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Behavioural traits are key to promote invasion success because they are easier to adjust to changing environmental conditions than morphological or life history traits. Often, research has overlooked variance in behavioural traits within populations or has assumed it to be mere noise. However, a recent focus towards individual variation of behaviour of successful invaders has revealed new and more profound insights into the invasion process. Behavioural variation within a population could lead to more successful invasions, as they include individuals with diverse behaviours, which ensures at least some individuals could be able to cope with changing conditions. The aim of this research was to examine if invasive guppies (Poecilia reticulata) present within-population differences in their sociability (time spent associating with a shoal) when interacting with conspecifics or heterospecifics. Guppies presented significant differences in their individual tendencies to associate with conspecific or heterospecific shoals. There were among-individual differences in the time spent shoaling with conspecifics versus heterospecifics, where most individuals did not differ in their sociability with conspecifics or heterospecifics, and only 22% of individuals presented a higher tendency to associate with conspecifics. Our results are the first to show individual differences in fish' tendencies to associate with heterospecifics among individuals of the same population and rearing conditions. Given that associations with heterospecific natives have been found to be as beneficial as associations with conspecifics for invaders, our results contribute to the understanding of mechanisms behind heterospecific sociability between natives and invaders.

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Many species often show male-male combat for mating opportunities and resources within the species. Sexual selection through this radical combat leads to the evolution of males with exaggerated traits used as weapons, such as horns or mandibles, that often result in victory during combat. However, heterospecific interaction due to errors in species identification has often been observed, which results in decreased mating opportunities within the same species and fewer fertilized eggs. Males with exaggerated weapons may show dominance in resource acquisition over males without weapons and may decrease the reproductive success of the latter due to competition between the two. However, few studies have examined heterospecific interaction focusing on males with or without weapons. In this study, we investigated the effects of the male weapon on reproductive traits in heterospecific interaction in two species: the broad-horned flour beetle (Gnatocerus cornutus), in which males have exaggerated weapon traits; and the red flour beetle (Tribolium castaneum), in which males have no weapon traits. Both species are closely related and use the same food resources. G. cornutus males interfered with the resource acquisition and reproductive opportunities of T. castaneum by attacking T. castaneum. The reproductive success of T. castaneum decreased when they cohabited with G. cornutus males. These findings show that male weapon traits, which are important for sexual selection within the same species, can also greatly influence reproduction in other species.

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Hybridization plays a significant role in biological evolution. However, it is not clear whether ecological contingency differentially influences likelihood of hybridization, particularly at ecological margins where parental species may exhibit reduced fitnesses. Moreover, it is unknown whether future ecosystem change will increase the prevalence of hybridization. Ficus heterostyla and F. squamosa are closely related species co-distributed from southern Thailand to southwest China where hybridization, yielding viable seeds, has been documented. As a robust test of ecological factors driving hybridization, we investigated spatial hybridization signatures based on nuclear microsatellites from extensive population sampling across a widespread contact range. Both species showed high population differentiation and strong patterns of isolation by distance. Admixture estimates exposed asymmetric interspecific gene flow. Signatures of hybridization increase significantly towards higher latitude zones, peaking at the northern climatic margins. Geographic variation in reproductive phenology combined with ecologically challenging marginal habitats may promote this phenomenon. Our work is a first systematic evaluation of such patterns in a comprehensive, latitudinally-based clinal context, and indicates that tendency to hybridize appears strongly influenced by environmental conditions. Moreover, that future climate change scenarios will likely alter and possibly augment cases of hybridization at ecosystem scales.

