Interspecific Resource Competition Research Articles

Stable isotope ratios indicate trophic niche overlap in three sympatric delphinid species in the Eastern Ionian Sea

AbstractStudying the sympatric ecology of closely related marine top predator species is of interest both from an ecological and conservation standpoint, because it provides insights into ecosystem functioning, how such species avoid competitive exclusion, and how human stressors may impact these patterns. In this study, we examine the isotopic niche of three sympatric dolphin species that inhabit the eastern Ionian Sea: the common dolphin (Delphinus delphis), the striped dolphin (Stenella coeruleoalba), and the common bottlenose dolphin (Tursiops truncatus). We used carbon, nitrogen, and sulfur isotope ratios to construct three‐dimensional isotope niches and calculate niche sizes and their overlaps among the three species to study interspecific competition for resources. Common dolphin niche overlapped with that of the striped dolphin by 77%, suggesting potential resource competition between these two species. The niche overlap between striped/common dolphins and bottlenose dolphins was much lower (47%). Large differences in isotopic ratios were found between the bottlenose dolphins of the Ionian Sea and those of a largely isolated population in the adjacent semienclosed Gulf of Ambracia, further corroborating the previously documented isolation between the two populations.

Reintroduction to the edge of its range: quenda (Isoodon fusciventer) to Wadderin Sanctuary in the eastern wheatbelt of Western Australia

Context Quenda (bandicoots, Isoodon fusciventer) have shown a major decline in range since European settlement, contracting to the more mesic coastal and forest zones in south-west Western Australia. Key actions to recover this species include broad-scale fox control, cat control and reintroductions. Most reintroductions have been to coastal and forest habitats. Aims To monitor the reintroduction of quenda to fox-free habitat of Wadderin Sanctuary in the wheatbelt of Western Australia, close to the eastern and drier margin of the species’ former range. Methods Relative abundance of the population was monitored over a 12-year period by regular standardised trapping throughout the sanctuary. Key results Quenda were reintroduced in 2010 and have persisted for >12 years. They were protected from fox predation by an exclusion fence, but were subject to a low level of cat predation for the first 8 years. Quenda showed both a ~20% drop in mean body condition over time and a trend of decreasing number of pouch young per female over time, likely a result of a succession of dry years and intra-and inter-specific competition for food resources. However, despite this, the index of abundance suggests that quenda numbers substantially increased, aided by high annual recruitment, in years following removal of the feral cat. Conclusions Quenda appear resilient at this site despite consecutive years of very low rainfall and apparent competition for food resources. Implications Quenda seem able to persist on the drier margin of their former range when protected from high levels of predation.

Invasive vegetation encroachment modulates dual threats faced by island-endemic scaly crickets

The mechanisms by which non-native species impact island-endemic populations are varied and often convoluted. For effective invertebrate conservation where capacity is limited, it is vital to understand both direct and indirect species interactions. Those interactions define specific threats and therefore highlight possible solutions. We quantified several of the non-native species threats faced by an endemic scaly cricket, Discophallus ascension (family: Mogoplistidae), found on Ascension Island’s naturally barren coastlines. We hypothesized that encroaching non-native Mexican thorn Prosopis juliflora (1) directly reduced microclimate suitability, (2) indirectly increased resource competition with non-native species, and (3) indirectly increased non-native predation. Our aim was to assess how rapidly spreading Mexican thorn might reduce endemic cricket populations. Lab trials first confirmed the temperature and diet preferences of D. ascension. Mexican thorn significantly increased ground-level temperature but not above the estimated optimum for D. ascension within key habitat. Observed interspecific resource competition was significantly greater in habitat degraded by Mexican thorn and was driven by non-native ants, house crickets Gryllodes sigillatus and cockroaches Periplaneta americana. Recorded cricket predation was almost entirely by non-native rats Rattus rattus in barren habitat but primarily by ants in Mexican thorn habitat. Threats to D. ascension were therefore modulated by invasive vegetation, but driven by non-native insects and rats at all sites. We conclude that removal of vegetation alone is likely to reduce resource competition but not predation. Managing multiple invasive species is likely necessary for successful species conservation.

