Herbivore Guilds Research Articles

New ages of the world's largest-ever marsupial: Diprotodon optatum from Pleistocene Australia

The extinction of large-bodied terrestrial ‘megafauna’ during earlier phases of the Quaternary had a significant impact on the transforming structure of ecosystems. However, the causes of such losses remains difficult to determine in part because of a paucity of reliable geochronological information about the taxa involved. This is especially true for continents such as Australia where the majority of extinct species have never been dated using radiometric and/or luminescence methods. Here we add new understanding about the geochronology of the world's largest-ever marsupial, the giant wombat-like Diprotodon optatum, an iconic member of the large herbivore guild of Pleistocene Australia. We present 28 new direct U-series ages (dentine) and 10 luminescence ages (sediments) for D. optatum fossils from three sites in tropical north and subtropical eastern Australia. The luminescence ages lie close to saturation for the tropical northern site of Floraville and therefore indicate minimum ages, and sediments from Gowrie Creek in the Darling Downs were mixed and can only be stated as a likely age range. Nevertheless the results assist in our broader understanding of the timing of persistence of the species. Our results demonstrate that the species roamed the northern tropics at least until the mid-Pleistocene (ca. 420 ka). They likely remained widespread during Marine Isotope Stage 5 (ca. 110 ka) and were abundant on the Darling Downs of eastern Australia. The youngest of the new ages that we report (ca. 60 ka) are from Neds Gully on the Darling Downs, a catchment previously considered by some to contain among the last survivors of the now-extinct megafauna. The new dated record demonstrates that deposits of varying ages occur within the catchment. Consequently, existing species lists that treat Neds Gully as a single faunal assemblage are likely significantly time-averaged and overinflated in terms of palaeo-diversity.

Importance of the chemical defenses and sugars in the feeding preference of Paracentrotus lividus over two sympatric template seagrass species

Herbivory is a fundamental process regulating the functioning of the ecosystems both in land and marine systems. Few decades ago, herbivory was thought to play only a minor role in seagrass dominated areas, while currently its importance has risen. However, the complex interrelationships between seagrasses and their consumers are not yet fully understood. For instance, seagrasses can tune up morphological, biomechanical, nutritional, and chemical traits in order to reduce the palatability of their leaves and therefore curtail tissue losses, but the final tradeoff of such changes may depend on herbivore guilds. This work focuses on the relative importance of nutritional versus chemical traits in the feeding behavior of the sea urchin Paracentrotus lividus, a temperate generalist mesograzer, over two sympatric seagrass species (Cymodocea nodosa and Zostera noltei). To do that, a set of no-choice and multiple-choice feeding assays were conducted using freeze-dried plants agar-based diets (i.e. whole nutritional properties), polar extracts of both species (i.e. soluble sugars and phenolic natural products), purified phenolic natural products, and also three different concentrations of soluble sugars. Later, a chemical identification and quantification of the phenolic natural products present in the extracts were performed to assess their ecological role as deterrents. Results clearly indicated that the feeding behavior of this generalist herbivore, once overlooked the structural, morphological and biomechanical traits, is mainly determined by nutritional properties, while the presence of phenolic compounds has only a minimal effect on its feeding behavior. In addition, although this study showed that sugars had a positive effect over P. lividus consumption rates, we demonstrated for the first time the deterrent properties of rosmarinic acid and the sulphated flavonoids produced by Z. noltei, which were able to reduce the attractive effect of sugars in the feeding preference of this generalist herbivore.

Niche partitioning shaped herbivore macroevolution through the early Mesozoic

The Triassic (252–201 Ma) marks a major punctuation in Earth history, when ecosystems rebuilt themselves following the devastating Permian-Triassic mass extinction. Herbivory evolved independently several times as ecosystems comprising diverse assemblages of therapsids, parareptiles and archosauromorphs rose and fell, leading to a world dominated by dinosaurs. It was assumed that dinosaurs prevailed either through long-term competitive replacement of the incumbent clades or rapidly and opportunistically following one or more extinction events. Here we use functional morphology and ecology to explore herbivore morphospace through the Triassic and Early Jurassic. We identify five main herbivore guilds (ingestion generalists, prehension specialists, durophagous specialists, shearing pulpers, and heavy oral processors), and find that herbivore clades generally avoided competition by almost exclusively occupying different guilds. Major ecosystem remodelling was triggered multiple times by external environmental challenges, and previously dominant herbivores were marginalised by newly emerging forms. Dinosaur dominance was a mix of opportunity following disaster, combined with competitive advantage in their new world.

