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1,187 results for “herbivores”
Data from: Herbivores enforce sharp boundaries between terrestrial and aquatic ecosystems
The transitions between ecosystems (ecotones) are often biodiversity hotspots, but we know little about the forces that shape them. Today, often sharp boundaries with low diversity are found between terrestrial and aquatic ecosystems. This has been attributed to environmental factors that hamper succession. However, ecosystem properties are often controlled by both bottom-up and top-down forces, but their relative importance in shaping riparian boundaries is not known. We hypothesize that (1) herbivores may enforce sharp transitions between terrestrial and aquatic ecosystems by inhibiting emergent vegetation expansion and reducing the width of the transition zone and (2) the vegetation expansion, diversity, and species turnover are related to abiotic factors in the absence of herbivores, but not in their presence. We tested these hypotheses in 50 paired grazed and ungrazed plots spread over ten wetlands, during two years. Excluding grazers increased vegetation expansion, cover, biomass, and species richness. In ungrazed plots, vegetation cover was negatively related to water depth, whereas plant species richness was negatively related to the vegetation N:P ratio. The presence of (mainly aquatic) herbivores overruled the effect of water depth on vegetation cover increase but did not interact with vegetation N:P ratio. Increased local extinction in the presence of herbivores explained the negative effect of herbivores on species richness, as local colonization rates were unaffected by grazing. We conclude that (aquatic) herbivores can strongly inhibit expansion of the riparian vegetation and reduce vegetation diversity over a range of environmental conditions. Consequently, herbivores enforce sharp boundaries between terrestrial and aquatic ecosystems.
Data from: Spatial memory shapes migration and its benefits: evidence from a large herbivore
From fine-scale foraging to broad-scale migration, animal movement is shaped by the distribution of resources. There is mounting evidence, however, that learning and memory also guide movement. Although migratory mammals commonly track resource waves, how resource tracking and memory guide long-distance migration has not been reconciled. We examined these hypotheses using movement data from four populations of migratory mule deer (n=91). Spatial memory had an extraordinary influence on migration, affecting movement 2–28 times more strongly than tracking spring green-up or autumn snow depth. Importantly, with only an ability to track resources, simulated deer were unable to recreate empirical migratory routes. In contrast, simulated deer with memory of empirical routes, used those routes and obtained higher foraging benefits. For migratory terrestrial mammals, spatial memory provides knowledge of where seasonal ranges and migratory routes exist, while resource tracking determines when to beneficially move within those areas.
Data from: Possible causes of divergent population trends in sympatric African herbivores
Sympatric herbivores experience similar environmental conditions but can vary in their population trends. Identifying factors causing these differences could assist conservation efforts aimed at maintaining fully functional ecosystems. From 1996 – 2013, tsessebe and wildebeest populations in the Okavango Delta, Botswana, declined by 73% and 90%, respectively, whereas zebra populations remained stable. These sympatric, medium sized herbivores are exposed to similar natural and anthropogenic pressures, but apparently differ in their responses to those pressures. To identify factors that could cause these differences, we fitted GPS-enabled collars to six zebra, eight tsessebe and seven wildebeest in the Moremi Game Reserve, Botswana. We calculated utilisation distributions (UDs) from GPS data, and used 95% isopleths to compare seasonal home range size between species. We calculated utilisation intensity (UI) from the UDs and generated spatial layers representing resources and disturbances, and then used model averaging to identify factors affecting UI for each species. We calculated second and third order habitat selection ratios to determine whether species were habitat specialists or generalists. Zebra occupied larger home ranges than tsessebe and wildebeest, showed weaker responses to spatial variables and displayed no third order habitat selection; zebra social systems are also more fluid, allowing for information exchange between stable harems. Herbivore species that are sedentary, occupy small home ranges, are habitat specialists and exist in relatively isolated groups are likely to be less resistant and resilient to the rapid pace of environmental change forecast by climate change scenarios. Resources contained within existing protected areas are unlikely to maintain populations of such species at sufficiently high levels, potentially leading to functional extinction. Special precautions may be needed to ensure that such species can persist in the wild, such as buffer zones around existing protected areas, which would allow greater potential for adaptive movement should current environmental conditions change.
