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To date, only two Cherax species have been reported to occur in Italy, i.e., C. destructor Clark, 1936 and C. quadricarinatus (von Martens, 1868), both in the wild and in aquaculture farms. Therefore, we aimed to update their current status and distribution in Italian mainland and Sicily. In addition, we investigated the origin of their known populations, and their possible routes of invasion. In order to genetically characterize the Cherax populations occurring in Italian inland waters and aquaculture facilities, the barcode region of the mtDNA gene cytochrome oxidase subunit I was sequenced in the available specimens originating from an aquaculture facility and a museum collection. The sampling campaigns conducted in 2021 did not lead to the collection of any Cherax individuals in the sites where the species was formerly reported to occur. The recent failures to detect Cherax spp. from Italian inland waters might be due to the inability of the species to cope with the Italian climate, which is likely for C. quadricarinatus but less so for C. destructor, to the possible impact of the alien red swamp crayfish Procambarus clarkii (as well as its indirect impact i.e., the spread of the crayfish plague for which yabby is susceptible), which occurs in both the sites where C. destructor was reported in Italy, or to the burrowing habits of the species, which might lead to overlook their presence when present at low densities. In the light of the well-known impact of invasive crayfish and considering the scant knowledge about the current distribution and status of Cherax species in Italy, a regular monitoring of their possible presence is recommended.

Transitional zones, such as edge habitat, are key landscapes for investigating biodiversity. "Soft edges" are permeable corridors that hosts can cross, while "hard edges" are impermeable borders that hosts cannot pass. Although pathogen transmission in the context of edges is vital to species conservation, drivers of host-parasite relationships in ecological edges remain poorly understood. Thus, we defined a framework for testing hypotheses of host-parasite interactions in hard and soft edges by (1) characterizing hard and soft edges from both the host and parasite perspectives, (2) predicting the types of parasites that would be successful in each type of edge, and (3) applying our framework to species invasion fronts as an example of host-parasite relationships in a soft edge. Generally, we posited that parasites in soft edges are more likely to be negatively affected by habitat fragmentation than their hosts because they occupy higher trophic levels but parasite transmission would benefit from increased host connectivity. Parasites along hard edges, however, are at higher risk of local extinction due to host population perturbations with limited opportunity for parasite recolonization. We then used these characteristics to predict functional traits that would lead to parasite success along soft and hard edges. Finally, we applied our framework to invasive species fronts to highlight predictions regarding host connectivity and parasite traits in soft edges. We anticipate that our work will promote a more complete discussion of habitat connectivity using a common framework and stimulate empirical research into host-parasite relationships within ecological edges and transitional zones.

Remnant natural populations of greater bilbies (Macrotis lagotis) are confined to the Australian arid zone where bilbies construct and shelter in multiple burrows within their home range. We investigated burrow use behaviour of bilbies in a translocated population in temperate southern Australia to determine if behaviour differed in this climatic zone. Over a 12 month period, 43 adult bilbies at Venus Bay Conservation Park were spool-and-line tracked to 118 burrows. Active burrow density was 0.55 per ha, and bilbies at the site used multiple burrows (up to 13 for males and 8 for females) and regularly moved between diurnal burrows. Male bilbies had significantly larger burrow ranges (10.2 ± 5.8 ha, MCP100, mean ± s.d.) than females (2.6 ± 1.8 ha), and were similar in size to those recorded in an arid zone population. Males’ burrow ranges tended to overlap with the burrow range of multiple other males and females. The density of burrows in the current study suggests that bilby burrows were likely to have been a common landscape feature within the southern parts of the species range prior to their local extinction. Further research is needed to determine the impact of the loss of bilby burrows from southern Australia on other burrow commensal species.

The conversion of natural grasslands into tree plantations has reduced the extent of natural habitats in southern Brazil, altering bird composition due to local species extinction and colonization. Tree plantations represent a new land use in the region and are within a mosaic of altered and native vegetation. We investigated whether bird composition of tree plantations immersed within a grassy landscape consists of a nested subset of species from adjacent riparian forests. We sampled birds in riparian forests and in eucalyptus plantations at two stages of development using the point count method. We partitioned beta-diversity into nestedness and turnover components to detect the strength of local extinction and colonization processes, respectively, in determining variation in composition among native forests and intermediate and old-aged plantations considering all birds together and only forest-specialist birds. We then used linear models to test the effect of land use on the pairwise turnover and nestedness that each plantation presents relative to native forests. We recorded 72 bird species, of which 62, 25, and 22 species were found in riparian forests, intermediate, and old-aged plantations, respectively. Turnover predominated in beta-diversity partitioning—whether all birds or just forest-specialist birds were analyzed—showing that the bird composition of tree plantations might not depend on adjacent forests, but instead on sparse resource availability within tree plantations. Finally, we found lower bird turnover for plantations relative to native forests with increasing cover of tree plantations in the landscape. Large extents of tree plantations in the landscape, therefore, homogenize bird composition across sites.

Human-induced ecological and climatic changes have led to the decline and even local extinction of many formerly widely distributed temperate and cold-adapted species. Determining the exact causes of this decline remains difficult. Bryodemella tuberculata was a widely distributed orthopteran species before the mid-19th century. Since then, many European populations have suffered drastic declines and are now considered extinct or critically endangered. We used ecological niche modelling based on a large dataset of extant and extinct occurrence data to investigate whether poor climatic suitability in the periphery of its global range was a possible cause of the local extinction of the European populations of B. tuberculata. We also used population genetics based on the COI marker to estimate and compare the genetic diversity of extant populations. We found that Europe still provides highly suitable habitats close to the climatic optimum, contradicting the assumption of climate change as major driver of this decline. Instead, changes in land-cover and other anthropogenic modifications of the habitats at the local scale seem to be the major reasons for local extinctions. Genetic analysis suggests Central Asia as center of diversity with a stable population size, whereas the effective sizes of the remaining European populations are decreasing. We found European genetic lineages nested within Central Asian lineages, suggesting a Central Asian source distribution area. Our results suggest that the declining European populations represent relics of a formerly wider distribution, which was fragmented by changes in land-use. These relics are now threatened by limited connectivity and small effective population sizes. Specific conservation actions, such as the restoration of former or potential new habitats, and translocation of individuals from extant populations to these restored sites may help slow, stall, or even revert the extinction process.

