Testing of divergent patterns of butterfly niche breadth in a peninsula

The butterfly fauna on the Korean peninsula are comprised of both the Palearctic and Oriental species. We hypothesized that the Oriental species (immigrated across the sea) tend to have a wider niche breadth compared with the Palearctic species (immigrated from the continent) since the former migrates long distances across the sea and has to adapt to new environments. We tested this hypothesis using Korean butterfly data on distribution, habitat, food and life history traits. The distribution and ecological traits such as habitat breadth, overwintering stage, and voltinism of the Oriental species were found to be significantly different from the Palearctic species. However, the diet breadth and food plant type were not different. These results partly confirm the peninsula niche breadth hypothesis, which predicted that Oriental species have a broader niche breadth than Palearctic species.     

Forage selection by mule deer: does niche breadth increase with population density?

Effects of population density of mule deer Odocoileus hemionus on forage selection were investigated by comparing diet characteristics of two subpopulations of deer in southern California, USA, that differed in population density during winter. Quality of diet for deer, as indexed by faecal crude protein, was higher at the low-density site than at the high-density site in winter, when deer densities were different. Quality of diet was similar in summer when both areas had comparable densities of deer. Both outcomes are consistent with predictions from density-dependent selection of diets by deer. Dietary niche breadth, however, differed in a manner opposite to predictions of niche theory based on diet selection under an ideal-free distribution. During winter, when differences in density between the two study sites were pronounced, niche breadth along the dietary axis in the low-density area was twice that of the high-density site. Generalist herbivores feeding primarily on low-quality browse at high population density in winter would be expected to increase their dietary breadth by feeding on additional species of plants as they depleted their food supply. Mule deer in our study, however, decreased the breadth of their dietary niche as population density increased. We hypothesize that by rapidly eliminating high-quality forages from an area by heavy grazing, deer at higher population densities narrowed their dietary niche. Theoretical models for changes in niche dimensions, including the ideal-free distribution, need to consider such empirical outcomes.     

Variation of butterfly diet breadth in relation to host-plant predictability: results from two faunas

Host‐plant data for North American and Australian butterflies were used to test the hypothesis that larval diet breadth increases with decreasing resource predictability (where the latter was estimated by host‐plant growth‐form/duration). For each region in turn we compared the diet breadths of butterflies which utilise herbaceous host‐plants with those of species having woody hosts. For North America alone we also compared the diet breadths of species having annual hosts with those utilising perennial hosts, and the diets of species having herbaceous‐annual hosts with those using woody‐perennial hosts. Studies of diet breadth may be biased by the host taxonomic level which contributes most to the diet index used. For example, the results of analyses which employ indices based on numbers of families of hosts utilised may differ from those using indices based on counts of host species or genera. To investigate this potential problem we performed cross‐species analyses where diet breadth was defined in turn as the number of host species, genera, or families eaten. We found that using different taxonomic levels did give inconsistent results. To avoid this we employed phylogenetic diet breadth indices in comparative analyses of Independent Contrasts. The former incorporate information from the whole of the host‐plant phylogeny, whilst the comparative method eliminates any confounding effects of butterfly phylogeny. The results indicated that there is a phylogenetic component to butterfly diet breadth. They also largely differed from those of the cross‐species investigations, although there were similarities (i.e. results differed between regions and varied according to whether the whole fauna or just endemics were investigated). Our results suggested that in both regions, non‐endemics which feed on herbaceous plants have wider diet breadths than non‐endemics which utilise woody hosts. However, we found no consistent evidence that the diet breadths of endemics increase with decreasing resource predictability (as estimated here).     

