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1,187 results for “herbivores”
Data from: Plant odour and sex pheromone are integral elements of specific mate recognition in an insect herbivore
Specific mate recognition relies on the chemical senses in most animals, and especially in nocturnal insects. Two signal types mediate premating olfactory communication in terrestrial habitats: sex pheromones, which blend into an atmosphere of plant odorants. We show that host plant volatiles affect the perception of sex pheromone in males of the African cotton leafworm Spodoptera littoralis and that pheromone and plant volatiles are not perceived as independent messages. In clean air, S. littoralis males are attracted to single synthetic pheromone components or even the pheromone of a sibling species, Oriental cotton leafworm S. litura. Presence of host plant volatiles, however, reduces the male response to deficient or heterospecific pheromone signals. That plant cues enhance discrimination of sex pheromone quality confirms the idea that specific mate recognition in noctuid moths has evolved in concert with adaptation to host plants. Shifts in either female host preference or sex pheromone biosynthesis give rise to new communication channels that have the potential to initiate or contribute to reproductive isolation.
Data from: Warming affects different components of plant-herbivore interaction in a simplified community but not net interaction strength
Global warming impacts natural communities through effects on performance of individual species and through changes in the strength of interactions between them. While there is a body of evidence of the former, we lack experimental evidence on potential changes in interaction strengths. Knowledge about multispecies interactions is fundamental to understand the regulation of biodiversity and the impact of climate change on communities. This study investigated the effect of warming on a simplified community consisting of three species: rosy apple aphid Dysaphis plantaginea feeding on plantain, Plantago lanceolata, and a heterospecific neighbouring plant species, perennial ryegrass, Lolium perenne. The aphid does not feed on L. perenne. The experimental design consisted of monocultures and mixtures of L. perenne and P. lanceolata at three temperature levels. We did not find indication for indirect temperature effects on D. plantaginea through changes in leaf nitrogen or relative water content. However, experimental warming affected the life history traits of the aphid directly, in a non-linear manner. Aphids performed best at moderate warming, where they grew faster and had a shorter generation time. In spite of the increased population growth of the aphids under warming, the herbivory rates were not changed and consequently the plant–herbivore interaction was not altered under warming. This suggests reduced consumption rates at higher temperature. Also plant competition affected the aphids but through an interaction with temperature. We provide proof-of-concept that net interactions between plants and herbivores should not change under warming despite direct effects of warming on herbivores when plant–plant interaction are considered. Our study stresses the importance of indirect non–trophic interactions as an additional layer of complexity to improve our understanding of how trophic interactions will alter under climate change.
Data from: Hemiparasites can transmit indirect effects from their host plants to herbivores
Parasitic plants can serve as critical intermediaries between their hosts and other organisms; however these relationships are not well understood. To investigate the relative importance of plant traits in such interactions, we studied the role of the root hemiparasite, Castilleja levisecta (Orobanchaceae), as a mediator of interactions between the host plants it parasitizes and the lepidopteran herbivore Euphydryas editha (Nymphalidae), whose caterpillars feed on Castilleja and sequester iridoid glycosides from it. We tested whether the hemiparasite's size, leaf N concentration, and iridoid glycoside concentrations were influenced by the identity of its host plant, and then whether these traits influenced outcomes for the herbivore. We found that the hemiparasite's size and leaf N depended on the host it parasitized, and these traits in turn affected outcomes for E. editha. Specifically, Euphydryas editha survival increased with hemiparasite size and caterpillar mass increased with leaf N; caterpillars with greater mass were more likely to survive during diapause. We also found preliminary evidence that host identity influenced iridoid glycoside sequestration by the herbivore. Mean iridoid glycoside concentrations in caterpillars ranged from 1-12% depending on the host being parasitized by Castilleja. This study demonstrates that root parasitism can result in strong indirect effects on higher trophic levels, influencing organisms' survival, growth, and chemical interactions.
Data from: Cascading effects of host plant inbreeding on the larval growth, muscle molecular composition, and flight capacity of an adult herbivorous insect.
