Interspecific Segregation Research Articles

Using Next-Generation Sequencing to Disentangle the Diet and Incidence of Intestinal Parasites of Falkland Flightless Steamer Duck Tachyeres brachypterus and Patagonian Crested Duck Lophonetta specularioides Sharing a South Atlantic Island

Species overlapping in habitat use can cohabit depending on how they exploit resources. To understand segregation in resource use, an exhaustive knowledge of the diet is required. We aimed to disentangle the diet composition of the Falkland Flightless Steamer Duck Tachyeres brachypterus and the Patagonian Crested Duck Lophonetta specularioides sharing a coastal environment. Using DNA extracted from scats and Illumina sequencing, we generated a list of molecular operational taxonomic units. Both ducks consumed a variety of invertebrates, frequently overlapping in the taxa consumed. However, only the Falkland Flightless Steamer Ducks consumed fish, which might be indicative of dietary specialization and inter-specific segregation in the restricted space that these birds share. Moreover, the female and male Falkland Flightless Steamer Ducks consumed different fish prey, with almost one-third of the fish taxa being consumed by females only and another similar number consumed by males only. This result might suggest a case of intra-specific competition, triggering sexual segregation. Additionally, we detected parasitic Platyelminthes (Cestoda and Trematoda), with different frequencies of occurrence, probably related to the different diet compositions of the ducks. This study provides the necessary baseline for future investigations of the ecological segregation of these ducks.

Spatial assembly of grassland communities and interrelationships with productivity

AbstractKnowledge on the fine‐scale spatial aggregation is pertinent for deciphering plant community dynamics, as interactions among sessile plants mainly occur in the neighbourhood. However, the spatial assemblage mechanism and interrelationships with productivity remain poorly understood.Here, species segregation index (Mscom) was used to quantify the interspecific segregation (or intraspecific aggregation) of the neighbourhood in plant communities from three contrasting plateaus. We employed the coordinates for 125,726 individual plants (within 1 m2plots) sampled in natural grassland communities across two temperate grasslands (Loess Plateau and Mongolian Plateau) and one alpine grassland (Tibetan Plateau) to elucidate the assembly mechanisms of Mscomand interrelationships with above‐ground net primary productivity (ANPP).We found that these grassland communities tended to assemble into intraspecific aggregations; the phenomenon was more apparent in regions with low annual precipitation. In grassland communities on Loess Plateau, the strong intraspecific aggregation was mainly due to low sexual reproduction allocation; on Mongolian Plateau, reproductive allocation was also the dominant factor for Mscomvariation, followed by the interactive effect of annual precipitation and species richness, whereas on Tibetan Plateau, low species richness was the main reason for increased intraspecific aggregation, followed by the interactive effect of annual precipitation and species richness, and reproductive allocation. More importantly, on all three plateaus, the independent influence of Mscomon ANPP is stronger than that of species and phylogenetic diversity.We elucidated the potential mechanisms shaping spatial aggregation in grassland communities at large scale, and emphasize the critical role of spatial aggregation in predicting the variation of ANPP.Read the freePlain Language Summaryfor this article on the Journal blog.

Environmental and ecological controls of the spatial distribution of microbial populations in aggregates.

In microbial communities, the ecological interactions between species of different populations are responsible for the spatial distributions observed in aggregates (granules, biofilms or flocs). To explore the underlying mechanisms that control these processes, we have developed a mathematical modelling framework able to describe, label and quantify defined spatial structures that arise from microbial and environmental interactions in communities. An artificial system of three populations collaborating or competing in an aggregate is simulated using individual-based modelling under different environmental conditions. In this study, neutralism, competition, commensalism and concurrence of commensalism and competition have been considered. We were able to identify interspecific segregation of communities that appears in competitive environments (columned stratification), and a layered distribution of populations that emerges in commensal (layered stratification). When different ecological interactions were considered in the same aggregate, the resultant spatial distribution was identified as the one controlled by the most limiting substrate. A theoretical modulus was defined, with which we were able to quantify the effect of environmental conditions and ecological interactions to predict the most probable spatial distribution. The specific microbial patterns observed in our results allowed us to identify the optimal spatial organizations for bacteria to thrive when building a microbial community and how this permitted co-existence of populations at different growth rates. Our model reveals that although ecological relationships between different species dictate the distribution of bacteria, the environment controls the final spatial distribution of the community.