Data from: Mycorrhizae alter constitutive and herbivore-induced volatile emissions by milkweeds
Plants use volatile organic compounds (VOCs) to cue natural enemies to their herbivore prey on plants. Simultaneously, herbivores utilize volatile cues to identify appropriate hosts. Despite extensive efforts to understand sources of variation in plant communication by VOCs, we lack an understanding of how ubiquitous belowground mutualists, such as arbuscular mycorrhizal fungi (AMF), influence plant VOC emissions. In a full factorial experiment, we subjected plants of two milkweed (Asclepias) species under three levels of AMF availability to damage by aphids (Aphis nerii). We then measured plant headspace volatiles and chemical defenses (cardenolides) and compared these to VOCs emitted and cardenolides produced by plants without herbivores. We found that AMF have plant species-specific effects on constitutive and aphid-induced VOC emissions. High AMF availability increased emissions of total VOCs, two green leaf volatiles (3-hexenyl acetate and hexyl acetate), and methyl salicylate in A. curassavica, but did not affect emissions in A. incarnata. In contrast, aphids consistently increased emissions of 6-methyl-5-hepten-2-one and benzeneacetaldehyde in both species, independent of AMF availability. Both high AMF availability and aphids alone suppressed emissions of individual terpenes. However, aphid damage on plants under high AMF availability increased, or did not affect, emissions of those terpenes. Lastly, aphid feeding suppressed cardenolide concentrations only in A. curassavica, and AMF did not affect cardenolides in either plant species. Our findings suggest that by altering milkweed VOC profiles, AMF may affect both herbivore performance and natural enemy attraction.
Data from: Herbivore resistance in congeneric and sympatric Nothofagus species is not related to leaf habit
Premise of the study Two fundamental hypotheses on herbivore resistance and leaf habit are the resource availability hypothesis (RAH) and the carbon-nutrient balance hypothesis (CNBH). The RAH predicts higher constitutive resistance by evergreens and the CNBH predicts higher induced resistance by deciduous species. Although support for these hypotheses is mixed, they have rarely been examined in congeneric species. Methods We compared leaf constitutive and induced resistance (as leaf polyphenols and tannin concentrations, and damage level in non-choice experiments) and leaf traits associated with herbivory of coexisting Nothofagus species using 1) a defoliation experiment, and 2) a natural defoliation caused by an outbreak of a common defoliator of Nothofagus species. Key Results In the defoliation experiment, polyphenol and tannin concentrations were similar between deciduous and evergreen species; regardless of leaf habit, polyphenols increased in response to defoliation. In the natural defoliation survey, N. pumilio (deciduous) had significantly higher herbivory, lower C/N ratio and leaf mass per area, and higher nitrogen and phosphorous concentrations than N. betuloides (evergreen); N. antarctica (deciduous) had intermediate values. Polyphenol concentrations and herbivore resistance indicated by the non-choice experiment were lower in N. pumilio than in N. antarctica and N. betuloides, which had similar values. Conclusions Higher herbivory in N. pumilio was associated with a higher nutritional value and a lower level of leaf C-based defenses compared to both the evergreen and the other deciduous species, indicating that herbivore resistance in Nothofagus species cannot be attributed to only leaf habit as predicted by the RAH or CNBH. Please be aware that if you ask to have your user record removed, we will retain your name in the records concerning manuscripts for which you were an author, reviewer, or editor. In compliance with data protection regulations, you may request that we remove your personal registration details at any time. (Use the following URL: https://www.editorialmanager.com/ajb/login.asp?a=r) Please contact the publication office if you have any questions.
