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Parasites as ecosystem modulators: Foliar pathogens suppress top-down effects of large herbivores

Parasites can catalyze or inhibit interactions between their hosts and other species, but the ecosystem-level effects of such interaction modifications are poorly understood. We conducted a large-scale field experiment in temperate grasslands of northeastern China to understand how foliar fungal pathogens (e.g., rusts and leaf spots) influenced top-down effects of large herbivores (cattle; Bos taurus) on plant diversity and productivity. In the absence of foliar pathogens, cattle grazing strongly suppressed biomass of the dominant grass, Leymus chinensis, (↓56%), generating competitive release that significantly increased plant species richness (↑75%) and evenness (↑15%). In the absence of grazing, pathogen attack on L. chinensis had no measurable effect on host biomass. However, pathogen infection greatly weakened top-down effects of herbivory by inhibiting cattle grazing on L. chinensis and negating grazing effects on plant biomass and species richness. Mechanistically, foliar pathogens were linked to increased alkaloid (↑45%) and reduced nitrogen levels (↓19%) in leaf tissue that appeared to deter cattle grazing on L. chinensis. Our results demonstrate that foliar pathogens can suppress top-down effects of large herbivores on grassland community structure and function by modifying the strength of its host's interactions with the dominant consumer. We propose that parasites may function primarily as modulators of ecosystem function when their direct effects on host density (often dampened by evolution) are overshadowed by influences on host traits that modify host interactions with strong competitors, herbivores, or predators.

Mixed-species groups of herbivorous reef fish show variable responses to ecosystem perturbations in the Lakshadweep Islands, India

This dataset contains data on mixed-species groups of herbivorous reef fish and local species composition in the Lakshadweep Islands, India. Herbivorous reef fish provide a vital function in reef ecosystems by removing algae and making space available to coral recruits. The high abundance of herbivores in the reefs of the Lakshadweep islands has potentially aided in reef recovery and helped avoid a phase shift to an algal-dominated system, despite most areas having suffered massive coral losses. Mixed-species grouping in herbivores could potentially benefit both the participant species and the reef ecosystem by improving foraging efficiency. We examined the grouping propensity and species richness for three types of herbivore groups after a mass-bleaching event in 2010 and a mass recruitment event in 2015. The species richness and number of parrotfish groups, as well as the grouping propensity of common species, declined starkly across years, indicating that these groups may have formed in response to the mass-bleaching event, slowly diminishing as the reefs recovered. Conversely, large surgeonfish, which varied in richness and propensity across islands and aspect, are likely influenced by local processes. Small surgeonfish only increased in species richness and number in 2015, which may have been in response to the recruitment event. Thus, herbivorous fish may respond differently to local ecosystem perturbations and play different roles in reef recovery.

Data for: Drought impairs herbivore-induced volatiles, but not through constraints on newly assimilated carbon

Volatile terpenes serve multiple biological roles including tree resistance against herbivores. The increased frequency and severity of drought stress observed in forests across the globe may hinder trees from producing defense-related volatiles in response to biotic stress. To assess how drought-induced physiological stress alters volatile emissions alone and in combination with a biotic challenge, we monitored pre-dawn water potential, gas exchange, needle terpene concentrations, and terpene volatile emissions of ponderosa pine (Pinus ponderosa) saplings during three periods of drought and in response to simulated herbivory via methyl jasmonate application. Although three-, six-, and seven-week drought treatments reduced net photosynthetic rates by 20%, 89%, and 105%, respectively, the magnitude of volatile fluxes remained generally resistant to drought. Herbivore-induced emissions, however, exhibited threshold-like behavior; saplings were unable to induce emissions above constitutive levels when pre-dawn water potentials were below the approximate zero-assimilation point. By comparing compositional shifts in emissions to needle terpene concentrations, we found evidence that drought effects on constitutive and herbivore-induced volatile flux and composition are primarily via constraints on the de novo fraction, suggesting that reduced photosynthesis during drought limits the carbon substrate available for de novo volatile synthesis. However, results from a subsequent 13CO2 pulse-chase labeling experiment then confirmed that both constitutive (<3% labeled) and herbivore-induced (<8% labeled) de novo emissions from ponderosa pine are synthesized predominantly from older carbon sources with little contribution from new photosynthates. Taken together, we provide evidence that in ponderosa pine, drought does not constrain herbivore-induced de novo emissions through substrate limitation via reduced photosynthesis, but rather, through more sophisticated molecular and/or biophysical mechanisms that manifest as saplings reach the zero-assimilation point. These results highlight the importance of considering drought severity when assessing impacts on the herbivore-induced response and suggest that drought-altered volatile metabolism constrains induced emissions once a physiological threshold is surpassed.

