Herbivore attack in Casearia nitida influenced by plant ontogenetic variation in foliage quality and plant architecture

Traits influencing plant quality as food and/or shelter for herbivores may change during plant ontogeny, and as a consequence, influence the amount of herbivory that plants receive as they develop. In this study, differences in herbivore density and herbivory were evaluated for two ontogenetic stages of the tropical tree Casearia nitida. To assess plant ontogenetic differences in foliage quality as food for herbivores, nutritional and defensive traits were evaluated in saplings and reproductive trees. Predatory arthropods were quantified and the foraging preferences of a parasitoid wasp of the genus Zacremnops were assessed. In addition, survival rates of lepidopteran herbivores (Geometridae) were evaluated experimentally. Herbivore density was three times higher and herbivory was 66% greater in saplings than in reproductive trees. Accordingly, concentrations of total foliar phenolics were higher in reproductive trees than in saplings, whereas leaf toughness, water and nitrogen concentration did not vary between ontogenetic stages. Survival rates of lepidopteran larvae exposed to natural enemies were equivalent in reproductive trees and saplings. Given the greater herbivore density on saplings, equal survival rates implied a greater foraging effort of predators on reproductive trees. Furthermore, observed foraging of parasitoid wasps was restricted to reproductive trees. I propose that herbivore density, and as a consequence, leaf damage were lower in reproductive trees than in saplings due to both traits influencing food quality, and architectural or unmeasured indirect defensive traits influencing foraging preference of natural enemies of herbivores.     

Explaining differential herbivory in sun and shade: the case of Aristotelia chilensis saplings

Differential herbivory in contrasting environments is commonly explained by differences in plant traits. When several plant traits are considered, separate correlation analyses between herbivory and candidate traits are typically conducted. This makes it difficult to discern which trait best explain the herbivory patterns, or to avoid spurious inferences due to correlated characters. Aristotelia chilensis saplings sustain greater herbivory in shaded environments than in open habitats. We measured alkaloids, phenolics, trichomes, leaf thickness and water content in the same plants sampled for herbivory. We conducted a multiple regression analysis to estimate the relationship between herbivory and each plant trait accounting for the effect of correlated traits, thus identifying which trait(s) better explain(s) the differential herbivory on A. chilensis. We also estimated insect abundance in both light environments. Palatability bioassays tested whether leaf consumption by the main herbivore on A. chilensis was consistent with field herbivory patterns. Overall insect abundance was similar in open and shaded environments. While saplings in open environments had thicker leaves, lower leaf water content, and higher concentration of alkaloids and phenolics, no difference in trichome density was detected. The multiple regression analysis showed that leaf thickness was the only trait significantly associated with herbivory. Thicker leaves received less damage by herbivores. Sawfly larvae consumed more leaf tissue when fed on shade leaves. This result is consistent with field herbivory and, together with results of insect abundance, renders unlikely that the differential herbivory in A. chilensis was due to greater herbivory pressure in open habitats.     

Herbivory-induced stress: Leaf developmental instability is caused by herbivore damage in early stages of leaf development

Herbivory is a major source of plant stress and its effects can be severe, decreasing plant fitness, or subtle, affecting the development of leaves by influencing the normal pattern of growth and expansion of leaf blades. Fluctuating asymmetry (FA) analysis is recognized as a measure of plant stress, and can be used to evaluate subtle effects of herbivory on the imperfect growth of bilaterally symmetrical traits, such as leaves. One general issue is that authors usually consider FA as an indicator of stress, which can attract herbivores (plant stress hypothesis), and studies showing that herbivores themselves affect leaf symmetry (herbivory-induced stress hypothesis) are scarce, with mixed results. Here, we investigated the relationship between herbivory by thrips and leaf FA in Banisteriopsis malifolia and Heteropterys escallonifolia (Malpighiaceae). Pseudophilothrips obscuricornis is a free-living, non-pest, sucking species that feeds mainly on leaf buds. We hypothesized that herbivory by thrips in the early stages of leaf development would provoke increased FA levels in mature leaves. The results showed that thrips herbivory rate was low, affecting barely more than 1% of the leaf blade. Nonetheless, thrips-attacked leaves of B. malifolia and H. escallonifolia presented increases of 15 and 27% in leaf asymmetry, respectively, compared to uninjured leaves, corroborating the herbivory-induced stress hypothesis. Since herbivory by thrips in leaf buds was related to significant increases in the stress of mature leaves, we assume that under these circumstances, FA can be used as a biomarker for plant stress following herbivory damage. To be useful as a biomarker of stress, FA in plants must be investigated with caution, taking into account the natural history of the herbivore species and timing of leaf damage.     

