Intensity Of Interspecific Competition Research Articles

Many More Consumers Not Always Induce Stronger Competition: Weaker Interspecific Competition Despite Higher Species Richness in Secondary Feeding Guild, as Compared to Primary

The species functional structuration (specifically in terms of species richness and average intensity of interspecific competition) is widely varying among species communities and this point is now very well documented in literature. But, what about the species functional structuration within the different feeding guilds that coexist in a same local community – in particular the primary and the secondary feeding guilds? Are there significant differences – or not – between them in this respect? This rather fundamental issue does not seem having been addressed yet, at least using appropriate investigative tools. However, a series of recently published case studies, precisely implementing such an adequate investigative approach, now deserves full consideration in this regard and makes the subject of the present review. Substantially, it results from this preliminary survey of the question that marked differences in the patterns of species functional structuration clearly singularize the secondary from the primary feeding guilds, within a same local community. More precisely, a consistent trend seems to arise, highlighting both: (i) a markedly greater species richness and, yet somewhat unexpectedly, (ii) a significantly reduced intensity in interspecific competition within secondary feeding guild as compared to primary. The point is discussed and interpreted as being the consequence of the fact that secondary feeders (typically carnivores) have obviously evolve quite more diversified feeding behaviors than did the primary feeders (typically herbivores).

Analyzing the Role of Increasing Water Pollution on Species-Richness, Interspecific-Competition and Abundance-Unevenness in Reef-Associated Fish Communities, off Jakarta Bay (Indonesia)

Not far from the exceptionally rich ‘Coral Triangle’ on the one hand but, on the other hand, exposed to strongly varying degree of anthropogenic environmental stresses, the reef-associated fish assemblages all along ‘Seribu Islands’ (off Jakarta Bay) are, thus, confronted to both positive and negative ecological influences. As such, these fish assemblages offer especially interesting opportunities to analyze these opposite ecological influences, at both the descriptive and the functional points of views. The least-biased numerical extrapolation of a series of recently reported – yet incomplete – samplings has allowed a sub-exhaustive account of both the estimated total species-richness and the completed distribution of species abundances – including the set of those rarer species which had remained unrecorded. Thanks to this numerically completed information, it became possible to tackle some important issues – which otherwise would have remained difficult to address properly. First, a remarkably good correlation was highlighted between the distance of fish assemblages to Jakarta Bay (distance considered as a reliable surrogate to the improvement of environmental conditions for fish assemblages) and a theoretically derived index characterizing the accommodation capacity of sites for fish assemblages. This good correlation suggests that this index offer a way to reliably accounts for the “environmental quality” of marine waters, as appreciated by fish communities. In quite another respect, comparing primary and secondary-feeding guilds, provides still further empirical support to a seemingly common trend according to which the guild of secondary-feeders features usually more species-rich, while exhibiting less interspecific competition intensity at niche overlaps, than does the primary-feeders guild.

Interspecific-Competition Strongly Constrains Species-Richness and Species-Abundance Evenness in a Tropical Marine Molluscan Community Inhabiting Caulerpa Beds, as Compared to Coral-Reefs