Experimental warming increases the vulnerability of high-elevation plant populations to a specialist herbivore

<ol> <li>Ongoing climate change may impact alpine plant populations via both direct effects of increased temperature and climate-driven changes in interactions between plants and other organisms, such as insect herbivores. Rates of herbivory in high-elevation environments are predicted to increase with warmer temperatures, which may also lead to changes in morphological and physiological traits that influence plant resistance. Yet, we currently know little about how temperature-mediated changes in traits will impact alpine plant vulnerability to herbivores, as well as the extent to which populations from high-elevation environments might need to rapidly adapt to increasing herbivore pressure with rising temperatures.</li> <li>We assessed the effect of experimental warming on the relative vulnerability of populations of the alpine plant Arabis alpina from different elevations to a specialist herbivore. Herbivore performance was measured on plants from nine populations grown in climate chambers at two temperatures, representing low (warm) and high (cold) elevations. We also measured changes in putative drivers of performance: plant phenological, chemical and defence traits. Assuming populations would be adapted to local climates and levels of herbivory, we predicted that low-elevation populations would be more resistant to herbivores under warmer temperatures than high-elevation populations.</li> <li>We found reduced performance of a specialist herbivore on A. alpina grown under warm rather than cold conditions, though this effect varied with elevation. Larvae grew faster on high-elevation populations than low-elevation populations when grown under warm temperatures, whereas similar growth rates were observed for plants grown under colder temperatures, consistent with plant adaptation to the lower existing herbivore pressure in cold, high-elevation environments. Regression analyses suggested that polar metabolite variation explained more variance in larval performance than changes in defensive glucosinolates or morphological traits.</li> <li>Our results suggest that although physiological responses to warming may increase the resistance of cold-adapted plants to herbivory, populations from different elevations may differ in their interactions with herbivores under climate warming. Without genetic adaptation, existing physiological responses of high-elevation populations to warmer temperatures may leave these populations vulnerable to the increases in herbivore pressure predicted under climate change.</li> </ol>

opencc-zeroApr 2023View details →

A unified meta-ecosystem dynamics model: Integrating herbivore-plant subwebs with the intermittent upwelling hypothesis

Determining the relative influence of biotic and abiotic processes in structuring communities at local to large spatial scales is best understood using a biogeographic comparative-experimental approach. Using this approach, previous work suggests that intertidal community dynamics (top-down and bottom-up effects) vary unimodally along an upwelling-based productivity gradient, termed the Intermittent Upwelling Hypothesis (IUH). Evidence consistent with the IUH comes from the sessile invertebrate/predator (SIP) subweb in certain rocky intertidal communities, but whether this pattern extends to macrophyte/herbivore (MH) subwebs is unknown. Here we ask: Are MH subwebs also structured as predicted by the IUH? What is the relative importance of herbivory and predation in structuring these communities? Under what conditions do ecological subsidies like nutrients or propagule production drive community dynamics? And are omnivorous interactions important? We hypothesize that MH subwebs are driven by a new construct, the Grazing-Weakening Hypothesis (GWH), which states that MH interactions weaken monotonically with increasing nutrients, with strong (weak) herbivory and low (high) macrophyte productivity at low (high) nutrients. We explored local-to-large spatial scale dynamics of both subwebs using a biogeographic comparative-experimental factorial field experiment testing joint and separate effects of herbivores and predators between two continents. Experiments at ten sites ranging across from persistent upwelling to persistent downwelling regimes ran for 26-29 months in Oregon and California, and New Zealand South Island. For the MH subweb, results were consistent with the GWH: herbivory declined and macrophytes increased with increasing nutrients. As expected, results for the SIP subweb were consistent with the IUH: predator effect size was unimodally related to upwelling. Overall, herbivory explained more variation in community structure than did predation, especially in New Zealand. Omnivory was weak, sessile invertebrates outcompeted macrophytes, and ocean-driven subsidies provided the basic template driving ecosystem dynamics. We propose a unified Meta-Ecosystem Dynamics Model (MEcoDynaMo) combining MH and SIP results: with increased upwelling, sessile invertebrates and underlying dynamics vary unimodally (as in the IUH), while herbivory decreases and macrophytes generally increase. While this model was based on research in temperate ecosystems varying in upwelling regime, its wider applicability remains to be tested.