A primary function of adult winged insects is dispersal. Limiting larval dietary intake (partial starvation) has been shown to affect the flight muscle metabolism of adult moths reared on artificial diet, but a more ecologically relevant question is whether natural variation in host plant quality can lead to differences in the flight capacity of adult insects. Recent studies have shown that inbreeding compromises plant anti-herbivore defenses. We created inbred and outbred progeny from locally collected horsenettle (Solanum carolinense L.) and examined how host plant inbreeding affects the growth, development, and flight muscle physiology of tobacco hornworm (Manduca sexta L.), a specialist herbivore on Solanaceae. We tested the hypothesis that within population genetic variation in host plant quality, resulting from inbreeding, can create significant changes to the larval development and flight physiology of an adult insect. We found that Manduca larvae reared on inbred horsenettle plants grew faster and developed into larger pupae compared to larvae reared on outbred plants. Adult flight metabolic rate was greater in adults reared on inbred plants compared to outbred plants, and this elevation was independent of body mass when we excluded one plant family that produced small, low metabolic rate moths regardless of breeding regime. Differences in mass-specific flight metabolism were associated with changes in alternative splicing of Troponin t, a flight muscle protein that regulates muscle contraction. These results show that host plant inbreeding can create effects that cascade through larval and pupal development to affect dispersal-related traits of the adult stage. Hence, plant inbreeding may also impact herbivore population dynamics, particularly their ability to spread away from, and possibly into, isolated patches of inbred plants creating increased herbivore pressure on these plant populations. More generally, our findings reveal that changes in population biology at one trophic level can affect the metabolic physiology and flight capacity of an animal at a higher trophic level.
Data from: Dietary protein and carbohydrates affect immune function and performance in a specialist herbivore insect (Manduca sexta)
Nutrition structures ecology and evolution across all scales of biological organization. It is well known that nutrition can have direct effects on performance and fitness, but indirect effects on physiological systems that mediate biotic interactions have been studied less frequently. Here, we focus on the interaction between nutrition, performance, and the immune system in a specialist herbivorous insect, Manduca sexta. We used a conceptual framework in nutritional ecology (the geometric framework) to examine how changes in diet quality affect aspects of the immune system used for defense against parasitoids. We raised caterpillars throughout their entire larval development on five different experimental diets that varied in protein and carbohydrate content and measured five aspects of the immune system: encapsulation, phenoloxidase activity, prophenoloxidase activity, total hemolymph protein, and hemocyte density. Overall, different parts of the immune function varied in response to interactions between carbohydrates, protein, and intake, but protein reductions had the largest impacts—mostly detrimental. In addition, our data suggest that diet quality mediates the relationship between performance (growth and survival) and immune function, as well as trade-offs among different components of immune function. Our work is the first to examine the interplay between nutrition, performance, and immune function with the geometric framework in a specialist insect herbivore.
Data from: Trade-offs and tritrophic consequences of host shifts in specialized root herbivores
Trade-offs in an herbivore's ability to feed, avoid predation and succeed on alternative hosts are thought to be major driving factors in host specialization. In this study, we compared how two closely related milkweed beetles (Tetraopes spp.) that have specialized on separate Asclepias species respond to host switching to alternative milkweed plants. By additionally examining effects on the beetles' entomopathogenic natural enemies, we test whether host plant specialization is driven by plant–herbivore interactions alone or whether there is a role for the tritrophic interactions. Tetraopes beetles feed on milkweed roots as larvae and on milkweed shoots as adults, and they sequester toxic cardenolides from their host plants. We predicted that growth and sequestration would be compromised on alternative hosts as a consequence of specialization. Larvae of each Tetraopes species were reared on their native host plant, the host plant of the other species and two closely related Asclepias species that do not typically host Tetraopes. Regardless of beetle specialization, survival of both beetles was highest on A. syriaca, which has the second-to-lowest levels of root cardenolides and is the native host for T. tetraophthalmus. Larval growth was not affected by host plant for T. texanus, but T. tetraophthalmus grew best on A. exaltata, a close relative of A. syriaca that does not typically experience beetle feeding. We found that larval sequestration of cardenolides largely mirrored host plant values in the roots, with the exception of T. texanus on A. asperula, which sequestered a low proportion of the cardenolides from this host. Although all larvae were susceptible to entomopathogenic nematodes (EPNs), the number of EPNs emerging from cadavers depended on the beetle–plant combination, with more EPNs produced when beetles were feeding on native compared to non-native hosts. The observed consequences for tritrophic interactions did not fit expectations for specialized herbivores (i.e. EPN predation was highest when beetles were on their native hosts), suggesting that specialization may be driven primarily by a plant–herbivore interaction in this system, not by a tritrophic effect.