黄土高原马栏林区主要植物种的生态位研究

应用L ev ins、Shannon-W iener生态位宽度公式和P ianka生态位重叠公式,定量研究了黄土高原马栏林区主要植物种的生态位宽度和生态位重叠特征,同时对主要种在演替系列上的生态位变化规律进行了分析.结果表明,在该地区森林群落演替系列中,乔木种生态位宽度的平均水平小于灌木种,建群种的生态位宽度小于主要伴生种;生态位宽度较大的种与其它各物种间生态位重叠的平均值较大,生态位宽度较小的种则相反,甚至没有重叠.由于物种生物生态学特性的不同和环境的异质性,具较宽生态位的物种间的生态位重叠也可能较小,生态位宽度较窄的物种间也可能有较大的生态位重叠,同属植物种对间也存在生态位重叠较大的情况.主要乔木和灌木种的生态位特征反映了森林群落演替的变化规律,该地区呈现出以自然恢复为主,同时又伴随着人为干扰的森林群落次生演替系列.     

民勤沙区几种荒漠植物群落的现实生态位研究

民勤沙区属于典型的干旱荒漠气候,植被以灌木荒漠为主,盖度一般只有5%~15%.植物群落内生态位宽度悬殊,植物种之间的生态位相似比例很小.生态位宽度和生态位相似比例小是受制于干旱荒漠生境条件的结果,是干旱荒漠生态环境中稀疏荒漠植物的主要特征之一.植物的现实生态位宽度与年际降水量关系密切,在地貌、土壤颗粒、土壤水分、土壤养分等影响因子中,土壤水分是主导因子.当地地下水位深20 m左右,植物无法利用,植物种之间对资源的竞争主要表现为对水分资源的竞争,降水资源是植物种之间竞争的关键资源.同一种植物在不同群落中的生态位宽度变幅较大,不同群落内部植物种竞争关系的差异是由物种的生态位和由相对稳定的地貌、土壤条件以及随年际变动的降水条件共同作用的结果.群落中的优势种植物的生态位最宽,当优势种生态位减小时,一年生短命植物往往会进入群落中.荒漠植物的冠层单一,以冠幅占样方面积比作为植物的特征值计算其生态位特征值比较准确可靠.     

Winter browsing of brown hares: evidence for diet breadth expansion

Foraging theory predicts that diet breadth should expand as food availability decreases. We tested this by looking at the winter browsing behaviour of the brown hare Lepus europaeus. We predicted selective feeding on different woody plant species, diet generalisation under increasingly severe winter conditions and a rank preference between the different food items. Following a period of severe winter conditions, we censused browsing marks of brown hares on woody plants at six sites situated at different altitudes (340 – 600 m a. s. l.) in Upper Franconia, Germany. We assumed that access to ground vegetation, which is the general diet of brown hares, was more restricted at sites with higher snow cover. The results provided support for all of our predictions: Feeding intensity varied strongly between the different plant species indicating selectivity of feeding. The number and also the percentage of browsed woody plant species was positively correlated with the altitude of the study site indicating a wider diet breadth in situations where less food was available. On the basis of a rank model on the food choice of brown hares, which was evaluated by an independent data set, we conclude that brown hares show a rank preference with regard to different groups of woody plant species. Our findings support the assumption that food restricted hares increasingly include unfavourable, low quality items into the diet.     

Plant functional traits reveal the relative contribution of habitat and food preferences to the diet of grasshoppers

Food preferences and food availability are two major determinants of the diet of generalist herbivores and of their spatial distribution. How do these factors interact and eventually lead to diet differentiation in co-occurring herbivores? We quantified the diet of four grasshopper species co-occurring in subalpine grasslands using DNA barcoding of the plants contained in the faeces of individuals sampled in the field. The food preferences of each grasshopper species were assessed by a choice (cafeteria) experiment from among 24 plant species common in five grassland plots, in which the four grasshoppers were collected, while the habitat was described by the relative abundance of plant species in the grassland plots. Plant species were characterised by their leaf economics spectrum (LES), quantifying their nutrient vs. structural tissue content. The grasshoppers’ diet, described by the mean LES of the plants eaten, could be explained by their plant preferences but not by the available plants in their habitat. The diet differed significantly across four grasshopper species pairs out of six, which validates food preferences assessed in standardised conditions as indicators for diet partitioning in nature. In contrast, variation of the functional diversity (FD) for LES in the diet was mostly correlated to the FD of the available plants in the habitat, suggesting that diet mixing depends on the environment and is not an intrinsic property of the grasshopper species. This study sheds light on the mechanisms determining the feeding niche of herbivores, showing that food preferences influence niche position whereas habitat diversity affects niche breadth.     