opencc-zeroApr 2023View details →

Exotic tree species have consistently lower herbivore load in a cross-Atlantic tree biodiversity experiment

It is commonly expected that exotic plants experience reduced herbivory, but experimental evidence for such enemy release is still controversial. One reason for conflicting results might be that community context has rarely been accounted for, although the surrounding plant diversity may moderate enemy release. Here, we tested the effects of focal tree origin and surrounding tree diversity on herbivore abundance and leaf damage in a cross-Atlantic tree diversity experiment in Canada and Germany. We evaluated six European tree species paired with six North American congeners in both their native and exotic range, expecting lower herbivory for the exotic tree species in each pair at each site. Such reciprocal experiments have long been called for, but have not been realized thus far. In addition to a thorough evaluation of overall enemy release effects, we tested whether enemy release effects change with the surrounding tree diversity. Herbivore abundance was indeed consistently lower on exotics across all six tree genera (12 comparisons). This effect of exotic status was independent of continent, phylogenetic relatedness and surrounding tree diversity. In contrast, leaf damage associated with generalist leaf chewers was consistently higher on North American tree species. Interestingly, several species of European weevils were the most abundant leaf chewers on both continents and the dominant herbivores at the Canadian site. Thus, most observed leaf damage likely reflects the effect of generalist herbivores that feed heavily on plant species they have not evolved with. At the German site, sap-suckers were the dominant herbivores and showed a pattern consistent with enemy release. Taken together, the consistently lower herbivory on exotics on both continents is not purely a pattern of enemy release in the strict sense, but to some degree additionally reflects the susceptibility of native plants to invasive herbivores. In conclusion, our cross-Atlantic study is consistent with the idea that non-native trees have generally reduced herbivory, regardless of tree community diversity and species identity, but for different reasons depending on the dominant herbivore guild.

opencc-zeroMay 2023View details →

Experimental manipulation of scavenger and herbivore functional role and their effects on plant communities following mass mortality events

We designed an experiment to measure the relative importance of bottom-up forces (nutrient addition) and top-down forces (impairment of obligate scavenger and herbivore functional roles) generated by experimental carrion deployment to simulate mass mortality events on the local plant community. In our experimental plots, we measured changes in plant functional groups before and for three years after experimental carrion deployment. Additionally, we monitored cherrybark oak (Quercus pagoda) seedlings' growth and survival three years after being transplanted in the experimental plots.

opencc-zeroMay 2023View details →

Data from: Phenotypic clines in herbivore resistance and reproductive traits in wild plants along an agricultural gradient

The conversion of natural landscapes to agriculture is a leading cause of biodiversity loss worldwide. While many studies examine how landscape modification affects species diversity, a trait-based approach can provide new insights into species responses to environmental change. Wild plants persisting in heavily modified landscapes provide a unique opportunity to examine species' responses to land use change. Trait expression within a community plays an important role in structuring species interactions, highlighting the potential implications of landscape mediated trait changes on ecosystem functioning. Here we test the effect of increasing agricultural landscape modification on defensive and reproductive traits in three commonly occurring Brassicaceae species to evaluate plant responses to landscape change. We collected seeds from populations at spatially separated sites with variation in surrounding agricultural land cover and grew them in a greenhouse common garden, measuring defensive traits through an herbivore no-choice bioassay as well as reproductive traits such as flower size and seed set. In two of the three species, plants originating from agriculturally dominant landscapes expressed a consistent reduction in flower size and herbivore leaf consumption. One species also showed reduced fitness associated with increasingly agricultural landscapes. These findings suggest that wild plants are responding to landscape modification, highlighting that species diversity alone does not fully capture the effects of land use change.

opencc-zeroMay 2023View details →

Raw data from: Environmental variation structures reproduction and recruitment in long-lived mega-herbivores: Galapagos Giant Tortoises