Data from: Defensive chemicals of neighboring plants limit visits of herbivorous insects: associational resistance within a plant population
Despite our understanding of chemical defenses and their consequences for plant performance and herbivores, we know little about whether defensive chemicals in plant tissues, such as alkaloids, and their spatial variation within a population play unappreciated and critical roles in plant-herbivore interactions. Neighboring plants can decrease or increase attractiveness of a plant to herbivores, an example of a neighborhood effect. Chemical defensive traits may contribute to neighborhood effects in plant-herbivore interactions. We examined the effects of nicotine in leaves (a non-emitted defense chemical) on plant-herbivore interactions in a spatial context, using two varieties of <i>Nicotiana tabacum</i> with different nicotine levels. A common garden experiment demonstrated that visits by grasshoppers decreased with increasing density of neighboring plants with a greater nicotine level. In contrast, visits of leaf caterpillars were not affected by neighbors, irrespective of nicotine levels. Thus, our results clearly highlighted that the neighborhood effect caused by the nicotine in leaves depended on the insect identity, and it was mediated by plant-herbivore interactions, rather than plant-plant interactions. This study demonstrates that understanding of effects of plant defensive traits on plant-herbivore interactions requires careful consideration of the spatial distribution of plant defenses, and provides support for the importance of spatial context to accurately capture the ecological and evolutionary consequences of plant-herbivore interactions.
Data from: Trait-matching and mass effect determine the functional response of herbivore communities to land use intensification
1. Trait-based approaches represent a promising way to understand how trophic interactions shape animal communities. The approach relies on the identification of the traits that mediate the linkages between adjacent trophic levels, i.e. "trait-matching". Yet, how trait-matching explains the abundance and diversity of animal communities has been barely explored. This question may be particularly critical in the context of land use intensification, currently threatening biodiversity and associated ecosystem services. 2. We collected a large dataset on plant and grasshopper traits from communities living in 204 sampled grasslands, in an intensively managed agricultural landscape. We used a multi-trait approach to quantify the relative contributions of trait-matching and land use intensification acting at both local and landscape scales on grasshopper functional diversity. We considered two key independent functional traits: incisor strength and body size of grasshopper species. Incisor strength, a resource-acquisition trait, strongly matches grasshopper feeding niche. Body size correlates with mobility traits, and may determine grasshopper dispersal abilities. 3. Plant functional diversity positively impacted the diversity of grasshopper resource-acquisition trait, according to the trait-matching observed between plants and herbivores. However, this positive effect was significantly higher in old grasslands. In addition, the presence of specific habitats in the landscape (i.e. wood and alfalfa) strongly enhanced grasshopper resource-acquisition trait diversity in the focal grassland. Finally, body size increased with landscape simplification, although its response was modulated by local factors such as soil depth. 4. Trait-matching between plants and herbivores was an important driver explaining the abundance and diversity of resource-acquisition traits within grasshopper communities. Herbivore functional diversity in grasslands, however, cannot be understood without taking into account the presence of specific habitats in the surrounding landscape, as well as the age of the grassland. Our study suggests mass effect and assembly time are central mechanisms promoting higher functional diversity within animal communities in highly disturbed anthropogenic system.
