Pulsed resource availability changes dietary niche breadth and partitioning between generalist rodent consumers

Identifying the mechanisms that structure niche breadth and overlap between species is important for determining how species interact and assessing their functional role in an ecosystem. Without manipulative experiments, assessing the role of foraging ecology and interspecific competition in structuring diet is challenging. Systems with regular pulses of resources act as a natural experiment to investigate the factors that influence the dietary niches of consumers. We used natural pulses of mast‐fruiting of American beech (Fagus grandifolia) to test whether optimal foraging or competition structure the dietary niche breadth and overlap between two congener rodent species (Peromyscus leucopus and P. maniculatus), both of which are generalist consumers. We reconstructed diets seasonally over a 2‐year period using stable isotope analysis (δ¹³C, δ¹⁵N) of hair and of potential dietary items and measured niche dynamics using standard ellipse area calculated within a Bayesian framework. Changes in niche breadth were generally consistent with predictions of optimal foraging theory, with both species consuming more beechnuts (a high‐quality food resource) and having a narrower niche breadth during masting seasons compared to nonmasting seasons when dietary niches expanded and more fungi (a low‐quality food source) were consumed. In contrast, changes in dietary niche overlap were consistent with competition theory, with higher diet overlap during masting seasons than during nonmasting seasons. Overall, dietary niche dynamics were closely tied to beech masting, underscoring that food availability influences competition. Diet plasticity and niche partitioning between the two Peromyscus species may reflect differences in foraging strategies, thereby reducing competition when food availability is low. Such dietary shifts may have important implications for changes in ecosystem function, including the dispersal of fungal spores.     

High resource overlap and small dietary differences are widespread in food-limited warbler (Parulidae) communities

Although both interspecific competition and coexistence mechanisms are central to ecological and evolutionary theory, past empirical studies have generally focused on simple (two-species) communities over short time periods. Experimental tests of these species interactions are challenging in complex study systems. Moreover, several studies of ‘imperfect generalists’, consistent with Liem's Paradox, raise questions about the ability of evolved species differences to partition niche space effectively when resources vary considerably across the annual cycle. Here we used a recently developed theoretical framework to combine past research on population-level processes with observational data on resource use to test for ongoing interspecific competition and understand the nature of resource overlap. We compared species diet overlaps and differences in several distinctive communities centred on a focal species, the American Redstart Setophaga ruticilla replicated both spatially and seasonally, in combination with documentation of population regulation to assess the ability of similar species to partition dietary niche space and limit interspecific competition. Our results document high dietary overlap in most of the communities studied, with only subtle differentiation consistent with known species differences in foraging behaviour and morphology. These findings are largely consistent with species foraging as imperfect generalists. However, in contrast to past studies, the high diet overlaps observed here during times of inferred resource scarcity were driven by low-value prey taxa (e.g. small ants) and did not involve truly ‘private’ resources. All of these factors increase the potential negative impacts of interspecific competition, and limit the ability of these birds to avoid competition if food availability deteriorates further than observed in our study, either seasonally or at longer intervals.     

Interspecific competition and torpor in golden spiny mice: two sides of the energy-acquisition coin

We studied the occurrence of torpor in golden spiny mice in a hot rocky desert near the Dead Sea. In this rodent assemblage, a congener, the nocturnal common spiny mouse, competitively excluded the golden spiny mouse from the nocturnal part of the diel cycle and forced it into diurnal activity; this temporal partitioning allows the two species to partition their prey populations, particularly in summer when the diet of the two species is comprised mainly of arthropods, and largely overlap. We studied the effect of the presence of the common spiny mice at two resource levels (natural food availability and food added ad libitum) on populations of golden spiny mice in four large outdoor enclosures: two with common spiny mice removed and two enclosures with populations of both species. We hypothesized that with interspecific competition and/or reduced resources, golden spiny mice will increase their use of torpor. As we expected, supplemented food reduced the total time spent torpid. In summer, when the different activity periods of the two species results in prey species partitioning, removal of the congener did not affect torpor in the golden spiny mouse. However, in winter, when insect populations are low and the two species of mice overlap in a largely vegetarian diet, removal of the common spiny mouse reduced torpor in golden spiny mice, whether food was supplemented or not. This result suggests that torpor, a mechanism that allows small mammals to sustain periods of low availability of resources or high energetic requirements, may also help them to tolerate periods of enhanced interspecific competition. This may be a significant short-term mechanism that reduces competition and hence increases fitness, in particular of individuals of the subordinate species whose accessibility to resources may be limited.     