Population and individual polyphagy in the grasshopperTaeniopoda eques during natural foraging

Dietary patterns of free-foraging individuals of the polyphagous grasshopperTaeniopoda eques Burmeister (Romaleidae) were studied at three desert grassland sites in southern Arizona. At the population level this species was highly polyphagous at all sites, but showed evidence of selectivity in terms of frequency of feeding relative to frequency of contacts with resources. Most feeding bouts were very short, suggesting that most plants were relatively unpalatable. Both diet diversity and the mean length of feeding bouts varied among the study sites, primarily because highly preferred resources and plant tissues were not encountered with equal frequency at all sites. Individual insects were highly polyphagous. Dietary overlap calculations showed that insects at a given site generally consumed diets less similar than the resources they contacted. This result does not support the idea that all insects preferred the same subset of resources. Most differences in diet among individuals were probably due to environmental heterogeneity, but factors such as sequence of encounter, compensatory feeding on complementary resources, and intrinsic differences in preference may also have contributed to variation in diets.     

舟山群岛獐的食性研究

利用野外观察、粪便显微组织学分析和投喂实验等方法对舟山群岛獐的食性进行了研究。结果表明,研究地的獐所食植物共有137种,隶属于6l科l15属,其中豆科植物在取食种类和取食频次上均多于其它科植物。尽管獐对植物科和种的选择在四季间没有显著差别,但取食科和种的数量依然从春天到冬天呈递减趋势,并且冬天与其它3个季节差别较大。獐的食物中,每个季节都含有非禾草类草本植物、禾草类草本植物、木本植物和蕨类植物,且其食物组成在季节间亦无显著差异;除木本植物外,獐对其它3类植物的选择在季节间有显著差异。獐在冬天较多选择木本植物,而其它季节较多选择草本植物,但木本植物和非禾草类草本植物在四季食物组成中均占较高比例,而禾草类植物所占的比例很小。因此,笔者认为舟山群岛的獐应该偏向于嫩食者。     

Do body size and diet breadth affect partitioning of species diversity? A test with forest Lepidoptera

Two of the major themes resulting from recent macroecological research are the central roles that body size and niche breadth may play as determinants of species geographical distribution. Unanswered questions, however, linger regarding how similarities in body size or niche breadth affect the allocation of α‐ and β‐diversity across spatial scales. Using data on moth diversity in the eastern deciduous forest of North America, we tested the predictions that smaller‐bodied and diet‐restricted species would have lower levels of α‐diversity within forest stands and greater β‐diversity at higher sampling scales compared to larger or more generalist species. Moths were sampled using a nested sampling design consisting of three hierarchical levels: 20 forest stands, 5 sites and 3 ecoregions. Body size for 492 species was estimated as mean forewing length, and diet breadth was assessed from the published literature. Moth species were then classified according to body size (small or large) or diet breadth (generalist or restricted), and partitioning was conducted on each group. Diversity partitions for large‐ and small‐bodied species yielded similar patterns. When observed diversity components differed from those derived from our null model, a consistent pattern was observed: α‐diversity was greater than expected, β‐diversity among forest stands was less than expected, and β‐diversity among sites and ecoregions was higher than expected. In contrast, diet‐restricted moths contributed significantly less to stand‐level α‐diversity than generalist feeders. Furthermore, specialists contributed to a greater proportion of β‐diversity across scales compared to generalist moths. Because absolute measures of β‐diversity among stands were greater for generalists than for restricted feeders, we suggest that regional β‐diversity of forest moths may be influenced by several possible factors: intraspecific aggregation of diet‐restricted species, local fluctuations in population size of eruptive generalists and small geographical distributions of generalist moths than predicted by the geographical extent of putative host plants     