The role of allochrony in influencing interspecific differences in foraging distribution during the non-breeding season between two congeneric crested penguin species.

Mechanisms promoting coexistence between closely related species are fundamental for maintaining species diversity. Mechanisms of niche differentiation include allochrony which offsets the peak timing of resource utilisation between species. Many studies focus on spatial and temporal niche partitioning during the breeding season, few have investigated the role allochrony plays in influencing interspecific segregation of foraging distribution and ecology between congeneric species during the non-breeding season. We investigated the non-breeding migrations of Snares (Eudyptes robustus) and Fiordland penguins (Eudyptes pachyrhynchus), closely related species breeding between 100–350 km apart whose migration phenology differs by two months. Using light geolocation tracking, we examined the degree of overlap given the observed allochrony and a hypothetical scenario where the species commence migration simultaneously. We found that Fiordland penguins migrated to the Sub-Antarctic Frontal Zone and Polar Frontal Zone in the austral autumn whereas Snares penguins disperse westwards staying north of the Sub-Tropical Front in the austral winter. Our results suggest that allochrony is likely to be at the root of segregation because the relative profitability of the different water masses that the penguins forage in changes seasonally which results in the two species utilising different areas over their core non-breeding periods. Furthermore, allochrony reduces relatively higher levels of spatiotemporal overlap during the departure and arrival periods, when the close proximity of the two species’ colonies would cause the birds to congregate in similar areas, resulting in high interspecific competition just before the breeding season. Available evidence from other studies suggests that the shift in phenology between these species has arisen from adaptive radiation and phenological matching to the seasonality of local resource availability during the breeding season and reduced competitive overlap over the non-breeding season is likely to be an incidental outcome.

Strategies for segregation during foraging in sympatric otariids of the Peruvian upwelling Humboldt Current System

The competitive exclusion principle predicts that species exhibit segregation mechanisms to coexist. In the Humboldt Current System, South American sea lions Otaria byronia (SASL) coexist with South American fur seals Arctocephalus australis (SAFS); however, the existence of temporal and spatial partitioning in foraging strategies remains unknown. To compare foraging strategies, we analyzed locations of 35 adults (18 SASL, 17 SAFS; 4 and 8 females, 14 and 9 males, respectively) equipped with satellite tags in Punta San Juan, Peru (2013-2017). We evaluated (1) distance and duration of foraging trips, (2) utilization distributions (UDs), (3) foraging by hour and (4) association of foraging with environmental variables. Regular interval tracks (every 30 min) were modeled, and residence time was estimated to determine foraging events. Proportion overlap and analysis of similarity compared groups in core areas (50% UD) and home ranges (95% UD). Generalized additive mixed models were built to determine if hour of day and environmental conditions had an effect on foraging. Multiple mechanisms for foraging segregation that explain coexistence were found. Duration and distance between species-sex groups were significantly different, except for trip duration between SASL sexes. SAFS traveled longer distances and duration than SASL, and males traveled longer distances and duration than conspecific females. Female UDs overlapped, while male UDs did not. Core areas between sexes overlapped in SAFS and SASL, but home ranges were significantly different. Hour of day had a significant effect on foraging events in SAFS females and SASL males. Environmental conditions during foraging by SASL and SAFS females reflected coastal and offshore habitats, respectively. However, interspecific segregation was not evident between males.

Diet of sympatric Barn Owls Tyto alba and Short-eared Owls Asio flammeus in an agricultural landscape in south-east Spain

The diets of the Barn Owl Tyto alba and the Short-eared Owl Asio flammeus have been extensively studied worldwide over the past few years, especially on the Iberian Peninsula. Nevertheless, very few studies have examined the diets and the trophic niche overlap in areas where these two raptor species occur in sympatry. As such, in this study we compared the diets of the Barn Owl and the Short-eared Owl inhabiting agricultural landscapes of the Vega de Granada, south-east Spain, based on pellet analysis. The diets were very similar, as both owls preyed mainly on small mammals, the Algerian Mouse Mus spretus being the prey most commonly found in pellets from both species. Although the diet of the Barn Owl was more diverse than that of the Short-eared Owl, the food niche overlap was very high, thus indicating a low interspecific trophic segregation. Despite the similarities between both diets, the frequency of the Mediterranean Pine Vole Microtus duodecimcostatus was much higher in pellets from the Barn Owl, thus suggesting that the Barn Owl may exert pest control in years when the Mediterranean Pine Vole occurs in high numbers.