Relative roles of dispersal dynamics and competition in determining the isotopic niche breadth of a wetland fish

1. The niche variation hypothesis predicts that among‐individual variation in niche use will increase in the presence of intraspecific competition and decrease in the presence of interspecific competition. We sought to determine whether the local isotopic niche breadth of fish inhabiting a wetland was best explained by competition for resources and the niche variation hypothesis, by dispersal of individuals from locations with different prey resources or by a combination of the two. We analysed stable isotopes of carbon and nitrogen as indices of feeding niche and compared metrics of within‐site spread to characterise site‐level isotopic niche breadth. We then evaluated the explanatory power of competing models of the direct and indirect effects of several environmental variables spanning gradients of disturbance, competition strength and food availability on among‐individual variation of the eastern mosquitofish (Gambusia holbrooki). 2. The Dispersal model posits that only the direct effect of disturbance (i.e. changes in water level known to induce fish movement) influences among‐individual variation in isotopic niche. The Partitioning model allows for only direct effects of local food availability on among‐individual variation. The Combined model allows for both hypotheses by including the direct effects of disturbance and food availability. 3. A linear regression of the Combined model described more variance than models limited to the variables of either the Dispersal or Partitioning models. Of the independent variables considered, the food availability variable (per cent edible periphyton) explained the most variation in isotopic niche breadth, followed closely by the disturbance variable (days since last drying event). 4. Structural equation modelling provided further evidence that the Combined model was best supported by the data, with the Partitioning and the Dispersal models only modestly less informative. Again, the per cent edible periphyton was the variable with the largest direct effect on niche variability, with other food availability variables and the disturbance variable only slightly less important. Indirect effects of heterospecific and conspecific competitor densities were also important, through their effects on prey density. 5. Our results support the Combined hypotheses, although partitioning mechanisms appear to explain the most diet variation among individuals in the eastern mosquitofish. The results also support some predictions of the niche variation hypothesis, although both conspecific and interspecific competition appeared to increase isotopic niche breadth in contrast to predictions that interspecific competition would decrease it. We think this resulted from high diet overlap of co‐occurring species, most of which consume similar macroinvertebrates.     

Are howler monkey species ecologically equivalent? Trophic niche overlap in syntopic Alouatta guariba clamitans and Alouatta caraya

According to the principle of competitive exclusion, niche differentiation allows the stable coexistence of closely related species. We analyzed dietary profile and diversity, and dietary overlap between syntopic brown howlers (BR; Alouatta guariba clamitans) and black and gold howlers (BLG; A. caraya) in the Atlantic Forest of NE Argentina, with the objective of evaluating the degree of trophic niche overlap and potential interspecific competition for food. During 12 months, we collected data on feeding behavior of two groups of each howler species using the scan sampling method, together with data on food availability. Both at the group‐ and species‐level, we analyzed feeding behavior in terms of monthly percentages of time spent feeding on each food type and specific food item, dietary diversity (Shannon index H′), and we estimated dietary overlap using the percentage index and the Morisita–Horn index (C_H). Across months, both howlers showed species‐specific preferences for certain food items, and BLG had a more diverse diet (mean±SE, H′=2.77±0.08) than BR (H′=2.39±0.09). However, diets of both species overlapped extensively (percentage index=45.64±2.97%; C_H=0.6±0.05) and diets of conspecific groups did not overlap more than diets of groups of different species. Given their high degree of trophic overlap, syntopic BR and BLG meet one of the conditions necessary for interspecific food competition to occur. Although at present we lack direct evidence for interspecific competition in these howler species, we conclude that high levels of niche overlap may have an important role in maintaining the essentially parapatric distribution of howler species throughout the Neotropics. Am. J. Primatol. 72:173–186, 2010. © 2009 Wiley‐Liss, Inc.     

