Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Optimality models designed to explain the occurrence of feeding territoriality predict that the frequency or intensity of aggression will peak at intermediate levels of food abundance. To test whether this prediction applies to the competition for ephemeral patches of food, we manipulated food abundance over a broad range of values in two separate experiments (24- and 64-fold, respectively) while monitoring the aggressive behaviour of juvenile convict cichlids,Archocentrus nigrofasciatum , competing for the food. In both experiments, the rate of aggression was low when food was scarce, increased as food abundance increased, and decreased when food was provided in excess. This dome-shaped pattern of aggression was caused partly by higher encounter rates between fish and partly by a higher proportion of encounters resulting in aggression, when food was at intermediate levels of abundance. Our results suggest that convict cichlids display behavioural flexibility: in response to changes in food abundance, they appear to change both their likelihood of using aggression when encountering a conspecific and their willingness to enter an occupied patch.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Gregarious populations of Barbados ground doves (Zenaida aurita), for instance, switch from aggressive food defense with escalated fighting to scramble tactics depending on the size and temporal predictability of the food patches they exploit (Goldberg et al., 2001). Similar behavioral plasticity in aggressive responses has been noted in a number of animal taxa including fish (Grant et al., 2002), birds (Zahavi, 1971), and mammals (Monaghan and Metcalfe, 1985). ...
... As the number of animals competing for a food clump decreases, as a result of an increased food abundance or a decreased number of foragers within the group, the net benefit of fighting increases, and so should the frequency of aggressive interactions. However, when food is abundant or competitors scarce, nonaggressive individuals can acquire the same amount of food as aggressive individuals without paying the cost of aggression (Grant et al., 2000(Grant et al., , 2002. So resource defense theory predicts that the total number of aggressive acts, the per-capita number of aggressive acts, and the intensity of aggressive encounters should follow a dome-shaped relationship with respect to either food or competitor abundance. ...
... So the hawk-dove game predicts that the average intensity of fighting, the frequency of fighting, and the per-capita frequency of fighting should increase as competitor density increases but decrease with increased food abundance. Experimental evidence for dome-shaped responses of aggression exists with respect to competitor density (Goldberg et al., 2001), food abundance (Carpenter and MacMillen, 1976;Grant et al., 2002), and competitor-to-resource ratio, which integrates competitor number and food abundance (Grant et al., 2000). In contrast, however, many observations of birds foraging in shared patches support the linear predictions of the hawkdove game (see Sirot, 2000). ...
Article
Full-text available
When foraging in groups, animals frequently use either scramble or contest tactics to obtain food at clumps found by others. The question of which competitive tactic should be used has been addressed from two different perspectives: a simple optimality approach and a game theoretic approach. Surprisingly, both approaches make strikingly different predictions about how per-capita frequency of aggression within groups should change as a function of food abundance and competitor density. Resource defense theory typically predicts dome-shaped relationships between the per-capita frequency of aggression and both food abundance and competitor density, whereas game theoretic models predict an increase in aggression with competitor density and a decline in aggression with increased food abundance. We developed a game theoretic model to explore whether the predictions of resource defense theory and the game theoretic approach can be reconciled. Our model assumes that players have different competitive abilities and can adopt roles of either finder or joiner that affect the quantity of food that can be gained from a food clump. In accordance with earlier game theoretic models, we predict an increase in aggression with com-petitor density when animals compete by pair-wise contests. However, when food clumps can be challenged by more than one competitor, both the costs and benefits of defending increase with competitor density, which results in a dome-shaped relation-ship between the two variables. Our model predicts that aggression should always decrease as the density of food clumps increases. Key words: aggression, competitor asymmetry, evolutionarily stable strategy model, finder's advantage, foraging groups, resource defense. [Behav Ecol 14:2–9 (2003)] W
... Two 10-cm long segments of PVC pipe were placed in each tank to provide shelter for the fish and reduce the aggressive behavior typical of the Cichlidae family (Grant et al. 2002;Leiser et al. 2004;Arnott and Elwood 2009;Heg 2010;Lorenz et al. 2011). ...
... Based on the aggressive behavior observed during feeding in treatments D6 and D9, intraspecific competition may have been the main factor that prevented the fish (22 g, 8.3 cm) in those treatments to grow similar to the fish in D3 (35 g, 9.9 cm). It has been reported that at high-density intraspecific competition increases, which generates social stress that results in poor condition of the attacked fish (Barcellos et al. 1999;Grant et al. 2002). However, in this study the condition in D6 and D9 was not different to that in treatment D3. ...
... These results robust the possibility that the greatest growth of the surviving fish in D3 could be related to the lack of competition after the surviving (dominant) fish killed the other two individuals in that treatment, which eradicated any stress related to intraspecific competition. This coincides with McCarthy et al. (1999) and Wong and Benzie (2003) who reported that low competition increases the availability of food, which is reflected in higher growth and greater SGR Aggression is common in cichlids (Grant et al. 2002;Leiser et al. 2004;Arnott and Elwood 2009;Heg 2010;Lorenz et al. 2011) and generally occurs in high densities where competition for food and space promote aggressive responses (Rose et al. 2001;Jiménez-Martínez et al. 2009). However, during the present study aggression that caused high mortality rates was observed in the treatment with the lowest density (D3). ...
Article
Full-text available
The Mexican cichlid Cichlasoma beani is currently exploited regionally as food and can be commercialized in the aquarium trade. Natural populations of C. beani may already be negatively affected by anthropogenic alteration of the areas in which it is distributed. The aim of the present study was to examine the effect on growth, survival, and condition of C. beani cultured in three stocking densities: three (D3), six (D6), and nine (D9) fish per each 40 L tank. At the end of a 6-wk trial the fish cultured in D3 were longer, heavier, and grew faster than the rest of the treatments but their survival was the lowest compared to D6 and D9. The mortalities were caused by a strong aggressive behavior in D3.
... In psychological terms, emotions, such as frustration, anger and resentment may lead to a 'loss of temper' which in turn promotes aggressive behaviour [11]. These emotional responses are often linked with expectancy of value and therefore may increase the individual's motivation to escalate levels of aggression [2,7,12,13]. Frustration, defined as 'an aversive motivational state preceded by the omission of an expected reward (OER)' [14], has been categorized as a potent trigger of intense aggression in mammals [15][16][17] and birds [18,19]. ...