Herbivory in sun versus shade at a natural meadow-woodland ecotone in the Rocky Mountains

We examined herbivore damage in a natural association in order to evaluate the hypothesis that herbivory is generally greater in the shade (Maiorana 1981). Damage was measured in relation to habitat, adult plant distribution, and plant size for 13 species of native herbaceous forbs that cross the natural shade/sun ecotone at the interface of montane meadow and aspen (Populus tremuloides) woodland. Eight of the 13 species had statistically significant differences in leaf area damaged between sun and shade individuals (p<0.05). Only 3 of those were more damaged in shade (Aquilegia coerulea, Epilobium angustifolium, and Galium biflorum), while six were more damaged in the sun (Delphinium nelsoni, Helianthella quinquenervis, Lupinus argenteus, Thalictrum fendleri, and Vicia americana). No pattern was detected for 5: Erigeron speciosus, Fragaria ovalis, Lathyrus leucanthus, Viguiera multiflora, and Viola nuttallii. Levels of herbivory were species-specific rather than habitat-related. Thus, the shade habitat hypothesis must be rejected for our system, and the null hypothesis accepted for this natural assemblage. Herbivory within the shade was generally related to plant and leaf size. Two equally common community level patterns of loss occurred in relation to plant distribution. These were: 1. frequency-related, where herbivory was higher in the habitat of highest adult plant occurrence, and 2. inversely-related, where herbivory was higher in the habitat where plants were less common.     

Perfect is best: low leaf fluctuating asymmetry reduces herbivory by leaf miners

Fluctuating asymmetry (FA) represents small, random variation from symmetry and can be used as an indicator of plant susceptibility to herbivory. We investigated the effects of FA of two oak species, Quercus laevis and Q. geminata, and the responses of three herbivore guilds: leaf miners, gallers, and chewers. To examine differences in FA and herbivory between individuals, 40 leaves from each tree were collected, and FA indices were calculated. To examine differences in FA and herbivory within-individuals, we sampled pairs of mined and unmined leaves for asymmetry measurements. Differences in growth of leaf miners between leaf types were determined by tracing 50 mines of each species on symmetric leaves and asymmetric leaves. Asymmetric leaves contained significantly lower concentrations of tannins and higher concentrations of nitrogen than symmetric leaves for both plant species. Both frequency of asymmetric leaves on plants and levels of asymmetry positively influenced the abundance of Brachys, Stilbosis and other leaf miners, but no significant relationship between asymmetry and herbivory was observed for Acrocercops. Brachys and Stilbosis mines were smaller on asymmetric leaves, but differences in mine survivorship between symmetric and asymmetric leaves were observed only for Stilbosis mines. This study indicated that leaf miners might use leaf FA as a cue to plant quality, although differential survivorship among leaf types was not observed for all species studied. Reasons for the different results between guilds are discussed.     