Increasing species-richness at the local scale (within species communities) is accommodated, first, by the diversification of the niches respectively associated to species. Yet, in case of excessive supply in colonizing species issued from the regional pool, the corresponding increase in the number of solicited niches may lead to some “niche-overcrowding” resulting in significant niche-overlaps. Then, second, strong interspecific competition for shared resource can arise, triggered by the density in individuals among those species co-occurring at niche-overlaps. Accordingly, the accommodation of species-richness within a local community involves a balance between (i) the positive contribution of improved niche-diversification and (ii) the negative consequence of induced interspecific-competition at increasing niche-overlaps once the number of colonizing species becomes too large. This balance can strongly differ according to the local ecological conditions, since the latter are expected to strongly influence the range of “overcrowding-free” diversification of niches. So that, concretely, each community requires a specific analysis, in order to disentangle and quantify the respective contributions of the niche-diversification and the intensity of interspecific-competition to this balance. And, in particular, their respective roles upon both the species-richness and the degree of unevenness of species abundance within community. Beyond its speculative interest, this deeper understanding of the process involved in the hierarchic-like organization of species within community also answers more practical concerns, in particular the stability of species-richness, partly dependent on the intensity of interspecific-competition.
 In this perspective, we quantify and compare how species-richness accommodation proceeds in two major taxonomic groups, Bivalves and Gastropods respectively, both belonging to a same molluscan community inhabiting Caulerpa beds, in the intertidal-zone of Siquijor Island (Philippines). Then, after having compared these two different taxonomic groups, the influence of environmental conditions on species-richness accommodation is addressed, showing that “Caulerpa-beds” habitat features far-less rewarding to Gastropods communities than can be the classical “coral-reef” habitat.

Influences of submerged plant collapse on diet composition, breadth, and overlap among four crane species at Poyang Lake, China

BackgroundInterannual variation in resource abundance has become more unpredictable, and food shortages have increasingly occurred in the recent decades. However, compared to seasonal fluctuations in resource abundance, the influences of interannual variation in resource abundance on the dietary niches of consumers remain poorly understood. Poyang Lake, China, is a very important wintering ground for the globally endangered Siberian Crane (Leucogeranus leucogeranus), White-naped Crane (Grus vipio), and Hooded Crane (G. monacha), as well as the non-endangered Eurasian Crane (G. grus). Tubers of Vallisneria spp., the dominant submerged macrophytes at Poyang Lake, is an important food for cranes. Nevertheless, submerged macrophytes have experienced serious degradation recently. In this study, we used metabarcoding technology to explore the consequences of Vallisneria tuber collapse on the diet compositions, breadths, and overlaps of the four crane species based on fecal samples collected in winter 2017 (a year with tuber collapse) and winter 2018 (a year with high tuber abundance).ResultsCompared to previous studies, our study elucidates crane diets in an unprecedented level of detail. Vallisneria tubers was confirmed as an important food source of cranes. Surprisingly, the grassland plant Polygonum criopolitanum was also found to be an important food source in the feces of cranes. Agricultural fields were important foraging sites for Siberian Cranes, White-naped Cranes, and Hooded Cranes, providing foods that allowed them to survive in winters with natural food shortages. However, the three crane species preferred natural wetlands to agricultural fields when the abundance of natural foods was high. The abundance of Vallisneria tubers, and probably P. criopolitanum, greatly influenced the dietary compositions, breadths and overlap of cranes. During periods of preferred resource shortage, White-naped Cranes and Hooded Cranes widened their dietary niches, while Siberian Cranes maintained a stable niche width. The dietary niche overlap among crane species increased substantially under conditions of plentiful preferred food resources.ConclusionsOur study emphasizes the superior quality of natural wetlands compared to agricultural fields as foraging habitats for cranes. To provide safer and better foraging areas for cranes, it is urgent to restore the submerged plants at Poyang Lake. While high dietary niche overlap is often interpreted as intense interspecific competition, our study highlights the importance of taking food abundance into account.

A New, Ecologically Self-Significant Metric of Species-Abundance Unevenness, Reliably Highlighting the Intensity of Interspecific Competition

