Outcome Of Interspecific Competition Research Articles

Ecological impact of a generalist invader in the aquatic food web is mediated by environmental context

Abstract Freshwater ecosystems are threatened by the introduction of invasive species. Generalist invaders often compete with native species for shared resources, resulting in possible native species niche displacement. However, environmental heterogeneity may modulate the level of individual specialisation in invasive species, altering the outcome of interspecific competition between invasive and native species. The objectives of our study were to (1) evaluate the environmental context of dietary specialisation and trophic position of an invasive species according to the Environmental Matching Hypothesis (EMH), and (2) consider how the environmental context of invasive species dietary resource use may influence the dietary niche of native species competing for similar resources. Resource use, trophic position and dietary niche were determined using gut content and stable isotope analyses for the invasive round goby (Negobius melanostomus) and the native yellow perch (Perca flavescens), along environmental gradients in an invaded fluvial ecosystem. Our results were in support of EMH for the invader diet and resource specialisation, but not trophic position. Under environmental conditions of high water‐conductivity, round gobies were generalists feeding mostly on pelagic prey. Under more challenging environmental conditions of low water‐conductivity, the invader specialised on preferred high‐quality benthic prey. The ecological impact of the round goby was greatest at low water‐conductivity sites where the invader was a benthic specialist; there was a greater relative dietary niche overlap between the invader and the native species. Our study uniquely illustrates how invasive species’ resource specialisation can be modulated by spatial environmental heterogeneity within ecosystems, and how this can subsequently alter the ecological impact of the invader on native species in aquatic food webs.

Hummingbird community structure and nectar resources modulate the response of interspecific competition to forest conversion

On-going land-use change has profound impacts on biodiversity by filtering species that cannot survive in disturbed landscapes and potentially altering biotic interactions. In particular, how land-use change reshapes biotic interactions remains an open question. Here, we used selectivity experiments with nectar feeders in natural and converted forests to test the direct and indirect effects of land-use change on resource competition in Andean hummingbirds along an elevational gradient. Selectivity was defined as the time hummingbirds spent at high resource feeders when feeders with both low and high resource values were offered in the presence of other hummingbird species. Selectivity approximates the outcome of interspecific competition (i.e., the resource intake across competing species); in the absence of competition, birds should exhibit higher selectivity. We evaluated the indirect effect of forest conversion on selectivity, as mediated by morphological dissimilarity and flower resource abundance, using structural equation models. We found that forest conversion influenced selectivity at low and mid-elevations, but the influence of morphological dissimilarity and resource availability on selectivity varied between these elevations. At mid-elevation, selectivity was more influenced by the presence of morphologically similar competitors than by resource abundance while at low-elevation resource abundance was a more important predictor of selectivity. Our results suggest that selectivity is influenced by forest conversion, but that the drivers of these changes vary across elevation, highlighting the importance of considering context-dependent variation in the composition of resources and competitors when studying competition.

Spinetoram resistance drives interspecific competition between Megalurothrips usitatus and Frankliniella intonsa.

Species displacement by the outcome of interspecific competition is of particular importance to pest management. Over the past decade, spinetoram has been extensively applied in control of the two closely related thrips Megalurothrips usitatus and Frankliniella intonsa worldwide, while whether its resistance is implicated in mediating interspecific interplay of the two thrips remains elusive to date. Field population dynamics (from 2017 to 2019) demonstrated a trend toward displacement of F. intonsa by M. usitatus on cowpea crops, supporting an existing interspecific competition. Following exposure to spinetoram, M. usitatus became the predominate species, which suggests the use of spinetoram appears to be responsible for mediating interspecific interactions of the two thrips. Further annual and seasonal analysis (from 2016 to 2020) of field-evolved resistance dynamics revealed that M. usitatus developed remarkably higher resistance to spinetoram compared to that of F. intonsa, implying a close relationship between evolution of spinetoram resistance and their competitive interactions. After 12 generations of laboratory selection, resistance to spinetoram in M. usitatus and F. intonsa increased up to 64.50-fold and 28.33-fold, and the average realized heritability (h2 ) of resistance was calculated as 0.2550 and 0.1602, respectively. Interestingly, two-sex life table analysis showed that the spinetoram-resistant strain of F. intonsa exhibited existing fitness costs, but not the M. usitatus. These indicate that a rapid development of spinetoram resistance and the lack of associated fitness costs may be the mechanism underlying recent dominance of M. usitatus over F. intonsa. Collectively, our results uncover the involvement of insecticide resistance in conferring displacement mechanism behind interspecific competition, providing a framework for understanding the significance of the evolutionary relationships among insects under ongoing changing environments. These findings also can be invaluable in proposing the most appropriate strategies for sustainable thrips control programs. © 2022 Society of Chemical Industry.

