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Concept: Niche differentiation

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Body size and metabolic rate both fundamentally constrain how species interact with their environment, and hence ultimately affect their niche. While many mechanisms leading to these constraints have been explored, their effects on the resolution at which temporal information is perceived have been largely overlooked. The visual system acts as a gateway to the dynamic environment and the relative resolution at which organisms are able to acquire and process visual information is likely to restrict their ability to interact with events around them. As both smaller size and higher metabolic rates should facilitate rapid behavioural responses, we hypothesized that these traits would favour perception of temporal change over finer timescales. Using critical flicker fusion frequency, the lowest frequency of flashing at which a flickering light source is perceived as constant, as a measure of the maximum rate of temporal information processing in the visual system, we carried out a phylogenetic comparative analysis of a wide range of vertebrates that supported this hypothesis. Our results have implications for the evolution of signalling systems and predator-prey interactions, and, combined with the strong influence that both body mass and metabolism have on a species' ecological niche, suggest that time perception may constitute an important and overlooked dimension of niche differentiation.

Concepts: Psychology, Evolution, Metabolism, Energy, Organism, Ecology, Information, Niche differentiation

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To explain diversity in forests, niche theory must show how multiple plant species coexist while competing for the same resources. Although successional processes are widespread in forests, theoretical work has suggested that differentiation in successional strategy allows only a few species stably to coexist, including only a single shade tolerant. However, this conclusion is based on current niche models, which encode a very simplified view of plant communities, suggesting that the potential for niche differentiation has remained unexplored. Here, we show how extending successional niche models to include features common to all vegetation-height-structured competition for light under a prevailing disturbance regime and two trait-mediated tradeoffs in plant function-enhances the diversity of species that can be maintained, including a diversity of shade tolerants. We identify two distinct axes of potential niche differentiation, corresponding to the traits leaf mass per unit leaf area and height at maturation. The first axis allows for coexistence of different shade tolerances and the second axis for coexistence among species with the same shade tolerance. Addition of this second axis leads to communities with a high diversity of shade tolerants. Niche differentiation along the second axis also generates regions of trait space wherein fitness is almost equalized, an outcome we term “evolutionarily emergent near-neutrality.” For different environmental conditions, our model predicts diverse vegetation types and trait mixtures, akin to observations. These results indicate that the outcomes of successional niche differentiation are richer than previously thought and potentially account for mixtures of traits and species observed in forests worldwide.

Concepts: Scientific method, Evolution, Life, Species, Ecology, Fern, Ecological niche, Niche differentiation

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Asexual reproduction is expected to reduce the adaptive potential to novel or changing environmental conditions, restricting or altering the ecological niche of asexual lineages. Asexual lineages of plants and animals are typically polyploid, an attribute that may influence their genetic variation, plasticity, adaptive potential, and niche breadth. The genus Boechera (Brassicaceae) represents an ideal model to test the relative ecological and biogeographic impacts of reproductive mode and ploidy because it is composed of diploid sexual and both diploid and polyploid asexual (i.e., apomictic) lineages. Here, we demonstrate a strong association between a transcriptionally conserved allele and apomictic seed formation. We then use this allele as a proxy apomixis marker in 1,649 accessions to demonstrate that apomixis is likely to be a common feature across the Boechera phylogeny. Phylogeographic analyses of these data demonstrate (i) species-specific niche differentiation in sexuals, (ii) extensive niche conservation between differing reproductive modes of the same species, (iii) ploidy-specific niche differentiation within and among species, and (iv) occasional niche drift between apomicts and their sexual ancestors. We conclude that ploidy is a substantially stronger and more common driver of niche divergence within and across Boechera species although variation in both traits may not necessarily lead to niche evolution on the species scale.

Concepts: Evolution, Biology, Species, Ecology, Asexual reproduction, Parthenogenesis, Apomixis, Niche differentiation

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A fundamental aim of conservation biology is to understand how species respond to threatening processes, with much research effort focused on identifying threats and quantifying spatial and temporal patterns of species decline. Here, we argue that threats often reduce the realized niche breadth of declining species because environmental, biotic, and evolutionary processes reduce or amplify threats, or because a species' capacity to tolerate threats varies across niche space. Our ‘niche reduction hypothesis’ provides a new lens for understanding why species decline in some locations and not others. This perspective can improve management of declining species by identifying where to focus resources and which interventions are most likely to be effective in a given environment.