Plant spatial configurations and their influences on phenological traits of cereal and legume crops under maize‐based intercropping systems

AbstractIntroductionIntercropping systems have a great potential for crop diversification thus increasing smallholder systems' resilience to climate change while improving soil health. However, optimal benefits associated with intercropping systems are rarely realised because of the interspecific competition for growth resources among the intercropped species.MethodologySix trials were established in the high and low rainfall agroecological zones of Babati district in Tanzania to assess how promising cropping systems with different plant spatial configurations would influence the phenological development of intercropped maize, bean and pigeonpea. Cropping systems under study included a sole maize system rotated with a pigeonpea‐bean intercrop dubbed Doubled‐up legume (DUL), maize‐pigeonpea system both with and without de‐topping, an innovation comprising double maize rows alternated with pigeonpea and beans (Mbili‐Mbili), maize‐pigeonpea system with two maize seeds sown within a 50 cm intra‐row space, a vertical‐architecture Meru H513‐pigeonpea system and a farmer practice.ResultsBranch formation was significantly higher in DUL than in maize‐based systems (p ≤ 0.05). Seasonal weather had upto 30% influence on pigeonpea flowering, with DUL having highest (p ≤ 0.05) flower production. The rate of pigeonpea branch and flower production in Mbili‐Mbili was stable across seasons relative to other maize‐pigeonpea systems. Doubled‐up legume and farmer practice had pigeonpea litter yield of between 1 and 2 t ha−1 which was at least 0.5 t ha−1 higher than in maize‐based systems (p ≤ 0.05). During the period preceding early maize reproductive stages, Mbili‐Mbili increased light interception by 30% and 63% compared to maize‐based systems and DUL, respectively. Maize toppings had higher (94%) P content than stover biomass that remained until harvest.ConclusionOverall, maize‐legume systems had higher intercropping efficacy than sole maize system, both in interception use efficiency, soil mulch cover, among other soil health benefits. Mbili‐Mbili and DUL also had increased phenological benefits on intercropped legumes however, the latter was prone to seasonal weather variability.

Available nitrogen and enzyme activity in rhizosphere soil dominate the changes in fine-root nutrient foraging strategies during plantation development

The variation in fine-root traits in response to soil resources (i.e., fine-root nutrient foraging strategy) is critical for plants to adapt to environmental changes and even win in intra- or interspecific resource competition. However, the patterns and driving mechanisms that change in fine-root traits and nutrient foraging strategies during the development of plantations remain unclear. We analyzed the relationships among fine-root traits, rhizosphere soil nutrient variables, and enzyme activities at four stages of Pinus massoniana plantations: 18 years (young), 30 years (middle-aged), 43 years (mature), and 63 years (overmature). We found that specific root area (SRA) and specific root length (SRL), which represent the speed of nutrient acquisition, decreased with stand development. Root tissue density (RTD) and specific root tip number (SRT), which represent the cost of nutrient foraging, decreased with stand development after peaking in the mature and middle-aged forests, respectively. Compared with young stands, fine-root organic carbon and total phosphorus contents decreased by 23 % in the overmature forest, but total nitrogen increased by nearly 50 %. Principal component analysis (PCA) showed that those fine-root traits significantly varied from young to overmature stands on PC1, and such a shift was consistent with changes in the growth period from fast (in the young forest) to slow (in the overmature forest) for P. massoniana. We suggest that those changes in fine-root traits along the PC1 represents a change in the fine-root foraging strategy of P. massoniana. This strategy (i.e., PC1) was negatively correlated with rhizosphere soil total nutrients (i.e., soil organic carbon and total nitrogen) and carbon (C)-nitrogen (N)-phosphorus (P) stoichiometry but positively correlated with available carbon, nitrogen, and C and N cycling-related enzyme activities. Specifically, the variation in rhizosphere soil NH4+ had the highest amount of explication (72 %) for the variation in the root nutrient foraging strategy. These results demonstrate that the intensity of the fine-root response to soil resources is related to the structure of rhizosphere soil available nutrients (especially soil available nitrogen) as well as carbon and nitrogen conversion enzyme activities during plantation development. Such relationships can reshape fine-root traits and change the fine-root nutrient foraging strategies during the development of plantations.