Maternal effects and the outcome of interspecific competition.

Maternal environmental effects create lagged population responses to past environments. Although they are ubiquitous and vary in expression across taxa, it remains unclear if and how their presence alters competitive interactions in ecological communities.Here, we use a discrete‐time competition model to simulate how maternal effects alter competitive dynamics in fluctuating and constant environments. Further, we explore how omitting maternal effects alter estimates of known model parameters from observational time series data.Our simulations demonstrate that (i) maternal effects change competitive outcomes, regardless of whether competitors otherwise interact neutrally or exhibit non‐neutral competitive differences, (ii) the consequences of maternal effects for competitive outcomes are mediated by the temporal structure of environmental variation, (iii) even in constant conditions, competitive outcomes are influenced by species' maternal effects strategies, and (iv) in observational time series data, omitting maternal effects reduces variation explained by models and biases parameter estimates, including competition coefficients.Our findings demonstrate that the ecological consequences of maternal effects hinge on the competitive environment. Evolutionary biologists have long recognized that maternal effects can be an important but often overlooked strategy buffering populations from environmental change. We suggest that maternal effects are similarly critical to ecology and call for research into maternal effects as drivers of dynamics in populations and communities.

Temperature-Dependent Competitive Outcomes between the Fruit Flies Drosophila santomea and Drosophila yakuba.

AbstractChanges in temperature associated with climate change can alter species' distributions, drive adaptive evolution, and in some cases cause extinction. Research has tended to focus on the direct effects of temperature, but changes in temperature can also have indirect effects on populations and species. Here, we test whether temperature can indirectly affect the fitness of Drosophila santomea and Drosophila yakuba by altering the nature of interspecific competition. We show that when raised in isolation, both D. santomea and D. yakuba display similar variation in relative fitness across temperatures of 18°, 22°, and 25°C. However, D. santomea has higher fitness than D. yakuba when experiencing interspecific competition at 18°C, while the inverse is true at 25°C. Patterns of fitness across thermal and competitive environments therefore indicate that the outcome of interspecific competition varies with temperature. We then use a coexistence experiment to show that D. santomea is rapidly (within eight generations) extirpated when maintained with D. yakuba at 25°C. By contrast, D. santomea remains as (or more) abundant than D. yakuba over the course of ∼10 generations when maintained at 18°C. Our results provide an example of how the thermal environment can affect interspecific competition and suggest that some species may become more prone to extinction under scenarios of climate change through indirect effects of the thermal environment on competitive advantages between species.

Interspecific social dominance networks reveal mechanisms promoting coexistence in sympatric charr in Hokkaido, Japan.

Coexistence of species requires equalizing mechanisms that minimize fitness differences, which are balanced by stabilizing mechanisms that enhance negative intraspecific interactions versus interspecific ones. Here, we develop a simple theoretical framework that allows measuring the relative strength of intraspecific versus interspecific competition in dominance hierarchies. We use it to evaluate mechanisms promoting coexistence between two congeneric charr that compete for foraging positions, which strongly influence density-dependent growth and survival. Agonistic interactions (n=761) among 71 Dolly Varden Salvelinus malma and whitespotted charr Salvelinus leucomaenis were measured by snorkelling in two pools in the sympatric zone of a Hokkaido stream during two summers. Interspecific dominance hierarchies, analysed using three methods, were closely correlated with fish length but the species treated each other equally. Ranks for the most dominant fish in each pool, determined directly by knockout experiments, were also virtually identical to ranks by length. Similarly, exponential random graph modelling of the social networks provided no evidence that either species was dominant over the other. Instead, larger fish were more likely to win contests, especially over fish of the next lower ranks. These results demonstrated that the two species were nearly ecological equivalents in accessing key resources in this sympatric zone. Nearly identical growth and stable densities over 4years further supported this inference, although Dolly Varden were a minority (29% of the assemblage), a sign of some fitness difference. Detailed foraging observations coupled with two concurrent studies revealed an effective stabilizing mechanism. Dolly Varden shifted to feeding directly from the benthos when drifting invertebrates declined, a behaviour enhanced by morphological character displacement, thereby partitioning food resources and enhancing intraspecific competition while avoiding agonistic encounters with whitespotted charr. The plurality of evidence indicates that fitness differences between these ecologically equivalent species are small in this local assemblage, and balanced by resource partitioning, a modest stabilizing mechanism that promotes coexistence. The theoretical framework presented here is a useful tool to evaluate the strength of interspecific versus intraspecific competition, which combined with information on trade-offs in ecological performance can contribute to a mechanistic understanding of species coexistence.

