Success of alien plants is often attributed to high competitive ability. However, not all aliens become dominant, and not all natives are vulnerable to competitive exclusion. Here, we quantified ...competitive outcomes and their determinants, using response‐surface experiments, in 48 pairs of native and naturalised alien annuals that are common or rare in Germany. Overall, aliens were not more competitive than natives. However, common aliens (invasive) were, despite strong limitation by intraspecific competition, more competitive than rare natives. This is because alien species had higher intrinsic growth rates than natives, and common species had higher intrinsic growth rates than rare ones. Strength of interspecific competition was not related to status or commonness. Our work highlights the importance of including commonness in understanding invasion success. It suggests that variation among species in intrinsic growth rates is more important in competitive outcomes than inter‐ or intraspecific competition, and thus contributes to invasion success and rarity.
Ecological release, originally conceived as niche expansion following a reduction in interspecific competition, may prompt invasion success, morphological evolution, speciation, and other ecological ...and evolutionary outcomes. However, the concept has not been recently reviewed. Here, we trace the study of ‘ecological release’ from its inception through the present day and find that current definitions are broad and highly varied. Viewing this development as a potential impediment to clear communication and hypothesis testing, we suggest a consensus definition for ecological release: niche expansions and shifts when a constraining interspecific interaction is reduced or removed. In rationalizing this definition, we highlight the various ways ecological release can unfold and address its potential evolutionary consequences.
Ecological release, as both a concept and a term, has not been recently reviewed.Ecological release was originally conceived as niche expansion following a reduction in interspecific competition.Modern definitions are broad and varied – they encompass underlying mechanisms other than competition and accept signals other than niche expansion as potential evidence that ecological release has occurred.Niche changes during ecological release may prompt consequent morphological evolution and/or adaptive speciation, but these evolutionary outcomes themselves do not constitute ecological release.Hypotheses about evolutionary outcomes may be improved by explicitly considering how population- and individual-level niche dynamics can vary during ecological release.
A major question in ecology is how often competing species evolve to reduce competitive interactions and facilitate coexistence. One untested route for a reduction in competitive interactions is ...through ontogenetic changes in the trophic niche of one or more of the interacting species. In such cases, theory predicts that two species can coexist if the weaker competitor changes its resource niche to a greater degree with increased body size than the superior competitor.
We tested this prediction using stable isotopes that yield information about the trophic position (δ15N) and carbon source (δ13C) of two coexisting fish species: Trinidadian guppies Poecilia reticulata and killifish Rivulus hartii.
We examined fish from locations representing three natural community types: (1) where killifish and guppies live with predators, (2) where killifish and guppies live without predators and (3) where killifish are the only fish species. We also examined killifish from communities in which we had introduced guppies, providing a temporal sequence of the community changes following the transition from a killifish only to a killifish–guppy community.
We found that killifish, which are the weaker competitor, had a much larger ontogenetic niche shift in trophic position than guppies in the community where competition is most intense (killifish–guppy only). This result is consistent with theory for size‐structured populations, which predicts that these results should lead to stable coexistence of the two species. Comparisons with other communities containing guppies, killifish and predators and ones where killifish live by themselves revealed that these results are caused primarily by a loss of ontogenetic niche changes in guppies, even though they are the stronger competitor. Comparisons of these natural communities with communities in which guppies were translocated into sites containing only killifish showed that the experimental communities were intermediate between the natural killifish–guppy community and the killifish–guppy–predator community, suggesting contemporary evolution in these ontogenetic trophic differences.
These results provide comparative evidence for ontogenetic niche shifts in contributing to species coexistence and comparative and experimental evidence for evolutionary or plastic changes in ontogenetic niche shifts following the formation of new communities.
The authors use stable isotopes of guppies and killifish to provide comparative evidence for ontogenetic niche shifts in contributing to species coexistence and comparative and experimental evidence for evolutionary or plastic changes in ontogenetic niche shifts following the formation of new communities.
