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opencc-zeroDec 2014View details →

Data from: Ecological explanations to island gigantism: dietary niche divergence, predation and size in an endemic lizard

Although rapid evolution of body size on islands has long been known, the ecological mechanisms behind this island phenomenon remain poorly understood. Diet is an important selective pressure for morphological divergence. Here we investigate if selection for novel diets has contributed to the multiple independent cases of island gigantism in the Skyros wall lizard (Podarcis gaigeae) and if diet, predation, or both factors best explain island gigantism. We combined data on body size, shape, bite force, and realized and available diets to address this. Several lines of evidence suggest that diet has contributed to the island gigantism. The larger islet lizards have relatively wider heads and higher bite performance in relation to mainland lizards than would be expected from size differences alone. The proportions of consumed and available hard prey are higher on islets than mainland localities, and lizard body size is significantly correlated with the proportion of hard prey. Furthermore, the main axis of divergence in head shape is significantly correlated with dietary divergence. Finally, a model with only diet and one including diet and predation regime explain body size divergence equally well. Our results suggest that diet is an important ecological factor behind insular body size divergence, but could be consistent with an additional role for predation.

opencc-zeroApr 2020View details →

Data from: Trophic niche size and overlap decreases with increasing ecosystem productivity

The production and transfer of biomass through trophic relationships is a core ecosystem function. The movement of energy through the food web is mediated by organisms operating in their niche space. For generalists, the size of this niche space is inherently plastic and changes in response to available food sources. Therefore, this relationship between ecosystem productivity and niche size is an important determinant of ecosystem function. Competing theories about the nature of this relationship predict that as productivity increases niche size will either increase as species capitalize on a general increase in resource availability or decrease as it becomes viable to focus on preferred production channels. Here, we test these two competing theoretical frameworks using a novel approach to determine trophic niche size using stable isotope analysis and hypervolume metrics. Resource use is quantified in two generalist fish species at three productivity levels in a seagrass ecosystem. Niche size of both species was inversely related to seagrass productivity, consistent with the hypothesis that increasing productivity allows species to focus on a narrower diet. This pattern describes the relationship between ecosystem production and niche size and provides an empirical ecological explanation for the resource maximization behaviors commonly observed in nature.

opencc-zeroDec 2012View details →

Data from: Increasing zooplankton size diversity enhances the strength of top-down control on phytoplankton through diet niche partitioning

1. The biodiversity-ecosystem functioning debate is a central topic in ecology. Recently, there has been a growing interest in size diversity because body size is sensitive to environmental changes and is one of the fundamental characteristics of organisms linking many ecosystem properties. However, how size diversity affects ecosystem functioning is an important yet unclear issue. 2. To fill the gap, with large-scale field data from the East China Sea, we tested the novel hypothesis that increasing zooplankton size diversity enhances top-down control on phytoplankton (H1) and compared it with five conventional hypotheses explaining the top-down control: flatter zooplankton size spectrum enhances the strength of top-down control (H2); nutrient enrichment lessens the strength of top-down control (H3); increasing zooplankton taxonomic diversity enhances the strength of top-down control (H4); increasing fish predation decreases the strength of top-down control of zooplankton on phytoplankton through trophic cascade (H5); increasing temperature intensifies the strength of top-down control (H6). 3. The results of univariate analyses support the hypotheses based on zooplankton size diversity (H1), zooplankton size spectrum (H2), nutrient (H3), and zooplankton taxonomic diversity (H4), but not the hypotheses based on fish predation (H5) and temperature (H6). More in depth analyses indicate that zooplankton size diversity is the most important factor in determining the strength of top-down control on phytoplankton in the East China Sea. 4. Our results suggest a new potential mechanism, that increasing predator size diversity enhances the strength of top-down control on prey through diet niche partitioning. This mechanism can be explained by the optimal predator-prey body-mass ratio concept. Suppose each size group of zooplankton predators has its own optimal phytoplankton prey size, increasing size diversity of zooplankton would promote diet niche partitioning of predators and thus elevates the strength of top-down control.

opencc-zeroOct 2021View details →

Data from: Species interactions, environmental gradients and body size shape population niche width

