Asymmetric interspecific aggression in New Guinean songbirds that replace one another along an elevational gradient

A common pattern in tropical avifaunas is for closely related species to inhabit largely parapatric elevational distributions such that they replace one another along the elevational gradient. A long‐standing hypothesis for this pattern is that parapatry is maintained by interspecific interference competition mediated by interspecific aggression. However, empirical tests of this hypothesis remain scarce. We used reciprocal playback experiments to measure interspecific aggression in five species‐pairs of New Guinean passerine elevational replacements. We found evidence of interspecific aggression in three species‐pairs. In these three cases, interspecific aggression was asymmetric, with the lower elevation species more aggressive towards the upper elevation species than vice versa. Two patterns suggest that this interspecific aggression is a learned response to the presence of a heterospecific competitor rather than misdirected intraspecific aggression or an evolved response to a competitor. First, when present, interspecific aggression was always strongest at the upper elevation range margin of the lower elevation species (i.e. in the elevational zone in which the two species were found in close proximity and thus interacted with each other), and diminished over very short distances away from this zone. Secondly, the two species‐pairs that did not exhibit interspecific aggression had narrow ‘no man's land’ gaps between their elevational distributions such that heterospecifics did not encounter one another, possibly explaining the lack of interspecific aggression in these examples. Our results support the hypothesis that interspecific aggression is one factor influencing elevational limits in species‐pairs of New Guinean elevational replacements.     

Aggression and Gause's law in ants

ABSTRACT. Myrmica rubra societies were faced with intruders of the following species: M.rubra, M.sabuleti, Tetramorium caespitum, Lasius flavus and L.niger. The aggression of the resident workers was quantified by frequencies of mandible openings, seizings and gaster flexings. Intraspecific aggression was lower than interspecific, and it is suggested that this might be due to the polygynous behaviour of M.rubra. There was no simple relationship between the intensity of aggression and the taxonomic remoteness of the intruder species. Differences in the levels of the aggressive response need to be better understood by analysis of the eco-ethological interrelations of the species concerned.     

Reproductive interference explains persistence of aggression between species

Interspecific territoriality occurs when individuals of different species fight over space, and may arise spontaneously when populations of closely related territorial species first come into contact. But defence of space is costly, and unless the benefits of excluding heterospecifics exceed the costs, natural selection should favour divergence in competitor recognition until the species no longer interact aggressively. Ordinarily males of different species do not compete for mates, but when males cannot distinguish females of sympatric species, females may effectively become a shared resource. We model how reproductive interference caused by undiscriminating males can prevent interspecific divergence, or even cause convergence, in traits used to recognize competitors. We then test the model in a genus of visually orienting insects and show that, as predicted by the model, differences between species pairs in the level of reproductive interference, which is causally related to species differences in female coloration, are strongly predictive of the current level of interspecific aggression. Interspecific reproductive interference is very common and we discuss how it may account for the persistence of interspecific aggression in many taxonomic groups.     

Attempted Integration of Multiple Species of Turaco Into a Mixed‐Species Aviary

Mixed‐species exhibits offer a variety of benefits but can be challenging to maintain due to difficulty in managing interspecific interactions. This is particularly true when little has been documented on the behavior of the species being mixed. This was the case when we attempted to house three species of turaco (family: Musophagidae) together with other species in a walk‐through aviary. To learn more about the behavior of great blue turacos, violaceous turacos, and white‐bellied gray go‐away birds, we supplemented opportunistic keeper observations with systematic data collection on their behavior, location, distance from other birds, and visibility to visitors. Keepers reported high levels of aggression among turacos, usually initiated by a go‐away bird or a violaceous turaco. Most aggression occurred during feedings or when pairs were defending nest sites. Attempts to reduce aggression by temporarily removing birds to holding areas and reintroducing them days later were ineffective. Systematic data collection revealed increased social behavior, including aggression, during breeding season in the violaceous turacos, as well as greater location fidelity. These behavioral cues may be useful in predicting breeding behavior in the future. Ultimately, we were only able to house three species of turaco together for a short time, and prohibitively high levels of conflict occurred when pairs were breeding. We conclude that mixing these three turaco species is challenging and may not be the most appropriate housing situation for them, particularly during breeding season. However, changes in turaco species composition, sex composition, or exhibit design may result in more compatible mixed‐turaco species groups. Zoo Biol. 32:216–221, 2013. © 2012 Wiley Periodicals, Inc.     