A wide series of commonly used metrics of abundance-evenness (or -unevenness) have been proposed to characterize synthetically the distributions of species-abundances, accounting for the hierarchic-like organization of species within natural communities. Among them, most – if not all–have been relevantly criticized on their serious limitations regarding both their “descriptive” and their “interpretative” capacities. From the descriptive point of view, many authors have already repeatedly emphasized the formal non-independenceof conventional (un-)evenness metrics with respect to species-richness, leading, in particular, to unacceptable bias when comparing communities differing by their species-richness, thus making these metrics unreliable descriptors in this respect. Now, as regards the capacity to provide relevant ecological interpretations, especially in terms of the intensity of competition among co-occurring species, the weakness of conventional (un-)evenness metrics is readily highlighted by the usual absence of any associated interpretation of this kind in the literature: the conventional (un-)evenness metrics beingrestricted to purely descriptive purpose only.
 Accordingly, a newly designed abundance-unevenness metric – the “standardized abundance-unevenness” index is proposed, positively addressing both kinds of limitations evoked above. By standardizing a conventional measure,U,of abundance-unevenness to the corresponding measure, U’, of the abundance-unevenness in the well-known “broken-stick” model, the resulting “standardized unevenness” index (Istr = U/U’) proves to be efficient against both themajor limitations pointed-out above:indeed,the new index does benefit by being both (i) formally independent from species-richness, thereby allowing reliable,unbiased comparisons of abundance unevenness between species-communities, whatever their difference in species-richness; (ii) able to relevantly quantify the mean intensity of interspecific-competition within community, in term of its direct outcomeuponthe degree of species-abundance unevenness. This double success being, of course, the direct consequences of the properties of the “broken-stick” distribution model, originally putforth in a well-known, yet insufficiently thoroughly exploited paper by the regretted Robert MacArthur.

Effects of mulch and irrigation regimes on water distribution and root competition in an apple–soybean intercropping system in Loess Plateau, China

Water scarcity seriously hinders the sustainable development of the fruit tree–crops intercropping system in the Loess Gully Area of western Shanxi. The combination of mulch measures and appropriate irrigation would help to maintain soil moisture and improve crop yield and water use efficiency (WUE). This study investigated the combined effects of mulch and irrigation on soil water and root distribution, yield, and water use of an apple–soybean intercropping system. A three-year field trial was performed with two factors: two types of mulch, namely straw mulch (M1), and plastic mulch (M2), and three levels of maximum irrigation (55%, 70%, or 85% of field capacity [Fc]), which were designated W1, W2, and W3, respectively. Three groups of non-irrigation controls i.e., CK0 (no mulch), CK1 (straw mulch), and CK2 (plastic mulch) were also included. These results indicated that the soil water contents (SWC) in each treatment initially decreased and then increased with increasing distance from the tree, whereas it increased gradually with depth. The SWCs in various sampling points under straw mulch was generally higher than under plastic mulch. The root length density (RLD) of apple tree decreased with increasing distance from the tree in the horizontal direction, while the opposite trend was observed for soybean. The RLD of both apple tree and soybean in the soil layer (0–60 cm) under plastic mulch was higher than that under straw mulch, and increased with increased irrigation level. The underground interspecific competition intensity index (UICII) of the apple–soybean intercropping system under straw mulch was higher than that under plastic mulch, and increased with the increased irrigation amount. Water consumption, soybean yield, and WUE under plastic mulch were significantly higher than under straw mulch. The results of this study suggested that the combination of plastic mulch and irrigation water supplied at 70–85% Fc could effectively increase the yield and WUE of the apple–soybean intercropping system.

Effects of pollution on individual size of a single species

In this paper, we develop a single species evolutionary model with a continuous phenotypic trait in a pulsed pollution discharge environment and discuss the effects of pollution on the individual size of the species. The invasion fitness function of a monomorphic species is given, which involves the long-term average exponential growth rate of the species. Then the critical function analysis method is used to obtain the evolutionary dynamics of the system, which is related to interspecific competition intensity between mutant species and resident species and the curvature of the trade-off between individual size and the intrinsic growth rate. We conclude that the pollution affects the evolutionary traits and evolutionary dynamics. The worsening of the pollution can lead to rapid stable evolution toward a smaller individual size, while the opposite is more likely to generate evolutionary branching and promote species diversity. The adaptive dynamics of coevolution of dimorphic species is further analyzed when evolutionary branching occurs.

Competition from sea to mountain: Interactions and aggregation in low-diversity monogenean and endohelminth communities in twospot livebearer Pseudoxiphophorus bimaculatus (Teleostei: Poeciliidae) populations in a neotropical river.

