Changes In Niche Breadth Research Articles

Climatic‐niche breadth, niche position, and speciation in lizards and snakes

AbstractAimThe climatic niche is associated with diversification in many groups of animals and plants. However, the relationships between climatic‐niche breadth evolution, climatic‐niche position evolution, and speciation remain underexplored. It is particularly unclear whether changes in climatic‐niche breadth are related to diversification. We tested two hypotheses relating niche breadth, niche position, and speciation using climatic data in Squamata (lizards and snakes), one of the largest radiations of tetrapods. These hypotheses were: (1) the oscillation hypothesis (niche breadth changes along with niche position and speciation) and (2) the musical‐chairs hypothesis (niche breadth remains relatively constant when niche position changes during speciation).LocationGlobal.TaxonSquamata (lizards and snakes).MethodsWe estimated rates of speciation and evolutionary rates for both climatic‐niche position and climatic‐niche breadth for 5320 squamate species. We tested relationships among these rates using Bayesian phylogenetic generalised linear‐mixed models.ResultsHigher speciation rates were associated with higher rates of evolution in niche position and in niche breadth. Faster rates of change in niche breadth were related to narrower niches and faster rates of change in niche position.Main ConclusionsOur results support the oscillation hypothesis to explain the relationships between speciation and changes in climatic‐niche position and climatic‐niche breadth. We found that species that changed climatic‐niche breadths more rapidly: (1) speciated faster; (2) evolved towards narrower niche breadths; and (3) changed climatic‐niche positions more rapidly. These results suggest that oscillation between wider and narrower niches is coupled with climatic‐niche divergence and speciation. These conclusions may apply to many other groups of plants and animals in which speciation is often related to climatic‐niche divergence.

Cultivation has selected for a wider niche and large range shifts in maize.

BackgroundMaize (Zea mays L.) is a staple crop cultivated on a global scale. However, its ability to feed the rapidly growing human population may be impaired by climate change, especially if it has low climatic niche and range lability. One important question requiring clarification is therefore whether maize shows high niche and range lability.MethodsWe used the COUE scheme (a unified terminology representing niche centroid shift, overlap, unfilling and expansion) and species distribution models to study the niche and range changes between maize and its wild progenitors using occurrence records of maize, lowland teosinte (Zea mays ssp. parviglumis) and highland teosinte (Zea mays ssp. mexicana), respectively, as well as explore the mechanisms underlying the niche and range changes.ResultsIn contrast to maize in Mexico, maize did not conserve its niche inherited from lowland and highland teosinte at the global scale. The niche breadth of maize at the global scale was wider than that of its wild progenitors (ca. 5.21 and 3.53 times wider compared with lowland and highland teosinte, respectively). Compared with its wild progenitors, maize at global scale can survive in regions with colder, wetter climatic conditions, as well as with wider ranges of climatic variables (ca. 4.51 and 2.40 times wider compared with lowland and highland teosinte, respectively). The niche changes of maize were largely driven by human introduction and cultivation, which have exposed maize to climatic conditions different from those experienced by its wild progenitors. Small changes in niche breadth had large effects on the magnitude of range shifts; changes in niche breadth thus merit increased attention.DiscussionOur results demonstrate that maize shows wide climatic niche and range lability, and this substantially expanded its realized niche and potential range. Our findings also suggest that niche and range shifts probably triggered by natural and artificial selection in cultivation may enable maize to become a global staple crop to feed the growing population and adapting to changing climatic conditions. Future analyses are needed to determine the limits of the novel conditions that maize can tolerate, especially relative to projected climate change.

Response of native and non-indigenous zooplankton to inherent system features and management in two Basque estuaries: A niche decomposition approach

