ABSTRACT
Animals often gather information from other species by eavesdropping on signals intended for others. We review the extent, benefits, mechanisms, and ecological and evolutionary consequences ...of eavesdropping on other species' alarm calls. Eavesdropping has been shown experimentally in about 70 vertebrate species, and can entail closely or distantly related species. The benefits of eavesdropping include prompting immediate anti‐predator responses, indirect enhancement of foraging or changed habitat use, and learning about predators. Eavesdropping on heterospecifics can provide more eyes looking for danger, complementary information to that from conspecifics, and potentially information at reduced cost. The response to heterospecific calls can be unlearned or learned. Unlearned responses occur when heterospecific calls have acoustic features similar to that used to recognize conspecific calls, or acoustic properties such as harsh sounds that prompt attention and may allow recognition or facilitate learning. Learning to recognize heterospecific alarm calls is probably essential to allow recognition of the diversity of alarm calls, but the evidence is largely indirect. The value of eavesdropping on different species is affected by problems of signal interception and the relevance of heterospecific alarm calls to the listener. These constraints on eavesdropping will affect how information flows among species and thus affect community function. Some species are ‘keystone’ information producers, while others largely seek information, and these differences probably affect the formation and function of mixed‐species groups. Eavesdroppers might also integrate alarm calls from multiple species to extract relevant and reliable information. Eavesdropping appears to set the stage for the evolution of interspecific deception and communication, and potentially affects communication within species. Overall, we now know that eavesdropping on heterospecific alarm calls is an important source of information for many species across the globe, and there are ample opportunities for research on mechanisms, fitness consequences and implications for community function and signalling evolution.
Social information obtained from heterospecifics can enhance individual fitness by reducing environmental uncertainty, making it an important driver of mixed-species grouping behavior. Heterospecific ...groups are well documented among fishes, yet are notably more prevalent among juveniles than more advanced life stages, implying that the adaptive value of joining other species is greater during this developmental period. We propose this phenomenon can be explained by the heightened ecological relevance of heterospecifically produced cues pertaining to predation risk and or resources, as body-size uniformity inherent in early ontogeny yields greater overlap in predator and prey guild membership across juveniles of disparate taxa. To evaluate the putative role of information in shaping juvenile fish assemblages, we employed a joint species distribution model (JSDM), identifying nonrandom relationships among fishes collected in 785 seine hauls within the shallow littoral zones of a subtropical island. After accounting for species–environment relationships, which explained 39% of observed covariation in the abundance of 11 taxa, we detected high rates of positive association (84% of significant correlations) predominantly between mutual foraging guild members, consistent with assemblage patterns predicted to evolve under widespread interspecific information use. Affiliations occurred primarily between species characterized by neutral (i.e., noninteracting) or negative (i.e., predator–prey) relationships in later life stages, supporting the notion that heightened niche overlap due to body size homogeneity acted to increase the pertinence of information among juveniles. Taxa exerted varying degrees of influence on assemblage structure; however Eucinostomus spp., a gregarious generalist with exceptional information-production potential, had an effect several times that of all other species combined, further evidencing the likely role of information in motivating observed relationships. Co-occurrence and qualitative behavioral data inferred from remote underwater video surveys reinforced these conclusions. Collectively, these results suggest that positive interactions linked to information exchange can be among the principal factors organizing juvenile fish assemblages at local scales, highlighting the role of ontogeny in mediating the relevance and exploitation of information across species.
Social information networks have the potential to shape the spatial structure of ecological communities by promoting the formation of mixed‐species groups. However, what actually drives social ...affinity between species in the wild will depend on the characteristics of the species available to group. Here we first present an agent‐based model that predicts trait‐related survival benefits from mixed‐species group formation in a multi‐species community and we then test the model predictions in a community‐wide field study of African savannah herbivores using multi‐layered network analysis. We reveal benefits from information transfer about predators as a key determinant of mixed‐species group formation, and that dilution benefits alone are not enough to explain patterns in interspecific sociality. The findings highlight the limitations of classical ecological approaches focusing only on direct trophic interactions when analysing community structure and suggest that declines in species occupying central social network positions, such as key informants, can have significant repercussions throughout communities.
Ecological theory has traditionally viewed community structure as the outcome of direct trophic interactions. We here combine agent‐based modelling of mixed‐species group formation with a field study of African savannah herbivores to show that also social interactions between species, such as social information use, can drive the spatial structure of communities. The study highlights that declines in species occupying central social network positions can have community‐wide repercussions.
