Seasonal dynamics of resource partitioning among foliage-gleaning passerines in northern Finland

Summary The five most abundant species were included in a year-round study with respect to six foraging niche dimensions. Approximately full multidimensional utilization functions were used for niche metrics. During summer foraging overlaps were invariably high, but in other seasons periodically lower. Foraging site breadth was lower in winter, when fewer sites are profitable for foraging than in summer. Feeding posture versatility, by contrast, was highest in winter. Seasonal foraging shifts were very prominent, as great in fact as between-species differences. Often seasonal trends were parallel in different species. Niche axes of macrohabitat-type (e.g. tree) were more open for foraging variation and axes of microhabitat-type (tree part) more rigid. Among the resident species seasonal variation in foraging was greatest in Regulus regulus and Parus cristatus, whereas the foraging behaviour was more stable for P. montanus (an abundant species with broad niche), perhaps owing to greater intraspecific competition. In these northern forests foliage-gleaners must be versatile generalists to cope with the unpredictable resources, and thus they overlap broadly in their general resource niches which are determined by their genetically fixed cost and benefit relations to each resource type. Anyhow, presumably during periodical food shortage, the actual resource uses adjusted by resource availability and competition may overlap narrowly.     

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.     

Does interspecific competition drive patterns of habitat use in desert bat communities?

Bodies of water are a key foraging habitat for insectivorous bats. Since water is a scarce and limiting resource in arid environments, bodies of open water may have a structuring effect on desert bat communities, resulting in temporal or spatial partitioning of bat activity. Using acoustic monitoring, we studied the spatial and temporal activity patterns of insectivorous bats over desert ponds, and hypothesised that sympatric bat species partition the foraging space above ponds based on interspecific competitive interactions. We used indirect measures of competition (niche overlap and competition coefficients from the regression method) and tested for differences in pond habitat selection and peak activity time over ponds. We examined the effect of changes in the activity of bat species on their potential competitors. We found that interspecific competition affects bat community structure and activity patterns. Competing species partitioned their use of ponds spatially, whereby each species was associated with different pond size and hydroperiod (the number of months a pond holds water) categories, as well as temporally, whereby their activity peaked at different hours of the night. The drying out of temporary ponds increased temporal partitioning over permanent ponds. Differences in the activity of species over ponds in response to the presence or absence of their competitors lend further support to the role of interspecific competition in structuring desert bat communities. We suggest that habitat use and night activity pattern of insectivorous bats in arid environments reflect the trade-offs between selection of preferred pond type or activity time and constraints posed by competitive interactions.     

Dietary opportunism,resource partitioning,and consumption of coffee berry borers by five species of migratory wood warblers (Parulidae) wintering in Jamaican shade coffee plantations

Diets reflect important ecological interactions, but are challenging to quantify for foliage‐gleaning birds. We used regurgitated stomach samples from five primarily insectivorous species of long‐distance migrant warblers (Parulidae) wintering in two moderate‐elevation shade coffee farms in Jamaica to assess both foraging opportunism and prey resource partitioning. Our results, based primarily on 6120 prey items in 80 stomach samples collected during a one‐week period in March 2000, confirm opportunism. The diets of all five warblers, including American Redstarts (Setophaga ruticilla), Black‐and‐White Warblers (Mniotilta varia), Black‐throated Blue Warblers (S. caerulescens), Northern Parulas (S. americana), and Prairie Warblers (S. discolor), overlapped strongly based on consumption of the same prey types, even many of the same prey species (4 of 10 interspecific overlaps >0.9, range = 0.74–0.97). Moreover, all five species fed on similarly small, often patchily distributed prey, including coffee berry borers (Hypothenemus hampei; Coleoptera, Curculionidae). Nonetheless, permutational multivariate analysis of variance also revealed that the diets of these species differed significantly, primarily with respect to prey mobility (winged vs. sessile); American Redstarts fed on the most mobile prey, and Northern Parulas on the least mobile prey and a relatively restricted set of prey taxa compared to the other four species of warblers. Overall, our results suggest both dietary opportunism consistent with a migratory life‐history, and interspecific resource partitioning consistent with differences in morphology and foraging behavior during a food‐limited season. Having provided evidence of the three necessary conditions, namely intraspecific competition, resource limitation, and interspecific overlap in resource use, the results of our study, in combination with those of other studies, also provide evidence of interspecific competition among wintering migrant insectivores. We thus argue that diffuse interspecific exploitative food competition may be more important than previously recognized.     