The realized ecological niches of native zooplankton and non-indigenous species (NIS) were analysed in the contrasting estuaries of Bilbao and Urdaibai from 1998 to 2015 in order to study their responses to the particular features of each estuary and the biotic and abiotic changes along the study period. The marginality and tolerance of zooplankton taxa was estimated for the two estuaries together using the OMI analysis, whilst, by means of the WitOMI analysis, niches were differentiated into spatial subniches to assess the differences between estuaries and into temporal subniches to determine the variations in time within each estuary. The changes in the niche overlap of the main native and NIS species were calculated with the D-metric. Results showed that the combined effect of salinity gradients and seasonal variations, linked to temperature, defined the main spatio-temporal niches of zooplankton taxa in the overall environmental scenario of both estuaries. Thus, those factors separated winter-spring neritic, summer-autumn neritic, warm water affinity brackish and limnetic species. Secondarily, river discharge and hydrological stability accounted for the higher presence of freshwater and some brackish species in the estuary of Bilbao and tychoplanktonic organisms in the estuary of Urdaibai. At the regional scale the marginality and tolerance of zooplankton taxa reflected a combination of spatial and seasonal niche breadth and difference of abundance between estuaries. The number of taxa with niches not clearly explained by the environmental variables studied was higher in the estuary of Urdaibai, whilst the new arriving species occupied realized niches well defined by the environmental variables and overall zooplankton taxa showed a better discrimination from generalist to specialist behaviours in the estuary of Bilbao. This was related to inherent abiotic and biotic features of each estuary, which make the estuary of Urdaibai more refractory to the settlement of NIS species. Moreover, in the estuary of Bilbao, several neritic and brackish species experienced temporal changes in niche breadth and overlap that was attributed both to the environmental improvement related to rehabilitation plans in the system and the impact of the species that arrived during the study period. In the estuary of Urdaibai only small changes attributable to the limited impact of NIS were inferred, since no meaningful changes in environmental conditions were perceived.

Plant-pollinator interaction niche broadens in response to severe drought perturbations.

The composition of plant-pollinator interactions-i.e., who interacts with whom in diverse communities-is highly dynamic, and we have a very limited understanding of how interaction identities change in response to perturbations in nature. One prediction from niche and diet theory is that resource niches will broaden to compensate for resource reductions driven by perturbations, yet this has not been empirically tested in plant-pollinator systems in response to real-world perturbations in the field. Here, we use a long-term dataset of floral visitation to Ipomopsis aggregata, a montane perennial herb, to test whether the breadth of its floral visitation niche (i.e., flower visitor richness) changed in response to naturally occurring drought perturbations. Fewer floral resources are available in drought years, which could drive pollinators to expand their foraging niches, thereby expanding plants' floral visitation niches. We compared two drought years to three non-drought years to analyze changes in niche breadth and community composition of floral visitors to I. aggregata, predicting broadened niche breadth and distinct visitor community composition in drought years compared to non-drought years. We found statistically significant increases in niche breadth in drought years as compared to non-drought conditions, but no statistically distinguishable changes in community composition of flower visitors. Our findings suggest that plants' floral visitation niches may exhibit considerable plasticity in response to disturbance. This may have widespread consequences for community-level stability as well as functional consequences if increased niche overlap affects pollination services.

Evolution of specialization in a plant-microbial mutualism is explained by the oscillation theory of speciation.

Specialization in mutualisms is thought to be a major driver of diversification, but few studies have explored how novel specialization evolves, or its relation to the evolution of other niche axes. A fundamental question is whether generalist interactions evolve to become more specialized (i.e., oscillation hypothesis) or if partner switches evolve without any change in niche breadth (i.e., musical chairs hypothesis). We examined alternative models for the evolution of specialization by estimating the mutualistic, climatic, and edaphic niche breadths of sister plant species, combining phylogenetic, environmental, and experimental data on Acmispon strigosus and Acmispon wrangelianus genotypes across their overlapping ranges in California. We found that specialization along all three niche axes was asymmetric across species, such that the species with broader climatic and edaphic niches, Acmispon strigosus, was also able to gain benefit from and invest in associating with a broader set of microbial mutualists. Our data are consistent with the oscillation model of specialization, and a parallel narrowing of the edaphic, climatic, and mutualistic dimensions of the host species niche. Our findings provide novel evidence that the evolution of specialization in mutualism is accompanied by specialization in other niche dimensions.

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.