Isotopic Niche Segregation among Darwin’s Finches on Santa Cruz Island, Galápagos

Darwin’s finches are a classic example of adaptive radiation involving differential use of dietary resources among sympatric species. Here, we apply stable isotope (δ13C, δ15N, and δ2H) analyses of feathers to examine ecological segregation among eight Darwin’s finch species in Santa Cruz Island, Galápagos collected from live birds and museum specimens (1962–2019). We found that δ13C values were higher for the granivorous and herbivorous foraging guilds, and lower for the insectivorous finches. Values of δ15N were similar among foraging guilds but values of δ2H were higher for insectivores, followed by granivores, and lowest for herbivores. The herbivorous guild generally occupied the largest isotopic standard ellipse areas for all isotopic combinations and the insectivorous guild the smallest. Values of δ2H provided better trophic discrimination than those of δ15N possibly due to confounding influences of agricultural inputs of nitrogen. Segregation among guilds was enhanced by portraying guilds in three-dimensional isotope (δ13C, δ15N, and δ2H) space. Values of δ13C and δ15N were higher for feathers of museum specimens than for live birds. We provide evidence that Darwin’s finches on Santa Cruz Island tend to be generalists with overlapping isotopic niches and suggest that dietary overlap may also be more considerable than previously thought.

Side Effects of Insecticides on Leaf-Miners and Gall-Inducers Depend on Species Ecological Traits and Competition with Leaf-Chewers.

Internal feeding is considered to shield sessile herbivorous insects from exposure to nonsystemic insecticides aerially sprayed against forest defoliators, although this has not been tested. It is, however, established that leaf damage caused by defoliators affects the survivorship and oviposition behavior of sessile herbivores. Thus feeding ecology and competition may mediate nontarget effects of insecticides on these insects. We tested the ecological sensitivity of 3 guilds of sessile herbivores (upper-surface leaf-miners, lower-surface leaf-miners, and gall-inducers) to the lipophilic larvicides diflubenzuron and tebufenozide aerially applied either at operational rates (12 g active ingredient [a.i.]/ha and 69.6 g [a.i.]/ha, respectively) or at maximum legal rates (60 g [a.i.]/ha and 180 g [a.i.]/ha, respectively), in German oak forests. Diflubenzuron affected leaf-miners at different life stages depending on their position on the leaf but had no effect on gall-inducers. Tebufenozide showed a similar, but not significant, pattern in leaf-miners and did not affect gall-inducers. By reducing the incidence of chewing damage on leaves, both insecticides offset the negative effect of competition on leaf-miner and gall-inducers. The net outcome of insecticide treatment was positive for guilds avoiding exposure, but negative for upper-surface leaf-miners. Exposure to insecticides in situ can be mediated by subtle differences in species biology and species interactions, with potential implications for organisms usually considered safe in risk assessment studies. Environ Toxicol Chem 2021;00:1-17. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Wild and domestic savanna herbivores increase smaller vertebrate diversity, but less than additively

Abstract Cattle and other livestock graze more than a quarter of the world's terrestrial area and are widely regarded to be drivers of global biodiversity declines. Studies often compare the effects of livestock presence/absence but, to our knowledge, no studies have tested for interactive effects between large wild herbivores and livestock at varying stocking rates on small‐bodied wild vertebrates. We investigated the effects of cattle stocking rates (none/moderate/high) on the diversity of wildlife 0.05–1,000 kg using camera traps at a long‐term exclosure experiment within a semi‐arid savanna ecosystem in central Kenya. In addition, by selectively excluding wild ‘mesoherbivores’ (50–1,000 kg) and ‘megaherbivores’ (>1,000 kg; elephant and giraffe), we tested whether the presence of these two wild herbivore guilds (collectively, ‘larger wild herbivores’) mediates the effect of cattle stocking rate on habitat use and diversity of ‘smaller wildlife’ (mammals ranging between 10 and 70 cm shoulder height and birds). Our results show that cattle enhance alpha diversity of smaller wildlife (with or without larger wild herbivore presence) and of all wildlife 0.05–1,000 kg (with or without megaherbivore presence), by altering vegetation structure. However, for smaller wildlife, this effect is less pronounced in the presence of larger wild herbivores, which also shorten grass. In the absence of cattle, mesoherbivore‐accessible sites showed higher alpha diversity of smaller wildlife than sites excluding mesoherbivores. Smaller wildlife habitat use was increased by high cattle stocking rates and wild mesoherbivores more in the presence of the other. Synthesis and applications. Our findings imply that grazing, whether by livestock or wildlife, can enhance local savanna wildlife diversity. The biodiversity benefits of localised increases in herbivory are likely to be due to shortened grass and associated visibility improvements (for predator avoidance/foraging). This suggests that land managers can increase local biodiversity by shortening grass, with wild or domestic herbivores (or both), at least in patches within a taller grass matrix.

