Leaf Herbivory Research Articles

Induced carbon reallocation and compensatory growth as root herbivore tolerance mechanisms.

Upon attack by leaf herbivores, many plants reallocate photoassimilates below ground. However, little is known about how plants respond when the roots themselves come under attack. We investigated induced resource allocation in maize plants that are infested by the larvae Western corn rootworm Diabrotica virgifera virgifera. Using radioactive (11) CO(2), we demonstrate that root-attacked maize plants allocate more new (11) C carbon from source leaves to stems, but not to roots. Reduced meristematic activity and reduced invertase activity in attacked maize root systems are identified as possible drivers of this shoot reallocation response. The increased allocation of photoassimilates to stems is shown to be associated with a marked thickening of these tissues and increased growth of stem-borne crown roots. A strong quantitative correlation between stem thickness and root regrowth across different watering levels suggests that retaining photoassimilates in the shoots may help root-attacked plants to compensate for the loss of belowground tissues. Taken together, our results indicate that induced tolerance may be an important strategy of plants to withstand belowground attack. Furthermore, root herbivore-induced carbon reallocation needs to be taken into account when studying plant-mediated interactions between herbivores.

Context-dependent patterns, determinants and demographic consequences of herbivory in an invasive species

Non-native invasive plants often lose many of their specialist herbivores in their invaded ranges, but new enemies may be recruited from the local generalist fauna, or from enemies themselves introduced to the same region. As a result, few invaders are free of herbivore damage; however, the incidence of this herbivory and its consequences for plant demography may depend on an array of biotic and abiotic factors. In Alliaria petiolata, a non-native invasive forb in Canada, we quantified the incidence of leaf herbivory, rosette survival and seed production along with conspecific plant density and environmental site conditions in wild populations in mesic forest understory and moist grasslands. We complemented the field survey by a laboratory experiment with Trichoplusia to test whether the palatability of leaf tissue of A. petiolata varies with plant life stage and habitat type. Incidence of herbivory was significantly higher in adults than in rosettes, and significantly higher in grasslands than in forest understory. The palatability experiment confirmed that leaves of adults were more palatable to a generalist herbivore than leaves of rosettes. Path analysis revealed negative plant density-dependent herbivory of adults in forest understory but positive density-dependent herbivory in grasslands. Incidence of herbivory in rosettes was positively associated with soil moisture in grasslands, but not in forest understory. Seed production was significantly positively associated with herbivory in adults and soil moisture, whereas rosette survival was significantly negatively associated with conspecific plant density. We conclude that the patterns, determinants and demographic consequences of herbivory in invasive Alliaria may strongly depend on a plant’s life stage and plant density and may further be confounded by landscape heterogeneity.

Variation in cyanogenic glycosides across populations of wild lima beans (Phaseolus lunatus) has no apparent effect on bruchid beetle performance.

Cyanogenic glycosides (CNGs) act as feeding or oviposition deterrents and are toxic after enzymatic hydrolysis, thus negatively affecting herbivore performance. While most studies on CNGs focus on leaf herbivores, here we examined seeds from natural populations of Phaseolus lunatus in Mexico. The predominant CNGs, linamarin and lotaustralin, were quantified for each population by using ultra-high pressure liquid chromatography-mass spectrometry. We also examined whether there was a correlation between the concentration of CNGs and the performance of the Mexican bean beetle, Zabrotes subfasciatus, on seeds from each population(.) The concentrations of CNGs in the seeds were relatively high compared to the leaves and were significantly variable among populations. Surprisingly, this had little effect on the performance of the bruchid beetles. Zabrotes subfasciatus can tolerate high concentrations of CNGs, most likely because of the limited β-glucosidase activity in the seeds. Seed herbivory does not appear to liberate hydrogen cyanide due to the low water content in the seed. This study illustrates the importance of quantifying the natural variation and activity of toxic compounds in order to make relevant biological inferences about their role in defense against herbivores.

