Intensity Of Herbivory Research Articles

The next frontier of plant–soil feedback research: unraveling context dependence across biotic and abiotic gradients

AbstractQuestionPlant–soil feedback (PSF) has emerged as a ubiquitous phenomenon and a potentially important predictor of plant community structure and dynamics. However, the predictive power of PSF in field contexts is mixed, and ecologists do not yet understand its relative importance compared to other factors that structure communities. Further progress requires a more nuanced understanding of how PSF interacts with other biotic and abiotic factors. Environmental factors (e.g. natural enemies, moisture, light, nutrients) are known to affect plant interactions with soil and soil organisms, leading to an expectation of environmental context dependence in plant–soil feedback. Such context dependence could explain when PSF is expected to be an important driver of community dynamics, and under what conditions PSF is likely to be positive (destabilizing) vs negative (stabilizing).MethodsWe conducted a literature review of studies that examined PSF across biotic and abiotic gradients.ResultsAlthough few relevant studies have been conducted in this emerging research area, results to date suggest that plant–soil feedback is sensitive to biotic factors, such as above‐ and below‐ground herbivory, and abiotic factors, such as nutrients and light.ConclusionsWe develop a conceptual framework to predict variation in the direction and strength of PSF depending on the biotic or abiotic drivers of feedback (e.g. pathogens, nutrients) and the environmental context (e.g. intensity of herbivory, soil fertility). We explore the utility of our predictive framework through discussion of case studies from the literature on context dependence in PSF. We also consider how different experimental approaches might yield different insights about PSF–environment interactions, and suggest key future research directions.

Invisible but consequential: root endophytic fungi have variable effects on belowground plant–insect interactions

AbstractEndophytic fungi are ubiquitous in nature and can play important roles in regulating plant–herbivore interactions. While some aboveground obligate symbionts are considered defensive mutualists of host plants, the importance of root endophytes in plant defense, especially against root‐feeding insects, remains unclear. This study aimed to investigate the effects of root fungal endophytes on plant resistance against belowground herbivores and the recovery of host plants from damage. We grew the common grassFestuca arundinacea(tall fescue) semi‐aeroponically in the laboratory and inoculated roots with one of five fungal endophytes isolated from field‐collected tall fescue or meadow soil. Endophyte‐inoculated and uninoculated control plants were subjected to feeding by larvae of the generalist root herbivoreRhizotrogus majalis(European chafer). Herbivory intensity was quantified after eight days, and regrowth of roots and shoots following root herbivory and mechanical shoot damage was measured thereafter for each treatment. Fungal identifications byDNAsequence analysis were conducted after completion of the herbivory experiments and revealed that the five endophytes included the decomposer fungiTrametes versicolorandMortierella alpina, the entomopathogenic fungiIsaria fumosoroseaandBeauveria bassiana, and a potential plant pathogen/entomopathogenFusariumcf.equiseti. The effects of these root endophytes on plant defense against root‐feeding insects were species‐specific. While four endophytes had few effects on plant resistance, endophyticB. bassianasignificantly reduced herbivore damage to roots. In comparison, plant tolerance to damage was impaired after colonization by all endophyte species exceptT. versicolorandM. alpina. The contrasting effects of endophytes on plant resistance and plant tolerance suggest that research solely evaluating plant resistance is likely to overestimate the benefits conferred by endophytes without accounting for potential negative effects on plant tolerance. We propose a conceptual framework to include both plant resistance and tolerance as two dimensions of a defensive strategy and show that plant associations with different root endophytes may shift the relative importance of resistance and tolerance for plant defense.