The Great Barrier Reef is a diverse ecosystem of outstanding universal value that is under an increasing level of cumulative threat. The status of biodiversity, particularly that of habitat-forming taxa is not known, and more data are needed to evaluate this. Here, we summarize scleractinian coral distribution records in the Lizard Island reef system from 1976 to 2020 to explore the persistence of the local species pool across 44 years. By undertaking replicated spatio-temporal biodiversity surveys (2011, 2015, 2017, 2020) at 14 sites and compiling published species records from this location (1976–2020), we determine that 368 species of hermatypic scleractinian coral have been recorded from Lizard Island and/or nearby reefs over the last 44 years. Two hundred and eighty-four of those species (77.2%) have ongoing records across this time period indicating temporal persistence at the local scale. However, 28 species (7.6%) that were reliably recorded prior to 2011 have not been recorded in subsequent years and may be at risk of local extinction. A further 31 species (8.4%) may be at risk of local range reduction as they have not been recorded at Lizard Island and/or at nearby reefs since 2015. The remaining 25 species (6.8%) were deemed taxonomically unreliable records. Fifty-three species are recorded from Lizard Island for the first time in the 2011–2020 surveys, however, further integrated taxonomic research is required to verify some of these records. At a site level, species diversity has been in a state of flux over the 2011–2020 period with significant declines in species richness notable from 2011 to 2017, and significant recovery from 2017 to 2020. Overall, this dataset indicates local extinction or local range reduction is a tangible risk for 59 species (16% of the species pool) in the Lizard Island region. Additional targeted searching for these species along with temporal monitoring of species abundance and size structure is warranted to better understand the status of coral biodiversity at this globally significant location.

On dynamic coastlines, populations of protected algal species with poor dispersal might be especially vulnerable to infrequent recruitment events and local extinction. As a model, we here consider the dispersal of the alga Padina pavonica from the largest remaining and physically isolated enclaves on the south coast of England. A bio-physical model was used to investigate the likely importance of local propagule dispersal in maintaining populations. Dispersal kernels that simulate the position of propagules at different time steps over 5 days were examined from five release sites. Exceptionally steep declines in model propagule density were observed over the first few hours from release, yet over the first day, 75–85% of model propagules remained close to their source but had not reached other enclaves. After five days, the dispersal from source populations ranged from 0 to 50 km, with only ~5% remaining within the source 1 km2 area. Although distances of modelled propagule dispersal might be adequate for maintaining a regional population network, vegetative perrenation also appears to be important for persistence of P. pavonica. For rare and protected species on isolated and energetic coastlines, local conservation efforts, rather than a reliance on a wider meta-population network, remain very important to ensure long-term protection and survival.

To understand the possible effects of changes in ambient temperature on spatial distribution and ecology of ostracods, samples were randomly collected from 70 aquatic sites with 12 different habitat types from Hatay (Turkey) province during the summer season of 2012. 14 of 19 ostracod species were newly reported for the province. The first two axes of CCA explained 79.7% of the cumulative variance of the relationship between the 12 most common species and five environmental variables. Accordingly, water temperature and electrical conductivity were the most effective factors on species occurrences (p, Ortam sıcaklığındaki değişimlerin ostrakodların mekansal dağılımı ve ekolojisi üzerindeki olası etkilerini anlamak için, 2012 yazında Hatay (Türkiye) ilinden 12 farklı habitat türüne sahip 70 su sahasından rastgele örnekler toplanmıştır. Elde edilen 19 türden 14 tanesi Hatay için yeni kayıttır. CCA’nın ilk iki ekseni en yaygın 12 tür ile beş çevresel değişken arasındaki ilişkinin toplam varyansının %79,7'sini açıklamıştır. Buna göre, su sıcaklığı ve elektriksel iletkenlik türlerin oluşu üzerinde en etkili faktörlerdir (p

Changes in geographical distributions underlie a variety of fundamental ecological and evolutionary processes, from allopatric speciation to local extinction. However, little is known about general principles governing the evolution of range sizes at macroevolutionary scales. In this study we measure rates of geographical range size and position in a large-scale dataset of nearly 20,000 species including mammals, birds, squamates and anurans to test three predictions regarding the relationship between endothermy and geographical range evolution, namely whether endotherms show (1) larger geographical ranges; (2) faster rates of range size evolution; and (3) faster changes in the geographical position of their ranges. We found evidence in favor of all of these predictions, suggesting that the evolution of endothermy was associated with a fundamental change in the tempo of range evolution in terrestrial vertebrates. These results are consistent with two previously hypothesized relationships between range size and metabolic rate: the thermal plasticity hypothesis, which suggests that high metabolic rate increases thermal tolerance, and the energy constraint hypothesis, which posits that due to the higher, sustained levels of energy requirements, individuals with high metabolic rates would necessitate to forage farther and to space themselves more broadly, which would result in lower population densities, larger home ranges and ultimately larger range sizes. On the other hand, there was substantial variation in rates of range size evolution among the studied taxa that cannot be explained by the evolution of endothermy alone.

Self-incompatible, non-clonal plant species are especially dependent on the activity of flower visitors for seed production. Therefore, populations of these plants are vulnerable to a reduced flower visitation rates, but also to increased isolation by extinction of local populations. To study how local populations ofCentaurea scabiosa, a self-incompatible, bee-pollinated herb species changed over time in the region of Bonn, we collected historical population records in the area and investigated their current status. We found that more than half of the subpopulations mentioned in the literature between 1950 and 2012 (38 of 65) have since disappeared. Small populations were most vulnerable, whereas medium to large populations increased in size. In a second step, we studied visitation frequencies and achene production and weight across 14 extant populations. We found that both flower visitation frequency and achene production were positively related to population size. Achene weight was neither related to the frequency of flower visitors nor to achene production. These results clearly indicate that reduced pollen transfer and lower pollination rates may contribute to local extinction in small populations ofCentaurea scabiosa. Overall our results call for an intensified monitoring of the populations of self-incompatible plant species.

Plant species exhibit current characteristics as a result of interactions with environmental conditions. The plants of Viola sp. have selected chasmogamous flowers with vigorous vegetative propagation or development of cleistogamous flowers as an adaptation strategy. Viola websteri is distributed on the Korean peninsula and the eastern part of Jilin Province, China. The center and edge of the distribution are expected to exhibit different population-dynamics. It is necessary to investigate the cause of its current limited distribution even though V. websteri has a mixed-mating strategy. Firstly, We examined the vegetation environment of habitats and evaluated its characteristics. Growth characteristics were examined through plant phenology. We then evaluated the population structure, characteristics of chasmogamous flowers, and productivity of cleistogamous flowers. Moreover, we compared population sizes between 2014 and 2018. Most habitats were located in deciduous broadleaf mixed forests adjacent to valleys. V. websteri produced chasmogamous flowers with self-incompatibility in April-May and cleistogamous flowers in June-September. The cleistogamous flower production is a strategy ensuring seed production under uncertain environmental fluctuations; these were approximately twice as numerous as chasmogamous flowers. The population structure was distinguished into stable and very unstable regions. There were sites where the population experienced a sharp decline in the 2018 compared to that of 2014. This large decline was found in the edge populations. The habitats had different microsites depending on the natural disturbances of drought and the matrix constituting the habitat, thus supporting various plants. Ensuring the production of seeds through cleistogamous flowers, it was determined that rapid seedling re-establishment and population replenishment were possible when the natural disturbance factor was removed. Environmental factors did not equally affect all populations or individuals. Therefore, it was expected that it would be able to persisted in a long time, despite the rapid decrease in the number of individuals in the population regionally. Local extinction and re-establishment are likely to repeat according to environmental change. We propose the additional population investigation based on this works are required. We also suggest a need to assess the long-term population dynamics and the genetic characteristics of chasmogamous flowers and cleistogamous flowers to establish and implement effective conservation strategies.