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.     

The foraging behavior of the central mudminnow and yellow perch: the influence of foraging site,intraspecific and interspecific competition

Summary The central mudminnow (Umbra limi) and yellow perch (Perca flavescens) are two species of fishes that commonly co-occur in small bog lakes in the Great Lakes region of North America. Both species are dietary generalists with a high degree of dietary overlap, and perch populations have been shown to have a strong negative effect on mudminnow populations. I compared the foraging rates of the two species in a series of laboratory experiments in which four foraging sites were simulated (open bottom substrate, water column, submerged aquatic macrophytes, and water surface). Fish were observed as they foraged singly, in monospecific pairs, and in mixed species pairs to evaluate the effects of intra- and interspecific competition on foraging success and the potential for resource partitioning based on foraging site. Single species trials showed that each species had similar foraging rates at each of the four sites. Across all sites combined, interspecific competition had a greater negative effect on the foraging success of mudminnows than did intraspecific competition. Conversely, intraspecific competition had a greater negative effect on the foraging success of perch than did interspecific competition. In mixed species trials perch took more food items from each of the four foraging sites than did mudminnows and caused shifts in site-use patterns of mudminnows. Differences in the foraging success of the two species reflected the superior ability of perch to discover the presence of food and to search rapidly for additional items, but were unrelated to handling times. These differences were linked to the species' foraging modes. The competitive superiority of perch, demonstrated in these experiments, could contribute to the negative impact of perch on mudminnow populations under natural conditions.     

Intraspecific and interspecific competition induces density‐dependent habitat niche shifts in an endangered steppe bird

Interspecific competition is a dominant force in animal communities that induces niche shifts in ecological and evolutionary time. If competition occurs, niche expansion can be expected when the competitor disappears because resources previously inaccessible due to competitive constraints can then be exploited (i.e., ecological release). Here, we aimed to determine the potential effects of interspecific competition between the little bustard (Tetrax tetrax) and the great bustard (Otis tarda) using a multidimensional niche approach with habitat distribution data. We explored whether the degree of niche overlap between the species was a density‐dependent function of interspecific competition. We then looked for evidences of ecological release by comparing measures of niche breadth and position of the little bustard between allopatric and sympatric situations. Furthermore, we evaluated whether niche shifts could depend not only on the presence of great bustard but also on the density of little and great bustards. The habitat niches of these bustard species partially overlapped when co‐occurring, but we found no relationship between degree of overlap and great bustard density. In the presence of the competitor, little bustard's niche was displaced toward increased use of the species' primary habitat. Little bustard's niche breadth decreased proportionally with great bustard density in sympatric sites, in consistence with theory. Overall, our results suggest that density‐dependent variation in little bustard's niche is the outcome of interspecific competition with the great bustard. The use of computational tools like kernel density estimators to obtain multidimensional niches should bring novel insights on how species' ecological niches behave under the effects of interspecific competition in ecological communities.     

Resource partitioning and interspecific competition in snakes: the search for general geographical and guild patterns

The role of interspecific competition as a key factor in the ecology of natural communities where species exploit limited resources is well established, and the study of competition dynamics in snake communities has received much attention in recent years. Twenty years ago, an acclaimed review ( Toft 1985 ) suggested that snakes were atypical among vertebrates because sympatric species usually partition the food niche. Here, I review the articles published in the last two decades with the aim of finding any general geographical or guild patterns and assessing if Toft's main conclusion is still supported by new evidence. Where appropriate, I use Monte Carlo simulations to establish whether observed patterns of niche overlap are real, or if they have occurred by chance. My study shows clear congruence in the patterns of coexistence exhibited by snake communities in different regions of the world, i.e.: (1) cold regions of the northern hemisphere (high latitudes and altitudes) exhibit low species richness and a very low, or even absent, potential for interspecific competition; (2) aquatic snakes that form communities in temperate regions generally partition the food type available and exhibit a broad similarity in habitat use with subtle differences in microhabitat use; (3) terrestrial snake communities in temperate regions are very variable in terms of their coexistence dynamics and show no evidence of generalised patterns; (4) sympatric viperids in Europe, North America and, most interestingly, tropical Asia partition the available habitat but not the prey resource; (5) competition is much stronger in tropical snake communities, and the intensity of this process fluctuates throughout the year being most intense during periods of low food availability; (6) in general, tropical snakes partition the food resource (prey type and/or prey size), but when this resource is not partitioned competitive exclusion can occur. Prey resource availability is a fundamental variable for all snake communities; this is clearly documented by studies on terrestrial snakes in Australia where, due to a relative scarcity of prey availability in the field, sympatry among species is much rarer than in other continents. I conclude that, although there are several notable exceptions, Toft's main conclusion is still supported by empirical evidence. However, I disagree with Toft's conclusion that most snakes are food specialists, and I contend that interspecific competition is important in structuring many (if not most) of the snake communities around the world.     