... Individuals with differing RHP may have different value expectancy based on their energy reserves, which may alter contest dynamics. This, in turn, may provoke inferior fighters (i.e. with lower RHP) to react with increased investment in aggressive contests [2,7,12,13]. Possible effects of unpredictable reward conditions in combination with unequal RHP during social competition have not been ascertained in fish species. ...
... frustration) are thought to represent adaptive evolutionary strategies contributing to an animal's fitness in a changing world [68]. For example, it could be speculated that inferior fighters with increased value expectancy may in some way gain from a bigger investment in agonistic behaviour against superior fighters [2,7,[11][12][13]. The adaptive value of such intensified agonistic behaviour, however, remains to be resolved. ...
Article
Full-text available
Animals use aggressive behaviour to gain access to resources, and individuals adjust their behaviour relative to resource value and own resource holding potential (RHP). Normally, smaller individuals have inferior fighting abilities compared with larger conspecifics. Affective and cognitive processes can alter contest dynamics, but the interaction between such effects and that of differing RHPs has not been adjudged. We investigated effects of omission of expected reward (OER) on competing individuals with contrasting RHPs. Small and large rainbow trout (Oncorhynchus mykiss) were conditioned to associate a light with reward. Thereafter, the reward was omitted for half of the fish prior to a contest between individuals possessing a 36-40% difference in RHP. Small control individuals displayed submissive behaviour and virtually no aggression. By contrast, small OER individuals were more aggressive, and two out of 11 became socially dominant. Increased aggression in small OER individuals was accompanied by increased serotonin levels in the dorsomedial pallium (proposed amygdala homologue), but no changes in limbic dopamine neurochemistry were observed in OER-exposed individuals. The behavioural and physiological response to OER in fish indicates that frustration is an evolutionarily conserved affective state. Moreover, our results indicate that aggressive motivation to reward unpredictability affects low RHP individuals strongest.
... When food is dispersed, spread, and thus not monopolized (scramble competition), foraging gains may increase for peripheral group members as spacing between them reduces feeding competition (Morrell and Romey, 2008). Conversely, when food patches are limited and defendable (i.e., contest competition; van Schaik and van Noordwijk, 1988), individuals may aggressively compete over food (Grant et al., 2002) resulting in a spatial distribution where highranking individuals are in the center, occupying food patches, while low-ranking individuals are distributed in peripheral positions (Hirsch, 2007). This spatial distribution, characterized by dominant and tolerated individuals in central positions having high food intake, is observed in different primate species (Robinson, 1981;Janson, 1990;Barton, 1993;Motro et al., 1996). ...
... This encourages contest competition resulting in a spatial distribution where high-ranking individuals control the food patch and low-ranking individuals are in peripheral positions. This behavior has been observed in different primate species (Long-Tailed Macaques, Macaca fascicularis: van Schaik and van Noordwijk, 1988; Wild chimpanzees, Pan troglodytes: Murray et al., 2007;White-faced capuchins, Cebus capuccinus: Hall and Fedigan, 1997;Brown capuchin Cebus apella: Janson, 1990) and other taxa (Convict cichlids, Archocentrus nigrofasciatum: Grant et al., 2002). Furthermore, frequencies of the presence of observations, either in proximity or far from the feeding zone, were also explained by the affiliative network. ...
... 31 Conversely, when food patches are limited and defendable (i.e. contest competition) (Van Schaik & 32 Van Noordwijk, 1988), individuals may aggressively compete over food (Grant et al., 2002) resulting 33 in a spatial distribution where high-ranking individuals are in the center, occupying food patches, while 34 low-ranking individuals are distributed in peripheral positions (Hirsch, 2007). This spatial distribution, 35 characterized by dominant and tolerated individuals in central positions having high food intake, is 36 observed in different primate species (Barton, 1993;Janson, 1990;Motro et al., 1996;Robinson, 1981). ...
... Archocentrus nigrofasciatum: Grant et al., 2002). Furthermore, frequencies of the presence of 336 observations, either in proximity or far from the feeding zone, were also explained by the affiliative 337 network. ...
Article
Full-text available
Although there exist advantages to group-living in comparison to a solitary lifestyle, costs and gains of group-living may be unequally distributed among group members. Predation risk, vigilance levels and food intake may be unevenly distributed across group spatial geometry and certain within-group spatial positions may be more or less advantageous depending on the spatial distribution of these factors. In species characterized with dominance hierarchy, high-ranking individuals are commonly observed in advantageous spatial position. However, in complex social systems, individuals can develop affiliative relationships that may balance the effect of dominance relationships in individual's spatial distribution. The objective of the present study is to investigate how the group spatial distribution of a semi-free ranging colony of Mandrills relates to its social organization. Using spatial observations in an area surrounding the feeding zone, we tested the three following hypothesis: (1) does dominance hierarchy explain being observed in proximity or far from a food patch? (2) Do affiliative associations also explain being observed in proximity or far from a food patch? (3) Do the differences in rank in the group hierarchy explain being co-observed in proximity of a food patch? Our results showed that high-ranking individuals were more observed in proximity of the feeding zone while low-ranking individuals were more observed at the boundaries of the observation area. Furthermore, we observed that affiliative relationships were also associated with individual spatial distributions and explain more of the total variance of the spatial distribution in comparison with dominance hierarchy. Finally, we found that individuals observed at a same moment in proximity of the feeding zone were more likely to be distant in the hierarchy while controlling for maternal kinship, age and sex similarity. This study brings some elements about how affiliative networks and dominance hierarchy are related to spatial positions in primates.
... Rates of aggression are expected to be lowest during food scarcity or over-abundance (Grant et al. 2002). In contrast, aggression is expected to peak with intermediate levels of food abundance (Grant et al. 2002). ...
... Rates of aggression are expected to be lowest during food scarcity or over-abundance (Grant et al. 2002). In contrast, aggression is expected to peak with intermediate levels of food abundance (Grant et al. 2002). Given flower loads on trees, eucalyptus and madera dura appeared to be at their annual height of flowering during our study, suggesting food abundance. ...