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The mutualistic network of plant-pollinator also involves interspecific pollination caused by pollinator sharing. Plant-pollinator networks are commonly based on flower visit observations, which may not adequately represent the actual pollen transfer between co-flowering plant species. Here, we compared the network structure of plant-pollinator interactions based on flower visits (FV) and pollen loads (PL) on the bodies of pollinators and tested how the degree of pollinator sharing in the two networks affected heterospecific pollen transfer (HPT) between plant species in a subalpine meadow. The FV and PL networks were largely overlapped. PL network included more links than FV network. The positions of plant and pollinator species in the FV and PL networks were positively correlated, indicating that both networks could detect major plant-pollinator interactions. The degree of pollinator sharing, based on either the FV or the PL network, positively influenced the amount of heterospecific pollen transferred between plant species pairs. However, the degree of pollinator sharing had a low overall explanatory power for HPT, and the explanatory powers of the FV and PL networks were similar. Overall, our study highlights the importance of FV and PL for understanding the drivers and outcomes of plant-pollinator interactions, as well as their relevance to HPT.

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Background: Like many cockroaches, Argentinian wood roaches, Blaptica dubia, prefer darker shelters over lighter shelters. In three experiments, we asked whether chemical cues from other roaches might influence shelter choice, a process known as conspecific or heterospecific cueing, depending on whether the cues come from an individual of the same or a different species, respectively. Methods: Each experiment involved trials with focal B. dubia cockroaches in testing arenas containing plastic shelters of varying levels of darkness, with filter paper under each shelter acting as a carrier for chemical cues. In Experiment 1, we tested female and male B. dubia cockroaches with two shelters matched for darkness but differing in cues (conspecific vs. none). The shelter with no cue contained a blank filter paper as a control. In Experiment 2 (conspecific cueing) and Experiment 3 (heterospecific cueing), we tested B. dubia cockroach choices for lighter or darker shelters with filter papers containing chemical cues of other roaches or no chemical cues. For the conspecific cueing study of Experiment 2, we used chemical cues from other B. dubia cockroaches. In contrast, for the heterospecific cueing study of Experiment 3, we used chemical cues from a different species, the death's head cockroach, Blaberus craniifer. Results: In Experiment 1, B. dubia cockroaches overwhelmingly preferred shelters with conspecific chemical cues over darkness-matched shelters without cues. In Experiments 2 and 3, they strongly preferred darker shelters, especially when chemical cues were present. Additionally, they were more likely to be under the lighter shelter when chemical cues were present there. These results reveal that the public information B. dubia cockroaches gain from chemical cues-including those from other species-can drive shelter choices in this species.

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Heterospecific pollen (HP) deposition varies widely among species in communities, which has been explicated by two adaptation strategies: HP avoidance and HP tolerance. Studies of the plant-pollinator network have uncovered that oceanic island communities are highly generalized and strongly connected. It remains unclear, however, which strategy prevails in such communities. We examined stigma pollen deposition on 29 plant species, and assessed patterns of HP load size and diversity in the Yongxing Island community. We assessed the effects of phenotypic specialization and species-level network structural properties of plant species on pollen deposition among species. The hypothesis of three accrual patterns of HP within species was tested by illustrating the relationship between conspecific pollen (CP) and HP receipt. Extensive variation occurred among species in HP receipt, while 75.9% of species received less than 10% HP and one species received more than 40% HP throughout the community. Flower size strongly drives the variation of HP receipt, while network structural properties had no effect on the pollen receipt. Nineteen species showed no relationship between the number of HP and CP loads, and they received smaller HP load sizes and lower HP proportions. Most plant species evolved HP avoidance strategy, and HP receipt was an occasional event for most plant species in the generalized community. HP and CP receipts are independent of each other in plant species with the HP avoidance mechanism. Our results highlight that plants in the generalized pollination system may preferentially select to minimize the HP load on stigmas.