Estimations of Fine-Scale Species Distributions of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Eastern Florida.

Many species distribution maps indicate the ranges of Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) overlap in Florida despite the well-documented range reduction of Ae. aegypti. Within the last 30 yr, competitive displacement of Ae. aegypti by Ae. albopictus has resulted in partial spatial segregation of the two species, with Ae. aegypti persisting primarily in urban refugia. We modeled fine-scale distributions of both species, with the goal of capturing the outcome of interspecific competition across space by building habitat suitability maps. We empirically parameterized models by sampling 59 sites in south and central Florida over time and incorporated climatic, landscape, and human population data to identify predictors of habitat suitability for both species. Our results show human density, precipitation, and urban land cover drive Ae. aegypti habitat suitability, compared with exclusively climatic variables driving Ae. albopictus habitat suitability. Remotely sensed variables (macrohabitat) were more predictive than locally collected metrics (microhabitat), although recorded minimum daily temperature showed significant, inverse relationships with both species. We detected minor Aedes habitat segregation; some periurban areas that were highly suitable for Ae. albopictus were unsuitable for Ae. aegypti. Fine-scale empirical models like those presented here have the potential for precise risk assessment and the improvement of operational applications to control container-breeding Aedes mosquitoes.

Outcome of interspecific competition depends on genotype of conspecific neighbours.

The outcome of interspecific competition is affected by numerous abiotic and biotic factors. However, the effects of genetic relatedness of conspecific neighbours have not been elucidated. Here, we demonstrate that the genotype of a conspecific neighbour determines the outcome of interspecific competition. We investigated effects of genotype of neighbour sibling or non-sibling Plantago asiatica plants on competition with Trifolium repens plants. Pairs of P. asiatica, sibling or non-sibling, were grown in competition with T. repens. Sibling P. asiatica plants, but not non-sibling plants, increased leaf placement towards competitor T. repens plants, and that placement was correlated negatively with the biomass of T. repens and positively with seed production by P. asiatica. Seed production by P. asiatica plants competing with T. repens was greater in individuals paired with siblings than in those paired with non-siblings. Thus, our results show that the genotype of conspecific neighbours can alter the outcome of interspecific competition.

Species displacement facilitated by ascarosides between two sympatric sibling species: a native and invasive nematode

Competitive displacement is not only the most extreme outcome of interspecific competition, but also an important strategy for invasive species to be successful invaders. Pinewood nematode, Bursaphelenchus xylophilus, the causal agent for pine wilt disease and global quarantine pest, usually displaces Bursaphelenchus mucronatus, a native sympatric sibling species, during its invasion process. Despite this prevalent outcome, the driving forces behind this displacement remain elusive. Ascarosides, an evolutionarily conserved family of nematode pheromones, are versatile in structure and function. We hypothesize these nematode pheromones play a role in species displacement. To investigate this hypothesis, we compared the ascarosides composition of B. xylophilus and B. mucronatus by LC–MS/MS followed by bioassays to test the responses of two nematodes to both crude and synthetic ascarosides. We found that asc-C5 (ascr#9) was the most abundant component and that there were no differences in pheromone composition between the two nematode species. B. xylophilus had faster growth rates under competition conditions. Furthermore, low concentrations of both crude and synthetic ascarosides [asc-C5, asc-C6 (ascr#12) and their mixture] enhanced female fecundity and body length growth in B. xylophilus but not in B. mucronatus. In contrast, body length of B. mucronatus was suppressed by a crude extract of its own ascarosides as well as by synthetic ascarosides (asc-C5, asc-C6 and their mixture). Our results strongly suggest that ascarosides play a role in the competitive displacement between two nematode species, which could explain the phenomena observed in B. xylophilus-invaded forests where B. mucronatus widely existed prior to B. xylophilus invasion.