The role of interspecific interactions in structuring low‐diversity helminth communities is a controversial topic in parasite ecology research. Most parasitic communities of fish are species‐poor; thus, interspecific interactions are believed to be unimportant in structuring these communities.We explored the factors that might contribute to the richness and coexistence of helminth parasites of a poeciliid fish in a neotropical river.Repeatability of community structure was examined in parasitic communities among 11 populations of twospot livebearer Pseudoxiphophorus bimaculatus in the La Antigua River basin, Veracruz, Mexico. We examined the species saturation of parasitic communities and explored the patterns of species co‐occurrence. We also quantified the associations between parasitic species pairs and analyzed the correlations between helminth species abundance to look for repeated patterns among the study populations.Our results suggest that interspecific competition could occur in species‐poor communities, aggregation plays a role in determining local richness, and intraspecific aggregation allows the coexistence of species by reducing the overall intensity of interspecific competition.

The distinct microbial community in Aurelia coerulea polyps versus medusae and its dynamics after exposure to 60Co-γ radiation

Radiation (e.g., nuclear leakage) is a common harmful factor in the ocean that potentially affects the microbial community in nearby benthic hosts such as jellyfish polyps, which is essential for the maintenance of jellyfish populations and high-quality medusae. After comparison with the microbial community of medusae, the effect of 60Co-γ on the microbial community in Aurelia coerulea polyps was dynamically tested using 16S rRNA gene sequencing. Our results suggested that Proteobacteria (76.19 ± 3.24%), Tenericutes (12.93 ± 3.20%) and Firmicutes (8.33 ± 1.06%) are most abundant in medusae, while Proteobacteria (29.49 ± 2.29%), Firmicutes (46.25 ± 5.59%), and Bacteroidetes (20.16 ± 2.65%) are the top three phyla in polyps. After 60Co-γ radiation, the proportion of Proteobacteria increased from 29.49 ± 2.29% to 59.40 ± 3.09% over 5 days, while that of Firmicutes decreased from 46.25 ± 5.59% to 13.58 ± 3.74%. At the class level, Gammaproteobacteria continually increased during the 5 days after radiation exposure, whereas Bacilli declined, followed by partial recovery, and Alphaproteobacteria and Flavobacteriia remained almost unchanged. Intriguingly, Staphylococcus from Firmicutes and three other genera, Rhodobacter, Vibrio, and Methylophaga, from Proteobacteria greatly overlapped according to their KEGG functions. It is concluded that the microbial community in A. coerulea polyps is distinct from that in the medusae and is greatly affected by 60Co-γ exposure, with a growth (0–3 d) period and a redistribution (3–5 d) period. The dynamic change in the microbial community is probably an important self-defense process in response to external interference that is regulated by the host's physiological characteristics and the intense interspecific competition among symbiotic microbes with similar functions and functional redundancies.

Difference in intra- and inter-specific competition of two endangered plant species (Toona ciliate var. pubescens and Taxus chinensis var. mairei)in the middle subtropical zone of China

Endangered plant species are an important part of global biodiversity. To understand the competition patterns and mechanisms of endangered tree species from plant growth forms in the middle subtropical forest ecosystems, we examined the differences in intra- and inter-specific competitions between Toona ciliate var. pubescens (an intolerant of shade, deciduous species) and Taxus chinensis var. mairei (a tolerant of shade, evergreen species) in the Jiulingshan National Nature Reserve, Jiangxi Province. The results showed that intra-specific competition was dominant in the T. ciliate var. pubescens population, accounting for 66.4% of the total competition intensity. In contrary, the competitive intensity of T. chinensis var. mairei was dominated by the inter-specific competition, which accounted for 68.7% of the total competition intensity. The intra- and inter-specific competition intensity of both species decreased gradually with increasing tree diameter, indicating that competitive pressure was prevalent in small trees. T. ciliate var. pubescens was mainly affected by self-thinning due to intra-specific competition, whereas T. chinensis var. mairei was dominated by alien-thinning due to inter-specific competition. The small individuals of both species could develop into mature stage only after experiencing intense competitive selection during stand regeneration. Considering the substantial difference in the sources of competition pressures, different biodiversity conservation measures should be taken for the two endangered species with contrasting growth forms in the middle subtropical regions.

