Habitat utilization patterns of sympatric populations of Pseudomys gracilicaudatus and Rattus lutreolus in coastal heathland: A multivariate analysis

Abstract Habitat usage characteristics of two species of native murid rodents, Pseudomys gracilicaudatus and Rattus lutreolus were investigated on an area of coastal heathland at Myall Lakes National Park. A grid of 151 trap stations comprising 17 traplines was positioned across a mosaic of habitats. At each trap station 19 structural vegetation and physical variables known to affect the microdistribution of small mammals were measured. Multivariate statistical procedures identified those microhabitat variables that contribute to individual species' habitat use and habitat partitioning, and reduce potential competition for space. Cluster analysis classified trap stations into one of six habitat types that were mapped on the study area, identifying a heterogeneous assemblage of interlocking habitats. The pattern is a consequence of topographic variation on the site and, to a lesser extent, its fire history. Trapping results show P. gracilicaudatus and R. lutreolus exhibit similar macrohabitat selection, preferring topographically low habitats, with both species predominantly occupying short dense heath with dense sedge cover. The high overlap in macrohabitat use is greatly reduced when considered trap station by trap station, so that discriminant function and multiple regression analyses demonstrate marked microhabitat selection. Elevation was a highly significant variable, accounting for 41% and 27% of the variance in the habitat used by P. gracilicaudatus and R. lutreolus, respectively. This variable represents a soil moisture gradient that determines changes in the floristic and structural components of the biotic environment. Two other structural vegetation variables and vegetation height contributed 30% of the variance in P. gracilicaudatus distribution. Sedge cover was found to be significant and explained 13% of the variance in R. lutreolus distribution. Within-habitat separation was explained best with a linear combination of variables in a discriminant function, rather than by any single variable. Differential microhabitat selection, interference competition and diet separation appear to be the major factors facilitating coexistence of these two species.     

同域分布大熊猫和水鹿生境利用分异特征

野生动物的生境利用特征研究是动物生态学核心问题之一,同域分布动物对生境的利用特征及共存机制是其重要组成部分,也是实现珍稀濒危物种保护与栖息地恢复的基础。基于空间利用和生境因子选择差异研究了卧龙自然保护区同域分布大熊猫(Ailuropoda melanoleuca)和水鹿(Rusa unicolor)的生境利用关系,探讨了同域分布野生动物在生境因子选择和空间利用的分异特征。结果表明:(1)空间利用上,大熊猫和水鹿的空间重叠系数为58.35%,其中,在原始林和次生林生境中的空间重叠系数分别为66.58%和36.64%,二者在原始林中的空间重叠较高;(2)生境因子选择上,大熊猫和水鹿对物理因子的选择有坡位、离小路距离和离水源距离3个变量有显著性差异,对生物因子的选择有乔木密度、灌木盖度、灌木密度、竹林盖度、幼竹密度、幼竹基径、幼竹高度、成竹高度和死竹密度9种变量有显著性差异;(3)大熊猫和水鹿都表现为更偏好原始林生境,但大熊猫对原始林的依赖性更强。分析同域分布动物的生境利用关系有利于深入了解不同动物对资源的空间利用特征及共存机制,可以为保护区制定珍稀野生动物保护和栖息地恢复政策提供科学依据。     

Resource partitioning in sympatric delphinids: space use and habitat preferences of Australian snubfin and Indo-Pacific humpback dolphins

1. Many species of delphinids co-occur in space and time. However, little is known of their ecological interactions and the underlying mechanisms that mediate their coexistence. 2. Snubfin Orcaella heinsohni, and Indo-Pacific humpback dolphins Sousa chinensis, live in sympatry throughout most of their range in Australian waters. I conducted boat-based surveys in Cleveland Bay, north-east Queensland, to collect data on the space and habitat use of both species. Using Geographic Information Systems, kernel methods and Euclidean distances I investigated interspecific differences in their space use patterns, behaviour and habitat preferences. 3. Core areas of use (50% kernel range) for both species were located close to river mouths and modified habitat such as dredged channels and breakwaters close to the Port of Townsville. Foraging and travelling activities were the dominant behavioural activities of snubfin and humpback dolphins within and outside their core areas. 4. Their representative ranges (95% kernel range) overlapped considerably, with shared areas showing strong concordance in the space use by both species. Nevertheless, snubfin dolphins preferred slightly shallower (1-2 m) waters than humpback dolphins (2-5 m). Additionally, shallow areas with seagrass ranked high in the habitat preferences of snubfin dolphins, whereas humpback dolphins favoured dredged channels. 5. Slight differences in habitat preferences appear to be one of the principal factors maintaining the coexistence of snubfin and humpback dolphins. I suggest diet partitioning and interspecific aggression as the major forces determining habitat selection in these sympatric species.     

