Niche construction in the light of niche theory

Ecological niche construction, the process whereby an organism improves its environment to enhance its growth and persistence, is an important missing element of niche theory. Niche theory has mainly focused on niche-deteriorating processes, such as resource consumption, predation and competition, which have negative effects on population growth. Here, we integrate niche construction explicitly into modern niche theory. We use a graphical approach to analyse how a species' niche-improving impacts interplay with niche-deteriorating impacts to modify its response to the environment. In a model of two consumers that compete for one limiting resource and one predator, we show how niche construction modifies the traditional niche-deteriorating impacts of its agent or of competing species, and hence the potential for species coexistence. By altering the balance between intraspecific and interspecific competitive effects, niche construction can either generate net interspecific facilitation or strengthen interspecific competition. The adaptive benefit derived from niche construction also strongly affects the realized niche of a niche-constructing species.     

Potential mechanisms of coexistence in closely related forbs

The stable coexistence of very similar species has perplexed ecologists for decades and has been central to the development of coexistence theory. According to modern coexistence theory, species can coexist stably (i.e. persist indefinitely with no long‐term density trends) as long as species' niche differences exceed competitive ability differences, even if these differences are very small. Recent studies have directly quantified niche and competitive ability differences in experimental communities at small spatial scales, but provide limited information about stable coexistence across spatial scales in heterogeneous natural communities. In this study, we use experimental and observational approaches to explore evidence for niche and competitive ability differences between two closely related, ecologically similar and widely coexisting annual forbs: Trachymene cyanopetala and T. ornata. We experimentally tested for stabilizing niche differences and competitive ability differences between these species by manipulating species' frequencies, under both well‐watered and water‐stressed conditions. We considered these experimental results in light of extensive field observations to explore evidence of niche segregation at a range of spatial scales. We found little evidence of intra‐specific stabilization or competitive ability differences in laboratory experiments while observational studies suggested niche segregation across pollinator assemblages and small‐scale microclimate heterogeneity. Though we did not quantify long‐term stabilization of coexisting populations of these species, results are consistent with expectations for stable coexistence of similar species via a spatial storage effect allowing niche differences to overcome even small (to absent) competitive ability differences.     

Periodic Lotka-Volterra competition equations

The Lotka-Volterra competition equations with periodic coefficients derived from the MacArthur-Levins theory of a one-dimensional resource niche are studied when the parameters are allowed to oscillate periodically in time. Specifically, niche positions and widths, resource availability and resource consumption rates are allowed small amplitude periodicities around a specified mean value. Two opposite cases are studied both analytically and numerically. First only resource consumption rates are allowed to oscillate while niche dimensions and resource availability are held constant. The resulting oscillations in population densities and the strength of the system stability as they depend upon crucial relative phase and amplitude differences between the species' consumption rates are studied. This leads to a clear notion of "temporal niche" and of the effects that such oscillations can have on competitive coexistence. Secondly, all system parameters are allowed to oscillate, although the oscillatory consumption rates are assumed identical for both species. The effects on the population density oscillations and their averages are studied and the "best" choice of the common, periodic resource consumption rate for these two "identical" species competing for similar (even identical) niches is considered.     

Limited niche differentiation within remarkable co‐occurrences of congeneric species: Monomorium ants in the Australian seasonal tropics

Niche theory predicts that few closely related species can co‐occur because such species tend to be ecologically similar and niche differentiation is required to avoid competitive exclusion. We analyse the co‐occurrence of a remarkable 10–15 species of the ant genus Monomorium occurring within single 10 × 10 m plots in a tropical savanna of northern Australia. Most of the species are undescribed, so we use genetic analysis to validate our species demarcations. We document nest dispersion patterns, and investigate differentiation in the three primary niche dimensions: space, time and food. We also examine species differences in competitive abilities, by describing rates of foraging activity, foraging ranges, worker aggression, and levels of behavioural dominance. Analyses of nest and forager distributions showed very limited evidence of spatial segregation within plots. The great majority of species foraged either exclusively or primarily during daylight hours. Body size and isotopic analyses indicated very limited dietary differentiation. Such limited niche partitioning occurred despite the species differing markedly in their competitive abilities as measured by rates of resource discovery, recruitment and monopolization. Our findings defy the traditional assumption that multiple closely related and ecologically similar species of highly interactive taxa cannot co‐occur. It seems very likely that species coexistence in our study system is determined to a very large degree by stochastic processes relating to dispersal and establishment, as predicted by neutral theory. However, neutral theory assumes competitive equivalence, whereas we found very marked differences in the competitive abilities of our co‐occurring species. We suggest that competitive exclusion is prevented by the modular nature of ant colonies, with competition limiting colony performance but not preventing occurrence. We conclude that other factors that allow species persistence, and not just competitive equivalence, can allow dispersal and establishment processes to drive species coexistence.     