张掖国家湿地公园优势鸟类种群生态位研究

PDF HTML阅读 XML下载 导出引用 引用提醒 张掖国家湿地公园优势鸟类种群生态位研究 DOI: 10.5846/stxb201701140116 作者: 作者单位: 西北师范大学地理与环境科学学院，甘肃省湿地资源保护与产业发展工程研究中心,西北师范大学地理与环境科学学院，甘肃省湿地资源保护与产业发展工程研究中心,西北师范大学地理与环境科学学院，甘肃省湿地资源保护与产业发展工程研究中心,西北师范大学地理与环境科学学院，甘肃省湿地资源保护与产业发展工程研究中心,西北师范大学地理与环境科学学院，甘肃省湿地资源保护与产业发展工程研究中心 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41461013，91125014）；甘肃省生态学重点学科基金项目 Study of the dominant bird population ecological niche in Zhangye National Wetland Park of Gansu Province Author: Affiliation: Research Center of Wetland Resources Protection and Industrial Development Engineering of Gansu Province,College of Geography and Environmental Science,Northwest Normal University,Research Center of Wetland Resources Protection and Industrial Development Engineering of Gansu Province,College of Geography and Environmental Science,Northwest Normal University,Research Center of Wetland Resources Protection and Industrial Development Engineering of Gansu Province,College of Geography and Environmental Science,Northwest Normal University,Research Center of Wetland Resources Protection and Industrial Development Engineering of Gansu Province,College of Geography and Environmental Science,Northwest Normal University,Research Center of Wetland Resources Protection and Industrial Development Engineering of Gansu Province,College of Geography and Environmental Science,Northwest Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:鸟类时空格局影响下鸟类种群生态位的变化是认识鸟类环境适应机制的理论基础。在张掖国家湿地公园保育区，采用样带法研究了冬春季节5种优势鸟类种群生态位宽度和生态位重叠的时间异质性。结果表明：随着月份的更替，5种优势鸟类种群的生态位宽度呈现出先增大后减小的变化趋势，赤麻鸭（Tadornaferruginea）、绿头鸭（Anasplatyrhynchos）、麻雀（Passer montanus）、白骨顶鸡（Fulicaatra）的最高值出现在1月分别为1.601、1.415、1.627、1.771，大白鹭（Ardea alba）的最高值出现在3月为0.556；不同月份间鸟类优势种群生态位重叠存在差异，3月、11月生态位的重叠值最大，1月份最小；优势鸟类种群的生态位宽度和重叠在时间尺度上表现出"此消彼长"的关系。湿地公园时间尺度上的鸟类生态位宽度和重叠的差异与湿地食物资源及隐蔽条件、鸟类群体迁徙规律、鸟类种间的竞争密切相关，反应了湿地鸟类适应生境变化的可塑性机制。 Abstract:The niche change of bird population affected by the temporal and spatial pattern of birds, is the theoretical basis of understanding the mechanism of birds environmental adaptation. The aim of this study is to investigate the niche breadth and overlap of five dominant bird species in wetland within the inland basin of northwest China,especially the diverse temporal changes in niche breadth and overlap as well as their formation mechanisms.The study, which was conducted in Zhangye National Wetland Park, Gansu Province, China,took place over three periods from November 1, 2013 to May 30, 2015. In this study, two sample lines were fixedaccording to the surface features of the Wetland Park Conservation Area. The transect lines, each approximately 1.5 km long, ran through the whole conservation area. Surveys of bird richness and abundance were performed every 3 to7 days along the transect lines, which were 3 to 5 days during the bird migration season and 5 to 7 days in the winter. These quantity surveys were carried out every month along the transect lines. During the surveys, the species, numbers, and behavioral habits of birds were recorded on both sides of the sample line, the walking speed of investigator was 1.5 km per hour.Those were tried to understand that the temporal diversity of bird niche breadth and overlap, and the patterns of variation and formative reasons for the niche breadth and overlap. The results were shown that the niche breadth of fives dominant species increased firstly and then decreased with the month replaced in Zhangye National Wetland Park.The highest values appeared in January, which were 1.601, 1.415, 1.627, and 1.771 for Tadornaferruginea, Anasplatyrhynchos, Passer montanus, and Fulicaatra, respectively. The highest value for Ardea alba in appeared in March was 0.556, The niche overlap of the five dominant species differed by month, with the maximum values in March and November, and minimum values in January and February. The niche breadth and overlap of dominant bird populations were shownthe relationship on time scales that one waned with the other waxed. 参考文献 相似文献 引证文献