The Pleistocene lion Panthera spelaea (Goldfuss, 1810) from Poland – A review

Panthera spelaea was recorded in Poland from 18 open-air and 42 cave sites dated in the range 750–28 ka. Most of these records are located in southern Poland (Silesia) and neighbouring areas. Among them, the find of Panthera spelaea in Kozi Grzbiet mentioned here for the first time is one of the oldest European records of the species. Most of the obtained AMS dates are concentrated on the second half of MIS 3 and showed that the Pleistocene lion disappeared more or less synchronously across Poland. The findings of its remains from open-air sites are mostly accidental discoveries during field works, while those in caves are mostly connected with archaeological research and the exploitation of cave sediments for producing fertilizers.Aside of a few juvenile bones and milk teeth, the remains of adult individuals, mostly males, predominate in the studied sample. Their behavior to hunting cave bear during the times, when the other, more typical food sources were scarce, tendention to hunt very big preys and went into the conflicts with other carnivores than females do, resulted in higher injuries and mortalities. Within the species, three chronosubspecies were recognized, with P. s. fossilis recorded from 7 sites, dated between 750 and 240 ka and P. s. intermedia only partially recognized in Wierzchowska Górna Cave. The most numerous are the remains of P. s. spelaea which were found in 48 localities dated between 150 and 28 ka. With the exception of four caves, the Polish finds of P. spelaea are generally less abundant at sites where they occur. Older P. s. fossilis, dated on MIS 19–12, was a large form with robust stature and broad cheek teeth. Younger P. s. fossilis dated on MIS 11–9 was represented by a large and massive specimens, but with more advanced morphological dental features. Polish individuals of P. s. spelaea were slightly smaller and less massive than P. s. fossilis, with narrower cheek teeth. Since MIS 3, a dwarf and gracile specimens appeared, which is correlated with the genetic turnover ca. 48–45 ka.The Pleistocene lion was one of the earliest disappeared large carnivores predated only by a cave hyena. There are no direct evidences of P. spelaea encounters with humans. The extinction of P. spelaea is broadly correlated with the general collapse of the “mammoth steppe” ecosystem and was resulted of multiple reasons like climatic changes, re-building of herbivore guilds, competition and human pressure. Wolf and, to a lesser extent, bears were the main competitors for the Pleistocene lion in Poland.

Work that body: fin and body movements determine herbivore feeding performance within the natural reef environment.

Herbivorous fishes form a keystone component of reef ecosystems, yet the functional mechanisms underlying their feeding performance are poorly understood. In water, gravity is counter-balanced by buoyancy, hence fish are recoiled backwards after every bite they take from the substrate. To overcome this recoil and maintain contact with the algae covered substrate, fish need to generate thrust while feeding. However, the locomotory performance of reef herbivores in the context of feeding has hitherto been ignored. We used a three-dimensional high-speed video system to track mouth and body kinematics during in situ feeding strikes of fishes in the genus Zebrasoma, while synchronously recording the forces exerted on the substrate. These herbivores committed stereotypic and coordinated body and fin movements when feeding off the substrate and these movements determined algal biomass removed. Specifically, the speed of rapidly backing away from the substrate was associated with the magnitude of the pull force and the biomass of algae removed from the substrate per feeding bout. Our new framework for measuring biting performance in situ demonstrates that coordinated movements of the body and fins play a crucial role in herbivore foraging performance and may explain major axes of body and fin shape diversification across reef herbivore guilds.