Spatial aggregation of native with non-native freshwater bivalves and activity depletion under summer heat waves: ‘dangerous liaisons’ in a climate change context

Freshwater mussels are considered sedentary organisms. However, their foot provides the organ of locomotion, which enables an active behaviour. Their behaviour includes righting, horizontal movements and burrowing into the substrate. The objective of this study was to analyse the influence of non-native (Corbicula fluminea) competitors on the pedal activity of native (Unio delphinus) freshwater mussels in a climate change context. The pedal activity was scored and compared among different species compositions, population density and exposure to heat wave progression. The results showed a significant effect of species composition and heat wave progression. In addition, a significant effect of species composition × population density was found. Mussels at low density conditions exposed to dense aggregations of C. fluminea showed lower pedal activity than individuals in intraspecific treatments, or individuals at high density conditions exposed to low densities of C. fluminea. Maximum pedal activity was recorded at the thermal peak. After that, pedal activity was reduced when high temperature was maintained over time. Altogether, present results suggest that lower pedal activity at high C. fluminea densities may expose mussels to more intense interspecific competition. In addition, heat waves may compromise mussels’ ability to locate refuge areas in front of receding waters.

同域分布红腹锦鸡和红腹角雉在不同空间尺度下的生境分化

PDF HTML阅读 XML下载 导出引用 引用提醒 同域分布红腹锦鸡和红腹角雉在不同空间尺度下的生境分化 DOI: 10.5846/stxb201809051894 作者: 作者单位: 西华师范大学,白水河国家级自然保护区,白水河国家级自然保护区,西华师范大学,西华师范大学,西华师范大学,,西华师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31572293）；四川省科技厅应用基础项目（2015JY0249）；西华师范大学博士科研启动项目（17E075）；西华师范大学国家级一般培育项目（18B028） Habitat partitioning between sympatric Golden Pheasant and Temminck's Tragopan at different spatial scales Author: Affiliation: China West Normal University,Baishuihe national nature reserve,Baishuihe national nature reserve,,China West Normal University,China West Normal University,, Fund Project: The National Natural Science Foundation of China 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:生境分化是群落物种缓解种间竞争压力，实现同域稳定共存的重要途径，是群落生态学领域的重要研究内容。同域动物的生境分化是空间尺度依赖的生态过程，从不同空间尺度分层研究物种的生境分化，对于全面了解同域动物的共存模式和机制，以及实现多物种整合保护都具有重要意义。2018年1月至8月，在四川白水河国家级自然保护区对同域分布的红腹锦鸡（Chrysolophus pictus）和红腹角雉（Tragopan temmminckii）进行了野外调查，基于MaxEnt模型和样方法，从宏生境和微生境两个空间尺度对其生境分化进行了研究。结果显示：1）在宏生境尺度，两种雉类的适宜宏生境重叠面积达44.59 km2，分别占红腹锦鸡和红腹角雉适宜宏生境面积的58.73%和44.3%，表明二者在宏生境尺度上没有发生明显的种间分化；2）微生境尺度是两种雉类生境分化的关键尺度，海拔、坡位、最近水源距离和乔木层盖度4个特征上的显著差异，使二者的微生境发生显著的种间分化；3）虽然在不同空间尺度下具有不同的分化程度和方式，但两种雉类在海拔适应性、人为干扰耐受性以及对水源的依赖性上的差异在两个尺度下表现出了一定的一致性。此外，基于二者生境需求的异同，提出了控制人为干扰、加强宣传教育、维持自然植被多样性和镶嵌格局等针对该区域雉类物种共同保护的建议。 Abstract:Habitat partitioning is an important approach by sympatric species to reduce interspecific competition intensity and achieve stable coexistence, and thus, has been of interest to community ecologists for many decades. Habitat partitioning between sympatric species is a spatial scale dependent ecological process. Studying interspecific habitat partitioning at different spatial scales is of great significance for understanding the coexistence mechanism comprehensively and improving multi-species joint conservation efforts. From January to August 2018, we conducted field surveys of Golden Pheasant (Chrysolophus pictus) and Temminck's Tragopan (Tragopan temmminckii) in Baishuihe National Nature Reserve, in Sichuan Province. Using MaxEnt modelling and quadrat sampling methods, we studied habitat partitioning between the two Phasianidae species at two spatial scales-macrohabitat and microhabitat. The results showed that:(1) At the macrohabitat scale, the overlap area of suitable macrohabitat is 44.59 km2, accounting for 58.73% and 44.3% of the macrohabitat area of Golden Pheasant and Temminck's Tragopan, respectively. This spatial distribution pattern indicated that there was no distinct interspecific partitioning between the two species' macrohabitats; (2) Microhabitat is a key scale for habitat partitioning between the two species. Four microhabitat characteristics, including altitude, slope position, distance to the nearest water resource, and tree coverage, varied significantly between species, leading to significant interspecific partitioning of microhabitats; (3) Although the two species showed different degrees and patterns of habitat partitioning at different spatial scales, they maintained consistency in altitude adaptability, tolerance to human disturbance, and dependence on water resources, across the scales. In addition, for multi-Phasianidae-species joint conservation efforts in this area, we made suggestions based on the similarities and differences in habitat requirements of Golden Pheasant and Temminck's Tragopan, such as controlling human disturbance, strengthening awareness and education, and maintaining natural vegetation diversity and their mosaic pattern. 参考文献 相似文献 引证文献

