Negative frequency-dependent foraging behaviour in a generalist herbivore (Alces alces) and its stabilizing influence on food web dynamics.

Resource selection is widely appreciated to be context-dependent and shaped by both biological and abiotic factors. However, few studies have empirically assessed the extent to which selective foraging behaviour is dynamic and varies in response to environmental conditions for free-ranging animal populations. Here, we assessed the extent that forage selection fluctuated in response to different environmental conditions for a free-ranging herbivore, moose (Alces alces), in Isle Royale National Park, over a 10-year period. More precisely, we assessed how moose selection for coniferous versus deciduous forage in winter varied between geographic regions and in relation to (a) the relative frequency of forage types in the environment (e.g. frequency-dependent foraging behaviour), (b) moose abundance, (c) predation rate (by grey wolves) and (d) snow depth. These factors are potentially important for their influence on the energetics of foraging. We also built a series of food-chain models to assess the influence of dynamic foraging strategies on the stability of food webs. Our analysis indicates that moose exhibited negative frequency dependence, by selectively exploiting rare resources. Frequency-dependent foraging was further mediated by density-dependent processes, which are likely to be predation, moose abundance or some combination of both. In particular, frequency dependence was weaker in years when predation risk was high (i.e. when the ratio of moose to wolves was relatively low). Selection for conifers was also slightly weaker during deep snow years. The food-chain analysis indicates that the type of frequency-dependent foraging strategy exhibited by herbivores had important consequences for the stability of ecological communities. In particular, the dynamic foraging strategy that we observed in the empirical analysis (i.e. negative frequency dependence being mediated by density-dependent processes) was associated with more stable food web dynamics compared to fixed foraging strategies. The results of this study indicated that forage selection is a complex ecological process, varying in response to both biological (predation and moose density) and abiotic factors (snow depth) and over relatively small spatial scales (between regions). This study also provides a useful framework for assessing the influence of other aspects of foraging behaviour on the stability of food web dynamics.

Diet selectivity in a terrestrial forest invertebrate, the Auckland tree weta, across three habitat zones.

Insects are important but overlooked components of forest ecosystems in New Zealand. For many insect species, information on foraging patterns and trophic relationships is lacking. We examined diet composition and selectivity in a large-bodied insect, the Auckland tree weta Hemideina thoracica, in three habitat zones in a lowland New Zealand forest. We asked whether H. thoracica selectively forage from available plant food sources, and whether these choices were lipid-rich compared to nonpreferred available plants. We also identified the proportion of invertebrates in their frass as a proxy for omnivory. From reconnaissance plot sampling, together with fecal fragment analysis, we report that more than 93% of individual tree weta had eaten invertebrates before capture. Additionally, weta in the highest elevation hillslope habitat zone consumed significantly fewer species of plants on average than weta on the low-elevation terrace habitat. Upper hillslope weta also had the highest average number of invertebrate fragments in their frass, significantly more than weta in the low-elevation terrace habitat zone. Weta showed high variability in the consumption of fruit and seeds across all habitat zones. Generally, we did not observe diet differences between the sexes (although it appears that male weta in the mid-hillslope habitat ate fruits and seeds more voraciously than females), suggesting that the sexes have similar niche breadths and display similar degrees of omnivorous behavior. Extraction of leaf lipids demonstrated a range of lipid content values in available plants, and Ivlev's Electivity Index indicated that plant species which demonstrated high electivity tended to have higher concentrations of lipids in their leaves. Our findings indicate that H. thoracica forage omnivorously and selectively, and hence play multiple roles in native ecosystems and food webs.

Dieta del Suri, Rhea pennata (Orbigny, 1834) (Aves: Rheidae), en ecosistemas altoandinos de Moquegua, Perú

Se estudió la dieta del suri Rhea pennata en la región de Moquegua al sur de Perú, mediante el análisis de heces. Esta especie considerada en "Peligro Crítico" en el Perú se mostró como estrictamente herbívora, principalmente folívora. Se identificaron 44 morfoespecies de plantas en su dieta, de las cuales Oxychloe andina (una especie de Juncaceae dominante en bofedales disturbados) presentó los mayores valores relativos de densidad, peso, volumen y frecuencia. A pesar de la aparente selectividad, esta especie presenta una dieta muy diversa que le permitiría adaptarse a las carencias nutricionales en el hábitat que ocupa. Los datos obtenidos en diferentes hábitats que ocupa el Suri, muestran que en zonas más áridas existe la tendencia a una mayor selectividad debido a la presencia de plantas con compuestos secundarios (fenoles, terpenos y alcaloides) para evitar la herbivoría, mientras que en ambientes con bofedales (como el del presente estudio) la selectividad disminuye, tendiendo a alimentarse de las especies dominantes.