Factors affecting tolerance to herbivory in a calcifying alga on coral reefs

Herbivores greatly influence the productivity of algae but their impact can depend on the nuances of the timing, location, and intensity of herbivory. While plants can escape herbivory in spatial refugia, small-scale variations in habitat quality play a critical role in plant tolerance to herbivory and might generate complex trade-offs. On coral reefs, overstory branching corals provide a refuge from fish herbivory but also provide refugia for many small fish that excrete nutrients. Therefore, algae living in this habitat might also benefit from higher nutrient delivery. However, because coral branches occlude sunlight, algal growth rates might be impaired despite experiencing elevated nutrients and lower herbivory. In lab-based experiments, light, nutrients, and simulated herbivory were manipulated in summer and winter to investigate how these processes interact to influence the tolerance of herbivory in the calcifying green algae Halimeda, an important producer of reef carbonate sediments worldwide. Halimeda heteromorpha which is commonly found associated with branching corals tolerated tissue damage by increasing rates of segment production. Greater tolerance was observed at levels of light resembling those experienced under the coral’s canopy. Nutrient additions increased compensatory segment growth in winter but not summer. Levels of tolerance were seasonal and nutrient dependent. Results show that small-scale variations in habitat quality may influence tolerance to herbivory in Halimeda. This suggests that if coral habitats are degraded or lost and oceans continue to warm, a likely negative impact on Halimeda populations and its contribution to carbonate sediments could be expected if high levels of herbivory are maintained.

Short-term herbivory has long-term consequences in warmed and ambient high Arctic tundra

Climate change is occurring across the world, with effects varying by ecosystem and region but already occurring quickly in high-latitude and high-altitude regions. Biotic interactions are important in determining ecosystem response to such changes, but few studies have been long-term in nature, especially in the High Arctic. Mesic tundra plots on Svalbard, Norway, were subjected to grazing at two different intensities by captive Barnacle geese from 2003–2005, in a factorial design with warming by Open Top Chambers. Warming manipulations were continued through 2014, when we measured vegetation structure and composition as well as growth and reproduction of three dominant species in the mesic meadow. Significantly more dead vascular plant material was found in warmed compared to ambient plots, regardless of grazing history, but in contrast to many short-term experiments no difference in the amount of living material was found. This has strong implications for nutrient and carbon cycling and could feed back into community productivity. Dominant species showed increased flowering in warmed plots, especially in those plots where grazing had been applied. However, this added sexual reproduction did not translate to substantial shifts in vegetative cover. Forbs and rushes increased slightly in warmed plots regardless of grazing, while the dominant shrub, Salix polaris, generally declined with effects dependent on grazing, and the evergreen shrub Dryas octopetala declined with previous intensive grazing. There were no treatment effects on community diversity or evenness. Thus despite no changes in total live abundance, a typical short-term response to environmental conditions, we found pronounced changes in dead biomass indicating that tundra ecosystem processes respond to medium- to long-term changes in conditions caused by 12 seasons of summer warming. We suggest that while high arctic tundra plant communities are fairly resistant to current levels of climate warming, underlying ecosystem processes are beginning to change. In addition, even short bouts of intense herbivory can have long-term consequences for some species in these communities.

Herbivore effects on productivity vary by guild: cattle increase mean productivity while wildlife reduce variability.

Wild herbivores and livestock share the majority of rangelands worldwide, yet few controlled experiments have addressed their individual, additive, and interactive impacts on ecosystem function. While ungulate herbivores generally reduce standing biomass, their effects on aboveground net primary production (ANPP) can vary by spatial and temporal context, intensity of herbivory, and herbivore identity and species richness. Some evidence indicates that moderate levels of herbivory can stimulate aboveground productivity, but few studies have explicitly tested the relationships among herbivore identity, grazing intensity, and ANPP. We used a long-term exclosure experiment to examine the effects of three groups of wild and domestic ungulate herbivores (megaherbivores, mesoherbivore wildlife, and cattle) on herbaceous productivity in an African savanna. Using both field measurements (productivity cages) and satellite imagery, we measured the effects of different herbivore guilds, separately and in different combinations, on herbaceous productivity across both space and time. Results from both productivity cage measurements and satellite normalized difference vegetation index (NDVI) demonstrated a positive relationship between mean productivity and total ungulate herbivore pressure, driven in particular by the presence of cattle. In contrast, we found that variation in herbaceous productivity across space and time was driven by the presence of wild herbivores (primarily mesoherbivore wildlife), which significantly reduced heterogeneity in ANPP and NDVI across both space and time. Our results indicate that replacing wildlife with cattle (at moderate densities) could lead to similarly productive but more heterogeneous herbaceous plant communities in rangelands.