Habitat preferences and biomasses of small mammals in Swaziland

This paper describes the distribution and abundance of small mammals in Swaziland in relation to quantified habitat features. Eighteen habitat sites were sampled at seven different locations in all four geographical regions of Swaziland. Small mammal diversity (as described by the Shannon diversity index) was positively correlated with vegetation density. A total of twelve species of rodents and seven species of shrews were captured; however, only six species were caught at more than three sites. Small mammal biomasses and densities were highest at the highveld and middleveld sites. Tall grassland at all elevations supported a high diversity of small mammals. Highveld montane forest supported a high biomass and diversity of species, while no species were captured in moist forest in the Lubombo mountains.     

Convergence and divergence in prey of sympatric canids and felids: opportunism or phylogenetic constraint?

Since the canids and felids diverged in the mid‐Eocene or earlier, each family has developed a suite of morphological and behavioural adaptations for obtaining and consuming prey. We here distinguish between prey taxa captured and eaten as a result of these phylogenetic adaptations, and those because they are fortuitously encountered, and argue that such supplementary prey, often opportunistically caught, create a buffer between sympatric, and potentially competitive, canids and felids and thus enhance coexistence. We base our analysis on dietary data derived from the stomach contents of four sympatric canid and felid species in the Free State Province, South Africa (canids: Cape fox Vulpes chama and black‐backed jackal Canis mesomelas; felids: African wild cat Felis silvestris lybica and caracal Caracal caracal), and from results of studies on these species elsewhere in southern Africa. The two canid species preyed heavily on invertebrates, and thus opportunistically, while the felids (especially the caracal) concentrated on mammals, prey they are phylogenetically adapted to capture. Only three species of mammalian prey are shared by the four species. The ratio of opportunistically‐to‐phylogenetically mediated prey taxa used (the O/P ratio) differ between the species, with the black‐backed jackal having the most opportunistically caught taxa in its diet, and the caracal the least. As predicted, a comparison of this data with those from dietary studies of the same species carried out elsewhere indicates that the number of opportunistically obtained prey taxa varies more than those resulting from phylogenetic adaptations. The largest canid had the widest food spectrum (35 prey taxa) while the smallest felid had the most restricted one (11 prey taxa). We argue that using the O/P distinction allows a better understanding of changes in food niche breadth of particular species, especially in xeric areas, and gives a better indication of possible exploitative competition for food by sympatric carnivores than when regarding all prey taxa as actively pursued. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83 , 527–538.     

贺兰山西坡啮齿动物生境选择及种间关系

为明确对贺兰山西坡啮齿动物生境选择起关键作用的主要环境因子,探讨各鼠种之间的相互作用如何影响鼠种的生境选择,选取地理因子（海拔、坡度、坡向）、植被因子（植被盖度、植被高度、灌木/乔木高度）和其他因子（距水源距离、距道路距离、距灌木/乔木距离）等9种生境因子,利用资源选择函数模型和logistic回归模型对啮齿动物生境选择和种间关系进行分析。结果表明,在贺兰山西坡,捕获数量最多的6种啮齿动物对的生境选择存在差异,大林姬鼠（Apodemus peninsulae）偏好高海拔、多灌木（乔木）的生境;子午沙鼠（Meriones meridianus）偏好海拔较低的半荒漠稀疏生境,对道路和人为干扰不回避;灰仓鼠（Cricetulus migratorius）偏好距水源较远、多灌木（乔木）、距道路较近的生境;阿拉善黄鼠（Spermophilus alaschanicus）偏好低海拔、植被丰富的生境;短尾仓鼠（Cricetulus eversmanni）偏好高海拔、距道路较近的生境;社鼠（Niviventer niviventer）偏好海拔较高、坡度较大、距水源较远的生境。鼠种间的相互关系主要呈现回避或随机关系。研究结果有助于了解啮齿动物分布的变化及种群动态规律,可为贺兰山生物资源保护,区域性鼠害的预测、预报和综合治理提供基础资料和科学依据。     

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

Abstract 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.     