Patterns of diet overlap between populations of non-indigenous and native fishes in shallow ponds

No significant differences in the diet composition were detected for any of the populations of four non-indigenous fish species (brown bullhead Ameiurus nebulosus , pumpkinseed Lepomis gibbosus , topmouth gudgeon Pseudorasbora parva and eastern mudminnow Umbra pygmaea ) and two native fish species (gudgeon Gobio gobio and roach Rutilus rutilus ), between two small shallow ponds and between habitats within the ponds, during late summer. Based on diet composition, groups of size classes within species ('functional groups') were distinguished. For most functional group combinations of exotic fishes, diet overlap values were low. Although chironomid larvae formed the most important food source, differential consumption of chironomid size classes allowed an important degree of niche differentiation between non-indigenous fishes. In contrast, high diet overlap was found between the functional groups of indigenous gudgeon and of several non-indigenous fishes, indicating a high potential for interspecific exploitative competition. The diet of roach consisted almost entirely of non-animal remains (detritus and plant material). The high proportion of such low-energy food in the diet of this species may be indicative for a competition induced niche shift to suboptimal food sources.     

浙江披山海域主要鱼类时空生态位

依据2015年11月(秋)、2016年2月(冬)、5月(春)、8月(夏)4个航次的渔业资源底拖网调查数据,运用相对重要性指数(IRI)、Shannon指数和Pianka指数对浙江披山海域主要鱼类的时空生态位宽度和重叠进行分析,并结合冗余分析和种间竞争系数研究了主要鱼类间的竞争共存关系及生态位分化。结果表明: 研究期间共采集鉴定鱼类61种,隶属13目29科48属,其中主要鱼类(IRI>100)有19种。绿鳍鱼与丽叶鲹的时间生态位重叠值最高,二者对时间资源利用的同步性最强;孔虾虎鱼与断线舌鳎的空间生态位重叠值和时空生态位重叠值均最高,二者在空间资源序列上的同域性最强,同时,物种对时空二维资源的利用趋于一致。披山海域时空二维生态位显著重叠(Q_ik>0.6)的种对仅占总种对数的5.8%,表明物种时空分布的差异较大,时空生态位重叠受季节变化的影响比较明显,种间竞争系数计测结果与生态位重叠基本一致。冗余分析揭示了主要鱼类与温度、盐度、溶解氧等环境因子之间的关系,进一步解释了物种间的生态位分化。     

Evidence for acoustic niche partitioning depends on the temporal scale in two sympatric Bornean hornbill species

Understanding niche partitioning of closely related sympatric species is a fundamental goal in ecology. Acoustic communication space can be considered a resource, and the acoustic niche hypothesis posits that competition between species may lead to partitioning of communication space. Here, we compare the calling behavior of two sympatric Bornean hornbill species—the rhinoceros hornbill (Buceros rhinoceros) and the helmeted hornbill (Rhinoplax vigil)—to test for evidence of acoustic niche partitioning. Both hornbill species emit calls heard over many kilometers and have similar habitat preferences which is predicted to result in interspecific competition. We collected acoustic data on sympatric populations of both hornbill species using 10 autonomous recording units in Danum Valley Conservation Area, Sabah, Malaysia. We found that there was substantial spectral overlap between the calls of the two species, indicating the potential for competition for acoustic space. To test for evidence of acoustic niche partitioning, we investigated spatial and temporal patterns of calling in each species. Both hornbills were strictly diurnal and called throughout the day, and we were equally likely to detect both species at each of our recorders. We did not find evidence of temporal acoustic avoidance at a relatively coarse timescale when we divided our dataset into 1 h bins, but we did find evidence of temporal acoustic avoidance at a finer timescale when we used null models to compare the observed duration of overlapping calls to the expected amount of overlap due to chance.     