Do grazing intensity and herbivore type affect soil health? Insights from a semi‐arid productivity gradient

Summary Grazing is one of the most widespread forms of intensive management on Earth and is linked to reductions in soil health. However, little is known about the relative influence of herbivore type, herbivore intensity and site productivity on soil health. This lack of knowledge reduces our capacity to manage landscapes where grazing is a major land use. We used structural equation modelling to assess the effects of recent (cattle, sheep, goats, kangaroos and rabbit dung) and historic (cattle, sheep/goat livestock tracks) herbivore activity on soil health at 451 sites across 0·5 M km2 of eastern Australia. We assessed the direct and indirect effects of increasing herbivore intensity, using dung and livestock tracks, on 15 morphological, physical and chemical attributes that are indicative of soil health, and we used these attributes to derive three indices representing the capacity of the soil to maintain its structural integrity (stability), cycle nutrients (nutrients) and maintain water flow (infiltration). Grazing had negative effects on the three soil health indices, but these effects varied with productivity. Grazing intensity was associated with strong reductions in the stability and nutrient indices under low productivity, but these effects diminished with increasing productivity. Herbivore effects on individual attributes varied in relation to productivity level and were strongly herbivore specific, with most due to cattle grazing, and to a lesser extent, sheep, goats and rabbits. Few effects due to kangaroos or historic grazing by livestock were observed. Synthesis and applications. Our study shows that livestock and rabbits degrade soil health through grazing, and its effects are strongest under low or moderate productivity; however, kangaroo effects are benign. Our findings support calls for resource management agencies to consider site productivity, as well as herbivore type and intensity, when developing strategies to manage grazing by livestock, and feral and native herbivores.

Herbivory on planted oak seedlings across a habitat edge created by timber harvest

Edge habitats create environmental gradients that affect plant community composition and herbivore behavior. Silvicultural disturbance creates edge habitat with direct (via changes in light) and indirect (via changes in herbivore behavior) consequences for the growth and survival of tree seedlings, and thus, the composition of the future forest stands. Herbivores, particularly ungulates, can be a major limiting factor in oak regeneration, and silvicultural disturbance may alter the abundance or behavior of herbivores following harvest. We measured the severity of herbivory on experimentally planted white (Quercus alba) and black oak (Quercus velutina) seedlings by white-tailed deer (Odocoileus virginianus) and eastern cottontail rabbits (Sylvilagus floridanus), as well as foliar damage from insects, across gradients created by clearcuts in a deciduous forest in Indiana, USA. Overall browse pressure on oaks was low in our study. Nonetheless, spatial variation in herbivory depended on herbivore taxa; herbivory by rabbits was highest inside harvest openings, whereas foliar damage by insects peaked in the forest. Intensity of deer herbivory was constant across the edge. In addition, we observed indirect interactions among herbivore species mediated by a seedling’s browsing history. Herbivore damage by deer was positively related to past browsing by rabbits, and foliar damage from insects was positively related to past browsing by both deer and rabbits. Increasing woody plant competition reduced herbivory on seedlings by both deer and rabbits. Given the lack of spatial variability in deer herbivory and low overall herbivory by rabbits, we suspect that interactions between timber harvesting and herbivory did not have a strong impact on oak seedlings at our study sites.

Red deer mediate spatial and temporal plant heterogeneity in boreal forests

AbstractSelective herbivory can influence both spatial and temporal vegetation heterogeneity. For example, many northern European populations of free‐ranging ungulates have reached unprecedented levels, which can influence plant species turnover, long‐term maintenance of biodiversity and the subsequent stability of boreal ecosystems. However, the mechanisms by which large herbivores affect spatial and temporal vegetation heterogeneity remain poorly understood. Here, we combined a 10‐year exclusion experiment with a herbivore intensity gradient to investigate how red deer (Cervus elaphus) acts as a driver of temporal and spatial heterogeneity in the understory of a boreal forest. We measured the two dimensions of heterogeneity as temporal and spatial species turnover. We found that temporal heterogeneity was positively related to herbivory intensity, and we found a similar trend for spatial heterogeneity. Removing red deer (exclosure) from our study system caused a distinct shift in species composition, both spatially (slow response) and temporally (quick response). Vegetation from which red deer had been excluded for 10 years showed the highest spatial heterogeneity, suggesting that the most stable forest understory will occur where there are no large herbivores. However, excluding red deer resulted in lower species diversity and greater dominance by a low number of plant species. If both stable but species rich ecosystems are the management goal, these findings suggest that naturally fluctuating, but moderate red deer densities should be sustained.