Patterns of avian tree usage in the primeval temperate forests of Białowieża National Park.

Species distribution and resource utilization are a fundamental aspect of ecology. By analyzing the tree space usage by birds and determining the species composition of birds across different parts of trees, our study could shed light on the mechanisms shaping co-occurrence patterns in bird communities. Therefore, our study aimed to determine the species composition of birds across different parts of trees. We investigated whether species richness differs between positions on a tree and how these positions influence the probability of occurrence of the 10 most frequently observed bird species. To achieve this, we observed birds within permanent plots in Białowieża National Park (BNP) and analyzed the distribution patterns of birds within six vertical and three horizontal sectors of trees. The compositional dissimilarity between tree sectors was assessed using detrended correspondence analysis. We employed generalized linear mixed-effects models to examine differences in species richness. The majority of the BNP bird community was associated with the branches, while other birds occupied the tree crown trunks and the understory trunks. Species richness was the highest on branches in the crown part of trees, followed by lower species richness on trunks associated with crowns, and the lowest richness was observed on branches and trunks in the understory. These results indicate that branches in the middle and lower parts of the crown serve as avian diversity hotspots on trees, likely due to the abundance of various food sources. The differing patterns of tree usage by specific bird species may suggest the avoidance of interspecific competition for resources. The study results of tree usage by bird species obtained in the primeval forest provides a reference point for studies conducted in human-altered woods.

Detailed analysis of prey taxonomic composition indicates feeding habitat partitioning amongst co-occurring invasive gobies and native European perch

One of the negative impacts of non-native invasive species on trophic interactions in an invaded ecosystem occurs via increased interspecific competition for food resources between the invader and local species of the same food niche. In freshwaters, there are usually several fish species that feed on similar food resources. Ponto-Caspian gobies are amongst the most successful and widespread invaders colonising European waterways. They have a wide food niche and an opportunistic feeding strategy, with a focus on benthic invertebrates and piscivory occurring occasionally mainly in the case of large individuals. Competition with native percids for food resources is predicted on the basis of high dietary overlap. However, studies published so far provide no unequivocal answer. In order to resolve this question, we conducted a comparative taxonomic analysis of gut content, with an emphasis on chironomids and amphipods, of the invasive monkey goby (Neogobius fluviatilis), racer goby (Babka gymnotrachelus) and the native Eurasian perch (Perca fluviatilis) occurring sympatrically in a large lowland European river, the Bug River in Poland. We found that each species forages in slightly different habitats, as indicated by the different composition of prey species in the gut content. This suggests feeding niche partitioning between the studied species facilitating their co-existence and reduction or avoidance of competition for food resources. Resource partitioning regarding prey types and foraging habitats is a mechanism for permitting the co-existence of closely-related alien gobies with similar food preferences in the invaded waters and co-occurrence with local species. This mechanism can contribute to their invasion success, as observed in European waters during the recent decades. We also demonstrate that precise prey identification to the lowest possible taxon is crucial to reveal the dietary overlap between co-occurring fish species and to predict the impact of alien invaders on native species through interspecific competition, as well as to recommend such an approach in studies upon fish foraging strategies.

Effect of Legume-Legume Replacement Series of Intercropping System on Growth, Yield and Quality of Chickpea

Chickpea is major pulse crop cultivated in India. Area under chickpea cultivation has been increasing day by day. Although area of chickpea is increasing still the productivity per unit area is not increasing. There are many factor responsible for lack of productivity including crop failure. Therefore, increasing productivity and for avoiding the risk associated with complete crop failure, intercropping is the way forward. Intercropping of legume in association with non-legumes helps in utilization of nitrogen being fixed by legumes in the current growing season, but also helps in residual build-up of nutrients in soil. Best utilization of nutrients, moisture, space and solar energy can be derived through intercropping system. Intercropping provides an insurance against calamities and helps in the maximization of productivity and profit by efficient utilization of natural resources. Hence, crop intensification is both in space and time dimensions. Selection of compatible genotype and appropriate planting pattern helps in minimizing the inter-specific and intra-specific competition for resources thereby boosting up the productivity of the system as a whole. Therefore, a field experiment was conducted at College Agronomy Farm, B. A. College of Agriculture, Anand Agricultural University, Anand, Gujarat during two consecutive rabi season of the year 2019-20 and 2020-21. The experiment was laid out in Randomized Block Design (RBD), consisting of nine treatment. viz.; T1: sole chickpea, T2: sole linseed, T3: sole fenugreek, T4: (chickpea + linseed 2:1), T5: (chickpea + linseed 3:1), T6: (chickpea + linseed 4:2), T7: (chickpea + fenugreek 2:1), T8: (chickpea + fenugreek 3:1) and T9: (chickpea + fenugreek 4:2) with four replication. Legume intercropping resulted in better growth due to complimentary actions of the both the crop. The total equivalent yield obtained from intercropping far surpasses the yield of the sole crop in unit area.