Matching consumer feeding behaviours and resource traits: a fourth‐corner problem in food‐web theory

For decades, food web theory has proposed phenomenological models for the underlying structure of ecological networks. Generally, these models rely on latent niche variables that match the feeding behaviour of consumers with their resource traits. In this paper, we used a comprehensive database to evaluate different hypotheses on the best dependency structure of trait‐matching patterns between consumers and resource traits. We found that consumer feeding behaviours had complex interactions with resource traits; however, few dimensions (i.e. latent variables) could reproduce the trait‐matching patterns. We discuss our findings in the light of three food web models designed to reproduce the multidimensionality of food web data; additionally, we discuss how using species traits clarify food webs beyond species pairwise interactions and enable studies to infer ecological generality at larger scales, despite potential taxonomic differences, variations in ecological conditions and differences in species abundance between communities.     

Coexistence via resource partitioning fails to generate an increase in community function

Classic ecological theory suggests that resource partitioning facilitates the coexistence of species by reducing inter-specific competition. A byproduct of this process is an increase in overall community function, because a greater spectrum of resources can be used. In contrast, coexistence facilitated by neutral mechanisms is not expected to increase function. We studied coexistence in laboratory microcosms of the bactivorous ciliates Paramecium aurelia and Colpidium striatum to understand the relationship between function and coexistence mechanism. We quantified population and community-level function (biomass and oxygen consumption), competitive interactions, and resource partitioning. The two ciliates partitioned their bacterial resource along a size axis, with the larger ciliate consuming larger bacteria than the smaller ciliate. Despite this, there was no gain in function at the community level for either biomass or oxygen consumption, and competitive effects were symmetrical within and between species. Because other potential coexistence mechanisms can be ruled out, it is likely that inter-specific interference competition diminished the expected gain in function generated by resource partitioning, leading to a system that appeared competitively neutral even when structured by niche partitioning. We also analyzed several previous studies where two species of protists coexisted and found that the two-species communities showed a broad range of biomass levels relative to the single-species states.     

Starve a competitor: evolution of luxury consumption as a competitive strategy

Organisms are often observed to acquire an excess of non-limiting resources, a process known as luxury consumption. Luxury consumption has been largely treated as a bet hedging strategy for temporal variation in resource supply, but may also function as a competitive strategy. We incorporate luxury resource consumption into a derivation of the classic resource ratio model for competition between terrestrial plant, and explore its consequences for population dynamics and competition. We show that luxury consumption reduces the potential for coexistence between two species competing for two resources. Furthermore, we demonstrate that luxury consumption can be selected for because of the competitive advantage that luxury consumers gain. Luxury consumption evolves when competition for resources is local rather than global, there is potential for coexistence between the two species and the competitive environment remains stable over a sufficient period of time to allow selection to act. The evolutionary outcome can be either extinction of one of the competing species or coexistence of the two species with maximum luxury consumption. The potential for selection to favor luxury consumption is well predicted by the competitive outcome between individuals of the two species with and without luxury consumption.     

群落中克隆植物的重要性

综述了群落水平上克隆植物的重要性,克隆植物的生态习性,克隆植物的竞争关系等方面的研究进展,并试图在克隆植物竞争关系的背景下,结合其生境状况,探讨植物克隆性与植物物种多样性的关系。克隆植物的等级系统（基株—分株系统—分株）使其具有克隆性所赋予的多样的生活史、资源利用以及空间占据方式。列举了克隆植物的特性及其在群落中的作用。这些例子表明,克隆性强烈地影响和制约着植物群落的空间格局与竞争关系。然而克隆性也能通过权衡活动性与局部持久性来缓解对物种共存的抑制。克隆植物具有在时空尺度上分株间相互调节的机制,直接体现在群落中小尺度（个体与个体间）与大尺度（种群与种群间）间的相互作用上。丰富了传统的竞争和生态位划分理论,为群落中物种共存提供了合理解释。因此克隆植物在群落中的出现拓宽了群落系统潜在机制的范围。     

Assessing niche partitioning of co‐occurring sibling bat species by DNA metabarcoding