Leaf Mimicry in a Climbing Plant Protects against Herbivory

Mimicry refers to adaptive similarity between a mimic organism and a model. Mimicry in animals is rather common, whereas documented cases in plants are rare, and the associated benefits are seldom elucidated [1, 2]. We show the occurrence of leaf mimicry in a climbing plant endemic to a temperate rainforest. The woody vine Boquila trifoliolata mimics the leaves of its supporting trees in terms of size, shape, color, orientation, petiole length, and/or tip spininess. Moreover, sequential leaf mimicry occurs when a single individual vine is associated with different tree species. Leaves of unsupported vines differed from leaves of climbing plants closely associated with tree foliage but did not differ from those of vines climbing onto leafless trunks. Consistent with an herbivory-avoidance hypothesis, leaf herbivory on unsupported vines was greater than that on vines climbing on trees but was greatest on vines climbing onto leafless trunks. Thus, B. trifoliolata gains protection against herbivory not merely by climbing and thus avoiding ground herbivores [3] but also by climbing onto trees whose leaves are mimicked. Unlike earlier cases of plant mimicry or crypsis, in which the plant roughly resembles a background or color pattern [4-7] or mimics a single host [8, 9], B. trifoliolata is able to mimic several hosts.

Above‐ground herbivory by red milkweed beetles facilitates above‐ and below‐ground conspecific insects and reduces fruit production in common milkweed

Summary Initial herbivory and induced plant responses can influence subsequent above‐ and below‐ground herbivore attack. When two life stages of the same herbivore damage different plant parts sequentially, there is strong potential for plants to respond with induced plant defence against the later attacker. Alternatively, the earlier attacker could manipulate the host plant to facilitate the later‐feeding life stage. We studied herbivory by foliage‐feeding adults and root‐feeding larvae of the red milkweed beetle (Tetraopes tetraophthalmus) on native common milkweed (Asclepias syriaca) in laboratory and field experiments. We applied factorial above‐ and below‐ground herbivory treatments to test for induced responses, effects on later‐feeding conspecific larvae, and damage by naturally colonizing herbivores, including adult T. tetraophthalmus. We found that the inducibility of toxic cardenolides was systemic across the root–shoot barrier, with the highest concentrations in plants damaged both above‐ and below‐ground. Initial above‐ground herbivory increased root damage and larval survival, suggesting an increase in root quality following leaf herbivory. Initial below‐ground herbivory did not affect the performance of later‐feeding larvae, indicating limited importance of induced root cardenolides and competition between clutches of T. tetraophthalmus. In a natural milkweed population, initial above‐ground herbivory attracted conspecific adults and milkweed leaf beetles (Labidomera clivicollis) and ultimately reduced fruit production by 33%. Nonetheless, the probability of damage by monarch caterpillars (Danaus plexippus) was reduced on plants initially damaged by T. tetraophthalmus above‐ground, likely due to reduced oviposition following induced plant responses. Synthesis. Induced plant responses of common milkweed to above‐ground damage by adult T. tetraophthalmus both facilitate further damage by adults and enhance the performance of their root‐feeding larvae, most likely as a result of host plant manipulation. Although the same induction reduced monarch herbivory, the net effect of these interactions was negative for the plant as fruit production was substantially reduced. These results imply that host plant manipulation may be especially common by specialist herbivores that have sequential above‐ and below‐ground life stages.

Consumo de hojas por herbívoros en manglares del estuario del Río Dagua, Costa Pacífica Colombiana

Herbivore leaf consumption of various mangrove species in relation to environmental factors and leaf hardness were studied in the Dagua river estuary, Colombia. Leaf consumption and damage were assessed by measuring the percentage of area attacked by herbivores, distinguishing between consumption and damage. The species that suffered the highest consumption, such as Avicennia germinans (Avicenniaceae) and Laguncularia racemosa (Combretaceae), had softer leaves and less herbivore species when compared with Rhizophora spp. (Rhizophoraceae) and Pelliciera rhizophorae (Theaceae). The abundance and diversity of leaf grazing and its variability among mangrove species in the Dagua River estuary, show the importance of the trophic dynamics of live vegetable matter, in spite of their relatively low contribution to removing organic matter.