Rising water temperatures across aquatic habitats, in the current global climate change scenario, can directly affect metabolism and food intake in fish species. This can potentially alter their ...physiological, behavioral, and shoaling properties. In the current study, we examined the effects of high temperatures on metabolism, foraging, and shoaling in tropical fish. Mixed-species (comprising flying barbs, zebrafish, and gambusia) and single-species (flying barbs and zebrafish) shoals were conditioned for 45 days to three kinds of temperature regimes: the current temperature regime (CTR), in which shoals were maintained at water temperature of 24°C (i.e., the current mean temperature of their habitat), the predicted temperature regime (PTR) at 31°C (i.e., simulating conditions projected for their habitat in 2100), and the dynamic temperature regime (DTR), which experienced daily temperature fluctuations between 24 and 31°C (i.e., resembling rapid temperature changes expected in their natural environments). We found species-specific responses to these temperature regimes. Flying barbs exhibited significantly lower body weight at PTR but maintained consistent muscle glycogen content across all temperature regimes. In contrast, zebrafish and gambusia displayed significantly elevated muscle glycogen content at PTR, with similar body weights across all three temperature regimes. Cohesion within flying barb shoals and cohesion/polarization in mixed-species shoals decreased significantly at PTR. Shoals exposed to DTR exhibited intermediate characteristics between those conditioned to CTR and PTR, suggesting that shoals may be less impacted by dynamic temperatures compared to prolonged high temperatures. This study highlights species-specific metabolic responses to temperature changes and their potential implications for larger-scale shoal properties.
Chemical signals are widespread in insects, but those resulting in interspecific communication (i.e., synomones) remain understudied. Here, we analysed chemicals left on substrates by two species of ...blow fly larvae, Lucilia sericata (Meigen) and Calliphora vomitoria (Linneaus) (Diptera: Calliphoridae), which can aggregate together on carrion. Using solid‐phase microextraction and dynamic headspace analysis, we identified six compounds common to both species: the decanoic, tetradecanoic, pentadecanoic, hexadecanoic and octadecanoic acids, and the 2‐ethylhexyl salicylate. We then tested the behavioural effects of the decanoic and pentadecanoic acids using binary‐choice experiments, along with the (Z)‐9‐tricosene, a pheromone found in many arthropods. The time spent by a larva and its average crawling speed were measured in two sides of an arena, where only one contained a compound at 0.25 or 25 μg/μl. No effect was observed when testing the decanoic acid. The pentadecanoic acid only reduced the speed of C. vomitoria larvae at 25 μg/μl. Finally, L. sericata larvae spent less time in the side containing the (Z)‐9‐tricosene at 0.25 μg/μl, whereas C. vomitoria spent more time and crawled faster in this side at 25 μg/μl. Although these results did not directly evidence synomones, they suggest that the (Z)‐9‐tricosene could regulate larval aggregations on carrion.
Chemical analyses of two necrophagous flies revealed six shared compounds (mainly acids) deposited on substrate by larvae. Synomone activity was experimented using behavioural tests on both species. Shared acids only slightly influence larval behaviour, while another candidate compound ((Z)‐9‐tricosene) was either retentive for Calliphora vomitoria or repulsive for Lucilia sericata depending on concentrations. The retentive effect of the (Z)‐9‐tricosene suggests that this well‐known pheromone in arthropods (also presents in C. vicina) could act as a synomone in blow flies, eliciting interspecific aggregation.
Animals acquire information produced by other species to reduce uncertainty and avoid predators. Mixed‐species flocks (MSFs) of birds are ubiquitous in forest ecosystems and structured, in part, ...around interspecific information transfer, with “nuclear” species providing information that other species eavesdrop on. We hypothesized that in a seasonal tropical forest, the amount of information produced by birds about predation would be dynamic and particularly would decrease inside MSFs when the nuclear species leave MSFs to breed. We obtained baseline information on MSF encounter rate and species composition along established sampling routes over 9 months near the Sino‐Vietnamese border. We also conducted three experiments to quantify information produced by different species in response to typical predator encounters, including a moving predator stimulus presented inside of MSFs, and a stationary predator model presented both inside and outside of MSFs. MSFs were much less frequent in the breeding season with fewer individuals of the nuclear species, David's Fulvetta (Alcippe davidi), participating, though the diversity of other species remained stable. Fulvettas were the dominant producer of alarm‐related information both to the moving and stationary stimuli in MSFs and were also among the most active mobbers to stimuli presented outside of MSFs. In the breeding season, they tended to call less to the moving stimulus, and substantially fewer individuals responded to the in‐flock stationary stimulus. Other species increased their own information production at stationary predator stimuli (inside and outside of MSFs) during the breeding season, perhaps due to their increased investment in offspring during this time. Yet even during the breeding season, David's Fulvetta remained the highest producer of information about predators in MSFs. Hence, while we show that information production in MSFs can be somewhat dynamic, we describe a continually asymmetric communication system, in which a nuclear species is important to the whole community.