Interaction between hunting strategy, habitat type and stratum drive intraguild predation and cannibalism

Intraguild predation (IGP) is a common interaction between generalist predators when they competitively exploit similar resources and prey on each other. Theoretical models predict limitations for intraguild predator coexistence unless some mechanisms, such as the utilization of alternative prey (i.e. trophic niche partitioning) and cannibalism, increase the relative intraspecific clustering and interspecific segregation. As hunting strategies determine trophic niches of predators and their own vulnerability to predation, the hunting strategies may also determine the relative importance of cannibalism, predation, and exploitative competition and consequently the intensity of IGP. The importance of hunting strategies on the potential outcome of IGP and how habitat properties modify the interaction between hunting strategies remain poorly understood. Using published data on spider prey of spider predators, we first investigated how predation of a top‐predator on a mesopredator is determined by the functional distance between both predators to understand how predation and exploitation are distributed in spider communities. Subsequently, we investigated the predation among spiders with particular hunting strategies to understand which strategies interact most frequently. We also investigated whether the interaction between hunting strategies was influenced by habitat type (forest, open (semi)natural habitat, agroecosystem) or by habitat stratum (ground versus vegetation). The hunting strategies of top‐predators and mesopredators interacted to determine the relative capture proportions of conspecifics and hetero‐specifics. This interaction was further modified by habitat type and stratum. Two mechanisms can reinforce coexistence in highly diverse spider communities. First, top‐predators preyed most frequently on functionally distinct mesopredators, which indicates the overall intensity of IGP may be relaxed by a balanced distribution between exploitative competition and predation. Second, cannibalism was common for top‐predators with a hunting strategy of frequently preying on functionally similar mesopredators. Cannibalism may lead to self‐limitation of top‐predator populations and may thereby facilitate coexistence between two predator species.

Characterization of Binary Biofilms of Listeria monocytogenes and Lactobacillus and Their Response to Chlorine Treatment.

In nature, Listeria may interact competitively and cooperatively with other organisms, resulting in unique spatial organization and functions for cells within the community. This study was undertaken to characterize the biofilm architecture of binary biofilms of Listeria monocytogenes and Lactobacillus species and to assess their effect on the survival of Listeria during exposure to hypochlorite. Three L. monocytogenes strains, ATCC 19115 (Lm5), ATCC 19117 (Lm7), and Coleslaw (LmC), were selected and combined individually with three Lactobacillus strains: L. fermentum (Lf), L. bavaricus (Lb), and L. plantarum (Lp). In binary Lm-Lp biofilms, the Lm cell counts were similar to single-species biofilms (8.5 log CFU/well), and the Lp cell numbers declined by 1.0 log CFU/well. In the presence of Lb, the Lm cell counts were reduced by 1.5 log CFU/well (p < 0.05), whereas the Lf cell counts increased at least by 3.5 log CFU/well. Confocal laser scanning microscopy (CLSM) determined that interspecies interactions significantly affected the spatial organization of three binary biofilms. Biofilm surface-to-volume ratio increased from 0.8 μm2/μm3 for Lm5 in the monoculture to 2.1 μm2/μm3 for Lm5-Lp in the dual-species model (p < 0.05), and was characterized by a thicker structure with a largely increased surface area. Biofilm roughness increased from 0.2 for Lm7 to 1.0 for Lm7-Lb biofilms (p < 0.05), which appeared as interspecific segregation. Biofilm thickness increased from 34.2 μm for LmC to 46.3 μm for LmC–Lf (p < 0.05), which produced flat and compact structures that covered the entire surface available. The biomass of the extracellular matrix was higher in the case of some binary biofilms (p < 0.05); however, this effect was dependent upon the species pair. When treated with hypochlorite, Lm5 in binary biofilms had an approximately 1.5 log CFU/well greater survival than individually. The unique spatial organization and greater protein production may explain the protective effect of Lp after hypochlorite exposure.