Potential impacts of climate change on patterns of insect herbivory on understorey plant species: A transplant experiment

Species-specific responses to climate change will lead to changes in species interactions across multiple trophic levels. Interactions between plants and their insect herbivores, in particular, may become increasingly disrupted if mobile herbivores respond more rapidly to climatic change than their associated host plants. We present a multispecies transplant experiment aimed at assessing potential climatic impacts on patterns of leaf herbivory. Four shrubby understorey plant species were transplanted outside their native range into a climate 2.5°C warmer in annual mean temperature. After 12 months, we assessed the types and amount of herbivore leaf damage, compared with plants transplanted to a control site within their native range. The overall amount of foliage loss to herbivores ranged from approximately 3–10% across species and sites, a range consistent with most estimates of leaf loss in other studies. The most common types of leaf damage were sucking and chewing and this pattern was consistent for all four plant species at all sites. There were no significant differences in levels and patterns of herbivory between control and warm sites for three out of four plant species. This suggests that with moderate climate warming, most herbivory will continue to be dominated by chewers and suckers, and that the overall level of foliage loss will be similar to that experienced presently.

Percentage leaf herbivory across vascular plant species

Herbivory is viewed as a major driver of plant evolution and the most important energy pathway from plants to higher trophic levels. Therefore, understanding patterns of herbivory on plants remains a key focus in evolution and ecology. The evolutionary impacts of leaf herbivory include altering plant fitness, local adaptation, the evolution of defenses, and the diversification of plants as well as natural enemies. Leaf herbivory also impacts ecological processes such as plant productivity, community composition, and ecosystem nutrient cycling. Understanding the impact of herbivory on these ecological and evolutionary processes requires species‐specific, as opposed to community‐level, measures of herbivory. In addition, species‐specific data enables the use of modern comparative methods to account for phylogenetic non‐independence. Although hundreds of studies have measured natural rates of leaf consumption, we are unaware of any accessible compilation of these data. We created such a data set to provide the raw data needed to test general hypotheses relating to plant–herbivore interactions and to test the influence of biotic and abiotic factors on herbivory rates across large spatial scales. A large repository will make this endeavor more efficient and robust. In total, we compiled 2641 population‐level measures for either annual or daily rates of leaf herbivory across 1145 species of vascular plants collected from 189 studies. All damage measures represent natural occurrences of herbivory that span numerous angiosperm, gymnosperm, and fern species. To enable researchers to explore the causes of variation in herbivory and how these might interact, we added information about the study sites including: geolocation, climate classification, habitat descriptions (e.g., seashore, grassland, forest, agricultural fields), and plant trait information concerning growth form and duration (e.g., annual vs. perennial). We also included extensive details of the methodology used to measure leaf damage, including seasons and months of sampling, age of leaves, and the method used to estimate percentage area missing. We anticipate that these data will make it possible to test important hypotheses in the plant–herbivore literature, including the plant apparency hypothesis, the latitudinal‐herbivory defense hypothesis, the resource availability hypothesis, and the macroevolutionary escalation of defense hypothesis.

The roots of plant defenses: integrative multivariate analyses uncover dynamic behaviors of gene and metabolic networks of roots elicited by leaf herbivory

High-throughput analyses have frequently been used to characterize herbivory-induced reconfigurations in plant primary and secondary metabolism in above- and below-ground tissues, but the conclusions drawn from these analyses are often limited by the univariate methods used to analyze the data. Here we use our previously described multivariate time-series data analysis to evaluate leaf herbivory-elicited transcriptional and metabolic dynamics in the roots of Nicotiana attenuata. We observed large, but transient, systemic responses in the roots that contrasted with the pattern of co-linearity observed in the up- and downregulation of genes and metabolites across the entire time series in treated and systemic leaves. Using this newly developed approach for the analysis of whole-plant molecular responses in a time-course multivariate data set, we simultaneously analyzed stress responses in leaves and roots in response to the elicitation of a leaf. We found that transient systemic responses in roots resolved into two principal trends characterized by: (i) an inversion of root-specific semi-diurnal (12h) transcript oscillations and (ii) transcriptional changes with major amplitude effects that translated into a distinct suite of root-specific secondary metabolites (e.g. alkaloids synthesized in the roots of N.attenuata). These findings underscore the importance of understanding tissue-specific stress responses in the correct day-night phase context and provide a holistic framework for the important role played by roots in above-ground stress responses.