Intra- and inter-specific territorial response of diurnal raptors in the tropical dry forest of western Mexico

Little is known of intra- and inter-specific territoriality in Neotropical raptors that may defend territories throughout the year, and face greater inter-specific competition for resources. We evaluated intra- and inter-specific territorial responses of four species of Neotropical raptors in the tropical dry forest of the Chamela-Cuixmala Biosphere Reserve, Mexico. We conducted broadcast calls in territories of the Collared Forest-Falcon (Micrastur semitorquatus), Crane Hawk (Geranospiza caerulescens), Gray Hawk (Buteo plagiatus), and Roadside Hawk (Rupornis magnirostris), and measured the latency, duration, and type of territorial response to broadcast calls of conspecifics and sympatric raptor species. We applied repeated measures analysis to determine differences in intra- and inter-specific territorial responses of raptors, and GLMMs to evaluate whether traits of body size, nest type, and hunting technique were associated with territorial response by focal raptors. Large-bodied focal raptor species showed high intra-specific territoriality, giving faster, prolonged responses of various types, including duets and combined responses, to broadcast calls of conspecifics compared to sympatric species. All focal raptors showed some inter-specific territorial response, but this was mainly as vocalizations or displacements towards sympatric species broadcast calls. Species traits of body size, nest type, and hunting technique were associated with latency and duration of territorial response by the larger raptor species that nest in the forest canopy. These traits may be more strongly associated with territorial response of forest raptors that defend limited resources in a structurally complex environment.

Isotopic niche overlap among foraging marine turtle species in the Gulf of Mexico.

Sympatric species may overlap in their use of habitat and dietary resources, which can increase competition. Comparing the ecological niches and quantifying the degree of niche overlap among these species can provide insights into the extent of resource overlap. This information can be used to guide multispecies management approaches tailored to protect priority habitats that offer the most resources for multiple species. Stable isotope analysis is a valuable tool used to investigate spatial and trophic niches, though few studies have employed this method for comparisons among sympatric marine turtle species. For this study, stable carbon, nitrogen, and sulfur isotope values from epidermis tissue were used to quantify isotopic overlap and compare isotopic niche size in loggerhead (Caretta caretta), green (Chelonia mydas), and Kemp's ridley (Lepidochelys kempii) turtles sampled from a shared foraging area located offshore of Crystal River, Florida, USA. Overall, the results revealed high degrees of isotopic overlap (>68%) among species, particularly between loggerhead and Kemp's ridley turtles (85 to 91%), which indicates there may be interspecific competition for resources. Samples from green turtles had the widest range of isotopic values, indicating they exhibit higher variability in diet and habitat type. Samples from loggerhead turtles had the most enriched mean δ34S, suggesting they may forage in slightly different micro-environments compared with the other species. Finally, samples from Kemp's ridley turtles exhibited the smallest niche size, which is indicative of a narrower use of resources. This is one of the first studies to investigate resource use in a multispecies foraging aggregation of marine turtles using three isotopic tracers. These findings provide a foundation for future research into the foraging ecology of sympatric marine turtle species and can be used to inform effective multispecies management efforts.