Habitat use and behavioural ecology of the juveniles of two sympatric damselfishes (Actinopterygii: Pomacentridae) in the south-western Atlantic Ocean

Spatial distribution, microhabitat use and territorial and feeding behaviours were compared between the juveniles of two sympatric territorial damselfishes Stegastes variabilis and Stegastes fuscus on a small tropical reef in the south-western Atlantic Ocean. Juvenile S. variabilis were most abundant at sites subject to stronger hydrodynamics and with mixed benthic cover, whereas juvenile S. fuscus were most abundant at sheltered sites with dense turf algae cover. No differences regarding feeding habits were detected, with both species preferentially feeding on turf algae. Also, despite similarities in territory area and agonistic encounter rates, the identity and proportion of intruders involved in agonistic interactions differed significantly between species. These interdependent traits suggest strong asymmetric competition, with juvenile S. fuscus dominating high-quality sites and evicting juvenile S. variabilis to low quality, marginal areas of the reef.     

Habitat characteristics and species interference influence space use and nest‐site occupancy: implications for social variation in two sister species

Nest‐site selection is an important component of species socio‐ecology, being a crucial factor in establishment of group living. Consequently, nest‐site characteristics together with space‐use proxies may reveal the social organization of species, which is critical when direct observation of social interactions is hindered in nature. Importantly, nest‐site choice is expected to be under strong selective pressures and the object of intra‐ and interspecific competition. Although the bulk of research on sociality focuses on its ecological drivers, our study introduces interspecific competition as a potential factor that could influence social evolution. We investigated the influence of habitat and interspecific competition on the social organization of two sister species of the African four striped mouse, Rhabdomys dilectus dilectus and Rhabdomys bechuanae, in a similar macroenvironment. These species diverged in allopatry and occupy distinct environmental niches. We radiotracked 140 adults to identify their nest‐sites, determine nest characteristics and record groups that shared nest‐sites. Group cohesion was estimated from nest‐site fidelity, group association strength, and home range overlap within versus between group members. We compared the two species in sympatry versus parapatry to determine the impact of species interference on sociality. In parapatry, the two species selected distinct nest‐site types, interpreted as different anti‐predator strategies: R. bechuanae selected fewer, spaced, less concealed nest‐sites whereas R. d. dilectus selected clumped and less visible nest‐sites. Rhabdomys bechuanae also showed more cohesive and stable social groups than R. d. dilectus. In sympatry, compared to R. bechuanae, R. d. dilectus occupied similar nest‐sites, however slightly more exposed and clumped, and displayed similar nest‐site fidelity and group association strength. We conclude that although habitat selection may be an important driver of social divergence in Rhabdomys, species interference, by limiting R. d. dilectus movements and forcing nest‐site sharing may induce new ecological pressures that could influence its social evolution.     

Comparative ecology of eleotrid fishes in Central American coastal streams

The population structure, abundance, reproductive status, and feeding interrelationships of eleotrid fishes from two freshwater streams of the Caribbean coast of Costa Rica were investigated over 10 continuous months. Eleotris amblyopsis was abundant in both streams. Dormitator maculatus, Eleotris pisonis, and Gobiomorus dormitor were present in both streams but common only in the larger stream that contained dense growth of floating aquatic macrophytes. Dormitator maculatus is a detritivore and overlaps with the other three eleotrids, all of which had diets dominated by shrimp and fishes. Intraguild predation and cannibalism was documented with E. amblyopsis as the prey. Except for the benthic G. dormitor, eleotrids were associated with dense mats of floating macrophytes in the large stream, and leaf peaks in the small stream. Diet similarity among the three carnivorous eleotrids declined during the wet seasons, the period when their prey disperse at lower per-unit-area densities within the flooded forests that surround the streams. Analysis of population size distributions and gonadal maturation indicated that at least some reproduction occurs on a nearly year-round basis within these eleotrid populations. The spring dry period may be associated with migration of ripe eleotrids to estuarine habitats for spawning. Juvenile Eleotris are the dominant fishes in the tismiche, mass migrations of juvenile shrimp and fish larvae and juveniles that enter and ascend the estuary, especially during the summer wet season.     