Paleoenvironment and paleoecology of a Late Paleocene high-latitude terrestrial succession, Arkose Ridge Formation at Box Canyon, southern Talkeetna Mountains, Alaska

Paleogene sedimentary rocks of the Arkose Ridge Formation (Talkeetna Mountains, Alaska) preserve a record of a fluvial–lacustrine depositional environment and its forested ecosystem in an active basin among the convergent margin tectonic processes that shaped southern Alaska. An ~800m measured succession at Box Canyon indicates braid-plain deposition with predominantly gravelly deposits low in the exposure to sandy and muddy facies associations below an overlying lava flow sequence. U–Pb geochronology on zircons from a tuff and a sandstone within the measured section, as well as an Ar/Ar date from the overlying lava constrain the age of the sedimentary succession to between ~59Ma and 48Ma. Fossil plant remains occur throughout the Arkose Ridge Formation as poorly-preserved coalified woody debris and fragmentary leaf impressions. At Box Canyon, however, a thin lacustrine depositional lens of rhythmically laminated mudrocks yielded fish fossils and a well-preserved floral assemblage including foliage and reproductive organs representing conifers, sphenopsids, monocots, and dicots. Leaf physiognomic methods to estimate paleoclimate were applied to the dicot leaf collection and indicate warm temperate paleotemperatures (~11–15±~4°C MAT) and elevated paleoprecipitation (~120cm/yr MAP) estimates as compared to modern conditions; results that are parallel with previously published estimates from the partly coeval Chickaloon Formation deposited in more distal depositional environments in the same basin. The low abundance of leaf herbivory in the Box Canyon dicot assemblage (~9% of leaves damaged) is also similar to the results from assemblages in the meander-plain depositional systems of the Chickaloon. This new suite of data informs models of the tectonostratigraphic evolution of southern Alaska and the developing understanding of terrestrial paleoecology and paleoclimate at high latitudes during the Late Paleocene–Early Eocene greenhouse climate phase.

Effects of Roads onCastanopsis carlesiiSeedlings and Their Leaf Herbivory in a Subtropical Forest in China

The effects of a forest road on Castanopsis carlesii (Hemsley) Hayata (Fagales: Fagaceae) seedlings and their leaf herbivory were investigated in a subtropical forest at Jiulianshan National Nature Reserve, Jiangxi, China. A total of 1124 seedlings, 33949 leaves, 468 leaf mines, and 205 leaf galls were found. Generally, individual numbers, tree heights, and leaf numbers of C. carlesii seedlings became lower with increasing distances from the road. These results might indicate that old seedlings were fewer and survival rate of seedlings was lower in forest interiors. Leaf miners preferred the seedlings close to the forest road, while leaf gallers preferred the seedlings about 2 m from the road. Species diversity of leaf miners was higher in the forest interior area, while species diversity of leaf gallers was higher near the road. However, both leaf miners and leaf gallers decreased in general from the road to the interior forest. There were interspecific differences in the effects of roads on leaf miner species and leaf galler species. The effects of the road on seedlings and insects could be explained by varying microhabitat conditions and different ecological strategies.

Effects of roads on Castanopsis carlesii seedlings and their leaf herbivory in a subtropical forest in China.