Population demography of the Blackbuck Antilope cervicapra (Cetartiodactyla: Bovidae) at Point Calimere Wildlife Sanctuary, India

Demographic research utilizing vital rates and life tables is a standard aspect of planning protection and management strategies for wildlife populations. The Blackbuck Antilope cervicapra population at Point Calimere Wildlife Sanctuary, Tamil Nadu, has undergone fluctuations in recent decades. The cause remains elusive, and conservation efforts may be hampered by a lack of population data. This study aimed to estimate demographic parameters using population count and age-sex classification data collected for the years 2017─2020. The overall mean population estimate derived from line-transect distance sampling was 719, with annual estimates of 716, 727, 711, and 722 for the years 2017–2020 respectively. In total, 64% of Blackbucks counted were adults, 19% subadults, and 17% fawns. Mortality was highest for adult and subadult classes for the composite female class, and fawn mortality was 20%. The net reproductive rate (R0) was as low as 3.28 offspring per generation contrasted with a rather longer mean generation time (G) as 4.75 years. Thus, the study observes a decrease in Blackbuck numbers postulated in earlier research to be driven principally by a conglomerate of factors, including reduction of usable space and interspecific resource competition. Our findings provide a baseline demography of the species and highlights the value of long-term demographic monitoring of age sex classes to understand the evolution of life histories.

Leaf senescence, nitrogen remobilization, and productivity of maize in two semiarid intercropping systems

It is unclear how interspecific resource competition affects crop leaf senescence in association with nitrogen (N) remobilization and overyielding in semiarid intercropping systems. To address this issue, maize intercropped with soybean (weakly competitive species) and wheat (strongly competitive species) was examined across three consecutive years to explore the effects of resource competition on maize relative and absolute yield gain, leaf senescence traits, N remobilization and physiological activities in a typical semiarid site. High yield (171.8 g plant−1), relative yield (0.63) and net effect (0.99 t ha−1) of maize were observed in the maizesoybean intercropping system, while the opposite trend was found in the maizewheat intercropping systems. Overall, maize benefited from intercropping with soybean but was negatively affected by intercropping with wheat. Interestingly, both intercropping systems significantly delayed the onset time of maize leaf senescence by approximately 5–20 days and prolonged the senescence duration by approximately 8–18 days. Intercropping with soybean increased maize leaf dry matter remobilization from 7.3 to 12.5 g per plant−1 and reduced N remobilization from 0.81 to 0.45 g plant−1, respectively. However, when intercropped with wheat, dry matter and N remobilization of maize leaves were decreased, at 4.8 and 0.13 g plant−1, respectively. Therefore, excessive delay and prolonged leaf senescence reduced leaf dry matter translocation and N to the grain which impaired yield formation. Our findings provided novel insights into the physiological mechanism of overyielding from the perspective of leaf senescence traits and remobilization function in the semiarid intercropping systems.

Development of a sensitivity analysis framework for aquatic biogeochemical models using machine learning

Our evolving understanding of ecosystem functioning along with the advent of computational power have paved the way for the development of complex mathematical models that explicitly represent the functional diversity of biotic communities and multiple biogeochemical cycles. The ever-growing demand for more complex models underscores the importance of robust sensitivity analysis (SA) to elucidate the impact of the uncertainty on model inputs and to untangle the parameter covariance patterns that ultimately lead to the emergence of equifinality problems. In this study, we propose a novel multi-pronged SA framework that integrates advanced statistical and machine learning (ML) techniques. Principal component analysis (PCA) is first applied to dissect the wide array of predictive outputs and identify modes of variability in time and/or space. Classification and Regression Tree (CART) analysis is then used to identify a set of splitting decisions connecting threshold values of key state variables and model parameters with different ranges of predictive outputs with management interest. Self-Organizing Maps (SOM) are implemented as a final step to unravel any non-linear associations between model parameters and responses. As a proof-of-concept, we used a complex aquatic biogeochemical model developed for the Bay of Quinte, a eutrophic embayment in Lake Ontario, to examine competition patterns and structural shifts among multiple functional phytoplankton (diatoms, N-fixing cyanobacteria, and Microcystis) and zooplankton (herbivores and omnivores) groups. Our sensitivity analysis framework showed that the parameters representing the dependence of growth and metabolic processes on temperature are particularly influential to recreate plankton community dynamics during the cold period of the year, whereas the interplay among the interspecific resource competition, strength of the prey-predator interactions, and phosphorus availability mainly regulate their dynamics during the growing season. The growth strategies of diatoms, their nutritional quality that determines the assimilation efficiency by zooplankton, along with the ambient nutrient availability determine our capacity to reproduce patterns of cyanobacteria dominance and faithfully depict the severity of harmful algal blooms. Finally, our study discusses the benefits of a broader use of the ML-based SA framework to unravel influential parametric interactions in modulating the behaviors of complex mathematical models.