Resource partitioning in sympatric langurs and macaques in tropical rainforests of the central Western Ghats, south India

In a competitive sympatric association, coexisting species may try to reduce interspecific interactions as well as competition for similar resources by several ecological and behavioral practices. We studied resource utilization of three sympatric primate species namely, lion-tailed macaques (Macaca silenus), bonnet macaques (M. radiata) and Hanuman langurs (Semnopithecus entellus) in a tropical rainforest of the central Western Ghats, south India. We studied resource use, tree-height use, foraging height, substrate use when consuming animal prey and interspecific interactions. The results revealed that across the year, there was very limited niche overlap in diet between each species-pair. Each primate species largely depended on different plant species or different plant parts and phenophases from shared plant species. Primate species used different heights for foraging, and the two macaque species searched different substrates when foraging on animal prey. We also recorded season-wise resource abundance for the resources shared by these three primate species. While there was low dietary overlap during the dry season (a period of relatively low resource abundance), there was high dietary overlap between the two macaque species during the wet season (a period of high resource abundance for the shared resources). We observed only a few interspecific interactions. None of these were agonistic, even during the period of high niche overlap. This suggests that the sympatric primate species in this region are characterized by little or no contest competition. Unlike in some other regions of the Western Ghats, the lack of interspecific feeding competition appears to allow these primates, especially the macaques, to remain sympatric year-round.     

Diets of sympatric native and introduced carnivores in the Barrington Tops,eastern Australia

Invasive predators have severe impacts on global biodiversity, and their effects in Australia have been more extreme than on any other continent. The spotted‐tailed quoll (Dasyurus maculatus), an endangered marsupial carnivore, coexists with three eutherian carnivores, the red fox (Vulpes vulpes), feral cat (Felis catus) and wild dog (Canis lupus ssp.) with which it did not coevolve. No previous study has investigated dietary overlap between quolls and the suite of three eutherian carnivores. By analysing scats, we aimed to quantify dietary overlap within this carnivore assemblage in eastern Australia, and to detect any differences that may facilitate coexistence. We also sought evidence of intraguild predation. Dietary overlap between predators was extensive, with the greatest similarity occurring between foxes and cats. However, some differences were apparent. For example, cats mainly consumed smaller prey, and wild dogs larger prey. Quolls showed greater dietary overlap with foxes and cats than with dogs. Intraguild predation was evident, with fox remains occurring in 3% of wild dog scats. Our results suggest wild dogs competitively dominate invasive foxes, which in turn are likely to compete with the endangered quoll.     

白颈长尾雉与白鹇秋冬季空间生态位比较

2008年9月-2009年2月,在江西官山国家级自然保护区对白颈长尾雉(Syrmaticus ellioti)和白鹇(Lophura nycthemera)及其栖息地生态因子进行调查,通过8个资源轴分析了2个种的多维生态位宽度、重叠及种间竞争.结果表明,白鹇和白颈长尾雉综合空间生态位宽度分别仅为0.268和0.294;白鹇的海拔和坡度空间生态位大于白颈长尾雉.而白颈长尾雉的坡向生态位宽度大于白鹇,在其他资源轴上二者接近;白颈长尾雉和白鹇的栖息地生态位相似性为0.425,竞争系数为0.584,竞争比较激烈.应加强低海拔地区植被及水源的保护,减少人为干扰.     