Niche partitioning through foraging is a mechanism likely involved in facilitating the coexistence of ecologically similar and co‐occurring animal species by separating their use of resources. Yet, this mechanism is not well understood in flying insectivorous animals. This is particularly true of bats, where many ecologically similar or cryptic species coexist. The detailed analysis of the foraging niche in sympatric, cryptic sibling species provides an excellent framework to disentangle the role of specific niche factors likely involved in facilitating coexistence. We used DNA metabarcoding to determine the prey species consumed by a population of sympatric sibling Rhinolophus euryale and Rhinolophus mehelyi whose use of habitat in both sympatric and allopatric ranges has been well established through radio tracking. Although some subtle dietary differences exist in prey species composition, the diet of both bats greatly overlapped (O_jk = 0.83) due to the consumption of the same common and widespread moths. Those dietary differences we did detect might be related to divergences in prey availabilities among foraging habitats, which prior radio tracking on the same population showed are differentially used and selected when both species co‐occur. This minor dietary segregation in sympatry may be the result of foraging on the same prey‐types and could contribute to reduce potential competitive interactions (e.g., for prey, acoustic space). Our results highlight the need to evaluate the spatial niche dimension in mediating the co‐occurrence of similar insectivorous bat species, a niche factor likely involved in processes of bat species coexistence.     

物种对资源竞争的动力机制及数值模拟

建立了集合种群物种在两个斑块中对资源竞争的数学模型,并进行了数值模拟实验,结果表明：（1）通过R^＊来预测竞争物种的结局,存在几种可能性：一是具有低R^＊值的物种竞争取代高R^＊值的物种;二是具有不同R^＊值的物种,甚至是具有相同R^＊值的物种也存在共存的可能性;三是具有高R^＊值的物种也可以竞争排斥低R^＊值的物种,结论存在不确定性。（2）竞争物种的随机迁移形成了源一汇结构,对物种竞争共存具有促进作用,但弱的资源利用者（较高的R^＊）的迁移率不宜过高。（3）在种群统计率相同的条件下,资源增长率差异越大,越不利于消费者物种的共存;若种群统计率不相同,在资源增长率相同的情况下,物种共存又是不可能的,在自然界中,物种共存需要资源增长率的差异。（4）不同类型的资源增长对竞争物种的稳定性的影响是不同的。     

Competitive exclusion through reproductive interference

A simple differential equation model was developed to describe the competitive interaction that may occur between species through reproductive interference. The model has the form comparable to Volterra's competition equations, and the graphical analysis of the outcome of the two-species interaction based on its zero-growth isoclines proved that: (1) The possible outcome in this model, as in usual models of resource competition, is either stable coexistence of both species or gradual exclusion of one species by the other, depending critically upon the values of the activity overlapping coefficient c_ij; (2) but, for the same c_ij-values, competitive exclusion is much more ready to occur here than in resource competition; (3) and moreover, the final result of the competition is always dependent on the initial-condition due to its non-linear isoclines, i.e., even under the parameter condition that generally allows both species to coexist, an extreme bias in intial density to one species can readily cause subsequent complete exclusion of its counterparts. Thus, it may follow that the reproductive interference is likely to be working in nature as an efficient mechanism to bring about habitat partitioning in either time or space between some closely related species in insect communities, even though they inhabit heterogeneous habitats where resource competition rarely occurs so that they could otherwise attain steady coexistence.     

Dynamics and coexistence in a system with intraguild mutualism

It is a tenet of ecological theory that two competing consumers cannot stably coexist on a single limiting resource in a homogeneous environment. Many mechanisms and processes have since been evoked and studied, empirically and theoretically, to explain species coexistence and the observed biological diversity. Facilitative interactions clearly have the potential to enhance coexistence. Yet, even though mutual facilitation between species of the same guild is widely documented empirically, the subject has received very little theoretical attention. Here, we study one form of intraguild mutualism in the simplest possibly community module of one resource and two consumers. We incorporate mutualism as enhanced consumption in the presence of the other consumers. We find that intraguild mutualism can (a) significantly enhance coexistence of consumers, (b) induce cyclic dynamics, and (c) give rise to a bi-stability (a ‘joint’ Allee effect) and potentially catastrophic collapse of both consumer species.     