The effects of a forest road on Castanopsis carlesii (Hemsley) Hayata (Fagales: Fagaceae) seedlings and their leaf herbivory were investigated in a subtropical forest at Jiulianshan National Nature Reserve, Jiangxi, China. A total of 1124 seedlings, 33949 leaves, 468 leaf mines, and 205 leaf galls were found. Generally, individual numbers, tree heights, and leaf numbers of C. carlesii seedlings became lower with increasing distances from the road. These results might indicate that old seedlings were fewer and survival rate of seedlings was lower in forest interiors. Leaf miners preferred the seedlings close to the forest road, while leaf gallers preferred the seedlings about 2 m from the road. Species diversity of leaf miners was higher in the forest interior area, while species diversity of leaf gallers was higher near the road. However, both leaf miners and leaf gallers decreased in general from the road to the interior forest. There were interspecific differences in the effects of roads on leaf miner species and leaf galler species. The effects of the road on seedlings and insects could be explained by varying microhabitat conditions and different ecological strategies. 摘要

Effects of an invasive herbivore at the single plant scale do not extend to population-scale seedling dynamics

A complex of nine invasive weevils has established in the northern hardwood forests of the Great Lakes Region. These weevils have become the numerically dominant arthropod fauna in the lower vegetation strata of this ecosystem. Effects of these folivorous adults and rhizophagous larvae on seedling survival and density are unknown. We measured the impact of adult weevil defoliation on individual sugar maple (Acer saccharum Marshall) seedlings, the numerically dominant flora in these stands. Over 14 500 seedlings were measured to examine the effects of larval abundance, adult abundance, and adult defoliation on seedling dynamics during 2005–2009. Heavy defoliation led to individual sugar maple seedling mortality. However, at the stand level there was no measureable net effect of invasive weevils against the high natural background rates of seedling mortality. Seedling growth and biomass were reduced by high adult or larval populations, which were associated with heavy leaf and root herbivory, but not by moderate adult or larval populations. We conclude that high levels of redundancy and compensatory processes in this environment allow sugar maple seedling populations to tolerate high levels of weevil damage, although additional stresses could reduce this resilience.

Circular distribution pattern of plant modulars and endophagous herbivory within tree crowns: the impact of roadside light conditions.

The circular distributions of plant modulars (branches, leaves) and endophagous herbivory (mines, galls) were investigated within the crowns of four dominant Fagaceae trees in a subtropical evergreen broadleaf forest at Jiulianshan National Nature Reserve, Jiangxi, China. The hypothesis is that more plant modulars and more endophagous herbivory should occur in the crown area perpendicular to the roads. Circular statistical techniques were used to verify new patterns of the impact of roads on plants and insects. The results confirmed that the roadside light environments had larger impacts on the circular distribution patterns of plant modulars than those of leaf herbivores. For herbivores, the impact of light was larger on mine distribution than on gall distribution. The branches of all four tree species were concentrated in the direction perpendicular to the roads. In the preferred direction, branches were longer and higher. More leaves, more mines, and more galls were found surrounding the preferred branch direction. In general, leaf miners and leaf gallers preferred leaves in the sun over those in the shade; however, leaf gallers had a lower degree of preference for sun than leaf miners. Different endphagous insects also showed clear interspecific differences in sun/shade leaf selection.

Contrasting impacts of defoliation on root colonization by arbuscular mycorrhizal and dark septate endophytic fungi of Medicago sativa

Individual plants typically interact with multiple mutualists and enemies simultaneously. Plant roots encounter both arbuscular mycorrhizal (AM) and dark septate endophytic (DSE) fungi, while the leaves are exposed to herbivores. AMF are usually beneficial symbionts, while the functional role of DSE is largely unknown. Leaf herbivory may have a negative effect on root symbiotic fungi due to decreased carbon availability. However, evidence for this is ambiguous and no inoculation-based experiment on joint effects of herbivory on AM and DSE has been done to date. We investigated how artificial defoliation impacts root colonization by AM (Glomus intraradices) and DSE (Phialocephala fortinii) fungi and growth of Medicago sativa host in a factorial laboratory experiment. Defoliation affected fungi differentially, causing a decrease in arbuscular colonization and a slight increase in DSE-type colonization. However, the presence of one fungal species had no effect on colonization by the other or on plant growth. Defoliation reduced plant biomass, with this effect independent of the fungal treatments. Inoculation by either fungal species reduced root/shoot ratios, with this effect independent of the defoliation treatments. These results suggest AM colonization is limited by host carbon availability, while DSE may benefit from root dieback or exudation associated with defoliation. Reductions in root allocation associated with fungal inoculation combined with a lack of effect of fungi on plant biomass suggest DSE and AMF may be functional equivalent to the plant within this study. Combined, our results indicate different controls of colonization, but no apparent functional consequences between AM and DSE association in plant roots in this experimental setup.