The turbulent counter-flow flame (TCF) has proven to be a useful benchmark to study turbulence-chemistry interactions, however, the widely observed bulk flow fluctuations and their influence on the flame stability remain unclear. In the present work, premixed TCFs are studied numerically using a Large Eddy Simulation (LES) method. A transported probability density function (pdf) approach is adopted to simulate the sub-grid scale (sgs) turbulence-chemistry interactions. A solution to the joint sgs-pdf evolution equation for each of the relative scalars is obtained by the stochastic fields method. The chemistry is represented using a simplified chemical reaction mechanism containing 15 reaction steps and 19 species. This work compares results with two meshing strategies, with the domain inside nozzles included and excluded respectively. A conditional statistical approach is applied to filter out the large scale motions of the flame. With the use of digital turbulence, the velocity field in the flame region is well reproduced. The processes of local extinction and re-ignition are successfully captured and analysed together with the strain rate field, and local extinctions are found correlated to the turbulent structures in the reactant stream. The predicted probability of localised extinction is in good agreement with the measurements, and the influence of flame stoichiometry are also successfully reproduced. Overall, the current results serve to demonstrate the capability of the LES-pdf method in the study of the premixed opposed jet turbulent flames.

Studies contrasting parasite prevalence and host-parasite community structure between pristine and disturbed environments will improve our understanding of how deforestation affects disease transmission and parasite extinction. To determine how infection rates of a common and diverse group of avian blood parasites (Plasmodium and Haemoproteus) respond to changes in avian host composition after mining, we surveyed 25 bird communities from pristine forests (two forest types: plateau and hillside) and reforested sites in Northeast Amazonia. Infection rates and both parasite and avian host community structure exhibited considerable variation across the deforestation gradient. In opposition to the emerging pattern of lower avian haemosporidian prevalence in disturbed tropical forests in Africa, we show that secondary forests had higher haemosporidian prevalence in one of the largest mining areas of Amazonia. The dissimilarity displayed by bird communities may explain, in part, the higher prevalence of Haemoproteus in reforested areas owing to the tolerance of some bird species to open-canopy forest habitat. On the other hand, deforestation may cause local extinction of Plasmodium parasites due to the loss of their avian hosts that depend on closed-canopy primary forest habitats. Our results demonstrate that forest loss induced by anthropogenic changes can affect a host-parasite system and disturb both parasite transmission and diversity.

Earth mounds, locally known as murundus, are ~ 4000 year old natural formations resulting from termite excavation and occur as mound fields in the Caatinga, the largest dry forest region in South America. Termites are ecosystem engineers and the bioturbation caused by them can influence the colonization of other insect species, e.g., the giant ants Dinoponera quadriceps, which are conspicuous in mound fields. We hypothesized that (i) nests and individuals of giant ants are more prevalent in mound fields when compared to regions in Caatinga with no earth mounds, (ii) nests may be located close to trees with large trunks, and (iii) amidst soils rich in organic matter. We placed sampling plots in four sites: two mound fields and two sites with no earth mounds in the state of Bahia, Brazil. Ant nests were more abundant in mound fields when compared to areas with no earth mounds. Thus, mound fields are important sites for ant nests at the landscape scale. The nests were more often found between mounds where termite tunnels occur, suggesting that ants avoid nesting on the top of earth mounds which are bare resulting from anthropogenic removal of vegetation and litter over the past few decades. Thus, the continued conversion of Caatinga into pasture may endanger populations of D. quadriceps, similar to the fate of D. lucida in the Atlantic Forest. The local extinction of the giant ant that are important seed dispersers in this biome can result in the impoverishment of Caatinga floristic structure and diversity.

Long-term field studies help unveil mechanisms of grass soil seed bank (SSB) persistence and resilience. We wonder whether grazing is a disruptive force that changes grass SSB composition and size, while heavy rainfall is a positive bottom-up force that restores the grass SSB in grazed areas of the Monte desert, Argentina. We used core sampling to study the grass SSB in cattle-free (17 year) and grazed (10 year) grasslands. The SSB size in cattle-free sites usually responded in a continuous positive fashion to rainfall, and the proportion of palatable grasses in the SSB was similar among years. Most grass species formed a transient SSB, but the presence of a stand of perennial plants would prevent their local extinction. In contrast, the SSB size in the grazed habitats showed a threshold response to rainfall (i.e. it did not increase under low-moderate rainfall), the seeds of palatable grasses were always scarce, and the proportion of seeds of less palatable grasses increased under extreme rainy conditions. Seed production from grasses that grew tillers from axillary buds during a drought was zero, suggesting that the bank of plants could have a role in the replenishment of the grass SSB only in mesic years. Within the time span assessed here, continuous heavy grazing together with scarce as well as heavy rainfall were disruptive forces that reduced the number and proportion of seeds from palatable grasses in the SSB, which are also the species preferred by seed-eating animals.

