Three-dimensional niche partitioning between two colonially nesting ardeid species in central China

Background:Interspecific competition is known to be strongest between those species that are both closely related and sympatric.Egrets are colonially nesting wetland birds that often overlap and can therefore be expected to compete in roosting and nesting habitat as well as in diet.According to the niche partitioning hypothesis,it is to be expected that these similar species would show differentiation in at least one of the main niche dimensions to reduce competition.We tested niche partitioning between the colonially nesting Little Egret(Egretta garzetta)and Cattle Egret(Bubulcus ibis)in temporal,spatial and trophic dimensions.Methods:Field study was conducted in three mixed egret colonies in Yangxian County,southwest Shaanxi Prov-ince,central China.For each nest colony we recorded its spatial location,the height of nesting trees and of nests,the height of roosting trees and of roosting individuals within the trees.We determined the first egg-laying and first hatching dates of the two species.Craw dissection of storm-killed egret nestlings was used to measure the diet.Six transects were surveyed to study foraging habitat selection.Results:We found that hatching time of Little Egrets peaked earlier(by about 1 month)than that of Cattle Egrets.Cattle Egrets nested and roosted higher than Little Egrets.The foraging habitats used by Little Egrets were dominated by river banks(73.49%),followed by paddy fields(13.25%)and reservoirs(10.84%),whereas Cattle Egret foraging sites were characterized by grasslands(44.44%),paddy fields(33.33%)and river banks(22.22%).Little Egrets consumed more fishes(65.66%)and Odonata larvae(13.69%)than Cattle Egrets,while Cattle Egrets were found feeding mainly on Coleoptera(29.69%)and Orthoptera(23.29%).Little Egrets preyed on larger mean biomasses of food items than Cattle Egrets.Conclusions:Our results confirm the niche partitioning hypothesis as a mechanism for coexistence among ecologi-cally similar species.In two coexisting egret species,niche partitioning is multidimensional,such that the two coexist-ent species occupy differing ecological space based on all three temporal,spatial and trophic niche dimensions.

Spatial niche segregation between bird species in the Białowieża primeval forest(NE Poland)

Drivers of bird niche separation in temperate primeval forests have not yet been determined,due to the low number of intact forest sites.Here,we analyzed the general patterns of niche usage on trees by birds’assemblages.We tested how tree species affect the sharing of space in an assemblage of birds and their level of specialization.We conducted our study in the Białowieża primeval forest(NE Poland).During two breeding seasons,we observed bird positions on trees,divided into three vertical and six horizontal zones in 768 observation points.Based on the interaction networks framework we calculated the Kullback-Leibler distance d′as a metric of species specialization and the resource range RR index,which estimates the species’specificity based on the fraction of space utilized with a non-zero performance.The d′index was the highest in the lower understory for all parts of the tree on the basis of the position from the trunk.The RR index was the highest in the lower understory for all parts based on the position from the trunk.Regarding the tree species,the lowest d′index was observed in all tree species together,and hornbeam,whereas the highest in oak.At the tree species level,the RR index was the lowest for hornbeam.We show tree species importance in forest space sharing in the case of bird assemblages.Hornbeam,alder,and spruce are universal species that were used by birds almost entirely.In contrast,oak,lime,and maple were only partially used.Tree species with less complex structures could shape bird assemblages,as they could offer birds much fewer niches to realize.Therefore,we showed that high specialization and niche separation are drivers of high bird diversity.Consequently maintaining a diverse stand structure is crucial for biodiversity conservation.

Activity patterns and resource partitioning: seven species at watering sites in the Altun Mountains, China

As part of a larger project to examine the richness and distribution of wildlife in Kumtag Desert area, we conducted camera trapping surveys during the period 2010–2012 at seven watering sites in an arid region of the Altun Mountains in western China. Information on activity patterns of the wild bactrian camel (Camelus ferus), kiang (Equus kiang), goitered gazelle (Gazella subgutturosa), argali (Ovis ammon), blue sheep (Pseudois nayaur), red fox (Vulpes vulpes), and wolf (Canis lupus) was obtained. We found that the wild camel, kiang, goitered gazelle, argali, and blue sheep were predominantly diurnal at watering sites, whereas red fox and wolf were nocturnal. Five herbivores partitioned the use of watering sites in a temporal manner to minimize the risk of predation by carnivores. The wild camel was the dominant herbivorous species at the watering sites. The kiang, goitered gazelle, argali, and blue sheep displayed adaptive water use by altering spatial or temporal patterns based on the presence or absence of wild camel, to minimize the risk of interspecific strife. These results are suggestive of the differences in activity patterns that might modulate water partitioning by different species, and provide insights for the development of conservation strategies for integrated species and decisions regarding water development in the Altun Mountains.