Small-scale spatial structure affects predator-prey dynamics and coexistence

Small-scale spatial variability can affect community dynamics in many ecological and biological processes, such as predator-prey dynamics and immune responses. Spatial variability includes short-range neighbour-dependent interactions and small-scale spatial structure, such as clustering where individuals aggregate together, and segregation where individuals are spaced apart from one another. Yet, a large class of mathematical models aimed at representing these processes ignores these factors by making a classical mean-field approximation, where interactions between individuals are assumed to occur in proportion to their average density. Such mean-field approximations amount to ignoring spatial structure. In this work, we consider an individual-based model of a two-species community that is composed of consumers and resources. The model describes migration, predation, competition and dispersal of offspring, and explicitly gives rise to varying degrees of spatial structure. We compare simulation results from the individual-based model with the solution of a classical mean-field approximation, and this comparison provides insight into how spatial structure can drive the system away from mean-field dynamics. Our analysis reveals that mechanisms leading to intraspecific clustering and interspecific segregation, such as short-range predation and short-range dispersal, tend to increase the size of the resource species relative to the mean-field prediction. We show that under certain parameter regimes these mechanisms lead to the extinction of consumers whereas the classical mean-field model predicts the coexistence of both species.

The importance of considering small-scale variability in macrobenthic distribution: spatial segregation between two fiddler crab species (genus Leptuca) (Decapoda, Ocypodidae)

ABSTRACT Defining the appropriate scale is important when trying to understand distribution patterns in community studies. Fiddler crabs are among the most common organisms inhabiting estuarine environments, and despite having a wide latitudinal distribution, are limited by shifts in temperature, current and wind pattern. Thus, many co-occur at a local scale, where their distribution is influenced by variables such as mean sediment grain diameter, salinity and tidal level. Our goal was to test intra and interspecific segregation in two similar and commonly co-occurring fiddler crabs species (Leptuca leptodactyla and Leptuca uruguayensis) at a small scale (10 m²). Interspecific segregation was observed, with L. leptodactyla occurring mainly at the upper level in relation to the water line and L. uruguayensis, at the lower. However, this pattern was irrespective of sex and developmental stage, as no intraspecific segregation was seen. Possible impacts of tidal level, soil silt/clay content and competition on interspecific segregation are discussed. Although L. leptodactyla and L. uruguayensis overlap in their occurrence when intertidal zonation is disregarded, they segregate when tidal levels are individually sampled as habitats. This highlights the importance of small-scale studies to identify patterns unobserved at regional scales, even when no environmental gradient is readily apparent.

Habitat segregation between brown bears and gray wolves in a human-dominated landscape.

Identifying how sympatric species belonging to the same guild coexist is a major question of community ecology and conservation. Habitat segregation between two species might help reduce the effects of interspecific competition and apex predators are of special interest in this context, because their interactions can have consequences for lower trophic levels. However, habitat segregation between sympatric large carnivores has seldom been studied. Based on monitoring of 53 brown bears (Ursus arctos) and seven sympatric adult gray wolves (Canis lupus) equipped with GPS collars in Sweden, we analyzed the degree of interspecific segregation in habitat selection within their home ranges in both late winter and spring, when their diets overlap the most. We used the K‐select method, a multivariate approach that relies on the concept of ecological niche, and randomization methods to quantify habitat segregation between bears and wolves. Habitat segregation between bears and wolves was greater than expected by chance. Wolves tended to select for moose occurrence, young forests, and rugged terrain more than bears, which likely reflects the different requirements of an omnivore (bear) and an obligate carnivore (wolf). However, both species generally avoided human‐related habitats during daytime. Disentangling the mechanisms that can drive interspecific interactions at different spatial scales is essential for understanding how sympatric large carnivores occur and coexist in human‐dominated landscapes, and how coexistence may affect lower trophic levels. The individual variation in habitat selection detected in our study may be a relevant mechanism to overcome intraguild competition and facilitate coexistence.