Similar responses of insect herbivores to leaf fluctuating asymmetry

Fluctuating asymmetry (FA) represents small, random variation from symmetry and it has been used as an indicator of plant quality and susceptibility to herbivory. In this study, the effects of FA on the responses of distinct herbivore species belonging to several guilds were examined along an environmental gradient in south Florida. This approach was chosen because it relies on a multi-species approach to the study of fluctuating asymmetry and patterns of herbivory between and within plants along an environmental gradient of salinity and plant stress. To examine differences in FA between and within plant communities, seven plant species were investigated. Four of these plants were coastal species and three species occurred in upland communities. Levels of FA were assessed before herbivory and plants were followed for the whole herbivory season in 2006. Coastal plants exhibited significantly higher salt concentration, higher percentage of asymmetric leaves and higher asymmetry levels than upland plants. Herbivore abundance varied widely amongst the seven species studied, but quantitative syntheses of our results indicated significant and positive responses of insect herbivores to leaf asymmetry: insects were 25.11% more abundant on more asymmetric plants and stronger effects of asymmetry were observed for leaf miners compared to gall-formers. As demonstrated by other recent studies, FA might be used as a reliable stress indicator, leading to similar responses of insect herbivores to variation in leaf symmetry.     

Facilitation and herbivory during restoration of California coastal sage scrub

Using nurse plants to facilitate native plant recruitment in degraded habitats is a common restoration practice across various arid and semiarid environments. Living trees or shrubs are typically considered nurse plants, whereas dead shrubs left in the landscape from prolonged drought are understudied prospective facilitators for native plant recruitment. The interaction between nurse plants and biotic pressures, such as herbivory, on native recruitment is also not well understood in semiarid plant communities. We investigated the effects of facilitation and herbivory on native seedling germination, growth, and survival in the restoration of degraded coastal sage scrub (CSS) habitat. Native shrub seedlings (Artemisia californica and Salvia mellifera) were planted, and native annual species (Amsinckia intermedia, Deinandra fasciculata, Phacelia distans, and Pseudognaphalium californicum) were sown in three Shrub Type treatments (live shrub, dead shrub, and exposed areas), with a nested Cage treatment (no cage and cage) in each Shrub Type treatment. Annual species grew equally well in all Shrub Type treatments; shrub seedlings grew largest in exposed areas. While there was little evidence of facilitation for all species tested, there were strong positive effects of caging on growth and establishment of all species. Caging palatable native species or planting species with anti‐herbivory traits around target plants may be more strategic approaches compared to using nurse plants in restoring degraded CSS after extended drought.     

Deciduous leaf drop reduces insect herbivory

Deciduous leaf fall is thought to be an adaptation that allows plants living in seasonal environments to reduce water loss and damage during unfavorable periods while increasing photosynthetic rates during favorable periods. Observations of natural variation in leaf shedding suggest that deciduous leaf fall may also allow plants to reduce herbivory. I tested this hypothesis by experimentally manipulating leaf retention for Quercus lobata and observing natural rates of herbivory. Quercus lobata is primarily deciduous although individuals show considerable natural variation in leaf retention. Oak saplings with no leaves through winter experienced reduced attack by cynipid gall makers the following spring. This pattern was consistent with the positive correlation between natural leaf persistence and gall numbers. These cynipids do not overwinter on the leaves that trees retain through winter, although they appear to use persistent leaves as oviposition cues. If these results are general for woody plants in continental temperate habitats, they suggest that an important and unrecognized consequence of deciduous leaf shedding may be a reduction in herbivore damage, and that this effect should be included in models of deciduous and evergreen behavior.     

Selenium protects the hyperaccumulator Stanleya pinnata against black-tailed prairie dog herbivory in native seleniferous habitats

Elemental hyperaccumulation in plants is hypothesized to represent a plant defense mechanism. The objective of this study was to determine whether selenium (Se) hyperaccumulation offers plants long-term protection from the black-tailed prairie dog (Cynomys ludovicianus). Prairie dogs are a keystone species. The hyperaccumulator Stanleya pinnata (prince's plume) co-occurs with prairie dogs in seleniferous areas in the western United States. Stanleya pinnata plants pretreated with high or low Se concentrations were planted on two prairie dog towns with different levels of herbivory pressure, and herbivory of these plants was monitored over 2 years. Throughout this study, plants with elevated Se levels suffered less herbivory and survived better than plants with low leaf Se concentrations. This study indicates that the Se in hyperaccumulator S. pinnata protects the plant in its natural habitat from herbivory by the black-tailed prairie dog. The results from this study support the hypothesis that herbivory by prairie dogs or similar small mammals has been a contributing selection pressure for the evolution of plant Se hyperaccumulation in North America. This study is the first to test the ecological significance of hyperaccumulation over a long period in a hyperaccumulator's natural habitat.     