A single adverse environment event can threaten the survival of small-ranged species while random fluctuations in population size increase the extinction risk of less-abundant species. The abundance-range-size relationship (ARR) is usually positive, which means that smaller-ranged species are often of low abundance and might face both problems simultaneously. The ARR has been reported to be negative on tropical islands, perhaps allowing endemic species in such environments to remain extant. But there is a need to understand how endemism and land-use interact to shape ARR. Using 41 highly replicated transects along the full elevational gradient of Sri Lanka, we determined the following: (a) the direction of ARR, (b) if endemism affects ARR and (c) if land-use (rainforest, buffer and agriculture) changes ARR differently for endemics and non-endemics. Additionally, (d) we identified endemics that had both lower abundances and smaller range sizes, and ranked them from most threatened (specific to rainforests) to least threatened using a weighted-interaction nestedness estimator. (a) We found a positive relationship between species abundances and range size. This positive ARR was maintained among endemic and non-endemic species, across land-use types and at local and regional scales. (b) The ARR interacted with endemicity and land-use. Endemics with smaller range sizes had higher abundances than non-endemics, and particularly higher in rainforests compared to agriculture. In contrast, species with larger range sizes had similar abundances across endemicity and land-use categories. Many endemics with smaller range sizes are globally threatened; therefore, higher abundances may buffer them from extinction risks. (c) Nine (29%) endemics had both below average abundance and elevational range size. The nestedness estimator ranked the endemics Sri Lanka Whistling Thrush Myophonus blighi, Red-faced Malkoha Phaenicophaeus pyrrhocephalus, Sri Lanka Thrush Zoothera imbricata and White-faced Starling Sturnornis albofrontus as the four most vulnerable species to local extinction risk, which corresponds to their global extinction risk. We demonstrate that ARR can be positive on tropical islands, but it is influenced by endemism and land-use. Examining shifts in ARR is not only important to understand community dynamics but can also act as a tool to inform managers about species that require monitoring programmes.

Early European land use of Dirk Hartog Island left a legacy of cats, sheep and goats that led to the local extinction of 10 of the Dirk Hartog Island’s 13 mammal species. A successful programme of eradication of these introduced species has resulted in improved habitat quality and is allowing the translocation of the island’s locally extinct native mammals. The island could potentially support one of the most diverse small‐medium‐sized terrestrial mammal assemblages in Australia and contribute significantly to their long‐term conservation.

Reproductive interference (costly interspecific sexual interactions) is well-understood to promote divergence in mating-relevant traits (i.e. reproductive character displacement: RCD), but it can also reduce population growth, eventually leading to local extinction of one of the species. The ecological and evolutionary processes driven by reproductive interference can interact with each other. These interactions are likely to influence whether the outcome is coexistence or extinction, but remain little studied. In this paper, we first develop an eco-evolutionary perspective on reproductive interference by integrating ecological and evolutionary processes in a common framework. We also present a simple model to demonstrate the eco-evolutionary dynamics of reproductive interference. We then identify a number of factors that are likely to influence the relative likelihoods of extinction or RCD. We discuss particularly relevant factors by classifying them into four categories: the nature of the traits responding to selection, the mechanisms determining the expression of these traits, mechanisms of reproductive interference and the ecological background. We highlight previously underappreciated ways in which these factors may influence the relative likelihoods of RCD and local extinction. By doing so, we also identify questions and future directions that will increase our holistic understanding of the outcomes of reproductive interference.

The phenotypic diversity of the Iranian orchids has sharply decreased during the last 15 years and is currently threatened with local extinction and global climatic changes. Harvest of tuberous orchids has recently been raised in Iran owing to the high prices of orchid's tubers and international demand from neighboring countries. This has caused competition among orchid harvesters in the country so that the orchids are not even allowed to produce seeds. The present study was done aimed at protecting and identifying the phenotypic diversity within Orchis mascula genotypes in Abr forest, which is a natural habitat of Orchis mascula in Shahrood area, Northeast Iran. The morphological variability of 101 collected samples of early purple orchids was analyzed based on a total of 57 morphological traits. In terms of the quantitative traits, the highest and lowest coefficients of variation (CV%) were observed in the number of side tubers (200%) and petal length (14.43%), respectively. When it comes to the qualitative traits, the highest and lowest CVs were observed in lip color (70.90%) and the flower form on the stem (0%), respectively. Among the studied traits, 11 attributes showed a CV value of less than 20%. The highest positive correlations were observed between tuber fresh weight and tuber dry weight (r = 0.908). Applying principal component analysis (PCA) indicated three main components that explained 45.81% of the total variance. The clusters number four and seven could arguably be suitable sources of parents in breeding crosses for tuber fresh and dry weight traits. In summary, this study confirmed that Abr forest would be one of the rich diversity areas for Orchis mascula and our findings might be satisfactorily applied for breeding, conservation, domestication and development of new traits depending on different breeding purposes.

Le changement climatique constitue un grand défi à relever par les politiques publiques et les gestionnaires des espaces naturels. La compréhension de ses impacts sur les écosystèmes forestiers constitue un préalable nécessaire à toute réflexion visant leur conservation et le maintien des services écosystémiques qu’ils offrent. Cette étude s’est intéressée à la modélisation de la distribution potentielle de Cedrus atlantica Manetti, à l’identification des variables environnementales conditionnant sa distribution, et à la définition de l’étendue géographique des aires qui sont favorables à sa présence sous les conditions climatiques passées, actuelles et futures. Ce travail a été réalisé en se basant sur le principe d’entropie maximale. La cartographie des aires potentielles révèle la sensibilité du cèdre aux changements climatiques passés et suggère une grande étendue (quadruple de la surface d’occurrence actuelle de l’espèce) des zones bioclimatiquement adaptées au développement de cette espèce sous les conditions climatiques actuelles. Cependant, les distributions potentielles futures semblent être dépendantes de certains sites spécifiques et risquent d’être affectées négativement par le climat futur. Ces résultats mettent en évidence l’ampleur des régressions projetées des superficies du cèdre dans le futur, ce qui pourrait impacter considérablement les fonctions et services de cet écosystème et augmenter les risques d’extinction locale. Ils constituent par ailleurs un bon outil de prise de décision pour les gestionnaires du territoire quant à la conservation de ce précieux écosystème forestier, afin d’éviter toute extinction de ce foyer de biodiversité marocaine.

Forests are the principal terrestrial ecosystem for protected and endangered large carnivores, providing the main habitat for species maintenance and survival. Changes in forest cover influence species distribution. The aim was (1) to test hypotheses on the natural environmental (abiotic) and biological (biotic) factors and human disturbances that determine the colonization and local extinction of three large carnivore species in relation to forest cover, (2) to infer the biotic interactions between these three large carnivore species occupying the same forested areas in Albania. Colonization is estimated to be positively affected by forest cover for brown bear, Balkan lynx and grey wolf. Brown bear and grey wolf tend to compete for the same forested areas. Local extinction increased with decreasing forest cover for brown bear and increased with decreasing mixed broadleaved forests for Balkan lynx. Anthropological variables (proximity to villages and to neighbourhood roads) increased local extinction for brown bear, grey wolf and Balkan lynx. Further studies are recommended for better understanding biotic interactions of large carnivore species in forest habitats in Albania and its neighbouring countries, which could contribute to conservation of large carnivore species on a large scale.