Evaluating potential competitive interactions following stocking through trophic niche breadth

Responsible fisheries enhancement should include comprehensive monitoring programs to detect ecological effects of fish releases and support adaptive management. Competition for food and shelter is one such impact, and density-dependent effects may occur if release numbers are above levels that the ecosystem can support. Herein we present a novel application of trophic niche breadth estimated from stable isotope data to examine potential competitive interactions arising from eastern king prawn (Melicertus plebejus) stocking. Eastern king prawn and potential competitors (Macrobrachium intermedium, Atherinosoma microstoma, Leptatherina presbyteroides, Ambassis jacksoniensis and Gobiopterus semivestitus) were sampled from two stocked and two reference estuaries, before and after stocking. Stable isotope ratios were measured and used to model trophic overlap and trophic niche breadth. A statistically significant increase in niche breadth was evident for two competing species in one stocked estuary, and one competing species in another. M. intermedium, the species that had the greatest trophic overlap with eastern king prawn, did not show any change in niche breadth. The potential for competition and the role of environmental variability (including rainfall and run-off, mouth opening regime and seasonal changes) in driving the patterns observed are discussed. This approach shows promise for monitoring competitive effects arising from aquaculture-based fisheries enhancements in the future.

Dietary resource use and competition between white-tailed deer and introduced sika deer

Content Native communities of herbivores have evolved fundamental dietary niches that avoid or minimise competition; the introduction of exotic species can change dietary niches, cause overlap in resource use, and result in competition for resources. Aims We compared niche breadth, overlap in diet, and quality of diet between introduced sika deer and native white-tailed deer in Maryland, USA. We investigated these changes in free-ranging populations where both species are allopatric as well as when they are sympatric. Methods We used microhistological analysis of faecal samples to determine the percentage of resources used by sika deer and white-tailed deer, as measured between geographical areas of similar habitat quality. We compared resource use specifically by controlling for harvest pressure and resource availability, which are known to alter resource use other than the presence of an additional deer species. Key results We observed a significant resource overlap (range 63–88%) between species. In the presence of sika deer, white-tailed deer displayed an increased niche breadth (108%) and a lower diet quality (17%). Sika deer consumed the same resources that comprised 78% of white-tailed deer diet. Unlike other native ungulates that have dietary overlap with white-tailed deer, sika deer is neither temporally nor geographically segregated in habitat use. Conclusions Resource overlap and changes in niche breadth and diet quality during sympatry strongly denote dietary competition between sika deer and white-tailed deer. This competition results in white-tailed deer altering the dietary selection, thereby consuming lower-quality forage. Implications White-tailed deer are concentrate selectors and require higher diet quality than do sika deer, which can tolerate diets higher in fibre, consistent with their classification as intermediate feeders. A decrease in the nutritional quality of resources used by white-tailed deer could contribute to the decline of white-tailed deer over time and allow the continued spread of sika deer.

Shifts in the ecological niche of Lutzomyia peruensis under climate change scenarios in Peru.

The Peruvian Andes presents a climate suitable for many species of sandfly that are known vectors of leishmaniasis or bartonellosis, including Lutzomyia peruensis (Diptera: Psychodidae), among others. In the present study, occurrences data for Lu. peruensis were compiled from several items in the scientific literature from Peru published between 1927 and 2015. Based on these data, ecological niche models were constructed to predict spatial distributions using three algorithms [Support vector machine (SVM), the Genetic Algorithm for Rule-set Prediction (GARP) and Maximum Entropy (MaxEnt)]. In addition, the environmental requirements of Lu. peruensis and three niche characteristics were modelled in the context of future climate change scenarios: (a) potential changes in niche breadth; (b) shifts in the direction and magnitude of niche centroids, and (c) shifts in elevation range. The model identified areas that included environments suitable for Lu. peruensis in most regions of Peru (45.77%) and an average altitude of 3289 m a.s.l. Under climate change scenarios, a decrease in the distribution areas of Lu. peruensis was observed for all representative concentration pathways. However, the centroid of the species' ecological niche showed a northwest direction in all climate change scenarios. The information generated in this study may help health authorities responsible for the supervision of strategies to control leishmaniasis to coordinate, plan and implement appropriate strategies for each area of risk, taking into account the geographic distribution and potential dispersal of Lu. peruensis.