Poblaciones de tiburones en las bahías Chatham y Wafer del Parque Nacional Isla del Coco, Costa Rica

&lt;p&gt;&lt;strong&gt; &lt;/strong&gt;At least fourteen species of sharks live in the Marine Protected Area of Isla del Coco National Park (ICNP), some are resident species such as the whitetip reef shark (&lt;em&gt;Triaenodon obesus&lt;/em&gt;); others are migratory and visit the National Park throughout the year, e.g. the scalloped hammerhead shark (&lt;em&gt;Sphyrna lewini&lt;/em&gt;) and the whale shark (&lt;em&gt;Rhincodon typus&lt;/em&gt;). Between March 2010 and August 2012 six expeditions out to the ICNP were carried, during this period 25 night trips (from 18:00 to 22:00 hr) for shark tagging were conducted in the Wafer and Chatham bays. During those trips, 185 sharks were analyzed: 81.1 % were whitetip reef sharks (&lt;em&gt;T. obesus&lt;/em&gt;), 16.7 % were blacktip sharks (&lt;em&gt;Carcharhinus limbatus&lt;/em&gt;), 1.1 % were blacktip reef sharks (&lt;em&gt;Carcharhinus melanopterus&lt;/em&gt;) and 1.1% were silvertip sharks (&lt;em&gt;Carcharhinus albimarginatus&lt;/em&gt;). The most common species in Bahía Chatham was &lt;em&gt;T. obesus&lt;/em&gt;, while the most common one in Bahía Wafer was &lt;em&gt;C. limbatus&lt;/em&gt;, which represented 80.9 % and 80.5 % of the total sharks caught, respectively. Regarding &lt;em&gt;T. obesus&lt;/em&gt;, a sex ratio of 1.2 males per female was estimated (X&lt;sup&gt;2&lt;/sup&gt;=0.09; p=0.17); in turn a sex ratio of 1.01 males per female was observed (X&lt;sup&gt;2&lt;/sup&gt;=0.04; p=0.79) for &lt;em&gt;C. limbatus&lt;/em&gt;. The average total length for &lt;em&gt;T. obesus &lt;/em&gt;and &lt;em&gt;C. limbatus&lt;/em&gt; was 103.66±13.91 cm and 76.58±14.56 cm respectively; suggesting that black tip sharks use those bays during immature stages. The results show an interspecific spatial segregation of the most common resident sharks at ICNP, apparently the clear waters and the coral cover of Chatham Bay are preferred by &lt;em&gt;T. obesus&lt;/em&gt;; while the turbid waters of the Genio River mouth are preferred by &lt;em&gt;C. limbatus&lt;/em&gt;&lt;/p&gt;

Reproductive constraints influence habitat accessibility, segregation, and preference of sympatric albatross species.

BackgroundThe spatiotemporal distribution of animals is dependent on a suite of factors, including the distribution of resources, interactions within and between species, physiological limitations, and requirements for reproduction, dispersal, or migration. During breeding, reproductive constraints play a major role in the distribution and behavior of central place foragers, such as pelagic seabirds. We examined the foraging behavior and marine habitat selection of Laysan (Phoebastria immutabilis) and black-footed (P. nigripes) albatrosses throughout their eight month breeding cycle at Tern Island, Northwest Hawaiian Islands to evaluate how variable constraints of breeding influenced habitat availability and foraging decisions. We used satellite tracking and light-based geolocation to determine foraging locations of individuals, and applied a biologically realistic null usage model to generate control locations and model habitat preference under a case–control design. Remotely sensed oceanographic data were used to characterize albatross habitats in the North Pacific.ResultsIndividuals of both species ranged significantly farther and for longer durations during incubation and chick-rearing compared to the brooding period. Interspecific segregation of core foraging areas was observed during incubation and chick-rearing, but not during brooding. At-sea activity patterns were most similar between species during brooding; neither species altered foraging effort to compensate for presumed low prey availability and high energy demands during this stage. Habitat selection during long-ranging movements was most strongly associated with sea surface temperature for both species, with a preference for cooler ocean temperatures compared to overall availability. During brooding, lower explanatory power of habitat models was likely related to the narrow range of ocean temperatures available for selection.ConclusionsLaysan and black-footed albatrosses differ from other albatross species in that they breed in an oligotrophic marine environment. During incubation and chick-rearing, they travel to cooler, more productive waters, but are restricted to the low-productivity environment near the colony during brooding, when energy requirements are greatest. Compared to other albatross species, Laysan and black-footed albatrosses spend a greater proportion of time in flight when foraging, especially during the brooding period; this strategy may be adaptive for locating dispersed prey in an oligotrophic environment.Electronic supplementary materialThe online version of this article (doi:10.1186/s40462-015-0063-4) contains supplementary material, which is available to authorized users.