Droughts typically result in a widespread decline in many vertebrate populations and even the local extinction of some species. However, different species vary considerably in their resistance to the effects of drought. This study aimed to estimate the relative species richness and the colonization and extinction rates in a bird community during an acute drought event in the Brazilian Caatinga. We mist-netted birds during 3 years throughout seven field seasons in two sampling plots to estimate community parameters using multi-season dynamic occupancy models. The relative richness to the regional species pool varied considerably during the study period (16–49%) with markedly low values in the severe onset of the drought. The estimates in the savanna were higher than those in the shrubby-woodland plot (~ 42 vs ~ 31 species, respectively). Pollinators and seed dispersers were characterized by median to high colonization (30–69%) and local extinction rates (37–69%), indicating low site fidelity. By contrast, granivores and insectivores made up the resident component of the community, with low local extinction and colonization rates (

For depleted wildlife populations, understanding and effectively mitigating the direct and indirect impacts of roads can be a key component of recovery efforts. The ocelot is a federally endangered wild felid at risk of local extinction in south Texas, where vehicle collisions are their largest known source of mortality. To support road mortality mitigation, we evaluated mortality risk across the south Texas road network. We also assessed whether a sympatric carnivore, the bobcat, could serve as a surrogate to inform mortality risk. We used several presence-only species distribution models to evaluate a suite of candidate landscape and road attributes and identify those associated with elevated road mortality risk using a 35-year wild felid road mortality dataset. Consensus predictions among models identified high-risk road segments for ocelots and bobcats. We compared predictions between species to determine overlap of high-risk areas. Areas where core ocelot habitat intersected roadways represented the greatest mortality risk, reflecting ocelot reliance on intact habitat and avoidance of degraded and fragmented landscapes. Bobcat road mortality risk had similar relationships to landscape features, with nearly all areas classified as high-risk for ocelots also identified as high-risk for bobcats. Ocelots are vulnerable to road mortality in areas where roads intersect their intact scrub habitat. Bobcats, with appropriate data filters in place, are an acceptable surrogate for informing ocelot road mortality, particularly when ocelot mortality data are limited and for time-sensitive conservation decision-making. For ocelots and other fragmentation-intolerant carnivore species, wildlife underpasses and fencing in focused areas where roads and intact habitat intersect may be feasible options to reduce road mortality.

The continued decline in the small breeding population of southern elephant seals Mirounga leonina at Gough Island (40°19′S, 9°57′W) over a period of 46 years (1973–2019) signals the likely extirpation of the species at the northernmost extent of its breeding range in the Southern Ocean. The estimated number of births declined from a high (n = 38) in 1975 to a low (n = 2) in 2019, a 95% reduction at an average decrease of 2.15% per annum. The estimated mean time to extinction of this population from a linear regression model is 2 years (95% CI: 0–23 years). This decline is consistent with observed or forecasted population trends of some other marine top predators at the northern extent of their breeding ranges in the Southern Ocean; adding to the prevailing evidence that environmental change is the most plausible hypothesis explaining the range reduction of these marine species limited by a paucity of breeding grounds.

The native communities of the Indian Himalayan Region are largely dependent on plant resources for their sustenance. Among the economically important plants, wild edibles are consumed as raw, roasted, boiled, fried, cooked or in the form of oil, spice and seasonal material i.e., jams and pickles. The local communities have rich knowledge base indigenous uses and traditional practices, but require proper documentation for their long time conservation. The present study is an attempt to assess the wild edibles of Pangi valley, located in Chamba District of Himachal Pradesh. Total 124 wild edibles, representing 68 genera and 41 families were recorded. Of these, 09 species were represented by trees, 33 shrubs, 77 herbs, 1 fern and 03 fungi. Of the total species, 63 species were native, 10 near endemic, 03 endemic and other are non-native to the Indian Himalayan Region. Various parts namely, whole plants, stem, rhizome, tuber, bark, aerial part, leaves, flowers, fruits, roots, etc. were used by tribal communities in various forms. Over utilization and habitat degradation may result in local extinction. Therefore, for the conservation of these species, studies on habitat ecology, development of conventional and in vitro propagation protocols; introduction in the natural habitats and awareness among the tribal communities have been suggested.

SummaryAfrican White-backed Vultures were recently uplisted to ‘Critically Endangered’ by IUCN due to declines across their range. Poisoning is widely accepted as the major reason for these declines. Botswana supports a high number of this species (breeding pairs > c.1,200), but as yet no published information exists on their breeding success in the country. However, mass poisonings within Botswana and neighbouring countries have killed thousands of White-backed Vultures in recent years. We therefore expected that nesting numbers may have declined in this region if these poisoning events killed local breeding birds. We used information from aerial surveys conducted between 2006 and 2017 in Khwai and Linyanti, two important breeding areas for this species in north-central Botswana, to determine if there was any change in nesting numbers and breeding success of White-backed Vultures. Results showed an overall 53.5% decline in nesting numbers, with a greater decline in Linyanti than in Khwai. In both areas, breeding success was significantly lower in 2017 than it was 10 ten years earlier. We recommend that similar repeat surveys are continued to provide greater confidence in the trends of both nesting numbers and breeding performance. Population viability analysis suggested that if the productivity levels detected in 2017 were a true indication of current productivity levels for this population, and if recent high poisoning rates continue, this population could be extirpated from the area in the next 13 years.

The bloodworm, Arenicola loveni, is commonly used as bait by fishers and may be vulnerable to local extinction owing to its K-selected life history strategies and overexploitation. Accurate populat...

Significance Forecasts of global change impacts on biodiversity often assume that the current geographical distributions of species match their ecological niches. Here we examine this assumption using an extensive dataset of large-scale variation in demographic rates that enables us to quantify demography-based ecological niches of 26 plant species. Contrasting these niches with the species’ geographic distributions reveals that niche–distribution mismatches can be large and depend on key life-history traits: poorly dispersed species are absent from suitable sites, and species with high persistence ability are present in sites that are currently unsuitable for them. Such niche–distribution mismatches need to be accounted for to improve forecasts of biodiversity dynamics under environmental change., The ecological niche of a species describes the variation in population growth rates along environmental gradients that drives geographic range dynamics. Niches are thus central for understanding and forecasting species’ geographic distributions. However, theory predicts that migration limitation, source–sink dynamics, and time-lagged local extinction can cause mismatches between niches and geographic distributions. It is still unclear how relevant these niche–distribution mismatches are for biodiversity dynamics and how they depend on species life-history traits. This is mainly due to a lack of the comprehensive, range-wide demographic data needed to directly infer ecological niches for multiple species. Here we quantify niches from extensive demographic measurements along environmental gradients across the geographic ranges of 26 plant species (Proteaceae; South Africa). We then test whether life history explains variation in species’ niches and niche–distribution mismatches. Niches are generally wider for species with high seed dispersal or persistence abilities. Life-history traits also explain the considerable interspecific variation in niche–distribution mismatches: poorer dispersers are absent from larger parts of their potential geographic ranges, whereas species with higher persistence ability more frequently occupy environments outside their ecological niche. Our study thus identifies major demographic and functional determinants of species’ niches and geographic distributions. It highlights that the inference of ecological niches from geographical distributions is most problematic for poorly dispersed and highly persistent species. We conclude that the direct quantification of ecological niches from demographic responses to environmental variation is a crucial step toward a better predictive understanding of biodiversity dynamics under environmental change.