Artificial seagrass leaves shield transplanted seagrass seedlings and increase their survivorship

Seagrass meadows provide important ecosystem functions and services. The progressive global deterioration of seagrass meadows requires management strategies to stop and recover seagrass losses. Seagrass restoration can be promoted using seagrass seedlings germinated in vitro, but early mortality of seedlings is a severe bottleneck for successful restoration programs. In this study, we tested a technique to promote in situ survivorship of in vitro germinated seedlings of the seagrass Cymodocea nodosa. In particular, we predicted that artificial seagrass leaves (plastic green raffia, i.e. ‘Artificial Seagrass Shields', ASSs) surrounding seagrass seedlings would increase the long-term survivorship of seedlings by decreasing herbivory-induced mortality. After 2 years, the survivorship of seagrass seedlings in plots without the ASSs was nil, whereas one third of plots containing ASSs developed small-sized seagrass patches, including a one order of magnitude exponential increase in shoot density. Herbivory intensity on seagrass leaves significantly decreased when surrounded with ASSs. This study demonstrates how ASSs facilitate the establishment of transplanted seagrass seedlings and suggests ASSs could be a cheap, easy-to-use, restoration element to promote the survivorship of seagrass seedlings by decreasing the magnitude of herbivory.

Susceptibility of silver birch (Betula pendula) to herbivorous insects is associated with the size and phenology of birch – implications for climate warming

ABSTRACTSusceptibility of trees to herbivorous insects is often associated with the tree growth and phenology, both of which are sensitive to a warming climate. Therefore, changes in these traits may affect the intensity of herbivory on trees in the future. We grew silver birch (Betula pendula) populations differing in their growth and phenology in a common garden experiment, and studied the effect of these plant traits on the leaf herbivory, insect herbivore density and community composition of herbivores in two consecutive years, 2011 and 2012. Differences in size and the timing of growth cessation among the birch genotypes were related to differences in herbivore community compositions and herbivory. In 2011, the most intensive herbivore damage was observed on birch genotypes of small size, late bud burst and early growth cessation, and these genotypes originated from high-latitude populations. The differences among birch genotypes in their susceptibility to herbivore damage may lead to differences in their competitive abilities. While climate warming will affect phenology and growth of plants, our study shows, that it may indirectly affect herbivory and herbivore communities as well.

Pattern and Drivers of White-Tailed Deer (Odocoileus virginianus) Herbivory on Tree Saplings across a Plateau Landscape

White-tailed deer (Odocoileus virginianus) populations are impacting long-term regeneration across eastern United States forests. Deer distribution and resulting herbivory patterns are variable across a landscape due to habitat patchiness and topography. It is poorly understood how features associated with topography control deer herbivory. We examined the heterogeneity of deer herbivory as it affects sapling densities across a single forest-type landscape on the Cumberland Plateau. The 1242 hectare site represented a peninsula of tableland that transitioned from developed land to forest and was surrounded on three sides by a bluff, irregularly punctuated by drainages. We examined the spatial variability of deer impacts on sapling density and modeled the relative importance of plateau accessibility features related to topography, proximity to edge, and deer culling as predictors of sapling variation. We used a stratified random design to sample sapling density across the landscape in 2012 and 2015. The intensity of deer herbivory on saplings varied, with the fewest saplings in forests surrounded by residential development. Our model predicted that plateau accessibility measures best determined sapling densities, followed by distance from edge and deer culling measures. Our results suggest that herbivory impacts may not be homogeneous in a contiguous uniform landscape if there are topographic barriers.