Relationship between Degree of Dominance and Species Richness in Grass Communities with Different Productivities

The aim of this study is to test the assumption that the relationship between the degree of dominance and local species richness may be different in grass communities with different productivities. Alpine, subalpine, and low-mountain grasslands, as well as subalpine mires, alpine communities of low-snow habitats and those with long-term snow cover, steppe communities, and the grass layer of low-mountain forest communities of the Western Caucasus and Ciscaucasia, are used as objects of research. The data on the phytomass of 419 plots with an area of 0.25 m2 are studied. The results show that, the higher the mean productivity of communities is, the closer the relationship between the degree of dominance and species richness is, and the closest relationship is observed in meadow communities. Possible causes of these relationships are considered. It is reasonably suggested that this may be due to the features of the organization of plant communities with high and low productivity (in particular, high or low intensity of interspecific competition).

Specific parasites indirectly influence niche occupation of non-hosts community members.

The coexistence of phylogenetically related species is an attractive topic because of the potentially intense interspecific competition. The most often investigated mechanisms mediating coexistence of these species are environmental filtering and niche partitioning. However, the role of other factors, such as species-specific parasites, is still poorly understood. Along the riparian understory of a tropical forest, we explored niche occupation and coexistence between Chrysso intervales and Helvibis longicauda, two related syntopic web-building spiders. We also investigated the effect of H. longicauda mortality induced by a specific fungus parasite, Gibellula pulchra, on the dynamic of C. intervales spatial distribution. Coexistence was mediated mainly by a fine-scale horizontal spatial segregation. H. longicauda built webs almost exclusively close to the river, while C. intervales occupied adjacent areas (10-20m away from margins). We also found differentiation in other niche dimensions that might allow coexistence, such as in plants occupied, height of web placement, width of leaves used for thread attachment and phenology. H. longicauda mortality caused by fungi was higher during winter than in summer. Consequently, the abundance of C. intervales increased at distances close to the river, indicating competitive release through a density-mediated indirect effect. This demonstrates how non-competitive specific-antagonists can indirectly affect other non-hosts competing community members and influence their spatial distribution in fine-scale ranges. We suggest that environmental filtering restricts H. longicauda to cooler regions; niche partitioning leads populations to occupy different vertical strata and competitive exclusion precludes C. intervales to reach river margins, generating an unusual horizontal zonation pattern.