Effects of simulated herbivory and resource availability on the invasive plant, Alternanthera philoxeroides in different habitats

In biological control programs, the insect natural enemy’s ability to suppress the plant invader may be affected by abiotic factors, such as resource availability, that can influence plant growth and reproduction. Understanding plant tolerance to herbivory under different environmental conditions will help to improve biocontrol efficacy. The invasive alligator weed (Alternanthera philoxeroides) has been successfully controlled by natural enemies in many aquatic habitats but not in terrestrial environments worldwide. This study examined the effects of different levels of simulated leaf herbivory on the growth of alligator weed at two levels of fertilization and three levels of soil moisture (aquatic, semi-aquatic, and terrestrial habitats). Increasing levels of simulated (manual) defoliation generally caused decreases in total biomass in all habitats. However, the plant appeared to respond differently to high levels of herbivory in the three habitats. Terrestrial plants showed the highest below–above ground mass ratio (R/S), indicating the plant is more tolerant to herbivory in terrestrial habitats than in aquatic habitats. The unfertilized treatment exhibited greater tolerance than the fertilized treatment in the terrestrial habitat at the first stage of this experiment (day 15), but fertilizer appears not to have influenced tolerance at the middle and last stages of the experiment. No such difference was found in semi-aquatic and aquatic habitats. These findings suggest that plant tolerance is affected by habitats and soil nutrients and this relationship could influence the biological control outcome. Plant compensatory response to herbivory under different environmental conditions should, therefore, be carefully considered when planning to use biological control in management programs against invasive plants.     

Effect of light environment on intra-specific variation in herbivory in the carnivorous plant Pinguicula moranensis (Lentibulariaceae)

Identifying the factors that affect a plant’s probability of being found and damaged by herbivores has been a central topic in the study of herbivory. Although herbivory could have important negative consequences on carnivorous plants, their interaction with herbivores remains largely unexplored. We evaluated the effect of spatial variation in light environment (sunny, shade and full-shade sites) on the pattern of leaf herbivory and florivory of the carnivorous plant Pinguicula moranensis. Plants’ overall probability of leaf damage was high (74.24%). Mean herbivory was four times higher in the sunny and shade sites than the observed in the full-shade site. Nearly 8% of plants suffered damage to reproductive structures, although the probability of florivory was similar among sites. Discussion addressed the inter-site variation in mean herbivory considering the effect of light exposure and the impact that herbivory could have on fitness components of this carnivorous plant.     

Deer Herbivory as an Ecological Constraint to Restoration of Degraded Riparian Corridors

Ungulate herbivory can impact riparian vegetation in several ways, such as by reducing vigor or reproductive output of mature plants, and through increased mortality of seedlings and saplings. Much work has focused on the effects of livestock grazing within riparian corridors, while few studies have addressed the influence of native ungulate herbivory on riparian vegetation. This study investigated the effect of deer herbivory on riparian regeneration along three streams with degraded riparian corridors in Mendocino County, California. We utilized existing stream restoration efforts by private landowners and natural resource agencies to compare six deer exclosures with six upstream control plots. Livestock were excluded from both exclosure and control plots. Three of the deer exclosures had been in place for 15 years, one for 6 years, and two for 4 years. The abundance and size distribution of woody riparian plant species such as Salix exigua, S. laevigata, S. lasiolepis, Alnus rhombifolia, and Fraxinus latifolia were quantified for each exclosure and control plot. The mean density of saplings in deer exclosures was 0.49 ± 0.15/m², while the mean density of saplings in control plots was 0.05 ± 0.02/m². Within exclosures, 35% of saplings were less than 1 m and 65% were greater than 1 m; within control plots, 97% of saplings were less than 1 m in height. The fact that little regeneration had occurred in control plots suggests that deer herbivory can substantially reduce the rate of recovery of woody riparian species within degraded riparian corridors. Exclusionary fencing has demonstrated promising results for riparian restoration in a region with intense deer herbivory.     