Influence of Life History Traits on Trophic Niche Segregation between Two Similar SympatricTupinambisLizards

Segregation of habitat resources is an important mechanism that allows the coexistence of species. The diet is an important and dynamic component that can generate interactions among co-existing species. Differences in food resource use between related sympatric species have been associated frequently with divergence in multiple phenotypic traits; hence, it is interesting to explore how phenotypic differences allow sympatric species to minimize niche overlap. We aimed to evaluate trophic niche segregation between Tupinambis merianae and T. rufescens in relation to life history traits in a sympatric zone. We compared the volume of the stomach food items between species considering sexual dimorphism, body size classes, sexual maturity and reproductive activity. The obtained Morisita's index indicated trophic niche overlap between T. merianae and T. rufescens; however, considering particular food items, we observed differences in diet composition. Moreover, our results indicate that body size, sexual maturity and reproductive activity are relevant factors influencing the diet of these species. Life history traits of these two species of Tupinambis are important because they shape diet composition, contributing to interspecific segregation of the trophic niche and, therefore, allowing species coexistence.

Love thy neighbour or opposites attract? Patterns of spatial segregation and association among crested penguin populations during winter.

AimCompetition for food among populations of closely related species and conspecifics that occur in both sympatry and parapatry can be reduced by interspecific and intraspecific spatial segregation. According to predictions of niche partitioning, segregation is expected to occur at habitat boundaries among congeners and within habitats among conspecifics, while negative relationships in the density of species or populations will occur in areas of overlap. We tested these predictions by modelling the winter distributions of two crested penguin species from three colonies in the south-western Atlantic.LocationPenguins were tracked from two large colonies on the Falkland Islands and one in South Georgia, from where they dispersed through the South Atlantic, Southern Ocean and south-eastern Pacific.MethodsForty macaroni penguins (Eudyptes chrysolophus) from South Georgia and 82 southern rockhopper penguins (Eudyptes chrysocome chrysocome) from two colonies in the Falkland Islands were equipped with global location sensors which log time and light, allowing positions to be estimated twice-daily, from April to August in 2011. Positions were gridded and converted into maps of penguin density. Metrics of overlap were calculated and density was related to remote-sensed oceanographic variables and competitor density using generalized additive models.ResultsMacaroni penguins from western South Georgia and southern rockhopper penguins from Steeple Jason Island, Falkland Islands, were spatially segregated by differences in their habitat preferences thus supporting our first prediction regarding interspecific segregation. However, southern rockhopper penguins from Beauchêne Island showed a marked spatial overlap with macaroni penguins as the two had similar habitat preferences and strong mutual associations when controlling for habitat. Contrary to our predictions relating to intraspecific segregation, southern rockhopper penguins from Beauchêne Island and Steeple Jason Island were segregated by differences in habitat selection.Main conclusionsMorphological differentiation probably allows macaroni penguins from South Georgia and southern rockhopper penguins from Beauchêne Island to coexist in areas of spatial overlap, whereas segregation of the two Falkland rockhopper penguin populations may have arisen from two distinct lineages retaining cultural fidelity to ancestral wintering areas.

Metabolic and Demographic Feedbacks Shape the Emergent Spatial Structure and Function of Microbial Communities

Microbes are predominantly found in surface-attached and spatially structured polymicrobial communities. Within these communities, microbial cells excrete a wide range of metabolites, setting the stage for interspecific metabolic interactions. The links, however, between metabolic and ecological interactions (functional relationships), and species spatial organization (structural relationships) are still poorly understood. Here, we use an individual-based modelling framework to simulate the growth of a two-species surface-attached community where food (resource) is traded for detoxification (service) and investigate how metabolic constraints of individual species shape the emergent structural and functional relationships of the community. We show that strong metabolic interdependence drives the emergence of mutualism, robust interspecific mixing, and increased community productivity. Specifically, we observed a striking and highly stable emergent lineage branching pattern, generating a persistent lineage mixing that was absent when the metabolic exchange was removed. These emergent community properties are driven by demographic feedbacks, such that aid from neighbouring cells directly enhances focal cell growth, which in turn feeds back to neighbour fecundity. In contrast, weak metabolic interdependence drives conflict (exploitation or competition), and in turn greater interspecific segregation. Together, these results support the idea that species structural and functional relationships represent the net balance of metabolic interdependencies.