Protection Mutualisms and the Community: Geographic Variation in an Ant-Plant Symbiosis and the Consequences for Herbivores

Protection mutualisms mediate trophic interactions in many systems, but their effects on the surrounding community are rarely studied. Ant-plant symbioses are classic examples of protection mutualisms: myrmecophytic plants provide nesting space and food for symbiotic ants in exchange for ant defense. Ant defense should thus reduce the abundance of herbivores, but studies of ant-plant symbioses usually measure damage to the plant without quantifying the herbivores themselves. In this study, we investigated whether geographic variation in the quality of ant defense in a symbiotic mutualism between Cordia alliodora trees and Azteca ants was associated with the abundance and species richness of plant herbivore communities. In three tropical-dry-forest sites in Middle America, we found that the density of Azteca ants within trees was negatively associated with the levels of leaf herbivory. At sites where ants were effective tree defenders, tree herbivores were less abundant and herbivore assemblages on trees exhibited lower species richness than at a site where ants were poor defenders. In addition, in a site where ants reduced herbivory, herbivore communities were less abundant and diverse in the presence of ants than in their absence, where as in a site where ants did not reduce herbivory, there were no differences in herbivore abundance or richness between trees with or without ants. We conclude that geographic variation in the quality of ant defense drives variation in myrmecophytic-plant herbivore communities. Moreover, ant-plant protection mutualisms should have important but rarely considered effects on herbivore population dynamics and food-plant specialization.

Dramatic vestigialization of floral fragrance across a transition from outcrossing to selfing inAbronia umbellata(Nyctaginaceae)

Vestigialization of traits that no longer enhance fitness is a common theme in evolution. Plants often use colorful, scented flowers to attract pollinators that mediate outcross pollination. After an evolutionary shift from outcrossing to self-fertilization, where cross-pollination is no longer necessary, attractive traits may be reduced, especially because these traits may also attract herbivores. Selection may be particularly strong in moth-pollinated lineages where pollinators are also herbivores. We used field surveys and common garden glasshouse experiments to test this hypothesis by quantifying components of flower size and display and floral volatiles in outcrossing vs. selfing populations of the moth-pollinated Pacific coastal dune endemic Abronia umbellata. Floral face diameter and flower tube length were 43% and 54% smaller in selfing than outcrossing populations, and selfers displayed 15% fewer flowers per umbel. Selfers emitted 99% less total floral volatiles per flower per hour than outcrossers; a much stronger reduction. The chemical composition of volatiles also differed between outcrossers and selfers. Similar differences were observed in a common glasshouse environment, suggesting genetic differentiation in these floral attractive traits among populations. Contrary to expectations, there were no differences in leaf or flower herbivory between selfing and outcrossing populations. Floral fragrance is much more dramatically reduced in selfing compared to outcrossing populations than other floral attractive traits, but probably not due to selection exerted by moth herbivory. Reduction in aspects of flower size may be constrained by developmental linkages with fruit and seed size.

Directed seed dispersal of Piper by Carollia perspicillata and its effect on understory plant diversity and folivory

Directed dispersal occurs when seeds are differentially deposited to sites where offspring survivorship is higher than at randomly chosen sites. Traditionally, characteristics of the dispersal target sites that could increase survivorship of the dispersed plants are thought to be intrinsic to the sites. If directed dispersal is constant over extended periods of time, however, it is likely that nonrandom patterns of dispersal could modify the ecological characteristics of the target site in ways that could increase survivorship and fitness of the dispersed plants. Here we report patterns of Piper diversity (richness, equitability, and similarity) and Piper folivory within plots near natural or artificial roosts of Carollia perspicillata vs. similar plots without bat roosts. Plots with bat roosts, both natural and artificial, had significantly higher Piper species diversity. Additionally, we found that plots with a higher Piper species diversity showed less specialist folivory, higher generalist folivory, and lower total herbivore leaf damage than plots with low Piper diversity. Finally, plots with bat roosts also showed less specialist folivory, lower generalist folivory, and lower total folivory when compared to plots without roosts. We propose that long-lasting nonrandom patterns of seed dispersal can change the local ecological characteristics of target sites via changes in plant diversity, and that these changes are likely to reduce the local rates of folivory and, therefore, increase seed and adult plant survivorship.