Understanding drivers of vital rates is important for testing life history theory, predicting population dynamics, and guiding conservation. Migratory, long-lived animals are important to life history theory because they present an extreme among trade-offs in vital rates: delayed maturity, low fecundity, variable recruitment rates, and long generation times. Understanding how vital rates respond to environmental variation has been elusive for such species because of difficulties in studying wide-ranging animals over extended periods. Populations that live on elevation gradients can provide tractable study systems because considerable environmental change occurs over small geographic distances. Galapagos tortoises are an iconic example; they are long-lived, migrate seasonally, face multiple anthropogenic threats, and have cryptic early life history stages for which vital rates are unknown. From 2012–2021, we studied the reproductive ecology of two species of Galapagos tortoises along elevation gradients that coincided with substantial change in climate and vegetation productivity. Specifically, we 1) measured physical and reproductive condition of adult females, 2) tracked the movements of 33 adult females using GPS telemetry, and re-located them seasonally to measure condition, 3) recorded nest temperatures, clutch characteristics, and egg survival from 107 nests, and 4) used radio telemetry to re-locate 104 hatchlings to monitor growth, survival, and movements. We also monitored temperature, rainfall, and primary productivity from field and remotely sensed data along the elevation gradient. Adult females were either elevational migrants or year-round lowland residents. Migrants had higher body condition than residents, and body condition was positively correlated with fecundity. Nests occurred in the hottest, driest part of the tortoise's range, between 6–165m elevation. Clutch size increased with elevation, egg survival declined, and hatchling survival and growth were highest at intermediate elevations. Hatchlings dispersed rapidly between 100–750 m from their nests before becoming sedentary in ranges <0.05 ha. Environmental variability mediated by elevation influenced adult fecundity and juvenile recruitment. Predicted future climates will profoundly impact the relationships between elevation and vital rates of Galapagos tortoises and other species living on elevation gradients. Resilience will be maximized by ensuring connectivity of foraging and reproductive areas within current and possible future elevational ranges of these species.

Age specific impacts of vegetation functional traits on gastro-intestinal nematode parasite burdens in a large herbivore

<ol> <li>Gastro-intestinal nematode (GIN) parasites play an important role in the ecological dynamics of many animal populations. Recent studies suggest fine-scale spatial variation in GIN infection dynamics is important in wildlife systems, but the environmental drivers underlying this variation remain poorly understood.</li> <li>We used data from over two decades of GIN parasite egg counts, host space use, and spatial vegetation data from a long-term study of Soay sheep on St Kilda to test how spatial autocorrelation and vegetation in an individual's home range predict parasite burden across three age groups. We developed a novel approach to quantify the plant functional traits present in a home range to describe the quality of vegetation present. </li> <li>Effects of space and vegetation varied between age classes. In immature lambs, strongyle parasite faecal egg counts (FEC) were spatially structured, being highest in the north and south of our study area. Independent of host body weight and spatial autocorrelation, plant functional traits predicted parasite egg counts. Higher egg counts were associated with more digestible and preferred plant functional traits, suggesting the association could be driven by host density and habitat preference.</li> <li>In contrast, we found no evidence that parasite FEC were related to plant functional traits in the host home range in yearlings or adult sheep. Adult FEC were spatially structured, with highest burdens in the north-east of our study area, while yearling FEC showed no evidence of spatial structuring.</li> <li>Our findings support the importance of fine-scale environmental variation for wildlife disease ecology and provide new evidence that such effects may vary across demographic groups within a population. Parasite burdens in immature individuals appear more readily influenced by fine-scale spatial variation in the environment, highlighting the importance of such heterogeneity for our understanding of wildlife epidemiology and health.</li> </ol>

Fear of predators alters herbivore regulation of soil microbial community function

Fear of predation can affect important ecosystem processes by altering the prey traits' expression that, in turn, regulates the quantity and quality of nutritional inputs to soil. Here, we aimed to assist in bridging a knowledge gap in this cascading chain of events by exploring how risk of spider predation may affect grasshopper prey performances, and the activity of various microbial extracellular enzymes in the soil. Using a mesocosms field‐experiment, we found that grasshoppers threatened by spider predation ate less, grew slower, and had a higher body carbon to nitrogen ratio. Herbivory increased activity of all microbial extracellular enzymes examined, likely due to higher availability of root exudates. Predation risk had no effect on C‐acquiring enzymes but decreased activity of P‐acquiring enzymes. We found contrasting results regarding the effect of predation on the activity of N‐acetyl‐glucosaminidase and leucine arylamidase N‐acquiring enzymes, suggesting that predation risk may alter the composition of N‐inputs to soil. Our work highlighted the importance of soil microbial enzymatic activity as a way to predict how changes in the aboveground food‐web dynamics may alter key ecosystem processes like nutritional‐cycling.