Tree species exhibit complex patterns of distribution in bottomland hardwood forests

& Context Understanding tree interactions requires an insight into their spatial distribution. & Aims We looked for presence and extent of tree intraspecific spatial point pattern (random, aggregated, or overdispersed) and interspecific spatial point pattern (independent, aggregated, or segregated). & Methods We established twelve 0.64-ha plots in natural bottomland hardwood stands in the southeastern USA. & Results Spatial point pattern analyses (Ripley’s K, L ,a nd L12) indicated that, when species were combined, trees were frequently aggregated and less commonly overdispersed. Plots with larger trees were more likely to exhibit overdispersion, confirming a shift to this pattern as trees grow. The intraspecific pattern of cherrybark oak and water oak was either aggregated or random. Sweetgum was aggregated on all plots and always at smaller distances (less than 5 m) than the two oak species. Intraspecific overdispersion was very rare. Interspecific segregation among the two oak species was more commonly observed (six plots) than aggregation (one plot). Cherrybark oak and sweetgum were segregated at some scale on seven of the 12 plots and aggregated on only two plots. & Conclusion The results from the analyses suggest that strong interspecific competition may result in segregation of trees from different species, while weaker intraspecific competition may lead to aggregations of conspecifics.

山西五鹿山白皮松群落乔灌层的种间分离

The Wulu Mountains,a part of the Luliang Mountain Range,are situated at 36°23′45″—36°38′20″N,111°08′—111°18′E in western Shanxi Province,China.This area has a warm-temperate continental monsoon climate with abundant plant resources and high biodiversity.Appropriate conditions for the growth of Pinus bungeana Zucc.ex Endl.are limited within the Wulu Mountains which include only a part of the overall range of P.bungeana.Therefore,building nature reserves in which P.bungeana can be studied systematically is important both ecologically and academically,with the goal of studying this species in its warm temperate north China climate so it can be preserved in natural forests indefinitely. Interspecific relationships are an important factor affecting community composition,structure,function and dynamics.Interspecific segregation refers to the relative distributions of two or more related species.It reflects the degree of mixing of two species based on their interrelationships.For example,the less two species mix,the higher the degree of interspecific segregation exists. The segregation relationship between different species pairs can be helpful in revealing the phenomena of species interactions,community structure and dynamics.This relationship can be used to explore the impacts of environmental differences on species distribution.Practically,such study is the scientific foundation of species conservation,restoration and the reconstruction of degraded ecosystems. We established 55 quadrats within natural P.bungeana communities to study the intraspecific and interspecific competition relationships of nine tree species and patterns of interspecific segregation of all species in the tree and shrub layers of P.bungeana communities.Using ArcView GIS software and the nearest neighbor method,interspecific segregation was studied with an N × N nearest-neighbor contingency table,a 2 × 2 nearest-neighbor contingency sub-table,and Hegyi′s competition index model for the individual tree species. The results indicate:(1) most of the species pairs are randomly segregated(80%),some species pairs are positively segregated(16.19%),and only a few species pairs are negatively segregated(3.81%).(2) There are some differences among different species in the interspecific segregation of all species.The larger individuals representing dominant species in the communities tended to be positively segregated with the other large trees and shrubs,probably because of their stronger competitive vigor.For example,P.bungeana,which is the most common and dominant species of this community,was positively segregated from Platycladus orientalis,Quercus wutaishanica,Ulmus pumila,Syringa pubescens,Cotoneaster multiflorus,Sophora davidii,Viburnum mongolicum,the dominant species of this community.Negative segregation appeared between dominant species and companion species in the communities,such as P.bungeana and Populus davidiana,P.orientalis and F.vulgaris,S.microphylla and Salix wallichiana.This appeared to be caused by the fact the companion species had fewer individuals,lower coverage and similar habitat requirements to the dominant species.Intensive interspecific competition resulted in a mosaic distribution and full competitive exploitation of resources among species,apparently causing them to be more likely to become negatively segregated. The 15 species from the forest plots were divided into three ecological species groups(ESG),based on their niches and relationships between the species,other plants and the environment.(3) The status of interspecific segregation of species has a close relationship to their intraspecific and interspecific competitive relationships and spatial distribution patterns.The larger individuals representing dominant species with more severe intraspecific competition than interspecific competition and appearing to have an aggregating distribution in the communities tended to be positively aggregated with the other large trees and shrubs.Negative aggregation(segregation) appeared between dominant species and companion species which have more severe interspecific competition than intraspecific competition in the communities.The interspecific competition of species within the same ESGs was more intense than in species in different ESGs.(4) The interspecific segregation is related to the heterogeneity in the communities,in that aggregation often occurs between two species which have different habitat requirements;while the segregation often appears between two species which have same or similar environmentally requirements.(5) The results show the 15 species we studied overlapped in distribution and were characterized by overall non-segregation.(6) The intraspecific and interspecific relationships were caused by ecological niches to which the different species are adapted and their biological requirements,and these differences may be the mechanisms which allow these species to stably coexist in the P.bungeana community of the Wulu Mountain Nature Reserve.

