scholarly journals Effects of Single- and Mixed-Species Group Composition on the Flight Initiation Distances of Plains and Grevy's Zebras

Ethology ◽  
2016 ◽  
Vol 122 (7) ◽  
pp. 531-541 ◽  
Author(s):  
Alexali S. Brubaker ◽  
Richard G. Coss
Keyword(s):  
Group Composition ◽  
Species Group ◽  
Mixed Species ◽  
Flight Initiation

scholarly journals Individuals from different-looking animal species may group together to confuse shared predators: simulations with artificial neural networks

2006 ◽  
Vol 274 (1611) ◽  
pp. 827-832 ◽  
Author(s):  
Colin R Tosh ◽  
Andrew L Jackson ◽  
Graeme D Ruxton
Keyword(s):  
Animal Species ◽  
Empirical Work ◽  
Species Group ◽  
Mixed Species ◽  
Retinotopic Maps ◽  
Species Groups ◽  
Artificial Neural ◽  
Mixed Species Groups ◽  
Species Grouping ◽  
Prey Items

Individuals of many quite distantly related animal species find each other attractive and stay together for long periods in groups. We present a mechanism for mixed-species grouping in which individuals from different-looking prey species come together because the appearance of the mixed-species group is visually confusing to shared predators. Using an artificial neural network model of retinotopic mapping in predators, we train networks on random projections of single- and mixed-species prey groups and then test the ability of networks to reconstruct individual prey items from mixed-species groups in a retinotopic map. Over the majority of parameter space, cryptic prey items benefit from association with conspicuous prey because this particular visual combination worsens predator targeting of cryptic individuals. However, this benefit is not mutual as conspicuous prey tends to be targeted most poorly when in same-species groups. Many real mixed-species groups show the asymmetry in willingness to initiate and maintain the relationship predicted by our study. The agreement of model predictions with published empirical work, the efficacy of our modelling approach in previous studies, and the taxonomic ubiquity of retinotopic maps indicate that we may have uncovered an important, generic selective agent in the evolution of mixed-species grouping.

scholarly journals Morph Composition Matters in the Gouldian Finch (Chloebia gouldiae): Involvement of Red-Headed Birds Increases Vigilance

Birds ◽  
2021 ◽  
Vol 2 (4) ◽  
pp. 404-414
Author(s):  
Claudia Mettke-Hofmann
Keyword(s):  
Predation Risk ◽  
Group Composition ◽  
Predation Pressure ◽  
Head Movements ◽  
Species Assemblages ◽  
Same Sex ◽  
Mixed Species ◽  
Polymorphic Species ◽  
Gouldian Finch ◽  
Tracking Strategy

Animals invest in costly vigilance to detect threats. Joining groups reduces these costs, which can be further reduced in mixed-species assemblages. In colour-polymorphic species, morphs often experience different predation pressure and vary in a variety of traits. However, little is known about differences in vigilance or how group composition affects vigilance. The aim was to investigate whether higher conspicuousness increased vigilance and whether vigilance was reduced in mixed-morph groups like in mixed-species assemblages. I tested vigilance in the colour-polymorphic Gouldian Finch (Chloebia gouldiae). Same sex pairs of different age and of either pure (red-red or black-black) or mixed head colour were exposed to three contexts (familiar, changed and novel environment) and head movements were recorded. All birds reduced the frequency of head movements with increasing novelty, indicating different vigilance strategies (switching from a searching to a tracking strategy) depending on the situation. While vigilance did not differ between morphs, morph composition mattered. Black-headed pairs made fewer head movements than mixed-head colour pairs. Results indicated that conspicuousness did not affect vigilance, possibly due to existing adaptations to reduce predation risk. However, whenever red-headed birds were involved, vigilance increased either because of higher group conspicuousness or prevalence of aggression.

scholarly journals Mixed-species associations of Diana and Campbell's monkeys: the costs and benefits of a forest phenomenon