Data from: To eat, or not to eat: A phantom decoy affects information-gathering behavior by a free-ranging mammalian herbivore

When foraging, making appropriate food choices is crucial to an animal's fitness. Classic foraging ecology theories assume animals choose food of greatest benefit based on their absolute value across multiple dimensions. Consequently, poorer options are considered irrelevant alternatives that should not influence decision-making among better options. But heuristic studies demonstrate that irrelevant alternatives (termed decoys) can influence decisions of some animals, indicating they use a relative rather than absolute evaluation system. Our aim was to test whether a decoy influenced the decision-making process – i.e. information-gathering and food choice – of a free-ranging mammalian herbivore. We tested swamp wallabies, Wallabia bicolor, comparing their behavior towards, and choice of, two available food options over time in the absence or presence of the decoy. We used a phantom decoy—unavailable option—and ran two trials in different locations and seasons. Binary preferences (decoy absent) for the two available food options differed between trials. Irrespective of this difference, across both trials the presence of the decoy resulted in animals more likely to overtly investigate available food options. But the decoy only shifted food choice, weakly, in one trial. Our results indicate that the decoy influenced the information-gathering behavior during decision-making, providing first evidence that decoys can affect decision-making process of free-ranging mammalian herbivores in an ecologically realistic context. It is premature to say these findings confirm the use of relative evaluation systems. Whether the foraging outcome is more strongly affected by other decoys, food dimensions, or ecological contexts, is yet to be determined.

Large mammalian herbivores affect arthropod food webs via changes in vegetation characteristics and microclimate

<ol> <li>Large mammalian herbivores are vital components of terrestrial ecosystems, influencing the plants they feed on, but also serving as ecosystem engineers that impact the occurrence and survival of many other organisms. Arthropods are the most abundant and diverse animal group on earth, filling all trophic levels in food webs and facilitating essential ecosystem services. However, the impacts of large herbivores on arthropod communities and the mechanisms via which these impacts are mediated are not fully understood. </li> <li>Here, we experimentally separated the mechanistic pathways whereby large herbivores affect arthropod food webs using a 24-year manipulative multi-site field experiment in the Netherlands. We analyzed the abundance, biomass, and community composition of arthropods in the plant canopy and on the soil surface, both in grazed sites or sites where large herbivores were excluded.</li> <li>We found that the presence of large herbivores resulted in considerable differences in vegetation properties and microclimate which influenced the abundance and biomass of arthropods to varying trophic levels. Large herbivore grazing enhanced the overall abundance and biomass of arthropod herbivores, pollinators, omnivores, and soil-dwelling predators, but reduced that of detritivores, scavengers, parasitoids, and canopy predators. Structural equation models revealed that different trophic groups are affected by grazing via different pathways. Specially, large herbivores facilitated herbivores via increasing plant quality and enhanced ground-dwelling predators via increasing plant diversity. In contrast, plant-dwelling predators were suppressed via decreased plant quantity, and parasitoids were mainly affected by changes in microclimate conditions. </li> <li> Synthesis. Our results show that large mammalian herbivores play a significant role in shaping grassland arthropod food webs and that these impacts were independently mediated by multiple aspects of vegetation properties, i.e., physical structure, plant diversity, standing crop biomass, and leaf nutrient content. Arthropods of different trophic groups responded differently to the large herbivores, and these functional group-specific responses in turn may have strong cascading effects on numerous ecosystem services.</li> </ol>

opencc-zeroJul 2023View details →

Data from: Silicon supplementation and jasmonate activation synergistically increase phenolic defences against a legume herbivore

The accumulation of silicon (Si) is widely reported to have anti-herbivore defensive properties in grasses. There is emerging, but fragmentary, evidence that Si could play a similar role in legumes. Here, we sought to understand the effects of Si supplementation on anti-herbivore defensive properties in lucerne (Medicago sativa), especially in relation to other potential defences (i.e. phenolics) and the phytohormone that regulates anti-herbivore defences, jasmonic acid or jasmonate (JA), which is also linked to Si accumulation. We determined how growth, root nodulation and chemistry (carbon, nitrogen and phenolic concentrations) of four genotypes of lucerne responded to Si supplementation, with and without the application of JA, and we used feeding assays to determine the subsequent effects on the feeding success of adult Sitona discoideus weevils. Si supplementation increased plant mass and root nodulation of M. sativa by 61% and 227%, respectively, and reduced relative consumption (RC) and frass production by S. discoideus by 38% and 30%, respectively. Si supplementation had no effect on foliar nitrogen concentrations, most likely due to the dilution effects of increased plant growth and foliar carbon. Phenolic concentrations were negatively correlated with leaf RC; RC also decreased by 34% when JA was applied to plants. When Si was combined with JA application, phenolics were significantly enhanced, demonstrating the potential to stimulate multiple anti-herbivore properties in M. sativa. The novel findings suggest that Si accumulation may play a more important role in legume resistance to herbivorous animals than previously thought. The ubiquity of soil Si and its emerging functional role in plant biology, including plant–animal interactions, suggest that these patterns could be common amongst legumes.