Productivity and benefits in intercropping systems are influenced by the overlapping period and competitive dynamics between species, which are contingent upon variety selection and planting ...schedules. However, there is limited research on improving the productivity of intercropping systems by adjusting sowing dates for combinations with minimal plant height differences.
A two-year field experiment utilizing a strip intercropping with four rows of cotton and five rows of soybeans was conducted. Three soybean varieties (Qihuang 34, Jidou 12, and Jidou 17) with varying plant heights and types, along with early and late sowing dates, were examined.
Intercropping cotton and soybeans resulted in higher yields than monoculture, with Jidou 12 identified as the most suitable variety for intercropping with cotton. The land equivalent ratio (LER) for the cotton-soybean intercropping system averaged between 1.04 and 1.15 over two years. Notably, intercropping cotton with late-sown Qihuang 34, Jidou 12, and Jidou 17 demonstrated increased LER by 4 %, 5 %, and 3 % respectively, compared to early-sown. This demonstrates that adjusting the soybean sowing date can modulate the competition dynamics between cotton and soybean, mitigating interspecific competition. Furthermore, intercropping cotton with late-sown Jidou 12 exhibited superior performance in terms of dry matter, canopy photosynthesis, photosynthetically active radiation, and root morphology in cotton compared to other treatments. Within the distance of 100–150 mm from the soybean, cottons were more competitive than soybeans, indicating subtle interspecific competition between the two species.
By carefully selecting soybean varieties and adjusting sowing dates, temporal complementarity and spatial niche differentiation can be achieved, alleviating interspecific competition and enhancing the productivity of cotton-soybean intercropping systems.
•Intense competition between cotton and soybean limits intercropping productivity.•Intercropping cotton with late-sown Jidou 12 mitigates interspecific competition.•It enhances niche differentiation through improved light utilization and root growth.•Niche differentiation increases the productivity in intercropping cotton with late-sown Jidou 12.
Trait intraspecific variability determines community dynamics and species coexistence. In response to competition, plants can display intraspecific variability to enhance their competitive ability or ...stabilise their niche differences with competitors. This response is multidimensional because it involves changes along different functional axes and inevitable trade‐offs between traits. Here, we transposed the recent concept of the multidimensional trait space to the analysis of intraspecific plant response to competition. We specifically tested the following: (a) in the absence of competitors, the plant multidimensional trait space will be packed towards strategies promoting plant colonisation; and (b) with competitors, the plant multidimensional trait space will be directed towards competition with its size and shaping characteristics dependent on competitor species richness.
We studied trait intraspecific variability of two clonal species, Brachypodium pinnatum (L.) P. Beauv. and Elytrigia repens (L.) Gould, in response to competition. We analysed plant response in the absence of competitors and in competition. Competition treatments included intraspecific and interspecific experimental mixtures with increasing species richness. For each target species and each treatment, we built an hypervolume based on six traits involved in the three‐dimensional competition (i.e., ramet and connection traits). We measured these hypervolumes for their size, similarity and the contribution of traits in their shaping.
In the absence of competitors and for both species, we demonstrated a multidimensional trait space packing towards a colonisation strategy. Under competition, the multidimensional trait spaces of the two target species were the widest at the extremes of the richness gradient, that is, intraspecific and interspecific high richness competition treatments. High intraspecific variability either promoted niche differentiation from individuals of similar species or reflected the large range of competitive responses deployed when plants were faced with many different competitor identities. The multidimensional response process was based on fine adjustments of various traits depending on the surrounding neighbourhood composition and more specifically, on the competitor functional similarity with the target species.
This study emphasises the multidimensionality of species competitive response, and also underlines the so far neglected importance of competitor species richness for trait intraspecific variability and subsequently community assembly.