How do host plant use and seasonal life cycle relate to insect body size: A case study on European geometrid moths (Lepidoptera: Geometridae)

We used European geometrid moths (>630 species) as a model group to investigate how life history traits linked to larval host plant use (i.e., diet breadth and host-plant growth form) and seasonal life cycle (i.e., voltinism, overwintering stage and caterpillar phenology) are related to adult body size in holometabolous insect herbivores. To do so, we applied phylogenetic comparative methods to account for shared evolutionary history among herbivore species. We further categorized larval diet breadth based on the phylogenetic structure of utilized host plant genera. Our results indicate that species associated with woody plants are, on average, larger than herb feeders and increase in size with increasing diet breadth. Obligatorily univoltine species are larger than multivoltine species, and attain larger sizes when their larvae occur exclusively in the early season. Furthermore, the adult body size is significantly smaller in species that overwinter in the pupal stage compared to those that overwinter as eggs or caterpillars. In summary, our results indicate that the ecological niche of holometabolous insect herbivores is strongly interrelated with body size at maturity.     

HOW IS THE RATE OF CLIMATIC‐NICHE EVOLUTION RELATED TO CLIMATIC‐NICHE BREADTH?

The rate of climatic‐niche evolution is important to many research areas in ecology, evolution, and conservation biology, including responses of species to global climate change, spread of invasive species, speciation, biogeography, and patterns of species richness. Previous studies have implied that clades with higher rates of climatic‐niche evolution among species should have species with narrower niche breadths, but there is also evidence suggesting the opposite pattern. However, the relationships between rate and breadth have not been explicitly analyzed. Here, we examine the relationships between the rate of climatic‐niche evolution and climatic‐niche breadth using phylogenetic and climatic data for 250 species in the salamander family Plethodontidae, a group showing considerable variation in both rates of climatic‐niche evolution and climatic‐niche breadths. Contrary to some expectations, we find no general relationship between climatic‐niche breadth and the rate of climatic‐niche evolution. Climatic‐niche breadths for some ecologically important climatic variables considered separately (temperature seasonality and annual precipitation) do show significant relationships with the rate of climatic‐niche evolution, but rates are faster in clades in which species have broader (not narrower) niche breadths. In summary, our results show that narrower niche breadths are not necessarily associated with faster rates of niche evolution.     

Comparing macroecological patterns across continents: evolution of climatic niche breadth in varanid lizards

Macroecological analyses often test hypotheses at the global scale, or among more closely related species in a single region (e.g. continent). Here, we test several hypotheses about climatic niche widths among relatively closely related species that occur across multiple continents, and compare patterns within and across continents to see if they differ. We focus on the lizard genus Varanus (monitor lizards), which occurs in diverse environments in Africa, Asia, and Australia. We address three main questions. 1) How do climatic niche breadths of species on a given niche axis change based on the position of species along that niche axis? (E.g. are species that occur in more extreme environments more narrowly specialized for those conditions?) 2) Are there trade‐offs in niche breadths on temperature and precipitation axes among species, or are niche widths on different axes positively related? 3) Is variation in niche breadths among species explained primarily by within‐locality seasonal variation, or by differences in climatic conditions among localities across the species range? We generate a new time‐calibrated phylogeny for Varanus and test these hypotheses within and between continents using climatic data and phylogenetic methods. Our results show that patterns on each continent often parallel each other and global patterns. However, in many other cases, the strength of relationships can change dramatically among closely related species on different continents. Overall, we found that: 1) species in warmer environments have narrower temperature niche breadths, but there is no relationship between precipitation niche breadth and niche position; 2) temperature and precipitation niche breadths tend to be positively related among species, rather than showing trade‐offs; and 3) within‐locality seasonal variation explains most variation in climatic niche breadths. Some of these results are concordant with previous studies (in amphibians and North American lizards), and might represent general macroecological patterns.     