A general parameterized mathematical food web model that predicts a stable green world in the terrestrial ecosystem

AbstractTerrestrial ecosystems are generally green with vegetation and only a small part (<10%) of the total plant matter is consumed by herbivores annually, which means herbivore density is consistently low and stable. Nonetheless, the mechanism underlying this pattern has been unclear without suitable food web models for predicting the absolute density of the herbivore biomass in physical units. Here, I present a parameterized mathematical food web model describing three‐trophic‐level systems that can predict the biomass density of herbivores h (kg protein/m3) and carnivores c from factors such as nutritive values of plants (np, kg protein/m3), herbivores (nh), and carnivores (nc), searching efficiency (volume) of carnivores (S, m3·m−3·d−1 = d−1), eating efficiency (speed) of herbivores (eh) and carnivores (ec; m3·m−3·d−1 = d−1), respiratory decreases in biomasses (dh and dc, kg·kg−1·d−1 = d−1), absorption efficiencies αh and αc (ratios), and probabilities of carnivores preying on herbivores or carnivores, Phc and Pcc (ratios). The model predicts a stable equilibrium with low herbivore biomass h sufficient to keep the world green provided the food web consists of the three trophic levels, plants, herbivores, and carnivores; intraguild predation exists but is rarer than interguild predation (Phc > Pcc > 0); plants are less nutritive than animals (np < nh, nc); and carnivore searches huge volume daily while eating speed of herbivore is limited (S _ eh). These conditions are well‐realized in aboveground terrestrial ecosystems where plant‐rich “green worlds” are common, vs. animal‐rich belowground and aquatic ecosystems where some conditions are not realized. The h and c calculated from our model agreed well with those from empirical observations in forest ecosystems, where both h and c are within an order of magnitude of 100 mg (fresh biomass/m2 forest), and in savannah ecosystems. The model predicts that plant nutritive value np, digestibility of plants by herbivores αh, and herbivore eating speed eh are positively correlated with h and the intensity of herbivory, which theoretically explains the outdoor defensive effects of plant anti‐nutritive or quantitative defenses (e.g., tannins, protease inhibitors), and predicts that c and the carnivore/herbivore ratio c/h are positively correlated with the relative growth rate of herbivores Gh. The present model introduced parameterized realities into food web theory that previous models lack.

Performance of two alpine plant species along environmental gradients in an alpine meadow ecosystem in central Tibet

AbstractUnderstanding how biotic interactions and abiotic conditions affect plant performance is important for predicting changes in ecosystem function and services in variable environments. We tested how performances of Astragalus rigidulus and Potentilla fruticosa change along gradients of biotic interactions (represented by plant species richness, abundance of the dominant plant species Kobresia pygmaea, and herbivory intensity) and abiotic conditions (represented by elevation, aspect, and slope steepness) across a semi‐arid landscape in central Tibet. Redundancy analyses showed that the biotic variables explained 30 and 39 % of the variation in overall performance of A. rigidulus (P = 0.03) and P. fruticosa (P = 0.01), respectively. Abiotic variables did not contribute significantly to variation among A. rigidulus populations. Plant size decreased with species richness in both species and was larger on south‐ rather than north‐facing slopes. Reproductive effort for both species was significantly negatively related to the abundance of K. pygmaea and both species had larger reproductive effort on south‐ rather than north‐ and west‐facing slopes. The proportion of biomass allocated to sexual reproduction in P. fruticosa was negatively correlated with K. pygmaea abundance and herbivory intensity. The population density of P. fruticosa was positively related to elevation, species richness, and K. pygmaea abundance. We conclude that plant performance at a local scale was more strongly related to biotic than abiotic conditions, but different components of plant performance responded differently to predictor variables and the responses were species‐specific. These findings have important implications for rangeland management under changing environmental conditions.

Impacts of introduced Rangifer on ecosystem processes of maritime tundra on subarctic islands