Species Identity and Water Availability Determine Establishment Success Under the Canopy of Retama sphaerocarpa Shrubs in a Dry Environment

Seedling establishment in harsh environments is often enhanced by the proximity of adult shrubs. This information has been used in restoration work by placing seedlings of species being restored under the canopy of some shrubs. However, monitoring this process is often restricted to a single species, and comparisons with practices that protect planted seedlings against harsh conditions are scant. Similarly, few studies have supplied seedlings with water in the summer to observe the effects of water availability on the interaction. We compared sapling survival of three woody species (Olea europaea, Pistacia lentiscus, and Ziziphus lotus) under the leguminous shrub Retama sphaerocarpa and in gaps covered with piled branches that mimicked a shrub canopy. After 3 years, survival of saplings planted under Retama differed depending on species identity and water supply. Survival of Olea saplings placed under Retama shrubs was twice that under piled branches if not watered (35 ± 8 vs. 17 ± 2 %, respectively), whereas survival of saplings under Retama, if watered, was less (48 ± 11 vs. 68 ± 8%, respectively). Retama shrubs had a negative effect on Ziziphus; most saplings died under its canopy, whereas survival in piled branches ranged 10–54%. Pistacia was neither facilitated nor outcompeted by Retama. Facilitation of Olea by Retama shrubs was more apparent under dry conditions where watering increased competition and decreased facilitation. Overall, we conclude that Retama shrubs can help dry land restoration to a greater extent than artificial shade for Olea when not watered. The critical role played by water supply in determining nursing success rates warrants further study.     

Conservation of an Ant–plant Mutualism in Native Forests and Ecologically‐managed Tree Monocultures

The Brazilian Atlantic Forest has been replaced by homogeneous tree monocultures with potentially drastic effect on ecological interactions. We expect that ecologically‐managed tree monocultures, however, can help to mitigate this impact. Here, we carried out an experiment with Inga vera (Fabaceae), an extrafloral nectary bearing plant, to test if the efficiency of ants as anti‐herbivory defense is affected by the replacement of its natural habitat (Araucaria Forest) by ecologically‐managed tree monocultures (plantations of Araucaria, Pinus, and Eucalyptus). Seedlings of Inga vera were transplanted to three patches of each habitat and ants were excluded from half of the plants. The abundance of ants and herbivores was low, similar among habitats, and exhibited temporal asynchrony. Number of herbivores and accumulated herbivory levels were lower in plant with ants. Rates of herbivory were extremely low and lower for young leaves than for mature leaves. The presence of ants did not affect plant performance traits measured by their growth in height, and their final numbers of leaves and leaflets. Contrary to what might be expected, ant‐protected plants produced fewer leaves and leaflets than unprotected ones. In conclusion, Inga vera‐ant interaction was similar between its natural habitat and the tree monocultures, indicating that potentially both species diversity and ecological processes can be conserved in ecologically‐managed tree monocultures.     