Interspecific aggressive behaviour by long-toed lapwings (Vanellus crassirostris)

In this paper interspecific aggression is related to ecological relationships between bird species. Three kinds of relationships are distinguished according to the presence or absence of aggression and the degree to which resources are exclusively utilized: interspecific territoriality (aggression, exclusive use), partial exclusion (aggression, no exclusive use), and tolerance (no aggression, no exclusive use). Aggression by long-toed lapwings (Vanellus crassirostris) is examined within this framework, using quantitative data gathered through observational sampling. Lapwings were interspecifically territorial with one species, partially excluded five species, and tolerated four species. The results indicate that the function of interspecific aggressive behaviour may be related to competition, predation, or both.     

Environmental filtering and taxonomic relatedness underlie the species richness–evenness relationship

We examined the relationship between species richness (S) and evenness (J) within a novel, community assembly framework. We hypothesized that environmental stress leads to filtering (increasing the proportional abundance of tolerant species) and taxonomic dispersion (decreasing the number of species within genera and families). Environmental filtering would cause a decline in S by eliminating some stress-sensitive species and a reduction of J by allowing only tolerant species to maintain large populations. Taxonomic relatedness may influence both S and J by controlling the nature of interspecific interactions—positive under taxonomic dispersion versus negative under taxonomic clustering. Therefore, the S–J relationship may be a product of environmental filtering and taxonomic relatedness. We tested this framework with redundancy analyses and structural equation models using continental stream diatom and fish data. We confirmed that (i) environmental stress, defined by watershed forest cover, slope, and temperature, caused filtering (lower sensitive:tolerant species abundance ratios) and taxonomic dispersion (elevated genus:species richness and family:species richness ratios); (ii) S and J, which declined with filtering and taxonomic dispersion, exhibited a positive relationship; and (iii) the role of filtering on J was pronounced only under stressful conditions, while taxonomic dispersion remained an important predictor of J across stressful and favorable environments.     

Habitat selection and aggression as determinants of spatial segregation among damselfish on a coral reef

Adults of many closely related coral reef fish species are segregated along gradients of depth or habitat structure. Both habitat selection by new settlers and subsequent competitive interactions can potentially produce such patterns, but their relative importance is unclear. This study examines the potential roles of habitat selection and aggression in determining the spatial distribution of adults and juveniles of four highly aggressive damselfishes at Lizard Island, northern Great Barrier Reef. Dischistodus perspicillatus, D. prosopotaenia, D. melanotus, and D. pseudochrysopoecilus maintain almost non-overlapping distributions across reef zones, with adults of one species dominating each reef zone. Juveniles exhibit slightly broader distributional patterns suggesting that subsequent interactions reduce overlap among species. Although habitat choice experiments in aquaria suggest that associations between juveniles and substrata types in the field are partly due to habitat selection, large overlaps in the use of substrata by the different species were also found, suggesting that substratum selection alone is insufficient in explaining the discrete spatial distributions of adults. The strength of aggressive interactions among all four species was tested by a "bottle" experiment, in which an adult or juvenile of each species was placed in the territories of adult fish on the reef. The greatest levels of interspecific aggression were directed against adults and juveniles of neighbouring species. The highest levels of aggression were associated with species exhibiting the greatest levels of overlap in resource use. Evidently both habitat selection and interspecific aggression combine to determine the adult distributions of these species.     