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.     

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。     

MULTIDIMENSIONAL ANALYSIS OF RESOURCE UTILIZATION IN ASSEMBLAGES OF RANGELAND GRASSHOPPERS (ORTHOPTERA: ACRIDIDAE)

Abstract  A study was conducted in a typical steppe area in central Inner Mongolia to determine resource utilization in time, space, and food by grasshopper assemblages. Pattern of use for these resources was analyzed from three vegetation types by examining species-specific niche breadths, overlaps and partitions of resource utilization as well as population sizes. Popular niche indices and the principal components analysis (PCA) procedure were used to indicate the interrelations among grasshopper species. In the heterogeneous grassland environments resulting from livestock grazing, eleven grasshopper species were categorized respectively based on the 3-dimensional niche segregation and overlap degree. Population sizes were determined by the calorific values of their realized population biomass. Comparison in niche breadth displayed that species which had a broad niche along one dimension at least had a narrow niche along another one. There were sufficient differences between species for overall overlap associated with resource use to explain coexistence in the assemblages by resource segregation. Distinct rule of niche complementarity in overlap was not found. Evidence from this study implied that the species-specific use of resource may be due primarily to grasshopper adaptive differentiation and to coevolutionary interactions between grasshopper and plant rather than interspecific competition among grasshopper species.     

草原蝗虫种团资源利用的多维分析(直翅目:蝗科)(英文)

本文研究了内蒙古典型草原蝗虫在时间、空间和食物资源利用方面的特点。对于这些资源利用的格局是通过对存在于三种类型植被中蝗虫种的生态位宽度、资源利用的分化和重叠以及每种蝗虫的种群大小来分析的。常用的生态位指数和主成份分析技术用来阐明蝗虫种间的关系。在放牧形成的异质性草原环境中,11种蝗虫根据它们在三维生态位方面的分化和重叠程度被划分成数个种组。种群的大小是根据种群实际生物量所含热能值来确定的。生态位宽度比较说明,在某一维生态位宽的种,在另一维上必定变窄。生态位重叠的差异说明共存的蝗虫种在资源利用上的分化。生态位重叠的补偿规律在本项研究中并不明显。本项研究结果说明,蝗虫种资源利用的分化主要归因于蝗虫的适应性分化和蝗虫——植物协同进化的相互作用关系,而不是蝗虫种间竞争所造成的。     

Seasonal dietary niche contraction in coexisting Neotropical frugivorous bats (Stenodermatinae)

Tropical dry forests are characterized by punctuated seasonal precipitation patterns that drive primary production and the availability of fruits, seeds, flowers, and insects throughout the year. In environments in which the quantity and quality of food resources varies seasonally, consumers should adjust their foraging behavior to maximize energy intake while minimizing overlap with competitors during periods of low food availability. Here, we investigated how the diets of frugivorous bats in tropical dry forests of NW Mexico varied in response to seasonal availability and how this affected dietary overlap of morphologically similar species. We performed stable isotope analyses to understand temporal and interspecific patterns of overall isotopic niche breadth, trophic position, and niche overlap in the diet of six frugivorous species of closely related New World leaf-nosed bats (family Phyllostomidae, subfamily Stenodermatinae). We estimated seasonal changes in resource abundance in two complementary ways: (a) vegetative phenology based on long-term remote sensing data and (b) observational data on food availability from previously published insect and plant fruiting surveys. In all species, there was a consistent pattern of reduced isotopic niche breadth during periods of low food availability. However, patterns of niche overlap varied between morphologically similar species. Overall, results from our study and others suggest that seasonal food availability likely determines overall dietary niche breadth in Phyllostomidae and that despite morphological specialization, it is likely that other mechanisms, such as opportunistic foraging and spatiotemporal niche segregation, may play a role in maintaining coexistence rather than simply dietary displacement.     

Foraging of rocky habitat cichlid fishes in Lake Malawi: coexistence through niche partitioning?