Habitat Usage, Dietary Niche Overlap, and Potential Partitioning between the Endangered Spotted Turtle (Clemmys guttata) and Other Turtle Species

Habitat loss and degradation affect populations in isolation while also modifying the intensity of interspecific interactions, which may be especially relevant for species of conservation concern coexisting with more common species. We explored habitat preferences and potential interspecific resource competition in the endangered Spotted Turtle (Clemmys guttata). For habitat data, water quality measurements were recorded once per trapping session, while canopy cover and vegetation data were recorded once per field season. We also investigated niche overlap in habitat and food resources between C. guttata and other, more common, turtle species. Our data indicated that the abundance of C. guttata was negatively correlated with dissolved O2 and pH levels and positively correlated with body of water depth and canopy cover. The investigation of niche overlap revealed that Mud Turtles (Kinosternon subrubrum) and Painted Turtles (Chrysemys picta), but not Snapping Turtles (Chelydra serpentina), were negatively correlated with the abundance of C. guttata despite differences in characteristics of bodies of water used by each species. We used structural equation modeling to better understand if the relationships between C. guttata and other turtles were due to direct interactions or simply reflected environmental influences. We then used stable isotope analyses to compare similarities in δ13C and δ15N isotopes as proxies for diet overlap between C. guttata and other turtles and ultimately found that all species had similar, broad diets. The inverse relationship between abundance of C. guttata and other species, paired with the overlap in dietary niche space, suggests there is potential for interspecific interactions to negatively impact the abundance of C. guttata within turtle communities on the Atlantic Coastal Plain. The results of this study highlight that management efforts may need to consider that species of conservation concern coexist with more common species, especially as habitat loss decreases the breadth of habitat available.

From diatoms to killer whales: impacts of pink salmon on North Pacific ecosystems

In response to a climate regime shift in 1977 and general heating of the North Pacific Ocean, pink salmon Oncorhynchus gorbuscha abundance reached record highs during 2005-2021, comprising 70% of all Pacific salmon. Pink salmon are approximately 25 times more numerous in odd- than even-numbered calendar years in some major North Pacific ecosystems, a unique demographic pattern analogous to repeating whole ecosystem treatment-control experiments. We found compelling examples indicating that in odd years, predation by pink salmon can initiate pelagic trophic cascades by reducing herbivorous zooplankton abundance sufficiently that phytoplankton densities increase, with opposite patterns in even years. Widespread interspecific competition for common-pool prey resources can be dominated by pink salmon, as indicated by numerous biennial patterns in the diet, growth, survival, abundance, age-at-maturation, distribution, and/or phenology of ecologically, culturally, and economically important forage fishes, squid, Pacific salmon and steelhead trout Oncorhynchus spp., seabirds, humpback whales Megaptera novaeangliae, and endangered southern resident killer whales Orcinus orca. In aggregate, the evidence indicates that open-ocean marine carrying capacity in the northern North Pacific Ocean and Bering Sea can be mediated by top-down forcing by pink salmon and by ocean heating, and that large-scale hatchery production (~40% of the total adult and immature salmon biomass) likely has unintended consequences for wild salmon, including Chinook salmon O. tshawytscha, and many other marine species. Further investigation of the effects of pink salmon on other species will increase our knowledge of ecosystem function and the important role top-down forcing plays in the open ocean