Competition for shared resources is commonly assumed to restrict population-level niche width of coexisting species. However, the identity and abundance of coexisting species, the prevailing environmental conditions, and the individual body size may shape the effects of interspecific interactions on species' niche width. Here we study the effects of inter- and intraspecific interactions, lake area and altitude, and fish body size on the trophic niche width and resource use of a generalist predator, the littoral-dwelling large, sparsely-rakered morph of European whitefish (Coregonus lavaretus; hereafter LSR whitefish). We use stable isotope, diet and survey fishing data from 14 subarctic lakes along an environmental gradient in northern Norway. The isotopic niche width of LSR whitefish showed a humped-shaped relationship with increasing relative abundance of sympatric competitors, suggesting widest population niche at intermediate intensity of interspecific interactions. The isotopic niche width of LSR whitefish tended to decrease with increasing altitude, suggesting reduced niche in colder, less productive lakes. LSR whitefish typically shifted to a higher trophic position and increased reliance on littoral food resources with increasing body size, although between-lake differences in ontogenetic niche shifts were evident. In most lakes, LSR whitefish relied less on littoral food resources than coexisting fishes and the niche overlap between sympatric competitors was most evident among relatively large individuals (>250 mm). Individual niche variation was highest among >200 mm long LSR whitefish, which likely have escaped the predation window of sympatric predators. We demonstrate that intermediate intensity of interspecific interactions may broaden species' niche width, whereas strong competition for limited resources and high predation risk may suppress niche width in less productive environments. Acknowledging potential humped-shaped relationships between population niche width and interspecific interactions can help us understand species' responses to environmental disturbance (e.g., climate change and species invasions) as well as the driving forces of niche specialization.

opencc-zeroMay 2024View details →

Data from: Trophic niches of Collembola communities change with elevation but also with body size and life form

Climate change increases habitat loss of endemic tree species and drives forest conversion in mountainous forests. Elevational gradients provide the opportunity to predict possible consequences of such changes. While species compositions of various taxa have been investigated along elevational gradients, data on trophic changes in soil-dwelling organisms is scarce. Here, we analyze trophic changes of the Collembola community along the northern slope of Changbai Mountain, China. We sampled seven elevations (800-1700 m asl) with 150 m elevational difference along a primary forest gradient. At eight subplots per elevation, we categorized Collembola species into life forms, measured individual body lengths and bulk stable isotopes. Mean and minimum Δ15N and mean Δ13C increased with increasing elevation, while the range of Δ15N decreased. Maximum and minimum of Δ13C differed between elevations but showed no linear response. Isotopic uniqueness increased with elevation. Δ15N values of Collembola species occurring across all elevations increased with elevation. Changes in Δ15N with elevation were most pronounced in hemiedaphic species. Δ15N values increased with decreasing body size in hemiedaphic and euedaphic species. Δ13C increased strongest with elevation in euedaphic species. Overall, the results suggest that Collembola species functioning as primary decomposers shift towards functioning as secondary decomposers at higher elevations. Further, access to alternative food resources may depend on Collembola life form and body size, this relationship, however, likely varies between ecosystems. Collembola functioning as secondary decomposers in coniferous forests may function as primary decomposers under climate driven forest conversion as species boundaries of tree species of lower elevations expand.

opencc-zeroDec 2017View details →

Data from: Naturalized distributions show that climatic disequilibrium is structured by niche size in pines (Pinus L.)

Aim: The assumption that species' native distributions are in equilibrium with climate has been shown to be frequently violated, despite its centrality to many niche model applications. We currently lack a framework that predicts these violations. Here we examine whether variation in climatic disequilibrium is structured by properties of species' native distributions and climatic niches. Location: Global Methods: We built climatic niche models for 106 pine (Pinus L.) species, including 25 that have naturalized outside their native range. We measured the extent of climate space occupied exclusively by naturalized populations and considered what fraction of this space was available within the native continent and near the native range. We examined the consequences of disequilibrium for estimates of potential range filling and sister-species niche conservatism. Results: Most species (23 of 25) have naturalized in climate conditions outside of the native niche, leading to increases in the total known suitable climate space. Increases in niche size were negatively related to native niche size. Increases were often large – one species expanded its niche by almost 10% of the global climate space. These increases were associated primarily with cooler, wetter, and less seasonal climates. Increases in known niche size lowered potential range filling estimates within species' native continent and ecoregion. Naturalized data did not strengthen support for niche conservatism among sister species. Main Conclusions: Among pines, climatic disequilibrium is the norm and not the exception. The magnitude of this disequilibrium can be vast, such that the native range greatly underrepresents the true climatic tolerances of some species. Fortunately, this disequilibrium can largely be predicted by the size of a species' native niche. Accounting for this disequilibrium can improve our ability to characterize ecological phenomena, including potential range filling. This is an essential step toward improving the conservation value of ecological niche models.

opencc-zeroDec 2012View details →

Data from: Trophic niche width increases with bill size variation in a generalist passerine: a test of the niche variation hypothesis