Modeling the impact of climate change on wild Piper nigrum (Black Pepper) in Western Ghats, India using ecological niche models.

The center of diversity of Piper nigrum L. (Black Pepper), one of the highly valued spice crops is reported to be from India. Black pepper is naturally distributed in India in the Western Ghats biodiversity hotspot and is the only known existing source of its wild germplasm in the world. We used ecological niche models to predict the potential distribution of wild P. nigrum in the present and two future climate change scenarios viz (A1B) and (A2A) for the year 2080. Three topographic and nine uncorrelated bioclim variables were used to develop the niche models. The environmental variables influencing the distribution of wild P. nigrum across different climate change scenarios were identified. We also assessed the direction and magnitude of the niche centroid shift and the change in niche breadth to estimate the impact of projected climate change on the distribution of P. nigrum. The study shows a niche centroid shift in the future climate scenarios. Both the projected future climate scenarios predicted a reduction in the habitat of P. nigrum in Southern Western Ghats, which harbors many wild accessions of P. nigrum. Our results highlight the impact of future climate change on P. nigrum and provide useful information for designing sound germplasm conservation strategies for P. nigrum.

Realized climate niche breadth varies with population trend and distribution in North American birds

AbstractAimEcological niche theory states that realized niche breadth should increase with population growth. This relationship has been studied extensively in the context of density‐dependent habitat selection, and there is evidence that animal populations at higher density occupy a wider range of vegetation types. To our knowledge, no previous studies have investigated the relationship between population growth and climate niche breadth (i.e. the range of climatic conditions occupied). Here we aim to estimate the influence of population trend, as well as changes in distribution, on realized climate niche breadth.LocationNorth America.MethodsWe estimated changes in realized climate niche breadth and distribution between 1980 and 2012 for 46 bird species using data from the North American Breeding Bird Survey (BBS) and standard ecological niche modelling techniques. We analysed changes in niche breadth in relation to population trends and distributional changes from the BBS for these same species.ResultsChanges in realized climate niche breadth were significantly and positively associated with population growth, as reflected by BBS population trends, and with changes in distributional extent. Using variance partitioning, we showed that 44.2% of the variation in change in niche breadth can be explained by population trend, and that roughly half of this was independent of changes in distribution.ConclusionsRealized climate niche breadth is variable on an ecological time‐scale as a function of population trend. Mechanisms associated with changes in distribution and those acting within current species range limits appear to be equally important in driving this relationship. Observed changes in niche breadth may violate distribution modelling assumptions of niche conservatism. Studying how population growth influences realized climate niche breadth is therefore important for understanding dynamic species distributions, responses to climate change and our ability to model future species distributions.

Specialization and generalization in the diversification of phytophagous insects: tests of the musical chairs and oscillation hypotheses.

Evolutionary biologists have often assumed that ecological generalism comes at the expense of less intense exploitation of specific resources and that this trade-off will promote the evolution of ecologically specialized daughter species. Using a phylogenetic comparative approach with butterflies as a model system, we test hypotheses that incorporate changes in niche breadth and location into explanations of the taxonomic diversification of insect herbivores. Specifically, we compare the oscillation hypothesis, where speciation is driven by host-plant generalists giving rise to specialist daughter species, to the musical chairs hypothesis, where speciation is driven by host-plant switching, without changes in niche breadth. Contrary to the predictions of the oscillation hypothesis, we recover a negative relationship between host-plant breadth and diversification rate and find that changes in host breadth are seldom coupled to speciation events. By contrast, we present evidence for a positive relationship between rates of host switching and butterfly diversification, consonant with the musical chairs hypothesis. These results suggest that the costs of trophic generalism in plant-feeding insects may have been overvalued and that transitions from generalists to ecological specialists may not be an important driver of speciation in general.

Current and future niche of North and Central American sand flies (Diptera: psychodidae) in climate change scenarios.