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Artificial light at night (ALAN) is a pervasive form of pollution largely affecting wildlife, from individual behaviour to community structure and dynamics. As nocturnal mammals, bats are often ...adversely affected by ALAN, yet some “light-opportunistic” species exploit it by hunting insects swarming near lights. Here we used two potentially competing pipistrelle species as models, Kuhl’s (Pipistrellus kuhlii) and common (Pipistrellus pipistrellus) pipistrelles, both known to forage in artificially illuminated areas. We set our study in a mountainous area of central Italy, where only recently did the two species become syntopic. We applied spatial modelling and radiotracking to contrast potential vs. actual environmental preferences by the two pipistrelles. Species distribution models and niche analysis showed a large interspecific niche overlap, including a preference for illuminated areas, presenting a potential competition scenario. Pipistrellus pipistrellus association with ALAN, however, was weakened by adding P. kuhlii as a biotic variable to the model. Radiotracking showed that the two species segregated habitats at a small spatial scale and that P. kuhlii used artificially illuminated sites much more frequently than P. pipistrellus, despite both species potentially being streetlamp foragers. We demonstrate that ALAN influences niche segregation between two potentially competing species, confirming its pervasive effects on species and community dynamics, and provide an example of how light pollution and species’ habitat preferences may weave a tapestry of complex ecological interactions.
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•Two pipistrelles recently became syntopic in a mountain region.•We used spatial modelling and radiotracking to explore bat habitat preferences.•Models supported an interspecific competition scenario.•In the field, one bat mostly fed near streetlamps, the other often hunted in dark habitat.•Light pollution influences species interactions and niche segregation.
•Maize/pea strip intercropping is unusual as legume (i.e. pea) had the greater competitive ability.•The suitable N management system intensified the interspecific competition of pea relative to maize ...in cogrowth period.•The N management system improved the recovery growth of intercropped maize after pea was harvested.•The N management system boosted grain yield of each component crop with the N2 fixation have been greatly enhanced.•Improving coordination of interspecific competition via N management boosts system productivity in maize/pea intercropping.
Intercropping has been considered to be an effective approach for producing large quantities of grain per unit of land. Maize (Zea mays L.)/pea (Pisum sativum L.) strip intercropping may serve as a model for effectively boosting a system’s productivity. However, how intercropped pea may compete for soil N sources with intercropped maize under various levels of N availability is unknown. Here, we determined the level of interspecific competition during the pea/maize cogrowth period, N2 fixation of pea, complementary growth effect on maize, and yield responses of the two component crops. The field experiment was conducted at Wuwei Experimental Station in northwestern China from 2012 to 2014. Different N management practices were implemented in the pea/maize systems. Intercropped pea was the dominant plant, as shown by the highly positive competitive ratio (averaging 1.35) and its aggressivity (averaging 0.31) values compared with intercropped maize. Ameliorating N application in the maize/pea strip intercropping intensified the interspecific competition, improved the N2 fixation of intercropped pea and increased the complementary growth of intercropped maize. On average, the N management system with 45kgNha−1 applied as the first topdressing plus 135kgNha−1 as the third topdressing increased the competitive ratio and aggressivity by 8% and 32%, respectively; improved N2 fixation of the pea by 39%; enhanced the complementary growth of maize by 10%; and boosted the grain yield by 13% (maize) and 6% (pea) compared to the N management system with 135kgNha−1 as the first and 45kgNha−1 as the third topdressing. Significant positive correlations were found among the interspecific competition, N2 fixation, and grain yield, clearly showing that improved coordination of interspecific competition can boost system productivity in maize/pea strip intercropping.