Alternative jet fuels are being developed for use with existing jet engines, however there are still knowledge gaps concerning how unusual compositions and properties of these fuels will affect combustion performance. Physical and chemical processes leading to problematic engine stability phenomena like flame extinction and lean blow-off (LBO) are still not well-understood for conventional spray flames, but alternative fuels provide additional challenges as they have been observed to have increased variability from expected behaviour at conditions close to LBO. Evaporation is known to be the limiting factor for combustion in spray flames, and experiments have shown both gaseous and spray flames exhibit increased amounts of local extinctions as the equivalence ratio is decreased. The flame structure and transient behaviour of spray flames behave very differently compared to gaseous flames at near-blow-off conditions and during the blowoff transient. Fuel starvation has been proposed in past experiments as a significant reason for why spray flames blow off more quickly and at richer equivalence ratio compared to gaseous flames but has been explored very little in computational studies. The prediction of fuel starvation and LBO phenomena using numerical simulations with detailed chemistry are the primary focus in this work. Large Eddy Simulations (LES) with the Conditional Moment Closure (CMC) turbulence-combustion model are used, as this methodology has shown good results in simulating extinction and blow-off in both gaseous and spray flames in a lab-scale bluff body swirl spray flame configuration. The jet fuels simulated are the Dagaut Jet-A1 surrogate and the U.S. National Jet Fuels Combustion Program (NJFCP) fuels of interest: A2, C1, and C5. A2 is a conventional Jet-A used as a reference fuel, whereas C1 and C5 are synthetic kerosenes with unusual fuel chemistry or liquid property characteristics. These NFJCP fuels are represented using the Hybrid Chemistry “HyChem” lumped pyrolysis detailed kinetic mechanisms. Simulations in non-premixed laminar counterflow flamelet configurations are conducted at pressures of 1 atm and 10 atm for stable scalar dissipation value flamelets up to extinction, and during the extinction transient. Species trends in the three HyChem fuels and the Dagaut Jet-A1 surrogate are compared in detail. In comparison with experimental blow-off trends, only C5 deviates from expected behaviour and is the most robust fuel against extinction via high scalar dissipation rate. This highlights the interplay of both chemical and physical forces contributing to a real fuel’s tendency for LBO. Reignition of an extinguishing laminar flamelet using the HyChem A2 mechanism is also achieved through decrease of the scalar dissipation rate, although after a certain time the flamelet is not recoverable due to lack of chain-branching radical species. A stable condition LES-CMC simulation using the HyChem A2 (Jet-A) chemical mechanism is used as a starting point and reference for lean blow-off simulations. The computational domain is based on the Cambridge bluff body swirl burner, with a structured LES mesh and a coarse structured CMC grid. The simulation is run using an Eulerian-Lagrangian framework for multiphase flow with the Abramzon and Sirignano evaporation model. Overall flame size and shape from the LES are fairly similar to experimental OH* and OH-PLIF with Mie scattering results, however there are significant differences in location of peak heat release rate and further work is required for validation of the simulations against experiments. CH is discussed as a promising experimental marker for local extinction and location of heat release. Three fuel mass flow rates from the experimental blow-off curve for the Jet-A flame are simulated. The three simulations exhibited LBO at air flows between 5–20% greater than experimental bulk air blow-off velocities. Heat release rate decreased by at least 80% in the flame zone around the stoichiometric mixture fraction, however globally the combustor saw an increase in heat release rate due to the presence of unburnt droplets continuing to vaporise downstream. The asymmetric flame structure and duration of the blow-off transient in the simulations align very well with previous experiments with kerosene and other low-volatility fuels. The LBO transient lasted between 10–30 ms. Fuel starvation is suggested to be a driver of spray flame extinction, through decreased temperature and reduced evaporation caused by increased quantities of cold air in the system. Unburnt vaporised fuel remains in regions of temperature below 1200 K, where the fuel is no longer able to pyrolyse completely, resulting in non-flammable local mixtures. The quantity of local extinctions observed in both conditional and unconditional space is lower than expected compared to gaseous flames, and is linked to low values of the conditional scalar dissipation rate. Changing the model used to close the conditional scalar dissipation rate in the CMC equations is suggested as a potential way to improve the LBO results, as the Amplitude Mapping Closure model does not account for the very lean mixtures experienced at LBO conditions., Rolls-Royce plc provided PhD scholarship funding

Summary Invasive species often drive native species to local extinction. A new study shows that removing invasive rats from tropical islands fosters recovery of native seabirds. Rising seabird populations reestablish key cross-ecosystem nutrient subsidies, reconnecting oceanic, island, and coral reef ecosystems.

Anthropogenic activities continue to degrade natural montane ecosystems globally. Bats communities are altered by these changes. We analyzed how bats are affected by human-induced habitat changes by comparing the bat species diversity and functional diversity in undisturbed forest habitats and disturbed forest habitats of the Afromontane biome of Cameroon. We recorded 244 individuals from 13 species in the undisturbed forest, while 233 individuals from 16 species were recorded in the disturbed forest. Bat diversity was higher in disturbed habitats (D = 0.84) than undisturbed habitats (D = 0.67). Jackknife 1 species richness estimator suggests 21.53 species for the disturbed forest and 19.30 in the undisturbed forest. Closed-space forager insectivorous bats made up nearly half of the species in the undisturbed forest, but this dropped to 25% in the disturbed forest, meanwhile, edge-space foragers increased in the disturbed forest. Bat community analyses by ordination revealed a distinct bat community composition between the two forest types, demonstrated as a significant difference in diversity between the two forest types. The distribution of Rousettus aegyptiacus, Myonycteris angolensis, Hipposideros cf. ruber, and Micropteropus pusillus contribute the most to the difference in bat community composition between the two forest types. Edge and open-space species were likely to benefit from additional resources provided by the disturbed area, by expanding their range and distribution. However, this may not compensate for the decline in the population of forest species caused by the loss of pristine forests, thus measures to conserve montane forest remnants should be of utmost significance.