Article
Full-text available
The critically endangered Juan Fernandez Firecrown hummingbird (Sephanoides femandensis) is restricted to only one island in the world, Robinson Crusoe. Reasons for its endangerment have not been quantitatively explored but may be linked to the recently self-introduced Green-backed Firecrown (Sephanoides sephaniodes), a potential competitor. We examined the Green-backed Firecrown's influence on the Juan Fernandez Firecrown's food availability and access by comparing time budgets for interference competition, frequency of interspecies interactions, and frequency of aggressive interactions during the hummingbirds' breeding season. We performed focal observations of both firecrown species and recorded all interactions, the bird species involved, and whether the focal bird was the aggressor or victim. Both hummingbird species spent < 2% of their time in chases. Contrary to observations by past researchers, most chases were between conspecifics. We found no evidence that male Juan Fernandez Firecrowns were negatively affected by Green-backed Firecrowns during the breeding season, although our results suggest that interference competition may negatively influence female Juan Fernandez Firecrowns. These females were more often the victims in both conspecific and interspecific interactions with Green-backed Firecrowns, suggesting that they may be marginalized from high quality foraging habitat. Overall, we did not find strong evidence for the Green-backed Firecrown's negative influence on Juan Fernandez Firecrown food availability or access during the breeding season. Accepted 16 January 2013.
... Individuals can benefit by forgoing resource defense when the payoff of increased access does not outweigh the cost of defense. For instance, cessation of territorial defense can occur when there is a decrease in food availability because little is gained from defending rare resources [17], while in contrast, the presentation of supplemental food can lead to an increase in social competition and defense [18]. In addition, competition can be low in contexts when food is so abundant that it is non-limiting, and so diverting time and energy into defense does not increase access to resources [19]. ...
... In addition, competition can be low in contexts when food is so abundant that it is non-limiting, and so diverting time and energy into defense does not increase access to resources [19]. These forms of strategic allocation to resource defense have been well studied [17,[19][20][21], and results indicate a general pattern where individuals are more likely to invest in defense when a resource has greater value (often when it is neither too rare nor too abundant) [22,23]. The decision rule to match aggression to resource value was nicely demonstrated by Dearborn and Dearborn [24], who found that territorial hummingbirds defended feeding patches more aggressively when the caloric value of the sugar within flowers was experimentally increased. ...
Article
Full-text available
Status signals allow competitors to assess each other’s resource holding potential and reduce the occurrence of physical fights. Because status signals function to mediate competition over resources, a change in the strength of competition may affect the utility of a status signaling system. Status signals alter competitor behavior during periods of high competition, and thus determine access to resources; however, when competition is reduced, we expect these signals to become disassociated from access to resources. We investigated seasonal changes in status signaling of the male black-crested titmouse (Baeolophus atricristatus), a species that experiences substantial changes in population density and competition for food over the annual cycle. We compared the size of the prominent head-crest to foraging success at community-used feeding stations; we tested this relationship when competition was seasonally high, and when competition was seasonally low. We then experimentally decreased the number of feeders to increase competition (during the season of low-competition), and again tested whether male crest size predicted access to feeders. When competition was seasonally high, males with longer crests had greater access to feeders, but this pattern was not apparent when competition was seasonally low. When competition was experimentally increased, males with longer crests were again more successful at maintaining access to feeders. These findings provide evidence of a context-dependent status signaling system, where the status signal only mediates access to resources during periods of high competition. We discuss possible hypotheses for why the signaling system may not be functional, or detectable, during periods of low competition, including that competitors may interact less frequently and so have reduced opportunity for signaling, or that status signals are disregarded by receivers during periods of low competition because signalers are unlikely to escalate a contest into a fight. In any case, these results indicate that resource availability affects a status signaling system, and that the potential for status signaling persists in this system between seasons, even though such signaling may not be overtly present or detectable during periods of low competition.
... On the other hand, the strength of exploitative competition that young cohorts potentially exert on older, larger cohorts may be significant (Persson 1985;Polis 1988;Hjelm and Persson 2001). Aggressive behavior can depend on density in a more complex manner (Grant et al. 2002;Kaspersson et al. 2010). Intercohort size dynamics and interactions, particularly the effects of young-cohort densities, have been understudied, probably due to technical difficulties in identifying and following individuals over time, and often due to the conspicuousness of cannibalistic and other aggressive behaviors compared to exploitative competition. ...
... In addition, young larvae may have an exploitative advantage as a result of feeding preferentially or more efficiently on the smaller, earlier stages of prey crustaceans, thus reducing the availability of the larger prey stages that may be preferred by the older larvae. Finally, aggressive interference can be related positively to resource level when their availability is low (Grant et al. 2002) and therefore related negatively to larval density. However, while we did not measure the frequency of aggressive behavior, we often observed characteristic interference behaviors ('move-toward', 'lunge', and 'bite'; as defined in Walls and Jaeger 1987) between pairs of individuals across treatments. ...
Article
Full-text available
The size structure of a larval population facilitates interaction asymmetries that, in turn, influence the dynamics of size-structure. In species that exhibit conspicuous aggressive interactions, the competitive effects of the smaller individuals may be overlooked. We manipulated initial size differences between two larval cohorts and young-cohort density of Salamandra infraimmaculata in mesocosms to determine: (1) whether young individuals function primarily as prey or as competitors of older and larger individuals; (2) the resulting dynamics of size variation; and (3) recruitment to the postmetamorph population. Intercohort size differences generally remained constant over time at low young-cohort densities, but reduced over time at high densities due to retardation of the old-cohort growth rate. This suggests a competitive advantage to the young cohort that outweighs the interference advantage of older cohorts previously documented in this species. The increase in mortality from desiccation due to high young-cohort density was an order of magnitude greater in the old cohort than in the young-cohort, further indicating size-dependent vulnerability to competition. However, the conditions least favorable to most of the old-cohort larvae (large size difference and high young-cohort density) promoted cannibalism. Among cannibals, mortality and time to metamorphosis decreased and sizes at metamorphosis increased substantially. Thus, a balance between the competitive advantage to young cohorts, and the interference and cannibalism advantage to old cohorts shapes larval size-structure dynamics. Larval densities and individual expression of cannibalism can shift this balance in opposite directions and alter relative recruitment rates from different cohorts.