BACKGROUND AND SCOPE: Multi-cropping approaches in production systems, where more than one crop cultivar or species are grown simultaneously, are gaining increased attention and application. Benefits ...can include increased production, effective pest, disease and weed control, and improved soil health. The effects of such practices on the range of interactions within the plant-soil system are manifest via plant interspecific competition, pest and disease attenuation, soil community composition and structure, nutrient cycling, and soil structural dynamics. Interplant diversity and competition effectively increases the nature and extent of root networks, tending to lead to more efficient resource use in time and space. Increased competitive ability at a system level, and allelopathic interactions, can reduce weed, pest and disease severity. Soil biotic communities are affected by plant diversity, which can increase abundance, diversity and activity of functional groups. Attendant rhizosphere-located processes can facilitate nutrient uptake between component crops. Whilst there are few studies into multi-cropping effects on soil structure, it is hypothesised that such processes are manifest particularly via the role which the belowground biota play in soil structural dynamics. A deeper understanding of eco-physiological processes affecting weed, pest and disease dynamics in the context of multiple cropping scenarios, and breeding cultivars to optimise mutualistic and allelopathic traits of crop mixtures could significantly increase productivity and adoption of more sustainable farming practices. CONCLUSIONS: Wider consideration needs to be given to plant: soil interactions when crop plants are grown in the context of mixtures, i.e. as communities as opposed to monotonous populations. In particular, a better understanding is required of how root systems develop in the context of mixtures and the extent to which resultant interactions with the soil biota are context-dependent. A significant challenge is that crop cultivars or production systems optimised for monocultural circumstances should not be assumed to be most suited for multi-cropping scenarios, and hence alternative strategies for developing new production systems need to take this into account.
The alpine treeline is commonly regarded as being sensitive to climatic warming because regeneration and growth of trees at treeline generally are limited by low temperature. The alpine treelines of ...the Tibetan Plateau (TP) occur at the highest elevations (4,900 m above sea level) in the Northern Hemisphere. Ongoing climatic warming is expected to shift treelines upward. Studies of treeline dynamics at regional and local scales, however, have yielded conflicting results, indicating either unchanging treeline elevations or upward shifts. To reconcile this conflict, we reconstructed in detail a century of treeline structure and tree recruitment at sites along a climatic gradient of 4 °C and mean annual rainfall of 650 mm on the eastern TP. Species interactions interacted with effects of warming on treeline and could outweigh them. Densification of shrubs just above treeline inhibited tree establishment, and slowed upward movement of treelines on a time scale of decades. Interspecific interactions are major processes controlling treeline dynamics that may account for the absence of an upward shift at some TP treelines despite continued climatic warming.
•Asymmetric mating: mating rate in the cross (Bxy♀×Bmu♂) higher than the reciprocal cross (Bxy♂×Bmu♀).•The ntr-1 plays a different role in conspecific mating behavior between the two species of ...nematodes.•The ntr-1 can regulate interspecific hybridization by nematocin-mediated signaling.
The pine-wood invasive species nematode Bursaphelenchus xylophilus causes great forestry damage globally, particularly in Eurasia. B. xylophilus can hybridize with its native sibling, Bursaphelenchus mucronatus, with whom it shares an interestingly asymmetric mating behavior. However, the molecular mechanism underlying interspecific asymmetric mating has yet to be clarified. ntr-1, a nematocin receptor gene, is involved in an oxytocin/vasopressin-like signaling system that can regulate reproduction. Structural analysis using bioinformatics revealed that both Bxy- and Bmu-ntr-1 encode 7TM-GPCR, a conserved sequence. In situ hybridization and qPCR showed that both Bxy- and Bmu-ntr-1 were highly expressed in adult nematodes. Specifically, Bxy-ntr-1 was expressed in the vulva of females and caudal gonad of males, whereas Bmu-ntr-1 was expressed in the postal vulva and uterus of females and the whole gonads of males. Furthermore, RNAi of ntr-1 further demonstrated the biological function of interspecific mating: ntr-1 can regulate mating behavior, lead to male–female specificity, and ultimately result in interspecific differences. In B. mucronatus, ntr-1 influenced male mating more than female mating success, while downregulation of ntr-1 in B. xylophilus resulted in a significant decline in the female mating rate. Competitive tests revealed that the mating rate of the cross significantly declined after downregulation of Bxy♀- and Bmu♂-ntr-1, but no obvious change occurred in the reciprocal cross. Thus, we speculate that ntr-1 may be the key factor behind interspecific asymmetric mating. The current study (1) demonstrated the regulatory function of ntr-1 on mating behavior and (2) theoretically revealed the molecular basis of interspecific asymmetric mating.
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