Variability of resource partitioning in sympatric tropical boobies

Inter- and intraspecific competition can lead to resource partitioning in sympatric species, processes likely affected by environmental productivity and population size. We investi- gated the foraging behaviour and diet of masked (Sula dactylatra) and red-footed (S. sula) boobies at Tromelin Island, western Indian Ocean, to examine the role of resource partitioning in the for- aging strategies of these sympatric species in an extreme oligotrophic environment. We compared our results to published studies with differing environmental conditions or population sizes. We used GPS loggers and Argos transmitters to track foraging movements and used time-depth recorders to estimate dive depths. Masked boobies travelled further and at faster rates than red- footed boobies, and sexes did not differ in foraging behaviour. Based on randomization tests, the foraging range of each species (95% utilization distribution; UD) overlapped significantly. How- ever, at core foraging areas (50% and 25% UD), interspecific segregation was greater than expected by chance alone. No intraspecific spatial segregation was detected between sexes. Envi- ronmental characteristics of area-restricted search zones differed between species, but not sexes; masked boobies utilized warmer, deeper, and less windy oceanic environments than red-footed boobies. Masked boobies attained greater diving depths than red-footed boobies and consumed primarily flying fish, whereas red-footed boobies consumed mostly squid. Red-footed and masked boobies breeding in the extreme oligotrophic environment near Tromelin demonstrated greater dietary partitioning differences in foraging ranges compared to a less oligotrophic environment. This suggests that environmental productivity may play a role in processes of resource partition- ing in these sympatric species.

Intraspecific and Interspecific Spatial Distribution of Three Eastern North Pacific Catshark Species and Their Egg Cases (Chondrichthyes: Scyliorhinidae)

Information on the distribution of three species of eastern North Pacific (ENP) catsharks (Apristurus brunneus, Apristurus kampae, and Parmaturus xaniurus) and their egg cases was previously unavailable despite being a species of interest for fisheries management evaluation and policy regulation. Data were generated from specimens collected by survey cruises from June 2001 through October 2004 between northern Washington to San Diego, California, U.S.A. and from known catch locations of specimens in museum collections. Longline catches consisted mainly of P. xaniurus, with occasional catch of gravid female A. brunneus. Conversely, trawl catches consisted mainly of Apristurus species. The three catshark species exhibited distinct differences in latitudinal and bathymetric range, albeit with partial overlap. Apristurus brunneus was typically found between 300 and 942 m along the entire area surveyed, while A. kampae always occurred .1,000-m depth and was not found north of 426N. Parmaturus xaniurus was caught between 300- and 550-m depth between 406N and 326N. Egg cases of A. brunneus and P. xaniurus were collected in trawl surveys and observed in video footage taken by remotely operated vehicle. These egg cases were located in specific sites on areas of high vertical relief at 300- to 500-m depth. Nursery grounds, which were previously unknown for these catshark species, were described within the Monterey Bay Canyon and along the California coastline were identified on the basis of recurrence and specificity of oviposition. This paper describes the range of A. brunneus, A. kampae, and P. xaniurus in the ENP, detailing latitudinal, bathymetric, sexual, and ontogenetic intra- and interspecific segregation patterns.