Diets of sexual and sperm‐dependent asexual dace (Chrosomus spp.): relevance to niche differentiation and mate choice hypotheses for coexistence

Sperm‐dependent asexual species must coexist with a sexual species (i.e. a sperm source) to reproduce. The maintenance of this coexistence, and hence the persistence of sperm‐dependent asexual species, may depend on ecological niche separation or preference by males for conspecific (i.e. sexual) mates. We first modified an analytical model to consider both of these mechanisms acting simultaneously on the coexistence of the two species. Our model indicates that a small amount of niche separation between parental species and hybrids can facilitate coexistence by weakening the requirement for male mate preference. We also estimated niche separation empirically in the Chrosomus (formerly Phoxinus) sexual‐asexual system based on diet overlap between sperm‐dependent asexuals and their two sexual host species. Diet overlap between the sexual species was not significant in either lake, whereas the sperm‐dependent asexual had an intermediate niche that overlapped significantly, but somewhat asymmetrically, with both sexual species. These empirical results were then used to parameterize our analytical model to predict the minimum strength of male mate preference required to maintain coexistence in each lake. Some male mate preference is likely required to maintain coexistence in the Chrosomus system, but the minimum required preference depends on the severity of density dependence. Future empirical work on understanding coexistence in sperm‐dependent asexual systems would benefit from taking both niche separation and mate choice into account, and from simultaneous empirical estimates of male mate choice, niche separation, and density dependence.     

戴云山罗浮栲林主要乔木树种营养生态位研究

通过生态位空间分割,应用多维生态位宽度和生态位重叠分析戴云山罗浮栲(Castanopsis fabri)群落主要乔木树种在不同资源空间中的营养利用情况。结果表明,各物种在不同资源空间的营养利用情况存在差异。同一物种不同龄级生态位宽度不同,同一龄级不同物种生态位宽度也存在差异。罗浮栲天然林主要种群生态位重叠值介于0.2~0.3的有33对,占27.5%;大于0.3的有51对,占42.5%,群落中优势种种群生态位具有较大程度重叠,对资源的利用能力相似且竞争格局明显。乔木层中,个体多度分布较大的罗浮栲与其它树种生态位重叠在0.042~0.424,罗浮栲与其它物种在资源利用上所受到的竞争相对较弱,在一定程度上决定了该种群在群落中的优势地位。按照经典的分层频度分析,罗浮栲种群属于典型的衰退种,与群落演替的实际情况相一致。     

Feeding strategies,resource utilisation and potential mechanisms for competitive coexistence of Atlantic salmon and alpine bullhead in a sub-Arctic river

We scrutinised the seasonal food-niche utilisation of river dwelling Atlantic salmon parr and alpine bullhead in order to examine potential mechanisms that may facilitate coexistence of species with similar niches. Fish were sampled monthly during the ice-free season, and diet composition and feeding strategy of the two species were compared by analyses of stomach contents. The dietary niches and feeding strategy of salmon parr and bullheads were highly similar both at the individual and population levels, with high within-phenotype contributions to niche width and pronounced generalisation observed during time periods with severe resource limitations. Our findings suggest that competitive coexistence with similar niches may be facilitated by a generalisation of niche width as predicted by optimal foraging theory, rather than the specialised niche width predicted by classic niche theory as a response to interspecific competition. Competitive coexistence may be particularly widespread in spatially and temporally dynamic habitats such as northern lotic systems, which thus may select for generalisation and convergence of ecological niches.     

Coexistence of insect species competing for a pulsed resource: toward a unified theory of biodiversity in fluctuating environments

Background

One major challenge in understanding how biodiversity is organized is finding out whether communities of competing species are shaped exclusively by species-level differences in ecological traits (niche theory), exclusively by random processes (neutral theory of biodiversity), or by both processes simultaneously. Communities of species competing for a pulsed resource are a suitable system for testing these theories: due to marked fluctuations in resource availability, the theories yield very different predictions about the timing of resource use and the synchronization of the population dynamics between the competing species. Accordingly, we explored mechanisms that might promote the local coexistence of phytophagous insects (four sister species of the genus Curculio) competing for oak acorns, a pulsed resource.

Methodology/Principal Findings

We analyzed the time partitioning of the exploitation of oak acorns by the four weevil species in two independent communities, and we assessed the level of synchronization in their population dynamics. In accordance with the niche theory, overall these species exhibited marked time partitioning of resource use, both within a given year and between different years owing to different dormancy strategies between species, as well as distinct demographic patterns. Two of the four weevil species, however, consistently exploited the resource during the same period of the year, exhibited a similar dormancy pattern, and did not show any significant difference in their population dynamics.

Conclusions/Significance

The marked time partitioning of the resource use appears as a keystone of the coexistence of these competing insect species, except for two of them which are demographically nearly equivalent. Communities of consumers of pulsed resources thus seem to offer a promising avenue for developing a unifying theory of biodiversity in fluctuating environments which might predict the co-occurrence, within the same community, of species that are ecologically either very similar, or very different.     