Intermediate harvesting intensities enhance native tree performance of contrasting species while conserving herbivore diversity in a Patagonian woodland

Sustainable forest management should optimise the balance between tree productivity and biodiversity conservation. One strategy to achieve both is the use of native plantations in biomass extraction systems. However, it is unknown how different native tree species and their herbivores respond to a gradient of biomass extraction. In a Patagonian woodland, we planted six native tree species of high wood value and contrasting physiological traits, in plots with increasing harvesting intensities (HI: 0, 30, 50 or 70% of basal area removal), and measured herbivory rates, herbivore guild diversity, and sapling survival and growth. To understand whether herbivore diversity in non-planted wild species was affected by harvesting intensity, we performed the same herbivore measures in six wild woodland plant species. Herbivory rates and herbivore guild diversity showed similar responses to HI, being highest on saplings growing at 30% (N. dombeyi, N. antarctica, N. pumilio and N. alpina) or 30% and 50% (N. obliqua) HI. Deciduous tree species were consumed at a higher rate and held more diverse guilds, whereas evergreen species were consumed at a lower rate or barely damaged. Differences among species seem to be mostly driven by leaf habit and nitrogen content. In turn, higher HI increased the heterogeneity of arthropod guild composition, being N. alpina and N. pumilio the species with most variation in guild composition across HI. Contrariwise, regarding the non-planted wild woodland species, there was no effect of HI on herbivory rates or guild diversity. Finally, planted tree species survived and grew more at 30% and 50% HI despite supporting higher leaf damage, except for N. antarctica which showed a similar survival rate across all HI. Species with highest performance were A. chilensis and N. obliqua; but differences regarding plant performance among species were not explained by their physiological traits. Approximately one-third to mid harvesting intensities in this Patagonian woodland were optimal for enhancing native tree plantation performance and sustaining herbivore guild diversity. Additionally, harvesting intensities did not affect guild diversity on woodland plants. Hence, both lines of evidence suggest an enhancement of both native-wood production and biodiversity conservation. Our study constitutes one step forward in the development of novel sustainable woodland management practices, applicable to other regions worldwide.

What drives gallers and parasitoids interacting on a host plant? A network approach revealing morphological coupling as the main factor

1. Ecological interaction networks, those built from linking interacting species in a biological community, can be structured according to neutral factors, like abundance, or depend on species distribution in space, time, or functional aspects of interacting species.2. Gall inducers are a specialized guild of herbivores producing a structure serving as shelter, food, and defence against natural enemies. Interactions between galling insects and their parasitoids can become complex; studies analysing processes influencing how these interactions occur are uncommon.3. We tested for ecological processes predictive of network structure: neutral (abundance), temporal, or morphological coupling factors.4. We used a single host plant, and six Cecidomyiidae species from subtropical forests of southern Brazil. There were 14 samples across two years; out of 1762 galls, 741 parasitoids emerged (45 species). The network had high specialization (39 exclusive parasitoid species) and low connectance (21%).5. Gall‐parasitoid morphological coupling (gall thickness vs. parasitoid ovipositor length) was the best factor explaining network structure, with little effect for time, or abundances. Modularity was significant, with two modules, one with only Pisphondylia brasiliensis and its parasitoids. This insect induces thick multichambered galls with the lowest parasitism rate, attacked by parasitoids with longer ovipositors. Thinner galls had higher parasitism rates and more attacking parasitoid species, implying an important adaptive role for gall shape/size in natural enemy interactions.6. Interaction networks are important tools to help understand how ecological function impacts community structure, but higher‐scale studies may be needed to reach more encompassing conclusions about galler‐parasitoid interactions.

Are invertebrate herbivores of freshwater macrophytes scarce in tropical wetlands?

Abstract In this study we assessed the abundance and composition (taxa and feeding guilds) of invertebrate communities occurring on 11 aquatic plant species in Neotropical and Afrotropical wetlands. We tested the hypothesis that invertebrate herbivores form only a minor component of the invertebrate assemblages associated with freshwater macrophytes. The waterbodies experienced differing intensities of disturbance pressure (grazing, trampling, sediment disturbance) from large mammalian herbivores. General analysis of macrophyte samples collected during 2012–2013 from Zambia and Argentina showed that in Afrotropical wetlands invertebrate herbivores were significantly less abundant than non-herbivorous invertebrate taxa. In the Neotropical wetlands, the abundance of herbivorous and non-herbivorous invertebrate taxa did not differ significantly. Analysis per macrophyte species showed that invertebrate herbivores occurred in higher or similar abundance compared to non-herbivores in 83 % of macrophyte species in the Neotropics, but only in one macrophyte species in the Afrotropics. Taxa and feeding guilds of invertebrate herbivores varied between macrophyte species and ecozones, but were dominated by semiaquatic insects. TWINSPAN analysis of the plant samples hosting invertebrate morphospecies (n = 91) produced a sample-classification of four sample groups, with substantial differences in invertebrate morphospecies associated with each group of plant samples. The results show that invertebrate herbivores, mainly insects, are both numerically important and likely to form an important component of nutrient-cycling processes involving macrophyte biomass in warm-water wetlands. Whether the differences observed between the two ecozones are related to differences in large-herbivore presence, or to other inter-ecozone biogeographical differences in habitat conditions, or both, remains an issue for further research.