Data from: Integration of two herbivore-induced plant volatiles results in synergistic effects on plant defense and resistance
Plants can use induced volatiles to detect herbivore‐ and pathogen‐attacked neighbors and prime their defenses. Several individual volatile priming cues have been identified, but whether plants are able to integrate multiple cues from stress‐related volatile blends remains poorly understood. Here, we investigated how maize plants respond to two herbivore‐induced volatile priming cues with complementary information content, the green leaf volatile (Z)‐3‐hexenyl acetate (HAC) and the aromatic volatile indole. In the absence of herbivory, HAC directly induced defense gene expression, while indole had no effect. Upon induction by simulated herbivory, both volatiles increased jasmonate signaling, defense gene expression and defensive secondary metabolite production and increased plant resistance. Defenses and resistance in dual‐volatile exposed plants were more strongly induced than in plants exposed to single volatiles. Induced defense levels in dual volatile‐exposed plants were significantly higher than predicted from the added effects of the individual volatiles, with the exception of induced plant volatile production, which showed no increase upon dual‐exposure relative to single exposure. Thus, plants can integrate different volatile cues into strong and specific responses that promote herbivore defense induction and resistance. Integrating multiple volatiles may be beneficial, as volatile blends are more reliable indicators of future stress than single cues.
Supplementary material 1 from: Solé R, Gripenberg S, Lewis OT, Markesteijn L, Barrios H, Ratz T, Ctvrtecka R, Butterill PT, Segar ST, Metz MA, Dahl C, Rivera M, Viquez K, Ferguson W, Guevara M, Basset Y (2019) The role of herbivorous insects and pathogens in the regeneration dynamics of Guazuma ulmifolia in Panama. Nature Conservation 32: 81-101. https://doi.org/10.3897/natureconservation.32.30108
Supplementary tables S1-S4, Appendix S1, Plate S1
Herbivore grazing mitigates the negative effects of nitrogen deposition on soil organic carbon in low-diversity grassland
<p>1. Changes in soil carbon (C) sequestration in grassland ecosystems have important impacts on the global C cycle. As such, it is important that researchers better understand the underlying mechanisms affecting soil C. Increasing evidence has shown that atmospheric nitrogen (N) deposition can cause dramatic changes in grassland soil C. It remains unclear whether herbivore grazing, a primary means to manage and utilize grassland resources, can regulate the effects of N deposition on soil C, and whether these effects are dependent on plant community diversity.</p> <p>2. Here, we examined the joint effects of herbivore grazing and N-addition on soil organic C (SOC) stocks in two types of communities with low and high plant diversity, respectively.</p> <p>3. Our results showed that the effects of N-addition and its combination with herbivore grazing on grassland SOC were inconsistent in the two types of communities. In the low-diversity community, N-addition greatly decreased SOC stocks, while grazing significantly increased it. Additionally, the grazing-induced increase in soil C stocks in presence of N-addition was so great that it completely counteracted the significant decline in SOC induced by N-addition. However, in the high-diversity community, we observed no effects of N-addition on SOC and grazing increased SOC only in the absence of N-addition and had no significant effect in presence of N-addition.</p> <p>4. Synthesis and applications. Our study suggests that increased N deposition can trigger a remarkable reduction in soil C sequestration in grasslands with low plant diversity, but that herbivore grazing can offset this decline, which may help to mitigate greenhouse gas emissions caused by atmospheric N deposition. As a result, we suggest that moderate herbivore grazing should be considered as an effective grassland management measure for maintaining and improving grassland soil C sequestration as the increasing global change such as elevated atmospheric carbon dioxide, N deposition, and biodiversity losses threat.</p>
Plant-plant communication and community of herbivores on tall goldenrod (dataset)