Intersexual segregation in foraging microhabitat use by Magellanic Woodpeckers (Campephilus magellanicus): Seasonal and habitat effects at the world's southernmost forests

Animals facing seasonal food shortage and habitat degradation may adjust their foraging behaviour to reduce intraspecific competition. In the harsh environment of the world's southernmost forests in the Magellanic sub‐Antarctic ecoregion in Chile, we studied intersexual foraging differences in the largest South American woodpecker species, the Magellanic Woodpecker (Campephilus magellanicus). We assessed whether niche overlap between males and females decrease when food resources are less abundant or accessible, that is, during winter and in secondary forests, compared to summer and in old‐growth forests, respectively. We analysed 421 foraging microhabitat observations from six males and six females during 2011 and 2012. As predicted, the amount of niche overlap between males and females decreased during winter, when provisioning is more difficult. During winter, males and females (i) used trees with different diameter at breast height (DBH); (ii) fed in trunk sections with different diameters; and (iii) fed at different heights on tree trunks or branches. Vertical niche partitioning between sexes was found in both old‐growth and secondary forests. Such a niche partitioning during winter may be a seasonal strategy to avoid competition between sexes when prey resources are less abundant or accessible. Our results suggest that the conservation of this forest specialist, dimorphic and charismatic woodpecker species requires considering differences in habitat use between males and females.     

Is resource partitioning the key? The role of intra‐interspecific variation in coexistence among five small endemic fish species (Characidae) in subtropical rivers

This study focused on intra and interspecific variations in the diet of small species in the Pelotas River, upper Uruguay River ecoregion. We tested the hypothesis that five small characids coexist via resource partitioning. Samplings were performed quarterly between August 2013 and May 2014 at 14 sites in the Pelotas River basin, using gillnets of different mesh sizes, seines, cast nets and electrofishing. In this study, the contents of 1,253 stomachs were analysed from Astyanax dissensus, A. paris, A. saguazu, A. xiru and Bryconamericus patriciae. The main food resources consumed were aquatic insects, leaves, seeds and detritus. There were significant seasonal intra and interspecific variations in the use of food resources by the five species. Permutational analysis of multivariate dispersions results indicated significant differences in individual intraspecific variability between the sampled periods, with the highest values found in November and February because of an increase in allochthonous resources (leaves and seeds). Besides this, significant differences in the proportions of consumption of allochthonous and autochthonous were observed. The trophic niche breadth was significantly different among the species, such that in August, the species had narrower niche breadths. In the other periods, the highest niche breadth values were due to an increase in the consumption of allochthonous items. Diet overlap was low (< 0.4) between 62% of the species pairs. The small characid species showed pronounced changes in resource use and intra and interspecific variations indicating resource partitioning. These factors appear to be essential in species interactions and for coexistence.     

The dietary basis for temporal partitioning: food habits of coexisting Acomys species

Two rodent species of the genus Acomys coexist on rocky terrain in the southern deserts of Israel. The common spiny mouse (A. cahirinus) is nocturnally active whereas the golden spiny mouse (A. russatus) is diurnally active. An early removal study suggested that competition accounts for this pattern of temporal partitioning: the golden spiny mouse is forced into diurnal activity by its congener. Theoretically, temporal segregation should facilitate coexistence if the shared limiting resources differ at different times (primarily among predators whose prey populations have activity rhythms), or if they are renewed within the period of the temporal segregation. We studied food preferences of the two Acomys species in a controlled cafeteria experiment in order to assess resource overlap and the potential for competition for food between the two species. We found no significant difference in food preferences between species. The dietary items preferred by both were arthropods. We also carried out a seasonal study of the percentage and identity of arthropods taken in the field by individuals of the two species. Individuals of both species took on annual average a high percentage of arthropods in their diets. Seasonal diet shifts reflect seasonal abundance of arthropods at Ein Gedi during day and night. Diurnal activity may also reduce interspecific interference competition between A. russatus and A. cahirinus. However, the strong interspecific dietary overlap in food preference, the heavy reliance on arthropods in spiny mouse diets, and the seasonal and circadian differences in arthropod consumption suggest that prey partitioning may be a viable mechanism of coexistence in this system. Received: 6 July 1998 / Accepted: 10 May 1999     