Novel co-occurrence of functionally redundant consumers induced by range expansion alters community structure.

Ongoing climate change is shifting the geographic distributions of some species, potentially imposing rapid changes in local community structure and ecosystem functioning. Besides changes in population-level interspecific interactions, such range shifts may also cause changes in functional structure within the host assemblages, which can result in losses or gains in ecosystem functions. Because consumer-resource dynamics are central to community regulation, functional reorganization driven by introduction of new consumer species can have large consequences on ecosystem functions. Here we experimentally examine the extent to which the recent poleward range expansion of the intertidal grazer limpet Scurria viridula along the coast of Chile has altered the role of the resident congeneric limpet S. zebrina, and whether the net collective impacts, and functional structure, of the entire herbivore guild have been modified by the introduction of this new member. We examined the functional role of Scurria species in controlling ephemeral algal cover, bare rock availability, and species richness and diversity, and compared the effects in the region of range overlap against their respective "native" abutted ranges. Experiments showed depression of per capita effects of the range-expanded species within the region of overlap, suggesting environmental conditions negatively affect individual performance. In contrast, effects of S. zebrina were commonly invariant at its range edge. When comparing single species versus polycultures, effects on bare rock cover were altered by the presence of the other Scurria species, suggesting competition between Scurria species. Importantly, although the magnitude of S. viridula effects at the range overlap was reduced, its addition to the herbivore guild seems to complement and intensify the role of the guild in reducing green algal cover, species richness and increasing bare space provision. Our study thus highlights that range expansion of an herbivore can modify the functional guild structure in the recipient community. It also highlights the complexity of predicting how functional structure may change in the face of natural or human-induced range expansions. There is a need for more field-based examination of regional functional compensation, complementarity, or inhibition before we can construct a conceptual framework to anticipate the consequences of species range expansions.

Shared Insights across the Ecology of Coral Reefs and African Savannas: Are Parrotfish Wet Wildebeest?

Abstract Comparison across terrestrial and aquatic ecosystems facilitates a broader understanding of ecological patterns. Although meta-analyses are important for quantitative synthesis across ecosystems, detailed comparisons of natural history and species interactions also illuminate convergence among systems. We compare the ecology of superficially dissimilar African savannas and coral reefs via shared characteristics including: (1) hyperdiverse guilds of large vertebrate herbivores and predators, (2) similar mechanisms driving positive feedback loops between herbivory and primary production, (3) similar roles of disturbance and herbivory in mediating ecosystem state, and (4) numerous smaller vertebrate and invertebrate species that underpin diversity and ecosystem processes. Our goal in comparing the natural history and ecology of these ecosystems is to facilitate others in finding their own comparative systems. We encourage scientists, especially early-career scientists, to explore ecosystems other than their primary focus. Whatever your ecosystem of study, examining the ecology of its analog in another environment may enliven your career.

Secondary foundation species foster novel plant–animal interactions in the forest canopy: evidence from mistletoe

Abstract Forest canopies provide the initial physical and biological framework to secondary, dependent species, such as parasitic plants. In a Mediterranean pine forest, we have taxonomically and functionally characterised the entire arthropod community that interacts with mistletoe during its flowering period. We hypothesise that a secondary foundation species such as mistletoe enhances the arthropod diversity and abundance, fostering novel plant–animal interactions in the canopy. Our results clearly show contrasting guilds of herbivores (highly specialised) and floral visitors (highly generalist) with markedly different taxonomic and ecological profiles, the latter determining the fruit set of the mistletoe. By acting as a secondary foundation species, mistletoe, during flowering, increases the diversity and abundance of newcomers in the pine canopy. New species attracted to the canopy include a specialised herbivore, Cacopsylla visci, and a diverse guild of floral visitors, including the orders Hymenoptera, Diptera, Hemiptera, and Lepidoptera. In conclusion, mistletoe creates conditions that support the co‐occurrence of functionally distinct organisms in the canopies, fostering pine forest biodiversity and complexity of ecological interactions.