Pollen Availability and Behavior of Visiting Bees of Solanum lycocarpum A. St. Hill (Solanaceae)

This study aimed to assess the pollen availability and foraging behavior of visiting bees to identify the effective pollinators of Solanum lycocarpum at a forest fragment. Five flowers of each of two floral morphs were used to determine pollen viability using optical microscopy. Bees were collected during the first 15 minutes of every hour of collection and classified into large, medium and small. Behavioral observations were performed during the remaining 45 minutes. Both floral morphs presented high percentage of viable pollen, without much difference between them. A total of 322 bees from 12 species were collected. Visits were more frequent when the anthers were maintained. Epi charis flava, Centris scopipes and Oxaea flavescens, along with Centris analis had large body size and, due to the behavior presented, were considered effective pollinators of S. lycocarpum. The intense intraspecific and interspecific competition observed among visiting bees may be advantageous for S. lycocarpum reproduction.

Transcriptome response of Atlantic salmon (Salmo salar) to competition with ecologically similar non-native species.

Non‐native species may be introduced either intentionally or unintentionally, and their impact can range from benign to highly disruptive. Non‐native salmonids were introduced into Lake Ontario, Canada, to provide recreational fishing opportunities; however, the establishment of those species has been proposed as a significant barrier to the reintroduction of native Atlantic salmon (Salmo salar) due to intense interspecific competition. In this study, we compared population differences of Atlantic salmon in transcriptome response to interspecific competition. We reared Atlantic salmon from two populations (LaHave River and Sebago Lake) with fish of each of three non‐native salmonids (Chinook salmon Oncorhynchus tshawytscha, rainbow trout O. mykiss, and brown trout S. trutta) in artificial streams. We used RNA‐seq to assess transcriptome differences between the Atlantic salmon populations and the responses of these populations to the interspecific competition treatments after 10 months of competition in the stream tanks. We found that population differences in gene expression were generally greater than the effects of interspecific competition. Interestingly, we found that the two Atlantic salmon populations exhibited similar responses to interspecific competition based on functional gene ontologies, but the specific genes within those ontologies were different. Our transcriptome analyses suggest that the most stressful competitor (as measured by the highest number of differentially expressed genes) differs between the two study populations. Our transcriptome characterization highlights the importance of source population selection for conservation applications, as organisms with different evolutionary histories can possess different transcriptional responses to the same biotic stressors. The results also indicate that generalized predictions of the response of native species to interactions with introduced species may not be appropriate without incorporating potential population‐specific response to introduced species.

Analysis of tree interactions in a mixed Mediterranean pine stand using competition indices

Studying species interactions in mixed forests allows us to assess their potential benefits and adapt current silvicultural tools developed in monospecific stands to multi-specific stands. We analyzed tree interactions in a Pinus halepensis Mill. and Pinus pinea L. mixed plantation using individual tree neighborhood models and competition indices that accounted for symmetric and asymmetric competition, to analyze whether the growth of each species was better explained by symmetric or asymmetric competition. We also split the competition indices into their intra- and interspecific forms, to test for competition effects on growth change based on competitor identity. Finally, we analyzed whether P. halepensis and P. pinea trees had different growth responses to competition. When calculating competition indices, we explored how spatial information and size of competitor trees contributed to the quantification of the process. Competition measurements were optimized to more precisely describe interactions. Results showed that the inclusion of competition indices generated important improvements in growth models. The main mode of competition was symmetric, which could be related to water restrictions typical of the Mediterranean climate. Considering competitor identity did not improve the growth models, while measurement without discriminating competitors by species generated more parsimonious models. P. halepensis and P. pinea trees had similar growth responses to competition, indicating that the two species cope with competition in similar ways. However, P. pinea showed lower average growth than P. halepensis in the period analyzed. Results suggest that preventing the onset of intense interspecific competition processes could help slow down the long-term replacement of P. pinea by P. halepensis and could have benefits for silvicultural management in systems with two species that share ecological niches but are capable of generating different goods and services.