1. The niche variation hypothesis (NVH) predicts that populations with wider niches are phenotypically more variable than populations with narrower niches, which is frequently used to explain diversifying processes such as ecological release. However, not all empirical evidence supports the NVH. Furthermore, a relationship between population phenotypic variation and niche width can be caused by sexual selection or environmental gradients, which should be carefully considered along with competition in explaining niche variation. 2. In this study we used eight populations of a generalist passerine species, Paradoxornis webbianus (vinous-throated parrotbill), to test the NVH. We assessed evidence of ecological sexual dimorphism and environmental gradients in bill morphology of P. webbianus. A total of 170 P. webbianus from eight sites ranging 24-2,668 m in altitude were included in this study. We used two principal components to quantify bill morphology, one describes bill size and the other describe bill slenderness. We used stable carbon and nitrogen isotope values of bird feathers to quantify trophic positions, and we estimated population trophic niche width using Bayesian standardized ellipse area. 3. Paradoxornis webbianus with larger and more slender bills fed at higher trophic levels and population trophic niche width tended to increase with bill size variation, supporting the NVH. The males had larger bills and marginally higher nitrogen isotope values than the females, suggesting ecological sexual dimorphism. Despite a positive correlation between bill size and wing length indicating sexual selection for larger male size, only three of the eight populations showed both male-biased bill size and male-biased wing length. Sexual dimorphism explained 13%-64% of bill size variation across sites, suggesting its role in niche variation could vary greatly among populations. The variation in bill slenderness in P. webbianus increased with elevation. However, neither bill size variation nor trophic niche width changed with elevation. Therefore, environmental gradients that could be reflected in the elevation are not likely to drive the observed morphological and niche variation. 4. This study provides an empirical case for the NVH and highlights the importance to investigate sexual dimorphism and environmental gradients in the studies of niche dynamics.

opencc-zeroNov 2021View details →

Vertical niche and elevation range size in tropical ants: implications for climate resilience

Aim: We propose that forest trees create a vertical dimension for ecological niche variation that generates different regimes of climatic exposure, which in turn drives species elevation distributions. We test this hypothesis by statistically modelling the vertical and elevation distributions and microclimate exposure of rainforest ants. Location: Wet Tropics Bioregion, Australia Methods: We conducted 60 ground-to-canopy surveys to determine the vertical (tree) and elevation distributions, and microclimate exposure of ants (101 species) at 15 sites along four mountain ranges. We statistically modelled elevation range size as a function of ant species' vertical niche breadth and exposure to temperature variance for 55 species found at two or more trees. Results: We found a positive association between vertical niche and elevation range of ant species: for every 3 m increase in vertical niche breadth our models predict a ~150% increase in mean elevation range size. Temperature variance increased with vertical height along the arboreal gradient and ant species exposure to temperature variance explained some of the variation in elevation range size. Main Conclusions: We demonstrate that arboreal ants have broader elevation ranges than ground-dwelling ants and are likely to have increased resilience to climatic variance. The capacity of species to expand their niche by climbing trees could influence their ability to persist over broader elevation ranges. We propose that wherever vertical layering exists - from oceans to forest ecosystems - vertical niche breadth is a potential mechanism driving macrogeographic distribution patterns and resilience to climate change.

opencc-zeroAug 2021View details →

Data and Code for: Isotopic Niche Size of Coregonus artedi (sensu lato) Increases in the Presence of Mysis diluviana, Expanded Habitat Use and Phenotypic Diversity

Post-glacial colonization of lakes in Algonquin Park, Ontario, Canada resulted in food webs with cisco (Coregonus artedi sensu lato) and either Mysis diluviana or Chaoborus spp. as the dominant diel migrator. Mysis as prey, its diel movements and benthic occupancy, are hypothesized to be key elements of ecological opportunity for cisco diversity in the Laurentian Great Lakes. If correct, the hypothesis strongly implies that lakes with Mysis would have greater trophic niche size and drive greater adaptive radiation of cisco forms relative to lakes without Mysis. The dichotomy in diel migrator in Algonquin Park lakes was an opportunity to assess the isotopic niche size of cisco (δ15N and δ13C) and determine if niche size expands with Mysis presence. We found the presence of Mysis is necessary to expand isotopic niche size in our study lakes. The use of habitats not typically associated with the ancestral form of cisco (e.g., benthic habitats) and phenotypic diversity (blackfin and cisco) also continue to expand niche size in Mysis-based food webs. Partial ecological speciation based on a large niche space appears to be present in one lake (Cauchon Lake) where use of alternative habitats is the only real difference in cisco. The presence of blackfin expands niche space in Cedar and Radiant Lakes. This was not matched in Hogan Lake where niche space was relatively smaller with similar forms. Possible reasons for this discrepancy may be related to the asymmetric basin of Hogan Lake and whether the two forms overlap during cool and cold-water periods of the annual temperature cycle. By comparing trophic niche size among lakes with and without Mysis we conclude that Mysis provides a key ecological opportunity for cisco diversity in our study lakes and likely more widely.