Behaviour ◽  
2003 ◽  
Vol 140 (3) ◽  
pp. 371-385 ◽  
Author(s):  
Sonja Wolters ◽  
Klaus Zuberbühler
Keyword(s):  
Resource Competition ◽  
Dilution Effect ◽  
Daily Basis ◽  
Species Group ◽  
Mixed Species ◽  
Predator Detection ◽  
Vocal Behaviour ◽  
Forest Strata ◽  
Species Groups ◽  
Mixed Species Groups

AbstractOne of the most striking behavioural patterns of many forest primates concerns their tendency to live in semi-permanent mixed-species groups. Functional investigations have ascertained that individuals obtain some antipredator benefits without paying the costs of intra-species resource competition. Despite these advances, very little is known about the subtle mechanisms that keep mixed species groups together on a daily basis. Our results showed that in the Diana-Campbell's monkey association both species benefited from each other in diverse and idiosyncratic ways. In the presence of Campbell's monkeys the conspicuous Diana monkeys were more likely to descend into the lower forest strata, increased their foraging behaviour, and individuals became less vigilant. The cryptic Campbell's monkeys, in turn, were able to use the higher forest strata and exposed areas more often, spread out over larger areas, were more likely to travel, and engaged in more conspicuous vocal behaviour when associated with Diana monkeys. These data suggested that both species benefited from each other in ways that went beyond passive group-size related antipredator benefits, such as a dilution effect and increased chances of predator detection. Instead, the increased safety of the mixed species group allowed individuals to exploit their ecological niche more broadly, to forage more efficiently, and to engage in more social behaviour, suggesting that the benefits of mixed species groups are much more varied and diverse than currently thought.

scholarly journals Can an Exponential Function Be Applied to the Asymptotic Density–Size Relationship? Two New Stand-Density Indices in Mixed-Species Forests

Forests ◽  
2018 ◽  
Vol 10 (1) ◽  
pp. 9 ◽  
Author(s):  
Gerónimo Quiñonez-Barraza ◽  
Hugo Ramírez-Maldonado
Keyword(s):  
Mortality Rate ◽  
Initial Density ◽  
Stand Density ◽  
Species Group ◽  
Mixed Species ◽  
Management Objectives ◽  
Density Index ◽  
Density Indices ◽  
Species Groups ◽  
Stand Density Index

This study presents two stand-density indices (SDIs) based on exponential density decline as a function of quadratic mean diameter for all species combined in mixed-species forests with 22 species mix grouped in four species groups. The exponential-based density–diameter relationship, as well the density index corresponding to the slope or instantaneous mortality rate parameters, was compared with those based on power-law density–diameter relationship. A dataset of 202 fully stocked circular plots at maximum density was used for fitting the models, and a dataset of 122 circular plots was used for validation stand density index for all species combined of mixed-species stands. The dataset for validation was independent of dataset for model development. The first stand-density index showed a density management graphic (DMG) with a variable intercept and common instantaneous mortality rate, and the second index showed a DMG with common intercept and variable mortality rate. Additionally, the value of the initial density of the fitted line was more realistic than those generated by the potential model for all species combined. Moreover, the density management diagrams showed a curvilinear trend based on the maximum stand density index in graphical log–log scale. The DMGs could be interpreted as forest scenarios based on variable initial density and common management objectives or the same density and different management objectives for forest-rotation periods involving all species combined in mixed-species stands. The fitting of exponential and potential equations for species or species groups showed that the density–size relationships in mixed-species forests should be modeled for all species combined because the disaggregation of mixture species represented a weak tendency for each species or species group and the resultant fitted equations were unrealistic.

scholarly journals The shoaling behavior of two cyprinid species in conspecific and heterospecific groups

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e3397 ◽  
Author(s):  
Zhong-Hua Tang ◽  
Hui Wu ◽  
Qing Huang ◽  
Lu Kuang ◽  
Shi-Jian Fu
Keyword(s):  
Swimming Speed ◽  
Collective Motion ◽  
Species Group ◽  
Activity Level ◽  
Mixed Species ◽  
Individual Level ◽  
Cyprinid Species ◽  
Percent Time ◽  
Significant Difference ◽  
Shoaling Behavior