Data from: Termite mounds differ in their importance for herbivores across savanna types, seasons and spatial scales
Herbivores do not forage uniformly across landscapes, but select for patches of higher nutrition and lower predation risk. Macrotermes mounds contain higher concentrations of soil nutrients and support grasses of higher nutritional value than the surrounding savanna matrix, attracting mammalian grazers that preferentially forage on termite mound vegetation. However, little is known about the spatial extent of such termite influence on grazing patterns and how it might differ in time and space. We measured grazing intensity in three African savanna types differing in rainfall and foliar nutrients and predicted that the functional importance of mounds for grazing herbivores would increase as the difference in foliar nutrient levels between mound and savanna matrix grasses increases and the mounds become more attractive. We expected this to occur in nutrient-poor areas and during the dry season when savanna matrix grass nutrient levels are lower. Tuft use and grass N and P content were measured along transects away from termite mounds, enabling calculation of the spatial extent of termite influence on mammalian grazing. Using termite mound densities estimated from airborne light detection and ranging (LiDAR), we further upscaled field-based results to determine the percentage of the landscape influenced by termite activity. Grasses in close proximity to termite mounds were preferentially grazed at all sites and in both seasons, but the strength of mound influence varied between savanna types and seasons. In the wet season, mounds had a relatively larger effect on grazers at the landscape scale in the nutrient-poor, wetter savanna, whereas in the dry season the pattern was reversed with more of the landscape influenced at the nutrient-rich, driest site. Our results reveal that termite mounds enhance the value of savanna landscapes for herbivores, but that their functional importance varies across savanna types and seasons.
Data from: Are tree species diversity and genotypic diversity effects on insect herbivores mediated by ants?
Plant diversity can influence predators and omnivores and such effects may in turn influence herbivores and plants. However, evidence for these ecological feedbacks is rare. We evaluated if the effects of tree species (SD) and genotypic diversity (GD) on the abundance of different guilds of insect herbivores associated with big-leaf mahogany (Swietenia macrophylla) were contingent upon the protective effects of ants tending extra-floral nectaries of this species. This study was conducted within a larger experiment consisting of mahogany monocultures and species polycultures of four species and –within each of these two plot types– mahogany was represented by either one or four maternal families. We selected 24 plots spanning these treatment combinations, 10 mahogany plants/plot, and within each plot experimentally reduced ant abundance on half of the selected plants, and surveyed ant and herbivore abundance. There were positive effects of SD on generalist leaf-chewers and sap-feeders, but for the latter group this effect depended on the ant reduction treatment: SD positively influenced sap-feeders under ambient ant abundance but had no effect when ant abundance was reduced; at the same time, ants had negative effects on sap feeders in monoculture but no effect in polyculture. In contrast, SD did not influence specialist stem-borers or leaf-miners and this effect was not contingent upon ant reduction. Finally, GD did not influence any of the herbivore guilds studied, and such effects did not depend on the ant treatment. Overall, we show that tree species diversity influenced interactions between a focal plant species (mahogany) and ants, and that such effects in turn mediated plant diversity effects on some (sap-feeders) but not all the herbivores guilds studied. Our results suggest that the observed patterns are dependent on the combined effects of herbivore identity, diet breadth, and the source of plant diversity.
Data from: Strong positive effects of termites on savanna bird abundance and diversity are amplified by large herbivore exclusion
Vast areas of the African savanna landscapes are characterized by tree-covered Macrotermes termite mounds embedded within a relatively open savanna matrix. In concert with termites, large herbivores are important determinants of savanna woody vegetation cover. The relative cover of woody species has considerable effects on savanna function. Despite the potentially important ecological relationships between termite mounds, woody plants, large herbivores, and birds, these associations have previously received surprisingly little attention. We experimentally studied the effects of termites and large herbivores on the avian community in Lake Mburo National Park, Uganda, where woody vegetation is essentially limited to termite mounds. Our experiment comprised of four treatments in nine replicates; unfenced termite mounds, fenced mounds (excluding large mammals), unfenced adjacent savanna, and fenced savanna. We recorded species identity, abundance, and behavior of all birds observed on these plots over a two-month period, from late dry until wet season. Birds used termite mounds almost exclusively, with only 3.5% of observations occurring in the treeless intermound savanna matrix. Mean abundance and species richness of birds doubled on fenced (large herbivores excluded) compared to unfenced mounds. Feeding behavior increased when large mammals were excluded from mounds, both in absolute number of observed individuals, and relative to other behaviors. This study documents the fundamental positive impact of Macrotermes termites on bird abundance and diversity in an African savanna. Birds play crucial functional roles in savanna ecosystems, for example, by dispersing fruits or regulating herbivorous insect populations. Thus, the role of birds in savanna dynamics depends on the distribution and abundance of termite mounds.