Diet and niche breadth variation in the marbled parrotfish,Leptoscarus vaigiensis,among coral reef sites in Kenya

Studies on feeding ecology of fishes are important for understanding ecosystem structure and function. This study tested the hypothesis of diet and niche breath variation in the marbled parrotfish (Leptoscarus vaigiensis) among coral reefs of different protection levels in Kenya. Fish samples were obtained from protected (Malindi and Watamu marine parks), moderately fished (Malindi and Watamu marine reserves) and highly fished (Vipingo and Kanamai) reefs. Total lengths of fish samples were measured and their stomach contents quantified using the point method. Seasonal dietary composition, niche breaths and feeding intensities were compared between the sites using multivariate statistics. Results showed the parrotfish is a predominantly reef macroalgal grazer. Fish from protected sites fed on diverse dietary items compared to those from reserves and highly fished sites. Fish niche breadths differed between sites and seasons. Higher niche breadths occurred in protected sites during the north‐east monsoon, while higher values occurred at fished sites during the south‐east monsoon season. This study, the first of its kind in Kenya and most of the western Indian Ocean, describes feeding in the marbled parrotfish and spatial variation in niche breadth as influenced by fishing pressure, environmental variability and biological interactions.     

Senescence‐feeders: a new trophic sub‐guild of insect herbivores

Herbivorous insects that have evolved to feed on senescing tissues of plants, or the phloem flowing from those tissues, comprise a distinct sub‐guild of the major trophic guilds, the senescence‐feeders. Some senescence‐feeders have evolved the capacity to accelerate the rate at which the tissues they feed on senesce, thus enhancing the quantity and quality of their food. Other species prolong their access to good food by feeding alternatively on both senescing and flushing tissues. Senescing plant tissues release a poorer quality food more slowly than the rapid inflow to new growth. As a result, senescence‐feeders grow more slowly than equivalent flush‐feeders. Any environmental stress of a plant that hastens its rate of senescence results in faster growth and higher survival of senescence‐feeders. Senescence‐feeders therefore succeed best on damaged or stressed plants and frequently reach outbreak levels on drought‐stressed trees. If the distinctive ecology of senescence‐feeders and the way in which they differ from flush‐feeders in their response to the condition of their host plants are to be recognized and understood, it is important to identify species that belong to this separate trophic sub‐guild. Such understanding is also necessary if attempts to control or manage their attacks on crops and forests are to succeed.     

Biogeography of the Primates of Guyana: Effects of Habitat Use and Diet on Geographic Distribution

Species that exploit a wide range of resources or habitats (generalists) tend to be widely distributed, whereas species that exploit a narrow range of resources or habitats (specialists) often have a limited distribution. The distribution patterns are thought to result from specialists using relatively smaller habitats than those exploited by generalists. I used data from 1,725 km of primate surveys that I conducted in Guyana to test these hypotheses. Habitat breadth is the total number of different habitat types occupied by each species. I used the total number of different food categories exploited by each species to measure dietary breadth. Geographic range size is correlated with habitat breadth but not with dietary breadth or body size for the 8 primate species in Guyana. Habitat generalists—red howlers and wedge-capped capuchins—range into all habitats. Habitat specialists—spider monkeys, brown bearded sakis, and golden-handed tamarins—range only into large habitats. Habitat generalists tend to be dietary type specialists in Guyana. I suggest that only habitat generalists can subsist on the low-quality foods in small habitats in Guyana. Conversely, habitat specialists tend to be dietary type generalists in Guyana. They must feed on a variety of food types in large habitats. However, using the number of food categories exploited as a measure of dietary breadth may be only a weak aspect of multidimensional niche. Researchers testing biogeographic hypotheses associated with dietary breadth should consider including multivariate indicators of both the types of food categories eaten and the number of plant species exploited.     