扎龙湿地藻类优势种生态位及其种间联结性动态分析

为了解扎龙湿地藻类群落结构的季节特征和演替规律,对扎龙湿地藻类群落进行了分析,主要涉及藻类优势度、生态位、MFG功能群划分、生态位重叠值及联结系数分析。结果表明：(1)在检出的8门311种藻类中,夏季种类丰富度最高,全年优势种为狭形纤维藻和啮蚀隐藻。(2)优势种种类和密度季节性差异较大,春季以金藻-绿藻种类为主,夏季以绿藻-隐藻种类为主,秋季以隐藻-绿藻种类为主。(3)生态位宽度值与MFG功能群划分结合分析表明,优势种可分为3个大类别,不同种类对资源利用情况的差异较大,各季节广生态位种能较好的反映扎龙湿地水体环境的季节变化趋势。(4)生态位重叠值在不同季节上有较大差异,O_ik>0.6的占比分别为42.86%(春)、28.57%(夏)和25.00%(秋),表明春季优势种种间资源的竞争最为突出,种间竞争强于夏、秋两季。(5)种间联结性检验结果显示,扎龙湿地藻类优势种间总体联结上呈正关联关系,但是种间联结较为松散,种与种之间相对独立。研究表明,扎龙湿地藻类群落结构生态位测度均存在明显的季节波动,较好反映出水环境季节变化特征,可用来指示湿地水体环境的变化。     

Trophic niche similarities of sympatric Turdus thrushes determined by fecal contents,stable isotopes,and bipartite network approaches

An ecological niche has been defined as an n‐dimensional hypervolume formed by conditions and resources that species need to survive, grow, and reproduce. In practice, such niche dimensions are measurable and describe how species share resources, which has been thought to be a crucial mechanism for coexistence and a major driver of broad biodiversity patterns. Here, we investigate resource partitioning and trophic interactions of three sympatric, phylogenetically related and morphologically similar species of thrushes (Turdus spp.). Based on one year of data collected in southern Brazil, we investigated niche partitioning using three approaches: diet and trophic niche assessed by fecal analysis, diet and niche estimated by stable isotopes in blood and mixing models, and bipartite network analysis derived from direct diet and mixing model outputs. Approaches revealed that the three sympatric thrushes are generalists that feed on similar diets, demonstrating high niche overlap. Fruits from C3 plants were one of the most important food items in their networks, with wide links connecting the three thrush species. Turdus amaurochalinus and T. albicollis had the greatest trophic and isotopic niche overlap, with 90% and 20% overlap, respectively. There was partitioning of key resources between these two species, with a shared preference for fig tree fruits—Ficus cestrifolia (T. amaurochalinus PSIRI% = 11.3 and T. albicollis = 11.5), which was not present in the diet of T. rufiventris. Results added a new approach to the network analysis based on values from the stable isotope mixing models, allowing comparisons between traditional dietary analysis and diet inferred by isotopic mixing models, which reflects food items effectively assimilated in consumer tissues. Both are visualized in bipartite networks and show food‐consumers link strengths. This approach could be useful to other studies using stable isotopes coupled to network analysis, particularly useful in sympatric species with similar niches.     

Resource partitioning in sympatric langurs and macaques in tropical rainforests of the central Western Ghats, south India

In a competitive sympatric association, coexisting species may try to reduce interspecific interactions as well as competition for similar resources by several ecological and behavioral practices. We studied resource utilization of three sympatric primate species namely, lion-tailed macaques (Macaca silenus), bonnet macaques (M. radiata) and Hanuman langurs (Semnopithecus entellus) in a tropical rainforest of the central Western Ghats, south India. We studied resource use, tree-height use, foraging height, substrate use when consuming animal prey and interspecific interactions. The results revealed that across the year, there was very limited niche overlap in diet between each species-pair. Each primate species largely depended on different plant species or different plant parts and phenophases from shared plant species. Primate species used different heights for foraging, and the two macaque species searched different substrates when foraging on animal prey. We also recorded season-wise resource abundance for the resources shared by these three primate species. While there was low dietary overlap during the dry season (a period of relatively low resource abundance), there was high dietary overlap between the two macaque species during the wet season (a period of high resource abundance for the shared resources). We observed only a few interspecific interactions. None of these were agonistic, even during the period of high niche overlap. This suggests that the sympatric primate species in this region are characterized by little or no contest competition. Unlike in some other regions of the Western Ghats, the lack of interspecific feeding competition appears to allow these primates, especially the macaques, to remain sympatric year-round.     