The haplochromine cichlid fish communities of the rocky habitats of Lake Malawi are highly diverse; however, many species live side by side with apparently very similar resource requirements. There is a long-standing debate concerning whether these species partition their resources on a finer scale than has been previously reported or if species that are truly ecologically indistinguishable can coexist. A field study of food resource use was conducted to determine whether coexisting species segregate their diet and foraging sites. Significant differences between species were found, yet considerable inter-specific resource use overlap was commonplace. The data indicate that these cichlid species coexist both with and without niche differentiation. We propose that alternatives to niche differentiation should be considered to explain how many species coexist in Lake Malawi cichlid communities. Received: 5 October 1998 / Accepted: 30 June 1999     

No evidence of strong host resource segregation by phorid parasitoids of leaf-cutting ants

Resource segregation by species is a cornerstone ecological concept that may result from several processes such as interspecific competition, and can help structuring communities, in particular parasitoid communities. Phorid parasitoid flies that use ants as hosts usually employ one host per individual parasitoid, and thus the pressure for segregating the host resource should be high. At a particular community, these parasitoids might segregate resources by temporal differences in activity patterns, using different host species or nests from those available. Even if parasitoid species coexist on the same nest, they can take advantage of worker polymorphism and task division, searching for ants performing different tasks at different microsites of the same nest. Here we evaluated the segregation of parasitoid species in these hypothesized axes using leaf-cutting ant phorid parasitoids as a model system. We analyzed temporal data collected at two localities with contrasting host species richness; and compared parasitoid co-occurrence at the different niche axis. For most of the hypothesized niche axes tested we found either no departures from random expectations or significantly more niche overlap than expected by chance, ruling out the existence of biologically relevant host resource segregation in this system. However, there was evidence of segregation for some species, since one parasitoid species was only found in winter and another species showed a negative correlation of its abundance over nests with other two species. Furthermore, we found that several species were flexible in host use; Atta phorids varied in average host sizes preferred, whereas Acromyrmex phorids that were generalists were able to use different host species or microsites for host location. From an applied perspective, these results are encouraging when selecting species for the control of leaf-cutting ants because parasitoids coexistence seems to be unaffected by their overlap in niche dimensions.     

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。     

两种鹪莺的种间生态位关系研究

本文研究了褐头鹪莺（Ｐｒｉｎｉａ ｓｕｂｆｌａｖａ）和黄腹鹪莺（Ｐ．ｆｌａｖｉｖｅｎｔｒｉｓ）在取食高度、取食基层和取食方法３个生态维度上的生态位宽度和生态位重叠以及它们与复合种群密度的关系。结果表明,两种鹪莺的现实生态位有较大的重叠,且种群密度变化时,生态位宽度和生态位重叠发生了显著移动,褐头鹪莺与黄腹鹪莺之 间存在着竞争;它们并没有采取生态位宽度来回避竞争,而是相反地各自扩展生态位宽度来减少重     

Persistent bill and corolla matching despite shifting temporal resources in tropical hummingbird‐plant interactions

By specialising on specific resources, species evolve advantageous morphologies to increase the efficiency of nutrient acquisition. However, many specialists face variation in resource availability and composition. Whether specialists respond to these changes depends on the composition of the resource pulses, the cost of foraging on poorly matched resources, and the strength of interspecific competition. We studied hummingbird bill and plant corolla matching during seasonal variation in flower availability and morphology. Using a hierarchical Bayesian model, we accounted for the detectability and spatial overlap of hummingbird‐plant interactions. We found that despite seasonal pulses of flowers with short‐corollas, hummingbirds consistently foraged on well‐matched flowers, leading to low niche overlap. This behaviour suggests that the costs of searching for rare and more specialised resources are lower than the benefit of switching to super‐abundant resources. Our results highlight the trade‐off between foraging efficiency and interspecific competition, and underline niche partitioning in maintaining tropical diversity.     

大山雀和褐头山雀种间关系研究

在地理分布重叠地区的大山雀Parus major和褐头山雀Parus montanus栖息地海拔高度不同。大山雀栖于海拔2,370米以下,集中于次生杨桦林和老年人工杨树林;褐头山雀栖于海拔2,300米以上,集中于混交林和山杨栎林。它们的栖息地有一定重叠,但重叠值较低。重叠地带觅食生态位的四维中,树种选择一维有所不同,其余三维生态位重叠值均较大。两个种营养生态位有一定重叠,食物大小的重叠值更大。在进化发展过程中,两种山雀间完全的生态分离没有发生。