Many regard the concentrations of nitrogen (N), tannins and plant cell wall constituents (fibre) as key indicators of food quality and habitat suitability for browsing herbivores; yet there is no ...method for measuring their combined effects. We have developed a simple in vitro assay for measuring the effects of tannins and fibre on N availability in browse. We determined the effects of tannins by measuring the polyethylene glycol (PEG)-binding capacity (PEG-BC) of Eucalyptus leaf samples, followed by a two-stage in vitro digestion with pepsin and cellulase to determine the digestibility of dry matter and N. There was a significant relationship between concentrations of digestible N and the PEG-BC of the leaves. Furthermore, adding PEG significantly improved the digestibility of N. Our results concur with in vivo observations from several mammalian species. This suggests that our method is effective for measuring the nutritional quality of browse and the benefits of adding PEG, providing some index of the detrimental effects of tannins. We further simplified the assay by removing the PEG step, allowing us to quickly analyse samples in bulk. Nevertheless, this simplified method is still not practical for analysing the many samples necessary to compare the nutritional values of different tracts of forest. We used near-infrared reflectance spectroscopy to produce calibration equations and predicted total and digestible N in 322 trees at eleven sites. Both within and between sites, we found a wide variation in concentrations of digestible N but a much lower variation in total N, with either no relationship or poor relationships between the two measures. This confirms the variability in the nutritional quality of eucalypt forests, which may explain the distribution and abundance of mammalian herbivores. Thus, our assay provides a useful tool for understanding how food resources influence herbivore populations at different scales.
In this Frontiers topic, we explore how the functions and fates of plant silicon interact with other organisms and ecosystem processes. By bringing together new data from multiple disciplines and ...scales, we present a cross-section of novel explorations into how plants use silicon and the implications for agriculture and ecosystems. Key aims in this field are to understand the determinants of plant silicon uptake and cycling, and the benefits that silicon uptake confers on plants, including reducing the impacts of stresses such as herbivory. Current research explores inter-specific interactions, including co-evolutionary relationships between plant silicon and animals, particularly morphological adaptations, behavioural responses and the potential for plant silicon to regulate mammal populations. Another emerging area of research is understanding silicon fluxes in soils and vegetation communities and scaling this up to better understand the global silicon cycle. New methods for measuring plant silicon are contributing to progress in this field. Silicon could help plants mitigate some effects of climate change through alleviation of biotic and abiotic stress and silicon is a component of some carbon sinks. Therefore, understanding the role of plant silicon across ecological, agricultural and biogeochemical disciplines is increasingly important in the context of global environmental change.
Estimating the nutritional value of a herbivore's diet is difficult because it requires knowing what the animal eats, the relative quality of each component and how these components interact in ...relation to animal physiology. Current methods are cumbersome and rely on many assumptions that are hard to evaluate. We describe a new method for estimating relative diet quality directly from faeces that avoids the problems inherent in other methods. We combine this method with near infrared reflectance spectroscopy (NIRS) to analyse many samples and thus provide a technique with immense value in ecological studies. The method stems from the correlation between the concentrations of dietary and faecal nitrogen in herbivores eating a tannin-free diet, but a weaker relationship in browsers that ingest substantial amounts of tannins, which form complexes with proteins. These complexes reduce the availability of nitrogen and may increase faecal nitrogen concentrations. Using the tannin-binding compound, polyethylene glycol, we showed that tannin-bound nitrogen is a significant and variable part of faecal nitrogen in wild common brushtail possums (Trichosurus vulpecula). We developed a technique to measure faecal available nitrogen and found that it predicted the reproductive success of female brushtail possums in northern Australia. Faecal available nitrogen combined with NIRS provides a powerful tool for estimating the relative nutritional value of the diets of browsing herbivores in many ecological systems. It is a better indicator of diet quality than other commonly used single-nutrient measures such as faecal nitrogen and foliage analysis paired with observed feeding behaviour.
1. Grazing has been implicated in the decline of heather-dominated moorlands in Britain, but there has been little consideration of the effects of different species of herbivores on plant diversity. ...Sheep stocks have recently decreased in Scotland, and quantification of how this affects biodiversity is essential for understanding how different grazing regimes modify upland habitats. 2. We investigated the effects of grazing on plant biodiversity in heather/grass mosaics at 16 upland sites in Scotland. Red deer Cervus elaphus L. were present at all sites, but sheep Ovis aries L. had been removed from half of the sites. Our experimental design incorporated replication at three spatial scales, from a landscape level down to 10 × 10 m plots. 3. We quantified the relative effects of different herbivore species, vegetation structure and rainfall on heather utilisation, species richness and evenness (alpha diversity; Shannon-Wiener index) and beta diversity. 4. At all spatial scales, deer dung counts were higher and heather was shorter when sheep were absent. Furthermore, utilisation of heather was positively correlated with the amount of deer dung, the amount of grass present and smooth grass height. 5. Alpha diversity was consistently positively correlated with the relative amount of grass, but was also positively related to the amount of sheep dung at the largest spatial scale. At the finest scale, alpha diversity was negatively correlated with the amount of deer dung. Beta diversity was higher when sheep were present at all scales. 6. Synthesis and applications. Mixed grazing by sheep and deer appears to be beneficial for increasing both alpha and beta diversity and minimizing damage to heather in the uplands. The absence of sheep is likely to result in expanding deer populations and greater impact on heather. Management of grazing herbivores is an important tool for maintaining biodiversity in many ecosystems. Our results indicate that reducing livestock may alter the impacts of wild grazers on their habitats and drive changes in diversity, whereas mixed grazing can enhance habitat quality and maintain plant diversity. Therefore, this effect should be considered when devising policy recommendations.