... However, increased competition with decreased food levels is not always observed. In the case of juvenile cichlids (Archocentus nigrofasciatum) low rates of aggression were observed when food was scarce, levels increased as food abundance increased and then declined again as food was provided in excess (Grant et al. 2002). Therefore, in some species levels of food may have to reach a minimum threshold before it becomes a defendable resource. ...
... Consequently, although more food was available in general, more dominant fish were consuming more whereas subordinates were not. In convict cichlids (Archoncentrus nigrofasciatum) rates of aggression have been shown to be low when food is scarce, increase as food availability increased and then declined again as food was in excess (Grant et al. 2002). In mixed tanks the two members of the same species were more similar in size than those in tanks containing only a single species. ...
... Time spent moving was recorded as the total time, in seconds, when the focal fish was not stationary (Brown et al., 2006(Brown et al., , 2014. Foraging was recorded as pecking at the substrate, with the body at an angle greater than 45 relative to the substrate (Grant et al., 2002). A reduction in time moving and frequency of foraging attempts is consistent with an increase in predator avoidance behaviour in juvenile convict cichlids (Brown et al., 2006(Brown et al., , 2014. ...
... While we did not directly measure competition during the pretesting phase of the study, decreased food abundance and resource distribution (i.e. clumped patches) are known to increase competition among juvenile cichlid shoals (Grant et al., 2002;Grant & Guha, 1993;Kim et al., 2004). As a result, we cannot make inferences regarding individual competitive abilities; rather, we can state that level of foraging costs may impact neophobia. ...
Article
Neophobia is defined as the avoidance of novel or unknown stimuli, including unknown predators, and can be induced by exposure to uncertain ecological conditions. In addition to uncertainty related to predation risk, uncertainty may also arise from increased foraging competition. Prey forced to spend time and energy competing for limited resources may not have enough time available to devote to predator identification and hence benefit from increased neophobia. Here, we tested the potential interaction of reduced foraging opportunities and elevated predation risk on the strength of neophobia (the antipredator response towards a novel chemical cue). In our first experiment, shoals of juvenile convict cichlids, Amatitlania nigrofasciata, were exposed to high (10% total body weight/day) or low (1% total body weight/day) relative food abundance for 7 days. During the final 3 days, we exposed the shoals to high versus low background predation risk, resulting in a 2 × 2 design. We found that while low food abundance alone and risk alone induced a weak neophobic response to a novel cue (versus water control), cichlids pre-exposed to high risk and low food abundance exhibited significantly a stronger neophobic response, in an additive pattern. In our second experiment, we exposed shoals of cichlids to a fixed amount of food distributed on a single (high competition) patch or across five (low competition) patches for 7 days, with the same risk manipulation as above for the final 3 days. As in experiment 1, we found that high competition alone and risk alone elicited a weak neophobic response to novel cues and that high risk and high competition had additive effects on the strength of induced neophobia among juvenile cichlids. Together, our results indicate that uncertainty of risk and of foraging opportunities exert additive effects on the phenotypically plastic neophobia among prey populations.
... (3) If a plant has access to two patches, one equidistant to a neighbour and one that it is in closer proximity to, how is root proliferation in each of the patches impacted? We predicted that the dynamics in the two patches should reflect behaviour seen in the above behavioural assays, but that plants may be less competitive when resources are more abundant [21,[43][44][45]. (4) Do plants respond the same way to neighbours in homogeneous environments as in patchy environments? ...
... Consistent with this interpretation, plants grown with a neighbour and two patches did not have a significantly lower percentage of nitrogen in their leaf tissue when compared with plants grown without a neighbour and two patches. This may be analogous to lower levels of aggression observed in animals when more resources are available [43,44], since proliferation in highquality patches can similarly allow plants to monopolize resources [30]. It is also consistent with a reduced tragedy of the commons at higher resource levels [25]. ...
Article
Plants regularly encounter patchily distributed soil nutrients. A common foraging response is to proliferate roots within high-quality patches. The influence of the social environment on this behaviour has been given limited attention, despite important fitness consequences of competition for soil resources among plants. Using the common sunflower (Helianthus annuus L.), we compared localized root proliferation in a high-quality patch by plants grown alone to that of plants in two different social environments: with a neighbouring plant sharing equal access to the high-quality patch, and with a neighbouring plant present but farther from the high-quality patch such that the focal individual was in closer proximity to the high-quality patch. Sunflowers grown alone proliferated more roots within high-nutrient patches than lower-nutrient soil. Plants decreased root proliferation within a high-nutrient patch when it was equidistant to a neighbour. Conversely, plants increased root proliferation when they were in closer proximity to the patch relative to a nearby neighbour. Such contingent responses may allow sunflowers to avoid competition in highly contested patches, but to also pre-empt soil resources from neighbours when they have better access to a high-quality patch. We also compared patch occupancy by sunflowers grown alone with two equidistant high-quality patches to occupancy by sunflowers grown with two high-quality patches and a neighbour. Plants grown with a neighbour decreased root length within shared patches but did not increase root length within high-quality patches they were in closer proximity to, perhaps because resource pre-emption may be less important for individuals when resources are more abundant. These results show that nutrient foraging responses in plants can be socially contingent, and that plants may account for the possibility of pre-empting limited resources in their foraging decisions.
... Food density and distribution, as well as the timing of when food is available and the density of those foraging, will impact on the aggression that is seen in foraging patches (Goldberg, Grant, & Lefebvre, 2001;Grant, Girard, Breau, & Weir, 2002). Sex differences on performance of aggression during foraging are also noted in some avian species, such as house sparrows, Passer domesticus (Johnson, Grant, & Giraldeau, 2004), where females are more aggressive than males and whose aggression intensifies with decreasing patch size. ...
... These authors also show that the number of females increases as patch size decreases, showing that amount of food available in a given area can influence the demographic of a foraging group and the aggression individuals can expect to receive. Aggression between juvenile convict cichlids (Archocentrus nigrofasciatum) foraging in ephemeral foraging patches is low when food density is low, rising with increasing food abundance and disappears when food is available in excess (Grant et al., 2002). Such findings may also be applicable to foraging flamingos who, in the wild, move between fluctuating food supplies (Sileo, Tuite, & Hopcraft, 1977) and therefore will experience foraging patches of a similar nature with different numbers of birds displaying different levels of aggression. ...