Climate Change is already seen as one of the biggest threats to biodiversity in the 21st century. Not much studies direct attention to its effects on whole communities of threatened hotspots. In the present work, we combine ecological niche modelling (ENM) with a future climate scenario of greenhouse gases emissions to study the future changes in alpha and beta diversity of birds of the Brazilian Cerrado biome, a hotspot of biodiversity with high velocity of climate change and agricultural expansion. In general, we found heterogeneous results for changes in species richness, spatial and temporal taxonomic and functional beta diversity, and mean ecological distinctiveness. Contrary to a previous study on Cerrado mammals, species richness is expected to increase in Northern Cerrado, where homogenization of communities (decreasing spatial turnover) is also expected to occur especially through local invasions. We show that biotic homogenization (which is composed of local extinction of natives and local invasion of exotic species) will occur in two biological groups but through different subprocesses: local extinctions for mammals and local invasions for birds. Distinct conservation management actions should be directed depending on the outcomes of analyzes of alpha and spatial and temporal beta diversity, for example controlling species invasions in Northern Cerrado. Conservation studies should continue evaluating Cerrado in Brazil even under covid pandemic, as environmental situation in the country is not good and incentives for scientific studies are almost nonexistent.

Author(s): Bonuso, Nicole; Zacherl, Danielle C.; Vreeland, Kelly; Ditmar, Jolene | Abstract: We culled abundance record data from the NSF-funded TCN, Eastern Pacific Invertebrate Communities of the Cenozoic (EPICC), including all southern California localities that recorded the presence of oysters from the last 3.6 million years to document how oyster communities change through time. In total, over 120,000 specimens from 78 localities throughout southern California (i.e., Los Angeles, Orange, and San Diego counties) were examined. The data were broken down into four-time bins: late Pliocene, middle Pleistocene, late Pleistocene, and Holocene. Using multivariate statistics, several statistically coherent groups based on occurrences and abundances through time were indentified. Results indicate that the late Pliocene coherent groups possessed a loose, facultative, individualistic community structure that allowed taxa to shift their latitudinal gradients as they tracked shifting environments. The dominant oyster—Dendrostrea vespertina—as well as other taxa, became extinct at the Plio-Pleistocene boundary. Afterwards, community structure changed, as did the dominant oyster. We suspect that the onset of northern hemisphere glaciation at the Plio-Pleistocene boundary changed both the magnitude and rate of sea surface temperatures such that local extinction occurred causing changes in dominance within marine communities. During the middle Pleistocene, Ostrea conchaphila (lurida) appeared and remained dominant throughout the Holocene. In addition, distinct spatial groups existed causing reduced migration along the coast of southern California. Perhaps southern California marine communities responded to the water-mass differences associated with the mid-Pleistocene transition from a mild, 41 ka glacial-interglacial cycle to the more variable ~100 ka glacial-interglacial cycle reducing migration along the coast of southern California. The loose, individualistic community structure seen in the late Pliocene returned during the late Pleistocene and continued through the Holocene allowing marine communities the flexibility to track shifting environments.

Insect populations show strong temporal fluctuations in abundance. This renders classical monitoring studies extremely difficult to provide insights into specific management actions. For rare species of conservation concern, it is not an option to develop large scale experiments to assess and steer landscape-level actions such as grazing management. Bembix rostrata (Linnaeus, 1758) is a threatened digger wasp from coastal dunes and inland sandy regions occurring in a limited number of populations in NW Europe. Since coastal dunes are rapidly being encroached by bushes, grazing management (cattle, sheep, and horses) has been implemented to keep this biotope open. In order to provide insights for local evidence based conservation, a BACI (before/after and control/impact) experiment was set up to assess the impact of sheep grazing on B. rostrata. We quantified the number of nests during 3 years at two grazed sites and a control-site excluded from grazing. We additionally assessed grazing pressure. The BACI design allowed us to directly adjust the current grazing management. The implemented sheep grazing reduced densities of B. rostrata, but did not lead to its local extinction. We discuss these findings in relation to the biology of the species. Our efficient and effective experimental design allowed a fast assessment of the current grazing management and showed that spatially heterogeneous sheep grazing could be used as a management tool to ensure the conservation of the emblematic digger wasp B. rostrata.

Large eddy simulations of turbulent swirl-stabilised flames gradually approaching blow-off conditions in a gas turbine model combustor are undertaken. The global equivalence ratio of the flames is reduced by increasing and decreasing the air and fuel flow rates respectively. The filtered reaction rate for partially premixed combustion is modelled using a presumed joint probability density function flamelet model. The average position of the flame is closer to the fuel nozzle when the global equivalence ratio is decreased, contrary to what is expected. Comparisons are made with simultaneous particle image velocimetry, and acetone and OH planar laser induced fluorescence imaging for the corresponding simulated case. It is demonstrated that the mechanisms leading to local extinction are well captured in the simulation and insufficient mixing induced by the precessing vortex core leads to local extinction. Further analysis of the simulations shows that including heat loss effects within the modelling is important for flames near or approaching blow-off. The non-adiabatic simulation influences the re-stabilisation of the flame after lift-off and shows that the flame leading edge follows the rotation of the PVC. A blow-off correlation based on the Damkohler number is proposed using the PVC rotation frequency and a chemical time scale. Analysis shows that the simulated flames respond to the correlation and including non-adiabatic flamelets is important for flames approaching blow-off.

Dianthus superbus is one of the most endangered species in Latvia and is on the verge of local extinction. Therefore, the aim of this study was to inventory previously identified populations of D. superbus in Latvia and to develop activities to conserve this species in accordance with the results obtained in situ. Expeditions on 18 previously documented locations, according to the data of Nature Conservation Agency, revealed only three existing D. superbus localities in Latvia with a significant number of specimens located in the Latgale region near Silenieki. In 2020, for the first time, two more new D. superbus localities were found in the vicinity of these three approved locations. As it is not possible to create micro-reserves in the existing localities which are mainly located either on roadsides or in a cemetery, additional activities are needed to preserve the D. superbus in Latvia. In vitro culture was initiated from shoot explants obtained in situ, from which, in turn, ex vitro plantings were done in the National Botanic Garden (NBG) and the Botanical Garden of the University of Latvia (BG UL). Their quality and compliance with plants in situ were analysed. Overall, it was concluded that the plants grown ex situ were qualitatively equivalent to those obtained in situ, as a very high percentage of seed viability and germination was found both for in situ and ex situ growing D. superbus. Based on the results obtained we could conclude that D. superbus is a species that is able to adapt to different soils with a wide range of nutrient levels, moisture conditions and pH, as long as there are three main preconditions—adequate lighting, low overgrowth of other plant species and non-destructive human activities., Ex situ conservation of the critically endangered species Dianthus superbus in Latvia outside natural habitats was carried out by introducing and maintaining in vitro collections and field plantings in the botanical gardens. As D. superbus is able to adapt to a wide range of soil conditions in terms of nutrient and organic matter content and soil reaction, the conservation of this species can also be implemented inter situs in urban areas and dendrological parks. There are three main preconditions for the successful growth of D. superbus in Latvia—adequate lighting, low overgrowth of other plant species and non-destructive human activity.