The ecology, diversity, and parasitoid complex of plant–sap feeding insects of the family Homotomidae (Hemiptera: Psylloidea) specialised on fig trees (Ficus) have so far received little research ...attention. They are ecologically important, however, as occasional outbreaks of the homotomid Mycopsylla fici may cause complete defoliation of its host plant, the Moreton Bay fig (Ficus macrophylla). Mycopsylla proxima, the only other species reported from Australia, feeds on F. rubiginosa without any recorded outbreaks.
We searched for homotomids and their parasitoids on eight Ficus species on the east coast of Australia, Lord Howe Island (LHI), and in Auckland, New Zealand, and detected them on three Ficus species. Using mitochondrial and nuclear DNA sequences, we delimited three Mycopsylla species, including a putative new species on F. watkinsiana. We also characterised six (including one previously described) parasitoid species of the genus Psyllaephagus (Hymenoptera: Encyrtidae) based on congruent morphological characters and molecular data.
Each of the homotomid species was highly host specific to a single fig species, whereas parasitoid species varied in host specificity: three host specific to M. fici and three host generalists. Geographic distribution varied among parasitoid species; e.g. one host‐specific species was found on both the mainland and LHI, but a second species only on LHI.
Our study revealed previously unrecognised diversity in fig homotomids and especially in their parasitoids. The herbivores and parasitoids showed contrasting patterns of host specificity. Interestingly, M. fici, the only outbreak species, had the highest diversity of associated parasitoid species and was the only species with host‐specific parasitoids.
Self-Medication: A Learning Process? [with Response] MOORE, BEN D.; FOLEY, WILLIAM J.; FORBEY, JENNIFER S. ...
Science (American Association for the Advancement of Science),
05/2013, Volume:
340, Issue:
6136
Journal Article
Plant secondary metabolites (PSMs) strongly influence diet selection by mammalian herbivores. Concentrations of PSMs vary within and among plant species, and across landscapes. Therefore, local ...adaptations may cause different populations of herbivores to differ in their ability to tolerate PSMs. Here, we tested the food intake responses of three populations of a marsupial folivore, the common brushtail possum (Trichosurus vulpecula Kerr), from different latitudes and habitat types, to four types of PSMs. We found clear variation in the responses of northern and southern Australian possums to PSMs. Brushtail possums from southern Australia showed marked decreases in food intake in response to all four PSMs, while the two populations from northern Australia were not as sensitive and their responses did not differ from one another. These results were unexpected, based on our understanding of the experiences of these populations with PSMs in the wild. Our results suggest that geographically separated populations of possums may have evolved differing abilities to cope with PSMs, as a result of local adaptation to their natural environments. Our results provide the basis for future studies to investigate the mechanisms by which populations of mammalian species differ in their ability to tolerate PSMs.
IntroductionSince Fraenkel (1959) proposed a leading role for plant secondary metabolites (PSMs) in the interactions between plants and herbivores, science has achieved broad insight into the ...diversity of PSMs and herbivores’ counter-adaptations to them (Freeland & Janzen, 1974; Foley et al., 1999; Foley & Moore, 2005). However, the more we learn about the distributions and functions of PSMs in natural systems, the sharper the limitations of our understanding become. In countless plant–herbivore interactions, ecologists have identified PSMs that act as feeding deterrents, toxins, digestibility reducers, feeding or oviposition cues, and signals for communicating to neighbouring plants and natural enemies of herbivores. However, most studies focus on the interaction between single species of herbivore and plant, usually with observations of captive animals fed diets containing PSMs under highly simplified conditions. Although such approaches are a necessary first step in isolating and characterising the actions of PSMs, they greatly oversimplify the complex interactions that occur between wild herbivores and plants. The next challenge for ecologists is to ‘scale up’ the roles of PSMs in plant–herbivore interactions, as we understand them from controlled experiments at small temporal scales, to predict ecological interactions at greater temporal and spatial extents.A captive herbivore may commonly eat less as PSM concentrations in its food increase, but can this predict the foraging decisions of a wild animal within its home range, or, ultimately the distributions and abundances of plant and herbivore species and genotypes? Scaling up has an obvious spatial component, because wild animals forage more extensively than do captive animals, but it also has a temporal component. Experiments usually describe plant–herbivore interactions over very short time intervals, but in nature they are continuous and the effects of PSMs can be long-lasting (Cheeke, 1998). Animal feeding preferences are dynamic and often change with season or reproductive state, or through the ongoing process of refinement of conditioned flavour aversions (Provenza, 1996). With increasing spatial extent and finer spatial grain size comes greater complexity in the interactions between plants and animals; PSMs are rarely distributed evenly throughout landscapes, and understanding how this influences plant–animal interactions requires approaches adopted from resource ecology, foraging theory and spatial ecology and often an extensive, high-resolution picture of the foodscapes within which animals forage (van Langevelde & Prins, 2008).
PDF