Article
Full-text available
For specialised feeders, accessing food resources may impact on the performance of appetitive foraging and social behaviours at individual and population levels. Flamingos are excellent examples of social species with complex, species-specific feeding strategies. As attainment of coloured plumage depends upon intake of dietary carotenoids, and as study of free-ranging flamingos shows that foraging is disrupted by aggression from other birds, we investigated the effect of four feeding styles on foraging and aggression in captive lesser flamingos. We evaluated individual and group differences in foraging and aggression when birds consumed bespoke "flamingo pellet" from a bowl, an indoor feeding pool and an outdoor feeding section of their pool. Natural foraging (when birds were feeding irrespective of the presence of pellet) was recorded for comparison with artificial feeding styles. One-minute long video footage of the birds' activities in these different locations, recorded between 2013 and 2016, was used to evaluate behaviour. Total number of seconds engaged in feeding and in aggression was recorded by continuous sampling. The colour of individual birds was scored from 1 (mainly white) to 4 (mainly pink). For natural filter feeding in the outdoor pool, maximum foraging was twice as much as bowl feeding, whilst aggression was less than half as much as other feeding methods. Overall, a more restricted feeding style significantly predicted aggression, along with increasing group size. Plumage colour significantly influenced aggression (brightest flamingos were more aggressive) and showed a non-significant trend with foraging (brighter birds fed less than paler birds). No sex effect on feeding or aggression was found. This study enhances our understanding of husbandry and species' biology impacts on captive behaviour and provides data-based evidence to improve food presentation. For flamingos, implementation of spacious outdoor feeding areas can encourage natural foraging patterns by reducing excess aggression and enhances welfare by improving flock social stability. K E Y W O R D S aggressive behaviour, feeding behaviour, flamingo, ornithology, plumage colour, welfare
... Aggressive behaviour is widespread in territorial reef fish species (e.g., Buckman and Ogden 1973;Vine 1974;Larson 1980;Grant et al. 2002). Territorial fishes usually defend one or more resources such as food, shelter, sexual partners, spawning site, or offspring (Warner 1980;Mumby and Wabnitz 2002). ...
... This is particularly evident whenever males control female harems and/or highquality spawning grounds. The level of aggressiveness can also be affected by external factors such as light intensity (Valdimarsson and Metcalfe 2001) or food availability (Grant et al. 2002). Usually, aggressive behaviours take the form of chasing, chafing or nipping. ...
Article
Aggressive behaviour in fishes, particularly in territorial species, is a common trait used to defend resources such as food or mates. Territorial males of the Mediterranean parrotfish Sparisoma cretense have been described to chase away conspecifics yet other aggressive behaviour repertoire has not been reported for this species. We describe, for the first time, an extreme aggressive behaviour between two male Mediterranean parrotfish which includes biting and prolonged mouth locking.
... Competition for limited resources is ubiquitous among fish under natural conditions, which is beneficial for the population reproduction and species evolution. However, fierce aggression affects fish growth, mortality, and physiology in intensive aquaculture system (Grant et al. 2002;Ashley 2007). Especially in the juvenile stage, inappropriate feeding ration is a common cause of aggressive behavior. ...
... The total aggressive (biting and chasing) frequency of gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) increased significantly during feeding at low ration (Oikonomidou et al. 2019). Higher aggression was also observed in juvenile convict cichlids (Archocentrus nigrofasciatus) when food abundance increased (Grant et al. 2002). In fact, aggressive behavior is an adaptive behavior, which is affected by environment and physiology (Gaffney et al. Abstract Aggressive behavior is important for animals to obtain limited resources. ...
Article
Full-text available
Aggressive behavior is important for animals to obtain limited resources. Understanding fish behavior and physiological response is of great significance to evaluate aquaculture production and fish welfare. Food is an important trigger of aggressive behavior in juvenile fish under high-density aquaculture conditions. The aim of this study was to investigate the aggressive behavior and monoamine levels of juvenile pufferfish (mean body mass of 6.29 ± 0.33 g) under normal feeding and restricted feeding. Our main results included the following: (1) The mortality and fin damage were higher and aggression was more intense of juvenile pufferfish at the 1% ration than those of the 3% ration; (2) during feeding, the velocity, body contact, and activity at the 1% ration were significantly higher than that of the 3% ration; (3) the concentrations of brain 5-hydroxyindoleacetic acid (5-HIAA) and monoamine oxidase A (MAOA) at the 1% ration were significantly lower, and dopamine (DA) concentrations were significantly higher. These results suggest that juvenile pufferfish shows serious aggressive behavior at the low ration, which may be related to the decrease of 5-HIAA and MAOA concentrations, and the increase of DA concentrations.
... Video monitoring in our study area revealed that raccoons interacted aggressively during only 7% of interactions occurring at feeding stations (Hauver et al. unpublished data). Given that aggression typically increases at concentrated food resources4849, the average amount of aggression and social contacts between healthy raccoons in nonhuman-altered habitats may be much lower [50]. Although raccoons infected with rabies may be more aggressive than uninfected individuals, it is likely that tenuous connections, such as brief encounters at feeding sites, may not be generally sufficient for the transmission of rabies. ...
... This suggests that the behavioral response of fish to competitive situations is dependent on their size relative to their opponents. This size-dependent behavioral response implies that a stronger competition for food does not necessarily raise the general levels of aggression as suggested by previous studies (e.g., Sakakura and Tsukamoto 1998;Grant et al. 2002). Observing the fish outside the feeding period might have revealed different patterns, however, this was beyond the scope of our study. ...