Discrimination of grasshopper (Orthoptera: Acrididae) diet and niche overlap using next‐generation sequencing of gut contents

Species of grasshopper have been divided into three diet classifications based on mandible morphology: forbivorous (specialist on forbs), graminivorous (specialist on grasses), and mixed feeding (broad‐scale generalists). For example, Melanoplus bivittatus and Dissosteira carolina are presumed to be broad‐scale generalists, Chortophaga viridifasciata is a specialist on grasses, and Melanoplus femurrubrum is a specialist on forbs. These classifications, however, have not been verified in the wild. Multiple specimens of these four species were collected, and diet analysis was performed using DNA metabarcoding of the gut contents. The rbcLa gene region was amplified and sequenced using Illumina MiSeq sequencing. Levins' measure and the Shannon–Wiener measure of niche breadth were calculated using family‐level identifications and Morisita's measure of niche overlap was calculated using operational taxonomic units (OTUs). Gut contents confirm both D. carolina and M. bivittatus as generalists and C. viridifasciata as a specialist on grasses. For M. femurrubrum, a high niche breadth was observed and species of grasses were identified in the gut as well as forbs. Niche overlap values did not follow predicted patterns, however, the low values suggest low competition between these species.     

Ontogenetic plasticity of food habits in the Mexican spiny-tailed iguana, Ctenosaura pectinata

Ontogenetic shifts from insect consumption by juveniles to plant consumption by adults are rare in the herbivorous lizard family Iguanidae. My investigations on diet and digestive tract anatomy of the iguanid lizard Ctenosaura pectinata show that this species has an ontogenetic diet shift. Insects were rare in adult diets but constituted 86.5% (by volume) of the food eaten by the smallest juveniles. All age classes ate some plant parts from a range of plant types, but flowers and leaves of legumes were a primarily food source. Non-adult lizards had the widest food niche breadths. Arthropods in the diet of juveniles and immatures covaried seasonally with the decline of arthropod abundance. Several hypotheses could explain this ontogenetic plasticity in diet. I rejected hypotheses that gut structure constrained juveniles to an arthropod diet and that insect consumption was purely an artifact of plant consumption because (1) size-adjusted gut morphology and capacity was similar among age classes, and (2) no food plants sampled had an excessive density of arthropods. I supported an alternative hypothesis that juveniles can eat plants but do not because insects provide a more nutritious diet. This conclusion was based on the observation that the juvenile hindgut is similar to that of herbivorous adults, and the propensity for juveniles to consume primarily, but not exclusively, insects when they were most abundant. The hindgut represents the site of fermentative plant fiber breakdown in many herbivorous lizards. Insect foods can compensate for size-related nutritional needs (energy and protein) and digestive limitations in juveniles. Opportunistic feeding to maintain a broad diet might help juvenile and immature lizards through high-predation-risk growth periods by reducing searching costs, increasing nutritional and energetic gains due to associative effects, and increasing new food exposure. Received: 20 January 1999 / Accepted: 25 January 2000     

皇甫川流域天然草地恢复演替进程中优势种的生态位分析

采用Levins,Shannon-Wiener生态位宽度公式和Levins生态位特定重叠指数公式对皇甫川流域天然草地恢复演替不同阶段植物群落中优势种生态位宽度和生态位重叠进行了测定,并分析各种群生态位宽度和生态位重叠的生态学意义。结果表明:演替过程中每一群落类型的优势种具有最大的生态位宽度;生态位宽度在演替序列的动态变化与种群动态有较好的对应关系;生态位重叠越大,种群间的生态相似性越大,利用资源的相似性程度越高,种间竞争可能越激烈;竞争是促使流域内各植物群落向顶级群落演替的一种动力机制。     