Data from: Temperature-related variation in growth rate, size, maturation, and lifespan in a marine herbivorous fish over a latitudinal gradient
1. In ectotherms, growth rate, body size, and maturation rate co-vary with temperature, with the direction and magnitude of variation predicted by the Temperature-Size Rule (TSR). Nutritional quality or availability of food, however, may vary over latitudinal gradients, resulting in ambiguous effects on body size and maturation rate. The Temperature-Constraint Hypothesis (TCH) predicts that marine herbivorous ectotherms are nutritionally compromised at latitudes exceeding 30o. This provides an opportunity to resolve the contrasting demographic responses of ectotherms to variation in temperature and nutritional status over latitudinal gradients. 2. This study uses analysis of demographic rates to evaluate the predictions of the TSR in a marine herbivorous ectotherm sampled over a significant latitudinal gradient. 3. The direction and magnitude of demographic variation was established in the marine herbivorous fish, Odax pullus (the butterfish), and compared with that of a phylogenetically related but trophically distinct species, the carnivorous Notolabrus fucicola (the banded wrasse). Both species were sampled at three locations across the length of New Zealand covering latitudes between 35oS and 49oS. Growth rate, mean size-at-age, age- and size-at-maturity, lifespan, and abundance were estimated for each species at each location. 4. Demographic traits of both taxa varied with latitude. Both species showed slower initial growth rates, and matured later at a larger body size at higher latitudes than populations sampled at lower latitudes. In addition, abundances increased significantly at higher latitudes in both species. 5. These results were consistent with the TSR but not the TCH, confirming that nutritional ecology (herbivore vs. carnivory) did not determine demographic patterns over a biologically significant latitudinal gradient. Results from this study suggest that the absence of herbivorous reef fishes from the higher latitudes of the northern hemisphere may not reflect a general physiological mechanism as suggested by the TCH, and highlights the need to clarify the evolutionary histories of the marine biotas of each hemisphere.
Data from: Multiple plant traits shape the genetic basis of herbivore community assembly
1. Community genetics research has posited a genetic basis to the assembly of ecological communities. For arthropod herbivores in particular, there is strong support that genetic variation in host plants is a key factor shaping their diversity and composition. However, the specific plant phenotypes underlying herbivore responses remain poorly explored for most systems. 2. We address this knowledge gap by examining the influence of both genetic and phenotypic variation in a dominant host-plant species, Salix hookeriana, on its associated arthropod herbivore community in a common garden experiment. Specifically, we surveyed herbivore responses among five different arthropod feeding guilds to 26 distinct S. hookeriana genotypes. Moreover, we quantified the heritability of a suite of plant traits that determine leaf quality (e.g. phenolic compounds, trichomes, specific leaf area, C : N) and whole-plant architecture, to identify which traits best accounted for herbivore community responses to S. hookeriana genotype. 3. We found that total herbivore abundance and community composition differed considerably among S. hookeriana genotypes, with strong and independent responses of several species and feeding guilds driving these patterns. We also found that leaf phenolic chemistry displayed extensive heritable variation, whereas leaf physiology and plant architecture tended to be less heritable. Of these traits, herbivore responses were primarily associated with leaf phenolics and plant architecture; however, different herbivore species and feeding guilds were associated with different sets of traits. Despite our thorough trait survey, plant genotype remained a significant predictor of herbivore responses in most trait association analyses, suggesting that unmeasured host-plant characteristics and/or interspecific interactions were also contributing factors. 4. Taken together, our results support that the genetic basis of herbivore community assembly occurs through a suite of plant traits for different herbivore species and feeding guilds. Still, identifying these phenotypic mechanisms requires measuring a broad range of plant traits and likely further consideration of how these traits affect interspecific interactions.