Interspecific correlation between exotic and native plants under artificial wetland forests on the Dianchi lakeside, south-west China

The core issue of community ecology and biodiversity is the coexistence of species in a real community, but few studies have considered species coexistence in artificial wetland forests. The present study focused on interspecific correlations of exotic and native species in 8-year-old artificial wetland forests. Four large plots (each 1500m2) were established to record the species and abundance of all plants; 160 quadrats (1×1m) were set to record the number, height and coverage of each plant species. In the large plots, 78 species (6 trees, 11 shrubs and 61 herbs) were recorded. The interspecific relationships of major species (frequency >3%) from quadrats were analysed using the Chi-Square test and Spearman rank correlation coefficient index. Of 253 species pairs, 49 and 45 were significant (P<0.05), with positive and negative correlations respectively, showing intense interspecific competition. Ward’s method of hierarchical clustering was used to divide the major species from quadrats into three and five ecological species groups at a rescaled distance cluster combine of 20 and 10 respectively. Dominant invasive species (Solidago canadensis, Ageratina adenophora and Bidens pilosa) formed monodominant patches; however, species of different sizes and ecological demands, whether exotic or native, could coexist. These findings imply that exotic species can coexist with native species and become a common species composition when they have existed for a sufficient period time in artificial wetland forests.

High competition between ant species at intermediate temperatures

Living organisms have been moving rapidly toward their favorable thermal regions as climate warms. Their competitive interactions will change significantly as a result of changes in distribution, abundance, and species composition. This study examines the relationship of competition intensity (frequency of competitive interactions) with temperature and the influence of competition on the occurrence of ant species. Competition between ants was surveyed at six different temperature sites using baits and the abundance of ants was surveyed using pitfall traps. The intensity of interspecific competition (abundance-corrected bait species displacement) was high at intermediate temperature sites (unimodal). Ant species are hierarchically organized in behavioral dominance. Two low-temperature ant species had decreased in the rank of behavioral dominance at warmer temperature sites because of the abundance of dominant intermediate temperature ant species. Ant species co-occurred randomly at the local scale. However, they were segregated at regional scale because of environmental filtering (temperature). Ant competition did not influence the occurrence of ant species at local or regional scale. These results suggest that the influence of changes in interspecific competition because of climate warming might not be great for ants in temperate regions.

Anthropogenic disturbance induces opposing population trends in spotted hyenas and African lions

Large carnivore populations are declining worldwide due to direct and indirect conflicts with humans. Protected areas are critical for conserving large carnivores, but increasing human-wildlife conflict, tourism, and human population growth near these sanctuaries may have negative effects on the carnivores within sanctuary borders. Our goals were to investigate how anthropogenic disturbance along the edge of the Masai Mara National Reserve, Kenya, influences the demography and space-use of two large carnivore species that engage in intense interspecific competition. Here we document, in one disturbed region of the Reserve, a rapid increase in the population size of one large predator, the spotted hyena (Crocuta crocuta), but a striking concurrent decline in numbers of another, the African lion (Panthera leo). Anthropogenic disturbances negatively affected lion populations, and decreasing lion numbers appear to have a positive effect on hyena populations, indicated here by an increase in juvenile survivorship. We also saw an increase in the number of livestock consumed by hyenas. Our results suggest human population growth and indirect effects of human activity along Reserve boundaries may be effecting a trophic cascade inside the Reserve itself. These results indicate both top-down and bottom-up processes are causing a shift in the carnivore community, and a major disruption of guild structure, inside the boundaries of one of the most spectacular protected areas in Africa.