Habitat Use by a Large Herbivore Guild in a Fenced South African Protected Area

In fenced protected areas with limited opportunities to disperse, resources and constraints vary in space and time, affecting herbivore behaviour. The distribution, availability and quality of resources, burnt areas, and potential inter-specific competition all play a role in sustaining populations of large sympatric African herbivores. We investigated the role of resources, constraints and interspecific relationships on habitat use by three ruminants – black and blue wildebeest (Connochaetes gnou, C. taurinus) and red hartebeest (Alcelaphus buselaphus), and a non-ruminant, plains zebra (Equus quagga), across seasons and in different landscape types in a South African reserve. Black wildebeest, blue wildebeest and red hartebeest preferred the open grassland landscape, with homogeneous vegetation, while zebra favoured the wooded grassland landscape, with more heterogeneous vegetation. Burnt areas and vegetation greenness were important for all species, while elevation represented a constraint for black wildebeest only. The presence/absence of other species was important in shaping landscape use for black and blue wildebeest, and this suggests the possibility of competition. Our findings confirm the importance of heterogeneity and, in particular, the important role of a planned burning regime in maintaining such heterogeneity to sustain multi-species herbivore assemblages in small fenced nature reserves, where competition might arise between species using similar resources.

Herbivory and anti-herbivore defences in wild and cultivated Cnidoscolus aconitifolius: disentangling domestication and environmental effects.

Phenotypic changes in plants during domestication may disrupt plant–herbivore interactions. Because wild and cultivated plants have different habitats and some anti-herbivore defences exhibit some plasticity, their defences may be also influenced by the environment. Our goal was to assess the effects of domestication and the environment on herbivory and some anti-herbivore defences in chaya (Cnidoscolus aconitifolius) in its centre of domestication. Herbivores, herbivory, and direct and indirect anti-herbivore defences were assessed in wild and cultivated plants. The same variables were measured in the field and in a common garden to assess environmental effects. Our results show that domestication increased herbivory and herbivore abundance, but reduced direct and some indirect defences (ants). The environment also affected the herbivore guild (herbivore abundance and richness) and some direct and indirect defences (trichome number and ants). There was also an interaction effect of domestication and the environment on the number of trichomes. We conclude that domestication and the environment influence herbivory and anti-herbivore defences in an additive and interactive manner in chaya.

Size-dependent vulnerability to herbivory in a coastal foundation species.

Ecologists have long wondered how plants and algae persist under constant herbivory, and studies have shown that factors like chemical defense and morphology can protect these species from consumption. However, grazers are also highly diverse and exert varying top-down control over primary producers depending on traits such as body size. Moreover, susceptibility of plants and algae to herbivory may vary across life stages and size classes, with juveniles potentially the most vulnerable. Here, we focus on diverse grazing communities within giant kelp forests and compared consumption on two size classes of juvenile giant kelp (Macrocystis pyrifera) across four herbivore species ranging in size. We also integrated field and literature densities to estimate impacts on populations of juvenile kelp. We found that purple sea urchins, a species known for exerting strong control over adult M. pyrifera, had weak per capita impact on microscopic kelp, on par with a much smaller crustacean species. While urchin consumption increased with macroscopic juvenile kelp, it never surpassed the smaller brown turban snail, suggesting that feeding morphology, in addition to herbivore body size, is a predictor of consumption at these smallsize classes. The smaller herbivores also occurred in high densities in the field, increasing their predicted population-level impacts on juvenile kelp compared to urchins and perhaps other larger, but less abundant, herbivores. This study highlights the variation in species' roles within an herbivore guild and the importance of age-related changes in grazing vulnerability to better understand herbivore control on plant and algae population dynamics.