opencc-zeroJul 2023View details →

The plant toxin 4-methylsulfinylbutyl isothiocyanate decreases herbivore performance and modulate cellular and humoral immunity

Insect herbivores frequently encounter plant defense molecules, but the physiological and ecological consequences for their immune systems are not fully understood. The majority of studies attempting to relate levels of plant defensive chemistry to herbivore immune responses have used natural population or species-level variation in plant defensive chemistry. Yet, this potentially confounds the effects of plant defense chemistry with other potential traits that may affect the expression of herbivore immunity such as development time and nutritional quality. We have used an artificial diet containing known quantities of a plant toxin (4-methylsulfinylbutyl isothiocyanate; 4MSOB-ITC or ITC), an isothiocyanate present in many plants in the genus Brassica, to explicitly explore the effects of a plant toxin on the cellular and humoral immune responses of the generalist herbivore Trichoplusia ni (Lepidoptera: Noctuidae) that frequently feeds on glucosinolate-containing plants. Caterpillars feeding on diets with high concentrations of ITC experienced reduced survivorship and growth rates. High concentrations of ITC suppressed the appearance of several types of hemocytes and melanization activity, which are critical defenses against parasitic Hymenoptera and microbial pathogens. In terms of T. ni humoral immunity, only the antimicrobial peptide (AMP) genes lebocin and gallerimycin were significantly upregulated in caterpillars fed on diets containing high levels of 4MSOB-ITC relative to caterpillars that were provided with ITC-free diet. Surprisingly, challenging caterpillars with a non-pathogenic strain of Escherichia coli resulted in the upregulation of the AMP gene cecropin. Feeding on high concentrations of plant toxins hindered caterpillar development and decreased cellular immunity but conferred mixed effects on humoral immunity. Our findings provide novel insights into the effects of herbivore diet composition on insect performance demonstrating the role of specific plant defense toxins that shape herbivore immunity and trophic interactions.

opencc-zeroJul 2023View details →

Parasitism rate differs between herbivore generations in the univoltine, but not bivoltine, range

With climate change, plant-feeding insects might increase their number of annual generations (voltinism). However, to what degree the emergence of a new herbivore generation affects the parasitism rate has not been explored. We performed a field experiment to test whether the parasitism rate differs between the first and the second generation of a specialist leaf miner (Tischeria ekebladella), both in the naturally univoltine and bivoltine parts of the leaf miner's distribution. We found an interactive effect between herbivore generation and geographical range on the parasitism rate. The parasitism rate was higher in the first compared to the second host generation in the part of the range that is naturally univoltine, whereas it did not differ between generations in the bivoltine range. Our experiment highlights that shifts in herbivore voltinism might release top-down control, with major consequences for natural and applied systems.

opencc-zeroAug 2023View details →

Rotational grazing with cattle-free zones supports the coexistence of cattle and wild herbivores in African rangelands