Tree seedling responses to leaf-cutting ants herbivory in Atlantic Forest restoration sites

Leaf-cutting ants (LCA) are generalist herbivores capable of causing severe plant damage. Negative impacts of ant herbivory vary according to the density of nests and availability of palatable plants; however, it is not yet clear how these herbivores affect tropical forest restoration sites. To investigate how LCA preference affects plant species performance, we evaluated the herbivory of Atta sexdens rubropilosa on native tree species seedlings in Atlantic Forest restoration sites. We expected pioneer species to suffer higher herbivory by LCA when compared with non-pioneer species and that species with higher damage will have poorer growth and higher mortality. The experiment was conducted in three restoration sites in northern Paraná state, southern Brazil, with 1,500 seedlings of 5 pioneer and 5 non-pioneer species. Sites share similar age, stand size, tree species composition, and LCA nest density. The number of attacks, degree of leaf damage, number of leaves, plant height, and survival were recorded. Specific leaf area, leaf polyphenols, flavonoids, tannins, and nitrogen content were analyzed for each species. Plant damage was similar between pioneer and non-pioneer plant species. This could be explained by trait variability among species in each group and by LCA generalist foraging. Preferred species suffered decreases in growth and survival. Less preferred species suffered fewer ant attacks and no change in performance. Results suggest that ant herbivory can influence plant species establishment and thus species composition in restoration sites by reducing performance and increasing mortality of some, but not all species, making LCA an important ecological filter.     

Ecophysiological responses of salt cedar (Tamarix spp. L.) to the northern tamarisk beetle (Diorhabdacarinulata Desbrochers) in a controlled environment

The northern tamarisk beetle (Diorhabda carinulata Desbrochers) was released in several western states as a biocontrol agent to suppress Tamarix spp. L. which has invaded riparian ecosystems; however, effects of beetle herbivory on Tamarix physiology are largely undocumented and may have ecosystem ramifications. Herbivory by this insect produces discoloration of leaves and premature leaf drop in these ecosystems, yet the cause of premature leaf drop and the effects of this leaf drop are still unknown. Insect herbivory may change leaf photosynthesis and respiration and may affect a plant’s ability to regulate water loss and increase water stress. Premature leaf drop may affect plant tissue chemistry and belowground carbon allocation. We conducted a greenhouse experiment to understand how Tamarix responds physiologically to adult beetle and larvae herbivory and to determine the proximate cause of premature leaf drop. We hypothesized that plants experiencing beetle herbivory would have greater leaf and root respiration rates, greater photosynthesis, increased water stress, inefficient leaf nitrogen retranslocation, lower root biomass and lower total non-structural carbohydrates in roots. Insect herbivory reduced photosynthesis rates, minimally affected respiration rates, but significantly increased water loss during daytime and nighttime hours and this produced increased water stress. The proximate cause for premature leaf drop appears to be desiccation. Plants exposed to herbivory were inefficient in their retranslocation of nitrogen before premature leaf drop. Root biomass showed a decreasing trend in plants subjected to herbivory. Stress induced by herbivory may render these trees less competitive in future growing seasons.     

Invading from the garden? A comparison of leaf herbivory for exotic and native plants in natural and ornamental settings

Abstract The enemies release hypothesis proposes that exotic species can become invasive by escaping from predators and parasites in their novel environment. Agrawal et al. (Enemy release? An experiment with congeneric plant pairs and diverse above‐ and below‐ground enemies. Ecology, 86, 2979–2989) proposed that areas or times in which damage to introduced species is low provide opportunities for the invasion of native habitat. We tested whether ornamental settings may provide areas with low levels of herbivory for trees and shrubs, potentially facilitating invasion success. First, we compared levels of leaf herbivory among native and exotic species in ornamental and natural settings in Cincinnati, Ohio, United States. In the second study, we compared levels of herbivory for invasive and noninvasive exotic species between natural and ornamental settings. We found lower levels of leaf damage for exotic species than for native species; however, we found no differences in the amount of leaf damage suffered in ornamental or natural settings. Our results do not provide any evidence that ornamental settings afford additional release from herbivory for exotic plant species.     

