nine congeneric pairs of native and exotic species. 4. In the first part of the study, diversity of damage morphotypes and damage levels of exotic populations were greater in resource-rich habitats. Co-occurrence of closely related, native species in the community significantly increased the probability of fruit damage. Herbivory on exotics was less likely in communities with high phylogenetic diversity. 5. In the second part of the study, exotic and native congeneric populations incurred similar damage diversity and levels, irrespective of whether they co-occurred in nutrient-poor or nutrient-rich habitats. 6. Synthesis. We identified habitat productivity as a major community factor affecting accumulation of enemy damage by exotic populations. Similar damage levels in exotic and native congeneric populations, even in species pairs from fertile habitats, suggest that the enemy release hypothesis or the R-ERH cannot always explain the invasiveness of introduced species.

Using a botanical garden to assess factors influencing the colonization of exotic woody plants by phyllophagous insects

“…Similar observations had been previously made by a large number of authors (e.g., Carpenter and Cappuccino 2005;Liu and Stiling 2006;Parker and Gilbert 2007;Proches et al 2008;Sugiura 2010;Harvey et al 2012;Litt et al 2014;van Hengstum et al 2014;Cronin et al 2015). However, in a significant amount of other studies, no difference in herbivory damage or abundance was found between native and exotic plants, especially when only congeneric native and exotic plant species were compared (e.g., Novotny et al 2003;Hawkes 2007;Sugiura et al 2008;Chun et al 2010;Dostál et al 2013), suggesting that the release from herbivory in the region of introduction is not a general pattern for exotic plants (Bezemer et al 2014). The herbivores' feeding guild also plays a role, with endophagous insects, such as leaf miners, bud borers or gall makers, showing a stronger preference for native plants than external feeders, probably because of their higher specificity (Kulfan et al 2010;Burghardt and Tallamy 2013;Kirichenko et al 2013).…”

“…Factors affecting the recruitment of exotic plants by indigenous herbivores have been studied through literature reviews and meta-analyses (e.g., Leather 1986;Brän-dle and Brandl 2001;Liu and Stiling 2006;Brändle et al 2008;Bezemer et al 2014), or field data on single or a small group of species (e.g., Siemann et al 2006;Parker and Gilbert 2007;Ando et al 2010;Harvey et al 2013;Castells et al 2014), but rarely through field data collected on a large number of species at the same place and the same time (Dietz et al 2004;Carpenter and Cappuccino 2005;Burghardt and Tallamy 2013;Dostál et al 2013). The examination of damage, population density and species richness in two functional groups of phyllophagous insects, leaf chewers and leaf miners allowed us to confirm the importance of some factors affecting the recruitment of exotic plants by phyllophagous insects, but not others.…”

Do local enemies attack alien and native Impatiens alike?

“…This method confirms the ERH when the obtained results show that an alien species is attacked less than a co-occurring native congener. The pair I. parviflora -I. noli-tangere was tested by this method in the Czech Republic [43]. In that study, the compared plants showed similar damage caused by natural enemies, which is consistent with 60% of the results presented here.…”

“…For the tests, we used the alien Impatiens glandulifera and I. parviflora, and the native I. noli-tangere. Despite the very high invasiveness of both alien species [41], they have not been subjected to such tests in Poland at all, and rarely elsewhere in Europe [42][43][44]; this is surprising in view of the efforts made to develop biological control methods against these plants [45,46].…”

Native insects and invasive plants encounters

“…The first category of papers studied the responses of specialist and generalist native insect herbivores to invasive plants (Harvey et al 2010;Herrera et al 2011;Novotny et al 2003). The second category of papers compared the herbivory on native and invasive plants and subsequent changes in the levels of herbivory load, damage, and pollination (Ballard et al 2013;Dostál et al 2013;Maron and Vilà 2001).…”