Food resource and temporal partitioning amongst a guild of predatory agroecosystem-inhabiting ant species

Prey diversity and temporal foraging patterns of six abundant,predatory ant species were investigated seasonally in an agroecosystem with two main vegetable crops.Pheidole sp.demonstrated the highest predation success and therefore appears to be the dominant species while Tapinoma melanocephalum showed the lowest success under the natural field conditions.Investigation of prey diversity and temporal activity patterns with the null model tests of niche overlap revealed a significant overlap indicating that the activity periods and prey diversity may not be solely influenced by interactions among the co-existing ant species.However,niche partitioning in the daily peak activity periods was demonstrated during all the three seasons(summer,rainy and winter)particularly between Pheidole sp.and T.melanocephalum.Pheidole sp.exhibited a high intensity,broadly extended mono-modal foraging pattern.Camponotus compressus and C.paria showed bi-modality in their foraging activity during the rainy season and mono-modal patterns during summer and winter seasons.Pachycondyla tesserinoda,Tetramorium sp.and T.melanocephalum exhibited peak foraging activities in the morning hours during the summer and rainy seasons.The activity profiles of C.compressus and T.melanocephalum were skewed towards late afternoon hours during the winter season indicating avoidance of foraging activity during the favourable periods when the more aggressive Pheidole sp.is active.In the sponge gourd agroecosystem,the ants captured predominantly hymenopteran,orthopteran and coleopteran insects.While Pheidole sp.hunted mainly the large orthopteran prey,other ant species captured worker ants in the sponge gourd agroecosystem.In the cauliflower agroecosystem,while other species captured prey chiefly belonging to six orders,i.e.,Lepidoptera,Hymenoptera,Coleoptera,Hemiptera,Isoptera and Diptera,Pheidole sp.and P.tesserinoda were the only species to also hunt many orthopteran prey.The agroecosystem-inhabiting ant species prey on a large number and wide variety of insect herbivores as evident from the differences in the peak foraging times and the proportion of each type of prey hunted.Overall,our results indicate that the structure of agroecosystem-inhabiting ant assemblage may be influenced by a variety of factors including competition,temporal heterogeneities,prey availability and its characteristics such as size and mobility.

Effects of functional phylogeny of light-response-related orthologous genes on seedling survival in a subtropical forest

Background: Light is an important environmental factor affecting the growth and survival of plants in forest communities. The competition for light resources and divergent responses to light may affect plant species coexistence in natural forests through niche partitioning and environmental filtering, respectively.Methods: In the present study, sequences of light-response-related functional genes were extracted from transcriptomic data of 99 tree species in a subtropical forest and average and nearest taxon phylogenetic diversity of adult(A_Apd’, A_NTpd’) and seedling neighbors(S_Apd’, S_NTpd’) around each focal seedling were calculated to evaluate effects of differentiation in light-response-related genes on community assembly processes.Results: The results showed that seedling survival was related to S_NTpd’, S_Apd’and A_Apd’of two chlorophyll ab-binding proteins involved in the assembly of photosystem Ⅱ and two genes responsive to light intensity,indicating seedlings surrounded by neighbors with distinct light responses tended to have high survival rates.Conclusions: Our results indicated that niche partitioning due to competition for light resources between plants may act as the key mechanism in determining seedling dynamics in subtropical forests.

The coexistence of seven sympatric fulvettas in Ailao Mountains,Ejia Town,Yunnan Province

The coexistence of ecologically similar species sharing sympatric areas is a central issue of community ecology. Niche differentiation is required at least in one dimension to avoid competitive exclusion. From 2012-2014, by adopting the methods of mist-nets and point counts to evaluate spatial niche partitioning and morphological differentiations, we explored the coexistence mechanisms of seven sympatric fulvettas in Ailao Mountains, Ejia town, Yunnan Province, China. The microhabitats of these seven fulvettas were significantly different in elevation, roost site height and vegetation coverage, indicating a spatial niche segregation in different levels. Approximately, 90.30% of the samples were correctly classified by linear discriminant analysis（LDA） with correct rates at 91.20%-100%, except the White-browed fulvetta（Alcippe vinipectus）（65.4%） and the Streak-throated fulvetta（A. cinereiceps）（74.6%）. The seven fulvettas were classified into four guilds based on their specific morphological characters, suggesting that the species in each guild use their unique feeding ways to realize resource partitioning in the overlapped areas. These finding indicate that through multi-dimensional spatial niche segregation and divergence in resource utilizing, the interspecific competition among these seven fulvettas is minimized, whereas, coexistence is promoted.