Data from: Feces nitrogen release induced by different large herbivores in a dry grassland
Large herbivores have pronounced effects on nutrient cycling in grasslands. These organisms are known to alter the quality and quantity of plant production as well as the amounts and quality of plant litter and animal wastes. The generalization that the relative quality of detritus inputs is enhanced by herbivores is well known, but how this process is affected by diet selection processing and feces production of different large herbivores remains largely unstudied. Here, we measured how these differences for cattle and sheep on a dry grassland might influence nitrogen (N) mineralization from feces. We found that cattle of larger body size tended to select low quality grass Stipa grandis as the major food source. In contrast, the subdominant grass Leymus chinensis with relatively high N content was a majority in the diet of smaller sheep, when palatable forbs were insufficient in the field. This diverse diet quality resulted in a C/N ratio of cattle feces that was higher than that of sheep feces. Relatively higher labile C availability in the cattle feces, namely relatively higher cellulose/hemicellulose contents, promoted microbial growth and in turn accelerated cattle feces decomposition. A surprise finding was that the feces from cattle mineralized about twice as much N as feces from sheep, despite the latter having slightly higher N content. From a grassland productivity perspective, increasing the proportion of large body-sized species in grazing herbivore assemblages perhaps is beneficial to forage productivity and nutrient recycling by the rapid degradation of feces.
Data from: Seascapes as drivers of herbivore assemblages in coral reef ecosystems
Herbivorous fish maintain a critical ecosystem function on coral reefs by grazing algae and maintaining highly productive algal turf assemblages. Current paradigms implicate habitat complexity, predation and primary productivity as major drivers of the distribution and abundance of herbivorous fish, yet little is known about the relative contribution of these factors. Here, we compare bottom-up and top-down drivers of notional herbivore assemblages across an environmental gradient of wave exposure in the Palau archipelago. We surveyed herbivore assemblages at reef slopes (6 - 9m) across 18 sites, and quantified proxies of top-down control (predator biomass, habitat complexity) and bottom-up drivers (net primary production, nutrients) at each site. Despite substantial variability in herbivore biomass throughout the archipelago (6 to 65 g m-2), general additive models indicate that neither top-down nor bottom-up drivers significantly predicted biomass or density of herbivores among sites. In contrast to expectations, herbivore biomass was highest at sites with high predator biomass, low structural complexity and low benthic productivity. Rather, the highest biomass of herbivores was associated with shallow, tidally emergent, productive reef flats located adjacent to steep vertical walls ('drop-offs'). The emergent nature of this neighbouring habitat precluded occupation by territorial fishes, and multiple species of herbivores were observed to make foraging runs into this habitat once tidally inundated. We hypothesize that this habitat configuration provides an important cross-habitat resource subsidy. Multivariate ordination and permutation of herbivore communities revealed strong evidence for biogeographic partitioning throughout the archipelago (western, south-western, inner eastern and outer eastern clusters), contributing to an emerging picture that the habitat heterogeneity of seascapes can overwhelm the effects of conventional top-down and bottom-up structuring of herbivory on coral reefs.
Data from: Insecticides promote viral outbreaks by altering herbivore competition
While the management of biological invasions is often characterized by a series of single-species decisions, invasive species exist within larger food webs. These biotic interactions can alter the impact of control/eradication programs and may cause suppression efforts to inadvertently facilitate invasion spread and impact. We document the rapid replacement of the invasive Bemisia MEAM1 cryptic species by the cryptic MED species throughout China, and demonstrate that MED is more tolerant of insecticides and a better vector of tomato yellow leaf curl virus ('TYLCV') than MEAM1. While MEAM1 usually excludes MED under natural conditions, insecticide application reverses the MEAM1-MED competitive hierarchy and allows MED to exclude MEAM1. The insecticide-mediated success of MED has led to TYLCV outbreaks throughout China. Our work strongly supports the hypothesis that insecticide use in China reverses the MEAM1-MED competitive hierarchy and allows MED to displace MEAM1 in managed landscapes. By promoting the dominance of a Bemisia species that is a competent viral vector, insecticides thus increase the spread and impact of TYLCV in heterogeneous agroecosystems.