Article
Full-text available
In many animal taxa, size-selective predation favors fast growth early in life. However, same-aged juveniles can diverge in size due to differences in genotype, environmental conditions, and parental effects and thus may vary in competitive ability. Under food scarcity, competitively inferior juveniles may suffer suppressed growth, whereas under benign conditions, small juveniles may exhibit growth compensation and perform as well as large ones. However, studies testing this while controlling for parental effects are lacking. Here, we hand-raised cichlids, Simochromis pleurospilus, from a wide range of egg sizes and manipulated their size by differential feeding. Afterward, high- and low-ration siblings were kept in groups assigned to either a high- or low-competition environment. We investigated how the degree of competition affected aggressiveness and growth of juveniles with different feeding histories. As predicted, when competition was high, high-ration offspring grew fastest. Interestingly, when competition was weak, low-ration juveniles grew at a similar rate as high-ration ones and many were able to catch up in size. High-ration fish were more aggressive than low-ration ones, and this effect was strongest under high competition. Additionally, in the high-competition environment, received aggression was negatively related to growth, and inflicted aggression correlated positively with the growth of the aggressor. These relationships were absent under low competition. Our findings suggest that the abilities to compensate for early growth depression depend on the prevalent level of competition. Aggression is likely used to monopolize food by juvenile S. pleurospilus; however, when competition is strong, aggression cannot compensate for a size disadvantage.
... Time spent moving was recorded as the total time, in seconds, and the focal fish was not stationary (Brown et al. 2006Brown et al. , 2014a). Foraging was recorded as pecking at the substrate, with the body at an angle greater than 45° relative to the substrate (Grant et al. 2002 ). A reduction in time moving and frequency of foraging attempts is consistent with an increase in predator avoidance behaviour in juvenile convict cichlids (Brown et al. 2006Brown et al. , 2014a). ...
Article
Full-text available
Recent studies have documented that exposure to high levels of background risk can induce neophobic predator avoidance in prey animals, whereby they respond to any novel cue with an anti-predator response. Such phenotypically plastic predator avoidance may allow prey to maximize anti-predator benefits in variable risk environments. It remains poorly understood whether risk assessment information from different sensory modalities can be integrated to induce generalized, cross-sensory system neophobic responses. Here, we directly test this hypothesis by exposing juvenile convict cichlids (Amatitlania nigrofasciata) to high- versus low-risk environments using either conspecific alarm cue (chemosensory risk) or a model avian predator (visual/mechanical risk) and testing their response to a novel chemosensory cue (Experiment 1) or visual cue (Experiment 2). Our results suggest that regardless of the sensory modality used to increased perceived risk, cichlids pre-exposed to high-risk conditions exhibited increased predator avoidance in response to any novel visual or chemical cue. As expected, cichlids pre-exposed to low-risk conditions did not display any neophobic responses. Our results suggest that induced neophobia is not cue specific; rather, it may function as a generalized response to perceived predation risk.
... While tolerance of joiners is common, optimal foraging theory predicts that when resources are defendable, food defence evolves or is facultatively expressed (Brown, 1964). In social foragers a discovered food patch may be aggressively defended by the finder if the cost of discovering another patch outweighs the cost of defence (Grant, 1993;Grant et al., 2002). This cost-benefit relationship depends on multiple factors including competitor density (Grant, 1993;Magellan et al., 2011); the finder's resource holding potential; the value of the discovered food patch; and the density of patches, which corresponds to the uncertainty of finding another patch (Grant, 1993;Dubois & Giraldeau, 2004Overington, Dubois & Lefebvre, 2008). ...
Article
Full-text available
Foraging in social groups has a number of benefits but can also increase the risk of exploitation. High tendency to shoal may be correlated with groups foraging, although facultatively social fish adjust both shoaling decisions and food resource defence based on intrinsic and extrinsic factors. The main aim of this study was to examine the relationships between shoaling, solitary foraging and aggression, forager tolerance of conspecifics joining at a discovered food patch and forager exploitation of resources discovered by others. We used two intra-lacustrine three-spined stickleback morph pairs, lava and mud, and monomorphic morphs from each of lava and mud habitats. The lava morph formed less cohesive shoals, was bolder during solitary foraging, approached and entered an occupied food patch less frequently than the mud morph, suggesting a link between shoaling and the propensity for social foraging. However, shoaling tendency and joiner tolerance were not correlated at a population level. Intralacustrine lava and mud morphs differed more markedly in joiner tolerance than morphs from single habitat lakes, whereas the opposite was true for shoaling tendency. We conclude that, in addition to differentiation in shoaling tendency, the lava and mud morphs differ in social foraging and these variations may act to promote population divergence.
... Time spent moving was recorded as the total time, in seconds, the focal fish was not stationary (Brown et al. 2006(Brown et al. , 2014. Foraging was recorded as pecking at the substrate, with the body at an angle [45°relative to the substrate (Grant et al. 2002). A reduction in time moving and frequency of foraging attempts is consistent with an increase in predator avoidance behaviour in juvenile convict cichlids (Brown et al. 2006(Brown et al. , 2014. ...
Article
Exposure to conditions of elevated predation risk, even for relatively short periods, has been shown to induce neophobic responses to novel predators. Such phenotypically plastic responses should allow prey to exhibit costly anti-predator behaviour to novel cues only in situations where the risk of predation is high. While there is evidence that the level of background risk shapes the strength of induced neophobia, we know little about how long neophobic responses are retained. Here we exposed juvenile convict cichlids (Amatitlania nigrofasciata) to three background levels of short-term background risk and then tested their responses to novel predator odours. Cichlids exposed to low risk did not show neophobic responses, while those exposed to intermediate and high risk did. Using extinction trials, we demonstrate that the retention of neophobic responses is greater among cichlids exposed to high versus intermediate predation risk conditions. Moreover, we found much longer retention of the neophobic responses when cichlids were tested a single time compared to when they were tested repeatedly in the extinction trials. This work supports the prediction that neophobic responses to specific odours are relatively long lasting but can quickly wane if the cues are experienced repeatedly without them being associated with risk. It is clear that background level of risk and the frequency of exposure to novel cues are crucial factors in determining the retention of risk-related information among prey.
... A group was deemed ready to start the experiment when all three fish would gather near the patches as soon as they were placed in the tank. To avoid satiation during trials but to ensure growth of the fish, each group was fed 5% of the total weight of the group in Kyowa cichlid pellets (1 mm diameter, Cape Girardeau, MO, U.S.A.) per day (Grant, Girard, Breau, & Weir, 2002). Because the energy budget of a fish typically scales with body mass (M) as M 0.75e1.0 ...