Differential adaptation to a harsh granite outcrop habitat between sympatric Mimulus species

Understanding which environmental variables and traits underlie adaptation to harsh environments is difficult because many traits evolve simultaneously as populations or species diverge. Here, we investigate the ecological variables and traits that underlie Mimulus laciniatus’ adaptation to granite outcrops compared to its sympatric, mesic‐adapted progenitor, Mimulus guttatus. We use fine‐scale measurements of soil moisture and herbivory to examine differences in selective forces between the species’ habitats, and measure selection on flowering time, flower size, plant height, and leaf shape in a reciprocal transplant using M. laciniatus × M. guttatus F₄ hybrids. We find that differences in drought and herbivory drive survival differences between habitats, that M. laciniatus and M. guttatus are each better adapted to their native habitat, and differential habitat selection on flowering time, plant stature, and leaf shape. Although early flowering time, small stature, and lobed leaf shape underlie plant fitness in M. laciniatus’ seasonally dry environment, increased plant size is advantageous in a competitive mesic environment replete with herbivores like M. guttatus’. Given that we observed divergent selection between habitats in the direction of species differences, we conclude that adaptation to different microhabitats is an important component of reproductive isolation in this sympatric species pair.     

Rapid recovery of an insect–plant interaction following habitat loss and experimental wetland restoration

This study examined the impact of wetland habitat loss and isolation on an insect–plant interaction, and the subsequent rate of recovery of the interaction following experimental habitat restoration. We compared herbivore colonisation rates and herbivory damage by ‘Batrachedra’ sp. (Lepidoptera: Coleophoridae) on experimentally placed potted Sporadanthus ferrugineus (Restionaceae) plants at increasing distances (up to 800 m) from an intact habitat (the source population). These tests showed that even a moderate degree of isolation (i.e. greater than 400 m) from the intact wetland habitat caused an almost complete collapse of the insect–plant interaction, at least in the short term. The number of eggs and larvae of colonising ‘Batrachedra’ sp., as well as average larval size and the proportion of S. ferrugineus stems damaged, all decreased logarithmically with increasing distance from the intact habitat, presumably due to dispersal limitation of the herbivore. Subsequently, to test whether the interaction can recover following habitat restoration, we surveyed herbivore colonisation rates and herbivory damage on naturally regenerated S. ferrugineus plants on experimentally restored ‘islands’ at increasing distances (up to 800 m) from an intact habitat. The rate of recovery of the interaction was surprisingly rapid (i.e. between 196 and 308 weeks). The degree of difference in the density of eggs and larvae, and in the proportion of stems damaged with increasing isolation from the intact wetland, gradually diminished over 196 weeks. After 308 weeks there was no significant difference in the insect–plant interaction between the intact wetland sites and any of the experimentally restored sites up to 800 m away. These results suggest that some insect–plant interactions can recover rapidly from habitat loss with restoration management.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Bird predation enhances tree seedling resistance to insect herbivores in contrasting forest habitats

According to the associational resistance hypothesis, neighbouring plants are expected to influence both the insect herbivore communities and their natural enemies. However, this has rarely been tested for the effects of canopy trees on herbivory of seedlings. One possible mechanism responsible for associational resistance is the indirect impact of natural enemies on insect herbivory, such as insectivorous birds. But it remains unclear to what extent such trophic cascades are influenced by the composition of plant associations (i.e. identity of ‘associated’ plants). Here, we compared the effect of bird exclusion on insect leaf damage for seedlings of three broadleaved tree species in three different forest habitats. Exclusion of insectivorous birds affected insect herbivory in a species-specific manner: leaf damage increased on Betula pendula seedlings whereas bird exclusion had no effect for two oaks (Quercus robur and Q. ilex). Forest habitat influenced both the extent of insect herbivory and the effect of bird exclusion. Broadleaved seedlings had lower overall leaf damage within pine plantations than within broadleaved stands, consistent with the resource concentration hypothesis. The indirect effect of bird exclusion on leaf damage was only significant in pine plantations, but not in exotic and native broadleaved woodlands. Our results support the enemies hypothesis, which predicts that the effects of insectivorous birds on insect herbivory on seedlings are greater beneath non-congeneric canopy trees. Although bird species richness and abundance were greater in broadleaved woodlands, birds were unable to regulate insect herbivory on seedlings in forests of more closely related tree species.