Transforming even-aged coniferous stands to multi-aged stands: an opportunity to increase tree species diversity?

Abstract Transforming even-aged coniferous stands into multi-aged ones is attracting growing interest in Europe. However, applying this silvicultural treatment, maintaining a continuous cover and relying on natural regeneration require a deep understanding of the factors driving interspecific competition in the understorey. In particular, knowledge of species-specific response to different light conditions is needed to plan silvicultural treatments and forecast long-term stand composition. In this context, we assessed regeneration (±10–400 cm in height) and light conditions (±1–40 per cent of transmittance) in nine coniferous stands with ranging stand age (±20–120 years) and species composition (Norway spruce, Douglas fir, larch, silver fir and western hemlock) in Belgium. We then modelled interspecific differences in regeneration height growth to forecast the outcome of interspecific competition in different light conditions. Controlling understorey light seems an efficient way to control the interspecific competition, but with some limits, and taking into account sapling size. Maintaining low light conditions (transmittance < 15 per cent) probably reduces interspecific competition as it allows small saplings (height < 100 cm) of most species to grow at a comparable rate. Maintaining higher light conditions might allow a few species to rapidly overgrow the others. Species ranking in height growth changed across the studied light range only between spruce and larch, suggesting that the competition between these two species can be driven through the control of understorey light. On the other hand, controlling canopy openness was found to be insufficient, for example, to promote an advanced regeneration (height ≥ 200 cm) of fir over advanced regeneration of spruce, to promote any species over western hemlock or to promote Douglas fir. Western hemlock, a very shade-tolerant species, was found to grow three times faster than the other species in all the observed conditions (PACL = 5–20 per cent). Douglas fir saplings showed weak growth and marked defoliation, which we hypothetically relate to the recent outbreak of Contarinia pseudotsugae in Western Europe.

Temperature-Mediated Competition Between the Invasive Larger Grain Borer (Coleoptera: Bostrichidae) and the Cosmopolitan Maize Weevil (Coleoptera: Curculionidae).

Interspecific competition between agricultural pests may affect the species that can establish, and may also affect food production. Prostephanus truncatus (Horn), the larger grain borer, is endemic to Central America, but invaded Africa with disastrous consequences for maize production. Its main competitor is Sitophilus zeamais Motschulsky, the maize weevil, which is cosmopolitan. These insects co-occur in many regions of the world and both are threats to maize. However, the impact of competition between these two species is not well-understood, nor is its effect on grain quality or potential to limit P. truncatus invasion in new areas. The aims of our study were to evaluate the outcome of interspecific competition between P. truncatus and S. zeamais at four different temperatures on a fixed quantity of grain, and determine effects on progeny production, grain damage, and mold growth. We found that coexistence may be possible at a range of 25-30°C, but mixed colonies experienced a direct competitive cost compared to single-species colonies. Prostephanus truncatus performed better at warmer temperatures, while S. zeamais favored cooler temperatures. The majority of grain damage was the result of P. truncatus activity as opposed to S. zeamais. Finally, mold growth was greater where both species were present, and species of mold that produce aflatoxin were identified. Although there are an increasing number of areas where both of these species occur, our results suggest P. truncatus will be capable of destroying much more maize in a shorter period compared to S. zeamais at temperatures greater than 25°C.