Article
Interspecific patterns of space use in mobile animals have been the subject of considerable study, with allometric slopes often varying between 0.63 and 1.36. Both the slopes and intercepts of these relationships have been typically related to the energetic requirements of the focal animal, in relation to the amount of energy available in the environment. However, other explanations for these patterns are possible, including the ability of the focal animal to move about and/or defend a home range. To provide insight into this issue, we investigated the allometry of patch defence in convict cichlids, Amatitlania siquia, in a laboratory setting while controlling for energetic requirements. By manipulating the distance between two patches of food (0, 20, 40, 60, 80 and 95. cm), we estimated the maximum diameter of an ephemeral territory for 15 dominant fish that differed in body size by almost 40-fold. As expected, dominant fish were less able to defend and monopolize the food as the distance between the patches increased. Furthermore, larger fish were able to defend larger territories than smaller fish. The allometric slope of 1.18 in our study was remarkably similar to the interspecific slopes of home range or territory size in the literature for a broad range of vertebrate taxa. While there are likely multiple causes for the interspecific patterns of space use, our results suggest that the mobility of the defender is just as likely an explanation as energetic requirements.
... Convict cichlid L Laboratory study of the effects of patch size upon prey monopolization and competitive aggression Dominant fish were seen to consumer more prey and exhibited more aggression when the patch size was smaller Grant et al. (2002) Archocentrus nigrofasciatus When prey patches were larger dominant fish were less able to monopolize them and more, and smaller fish were seen to feed. Perceived predation risk also led to lower levels of aggression in smaller patches Robb and Grant (1998) ...
Article
Intraspecific food competition exerts powerful selective forces on all animals; successful foragers thrive relative to weaker conspecifics. Understanding competition is therefore fundamental both to ecological insight and to conservation efforts. Fish are adaptable and tractable experimental organisms, offering excellent model systems for studies on competition, and they lend themselves to two approaches: (i) studies of short-term competition, which quantify the components of behavioural interactions; (ii) studies of long-term interactions, in which the indeterminate nature of fish growth makes it possible to measure rates directly and correlate them with competitive success. The nature and the intensity of competition vary according to resource characteristics and distributions in time and space, the ecological context, and the relative competitive abilities of the foragers. Second-order effects, such as winner and loser consequences, add to the complexity and frustrated early attempts to develop realistic models of intraspecific competition. Recently, however, considerable advances have been made in both laboratory and field studies on fishes adding to our understanding of these interacting effects. At the same time, the application of individual-based modelling offers the prospect of progress towards greater realism and accuracy in predicting competitive outcomes. This review draws together a wide and disparate literature on intraspecific competition in fishes to facilitate the work of both empiricists and theoreticians towards these important goals.
... Pairs of cichlids typically moved together within the test tank, so we arbitrarily followed one of the two in order to quantify time moving. For cichlids, foraging was defined as pecking at the substrate, with the body at an angle greater than 45° relative to the substrate (Grant et al., 2002). For trout, foraging behaviour was defined as any visible snapping movement directed towards the substrate or within the water column (Vavrek et al., 2008). ...
Article
Full-text available
Freshwater vertebrate and invertebrate prey species commonly rely on chemosensory information, including non-injury released disturbance cues, to assess local predation threats. We conducted laboratory studies to (1) determine if urea can function as a disturbance cue in juvenile convict cichlids and rainbow trout and (2) determine if the background level of urea influences the behavioral response to a subsequent pulse of urea ('background noise' hypothesis). In the first series of trials, juvenile cichlids and trout were exposed to urea at varying concentrations (0 to 0.5 mg L-1 for cichlids and 0 to 1.0 mg L-1 for trout). Our results suggest that both cichilds and trout exhibited functionally similar responses to urea and conspecific disturbance cues and that increasing the concentration of urea results in an increase intensity of antipredator behaviour. In the second series of trials, we pre-exposed cichlids or trout to intermediate or high concentrations of urea (or a distilled water control) and then tested for the response to a second pulse of urea at at intermediate or high concentrations (versus a distilled water control). Our results demonstrate that pre-exposure to urea reduces or eliminates the response to a second pulse of urea, supporting the background noise hypothesis. Together, our results suggest that pulses of urea, released by disturbed or stressed individuals, may function as an early warning signal in freshwater prey species.
... Time spent moving was recorded as the total time (s) that the focal fish was not stationary (Brown et al., 2006). We defined a foraging attempt as pecking towards the substrate with the body inclined at an angle greater than 45 to the substrate (Grant, Girard, Breau, & Weir, 2002). Decreased frequency of foraging attempts and time spent moving are indicative of an antipredator response in juvenile cichlids (Brown et al., 2006;Foam, Harvey, Mirza, & Brown, 2005;Wisenden & Sargent, 1997). ...
Article
Recent studies have established that variation in background level of risk has profound effects on antipredator phenotypes. Elevated levels of background risk not only change behaviour, but also physiology, morphology and cognitive function. A variety of prey show neophobic predator avoidance when exposed to short-term elevation in risk. Such phenotypically plastic responses allow prey to balance behavioural trade-offs in the face of uncertain risks. Here, we test the hypothesis that ontogeny functions as a constraining factor in the induction of neophobic predator avoidance. In a series of laboratory trials, we exposed convict cichlids, at three different ontogenetic stages (eggs/wrigglers, juveniles and adults), to conditions of elevated (versus low) risk and tested their response to a novel predator odour (rainbow trout, Oncorhynchus mykiss). When cichlids were exposed as eggs and newly hatched ‘wrigglers’ and tested 21 days later, they showed a significant antipredator response to trout odour. When exposed as ∼18 mm juveniles, cichlids showed a significant avoidance when tested 24 h post-exposure, but not 21 days post-exposure. However, when conditioned as ∼50 mm adults, we found no evidence of induced neophobia. Combined, these results suggest that ontogenetic stage may limit phenotypically plastic neophobia.
... The frequency of aggression is predicted to show a dome-shaped relationship (i.e. a peak at an intermediate value with decreasing values on either side) with a number of variables including competitor density (Grant, 1993(Grant, , 1999. For example, in the convict cichlid, this pattern is found in Competitor density and resource defence 913 relation to the competitor-to-resource ratio (Noe¨l et al., 2005) and food abundance (Grant et al., 2002); theoretical models support this prediction (Dubois et al., 2003;Dubois and Giraldeau, 2005). A feature of this relationship is a lower threshold, below which the chance of encountering a conspecific is so low that resource defence is unnecessary, and an upper threshold above which the encounter rate is so high that costs of defence exceed the benefits making it uneconomical. ...