Figure 2 in Body size estimation and evolution in metriorhynchid crocodylomorphs: implications for species diversification and niche partitioning

Figure 2. Evolutionary relationships of metriorhynchid genera based on the new phylogenetic analysis presented herein. Geological ranges are based on the taxonomic compendium in Young et al. (2010). Labelled nodes represent clades: (1) Metriorhynchidae; (2) Metriorhynchinae; (3) Geosaurinae; and (4) Geosaurini.

Figure 5 in Body size estimation and evolution in metriorhynchid crocodylomorphs: implications for species diversification and niche partitioning

Figure 5. Ordination plot of femoral length against total body length in living and fossil crocodylomorphs. The taxa from Farlow et al. (2005) are in light grey, and their Alligator 95% prediction interval is shown by the two parallel oblique lines.

Figure 4 in Body size estimation and evolution in metriorhynchid crocodylomorphs: implications for species diversification and niche partitioning

Figure 4. Ordination plot of cranial length against total body length in living and fossil crocodylomorphs. Convex hulls surround the different clades of crocodylomorphs.

Figure 3 in Body size estimation and evolution in metriorhynchid crocodylomorphs: implications for species diversification and niche partitioning

Figure 3. Evolutionary relationships of metriorhynchid species with body size data. Phylogeny based on the new phylogenetic analysis presented herein. Labelled nodes represent clades: (1) Metriorhynchidae; (2) Metriorhynchinae; (3) Geosaurinae; and (4) Geosaurini.

Fig. 2 in Explaining mammalian abundance and elevational range size with body mass and niche characteristics

Fig. 2.—Relationship between ABD (mean abundance) and ER (elevational range size) of small mammals along the (a) Wolong, (b) Luoji, (c) Gongga, (d) Baima Snow, and (e) Sejila gradients. ABD and ER were log10(x + 1) transformed. Open circles indicate individual species (n value represents the number of species), and the best fitted line as calculated by linear regression analysis (not accounting for the effects of phylogeny) is shown.

Fig. 4 in Explaining mammalian abundance and elevational range size with body mass and niche characteristics

Fig. 4.—Scatterplots illustrating the relationships between NP (niche position) and ABD (mean abundance, a–e) and ER (elevational range size, f–j) of small mammals along the Wolong, Luoji, Gongga, Baima Snow, and Sejila gradients. All the three variables were log10(x + 1) transformed. Open circles indicate individual species, and the best fitted line as calculated by linear regression analysis (not accounting for the effects of phylogeny) is shown.

Fig. 1 in Explaining mammalian abundance and elevational range size with body mass and niche characteristics

Fig. 1.—Alternative path models used in phylogenetic path analysis to assess the relationships among body mass (MASS), niche breadth (NB), niche position (NP) on mean abundance (ABD) and elevation range size (ER) of species. The hypothesized relationships among variables are described via regression formulas shown at the top of each model and depicted by the direction of the arrows.

Fig. 3 in Explaining mammalian abundance and elevational range size with body mass and niche characteristics

Fig. 3.—Scatterplots illustrating the relationships between MASS (body mass) and ABD (mean abundance, a–e) and ER (elevational range size, f–j) of small mammals along the Wolong, Luoji, Gongga, Baima Snow, and Sejila gradients. All the three variables were log10(x + 1) transformed. Open circles indicate individual species, and the best fitted line as calculated by linear regression analysis (not accounting for the effects of phylogeny) is shown.

Fig. 5 in Explaining mammalian abundance and elevational range size with body mass and niche characteristics

Fig. 5.—Scatterplots illustrating the relationships between NB (niche breadth) and ABD (mean abundance, a–e) and ER (elevational range size, f–j) of small mammals along the Wolong, Luoji, Gongga, Baima Snow, and Sejila gradients. All the three variables were log10(x + 1) transformed. Open circles indicate individual species, and the best fitted line as calculated by linear regression analysis (not accounting for the effects of phylogeny) is shown.

Fig. 6 in Explaining mammalian abundance and elevational range size with body mass and niche characteristics

Fig. 6.—Best supported model from phylogenetic path analysis along the five gradients. Arrows represent the effects of MASS (body mass), NP (niche position), and NB (niche breadth) on ABD (mean abundance) and ER (elevational range size), and values aside are standardized regression coefficients. Red arrows indicate positive effects and blue arrows indicate negative effects. See the results of all six candidate models for each gradient in Supplementary Data SD7.