Intraguild dietary overlap and its possible relationship to the coexistence of mesocarnivores in intensive agricultural habitats

The stone marten (Martes foina) and the pine marten (M. martes) are closely related mammalian carnivores potentially subject to exploitative competition. The recent expansion of the pine marten into the intensively cultivated plain of the River Po (NW Italy), where previously only stone marten occurred, offered an interesting opportunity to analyse their relationships. We studied the distribution and diet of Martes species and trophic niche overlap between martens and red foxes (Vulpes vulpes) in two study areas, each with two pseudoreplicates, by analysing genotyped faeces. Our results seem to confirm the displacement of the stone marten from one study area, the pine marten being the only Martes species occurring where previously the stone marten had been reported. We found a large food niche overlap between red fox and both stone and pine martens, but with evidence of size-related differences in the consumption of some food items. We hypothesised that, due to the poor prey-base of the environment, highly altered by intensive crop cultivation, intense interspecific competition originally occurred between the red fox and stone marten. The heightening of interspecific competition caused by the entry of the pine marten in the predator guild may have caused the displacement of the stone marten, at least temporarily. The mechanism of such displacement needs to be clarified through further surveys in areas where the three species occur sympatrically.     

Darwin's finches and their diet niches: the sympatric coexistence of imperfect generalists

Adaptive radiation can be strongly influenced by interspecific competition for resources, which can lead to diverse outcomes ranging from competitive exclusion to character displacement. In each case, sympatric species are expected to evolve into distinct ecological niches, such as different food types, yet this expectation is not always met when such species are examined in nature. The most common hypotheses to account for the coexistence of species with substantial diet overlap rest on temporal variation in niches (often diets). Yet spatial variation in niche overlap might also be important, pointing to the need for spatiotemporal analyses of diet and diet overlap between closely related species persisting in sympatry. We here perform such an analysis by characterizing the diets of, and diet overlap among, four sympatric Darwin's ground finch species at three sites and over 5 years on a single Galápagos island (Santa Cruz). We find that the different species have broadly similar and overlapping diets – they are to some extent generalists and opportunists – yet we also find that each species retains some ‘private’ resources for which their morphologies are best suited. Importantly, use of these private resources increased considerably, and diet overlap decreased accordingly, when the availability of preferred shared foods, such as arthropods, was reduced during drought conditions. Spatial variation in food resources was also important. These results together suggest that the ground finches are ‘imperfect generalists’ that use overlapping resources under benign conditions (in space or time), but then retreat to resources for which they are best adapted during periods of food limitation. These conditions likely promote local and regional coexistence.     

Resource partitioning of roach Rutilus rutilus and bleak Alburnus alburnus in two eutrophic lakes in SE Norway

In this paper I investigate the resource partitioning of roach Rutilus rutilus and bleak Alburnus alburnus in two eutrophic lakes in SE Norway. Zooplankton was the preferred food item for both species during summer, whereas blue-green algae dominated the diet in September/October. There was no diet overlap in May, with the roach feeding mainly on detritus and the bleak feeding on surface insects. During summer the diet overlap increased, reaching high values in autumn. Habitat overlap was close to unity in spring and early summer. Coinciding with increasing diet overlap during summer and autumn the overlap in habitat decreased.     