Conservation unit status inferred for plants by combining interspecific crosses and AFLP

Hybridization and introgression are common in plants and lead to morphological similarity between species and taxonomic confusion. This gene flow with closely related species can complicate efforts to determine whether an endangered taxon is evolutionarily distinctive and should be identified as a separate conservation unit. Potentilla delphinensis is a rare and threatened endemic species of the Southern French Alps. Two common related taxa (P. grandiflora and P. thuringiaca) are morphologically similar and occur in the same geographical locations. Thus, whether P. delphinensis represents a reliable conservation unit remained unclear. Our evaluation procedure based on a combination of molecular biology and interspecific crosses was used to define taxa within these plants. Plants were sampled from a total of 23 single and mixed localities for the three supposed taxa and were genotyped with 68 polymorphic Amplified Fragment Length Polymorphism (AFLP) loci. Fourty-one seedlings from interspecific crosses were obtained and genotyped. Amplified Fragment Length Polymorphism markers identified four genetically distinct units (P. delphinensis, P. grandiflora and two distinct groups of P. thuringiaca). All individuals of P. delphinensis formed a homogeneous and distinct taxon. This taxon was most probably an old allopolyploid from P. grandiflora and the related group of P. thuringiaca. Interspecific crosses gave low seed set and low germination rate. Furthermore, assignment test indicated that seedlings obtained from interspecific crosses were essentially apomictic rather than hybrids. These results suggest that a reproductive barrier exists between the different taxa. In conclusion, all results supported P. delphinensis as a true biological species and justified its conservation unit status. A surprising outcome of this work was the evidence of a potential new cryptic species. This study demonstrated the need to combine a molecular marker-based approach and pollination experiments for an accurate evaluation of plant taxa.     

Exorcising of a Cage: A Review of American Zoo Exhibits,Part III

Enlargement of captive space has become a trend in zoos, frequently designed with geographic and mixed species themes. Geographic exhibits, however, often mislead the public; in mixed species exhibits, welfare of individual animals and their breeding potentials in some species are ignored. Another popular “natural” open and outdoor exhibit system commonly runs contrary to nature and the requirements of the inhabitants. In all this, the quality of space is forgotten. Zoos need to reevaluate the advantages of cages as well as animal housing in buildings, to ensure management of diverse species in a larger number of taxonomic groups. As zoos reach a crossroad in history, renewed significance of wildlife conservation must be realized in exhibit design consideration. The importance of cohesive and proper exhibit design processes cannot be over-emphasized.     

Taxonomic homogenization in ungulates: patterns and mechanisms at local and global scales

Aim The aim of this paper is to examine taxonomic homogenization in ungulates globally and at the local scale in South Africa. Specifically, we aim to examine the roles of distance, scale, time, extinctions vs. introductions, and extralimital vs. extraregional introductions in the homogenization of ungulate biotas, and to determine pathways of introduction of ungulate species globally and the proximate explanatory variables of ungulate introductions in South Africa. Location Forty‐one countries globally and three spatial resolutions in South Africa. Methods Indigenous, extirpated and established introduced ungulate species data were obtained for countries globally, and at a quarter‐degree grid‐cell resolution in South Africa. Homogenization was calculated using Jaccard’s index of similarity (JI) for countries globally and for three spatial resolutions in South Africa. Zoo holdings and transfer data from the International Species Information System database were used to investigate the relationship between non‐indigenous ungulate species introductions and the number of non‐indigenous ungulate species in zoos. Relationships between JI and species richness, and between numbers of introductions and several environmental and social factors were examined using generalized linear models. Results Homogenization in ungulates was 2% for countries globally and 8% at the coarsest resolution in South Africa. Homogenization increased with increasing resolution and with time, but it decreased with increasing percentage change in species richness. Globally, introductions contributed more to homogenization than did extinctions. Within South Africa, extralimital introductions contributed more to the homogenization of ungulate assemblages than did extraregional ones, and ungulates were typically introduced to high‐income areas with high human population and livestock densities. The same was not true in the past, when ungulates were introduced to ungulate species‐poor areas. The number of non‐indigenous ungulate species established in a country is significantly related to the number of non‐indigenous ungulate species in zoos in the country, possibly owing to sales of surplus animals from zoos. Main conclusions Ungulate faunas are homogenized at both the global scale and in South Africa, with extralimital introductions being of considerable significance regionally. In consequence, increasing attention will have to be given to the conservation consequences of ungulate translocations, both within particular geopolitical regions and across the globe.     