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Many vertebrates eavesdrop on alarm calls of other species, as well as responding to their own species' calls, but eavesdropping on heterospecific alarm calls might be harder than conspecific reception when environmental conditions make perception or recognition of calls difficult. This could occur because individuals lack hearing specializations for heterospecific calls, have less familiarity with them, or require more details of call structure to identify calls they have learned to recognize. We used a field playback experiment to provide a direct test of whether noise, as an environmental perceptual challenge, reduces response to heterospecific compared to conspecific alarm calls. We broadcast superb fairy-wren (Malurus cyaneus) and white-browed scrubwren (Sericornis frontalis) flee alarm calls to each species with or without simultaneous broadcast of ambient noise. Using two species allows isolation of the challenge of heterospecific eavesdropping independently of any effect of call structure on acoustic masking. As predicted, birds were less likely to flee to heterospecific than conspecific alarm calls during noise. We conclude that eavesdropping was harder in noise, which means that noise could disrupt information on danger in natural eavesdropping webs and so compromise survival. This is particularly significant in a world with increasing anthropogenic noise.

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Interspecific information flow is known to affect individual fitness, population dynamics and community assembly, but there has been less study of how species diversity affects information flow and thereby ecosystem functioning and services. We address this question by first examining differences among species in the sensitivity, accuracy, transmissibility, detectability and value of the cues and signals they produce, and in how they receive, store and use information derived from heterospecifics. We then review how interspecific information flow occurs in communities, involving a diversity of species and sensory modes, and how this flow can affect ecosystem-level functions, such as decomposition, seed dispersal or algae removal on coral reefs. We highlight evidence that some keystone species are particularly critical as a source of information used by eavesdroppers, and so have a disproportionate effect on information flow. Such keystone species include community informants producing signals, particularly about predation risk, that influence other species' landscapes of fear, and aggregation initiators creating cues or signals about resources. We suggest that the presence of keystone species means that there will likely be a positive relationship in many communities between species diversity and information through a 'sampling effect', in which larger pools of species are more likely to include the keystone species by chance. We then consider whether the number and relative abundance of species, irrespective of the presence of keystone species, matter to interspecific information flow; on this issue, the theory is less developed, and the evidence scant and indirect. Higher diversity could increase the quantity or quality of information that is used by eavesdroppers because redundancy increases the reliability of information or because the species provide complementary information. Alternatively, there could be a lack of a relationship between species diversity and information if there is widespread information parasitism where users are not sources, or if information sourced from heterospecifics is of lower value than that gained personally or sourced from conspecifics. Recent research suggests that species diversity does have information-modulated community and ecosystem consequences, especially in birds, such as the diversity of species at feeders increasing resource exploitation, or the number of imitated species increasing responses to vocal mimics. A first step for future research includes comprehensive observations of information flow among different taxa and habitats. Then studies should investigate whether species diversity influences the cumulative quality or quantity of information at the community level, and consequently ecosystem-level processes. An applied objective is to conserve species in part for their value as sources of information for other species, including for humans.

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The dynamics and processes underlying the codiversification of plant-pollinator interactions are of great interest to researchers of biodiversity and evolution. Cospeciation is generally considered a key process driving the diversity of figs and their pollinating wasps. Groups of closely related figs pollinated by separate wasps occur frequently and represent excellent opportunities to study ongoing diversification in this textbook mutualism. We study two closely related sympatric dioecious figs (Ficus heterostyla and Ficus squamosa) in Xishuangbanna, southwest China, and aim to document what is likely to be the final stages of speciation between these species using a combination of trait data and experimental manipulation. Volatile profiles at the receptive phase, crucial for attracting pollinators, were analyzed. In total, 37 and 29 volatile compounds were identified from receptive F. heterostyla and F. squamosa figs, respectively. Despite significant interspecific dissimilarity, 25 compounds were shared. Ovipositor lengths lie well within range required for access to heterospecific ovules, facilitating hybridization. Cross introduction of wasps into figs was conducted and hybrid seeds were generated for all donor/recipient combinations. F. heterostyla wasps produce adult offspring in F. squamosa figs. While F. squamosa wasps induce gall development in F. heterostyla figs and their offspring fail to mature in synchrony with their novel host. We record limited geographic barriers, minimal volatile dissimilarity, compatible morphology, complementary reproductive phenologies, and the production of hybrid seeds and wasp offspring. These findings suggest ongoing wasp specialization and reproductive isolation, potentially applicable to other related fig species.