We study the Lesser Rhea (Rhea pennata) diet in the Moquegua region of southern Peru, using analysis of feces. This species considered "Critically Endangered" in Peru, was shown as strictly herbivorous, mainly folivorous. A total of 44 plant morphospecies were identified in the diet, of which Oxychloe andina (a Juncaceae species dominant in disturbed wetlands of the Puna) had the highest values of relative density, weight, volume and frequency. Despite the apparent selectivity, this species presents a very diverse diet that would allow it to adapt to the nutritional deficiencies in the habitat that it occupies. The data obtained in different habitats of the Lesser Rhea show that in more arid zones there is a tendency for greater selectivity due to the presence of plant with secondary compounds (phenols, terpenes and alkaloids) to avoid herbivory, while in environments with wetlands (as the present study) the selectivity decreases, tending to feed on the dominant species.

Nutrient and mineral composition during shoot growth in seven species of Phyllostachys and Pseudosasa bamboo consumed by giant panda.

During the annual period of bamboo shoot growth in spring, free-ranging giant pandas feed almost exclusively on the shoots while ignoring the leaves and full- height culm. Little is known about the nutritional changes that occur during bamboo shoot growth, if nutritional changes differ among species, or how these changes might influence forage selection. Our objective was to examine the nutrient and mineral composition during three phases of shoot growth (<60, 90-150 and >180 cm) for seven species of bamboo (Phyllostachys (P.) aurea, P. aureosulcata, P. bissetii, P. glauca, P. nuda, P. rubromarginata, Pseudosasa japonica) fed to captive giant pandas at the Memphis Zoo. Total dietary fiber content of bamboo shoots increased (p < 0.0001) from an overall species average of 61% dry matter (DM) at < 60 cm to 75% DM at shoot heights > 180 cm, while crude protein, fat and ash exhibited significant declines (p < 0.05). Phyllostachys nuda had the overall greatest (p = 0.007) crude protein (21% DM) and fat (4% DM) content, and lowest overall total fibre (61% DM) content compared to the other species examined. In contrast, Pseudosasa japonica had the overall lowest crude protein and fat, and relatively higher fibre content (9%, 3% and 74% respectively). Concentrations of Zn and Fe were highest in shoots <60 cm (10-50 µg/g DM) and decreased (p < 0.05) during growth in all species examined. Concentrations of Ca, Cu, Mn, Na and K varied among species and were largely unaffected by growth stage. Due to their higher concentrations of nutrients and lower fibre content in comparison to culm and leaf, bamboo shoots should be a major component of captive giant panda diets when available.

Faecal avoidance and selective foraging: do wild mice have the luxury to avoid faeces?

Host-parasite interactions are a key determinant of the population dynamics of wild animals, and behaviours that reduce parasite transmission and infection may be important for improving host fitness. While antiparasite behaviours have been demonstrated in laboratory animals and domesticated ungulates, whether these behaviours operate in the wild is poorly understood. Therefore, examining antiparasite behaviours in natural populations is crucial for understanding their ecological significance. In this study, we examined whether two wild rodents (white-footed mice, Peromyscus leucopus, and deer mice, Peromyscus maniculatus), selectively foraged away from conspecific faeces or avoided faeces altogether, and whether faecal gastrointestinal parasite status affected their behaviour. We also tested whether wild mice, when nesting, avoided using material that had previously been used by healthy or parasite-infected conspecifics. Our results, in contrast to laboratory mouse studies, suggest that wild mice do not demonstrate faecal avoidance, selective foraging or selective use of nesting material; they preferred being near faeces and did not differentiate between faeces from parasitized and uninfected conspecifics. Behavioural avoidance to reduce parasite infection may still represent an important strategy; however, mice in our study population appeared to favour the opportunity to feed and nest over the risks of coming into contact with faecal-transmitted parasites. Furthermore, the presence of conspecific faeces may actually provide a positive cue of a good foraging or nesting location. Ultimately, balancing the trade-off of performing antiparasite behaviours to reduce infection with missing an important feeding or nesting opportunity may be very different for animals in the wild facing complex and stochastic environments.