Nutritional ecology provides insights into competitive interactions between closely related Martes species

Abstract Closely related predator species often share several prey items, making it hard to differentiate the effects on their feeding habits of variation in food availability and of competition. We hypothesised that we could overcome this obstacle by quantifying and comparing nutritional niches. We reviewed dietary studies that assessed the relative bulk of each food item, as either per cent biomass or per cent mean volume, in the diet of two closely related species, pine marten Martes martes and stone marten Martes foina, and calculated the nutrient profiles (intakes of protein, lipids and carbohydrates) of each diet. Both martens’ diets were tightly clustered (mean values: 47% of energy from protein, 39% from lipid, and 14% from carbohydrate). In allopatry, the nutritional niches of the two species did not differ, but in sympatry, the stone marten ate more carbohydrates and less protein than the pine marten. In allopatry, the protein intake of the stone marten remained high (45–52%) in very different habitats, from cultivated lowland to Alpine forests. Our data suggest that stone marten frugivory may, at least partially, be the result of interspecific competition. By analysing dietary data in the framework of nutritional ecology, we could compare the feeding requirements of pine martens and stone martens more effectively than by using classical estimates of trophic niche overlap at the food item level. This approach may help to shed light on the trophic relationships of other competing species.

Sperm-dependent asexual hybrids determine competition among sexual species

Interspecific competition is a fundamental process affecting community structure and evolution of interacting species. Besides direct competition, this process is also mediated by shared enemies, which can change the outcome of competition dramatically. However, previous studies investigating interactions between competing species and their parasites (parasite-mediated competition) completely overlooked the effect of ‘sperm’ parasites (i.e. sperm-dependent parthenogens or pseudogams) on competition. These organisms originate by interspecific hybridization, produce clonal gametes, but exploit parental species for their own reproduction, being therefore analogous to classical parasites. Here we use the reaction-diffusion model and show that pseudogams alter the outcome of interspecific competition significantly. They may either slow down competitive exclusion of the inferior competitor or even turn the outcome of competition between the species. Asexual organisms may thus have unexpectedly strong impact on community structure, and have more significant evolutionary potential than was previously thought.

Potential competitive outcomes among three solitary larval endoparasitoids as candidate agents for classical biological control of Drosophila suzukii

Predicting the outcome of interspecific interactions is important in designing biological control programs that involve multiple species introductions. Three solitary larval endoparasitoids, Asobara japonica Belokobylskij (Hymenoptera: Braconidae), Ganaspis brasiliensis Ihering and Leptopilina japonica Novković & Kimura (both Hymenoptera: Figitidae) from Asia are potential agents for classical biological control of the invasive Drosophila suzukii Matsumura (Diptera: Drosophilidae) in North America. We compared the developmental rates of early immature stages of the three parasitoids and then evaluated their potential interactions, including elimination of competitors in intrinsic competition, interspecific discrimination of previously parasitized hosts, and the outcomes of interspecific competition at three host densities (5, 15 or 30 host larvae). On average, L. japonica eggs hatched first, followed by A. japonica and then G. brasiliensis. All three species exhibited interspecific competition after egg hatch through physical combat or in some cases through physiological suppression, with L. japonica out-competing the other two parasitoid species in multi-parasitized hosts. Ganaspis brasiliensis adults discriminated strongly against hosts previously parasitized by L. japonica, and A. japonica adults discriminated against hosts previously parasitized by L. japonica, whereas L. japonica only discriminated against hosts parasitized by G. brasiliensis. Regardless of host density, the observed parasitism when both A. japonica and L. japonica were present was lower than expected, a likely consequence of interspecific competition, but the combined impacts on host suppression by L. japonica and G. brasiliensis were additive, likely due to strong interspecific discrimination by G. brasiliensis.

The exploitation of fresh remains by Dermestes maculatus De Geer (Coleoptera, Dermestidae) and their ability to cause a localised and prolonged increase in temperature above ambient