Habitat segregation by breeding origin in the declining populations of European Robins wintering in southern Iberia

Mediterranean woodlands and associated shrub formations of southern Iberia are key habitats for conservation of migratory birds. In some bird species, migratory and sedentary conspecifics meet in these areas during winter, but our understanding of how each population group is distributed over available habitats and the factors that determine their spatial organization are still unclear. This seriously limits our ability to assess their vulnerability to ongoing environmental changes affecting wintering habitats in this region. We used hydrogen isotopic signatures of feathers (δD_f) to shed light on the habitat distribution of seasonally sympatric European Robin Erithacus rubecula populations wintering in Campo de Gibraltar that are currently facing a drastic decline. In contrast to previous studies that used morphological methods to distinguish the migratory behaviour of wintering Robins in this area, our isotopic approach revealed that sedentary Robins were not outcompeted upon the arrival of migrants and remained in the woodlands where they reproduce, which agrees with results obtained in other regions. Interestingly, we also found that migratory Robins with a closer breeding origin (higher δD_f values) had a higher probability of occupying woodlands than did migrants coming from further away. Overall, our results suggest that the role of breeding origin in shaping the distribution of Robins during winter in Campo de Gibraltar is more relevant than the effects of sex, age or body size, which might facilitate the evolution of local adaptations for the exploitation of each habitat type.     

Coexistence between two fruit fly species is supported by the different strength of intra‐ and interspecific competition

1. Unravelling the strength and modes of interspecific interactions between resident and introduced species is necessary in order to understand the basis of their coexistence or the displacement of the former by the latter. In Argentina, the indigenous Tephritidae fly Anastrepha fraterculus overlaps its distribution and host fruit with the introduced species Ceratitis capitata. 2. This study focused on the relative strength of intra‐ and interspecific competition during the larval stage as a potential factor supporting coexistence. Classical competition experiments (addition and substitution) were conducted between larvae of the two species reared in artificial larval diet. The study evaluated whether a temporal separation between oviposition events affects the outcome of the competition. 3. When both species started to consume the resource at the same time, A. fraterculus experienced a negative effect in larval survival, pupal weight and duration of larval stage, while for C. capitata, pupal weight decreased. When A. fraterculus started feeding 1 day earlier than C. capitata, the negative effects became milder, and when the temporal separation increased, these effects were reversed. Substitution experiments showed an increase in pupal weight when larvae had to share the resource with heterospecific larvae, and showed negative effects suffered for both species when they shared the resource with conspecific individuals. 4. These results suggest that intraspecific competition is stronger than interspecific competition, and a differential oviposition preference could generate an asynchrony of these species in nature. Such mechanisms could favour coexistence between A. fraterculus and C. capitata in an environment previously occupied only by the former.     

Adaptative evolution of the Vkorc1 gene in Mus musculus domesticus is influenced by the selective pressure of anticoagulant rodenticides

Anticoagulant rodenticides are commonly used to control rodent pests worldwide. They specifically inhibit the vitamin K epoxide reductase (VKORC1), which is an enzyme encoded by the Vkorc1 gene, involved in the recycling of vitamin K. Therefore, they prevent blood clotting. Numerous mutations of Vkorc1 gene were reported in rodents, and some are involved in the resistant to rodenticides phenotype. Two hundred and sixty‐six mice tails were received from 65 different locations in France. Coding sequences of Vkorc1 gene were sequenced in order to detect mutations. Consequences of the observed mutations were evaluated by the use of recombinant VKORC1. More than 70% of mice presented Vkorc1 mutations. Among these mice, 80% were homozygous. Contrary to brown rats for which only one predominant Vkorc1 genotype was found in France, nine missense single mutations and four double mutations were observed in house mice. The single mutations lead to resistance to first‐generation antivitamin K (AVKs) only and are certainly associated with the use of these first‐generation molecules by nonprofessionals for the control of mice populations. The double mutations, probably obtained by genetic recombination, lead to in vitro resistance to all AVKs. They must be regarded as an adaptive evolution to the current use of second‐generation AVKs. The intensive use of first‐generation anticoagulants probably allowed the selection of a high diversity of mutations, which makes possible the genetic recombination and consequently provokes the emergence of the more resistant mutated Vkorc1 described to date.