Concepts: Biodiversity, Conservation biology, Evolution, Biology, Species, Ecology, Knowledge, Niche differentiation

1

Differential resource use allows a diversity of species to co-exist in a particular area by specializing in individual ecological niches. Four-horned antelope Tetracerus quadricornis is endemic to the Indian subcontinent and has a restricted distribution in Nepal and India; however, the barking deer Muntiacus vaginalis is relatively common throughout its wide distribution range. We wanted a better understanding of their habitats and how these two similarly sized solitary ungulates manage to coexist in lowland Nepal. We used fecal pellet belt transect surveys in the Babai valley, Bardia National Park to study the habitat associations of both species. We found empirical evidence that four-horned antelope prefer hill sal forest and deciduous hill forest at higher elevations, whereas barking deer preferred riverine and sal forest in lower elevations. We found a clear niche differentiation of four-horned antelope and barking deer that made the coexistence of these similarly sized solitary ungulates possible. Hence, resource partitioning is the key to coexistence of these solitary ungulates, and the fine-grained habitat mosaic of different forest types in the study landscape appears to be the underlying feature. Therefore, maintaining the habitat mosaic and preserving valuable hill sal and deciduous hill forests will facilitate the coexistence of herbivores in sub-tropical regions.

Concepts: Ecology, Deer, Habitats, Ecological niche, Bovinae, Antelope, Niche differentiation, Four-horned Antelope

1

Partitioning of ecological niche is expected in lekking species that show marked sexual size dimorphism as a consequence of sex-specific ecological constraints. However, niche partitioning is uncertain in species with moderate sexual dimorphism. In addition, the ecological niche of a species may also be affected by landscape composition; particularly, agricultural fragmentation may greatly influence the trophic behavior of herbivores. We studied trophic niche variation in Greater Prairie-Chickens (Tympanuchus cupido), a grouse species that shows moderate sex-dimorphism. Greater Prairie-Chickens are native to tallgrass prairies of North America, although populations persist in less natural mosaics of cropland and native habitats. We used stable isotope analysis of carbon and nitrogen in blood, claws and feathers to assess seasonal differences in trophic niche breadth and individual specialization between male and female Greater Prairie-Chickens, and between birds living in continuous and fragmented landscapes. We found that females showed broader niches and higher individual specialization than males, especially in winter and autumn. However, differences between females and males were smaller in spring when birds converge at leks, suggesting that females and males may exhibit similar feeding behaviors during the lekking period. In addition, we found that birds living in native prairies showed greater annual trophic variability than conspecifics in agricultural mosaic landscapes. Native habitats may provide greater dietary diversity, resulting in greater diversity of feeding strategies.

Concepts: Human, Male, Ecology, Sexual dimorphism, Gender, Sex, Grouse, Niche differentiation

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Tephroseris longifolia agg. is a complex group of outcrossing perennials distributed throughout Central Europe. Recent morphological study revealed six morphotypes corresponding to five previously distinguished subspecies, together with Alpine and Pannonian morphotypes ofT. longifoliasubsp.longifolia. The delimited morphotypes differ in relative DNA content, geographical range, and rarity. We compared ecological niches of the six morphotypes in order to assess the impact of ecological differentiation on the speciation processes within theT. longifoliaagg. Further, we examined whether morphotypes with small range are more ecologically specialized than their widespread relatives. The distribution area of the aggregate includes the Alps, Apennines, Carpathians, and the Pannonian Basin. Ecological variables linked to climate, topography, soil, and vegetation were gathered from 135 circular plots recorded in 35 localities. Related variables were grouped to describe the partial ecological niches: climatic, topographic, pedological, biotic, and coenotic (based either on vascular plants or on bryophytes), each of them visualized as an envelope in the two-dimensional nonmetric multidimensional scaling ordination space. Each partial ecological niche for a given morphotype was characterized by its position (location of the envelope centroid), breadth (surface of the envelope), and overlaps with envelopes of the other morphotypes. Mantel statistics based on Spearman correlation coefficients were used to quantify differentiation of morphotypes in ecological parameters represented by the partial ecological niches. The significant niche differentiation was confirmed for climatic, topographic, pedological, and vascular plant-based coenotic niches. Ecological niche differentiation corresponded well to morphological and partially also to karyological differentiation. Narrowly distributed morphotypes occupied more specific habitats and had narrower ecological niches than their widespread relatives. Ecological differentiation could be considered an important driver in allopatric speciation within theT. longifoliaagg. Our results demonstrate that quantification of ecological divergence is helpful in assessing evolutionary history of closely related taxa.