African wildlife populations are declining at an alarming rate. To stop further population declines and restore ecosystems, more areas for wildlife are needed. Community-based conservation with wildlife-livestock coexistence in the vast rangelands of Africa presents a major opportunity. However, the efficacy of wildlife conservation in mixed land-use areas remains an outstanding question. To assess the ecological outcomes of land-sharing between regulated livestock herds and wildlife populations in African savannas, we test how rotational cattle grazing affects spatiotemporal dynamics of 15 large herbivore species in the Maasai Mara, Kenya. First, we tested how wild herbivore distributions across the Greater Mara Ecosystem (the Mara, ~2,600 km2) are related to cattle density and environmental variables using 584,561 observations of wild herbivores (ecosystem scale). In a second analysis, we tested how rotational cattle grazing affects wild herbivore distributions in a 300 km2 subsection of the Mara using 30,583 observations (landscape scale). Finally, we tested how functional traits of wild herbivores affect species-level spatiotemporal responses to cattle grazing. At the ecosystem scale, the presence of five wild herbivore species was positively correlated with cattle density, while cattle effects on wild herbivore abundances were species-dependent with both increases and decreases. At the landscape scale, rotational cattle grazing strongly impacted the spatiotemporal habitat selection of wild herbivores, resulting in distinct lag periods with which different species are attracted to areas previously grazed by cattle. These lag periods were linked to functional traits, with body mass and herd size explaining 35% of the interspecific differences. Small to medium-sized herbivores with large herds select areas recently grazed by cattle, whereas large species with large herd sizes and small species with small herd sizes avoid recently grazed areas. Synthesis and applications Our results revealed that the effect of cattle on wild herbivores varies considerably among species, suggesting that cattle-wildlife interactions range from facilitation to competition. To maintain species that strongly avoid cattle, designated livestock-free zones remain essential, also in rotational grazing systems. Rotational grazing systems with regulated livestock densities present an important opportunity to better manage wildlife-livestock coexistence and thus improve wildlife conservation in African rangelands.

opencc-zeroAug 2023View details →

Performance and preference of four above- and below-ground invertebrate and generalist herbivores on regionally and locally rare plant species

<ol> <li>Rare plant species are suggested to be less resistant to herbivores than common species. Their lower apparency and the fact that they often live in isolated populations, resulting in fewer herbivore encounters, might have led to the evolution of reduced defences. Moreover, their frequently lower levels of genetic diversity compared with common species could negatively affect their resistance against enemies. However, the hypothesis that plant resistance depends on plant regional and local rarity, independently of habitat and competitive and growth strategy, lacks evidence.</li> <li>To test this hypothesis, we assessed the performance and preference of one belowground and three aboveground generalist invertebrate herbivores from different taxonomic groups as indicators of plant resistance. Herbivores were fed a total of 62 regionally and locally rare and common plant species from Switzerland. We accounted for differences in a plant's growth and competitive strategy and habitat resource availability.</li> <li>We found that regionally and locally rare and common plant species did not generally differ in their resistance to most generalist herbivores. However, one herbivore species even performed better and preferred locally and regionally common plant species over rarer ones, indicating that common species are not more resistant, but tend to be less resistant. We also found that all herbivore species consistently performed better on competitive and large plant species, although different herbivore species generally preferred and performed better on different plant species. The latter indicates that the use of generalist herbivores as indicators of plant-resistance levels can be misleading.</li> <li> Synthesis: Our results show that rare plant species are not inherently less resistant than common ones to herbivores. Instead, our results suggest that the ability of plants to allocate resources away from defence towards enhancing their competitive ability might have allowed plants to tolerate herbivory, and to become locally and regionally common.</li> </ol>

opencc-zeroAug 2023View details →

Functional identity of dominant species in a predator community prevails over functional diversity in shaping the top-down control of herbivores

<ol> <li>Decline in species richness as well as changes in community evenness or functional diversity have been hypothesized to jointly affect ecosystem functioning. However, disentangling the relative effects of these changes in community structure is hard as these different aspects often covary with species richness in real-world ecosystems. In this study, we investigated the individual and interactive effects of functional diversity and community evenness of predators on the level of control of herbivorous prey. </li> <li>Using a highly-replicated mesocosm experiment, we crossed three levels of functional diversity of arthropod predators with two levels of community evenness while controlling for the effect of species richness. Using this experimental setting, we hypothesized that the effect size of functional diversity of predators depends on community evenness. We expected a positive effect of functional diversity of predators on top-down control at a high level of community evenness while we thought that species identity and their associated traits should drive most of the effect on top-down control at a low level of community evenness. </li> <li>Our results did not provide any evidence for an interaction between functional diversity and community evenness nor any beneficial effect of increased functional diversity overall on predation rates of herbivorous prey. In addition, our results revealed that species and functional identity drives most of the effects of predator community composition on top-down control of their prey in our study system. Assemblages composed of active hunters with low handling time and no starvation ability tended to have the highest impacts on prey biomass.</li> <li>By indicating that top-down control of herbivorous prey by arthropod predators is mainly driven by species and functional identity and not by functional diversity, our study provides insights into the consequences of ongoing species loss on ecosystem functioning. Future research should now explore the predictability of trophic interactions based on functional traits of predator and herbivorous prey to anticipate the consequences of changes in species composition on ecosystem functioning.</li> </ol>