Data from: Host plant associations and geography interact to shape diversification in a specialist insect herbivore
Disentangling the processes underlying geographic and environmental patterns of biodiversity challenges biologists as such patterns emerge from eco-evolutionary processes confounded by spatial autocorrelation among sample units. The herbivorous insect, Belonocnema treatae (Hymenoptera: Cynipidae), exhibits regional specialization on three plant species whose geographic distributions range from sympatry through allopatry across the southern USA. Using range-wide sampling spanning the geographic ranges of the three host plants and genotyping-by-sequencing of 1,217 individuals, we tested whether this insect herbivore exhibited host-plant-associated genomic differentiation while controlling for spatial autocorrelation among the 58 sample sites. Population genomic structure based on 40,699 SNPs was evaluated using the hierarchical Bayesian model ENTROPY to assign individuals to genetic clusters and estimate admixture proportions. To control for spatial autocorrelation, distance-based Moran's eigenvector mapping was used to construct regression variables summarizing spatial structure inherent among sample sites. Distance based redundancy analysis (dbRDA) incorporating the spatial variables was then applied to partition host-plant-associated differentiation (HAD) from spatial autocorrelation. By combining ENTROPY and dbRDA to analyze SNP data we unveiled a complex mosaic of highly structured differentiation within and among gall former populations finding evidence that geography, HAD and spatial autocorrelation all play significant roles in explaining patterns of genomic differentiation in B. treatae. While dbRDA confirmed host association as a significant predictor of patterns of genomic variation, spatial autocorrelation among sites explained the largest proportion of variation. Our results demonstrate the value of combining dbRDA with hierarchical structural analyses to partition spatial/environmental patterns of genomic variation.
Data from: Cascading effects of mammalian herbivores on ground-dwelling arthropods: variable responses across arthropod groups, habitats and years
1. Large mammalian herbivores are well known to shape the structure and function of ecosystems worldwide and these effects can in turn cascade through systems to indirectly influence other animal species. A wealth of studies have explored the effects of large mammals on arthropods, but to date they have reported such widely varying results that generalizations have been elusive. Three factors are likely drivers of this variability: the widely varying life-history characteristics of different arthropod groups, the highly variable landscapes that mammalian herbivores commonly inhabit, and temporal variation in environmental conditions. 2. Here, we use an 18-year-old exclosure experiment stratified across three distinct coastal prairie habitats in northern California to address the effects of a reintroduced mammalian herbivore, tule elk (Cervus canadensis nannodes) on the composition, richness, and abundance of ground-dwelling arthropods over two years with very different precipitation regimes. 3. We found that elk shifted the composition of arthropod communities, increasing the abundance of ants, beetles, spiders and mites, decreasing the abundance of woodlice and bristletails in some but not all habitats types, and having no effect on the abundance of bugs, crickets and springtails. Elk also increased richness and changed the composition of ant-genera and beetle morpho-species. Interestingly, the effects of elk on arthropod composition, richness and abundance varied little between years, despite very different precipitation levels, biomass accumulation, and thatch height. 4. Elk reduced shrub cover, aboveground herbaceous biomass, and thatch height and increased soil compaction, and these changes predicted the abundance and richness of arthropods, although taxonomic groups varied in their responses, presumably due to differences in environmental requirements. 5. Synthesis. Our research highlights the importance of using long-term experiments to assess the cascading effects of large herbivores on the composition of ground-dwelling arthropod communities and to identify the mechanisms that indirectly shape arthropod responses to herbivores among variable habitats and years in order to develop a greater understanding of the variable responses of arthropods to large mammalian herbivores.
Data from: Contemporary evolution of plant growth rate following experimental removal of herbivores
Herbivores are credited with driving the evolutionary diversification of plant defensive strategies over macroevolutionary time. For this to be true, herbivores must also cause short-term evolution within plant populations, but few studies have experimentally tested this prediction. We addressed this gap using a long-term manipulative field experiment where exclosures protected 22 plant populations from natural rabbit herbivory for <1 to 26 years. We collected seeds of Rumex acetosa L. (Polygonaceae) from our plots and grew them in a common greenhouse environment to quantify evolved differences among populations in individual plant growth rate, tolerance to herbivory, competitive ability, and the concentration of secondary metabolites (tannins and oxalate) implicated in defense against herbivores. In 26 years without rabbit herbivory, plant growth rate decreased linearly by 30%. We argue that plant growth rate has evolved as a defense against intense rabbit herbivory. In contrast, we found no change in tolerance to herbivory or concentrations of secondary metabolites. We also found no change in competitive ability, suggesting that contemporary evolution may not feed back to alter ecological interactions within this plant community. Our results combined with those of other studies show that the evolution of gross morphological traits such as growth rate in response to herbivory may be common, which calls into question assumptions about some of the most popular theories of plant defense.