Plant invasion modifies isohydricity in Mediterranean tree species

Abstract Understanding of plant hydraulic strategies (i.e. the degree of iso‐/anisohydricity) is crucial to predict the response of plants to changing environmental conditions such as climate‐change induced extreme drought. Several abiotic factors, including evaporative demand, have been shown to seasonally modify the isohydricity of plants. However, the impact of biotic factors such as plant–plant interactions on hydraulic strategies has seldom been explored. Here, we investigated adaptations and changes in hydraulic strategies of two woody species in response to seasonal abiotic conditions, experimental drought and plant invasion in a Mediterranean cork oak (Quercus suber) ecosystem with a combined shrub invasion (Cistus ladanifer) and rain exclusion experiment. From the dry to wet season, Q. suber shifted from a partial isohydric to an anisohydric behaviour while C. ladanifer shifted from strict anisohydric to partial isohydric. During drought, water competition by plant invasion significantly modified the hydraulic strategy of invaded Q. suber, which was accompanied by lower pre‐dawn leaf water potentials, sap flow density, leaf area index and trunk increment rates. This altered isohydricity of invaded Q. suber trees was most likely caused by interspecific competition for water resources by water spending C. ladanifer shrubs. Both species do have the highest proportion of fine roots in the topsoil and thus, an additional water consumer, such as C. ladanifer can lead to more stressful conditions for Q. suber during times of water scarcity. Further underlying mechanisms of the altered isohydricity of Q. suber, such as potential allelopathic effects of C. ladanifer exudates on root growth of Q. suber, have to be investigated in the future. In conclusion, we demonstrate that the degree of isohydricity of two woody Mediterranean plant species is dynamically determined by the interplay of species‐specific hydraulic traits and their abiotic and biotic environment. Read the free Plain Language Summary for this article on the Journal blog.

Coexistence mechanism between sympatric snapper species revealed by stomach contents analysis and stable isotope analysis in the central Gulf of California, Mexico

Sympatric species can overlap in different ecological niche dimensions, which can increase interspecific competition for resources. The objective of this study was to assess the trophic interactions between two sympatric snapper species (Lutjanus guttatus and Lutjanus peru) coexisting in the area of Santa Rosalía, Central Gulf of California. Interactions were analyzed using two complementary techniques: stomach contents analysis and stable isotope analysis (δ13C and δ15N). Specimens were captured from June 2016 to October 2017 and were separated into three categories: sex, size group (1, 2, and 3), and season (warm or cold). A total of 187 L. guttatus stomachs and 397 L. peru stomachs were analyzed; 43 L guttatus and 45 L. peru muscle samples were also obtained for isotopic analysis. Results showed that L. guttatus consumed 28 prey items, whereas L. peru consumed 30 prey items. The %PSIRI showed that the sardines S. sagax (L. guttatus: 34.78% and L. peru 37.42%) and H. thrissina (L. guttatus: 34.61% and L. peru: 24.92%), and the euphausiid N. simplex (L. guttatus: 9.66% and L. peru: 15.20%) were the most important prey in the diet. However, secondary prey differed between snapper species. The PERMANOVA showed significant differences (p < 0.05) for most categories, except for size groups 1 and 3. L. guttatusδ15N values were higher (18.00‰–19.90‰) than those of L. peru (17.71‰–19.51‰), showing the importance of fish in the L. guttatus diet; lower L. peru values could reflect a greater consumption of crustaceans. δ13C values indicated that the two species occupied a coastal habitat with possibility of movements towards the pelagic area, especially for L. peru. Trophic and isotopic niches of the two species were narrow, showing an opportunist strategy. The trophic level showed that the two species could be considered linking species within the trophic web. The mixing models (SIMMR) showed that sardines and myctophids were the best assimilated prey. Interspecific competition between L. guttatus and L. peru was reduced; the two species shared trophic resources that are abundant in different proportions, as a coexistence mechanism.