Ecological communities face a high risk of extinction to climate change which can destabilize ecological systems. In the face of accelerating environmental change, understanding the factors and the mechanisms that stabilize the ecological communities is a central focus in ecology. Although dispersal has been widely used as an important stabilizing process, it remains unclear how individual species dispersal affects the stability and persistence of an ecological community. In this study, using a spatially coupled predator-prey community, we address the effects of individual species dispersal and nutrient enrichment on metacommunity stability in constant and varying environments. We show two contrasting effects of dispersal on metacommunity persistence in temporally constant and varying environments. Specifically, predator dispersal in constant environments shows stronger stability through inhomogeneous (asynchronized) states, whereas prey dispersal shows an increasing extinction risk through a homogeneous (synchronized) state. On the contrary, the metacommunity dynamics in temporally varying environments reveal that predator dispersal causes a local extinction through tracking unstable states and also a delayed shift between dynamical states. Moreover, our results emphasize that metacommunity persistence depends on individual species dispersal and environmental variations. Thus, our findings of the individual species dispersal can help to develop conservation measures that are tailored to varying environmental conditions.

Due to local extinction, the endangered green carpenter bee (Xylocopa aerata) has a disjunct distribution in the southeast of Australia. The species relies on dead softwood from a small selection of plant species for making its nests. Habitat fragmentation, combined with deleterious fire events, is thought to have negatively impacted on nesting substrate availability and recolonisation chances. Here, we use MaxEnt algorithm to model both the current distribution and the effect of climate change scenarios on the distribution of both X. aerata and four plant species that provide most of its nesting substrate: Banksia integrifolia, B. marginata, Xanthorrhoea arborea and Xanthorrhoea semiplana subsp. tateana. The annual mean temperature is the strongest climatic predictor of the distribution of X. aerata and its host plants. The modelled distribution of the bee under current climatic conditions indicates that climatic factors are unlikely to cause local extinctions. In all future scenarios, suitable areas for X. aerata and each of its nesting hosts are expected to contract towards the southeast of mainland Australia. The suitability of Kangaroo Island for the bee and its current local current host species is maintained in all scenarios, while Tasmania will become increasingly suitable for all species. The Grampians National Park in western Victoria, where the bee species were last seen outside of its current range (in the 1930s), is predicted to remain suitable for X. aerata and several host plants under all scenarios. Therefore, this relatively large area of native vegetation may be a good case study for re‐introduction as part of future conservation efforts.

Background. In this study a population of the rock dwelling terrestrial gastropod Montenegrina subcristata was monitored over one season and data about life cycle, population density and dispersal were gathered. Three study sites (A, B, C) near Virpazar, Montenegro were selected. Snails were categorized into three size classes. (1) The smallest juveniles were counted but not marked because of their tiny and dainty shell, middle sized snails (2) were marked with a dot and (3) larger subadults and adults were marked with an individual number. The sites were observed 25 times from April to October 2017. The study sites were equipped with data loggers to register microclimate data like temperature and humidity. Based on counts and recapture counts population estimates were calculated. Positions of the snails were recorded throughout the season and minimum distances between each two observations were calculated.Results. Small juveniles (not marked) were observed in high numbers at the beginning of the season and disappeared during summer. Site C had to be excluded from the calculations because snails nearly disappeared as early as the second visit. Population size estimations of sites A and B provided similar results for the beginning of the season, whereas for June the high estimates stood in high contrast to the number of observed snails in that period. Concerning "minimum distances" (MD; distance between two subsequent observations), the majority of MDs with a 1-week interval resulted in 0–0.1m. Yet, some individuals were more mobile, with sums of MDs over the season of up to 8.0 m. The sum of MDs over the season was on average 1.6 m (sites A+B).The temperature and humidity curves of the data loggers showed a seasonal pattern. The average temperatures of all three sites were rather similar. However, daily oscillations in temperature and humidity were high in some periods and differed between sites. In site C temperature and humidity extremes and fluctuations were pronouncedly higher, with the highest temperatures reaching more than 60 °C and relative humidity dropping each day below 3.7% in June.Conclusions. Dispersal ability is in general low but single individuals might cover distances of at least several meters over the season. Together with further observations we conclude that fluctuations of population size can be considerable and might be strongly influenced by climatic conditions. On the other hand, also population estimates may be influenced by climatic conditions. This study provided first hints to assess the potential of migration, local extinction and recolonization in Montenegrina and other rock dwelling snails.

Espécies próximas filogeneticamente usam recursos similares e podem ser potenciais competidores. Porém, para minimizar a competição interespecí­fica, as espécies podem apresentar estratégias de divisão de recursos no espaço (entre habitats diferentes), no tipo de alimento consumido e no tempo (diferenças no perí­odo de atividade). Essas diferenças podem ser determinantes para a coexistência das espécies. Neste trabalho descrevemos a dieta e investigamos a sobreposição de nicho trófico entre duas espécies de peixes de riachos em dois perí­odos hidrológicos da bacia do alto rio Tocantins. Descrevemos a dieta das espécies a partir da análise do conteúdo estomacal e a preferência alimentar foi determinada pelo ndice de Importância Alimentar (IAi) para as duas espécies. Knodus aff. chapadae e Hyphessobrycon heterorhabdus preferem consumir invertebrados terrestres e aquáticos durante os dois perí­odos hidrológicos, embora consumam outros tipos de alimentos de origem vegetal ou animal. As duas espécies possuem uma alta sobreposição de nicho trófico, logo são potenciais competidoras por alimentos. Esses resultados indicam que a coexistência entre esses pequenos carací­deos é mediada por divergência em outras dimensões do nicho e não por diferenças na dieta. Como essas duas espécies possuem uma morfologia semelhante e são filogeneticamente próximas, acredita-se que haja entre elas certa segregação espaço-temporal, permitindo sua coexistência. Ao longo do tempo a coexistência entre essas duas espécies pode ser mantida por divergência na utilização de recursos ou pode haver a extinção local de uma das espécies por exclusão competitiva.