Data from: Land-use history alters contemporary insect herbivore community composition and decouples plant-herbivore relationships
1. Past land use can create altered soil conditions and plant communities that persist for decades, although the effects of these altered conditions on consumers are rarely investigated. 2. Using a large-scale field study at 36 sites in longleaf pine (Pinus palustris) woodlands, we examined whether historic agricultural land use leads to differences in the abundance and community composition of insect herbivores (grasshoppers, families Acrididae and Tettigoniidae). 3. We measured the cover of six plant functional groups and several environmental variables to determine whether historic agricultural land use affects the relationships between plant cover or environmental conditions and grasshopper assemblages. 4. Land-use history had taxa-specific effects and interacted with herbaceous plant cover to alter grasshopper abundances, leading to significant changes in community composition. Abundance of most grasshopper taxa increased with herbaceous cover in woodlands with no history of agriculture, but there was no relationship in post-agricultural woodlands. We also found that grasshopper abundance was negatively correlated with leaf litter cover. Soil hardness was greater in post-agricultural sites (i.e. more compacted) and was associated with grasshopper community composition. Both herbaceous cover and leaf litter cover are influenced by fire frequency, suggesting a potential indirect role of fire on grasshopper assemblages. 5. Our results demonstrate that historic land use may create persistent differences in the composition of grasshopper assemblages, while contemporary disturbances (e.g. prescribed fire) may be important for determining the abundance of grasshoppers, largely through the effect of fire on plants and leaf litter. Therefore, our results suggest that changes in the contemporary management regimes (e.g. increasing prescribed fire) may not be sufficient to shift the structure of grasshopper communities in post-agricultural sites towards communities in non-agricultural habitats. Rather, repairing degraded soil conditions and restoring plant communities are likely necessary for restoring grasshopper assemblages in post-agricultural woodlands.
Data from: Grass competition overwhelms effects of herbivores and precipitation on early tree establishment in Serengeti
1. Savanna ecosystems span a diverse range of climates, edaphic conditions and disturbance regimes, the complexity of which has stimulated long-standing interest in the mechanisms that maintain tree-grass coexistence. One hypothesis suggests that tree establishment is strongly limited by one or several demographic bottlenecks at early stages of the tree life cycle. A major impediment to testing this hypothesis is the lack of data on the relative strengths of different bottlenecks across key environmental gradients. 2. To identify demographic bottlenecks that limit early tree establishment (0-18 months), we conducted a series of transplant experiments with two savanna trees species (Acacia robusta and A. tortilis) across a natural rainfall and soil fertility gradient in the Serengeti ecosystem, Tanzania. We tested the interactive effects of precipitation, herbivory, seed scarification, grass competition, water limitation and tree species identity on two key life stages: germination and early seedling survival (0-2 months) and juvenile seedling survival (2-18 months). 3. Germination and early seedling survival increased as a function of rainfall, in the absence of herbivores and when seeds were scarified. Juvenile seedling survival, in contrast, decreased with rainfall but increased in the absence of herbivores. Grass removal had the single strongest (positive) effect on juvenile seedling survival of any treatment. Soil moisture monitoring and grass-addition treatments revealed that grasses negatively affected seedlings in ways that were not necessarily linked to soil moisture. 4. A demographic model combining all effects across early life stages showed that the strength of grass competition on juvenile seedling survival was the key factor limiting early tree establishment. While rainfall had an unexpected opposing effect on the two life stages, the net effect of mean annual precipitation on early tree establishment was positive. 5. Synthesis: Successful tree establishment in Serengeti is maximized by a seemingly unlikely sequence of events: (1) scarification of seeds by browsers, (2) heavy rainfall to promote germination, (3) intensive grazing (but absence of browsers) and (4) dry conditions during juvenile seedling growth (>2 months) to reduce competition with grasses. By considering a wide suite of conditions and their interactions, our experimental results are relevant to ongoing debates about savanna vegetation dynamics and structural shifts in tree:grass ratios.