AbstractIntroductions of mammalian herbivores to remote islands without predators provide a natural experiment to ask how temporal and spatial variation in herbivory intensity alter feedbacks between plant and soil processes. We investigated ecosystem effects resulting from introductions of Rangifer tarandus (hereafter “Rangifer”) to native mammalian predator‐ and herbivore‐free islands in the Aleutian archipelago of Alaska. We hypothesized that the maritime tundra of these islands would experience either: (1) accelerated ecosystem processes mediated by positive feedbacks between increased graminoid production and rapid nitrogen cycling; or (2) decelerated processes mediated by herbivory that stimulated shrub domination and lowered soil fertility. We measured summer plant and soil properties across three islands representing a chronosequence of elapsed time post‐Rangifer introduction (Atka: ~100 yr; Adak: ~50; Kagalaska: ~0), with distinct stages of irruptive population dynamics of Rangifer nested within each island (Atka: irruption, K‐overshoot, decline, K‐re‐equilibration; Adak: irruption, K‐overshoot; Kagalaska: initial introduction). We also measured Rangifer spatial use within islands (indexed by pellet group counts) to determine how ecosystem processes responded to spatial variation in herbivory. Vegetation community response to herbivory varied with temporal and spatial scale. When comparing temporal effects using the island chronosequence, increased time since herbivore introduction led to more graminoids and fewer dwarf‐shrubs, lichens, and mosses. Slow‐growing Cladonia lichens that are highly preferred winter forage were decimated on both long‐term Rangifer‐occupied islands. In addition, linear relations between more concentrated Rangifer spatial use and reductions in graminoid and forb biomass within islands added spatial heterogeneity to long‐term patterns identified by the chronosequence. These results support, in part, the hypothesis that Rangifer population persistence on islands is facilitated by successful exploitation of graminoid biomass as winter forage after palatable lichens are decimated. However, the shift from shrubs to graminoids was expected to enhance rates of nitrogen cycling, yet rates of net N‐mineralization, pools, and soil δ15N declined markedly along the chronosequence and were weakly associated with spatial use within islands. Overall plant and soil patterns were disrupted but responded differently to intermediate (50 yr) and long‐term (100 yr) herbivory, and were correlated with distinct stages of irruptive population dynamics.

Herbivory causes increases in leaf spinescence and fluctuating asymmetry as a mechanism of delayed induced resistance in a tropical savanna tree

Background and aims – Leaf spinescence is thought to be a defense against herbivory and may increase in years following high herbivory pressure (DIR – delayed induced resistance). Besides DIR, herbivory also causes plant stress, which can be assessed using fluctuating asymmetry analysis (FA – random departures from leaf bilateral symmetry). In this two-year field study we first investigated the relationships between herbivory, FA and spinescence in Solanum lycocarpum trees during an outbreak of moth caterpillars in 2010; then in 2011 we examined whether plants with intense herbivory the previous year presented changes in FA (herbivory induced stress) and spinescence. Key results – In 2010, leaves damaged by moths were significantly more asymmetrical than undamaged leaves. In addition, moths preferentially fed on leaves with fewer and shorter spines. In 2011, plants severely attacked by moths the year before showed significant increases in FA (28%), spine abundance (21%) and spine length (84%), compared to less damaged plants. Conclusions – Our data suggest a delayed response of S. lycocarpum to herbivory, in that plants subjected to high leaf damage the previous year maximized their display of anti-herbivore mechanisms, in this case, leaf spinescence. This is one of the few studies to show that FA increased as a response to herbivore attack. We conclude that FA can be used as an indicator of plant stress following leaf damage.

The invasive mud crab enforces a major shift in a rocky littoral invertebrate community of the Baltic Sea

In rocky littoral communities, intense herbivory allows for the occurrence of trophic cascades where higher trophic levels influence producer communities. Invasive predators can be especially effective in imposing trophic cascades. The North American mud crab Rhithropanopeus harrisii is a recent invader in the Baltic Sea, with an expanding distribution range. Here, we document the effects of mud crab on the native invertebrate community associated with the key foundation species Fucus vesiculosus. During the initial 3 years of invasion, mud crab abundance in F. vesiculosus increased from 2 % to about 25 % of the algae being inhabited by crabs. Simultaneously, the invertebrate community underwent a major transition: Species richness and diversity dropped as a consequence of decreasing abundance and the loss of certain taxa. The abundance of gastropods decreased by 99 % and that of crustaceans by 75 %, while chironomids completely disappeared. Consequently, the community dominated earlier by herbivorous and periphyton-grazing gastropods and crustaceans shifted to a mussel dominated community with overall low abundances of herbivores. At the same time filamentous epiphytic algae prospered and the growth rate of F. vesiculosus decreased. We suggest that this shift in the invertebrate community may have far reaching consequences on ecosystem functioning. These arise through changes in the strength of producer–herbivore interaction, caused by mud crab predation on the dominating grazer taxa. This interaction is a major determinant of ecological function of ecosystems, i.e. productivity and energy flow to higher trophic levels. Therefore, the decrease in herbivory can be expected to have a major structuring role in producer communities of the rocky littoral macroalgal assemblages.