This article discusses the ability of adults of the coleopteran beetle Dermestes maculatus (De Geer) to colonise fresh remains. It also considers whether colonisation results in localised thermogenesis in a similar manner to that induced by blowfly larvae.In the laboratory, adult D. maculatus instantly colonised fresh killed rats and mice. The adults entered the oral cavity within 1–2 h and the eyes and ears were among the first parts of the body consumed. Egg laying occurred on the torso and head within an hour of death and eggs hatched within 3–4 days. The larvae remained on the body whilst the adults (>70%) rested in the surrounding wood chippings when not feeding or laying eggs. Larvae grew rapidly on the dead bodies and some were starting to pupate within 28 days.The dermestids consumed the corpses predominantly from the head downwards and weight loss correlated with the number of larvae produced. In both rats and mice, colonisation of the abdominal region was associated with an increase in temperature. The maximum abdominal temperature and the length of time the temperature remained 1 °C or more above ambient correlated with the number of larvae produced. This rise in temperature would probably be sufficient to increase the rate of development of dermestid larvae and that of any other invertebrate or microbe in the region. In the absence of dermestids, the internal temperature rarely rose 1 °C above ambient.Although there are previously published accounts of dermestid beetles consuming fresh corpses, they are reputed to favour older desiccated remains. This paper confirms that D. maculatus rapidly consumes and reproduces on fresh remains. The fact that dermestid beetles are seldom found on fresh remains under field conditions is therefore probably a result of inter-specific competition among decomposing insects rather than food preference. This information could be useful when determining the forensic significance of D. maculatus recovered from dead bodies.

Nonlinear effects of phenological shifts link interannual variation to species interactions.

The vast majority of species interactions are seasonally structured and depend on species' relative phenologies. However, differences in the phenologies of species naturally vary across years and are altered by ongoing climate change around the world. By combining experiments that shifted the relative hatching of two competing tadpole species across a productivity gradient with simulations of inter-annual variation in arrival times I tested how phenological variation across years can alter the strength and outcome of interspecific competition. Shifting the relative timing of hatching (phenology) of a species fundamentally altered interspecific competition, and the effect of shifting the timing on competition was highly non-linear for most demographic rates. Furthemore, this relationship varied with productivity of the system. As a consequence, (a) shifts in relative timing of phenologies had small or large effects depending on the average natural timing of interactions, and (b) changes in the inter-annual variation in onset of interaction alone can alter species interactions in simulations even when mean phenologies (timing) remain unchanged across years. Studies on phenologies traditionally focus on directional shifts in the mean of phenologies, but these results suggest that we also need to consider inter-annual variation in phenologies of interacting species to predict dynamics of natural communities and how they will be modified by climate change.

Invasive predator tips the balance of symmetrical competition between native coral-reef fishes.

The importance of competition and predation in structuring ecological communities is typically examined separately such that interactions between these processes are seldom understood. By causing large reductions in native prey, invasive predators may modify native species interactions. I conducted a manipulative field experiment in The Bahamas to investigate the possibility that the invasive Pacific red lionfish (Pterois volitans) alters competition between planktivorous fairy and blackcap basslets (Gramma loreto and Gramma melacara, respectively). Competition between these coral-reef fishes is known to have symmetrical effects on the juveniles of both species, whereby the feeding positions under reef ledges and growth rates of these individuals are hindered. Following baseline censuses of local populations of competing basslets, I simultaneously manipulated the abundance of lionfish on entire reefs, and the abundance of basslets in local populations under isolated ledges within each reef, resulting in three treatments: unmanipulated control populations of both basslets, reduced abundance of fairy basslet, and reduced abundance of blackcap basslet. For eight weeks, I measured the change in biomass and feeding position of 2-5cm size classes of each basslet species and calculated the growth rates of ~2cm individuals using a standard mark-and-recapture method. Experimental populations were filmed at dusk using automated video cameras to quantify the behavior of lionfish overlapping with basslets. Video playback revealed lionfish hunted across all ledge positions, regardless of which basslet species were present, yet lionfish differentially reduced the biomass of only juvenile (2cm) fairy basslet. Predation reduced the effects of interspecific competition on juvenile blackcap basslet as evidenced by corresponding shifts in feeding position toward coveted front edges of ledges and increases in growth rates that were comparable to the response of these fish in populations where competition was experimentally reduced. Thus, an invasive marine predator altered the outcome of interspecific competition via differential predation, which tipped the balance of competition between native prey species from symmetrical to asymmetrical effects on juveniles. This study reveals a newly demonstrated context in which predation can indirectly facilitate prey, further broadening our understanding of the interactive effects of predation and competition in the context of invasive species.

Habitat orientation alters the outcome of interspecific competition: A microcosm study with zooplankton grazers.