Niche overlap in allotopic and syntopic populations of sexually interacting ground-hopper species

There is accumulating evidence that sexual interactions among species （reproductive interference） could have dramatic effects for species＇ coexistence. It has been shown that the fitness of individuals can be substantially reduced as a consequence of reproductive interference. This might subsequently lead to displacement of a species （sexual exclusion）. On the other hand, some evolutionary and ecological mechanisms might enable species to coexist, such as the divergence of mate recognition systems （reproductive character displacement）, habitat partitioning, clumped dispersion patterns or different colonization capabilities. We have previously shown that the two ground-hopper species Tetrix subulata and Tetrix ceperoi interact sexually in the laboratory as well as in the field. At sites where both species co-occur niche overlap was high, suggesting that coexistence is maintained by different niche breadths rather than by habitat partitioning. To test the hypothesis that habitat partitioning does not contribute to species＇ coexistence, we examined whether allotopic and syntopic populations of these two species differ in niche overlap （competitive release）, Our results show that niche overlap is higher in syntopic than in allotopic populations, suggesting that the site-specific habitat structure （heterogeneity） has a stronger influence on microhabitat utilization than the presence of heterospecifics. Hence, our data do not support the hypothesis that habitat partitioning plays a substantial role for the coexistence of these sexually interacting species.

Temporal niche overlap among insectivorous small mammals

Being active in the same environment at different times exposes animals to the effects of very different environmental factors,both biotic and abiotic.In the present study,we used live traps equipped with timing devices to evaluate the potential role of biotic factors(competition and food abundance)on overall overlap in the temporal niche axis of 4 insectivorous small mammals in high-elevation grassland fields(‘campos de altitude’)of southern Brazil.Based on resources availability(invertebrates),data on animal captures were pooled in 2 seasons:‘scarcity’(June 2001−September 2001)and‘abundance’(November 2001-May 2002)seasons.We tested for non-random structure in temporal niche overlap among the species in each season.These species were the rodents Oxymycterus nasutus(Waterhouse,1837),Deltamys sp.,Akodon azarae(Fischer,1829),and the marsupial Monodelphis brevicaudis Olfers,1818.The studied community was mainly diurnal with crepuscular peaks.Simulations using the Pianka index of niche overlap indicated that the empirical assemblage-wide overlap was not significantly different from randomly generated patterns in the abundance season but significantly greater than expected by chance alone in the scarcity season.All the species showed an increase in temporal niche breadth during the abundance season,which appears to be related to longer daylength and high nocturnal temperatures.Patterns on both temporal niche overlap and temporal niche breadth were the opposite to those that we were expecting in the case of diel activity patterns determined by competition for dietary resources.Therefore,we conclude that competition did not seem to be preponderant for determining patterns of temporal niche overlap by the studied community.

Stable isotope analysis of diet confirms niche separation of two sympatric species of Namib Desert lizard

We used stable isotopes of carbon and nitrogen to study the trophic niche of two species of insectivorous lizards,the Husab sand lizard Pedioplanis husabensis and Bradfield’s Namib day gecko living sympatrically in the Namib Desert.We measured theδ13C andδ15N ratios in lizard blood tissues with different turnover times(whole blood,red blood cells and plasma)to investigate lizard diet in different seasons.We also measured theδ13C andδ15N ratios in available arthropod prey and plant tissues on the site,to identify the avenues of nutrient movement between lizards and their prey.Through the use of stable isotope mixing models,we found that the two lizard species relied on a largely non-overlapping but seasonally variable array of arthropods:P.husabensis primarily fed on termites,beetles and wasps,while R.bradfieldi fed mainly on ants,wasps and hemipterans.Nutrients originating from C3 plants were proportionally higher for R.bradfieldi than for P.husabensis during autumn and late autumn/early winter,although not summer.Contrary to the few available data estimating the trophic transfer of nutrients in ectotherms in mixed C3 and C4/crassulacean acid metabolism(CAM)plant landscapes,we found that our lizard species primarily acquired nutrients that originated from C4/CAM plants.This work adds an important dimension to the general lack of studies using stable isotope analyses to estimate lizard niche partitioning and resource use.