Intra- and interspecific aggression do not modulate androgen levels in dusky gregories,yet male aggression is reduced by an androgen blocker

Discussions about social behavior are generally limited to fitness effects of interactions occurring between conspecifics. However, many fitness relevant interactions take place between individuals belonging to different species. Our detailed knowledge about the role of hormones in intraspecific interactions provides a starting point to investigate how far interspecific interactions are governed by the same physiological mechanisms. Here, we carried out standardized resident–intruder (sRI) tests in the laboratory to investigate the relationship between androgens and both intra- and interspecific aggression in a year-round territorial coral reef fish, the dusky gregory, Stegastes nigricans. This damselfish species fiercely defend cultivated algal crops, used as a food source, against a broad array of species, mainly food competitors, and thus represent an ideal model system for comparisons of intra-and interspecific territorial aggression. In a first experiment, resident S. nigricans showed elevated territorial aggression against intra- and interspecific intruders, yet neither elicited a significant increase in androgen levels. However, in a second experiment where we treated residents with flutamide, an androgen receptor blocker, males but not females showed decreased aggression, both towards intra- and interspecific intruders. Thus androgens appear to affect aggression in a broader territorial context where species identity of the intruder appears to play no role. This supports the idea that the same hormonal mechanism may be relevant in intra- and interspecific interactions. We further propose that in such a case, where physiological mechanisms of behavioral responses are found to be context dependent, interspecific territorial aggression should be considered a social behavior.     

Morphological correlates of diet in an assemblage of West African freshwater fishes

Morphological correlates of diet were sought among 18 species of distantly related freshwater fishes from Guinea (West Africa). With regard to the percentage occurrence of six food items, the studied species could be classified into four broad trophic categories reflecting what was eaten and where: detritivores, piscivores, surface feeders and benthic invertivores. Detrivory was associated with a high relative gut length and eyes in a dorsal position; piscivory with large body and mouth size; surface feeding with a dorsally orientated mouth; and benthic invertivory with eyes in a lateral position and small relative gut length. Similarity in diet and in morphology were both significantly correlated with taxonomic relatedness. Nevertheless, when taxonomic relatedness was accounted for, the relationship between observed similarity in diet and similarity in diet predicted from morphology was still significant. This result leads to the conclusion that species having similar diet tend to converge for some morphological attributes.     

Factors Affecting Interspecific Aggression in a Year‐Round Territorial Species,the Jewel Damselfish

Vertebrates live in complex species networks in which interspecific interactions are common. In some contexts, the aggressive behaviours shown in these interspecific interactions are very similar to those shown in intraspecific interactions. It is still an open question whether intra‐ and interspecific aggression share common causality. We studied a year‐round territorial species the jewel damselfish, (Plectroglyphidodon lacrymatus), which cultivate algae they feed on. Territory holders aggressively defend these algae that are an attractive resource for many other species. In this study, we recorded territorial aggression in free‐living individuals and recorded aggressive responses to a standardized territorial intrusion test in captive individuals. Field observations indicated that territorial aggression was selectively targeted towards food competitors. Independent of the size of the species, aggression was more frequent towards common species around their territories. This relationship was confirmed experimentally by confronting the jewel damselfish with novel objects to which the subjects were exposed either frequently or rarely. We suggest that jewel damselfish have to learn which species are competitors and therefore should be chased. In a standardized intrusion test with captive individuals, no significant differences were found in territorial responses towards intra‐ or interspecific intruders. Neither territorial aggression nor the intrusion showed any relationship with plasma androgen levels. Together, these data suggest that experience might be more important in non‐seasonal territorial aggression than circulating hormonal factors.     

Climate and Species Richness Predict the Phylogenetic Structure of African Mammal Communities