Habitat orientation has recently been demonstrated to affect the foraging behavior, growth, and production of plankton grazers. Because the orientation effect may vary with species, we hypothesize that habitat orientation may alter interspecific interactions between animal species. We experimentally investigated how habitat orientation (placing cuboid chambers in three orientations with long, medium, and small side as the chamber height) affected the interaction between two common cladoceran species, Daphnia magna and Moina micrura, which competitively exploited green algae of Chlorella pyrenoidosa at two volume scales (64 and 512 ml). Results show that chamber orientation and volume additively affected the behavior and species performance of the grazers. Specifically, both grazer species generally decreased their average swimming velocity, grazing rate (on algal cells), body size, and survival and reproduction rates with increasing chamber height for both chamber volumes and with decreasing chamber volume regardless of chamber orientation. Nevertheless, the decrease magnitude was greater for M. micrura with increasing chamber height but was greater for D. magna with decreasing chamber volume. Correspondingly, when cocultured, the density ratio of D. magna to M. micrura increased with increasing chamber height but decreased with decreasing chamber volume. At the end of the experiment, none of D. magna individuals survived in the small and short (large‐based) chambers, and few M. micrura individuals survived in large and tall (small‐based) chambers. These results indicate that both habitat orientation and size affect the outcome of interspecific competition between grazer species. We suggest that variation in habitat orientation may improve community coexistence and species diversity in nature.

Identifying critical interactions in complex competition dynamics between bean beetles

Identifying behavioural basis of competitive relationship is essential to understand outcome of interspecific competition. However, it remains difficult to investigate demographic effect of competitive behaviour, because various kinds of behaviours may co‐occur in the competition and make the dynamics far complicated in nonlinear ways. We report that the behavioural basis of interspecific interaction can be identified, by focusing on the timescale difference from the occurrence of each behaviour to the appearance of its demographic effect. Between two bean beetles, Callosobruchus chinensis and C. maculatus, major interspecific interactions are resource competition (RC) at the larval stage and reproductive interference (RI) at the adult stage. RC has longer time lag than RI, because effect of RC appears in the adult number of the next generation through larval competition while effect of RI appears instantaneously in the adult number through early death of females. If we detect two effects with different time lags from the competition dynamics, an effect with intergenerational time lag and with no time lag would be considered as RC and RI, respectively. We applied empirical dynamic modelling approach, which is a nonlinear time series analysis for detecting causal interactions and the strength, to two published datasets of experimental competition between those beetles. Results showed the significant causality from the winner species to the loser one in both experiments, but the causality time lag differed between experiments: the causality had no time lag in the C. chinensis‐win data, while intergenerational time lag in C. maculatus‐win data. Furthermore, detection of the causality with intergenerational time lag from C. maculatus to C. chinensis in both experiments suggests interplay of constant RC and variable RI which can reverse the outcome. This study is the first successful case study that links behavioural‐level interactions to demographic‐level effects in interspecific competition.

Intraspecific and interspecific competition induces density-dependent habitat niche shifts in an endangered steppe bird.

Interspecific competition is a dominant force in animal communities that induces niche shifts in ecological and evolutionary time. If competition occurs, niche expansion can be expected when the competitor disappears because resources previously inaccessible due to competitive constraints can then be exploited (i.e., ecological release). Here, we aimed to determine the potential effects of interspecific competition between the little bustard (Tetrax tetrax) and the great bustard (Otis tarda) using a multidimensional niche approach with habitat distribution data. We explored whether the degree of niche overlap between the species was a density‐dependent function of interspecific competition. We then looked for evidences of ecological release by comparing measures of niche breadth and position of the little bustard between allopatric and sympatric situations. Furthermore, we evaluated whether niche shifts could depend not only on the presence of great bustard but also on the density of little and great bustards. The habitat niches of these bustard species partially overlapped when co‐occurring, but we found no relationship between degree of overlap and great bustard density. In the presence of the competitor, little bustard's niche was displaced toward increased use of the species' primary habitat. Little bustard's niche breadth decreased proportionally with great bustard density in sympatric sites, in consistence with theory. Overall, our results suggest that density‐dependent variation in little bustard's niche is the outcome of interspecific competition with the great bustard. The use of computational tools like kernel density estimators to obtain multidimensional niches should bring novel insights on how species' ecological niches behave under the effects of interspecific competition in ecological communities.