<p>1. The volatiles from damaged plants induce defense in neighboring plants. The phenomenon is called plant-plant communication, plant talk or plant eavesdropping. Plant-plant communication has been reported to be stronger between kin plants than genetically far plants in sagebrush.</p> <p>2. Why do plants distinguish volatiles from kin or genetically far plants? We hypothesize that plants respond only to important conditions; the induced defense is not free of cost for the plant. To clarify the hypothesis, we conducted experiments and investigations using goldenrod of 4 different genotypes.</p> <p>3. The arthropods community on tall goldenrods were different among 4 genotypes. The response to volatiles was stronger from genetically close plants to the emitter than from genetically distant plants from the emitter. The volatiles from each genotype of goldenrods were different; and they were categorized accordingly. Moreover, the arthropod community on each genotype of goldenrods were different.</p> <p>4. Synthesis: Our results support the hypothesis: goldenrods respond to volatiles from genetically close plants because they would have similar arthropod species. These results are important clues elucidating adaptive significance of plant-plant communication.</p>
Supplementary material 2 from: Mally R, Ward SF, Trombik J, Buszko J, Medzihorský V, Liebhold AM (2021) Non-native plant drives the spatial dynamics of its herbivores: the case of black locust (Robinia pseudoacacia) in Europe. NeoBiota 69: 155-175. https://doi.org/10.3897/neobiota.69.71949
Tables S2–S9
Large herbivores facilitate an insect herbivore by modifying plant community composition in a temperate grassland
<p>Large herbivores often co-occur and share plant resources with herbivorous insects in grassland ecosystems, yet how they interact with each other remains poorly understood. We conducted a series of field experiments to investigate whether and how large domestic herbivores (sheep; <i>O</i><i>vis</i><i> </i><i>aries</i>) may affect the abundance of a common herbivorous insect (aphid; <i>Hyalopterus</i><i> </i><i>pruni</i>) in a temperate grassland of northeast China. Our exclosure experiment showed that three years (2010-2012) of sheep grazing had led to 86% higher aphid abundance compared with ungrazed sites. Mechanistically, this facilitative effect was driven by grazing altering the plant community, rather than by changes in food availability and predator abundance for aphids. Sheep significantly altered plant community by reducing the abundance of unpalatable forbs for the aphids. Our small-scale forb removal experiment revealed an "associational plant defense" by forbs which protect the grass <i>Phragmites australis</i><i> </i>from being attacked by the aphids. However, selective grazing on forbs by sheep indirectly disrupted such associational plant defense, making <i>P</i><i>.</i><i> australis</i> more susceptible to aphids, consequentially increasing the density of aphids. These findings provide a novel mechanistic explanation for the effects of large herbivores on herbivorous insects by linking selective grazing to plant community composition and the responses of insect populations in grassland ecosystems. </p>
Spotted hyaena (Crocuta crocuta) feeding ecology and selectivity of large herbivorous prey in the Namib Desert
<p>We have investigated the relationship between spotted hyaenas in the south Namib Desert and large herbivorous prey, and have summarized an updated overview of predator-prey relationships in this resource-limited arid environment. Over the 52-month study, we recorded the densities (#/km<sup>-2</sup>, <u>+</u> SE) of the four local large herbivorous prey species: gemsbok (1.229, <u>+</u> 0.50), springbok (1.352, <u>+</u> 0.48), ostrich (0.648, <u>+</u> 0.23), and greater kudu (0.343, <u>+</u> 0.00). A faecal analysis was performed on 146 collected spotted hyaena scats, and prey items were identified and hairs cross-follicle analysed to the species level. Spotted hyaena diet at the study area remained opportunistic with 240 identified prey items representing eight differing prey species being recorded, ranging from ostrich eggs to large ungulates. The Ivlev's Electivity Index was used to determine which large herbivorous prey was most selected for. Although gemsbok had a higher representation of prey items in the sampled scats, all sampled large herbivorous prey species scored below 0, and are thus generally avoided in relation to their availability in the environment. If any prey preferences are expressed by spotted hyaena in the Namib, it can be presumed to be a non-sampled prey species. We therefore promote further detailed investigations into all other prey species present, and seasonal variations of prey densities and scat sampling, within the study environment.</p>
Coupled changes in pH, temperature and dissolved oxygen impact the physiology and ecology of herbivorous kelp forest grazers