Herbivores equalize the seedling height growth of three dominant tree species in an African tropical rain forest

Determining the impact of insect herbivores on forest tree seedlings and saplings is difficult without experimentation in the field. Moreover, this impact may be heterogeneous in time and space because of seasonal rainfall and canopy disturbances, or ‘gaps’, which can influence both insect abundance and plant performance. In this study we used fine netting to individually protect seedlings of Microberlinia bisulcata, Tetraberlinia bifoliolata and Tetraberlinia korupensis trees (Fabaceae=Leguminosae) from insects in 41 paired gap-understorey locations across 80ha of primary rain forest (Korup, Cameroon).For all species, growth in height and leaf numbers was negligible in the understorey, where M. bisulcata had the lowest survival after c. 2years. In gaps, however, all species responded positively with pronounced above-ground growth across seasons. When exposed to herbivores their seedling height growth was similar, but in the absence of herbivores, M. bisulcata significantly outgrew both Tetraberlinia species and matched their leaf numbers. This result suggests that insect herbivores might play an important role in maintaining species coexistence by mitigating sapling abundance of the more palatable M. bisulcata, which in gaps was eaten the most severely. The higher ratio in static leaf damage of control-to-caged M. bisulcata seedlings in gaps than understorey locations was consistent with the Plant Vigour Hypothesis. This result, however, did not apply to either Tetraberlinia species. For M. bisulcata and T. korupensis, but not T. bifoliolata (the most shade-tolerant species), caging improved relative seedling survival in the understory locations compared to gaps, providing restricted support for the Limiting Resource Model. Approximately 2.25years after treatments were removed, the caged seedlings were taller and had more leaves than controls in all three species, and the effect remained strongest for M. bisulcata.We conclude that in this community the impact of leaf herbivory on seedling growth in gaps is strong for the dominant M. bisulcata, which coupled to a very low shade-tolerance contributes to limiting its regeneration. However, because gaps are common to most forests, insect herbivores may be having impacts upon functionally similar tree species that are also characterized by low sapling recruitment much more widely than currently appreciated. An implication for the restoration and management of M. bisulcata populations in forests outside of Korup is that physical protection from herbivores of new seedlings where the canopy is opened by gaps, or by harvesting, should substantially increase its subcanopy regeneration, and thus, too, its opportunities for adult recruitment.

Annual leaf loss caused by folivorous insects in tropical rain forests on Mt. Kinabalu, Borneo

Few studies have been done on the quantification of stand-level leaf herbivory in tropical forests. We evaluated the significance of annual leaf loss due to folivorous insects on the calculation of aboveground net primary production (ANPP) in tropical rain forests along broad climatic and edaphic gradients on Mt. Kinabalu, Borneo. We estimated insect folivory at the stand level as the product of a lifetime leaf loss ratio and annual leaf production in the stand. We defined the lifetime leaf loss ratio as the ratio of litter-leaf mass consumed by folivorous insects to the total litter-leaf mass at the stand level. The lifetime leaf loss ratio ranged from 1.6 to 8.4 %. The annual leaf loss caused by folivorous insects ranged from 0.01 to 0.38 Mg C ha−1 year−1, or from 1.2 to 5.9 % of ANPP in these tropical rain forests. Our method of estimating folivory (1) simultaneously considers all the tree species, canopy layers, and species of folivorous insects, (2) avoids underestimating leaf herbivory due to the resorption of mobile organic and inorganic matter from senescent leaves at the time of leaf abscission, and (3) can readily be applied in forests elsewhere.