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Reproductive isolation is conferred by several barriers that occur at different stages of reproduction. Comprehensive reviews on the topic have identified that barriers occurring prior to zygote formation are often stronger than those that occur afterward. However, the overrepresentation of temperate perennial herbs in the current literature precludes any generalization of this pattern to plants that present other life forms and patterns of distribution. Here, we assessed reproductive isolation barriers and their absolute contribution to reproductive isolation and asymmetry in Cnidoscolus aconitifolius and C. souzae, two closely related tropical shrub species that co-occur on the Yucatan peninsula. The reproductive barriers assessed were phenological mismatch, pollinator differentiation, pollen-pistil incompatibility (three pre-zygotic barriers), fruit set failure, and seed unviability (post-zygotic barriers). Reproductive isolation between the study species was found to be complete in the direction C. aconitifolius to C. souzae, but only partial in the opposite direction. One post-zygotic barrier was the strongest example. Most barriers, particularly the pre-zygotic examples, were asymmetrical and predicted the direction of heterospecific pollen flow and hybrid formation from C. souzae to C. aconitifolius. Both parental species, as well as the hybrids, were diploid and had a chromosome number 2n = 36. More studies with tropical woody perennials are required to fully determine whether this group of plants consistently shows stronger post-zygotic barriers.

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MAIN CONCLUSION: This work mainly found that the stigma and style of Q. variabilis did not completely lose the specific recognition towards heterologous pollen, a fact which is different from previous studies. Quercus is the foundation species in the Northern Hemisphere, with extreme prevalence for interspecific hybridization. It is not yet entirely understood whether or how the pollen tube-female tissue interaction contributes to the "extensive hybridization" in oaks. Pollen storage conditions correlate with distant hybridization. We conducted hybridization experiments with Q. variabilis as female and Q. variabilis and Q. mongolica as male parents. And the differences in pollen tube (PT) development between intra- and distant interspecific hybridization were studied by fluorescence microscopy and scanning electron microscopy (SEM). Our results showed that -20 °C allowed pollen of both species to maintain some viability. Both Q. variabilis and Q. mongolica pollen germinated profusely on the stigmas. SEM results indicated that in the intraspecific hybridization, Q. variabilis pollen started to germinate at 6 h after pollination (hap), PTs elongated significantly at 12 hap, and entered the stigma at 24 hap. By contrast, Q. mongolica pollen germinated at 15 hap, and the PTs entered the stigma at 27 hap. By fluorescence microscopical studies it was observed that some PTs of Q. variabilis gathered at the style-joining at 96 hap, unlike the Q. mongolica which reached the style junction at 144 hap. The above results indicate that the abundant germination of heterologous pollen (HP) on the stigma and the "Feeble specificity recognition" of the stigma and transmitting tract to HP may create opportunities for the "extensive hybridization" of oaks. This work provides a sexual developmental reference for clarifying the causes of Quercus "extensive hybridization".

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Alarm signals have evolved to communicate pertinent threats to conspecifics, but heterospecifics may also use alarm calls to obtain social information. In birds, mixed-species flocks are often structured around focal sentinel species, which produce reliable alarm calls that inform eavesdropping heterospecifics about predation risk. Prior research has shown that Neotropical species innately recognize the alarm calls of a Nearctic sentinel species, but it remains unclear how generalizable or consistent such innate signal recognition of alarm-calling species is. We tested for the responses to the alarm calls of a Neotropical sentinel forest bird species, the dusky-throated antshrike (Thamnomanes ardesiacus), by naive resident temperate forest birds across three continents during the winter season. At all three sites, we found that approaches to the Neotropical antshrike alarm calls were similarly frequent to the alarm calls of a local parid sentinel species (positive control), while approaches to the antshrike's songs and to non-threatening columbid calls (negative controls) occurred significantly less often. Although we only tested one sentinel species, our findings indicate that temperate forest birds can recognize and adaptively respond globally to a foreign and unfamiliar tropical alarm call, and suggest that some avian alarm calls transcend phylogenetic histories and individual ecological experiences.