Data from: Spatially heterogeneous perturbations homogenize the regulation of insect herbivores
Anthropogenic influences on resources and consumers can affect food web regulation, with impacts on trophic structure and ecosystem processes. Identifying how these impacts unfold is challenging because alterations to one or both resources and consumers can similarly transform community structure, especially for intermediate consumers. To date, empirical testing of perturbations on trophic regulation has been limited by the difficulty in separating the direct effect of perturbations on species composition and diversity from those unfolding indirectly via altered feeding pathways. Moreover, disentangling the independent and interactive impacts of covarying stressors that characterize human-altered systems has been an ongoing analytical challenge. We used a large-scale metacommunity experiment in grasslands to test how resource inputs, stand perturbation, and spatial factors affect regulation of insect herbivores in tritrophic grassland food webs. Using path-model comparisons, we observed significant simplification of food web regulation on insect herbivores, shifting from mixed predator-resource regulation in unaltered mainland areas to strictly resource-based regulation with landscape perturbation and fragmentation. Most changes were attributed to homogenization of plant community caused by landscape fragmentation and the deterministic influence of eutrophication that reduced among-patch beta diversity. This led to a simplified food web dominated by fewer but more abundant herbivore taxa. Our work implies that anthropogenic perturbation relating to resources and spatial isolation can transform the regulation of food web diversity, structure, and function.
Data from: Contribution of predation to the biological control of a key herbivorous pest in citrus agroecosystems
Biological control has traditionally simplified the view of trophic relationships between herbivorous pests and their natural enemies in agriculture. The success or failure of this pest management strategy is still mainly attributed to the ability of a few key natural enemies to suppress the pest density. For example, successful regulation of the California red scale (Aonidiella aurantii) a key citrus pest, is generally credited to specific parasitoids of the Aphytis genus. Currently, research is revealing how herbivore regulation in agroecosystems can be alternatively achieved with a greater number of trophic associations within the system. The goals of the present study were: i) to unravel species‐specific trophic links between A. aurantii, and its natural enemies in citrus agroecosystems, and ii) to assess their contribution to control of A. aurantii. Predation and parasitism of this herbivorous pest were assessed through exclusion experiments. Species‐specific trophic links between this herbivorous pest and its natural enemies were studied using gut‐content analysis of field collected predators employing prey specific DNA molecular markers. Relative predation rates of the species involved in A. aurantii regulation were estimated. Predation was found to be the main biotic component of A. aurantii mortality, causing reductions of more than 75% in recently settled cohorts. Aonidiella aurantii DNA was detected in the digestive system of 11 species of predators. Generalist and stenophagous predators, mainly associated with other citrus pests such as aphids, proved to be the most important biological control agents of this pest. Complex trophic relationships, such as apparent competition between two key citrus pests, were revealed. The present study highlights the role of predation as biotic mortality factor of key pests in perennial agroecosystems; wherein, it is a rich complex of indigenous or naturalized generalist predators that are primarily responsible for this mortality. The results herein presented may therefore offer another perspective on the biological control of one of the key worldwide citrus pests; at least in those regions where specific parasitoids are not able to successfully regulate the scale populations.
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Allen Brain Atlas
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Annotated Behaviour and Observability Dataset (ABODe)
ABODe is a University of Edinburgh DataShare dataset for behavior classification in group-housed mice using home-cage video, identities, bounding boxes, ground-plate positions, and annotator labels.
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DANDI is a BRAIN Initiative archive for publishing and sharing neurophysiology data, including electrophysiology, optophysiology, and behavioral data packaged as NWB and related standards.
International Brain Laboratory public data
The International Brain Laboratory public data releases expose standardized mouse decision-making experiments, including Neuropixels recordings, widefield calcium imaging, behavior, and session metadata accessed through the ONE API.
OpenNeuro
OpenNeuro is a free, open platform for sharing neuroimaging datasets, with public search, dataset pages, and download paths for web, S3, DataLad, and the OpenNeuro CLI.