Impacts of introduced species on the biota of an oceanic archipelago: the relative importance of competitive and trophic interactions

AbstractIntroduced species negatively impact native species through competitive and trophic interactions, particularly on oceanic islands that have never been connected to any continental landmass. However, there are few studies on the relative importance of competitive interactions (resource competition with introduced species) and trophic interactions (predation or herbivory by introduced species) with respect to the negative impacts on native organisms on oceanic islands. A literature review on introduced and native species of the oceanic Ogasawara (Bonin) Islands in the western Pacific Ocean indicated that many native species (e.g., bees, beetles, damselflies, butterflies, land snails, birds, and plants) have been negatively impacted by introduced predators and herbivores (e.g., lizards, rats, flatworms, and goats). Several native plants and bees have been negatively affected by introduced competitors. However, the native species that have competed with introduced species have also suffered from either intense herbivory or predation by other introduced species. Thus, introduced predators and herbivores have had greater impacts on native species than introduced competitors in the Ogasawara Islands.

Spatial Quantification of White-tailed Deer Habitat of a Wetland-dominated Landscape in Central Lower Michigan

ABSTRACT White-tailed deer (Odocoileus virginianus), can be a keystone herbivore that can greatly impact conditions in forest ecosystems. Results of previous deer herbivory research could cause biologists concern when managing wetlands as suitable habitat for migratory waterfowl because intense herbivory can negatively impact plant communities. Biologists at Shiawassee National Wildlife Refuge (SNWR), Saginaw, Michigan, observed obvious effects of white-tailed deer herbivory within wetland plant communities. Our objective was to evaluate white-tailed deer habitat suitability within a landscape dominated by wetland vegetation types used by deer during the 2011 and 2012 growing seasons to help inform deer and water bird habitat management decision making. We classified 1m x 1m aerial imagery data in ArcGIS v10.0 and developed a white-tailed deer habitat suitability index (HSI) model. Moist soil units, lakeplain prairie, and bottomland hardwood forests demonstrated high habitat suitability for white-tailed d...

Effects of simulated and insect herbivory on nitrogen and protein precipitable phenolic concentrations of two legumes

ABSTRACTProtein-precipitating polyphenolics (PPPs) serve as a plant defense against herbivory, increasing with stress. We studied how varying intensities of simulated and Melanoplus differentialis herbivory affected (1) PPP concentration; (2) protein bound by PPP (PB); and (3) N concentration of panicled tick-clover (Desmodium paniculatum; PTC) and sericea lespedeza (Lespedeza cuneata; SL) leaf regrowth. Leaves of PTC that were submitted to simulated herbivory had lesser (p ≤ .05 for all significant differences) PPP concentration than the control for most treatments. For PTC, PPP concentration decreased with increasing herbivory intensity for both herbivory types. For SL, PPP was similar between herbivory types for Harvest 1 but not for 2, decreasing as herbivory intensity increased for both herbivory types. Simulated herbivory resulted in lower PB concentrations for PTC and SL compared to the grasshopper herbivory. Nitrogen concentration was similar for PTC and SL between herbivory types but variable among degree of herbivory. Herbivory type affects PPP.

Long-Term Deer Exclusion Has Complex Effects On A Suburban Forest Understory

Abstract Herbivory by deer is one of the leading biotic disturbances on forest understories (i.e., herbs, small shrubs, and small tree seedlings). A large body of research has reported declines in height, abundance, and reproductive capacity of forbs and woody plants coupled with increases in abundance of graminoids, ferns, and exotic species due to deer herbivory. Less clear is the extent to which (and the direction in which) deer alter herbaceous layer diversity, where much of the plant diversity in a forest occurs. We examined the effect of 15 y of deer exclusion on the understory of a suburban hardwood forest in Connecticut exposed to decades of intensive herbivory by white-tailed deer (Odocoileus virginianus). We compared species richness (at subplot and plot scale), individual species and life form group abundance (% cover), and community composition between grazed and exclosure plots, as well as between mesic and wet soil blocks. Forb cover was more than twice as abundant in exclosure as in grazed ...