Índices de eficiência bio-agronômica do consórcio de berinjela e tomate

ABSTRACT The successful intercropping with vegetables depends on the type of crops grown and on the proper handling of tested treatments, such as the time of transplanting a crop in relation to transplanting another crop, among others. Thus, the objective of this work was to evaluate the bio-agronomic performance of eggplant and tomato for industry, in intercropping, in relation to their single crops, as a function of the transplanting time of the eggplant in relation to the tomato and of the cultivation season (summer or winter). The experimental design used was a randomized complete block with ten treatments and four replications, implanted in two growing seasons (from February to September and from August to February), where the treatments consisted of ten eggplant transplanting times (-30, -25, -20, -15, -10, -5, 0, +5, +10 and +15 days in relation to tomato transplantation). In each block, plots of eggplant monocultures were planted in each transplanting time, as well as a plot in tomato monoculture in order to obtain the bio-agronomic indices. The competition and bio-agronomic efficiency indices of the crops and of the intercropped systems were evaluated. The variation in the transplanting time of eggplant in relation to tomato significantly interferes in the bio-agronomic performance of both species. Eggplant transplanting performed between -20 and -15 days compared to tomato transplantation reduces the dominance of one crop over the other and the interspecific competition for environmental resources. The intercropped system has greater land equivalent ratio when the eggplant is transplanted at +15 days after transplanting the tomato.

Functional Diversity of Plant Communities in Relationship to Leaf and Soil Stoichiometry in Karst Areas of Southwest China

Assessment of relationships between functional diversity and ecological stoichiometry in plant communities can aid in determining the relative variability and ecological complementarity of functional attributes among species, which is a better approach to understanding ecosystem processes and functions than studying species taxonomic diversity. Here, we analyzed the relationships among community weighted means of functional traits, functional diversity, and leaf and soil chemical properties of plant communities during various stages of vegetation restoration in Mao Lan National Karst Forest Nature Reserve, located in humid subtropical Guizhou of China. Our results showed significant changes in four weighted functional traits of plant communities at different restoration stages, namely, plant height, leaf width to leaf length ratio, and leaf area. Additionally, with the progression of the recovery of plant communities, functional richness, functional separation, and quadratic entropy, the coefficient tended to increase. Functional divergence tended to gradually decrease. The association of functional diversity with soil chemical properties was stronger than that with leaf ecological stoichiometry. Regarding leaf and soil chemical properties, soil phosphorus content and leaf C:P were particularly important in influencing functional diversity. Our overall findings indicate that functional traits shift from “acquisitive” to “conservative” as the community is restored. Karst plant communities reduce interspecific resource competition as restoration proceeds, thereby increasing functional overlap effects.

Dietary Diversity and Evolution of Cranial Adaptations in Turtles

The evolution of the turtle skull has involved a series of unique modifications resulting in increased bite force stemming from cranial elongation, rearrangement of jaw adductor musculature, and reduction of cranial kinesis. Loss of teeth, development of the keratinous rhamphotheca, and evolution of a highly flexible neck have also driven turtle cranial evolution. Dietary diversity across the clade has resulted in a diverse range of morphological variations of the turtle cranial Bauplan, including those associated with suction feeding and tongue‐dependent food uptake.The Cenomanian Arlington Archosaur Site (AAS) from the Woodbine Formation of Texas was home to numerous mid‐Cretaceous turtle taxa. This diverse faunal assemblage allows an evaluation of how dietary adaptations can facilitate partitioning of the available niche space among co‐occurring turtle species. Baenids, such as Trinitichelys maini at AAS, are typically reconstructed as being primarily carnivorous, although there is evidence that some taxa were molluscivorous. The AAS helochelydrid Naomichelys was likely a generalized omnivore, being more terrestrial than the other AAS turtle taxa. Bothremydids, such as the AAS species Pleurochayah appalachius, have a wide range of dietary specializations including durophagy and suction‐feeding. These adaptations are evidenced by the broad range of bothremydid cranial morphologies including expanded triturating surfaces and an inflated face. Highly aquatic trionychids are predominantly piscivorous, although they will also opportunistically hunt other small prey such crustaceans and amphibians. Many trionychid species must be fully submerged under water in order to properly swallow their food in contrast to some semi‐aquatic turtles. A newly identified protostegid turtle reveals a marine component to the AAS turtle fauna, suggesting the presence of an open ocean piscivore. Finally, an intriguing new lower jaw with well‐developed denticles indicates the presence of an obligate herbivore among the AAS turtle fauna. This diverse array of dietary proclivities and adaptations reveals how AAS turtle communities divided the available ecospace in order to avoid interspecific competition for available resources among turtle taxa and with the other AAS herpetofauna.