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AbstractAnimals as diverse as cephalopods, insects, fish, and mammals signal social dominance to conspecifics to avoid costly fights. Even though between-species fights may be equally costly, the extent to which dominance signals are used between species is unknown. Here, we test the hypothesis that differences in color are associated with dominance between closely related species that aggressively interact over resources, examining between-species variation in colors that are used in within-species badges of status (black, white, and carotenoid coloration) in a comparative analysis of diverse species of birds. We found that dominant species have more black, on average, than subordinate species, particularly in regions important for aggressive signaling (face, throat, and bill). Furthermore, dominant species were more likely to have more black in comparisons in which the dominant species was similar in size or smaller than the subordinate, suggesting that black may be a more important signal when other signals of dominance (size) are missing. Carotenoid colors (i.e., red, pink, orange, and yellow) were not generally associated with dominance but may signal dominance in some taxonomic groups. White may have opposing functions: white was associated with dominance in species in which black was also associated with dominance but was associated with subordinance in species in which carotenoid-based dominance signals may be used. Overall, these results provide new evidence that colors may function broadly as signals of dominance among competing species. Such signals could help to mediate aggressive interactions among species, thereby reducing some costs of co-occurrence and facilitating coexistence in nature.

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Controlled experiments at the level of individual plants show that legume species use different strategies for the regulation of symbiotic dinitrogen fixation in response to nitrogen availability. These strategies were suggested to improve legume fitness in the context of the plant community, although rarely studied at this level. We evaluated how nitrogen availability and conspecific vs heterospecific interactions influenced the strategy of regulation of nitrogen fixation. We grew two species of herbaceous legumes representing two different strategies of regulation without interaction, under treatments of deficient and sufficient nitrogen availability, with conspecific or heterospecific interaction. We found that Hymenocarpus circinnatus maintained a facultative strategy of downregulating nitrogen fixation when nitrogen was available under both con- and heterospecific interactions, as was also found for this species when grown alone. Vicia palaestina also downregulated nitrogen fixation under both con- and heterospecific interactions but did not regulate fixation when grown alone. Our results showed that under nitrogen limitation, interaction with a neighboring plant reduced fitness, reflecting a competitive effect. Our findings suggest that when interacting with other plants, downregulation of nitrogen fixation is more likely, therefore reducing the energetic cost of fixation, and improving plant performance in competitive ecological communities, especially when nitrogen is available.

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After an overview of the discussion about the existence of intra- and interspecific competition that illustrates the contradictory opinions I conclude that long-term field experiments are needed for firm conclusions. I discuss in some detail the role of two factors that limit population size of secondary cavity nesting birds e.g. territorial behavior and adequate cavities. This is followed by an overview of experimental long-term field studies in Belgium showing that intra- and interspecific competition in a great tit-blue tit system exists. By using nestbox configurations with high densities of nestboxes that differ in the diameter of their entrance hole in replicate study plots it is possible to manipulate the breeding densities of great tit Parus major and blue tit Cyanistes caeruleus independently, thereby varying the intensity of intra- and interspecific competition between these two coexisting species. When blue tit densities are experimentally increased local recruitment of great tits increases, and adult great tit post-breeding dispersal to other study plots decreases, implying that great tits use blue tit density to evaluate habitat quality and that high blue tit density results in heterospecific attraction. The reverse is not true. An experimental increase in great tit density leading to an increase in interspecific competition in a plot where blue tit density was already high leads to a decrease in blue tit nestling mass (illustrating interspecific competition for food), but to a gradual increase in blue tit body size. Both are primarily caused by an increase in the body size of immigrants (caused by intraspecific competition for protected roosting holes) in contrast to the control plot, where neither is observed. I also summarize behavioral, ecological and possible evolutionary effects of sparrowhawks on blue tits after sparrowhawks settled in an isolated study plot halfway through the study: adult survival substantially decreased for both sexes, but more for females that laid large clutches, leading to selection for females that laid a smaller clutch. This led to a change in the reproduction/survival life-history trade-off. Adult winter weights and nestling weights decreased, and the heaviest fledglings were selected against. Furthermore the frequency of polygyny increased. The long-term experiments also document the role of the use of public information and that species that compete can be attracted to sites in which competitor density is high.