Ecological niche models are useful tools to infer potential spatial and temporal distributions in vector species and to measure epidemiological risk for infectious diseases such as the Leishmaniases. The ecological niche of 28 North and Central American sand fly species, including those with epidemiological relevance, can be used to analyze the vector's ecology and its association with transmission risk, and plan integrated regional vector surveillance and control programs. In this study, we model the environmental requirements of the principal North and Central American phlebotomine species and analyze three niche characteristics over future climate change scenarios: i) potential change in niche breadth, ii) direction and magnitude of niche centroid shifts, iii) shifts in elevation range. Niche identity between confirmed or incriminated Leishmania vector sand flies in Mexico, and human cases were analyzed. Niche models were constructed using sand fly occurrence datapoints from Canada, USA, Mexico, Guatemala and Belize. Nine non-correlated bioclimatic and four topographic data layers were used as niche components using GARP in OpenModeller. Both B2 and A2 climate change scenarios were used with two general circulation models for each scenario (CSIRO and HadCM3), for 2020, 2050 and 2080. There was an increase in niche breadth to 2080 in both scenarios for all species with the exception of Lutzomyia vexator. The principal direction of niche centroid displacement was to the northwest (64%), while the elevation range decreased greatest for tropical, and least for broad-range species. Lutzomyia cruciata is the only epidemiologically important species with high niche identity with that of Leishmania spp. in Mexico. Continued landscape modification in future climate change will provide an increased opportunity for the geographic expansion of NCA sand flys' ENM and human exposure to vectors of Leishmaniases.

Environmental Variability and Ontogenetic Niche Shifts in Exotic Plants May Govern Reinvasion Pressure in Restorations of Invaded Ecosystems

When restoring ecosystems dominated by exotic plants, reinvasion pressure, or the rate of new exotic recruitment following mature exotic removal, can vary broadly between similarly invaded habitats. Reinvasion pressure strongly influences restoration costs and outcomes but is difficult to predict. Ontogenetic niche shifts (ONSs, changes in niche breadth or position during development) in exotic species paired with interannual variation in abiotic conditions may decouple pre‐removal mature exotic density and average reinvasion pressure. Identifying such decouplings could improve restoration efficiency by informing site selection and management strategies, but requires estimates of average reinvasion pressure that mandate greater understanding of its principle drivers. We hypothesize that reinvasion pressure is predominantly driven by exotic propagule abundance and spatiotemporal availability of realized recruitment windows, which are periods of variable duration that permit exotic establishment from propagules. Realized recruitment windows are based on the “safe sites” concept but account for ONSs and are determined by abiotic conditions and interspecific interactions with recipient communities. Biotic resistance or facilitation may increase or decrease times required for establishment by influencing exotic growth rates or altering niche availability and may permit or preclude establishment in marginal abiotic conditions. We discuss factors influencing reinvasion pressure, basic approaches to estimate reinvasion pressure, and potential ways to increase management efficiency under different reinvasion pressure scenarios. Accurate estimates of reinvasion pressure could improve restoration efficacy, efficiency, and predictability in ecosystems dominated by exotic plants. We argue that greater theoretical and practical considerations of reinvasion pressure and ONSs are merited.

A network-based approach to the analysis of ontogenetic diet shifts: An example with an endangered, small-sized fish

Many organisms exhibit ontogenetic shifts in their diet and habitat use, which often exert a large influence on the structure and expected dynamics of food webs and ecological communities. Nevertheless, reliable methods for detecting these niche shifts from consumption data are limited. In this study we present a new approach for the detection and analysis of ontogenetic diet shifts, based on complex network theory. As a case study, we apply these methods to the endangered, small fish Aphanius iberus. The stage-structured consumer population and its set of consumed prey are represented as an unweighted bipartite network. A statistical evaluation of the resulting network structure permits to uncover empirical patterns of ontogenetic diet shifts. We test for changes in niche breadth, as well as nestedness and diet modularity along ontogeny. These tests were carried out on the subnetworks describing consumption, positive electivity, and negative electivity on prey items. The statistical significance was established by means of null model analyses. Our analyses reveal a nested diet, along with a gradual decrease in diet breadth and a modular structure (i.e. abrupt changes) of elected preys along the ontogeny of A. iberus. The detection of network structure by means of the use of tools from complex network theory is shown to be a promising method for studying ontogenetic niche shifts.