<p>Understanding species' responses to upwelling may be especially important in light of ongoing environmental change. Upwelling frequency and intensity are expected to increase in the future, while ocean acidification and deoxygenation are expected to decrease the pH and dissolved oxygen of upwelled waters. However, the acute effects of a single upwelling event and the integrated effects of multiple upwelling events on marine organisms are poorly understood. Here, we use <em>in situ </em>measurements of pH, temperature, and dissolved oxygen to characterize the covariance of environmental conditions within upwelling-dominated kelp forest ecosystems. We then test the effects of acute (0-3 days) and chronic (1-3 month) upwelling on the performance of two species of kelp forest grazers, the echinoderm, <em>Mesocentrotus franciscanus, </em>and the gastropod, <em>Promartynia pulligo</em>. We exposed organisms to static conditions in a regression design to determine the shape of the relationship between upwelling and performance and provide insights into the potential effects in a variable environment. We found that respiration, grazing, growth, and net calcification decline linearly with increasing upwelling intensity for <em>M. francicanus </em>over both acute and chronic timescales. <em>Promartynia pulligo </em>exhibited decreased respiration, grazing, and net calcification with increased upwelling intensity after chronic exposure, but we did not detect an effect over acute timescales or on growth after chronic exposure. Given the highly correlated nature of pH, temperature, and dissolved oxygen in the California Current, our results suggest the relationship between upwelling intensity and growth in the 3-month trial could potentially be used to estimate growth integrated over long-term dynamic oceanographic conditions for <em>M. franciscanus</em>. Together, these results indicate current exposure to upwelling may reduce species performance and predicted future increases in upwelling frequency and intensity could affect ecosystem function by modifying the ecological roles of key species.</p>
Physiological status is a stronger predictor of nutrient selection than ambient plant nutrient content for a wild herbivore
<p class="MsoCommentText">There is generally a close relationship between a consumer's food and its optimal nutrients. When there is a mismatch, it is hypothesized that mobile herbivores switch between food items to balance nutrients, however, there are limited data for field populations. In this study, we measured ambient plant nutrient content at two time points and contrasted our results with the nutrient ratio selected by wild female and male grasshoppers (<em>Oedaleus senegalensis</em>). Few plants were near <em>O. senegalensis'</em> optimal protein:carbohydrate ratio (P:C), nor were plants complementary. Grasshoppers collected earlier all regulated for a carbohydrate-biased ratio but females ate slightly more protein. We hypothesized that the long migration undertaken by this species may explain its carbohydrate needs. In contrast to most laboratory studies, grasshoppers collected later did not tightly regulate their P:C. These results suggest that field populations are not shifting their P:C to match seasonal plant nutrient shifts and that mobile herbivores rely on post-ingestive mechanisms in the face of environmental variation. Because this is among the first studies to examine the relationship between ambient nutrient landscape and physiological state our data are a key step in bridging knowledge acquired from lab studies to hypotheses regarding the role ecological factors play in foraging strategies.</p>
Ecological specialisation and range size determine intraspecific body size variation in a speciose clade of insect herbivores
<p><span>The body size of an adult insect is strongly determined by the environmental factors to which it is exposed during growth and development. Insect species confronted with a high environmental variability across their geographical range (i.e., wide ecological niche breadth) may therefore reveal broader variation in body size than those species which are more specialised (i.e., narrow ecological niche). </span><span>In this study, we aim to investigate whether characteristics related to the ecological niche breadth of a holometabolous insect species (i.e., its ecological specialisation) affect its intraspecific variation in adult body size. By using European geometrid moths as a model group, we specifically tested whether latitudinal range size, larval resource use, and voltinism affect intraspecific body size variation. We hypothesised that plasticity will increase along with latitudinal range and larval diet breadth. We further expected that univoltine species reveal a lower body size variation compared to those with multiple generations per year. To test these hypotheses, w</span><span>e compiled a comprehensive trait database for 631 species of European geometrid moths from literature, including information on adult body size, life history, and distribution. </span><span>We further </span><span>reconstructed a molecular phylogeny including all analysed geometrid species and applied </span><span>phylogenetic comparative methods in order to test our predictions. In support of our hypotheses, we found that intraspecific size variation is positively related to latitudinal range size and larval diet breadth, and that multivoltine species reveal a higher heterogeneity in body size than taxa with a strictly univoltine life style. </span><span>Based on our results, we demonstrated that intraspecific body size variation in geometrid moths is negatively related to ecological specialisation. We further suggest that increased variation in body size with increasing niche breadth is a general pattern, which likely applies to many other insect groups as well. This assumption, however, demands further empirical scrutiny.</span></p>