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Invasive species and chemical pollution both threaten biodiversity. Here, we discuss how pollution, through its impacts on wildlife behaviour, shapes invasion dynamics by altering species interactions. Addressing knowledge gaps will have implications for the management of invasive species and conservation of native ecosystems in an increasingly toxic world.

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Research from terrestrial communities shows that diminished predation risk is a principal driver of heterospecific grouping behavior, with foraging ecology predicting the roles that species play in groups, as more vulnerable foragers preferentially join more vigilant ones from whom they can benefit. Meanwhile, field studies examining the adaptive significance of heterospecific shoaling among marine fish have focused disproportionately on feeding advantages such as scrounging or prey-flushing. Juvenile bonefish (Albula vulpes) occur almost exclusively among mojarras (Eucinostomus spp.) and even elect to join them over conspecifics, suggesting they benefit from doing so. We evaluated the roles of risk-related and food-related factors in motivating this pattern of affiliation, estimating: (1) the relative levels of risk associated with each species' search and prey capture activities, via behavioral vulnerability traits discerned from in situ video of heterospecific shoals, and (2) resource use redundancy, using stable isotopes (δ13C, δ15N, and δ34S) to quantify niche overlap. Across four distinct metrics, bonefish behaviors implied a markedly greater level of risk than those of mojarras, typified by higher activity levels and a reduced capacity for overt vigilance; consistent with expectations if their association conformed to patterns of joining observed in terrestrial habitats. Resource use overlap inferred from stable isotopes was low, indicating that the two species partitioned resources and making it unlikely that bonefish derived substantive food-related benefits. Collectively, these findings suggest that the attraction of juvenile bonefish to mojarras is motivated primarily by antipredator advantages, which may include the exploitation of risk-related social cues.

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Pollen plays a key role in plant reproductive biology. Despite the long history of research on pollen and pollination, recent advances in pollen-tracking methods and statistical approaches to linking plant phenotype, pollination performance, and reproductive fitness yield a steady flow of exciting new insights. In this introduction to the Special Issue "Pollen as the Link Between Phenotype and Fitness," we start by describing a general conceptual model linking functional classes of floral phenotypic traits to pollination-related performance metrics and reproductive fitness. We use this model as a framework for synthesizing the relevant literature, highlighting the studies included in the Special Issue, and identifying gaps in our understanding and opportunities for further development of the field. The papers that follow in this Special Issue provide new insights into the relationships between pollen production, presentation, flower morphology, and pollination performance (e.g., pollen deposition onto stigmas), the role of pollinators in pollen transfer, and the consequences of heterospecific pollen deposition. Several of the studies demonstrate exciting experimental and analytical approaches that should pave the way for continued work addressing the intriguing role of pollen in linking plant phenotypes to reproductive fitness.

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Few species play socially with another species, hereafter called interspecific social play (ISP). ISP involves reading and responding appropriately to social cues of other species, often taxonomically remote, and has implications for perception, communication, and cognition. We reviewed information on non-human ISP from both print media and videos from YouTube and Reddit. We found over 200 instances of ISP. The literature predominantly featured wild primates, carnivores, and marine mammals. Carnivores and terrestrial ungulates were common in videos. ISP in avian and reptile species were found in both sources, including instances of playing with mammals. Animals may engage in ISP because it is risky and stimulating, they lack age-appropriate conspecifics, the play motivation is high, or to maintain social bonds in mixed-species groups. Cataloguing ISP uncovers which species are interacting and how. Systematic studies of ISP are difficult and many reports are brief and anecdotal. Minimally, future research should record information about each observation, including the age, sex, and history of participants.

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