Mixed-species shoals of fish are frequently found in the field; however, little is known about individual-level interactions within these groups. We examined the collective motion of two cyprinid species (Chinese bream, Parabramis pekinensis, and qingbo, Spinibarbus sinensis) that occupy partially overlapping habitats but differ in social behavior (high vs low aggressiveness) and preferred flow regime (slow vs fast water velocity). We extracted measures of collective motion from video recordings of eight replicate groups of four individuals of either Chinese bream or qingbo (conspecific group) or two Chinese bream plus two qingbo (heterospecific group). Chinese bream in conspecific groups showed lower percent time moving and mean swimming speed but a similar speed while moving as compared to the qingbo conspecific groups. However, the difference in mean swimming speed and percent time moving vanished in the heterospecific group as Chinese bream elevated their swimming activity to coordinate with qingbo. This finding suggests that the two species may share similar interaction rules regarding shoaling behavior. The conspecific groups of qingbo exhibited a greater distance between group members than Chinese bream, suggesting a difference in cohesion. However, the inter-individual distances of all fish were similar in the heterospecific group. Qingbo in the heterospecific group swam more frequently at the front compared to Chinese bream, possibly due to their higher activity level. We also measured the startle response to an artificial stimulus and found that there was no significant difference among groups. In conclusion, the present study demonstrated that in the heterospecific groups, Chinese bream elevated their percent time moving while qingbo decreased their inter-individual distance to achieve consistent collective movement; thus, the two species showed similar behavior in the mixed-species group.

scholarly journals Dynamics of Cetacean Mixed-Species Groups: A Review and Conceptual Framework for Assessing Their Functional Significance

2021 ◽  
Vol 8 ◽  
Author(s):  
Jonathan Syme ◽  
Jeremy J. Kiszka ◽  
Guido J. Parra
Keyword(s):  
Conceptual Framework ◽  
Predation Risk ◽  
Species Group ◽  
Potential Functions ◽  
Social Benefits ◽  
Spatial Proximity ◽  
Mixed Species ◽  
Species Pairs ◽  
Species Groups ◽  
Mixed Species Groups

Numerous species of cetaceans have been recorded in mixed-species groups (MSGs). By forming groups with individuals of different species, cetaceans may reduce predation risk, improve foraging, and gain social benefits. Most accounts of cetacean MSGs, however, are descriptive and little is known about their functions. Furthermore, research has been hindered by inconsistent use of terminology and the lack of a conceptual framework to guide investigations. We reviewed the cetacean literature to compare how MSGs have been termed and defined, to assess their characteristics, to evaluate what is known about their potential functions, and to provide directions for future study. In total, we reviewed 203 studies reporting observations of cetacean MSGs. These MSGs involved 54 different species, predominantly delphinids, that formed 216 different species pairs with varied morphologies and levels of relatedness. Cetacean MSGs occurred across the globe, from tropical to cold temperate seas, from shallow coastal waters to the open ocean, and varied in characteristics such as group size and frequency of occurrence. Only 27 of the reviewed studies proposed and discussed the potential functions of cetacean MSGs, suggesting reduced predation risk (5 species pairs), improved foraging (17 species pairs), and social benefits (12 species pairs) as the main drivers. In most cases, however, the factors that drive the formation of cetacean MSGs remain unknown. Amongst the reviewed studies, MSGs were referred to by various terms, often with no explicit definitions. To reduce this inconsistency, we recommend that future studies use only the term mixed-species group which we define as individuals of two or more species found in close spatial proximity due to mutual or unreciprocated attraction derived from evolutionary grouping benefits. There were also few structured investigations to confirm MSG occurrence and to analyse their potential causes and consequences. To facilitate the study of cetacean MSGs, we developed a conceptual framework that establishes diverse approaches to, firstly, distinguish MSGs from chance encounters and aggregations and to, secondly, investigate their potential functions. This is necessary if we are to advance this field of study and improve our understanding of the role that MSGs play in species and community ecology.

Sign in / Sign up

Export Citation Format

Share Document