We have little knowledge of how climatic variation (and by proxy, habitat variation) influences the phylogenetic structure of tropical communities. Here, we quantified the phylogenetic structure of mammal communities in Africa to investigate how community structure varies with respect to climate and species richness variation across the continent. In addition, we investigated how phylogenetic patterns vary across carnivores, primates, and ungulates. We predicted that climate would differentially affect the structure of communities from different clades due to between-clade biological variation. We examined 203 communities using two metrics, the net relatedness (NRI) and nearest taxon (NTI) indices. We used simultaneous autoregressive models to predict community phylogenetic structure from climate variables and species richness. We found that most individual communities exhibited a phylogenetic structure consistent with a null model, but both climate and species richness significantly predicted variation in community phylogenetic metrics. Using NTI, species rich communities were composed of more distantly related taxa for all mammal communities, as well as for communities of carnivorans or ungulates. Temperature seasonality predicted the phylogenetic structure of mammal, carnivoran, and ungulate communities, and annual rainfall predicted primate community structure. Additional climate variables related to temperature and rainfall also predicted the phylogenetic structure of ungulate communities. We suggest that both past interspecific competition and habitat filtering have shaped variation in tropical mammal communities. The significant effect of climatic factors on community structure has important implications for the diversity of mammal communities given current models of future climate change.     

Behavioral effects of introducing pied tamarin (Saguinus bicolor) to black howler monkey (Alouatta caraya) and white-faced saki (Pithecia pithecia) in a zoological park

Mixed-species primate exhibits are becoming more common in zoological parks as a means to display a diverse array of animals both more naturalistically and with more economy of space. Here, we describe behavioral changes during the introduction process of a pair of pied tamarins (Saguinus bicolor) to an established group of black howler monkeys (Allouatta caraya) and white-faced saki monkeys (Pithecia pithecia). Data were collected during six phases, representing introductions among the various species and to exhibit space and off-exhibit holding. The pied tamarins were consistently the most active of the three species. Although activity levels of the howler and saki monkeys remained constant throughout, that of the tamarins declined as the introduction progressed. Several episodes of aggression between the tamarins and the sakis were observed, but did not coincide with patterns predicted by previous intra-specific introductions. The three-species mix remained stable for several months; however, escalating aggression ultimately led to the removal of the sakis from the mixed-species exhibit. Despite our mixed results, we contend that only through continued trials, coupled with careful and systematic monitoring, can we ultimately identify stable mixes of species.     

Male aggressiveness in a polygynous ungulate varies with social and ecological context

Aggression is a social behaviour which can be affected by numerous factors. The quality and quantity of food resources may play an important role in the aggressiveness of territorial ungulates as the defence of these resources influences female choice and mating opportunities. However, the relationship between food resources and aggression remains poorly understood. We assessed the ecological and social factors that influence aggression in Lama guanicoe, a territorial ungulate exhibiting resource‐defence polygyny, during three periods (group‐formation, mating and post‐mating) in the reproductive seasons of 2014 and 2016. We recorded 460 focal observations of territorial (family groups, solitary) and non‐territorial (mixed and bachelor groups) males. We performed analyses at the population level (including all focal observations) and at the group level (each social unit separately), to test whether the factors that influence aggression differ at these different scales. We also identified proxies of vegetation quality as potential predictors of aggression. At the population level, we found that the presence of aggressive behaviour peaked during the mating season and that post‐mating aggression may have been driven by inter‐annual environmental variations. For family groups and solitary males, variables reflecting high vegetation quality/quantity were predictors of aggressive behaviour, reflecting the resource‐defence strategy of this species. Conversely, for mixed‐group males, aggression may be more associated with social instability and group size, although this hypothesis has yet to be tested. Our research reinforces the idea that aggression can occur in multiple contexts depending on male status (e.g. territorial or non‐territorial) and contributes to our understanding of how ecological (i.e. availability of food resources) and social factors influence aggression in a territorial ungulate.     

Living together: behavior and welfare in single and mixed species groups of capuchin (Cebus apella) and squirrel monkeys (Saimiri sciureus)