How competitive intransitivity and niche overlap affect spatial coexistence

Competitive intransitivity is mostly considered outside the main body of coexistence theories that rely primarily on the role of niche overlap and differentiation. How the interplay of competitive intransitivity and niche overlap jointly affects species coexistence has received little attention. Here, we consider a rock–paper–scissors competition system where interactions between species can represent the full spectra of transitive–intransitive continuum and niche overlap/differentiation under different levels of competition asymmetry. By comparing results from pair approximation that only considers interference competition between neighbouring cells in spatial lattices, with those under the mean-field assumption, we show that 1) species coexistence under transitive competition is only possible at high niche differentiation; 2) in communities with partial or pure intransitive interactions, high levels of niche overlap are not necessary to beget species extinction; and 3) strong spatial clustering can widen the condition for intransitive loops to facilitate species coexistence. The two mechanisms, competitive intransitivity and niche differentiation, can support species persistence and coexistence, either separately or in combination. Finally, the contribution of intransitive loops to species coexistence can be enhanced by strong local spatial correlations, modulated and maximised by moderate competition asymmetry. Our study, therefore, provides a bridge to link intransitive competition to other generic ecological theories of species coexistence.     

Swimming with the giant: coexistence patterns of a new redfin minnow Pseudobarbus skeltoni from a global biodiversity hot spot

Ecological niche theory predicts that coexistence is facilitated by resource partitioning mechanisms that are influenced by abiotic and biotic interactions. Alternative hypotheses suggest that under certain conditions, species may become phenotypically similar and functionally equivalent, which invokes the possibility of other mechanisms, such as habitat filtering processes. To test these hypotheses, we examined the coexistence of the giant redfin Pseudobarbus skeltoni, a newly described freshwater fish, together with its congener Pseudobabus burchelli and an anabantid Sandelia capensis by assessing their scenopoetic and bionomic patterns. We found high habitat and isotope niche overlaps between the two redfins, rendering niche partitioning a less plausible sole mechanism that drives their coexistence. By comparison, environment–trait relationships revealed differences in species–environment relationships, making habitat filtering and functional equivalence less likely alternatives. Based on P. skeltoni's high habitat niche overlap with other species, and its large isotope niche width, we inferred the likelihood of differential resource utilization at trophic level as an alternative mechanism that distinguished it from its congener. In comparison, its congener P. burchelli appeared to have a relatively small trophic niche, suggesting that its trophic niche was more conserved despite being the most abundant species. By contrast, S. capensis was distinguished by occupying a higher trophic position and by having a trophic niche that had a low probability of overlapping onto those of redfins. Therefore, trophic niche partitioning appeared to influence the coexistence between S. capensis and redfins. This study suggests that coexistence of these fishes appears to be promoted by their differences in niche adaptation mechanisms that are probably shaped by historic evolutionary and ecological processes.     

Habitat Selection,the Included Niche,and Coexistence in Plant‐Specialist Frogs from Madagascar

Classic niche partitioning suggests that coexistence among asymmetric competitors is facilitated by differential resource use. Coexistence is also possible, however, when a species only has access to resources that are shared with a competitor, providing it is the superior competitor on that resource (the ‘included niche’). To test predictions of these two coexistence mechanisms, we studied habitat selection of two closely related sympatric plant‐specialist frogs from Madagascar (Guibemantis bicalcaratus and Guibemantis punctatus). Both species live and breed only in the water‐filled leaf axils of Pandanus plants, and previous experiments with their tadpoles demonstrated asymmetric competition. In a 3‐yr field study, we: (1) monitored the biotic and abiotic conditions of 348 plants; (2) surveyed these plants for frogs; (3) undertook a mark‐recapture study; and (4) conducted an experiment where we manipulated the amount of detritus in plants. We identified several differences in the conditions of the habitats selected by both species (e.g., plant height, canopy cover over the plant, abundance of heterospecifics). Co‐occurrence was nevertheless common, and G. punctatus persisted almost exclusively in plants it shared with G. bicalcaratus. As predicted by theory, G. punctatus was the superior competitor, at least in the tadpole stage. The inferior competitor (G. bicalcaratus) had access to exclusive resources not available to G. punctatus, by virtue of a faster developmental rate that permitted reproduction in lower quality plants. While there was some evidence of weak niche partitioning, we conclude that coexistence in these plant‐specialist frogs is primarily via an included niche mechanism. Abstract in French is available at http://www.blackwell‐synergy.com/loi/btp .     

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.