Concepts: Evolution, Ecology, Spearman's rank correlation coefficient, Invasive species, Allopatric speciation, Ecological niche, Charles Sutherland Elton, Niche differentiation

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Intercropping studies usually focus on yield advantage and interspecific interactions but few quantify temporal niche differentiation and its relationship with intercropping yield advantage. A field experiment conducted in northwest China in 2013 and 2014 examined four intercropping systems (oilseed rape/maize, oilseed rape/soybean, potato/maize, and soybean/potato) and the corresponding monocultures. Total dry matter data collected every 20 d after maize emergence were fitted to logistic models to investigate the temporal dynamics of crop growth and interspecific interactions. All four intercropping systems showed significant yield advantages. Temporal niche complementarity between intercropped species was due to differences in sowing and harvesting dates or the time taken to reach maximum daily growth rate or both. Interspecific interactions between intercropped species amplified temporal niche differentiation as indicated by postponement of the time taken to reach maximum daily growth rate of late-maturing crops (i.e. 21 to 41 days in maize associated with oilseed rape or potato). Growth trajectories of intercropped maize or soybean recovered after the oilseed rape harvest to the same values as in their monoculture on a per plant basis. Amplified niche differentiation between crop species depends on the identity of neighboring species whose relative growth rate is crucial in determining the differentiation.

Concepts: Biodiversity, Agriculture, Interspecific competition, Harvest, Crops, Crop, Fodder, Niche differentiation

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1.Species interact with each other and their environment over a range of temporal scales, yet our understanding of resource partitioning and the mechanisms of species coexistence is largely restricted to modern time-scales of years to decades. Furthermore, the relative magnitudes of inter- versus intraspecific variation in resource use are rarely considered, despite the potential for the latter to influence a species' ability to cope with changing environmental conditions. 2.Modern desert rodent communities are thought to be strongly structured by competitive interactions, with niche partitioning of food resources hypothesized to explain the coexistence of multiple sympatric granivores. Yet the stability of niche dynamics over extended temporal scales within desert rodent communities is unknown. 3.I examined the isotopic niche dynamics of four common sympatric desert mice (three granivores: Chaetodipus formosus, Perognathus longimembris, and Reithrodontomys megalotis, and one omnivore: Peromyscus maniculatus) in the Smoke Creek Desert of northwestern Nevada using (13) C and (15) N isotopes obtained from “Modern” (2008-2013 CE), “Historical” (1989-2005 CE), and Holocene fossil specimens spanning the last ca. 7,500 years. 4.I found significant variation in niche position, niche breadth, and interspecific niche overlap of these species through time. The niche breadth dynamics of the cricetids (P. maniculatus and R. megalotis) were positively correlated with one another, while the niche breadth dynamics of the heteromyid C. formosus were negatively correlated with those of all other species. Body size, dietary functional group, paleoenvironmental trends, and time-averaging provided little explanatory power. Importantly, Modern and Historical patterns of resource use and partitioning differed from Holocene baselines in terms of decreased niche overlap and in the absolute and relative position of each species' niche in at least one isotopic axis. 5.These observations suggest that each species' resource use changed individualistically over the Holocene, hence niche dynamics are poorly explained by the hypothesis of temporally-stable species interactions at millennial time-scales. Furthermore, changes to the resource base over the last century (likely due to the spread of invasive cheatgrass) may be increasing resource partitioning in the Modern, pushing species past their baseline ranges of resource use variation. This article is protected by copyright. All rights reserved.

Concepts: Scientific method, Theory, Ecological niche, Neotominae, Niche differentiation, Perognathus

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Fundamental to competitive displacement in biological invasion is that exotic species occupy the ecological niches of native species in novel environments. Contrasting outcomes of competitive displacement have occurred between Liriomyza trifolii and L. sativae in different geographical regions following their introduction. Various factors have been advanced in an attempt to explain these different competitive outcomes, although none of these explanations have addressed the effects of niche differences. We conducted field cage experiments to compare the feeding and habitat niches of the two leafminer species and their primary parasitoid, Opius biroi, when occurring together on kidney bean. A wider spatiotemporal niche breadth was found in L. trifolii (0.3670) than in L. sativae (0.3496). With respect to the parasitoid, the proportional niche similarity between L. sativae and the parasitoid was 0.3936 but only 0.0835 for L. trifolii, while similar results were found for niche overlap, indicating that stronger trailing behaviour and parasitic effects of O. biroi occurred in L. sativae. In conclusion, L. trifolii has outperformed L. sativae in occupying the ecological niche and is superior to L. sativae in avoiding parasitization by the pupal parasitoid, O. biroi.

Concepts: Ecology, Parasitism, Difference, Invasive species, Ecological niche, Biogeography, Charles Sutherland Elton, Niche differentiation