Sagittal crest morphology decoupled from relative bite performance in Pleistocene tapirs(Perissodactyla:Tapiridae)

Bite force is often associated with specific morphological features,such as sagittal crests.The presence of a pro-nounced sagittal crest in some tapirs(Perissodactyla:Tapiridae)was recently shown to be negatively correlated with hard-object feeding,in contrast with similar cranial structures in carnivorans.The aim of this study was to investi-gate bite forces and sagittal crest heights across a wide range of modern and extinct tapirs and apply a comparative investigation to establish whether these features are correlated across a broad phylogenetic scope.We examined a sample of 71 specimens representing 15 tapir species(5 extant,10 extinct)using the dry-skull method,linear measurements of cranial features,phylogenetic reconstruction,and comparative analyses.Tapirs were found to ex-hibit variation in bite force and sagittal crest height across their phylogeny and between different biogeographical realms,with high-crested morphologies occurring mostly in Neotropical species.The highest bite forces within tapirs appear to be driven by estimates for the masseter–pterygoid muscle complex,rather than predicted forces for the temporalis muscle.Our results demonstrate that relative sagittal crest height is poorly correlated with relative cranial bite force,suggesting high force application is not a driver for pronounced sagittal crests in this sample.The divergent biomechanical capabilities of different contemporaneous tapirids may have allowed multiple species to occupy overlapping territories and partition resources to avoid excess competition.Bite forces in tapirs peak in Pleistocene species,independent of body size,suggesting possible dietary shifts as a potential result of climatic changes during this epoch.

Density dependence and habitat preference shape seedling survival in a subtropical forest in central China

Aims seedlings are vulnerable to many kinds of fatal abiotic and biotic agents,and examining the causes of seedling dynamics can help understand mechanisms of species coexistence.To disentangle the relative importance of neighborhood densities,habitat factors and phylogenetic relatedness on focal seedling survival,we monitored the survival of 5306 seedlings of 104 species>15 months.We address the following questions:(i)How do neighborhood densities,habitat variables and phylogenetic relatedness affect seedling survival?What is the relative importance of conspecific densities,habitat variables and phylogenetic relatedness to seedling survival?(ii)Does the importance of the neighborhood densities,habitat variables and phylogenetic relatedness vary among growth forms,leaf habits or dispersal modes?specially,does the conspecific negative density dependence inhibit tree and decidu-ous seedlings more compared with shrub and evergreen species?Does density dependence affect the wind and animal-dispersed species equally?Methods We established 135 census stations to monitor seedling dynamics in a 25-ha subtropical forest plot in central China.Conspecific and heterospecific seedling density in the 1-m2 seedling plot and adult basal area within a 20-m radius provided neighborhood density var-iables.mean elevation,convexity and aspect of every 5-×5-m grid with seedling plots were used to quantify habitat characteristics.We calculated the relative average phylodiversity between focal seed-ling and heterospecific neighbors to quantify the species related-ness in the neighborhood.Eight candidate generalized linear mixed models with binominal error distribution were used to compare the relative importance of these variables to seedling survival.akaike’s information criteria were used to identify the most parsimonious models.Important Findingsat the community level,both the neighborhood densities and phylogenetic relatedness were important to seedling survival.We found negative effects of increasing conspecific seedlings,which suggested the existence of species-specific density-dependent mortality.Phylodiversity of heterospecific neighbors was negatively related to survival of focal seedlings,indicating similar habitat preference shared among phylogenetically closely related species may drive seedling survival.The relative importance of neighborhood densities,habitat variables and phylogenetic relatedness varied among ecological guilds.Conspecific densities had significant negative effect for deciduous and wind-dispersed species,and marginally significant for tree seedlings>10 cm tall and animal-dispersed species.Habitat variables had limited effects on seedling survival,and only elevation was related to the sur-vival of evergreen species in the best-fit model.We conclude that both negative density-dependent mortality and habitat preference reflected by the phylogenetic relatedness shape the species coex-istence at seedling stage in this forest.