Reduction in biomass of freshwater arctic vegetation by foraging and nesting hyperabundant herbivores shows recovery
Arctic-nesting geese are specialist herbivores of grasses and sedges (collectively, graminoids). Under moderate grazing pressure, these migratory herbivores can create and maintain arctic grazing lawns with high nutritional content and low aboveground biomass. Nutrient and energy subsidies from southern agricultural landscapes during winter have improved survival among populations of Ross's (Anser rossii) and lesser snow geese (Anser caerulescens caerulescens), leading to marked population growth. Resulting goose hyperabundance has raised conservation concern for resilience of arctic ecosystems to withstand cumulative and intense pressures of herbivory and nest construction. We used both design-based (experimental herbivore exclosures) and model-based methods to investigate changes to plant community structure in direct response to foraging and nesting by these species within the Queen Maud Gulf (Ahiak) Migratory Bird Sanctuary, Nunavut, Canada. Annual nest construction and foraging by up to ~1.3 million geese at a large colony at Karrak Lake markedly reduced aboveground biomass of forage (graminoids) and non-forage (foliose and fruticose lichens) vegetation, with spatial variation in reduction associated with intensity of use by geese. Within vast brood-rearing regions, foraging reduced above- and belowground plant biomass of lowland plant communities by 61% and 29%, respectively, between 1994 (when herbivore exclosures were established) and 2017. In addition to landscape diversity associated with abiotic properties created by geomorphic processes, long-term herbivory by geese further increased spatial heterogeneity in vegetation at the landscape scale. Although foraging geese nearly completely depleted aboveground plant biomass in some parts of their brood-rearing areas, belowground biomass was largely conserved, and thus, plant communities had strong potential for aboveground regeneration. We propose that effects of high-density nesting and foraging by Ross's and lesser snow geese in the central Canadian Arctic, while extensive, are ephemeral and prone to reversion following cessation of grazing and nesting pressure, such as that afforded by shifts in herbivore distribution or local population decline.
Large and small herbivores have strong effects on tundra vegetation in Scandinavia and Alaska
<p>Large and small mammalian herbivores are present in most vegetated areas in the Arctic, and often have large impacts on plant community composition and ecosystem functioning. The relative importance of different herbivores and especially how their specific impact on the vegetation varies across the Arctic is however poorly understood.</p> <p>Here, we investigate how large and small herbivores influence vegetation density and plant community composition in four arctic vegetation types in Scandinavia and Alaska. We used a unique set of exclosures, excluding only large (reindeer and muskoxen) or all mammalian herbivores (also voles and lemmings) for at least 20 years.</p> <p>We found that mammalian herbivores in general decreased Leaf Area Index, NDVI and abundance of vascular plants in all four locations, even though the strength of the effect and which herbivore type caused these effects differed across locations. In three locations, herbivore presence caused contrasting plant communities, but not in the location with lowest productivity. Large herbivores had a negative effect on plant height, whereas small mammalian herbivores increased species diversity by decreasing dominance of the initially dominating plant species. Above- or belowground disturbances caused by herbivores were found to play an important role in shaping the vegetation in all locations.</p> <p>Synthesis: Based on these results, we conclude that both small and large mammalian herbivores influence vegetation in Scandinavia and Alaska in a similar way, some of which can mitigate effects of climate change. We also see important differences across locations, but these depend rather on local herbivore- and plant community composition than large biogeographical differences among continents.</p>
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