On the northern border of the tropics, we studied the seasonality of mixed‐species bird flocks and vocal information production, in response to a moving object in flocks (hawk‐flock), an owl model in flocks (mob‐flock), and the same model outside of flocks (mob). We found information from the nuclear species, David's Fulvetta (DAFU), tended to decrease in the breeding season in hawk‐flock experiments, and there were fewer responding individuals in mob‐flock experiments. In contrast, there were more species (other than DAFU) that responded during the breeding season in the mob‐flock experiment, and these species produced more information in the mob experiment.
Dominance interactions and hierarchies are of long-standing interest in the field of animal behaviour. Currently, dominance hierarchies are viewed as complex social structures formed by repeated ...interactions between individuals. Most studies on this phenomenon come from single-species groups. However, animals are constantly surrounded by and interact with individuals of other species. Behaviour and social interactions of individuals can be shaped by the presence or behaviour of other species in their social ecosystem, which has important implications for social behaviour in groups. Given how ubiquitous mixed-species animal groups are, deeper study of the relationships between mixed-species group (MSG) structure and dominance will be key to understanding constraints on individual behaviour and decision making. Here we call for more research into dominance interactions among individuals in MSGs. Greater understanding of the dynamics of dominance relationships among individuals in MSGs, whose size and composition can change considerably over shorter and longer term time frames, will be crucial to understanding their structure and functioning. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.
ABSTRACT
Throughout many regions of the tropics, non‐primate animals – mainly birds and mammals – have been observed to follow primate groups and to exploit dropped food and flushed prey. The ...anecdotal nature of most of the numerous reports on these primate–non‐primate associations (PNPAs) may obscure the biological significance of such associations. We review the existing literature and test predictions concerning the influence of primate traits (body size, activity patterns, dietary strategies, habitat, group size) on the occurrence of PNPAs. Furthermore, we examine the influence of non‐primates' dietary strategies on the occurrence of PNPAs, and the distribution of benefits and costs. We detected a strong signal in the geographic distribution of PNPAs, with a larger number of such associations in the Neotropics compared to Africa and Asia. Madagascar lacks PNPAs altogether. Primate body size, activity patterns, habitat and dietary strategies as well as non‐primate dietary strategies affect the occurrence of PNPAs, while primate group size did not play a role. Benefits are asymmetrically distributed and mainly accrue to non‐primates. They consist of foraging benefits through the consumption of dropped leaves and fruits and flushed prey, and anti‐predation benefits through eavesdropping on primate alarm calls and vigilance. Where quantitative information is available, it has been shown that benefits for non‐primates can be substantial. The majority of PNPAs can thus be categorized as cases of commensalism, while mutualism is very rare. Our review provides evidence that the ecological function of primates extends beyond their manifold interactions with plants, but may remain underestimated.
Animals gathered around a specific location or resource may represent mixed-species aggregations or mixed-species groups. Patterns of individuals choosing to join these groups can provide insight ...into the information processing underlying these decisions. However, we still have little understanding of how much information these decisions are based upon. We used data on 12 parrot species to test what kind of information each species may use about others to make decisions about which mixed-species aggregations to participate in. We used co-presence and joining patterns with categorization and model fitting methods to test how these species could be making grouping decisions. Species generally used a simpler lower-category method to choose which other individuals to associate with, rather than basing these decisions on species-level information. We also found that the best-fit models for decision-making differed across the 12 species and included different kinds of information. We found that not only does this approach provide a framework to test hypotheses about why individuals join or leave mixed-species aggregations, it also provides insight into what features each parrot could have been using to make their decisions. While not exhaustive, this approach provides a novel examination of the potential features that species could use to make grouping decisions and could provide a link to the perceptive and cognitive abilities of the animals making these minute-by-minute decisions. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.
Larvae of several blowfly species grow on carcasses and actively aggregate together. They face harsh developmental conditions resulting in a strong pressure to reduce development time: this is ...achieved either through thermoregulation or aggregation. We investigate how these two developmental strategies are modulated within heterospecific groups. In a first experiment, larvae of two species with different thermal requirements were deposited simultaneously on a thermal gradient. This resulted in the formation of two monospecific groups, each located at the species-specific thermal preferendum. However, when
(Linnaeus) larvae were placed first, the later arriving
(Meigen) larvae attracted the whole group to its own thermal preferendum. In the reverse experiment, half of the replicates resulted in single dense heterospecific groups observed at temperatures ranging from
to
preferendum. The other half of the replicates resulted in loose groups spread out on the thermal gradient. These results highlight the emergence of collective decisions ranging from thermal optimization to heterospecific aggregation at suboptimal temperatures. They demonstrate that species settlement order strongly affects self-organization processes and mixed-species group formation. We conclude that thermal optimization and heterospecific niche construction are two developmental strategies of carrion fly larvae. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.
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