Seasonal variations in food resource partitioning among four sympatric gudgeon species in the upper Yangtze River

Knowledge of food resource partitioning among sympatric fish species is crucial for understanding the potential mechanisms of species coexistence. Gudgeons (Teleostei: Cyprinidae: Gobioninae) often dominate fish assemblages in the upper Yangtze River. However, little research has been conducted on their trophic interactions. In this paper, seasonal diet and feeding strategy variations of four sympatric gudgeon species, Coreius guichenoti, Coreius heterodon, Rhinogobio ventralis, and Rhinogobio cylindricus, were investigated by analysis of intestinal tract contents, aiming to explore whether food resource partitioning occurred among them. Fish specimens were collected during spring (April–May) and autumn (August–October) in 2010 in Hejiang, a free‐flowing stretch of the upper Yangtze River. Coreius guichenoti, C. heterodon, and R. cylindricus showed omnivorous feeding habits, while R. ventralis exhibited an obligate carnivore feeding habit. Diet overlap among the four studied species was high, especially in spring. However, changes in feeding strategies were observed in autumn. Specifically, C. guichenoti and R. cylindricus expanded their dietary niche breadth and consumed detritus, Sinopotamidae or Hydropsychidae as important complementary food resources. In contrast, C. heterodon and R. ventralis reduced their dietary niche breadth and became more specialized on mussels (Limnoperna lacustris). These results confirmed that sympatric fish species can coexist with high diet overlap, and food resource partitioning among these species may also fluctuate with the seasons.     

Seasonal and successional dietary shifts of two sympatric rodents in coastal heathland: A possible mechanism for coexistence

Abstract Using microscopic analysis of faecal pellets, we compared the seasonal and successional patterns of food resource use of two Australian native rodents, the eastern chestnut mouse (Pseudomys gracilicaudatus) and the swamp rat (Rattus lutreolus) in a coastal heathland at Myall Lakes National Park, New South Wales. Using the Mantel test, the diets of the two mammal species were significantly different in autumn and winter but not in spring and summer. Further, the two species showed differential use of resources at the young and middle-aged stages of vegetation succession following fire. The mean dietary overlaps for pairs of individuals between the two species were relatively high in all seasons and successional stages, but they were significantly lower than those for pairs of individuals within each species in autumn and winter, and at the young and middle successional stages. Analysis of dietary niche position (γ) and breadth (β) showed lower γ and larger β for P. gracilicaudatus than for R. lutreolus, confirming previous observations that R. lutreolus is more specialized, and less opportunistic in diet than P. gracilicaudatus. Overall, the dietary separations of the two species were less marked in canonical space than they were for specific seasons and successional stages. These results, together with previous studies, indirectly suggest that while these two mammal species may be partitioning diet in autumn and winter in the middle stages, for spring and summer in the old successional stage they might need to partition habitats to facilitate their coexistence. Our results indicate that the local community is more dynamic and complex than previously thought and that other mechanisms of coexistence (e.g. temporal rotation of food resources) may be operating rather than traditional habitat and diet separation.     

Niche partitioning among three montane ground‐dwelling pheasant species along multiple ecological dimensions

Pheasants (order Galliformes) are typical ground‐dwelling birds, having a large body size and weak flight abilities. Sympatric pheasants are expected to share narrower niche space and face more extensive interspecific competition. However, little work has been undertaken simultaneously to investigate niche partitioning among sympatric pheasant species across multiple ecological dimensions. We compared microhabitat use, activity pattern and foraging strategy of sympatric Blood Pheasant Ithaginis cruentus, Buff‐throated Partridge Tetraophasis szechenyii and White Eared‐pheasant Crossoptilon crossoptilon on the Qinghai‐Tibet Plateau, China, to identify potential interspecific niche partitioning along different ecological dimensions in the breeding season. We found that the Buff‐throated Partridge differed significantly from the other two species in microhabitat use, and the three species showed different foraging strategies. It is likely that niche partitioning reduced potential interspecific competition, thus facilitating the species’ stable coexistence. Our study provides practical evidence of multidimensional niche theory within sympatric ground‐dwelling pheasant species, emphasizing that species interactions and coexistence within a guild are often not uni‐dimensional. Given global conservation concern for maintaining bird diversity, we recommend further restriction of yak grazing in these species’ habitat.