FEEDING BEHAVIOR OF FOUR ARBOREAL DARWIN'S FINCHES: ADAPTATIONS TO SPATIAL AND SEASONAL VARIABILITY

Abstract In the Galapagos Islands climate and food abundance vary strongly among vegetation zones and between seasons. We studied the foraging behavior of four mainly insectivorous Darwin's finch species on Santa Cruz Island. We compared foraging behavior between (1) the arid zone, where food is scarce, with the humid Scalesia zone, where food is abundant; and (2) within each zone between dry and wet seasons. The four species used different feeding substrates in the two vegetation zones and reacted flexibly to the seasonal variation by changing feeding techniques and substrates. Species mainly specialized in resource use and feeding techniques or showed no change in niche breadth when food became more limited in dry conditions. In the arid zone during the dry season, the Large Tree Finch (Camarhynchus psittacula) relied on its powerful biting beak to bite open the bark of dry twigs. The Woodpecker Finch (Cactospiza pallida) used twigs and cactus spines to access arthropods in tree holes and was the only s...

Ontogenetic niche shifts and their implications for recruitment in three clonalVacciniumshrubs:Vaccinium myrtillus,Vaccinium vitis-idaea, andVaccinium oxycoccos

Ontogenetic niche shifts, i.e., changes in niche breadth and (or) position during the life of individuals, have received rather limited attention in plant ecology. An experiment was designed to assess ontogenetic niche shifts in three clonal Vaccinium shrubs in order to examine their recruitment behavior. Seeds were sown, and juveniles transplanted, at sites along a gradient of changing occurrence of the three species. Recruitment was seed limited, varied among sites, and was correlated with juvenile survivorship. No niche shift occurred during seed to seedling stages for any of the plants. For Vaccinium myrtillus L., recruitment was not related to adult occurrence, whereas for Vaccinium oxycoccos L., recruitment was highest at the site where adults dominated. However, for both of these species, recruitment also occurred outside the range of adult occurrence. Vaccinium vitis-idaea L. exhibited a negative relationship between adult occurrence and recruitment and between adult occurrence and juvenile survivorship, indicating an ontogenetic niche shift. For V. myrtillus the results suggested an uncoupling of niche requirements of juvenile and adult stages, whereas for V. oxycoccos the results suggested a niche contraction towards the requirements for adults. Thus, the form of ontogenetic niche shifts differs among the species. These differences in niche shifts contribute to understanding dispersal and recruitment behavior of the species.Key words: clonal plants, dispersal, niche shifts, recruitment.

Patterns of prey size and taxonomic composition in larval fish: are there general size‐dependent models?

The allometric relationship of maxilla length to larval fish weight approached a slope of 1/3 for 11 species from Conception Bay, Newfoundland. In 10 of these species, mean prey size increased with length of the maxilla but not constantly. In six species, niche breadth increased with length of maxilla. The rate of change in niche breadth was inversely related to the rate of change in mean prey size. Nauplii and copepodites of calanoids were selected positively, and cyclopoids negatively for almost all species of larval fish.

Effects of environment and plant characteristics on the distribution of Bryozoa in a Fucus serratus L. Community

Five species of Bryozoa were commonly found in the epifaunal communities of Fucus serratus L. plants in Strangford Lough, Northern Ireland. Membranipora membranacea (L.) was most abundant on silt-laden plants in quiet slow-flowing waters, a habitat avoided by the other species. Flustrellidra hispida (Fabricius) and to a lesser extent Alcyonidium hirsutum (Fleming) were more abundant in the faster currents, whereas Electra pilosa (L.) was less abundant here. The responses of the species to their physical environment were modified by the density of Fucus present. Excepting Membranipora the species showed different preferences for plant structure (as measured by total length and degree of bushiness). Each species showed a specific pattern of distribution along the plant fronds, but the interspecific differences were less pronounced on the shorter fronds. Weak preferences in respect of side of frond (concave or convex surface) and of distal or non-distal segments were present. For some species there were major changes in niche breadth or niche position between sites of different environments. All species except Membranipora were more abundant on large than on small segments, even after controlling for plant size, and the number of species on a given segment was strongly correlated with segment area. Species diversity was greatest at about mid-frond level.