Wild reindeer foraging-niche organization

Part 1: Diet selection was studied on free-ranging reindeer fitted with an esophageal fistula (EF) and by analysis of rumen samples from reindeer shot in the field. Plant density was assessed from quadrats on field plots. Three measures of palatability were used, the nitrogen, fiber, and total non structural carbohydrate (TNC) contents of samples from clipped vegetation. As lichen density decreased the EK reindeer included progressively more vascular litter and pieces of winter dormant species in their diet. Diets with highest TNC and N/F and the lowest fiber, providing the most readily digestible diets, were selected. The combined density-quality criterion gave the best prediction of their diets. In summer, forbs, and to some extent grasses and dwarf shrubs, were selected. Plants of highest density and in an early growth phase gave the best prediction of summer diets. In winter the variety of vascular plants utilized increased with increasing herd size and decreasing density of lichens in the vegetation. The width of diets was a function of diversity of available plants. It is suggested that dietary selection by reindeer has been a three stage process: evolution of a gastro-intestinal system capable of digesting lichens containing secondary compounds, behavioural tracking of the plant production pulse, and diet width scaling according to density-quality of all potential foods. Part 2: Wild reindeer closely followed the wave of vascular plant production in spring and summer with a significant correlation being found between the daily foraging time per habitat type and the highest concentration of green phytomass. Snow-bed meadows were the most consistently selected vegetation type by the four herds studied, viz. Hardangervidda, Snøhetta, Prudhoe Bay, and Svalbard, during the summer. Habitat niche-breadths were narrow during the winter, largely due to the limitation of access to the food supply by the snow-cover, broadened as the landscape became clear of snow, narrowed again with the initiation of plant growth and broadened once more as the wave of plant production reached all habitat types. At high levels of food resources the alpine herd (Hardangervidda) narrowed the feeding niche breadth (or adopted a selective feeding strategy) as the habitat niche breadth increased. The high arctic herd (Svalbard) living in the least productive environment, at the same time of year adopted a generalist feeding strategy as their habitat niche breadth expanded. Part 3: In this part the temporal organization of a low-alpine herd of reindeer (Hardangervidda) is described, and subsequently compared with those of two arctic herds. Their foraging efficiencies under different degrees of food availability were analysed, in order to test the hypothesis that food intake changes in response to the prevailing state of the food resources. The number of daily feeding bouts increased from 2 to 6 as the diet changed from the winter to the summer pasturage. Strong winds in winter and insect harassment in summer severely depressed the daily time spent foraging. When these environmental factors were accounted for no significant inter-seasonal differences in daily foraging time of the low alpine herd were found; on average 50% of each day was spent grazing, of which 78% of the time was spent on actual ingestion (feeding rate). The feeding rate within the active periods varied with the snow-depth, due to the need to dig a food crater in the snow and due to the particular selective feeding strategy adopted. The data from the present and from other studies suggest that the foraging efficiency of wild reindeer, expressed as their daily food intake follows a Holling type II functional response as food availability changes. Part 4: Sheep is the only sympatric ruminant which grazes with the reindeer on alpine pastures in Norway. The inter-specific niche relationships ot the wild reindeer and the domestic sheep in summer were studied on part of the western Hardangervidda. to test the hypothesis of inter-specific competition. Three niche dimensions were meas-ured, diel, habitat utilization, and spatial distribution. The estimates of the degree of overlap obtained suggest that this is relatively high for diet and habitat utilization but low for spatial distribution, which leads to a low degree of foraging interference. Since the intensity of both interspeeific and intra-specific competition depends on the ratio of the herbivore densities to the food resource density, the degree ol overlap in utilization by the two species tell us nothing about the degree of competition. Present numbers of both species on Hardangervidda have a beneficial influence on the vegetation, by opening-up the shrub-layer canopy and thus facilitating the main-tenance of grasses and forbs in the field layer, which has a higher carrying capacity for ruminants. The balance between the beneficial effects and inter-generic competition (if any) deriving from the present-day stocking rales is so tar unknown. Only long-term monitoring of the performance of both populations will shed light on this competitive aspect.