Testing the effects of anthropogenic pressures on a diverse African herbivore community

AbstractLarge herbivore communities around the world have declined steeply in recent decades. Although excessive bushmeat harvesting is thought to be the primary cause of herbivore declines in many ecosystems, the direct effects of anthropogenic pressures on large herbivore populations remain poorly described in most of the systems experiencing decline. To test the extent to which large herbivores are impacted by ecological and anthropogenic factors in a protected area (PA) thought to be experiencing human‐caused decline, we fit distance sampling models to seven years of data from systematic ground‐based surveys in Kafue National Park (KNP) to estimate the population densities and distributions of 10 species of large herbivores, and to test what factors affect these parameters. Population densities of the ten most abundant large herbivores in KNP were substantially lower than those reported for an ecologically similar PA with less poaching pressure. Low densities were consistent across species and areas, though there was ecologically important variation among species and size classes. Densities of larger‐bodied herbivores were greatly depressed relative to smaller species. This pattern has direct and indirect effects on large carnivore populations, with broad implications for the ecotourism and trophy hunting industries. Statistically and methodologically rigorous methods to test the effects of anthropogenic and environmental variables on density and distribution exist, but are rarely applied to large herbivores. To quantify trends in herbivore populations and evaluate the effectiveness of conservation actions, our results show that distance sampling with stratified ground‐based monitoring is an efficient and effective method. In the Greater Kafue Ecosystem (GKE), continued increases in resource protection are needed to facilitate the recovery of an economically and ecologically important large herbivore guild. More broadly, our results confirm that anthropogenic effects on large herbivore distribution and abundance can be strong over wide areas for all species (particularly the larger members of the guild), even in very large PAs.

Pleistocene Arctic megafaunal ecological engineering as a natural climate solution?

Natural climate solutions (NCS) in the Arctic hold the potential to be implemented at a scale able to substantially affect the global climate. The strong feedbacks between carbon-rich permafrost, climate and herbivory suggest an NCS consisting of reverting the current wet/moist moss and shrub-dominated tundra and the sparse forest-tundra ecotone to grassland through a guild of large herbivores. Grassland-dominated systems might delay permafrost thaw and reduce carbon emissions-especially in Yedoma regions, while increasing carbon capture through increased productivity and grass and forb deep root systems. Here we review the environmental context of megafaunal ecological engineering in the Arctic; explore the mechanisms through which it can help mitigate climate change; and estimate its potential-based on bison and horse, with the aim of evaluating the feasibility of generating an ecosystem shift that is economically viable in terms of carbon benefits and of sufficient scale to play a significant role in global climate change mitigation. Assuming a megafaunal-driven ecosystem shift we find support for a megafauna-based arctic NCS yielding substantial income in carbon markets. However, scaling up such projects to have a significant effect on the global climate is challenging given the large number of animals required over a short period of time. A first-cut business plan is presented based on practical information-costs and infrastructure-from Pleistocene Park (northeastern Yakutia, Russia). A 10 yr experimental phase incorporating three separate introductions of herds of approximately 1000 individuals each is costed at US$114 million, with potential returns of approximately 0.3-0.4% yr-1 towards the end of the period, and greater than 1% yr-1 after it. Institutional friction and the potential role of new technologies in the reintroductions are discussed. This article is part of the theme issue 'Climate change and ecosystems: threats, opportunities and solutions'.

Comparing the plant–herbivore network topology of different insect guilds in Neotropical savannas

1. Herbivorous insects can be classified into several trophic guilds with different levels of specialisation on their host plants, which may influence the topological structure of their trophic networks. The present study tested the hypothesis that the structure of plant–herbivore networks differs between guilds of galling, sucking, and chewing insects.2. Six areas of Neotropical savannas were studied in two localities in the North of the state of Minas Gerais, Brazil. In each area, interactions between plant and insect species were used to build networks for different guilds.3. In total, 18 plant–herbivore networks were built, comprising 317 insect morphospecies, 50 plant species, and 489 distinct interactions. The networks were characterised using species richness and different network topological measures (connectance, modularity, nestedness, and specialisation).4. The results obtained showed no difference in species richness, network size, and connectance between distinct insect herbivore guilds. However, it was found that modularity was higher for exophagous than galling insect networks and nestedness was higher for chewers than for other guilds. On the other hand, galling insect networks showed higher specialisation than exophagous insect networks, and sucking insect networks were more specialised than chewing insect networks.5. The findings of the present study indicate that, although species richness did not differ between insect guilds of herbivores in Neotropical savannas, the topological structure of networks is sensitive to biological and ecological differences between these herbivore groups. The present study stands out as the first to systematically compare the network structure of different herbivore guilds in Neotropical savannas.