Habitat specialization and phylogenetic structure of tree species in a coastal Brazilian white-sand forest

Aims The coastal Brazilian rainforest on white-sand(restinga)ranks among the most fragmented forest types in the tropics,owing to both the patchy distribution of sandy soils and widespread coastal development activities.Here we study the environmental and evolutionary determinants of a forest tree assemblage at a single restinga forest in Southeastern Brazil.We also explore the ability of competing hypotheses to explain the maintenance of species diversity in this forest type,which includes contrasting extremes of edaphic conditions associated with flooding stress.Methods The study was conducted in a white-sand forest permanent plot of 10.24 ha on the coastal plain of Southeastern Brazil.This plot was divided into 256 quadrats of 20×20 m,which were classified into two main edaphic habitats(flooded and drained).Trees with a diameter≥1 cm at breast height were identified.We assembled DNA sequence data for each of the 116 morphospecies recognized using two chloroplast markers(rbcL and matK).A phylogenetic tree was obtained using the maximum likelihood method,and a phylogenetic distance matrix was produced from an ultrametric tree.We analyzed similarity in floristic composition and structure between habitats and related them to cross-plot distances using permutation procedures.Null model torus shift simulations were performed to obtain a statistical significance level for habitat association for each species.The phylogenetic structure for the two habitats and for each 20×20 m quadrat was calculated using the mean phylogenetic distance weighted by species abundance and checked for significance using the standardized effect size generated by 5000 randomizations of phylogenetic tip labels.Important Findings Our results indicate that partitioning among edaphic habitats is important for explaining species distributions and coexistence in restinga forests.Species distributions within the plot were found to be non-random:there was greater floristic similarity within than between habitats,and>40%of the more abundant species were positively or negatively associated with at least one habitat.Patterns of habitat association were not independent of phylogenetic relatedness:the community was overdispersed with respect to space and habitat type.Closely related species tended to occur in different habitats,while neighboring trees tended to belong to more distantly related species.We conclude that habitat specialization is important for the coexistence of species in restinga forests and that habitat heterogeneity is therefore an essential factor in explaining the maintenance of diversity of this unique but fragile and threatened type of forest.

Personality of hosts and their brood parasites

Brood parasites such as the common cuckoo Cuculus canorus exploit the parental abilities of their hosts,hosts avoid brood parasitism and predation by showing specific behavior such as loss of feathers,emission of fear screams and contact calls,displaying wriggle behavior to avoid hosts or potential prey,pecking at hosts and prey,and expressing tonic immobility(showing behavior like feigning death or rapid escape from predators and brood parasites).These aspects of escape behavior are consistent for individuals but also among sites,seasons,and years.Escape behavior expressed in response to a broad range of cuckoo hosts and prey are consistently used against capture by humans,but also hosts and brood parasites and predators and their prey.An interspecific comparative phylogenetic analysis of escape behavior by hosts and their brood parasites and prey and their predators revealed evidence of consistent behavior when encountering potential parasites or predators.We hypothesize that personality axes such as those ranging from fearfulness to being bold,and from neophobic to curiosity response in brood parasites constitute important components of defense against brood parasitism that reduces the overall risk of parasitism.

Competitor densities,habitat,and weather:effects on interspecific interactions between wild deer species

There is a growing interest on the potential interplay between weather,habitat,and interspecific competition on population dynamics of wild herbivores.Favorable environmental conditions may buffer the negative effects of competition;conversely,competition may be expected to be stronger under harsh environmental conditions.We investigated relationships between competitor abundance,weather,and habitat cover on density and local distribution of a medium-sized herbivore,the roe deer Capreolus capreolus,as well as its spatial overlap with fallow deer Dama dama in a Mediterranean protected area.Over 11 years(2007–2017),roe deer density was not affected by spring–summer rainfall in the previous year and decreased with increasing density of fallow deer in the previous year.Hence,over the considered temporal scale,results supported a major role of competition over weather in influencing population trends of roe deer.At a finer spatial scale,roe deer occupancy was negatively affected by local abundance of fallow deer,especially in“poorer”habitats.We found a slight support for a positive effect of fallow deer density on interspecific spatial overlap.Moreover,fine-scale spatial overlap between deer species increased with decreasing rainfall in spring–summer.Fallow deer were introduced to our study area in historical times and their role as superior competitors over roe deer has been found also in other study areas.We suggest a potential role of harsh weather conditions during the growing season of vegetation(i.e.scarce rainfall)in triggering the potential for ecological overlap,emphasizing the negative effects of interspecific competition.