There are potential advantages of housing primates in mixed species exhibits for both the visiting public and the primates themselves. If the primates naturally associate in the wild, it may be more educational and enjoyable for the public to view. Increases in social complexity and stimulation may be enriching for the primates. However, mixed species exhibits might also create welfare problems such as stress from interspecific aggression. We present data on the behavior of single and mixed species groups of capuchin monkeys (Cebus apella) and squirrel monkeys (Saimiri sciureus) housed at the Living Links to Human Evolution Research Centre in the Royal Zoological Society of Scotland's Edinburgh Zoo. These species associate in the wild, gaining foraging benefits and decreased predation. But Cebus are also predators themselves with potential risks for the smaller Saimiri. To study their living together we took scan samples at ≥15 min intervals on single (n=109) and mixed species groups (n=152), and all occurrences of intraspecific aggression and interspecific interactions were recorded. We found no evidence of chronic stress and Saimiri actively chose to associate with Cebus. On 79% of scans, the two species simultaneously occupied the same part of their enclosure. No vertical displacement was observed. Interspecific interactions were common (>2.5/hr), and equally divided among mildly aggressive, neutral, and affiliative interactions such as play. Only one aggressive interaction involved physical contact and was non‐injurious. Aggressive interactions were mostly (65%) displacements and vocal exchanges, initiated almost equally by Cebus and Saimiri. Modifications to the enclosure were successful in reducing these mildly aggressive interactions with affiliative interactions increasing in frequency and diversity. Our data suggest that in carefully designed, large enclosures, naturally associating monkeys are able to live harmoniously and are enriched by each other. Am. J. Primatol. 72:33–47, 2010. © 2009 Wiley‐Liss, Inc.     

Redstart Phoenicurus phoenicurus and black redstart P. ochruros in a mosaic urban environment: neighbours or rivals?

Redstart and black redstart inhabit different types of habitats under natural conditions. However, they come into close contact in a mosaic urban environment. Mechanisms enabling their local coexistence were looked for. We found that: 1) The two species occupied exclusive territories of different habitat compositions. 2) Territories differed in the proportion of trees and buildings. 3) Within their territories, the two species used the same foraging techniques, but with different frequencies. 4) Prey size was similar, but the proportions of taxonomic groups differed. 5) Spontaneous interspecific conflicts were observed. Interspecific aggression was confirmed in playback experiments. The black redstart was dominant in both natural and simulated encounters. We conclude that the main mechanism enabling coexistence of the two redstarts in a mosaic urban environment is different habitat selection with the proportion of trees as a key parameter. This proportion was always below 26% in black redstart territories, and above 27% in redstart territories. This is consistent with the habitat preferences these two species show in non-urban conditions. This pattern is compared to the other cases of coexistence of congeneric bird species such as chickadees Poecile or Sylvia warblers. As the two redstart species are able to hybridise in the wild, the observed interspecific aggression may operate as a pre-copulation barrier.     

Male reproductive skew, paternal relatedness, and female social relationships

Female social relationships among primates are thought to be shaped by socio-ecological factors and phylogenetic constraints. We suggest that patterns of paternal relatedness among females influence measures of social tolerance that have been used to classify species into different social relationship categories. As kin support and kin preference have only been measured for matrilineal kin and related individuals exchange less aggression and have a higher conciliatory tendency, the observed low nepotism levels and high tolerance levels may be an artifact of hidden paternal relatedness among the nonkin category. Using comparative data on macaques, we investigate this hypothesis using male reproductive skew as a proxy for paternal relatedness. Within the limitations of the study we show that populations classified as being less nepotistic, and more tolerant exhibit higher levels of reproductive skew. This first result and the reasoning behind may motivate future students of social relationships to take paternal relatedness into consideration. Potential implications of this finding if repeated with larger samples include that variation in aspects of macaque social relationships may be explained without considering phylogeny or the strength of between-group contest competition for food.     

Interspecific aggression causes negative selection on sexual characters

Interspecific aggression originating from mistaken species recognition may cause selection on secondary sexual characters, but this hypothesis has remained untested. Here we report a field experiment designed to test directly whether interspecific aggression causes selection on secondary sexual characters, wing spots, in wild damselfly populations. Males of Calopteryx virgo are more aggressive toward males of C. splendens with large than with small wing spots. This differential interspecific aggression may cause negative selection on wing spot size. Indeed, our results show that directional survival selection on wing spot size of C. splendens males was changed by experimental removal of C. virgo males. Without removal, directional selection went from positive to negative with increasing relative abundance of C. virgo males. In populations where C. virgo males were removed, this relationship disappeared. These results verify that interspecific aggression can cause negative selection on sexual characters. Thus, interspecific aggression has the potential to cause divergence on these characters between two species offering an alternative explanation for reinforcement for generating character displacement in secondary sexual characters.