Article
Full-text available
The concept of economic defendability states that individuals will only defend resources when the benefits outweigh the costs. Competitor density is one factor that influences resource defence among fishes, resource defence being predicted to be highest at intermediate competitor densities and reduced at higher and lower densities, producing a dome shaped relationship. We investigated the effects of competitor density using male swordtails, which form dominance hierarchies and have already been demonstrated to defend a food resource. We found that both aggression (F2,32 = 5.392; P = 0.010) and time at a food resource (F2,32 = 3.574; P = 0.040) vary with differences in competitor density, and that the frequency of aggression significantly predicts time at the food resource only at an intermediate density (P = 0.033; r2adj = 0.219). The ability to vary the level of defence with respect to the immediate environment may result in fitness benefits to male swordtails. Further studies examining changes in behaviour over time and examining interacting influencing factors would be beneficial.
... Convict cichlid fish were chosen because they engage in aggressive interactions to secure and maintain access to a number of different resources. Males of this serially monogamous fish aggressively defend their nest, mate, and offspring from any predator or opponent, compete for access to food, and perform similar types of aggressive behavior in the field and the laboratory (Wisenden, '95;Grant et al., 2002;Leiser et al., 2004;Santangelo and Itzkowitz, 2006). Adults were obtained from Pet Solutions (Beavercreek, OH), and housed in the laboratory as mixed-sex groups of 30-35 individuals in holding ponds maintained at 26˚C (±2˚C) with chemical and biological filtration, a gravel substrate, and overabundant shelter (broken terra cotta pots). ...
Article
This study explored whether convict cichlid fish mount a hormonal response to aggressive encounters where dominance status remains unresolved. Hormone samples were collected at two time points before an aggressive interaction to obtain confinement-induced and baseline measures, and at one time point following a contest across a clear partition (experimental) or exposure to an opaque partition with an opponent on the opposite side (control). There was no overall significant effect of treatment (control vs. experimental) on hormone release rates but there were trends for cortisol and testosterone (T). A priori linear contrasts showed that individuals that engaged in aggressive interactions had lower postfight cortisol and T release rates than controls, suggesting that aggression, in this context, might attenuate the synthesis of both hormones. Cortisol decreased significantly between initial confinement and baseline, indicating that individuals habituate to the water-borne hormone collection procedure. Contrary to expectation, individuals with higher baseline T and 11-ketotestosterone (KT) release rates took longer to initiate conflict. None of the other measures of behavior were predicted by baseline hormone release rates, and contest behavior did not predict postfight hormone release rates. There was a significant positive relationship between KT and T at all time points. As with studies that employ mirror image stimulation, we found no hormonal response to unresolved contests despite high levels of aggressive behavior. Our study is unique because we demonstrate that animals engaged in conflict with live opponents also do not mount a significant hormonal response when clear dominance relationships are not established.
... temperature of 26°C, and a salinity of 0 (Martinez-Cardenas et al. 2013. As reported in most studies, in high stocking densities, the intraspecific competition increases, which generates stress that results in poor condition of the attacked fish (Barcellos et al. 1999, Grant et al. 2002, Lin et al. 2009, Osofero et al. 2009, Van de Nieuwegiessen et al. 2009, Zhang et al. 2010, Narejo et al. 2010, Castillo-Vargasmachuca et al. 2012, Chattopadhyay et al. 2012, Luo et al. 2012. High stocking densities can lead to poor food intake and increased energy expenditure due to competition for space and food (Diana et al. 2004), leading to anorexia or deformities due to nutritional deficiencies (Garcia et al. 2013). ...
Article
Full-text available
The present study aimed to test the effect of three stocking densities: 100, 200, and 300 ind m-3 (D100, D200, and D300, respectively) on survival, growth (weight and total length), and condition factor of Microphis brachyurus. At the end of the six-week trial, there were no significant differences in the fish's survival, growth, and condition. The results suggest that this species presents high adaptability under culture conditions. A suboptimal stocking density generates a suboptimal use of infrastructure and decreases the production system's profitability. Based on the present study, a stocking density of 300 ind m-3 is recommended to increase the aquaculture infrastructure's profitability for ornamental or conservation purposes.
... Conversely, when food is extremely abundant, an aggressive individual excluding others from a food source may waste energy that could be allocated to more profitable activities, such as feeding or resting, and may expose itself to higher predation risks (Carpenter 1987;Martel 1996;Diaz-Uriarte 1999;Kim et al. 2004;LaManna and Eason 2007). Hence, resource defense should usually peak at intermediate levels of abundance as well as of spatial clumping of resources (Grant 1993;Grant and Guha 1993;Grant et al. 2002;No€ el et al. 2005). This leads to variable levels of resource monopolization in a population and can thereby affect mating systems (Emlen and Oring 1977) and population dynamics (Patterson 1980;Newton 1992;Lopez-Sepulcre and Kokko 2005). ...
Article
Full-text available
Resource defense behavior is often explained by the spatial and temporal distribution of resources. However, factors such as competition, habitat complexity, and individual space use may also affect the capacity of individuals to defend and monopolize resources. Yet, studies frequently focus on one or two factors, overlooking the complexity found in natural settings. Here, we addressed defense and monopolization of nectar feeders in a population of free-ranging ruby-throated hummingbirds marked with passive integrated transponder (PIT tags). Our study system consisted of a 44 ha systematic grid of 45 feeders equipped with PIT tag detectors recording every visit made at feeders. We modeled the number of visits by competitors (NVC) at feeders in response to space use by a focal individual potentially defending a feeder, number of competitors, nectar sucrose concentration, and habitat visibility. Individuals who were more concentrated at certain feeders on a given day and who were more stable in their use of the grid throughout the season gained higher exclusivity in the use of those feeders on that day, especially for males competing against males. The level of spatial concentration at feeders and its negative effect on NVC was, however, highly variable among individuals, suggesting a continuum in resource defense strategies. Although the apparent capacity to defend feeders was not affected by competition or nectar sucrose concentration, the level of monopolization decreased with increasing number of competitors and higher nectar quality. Defense was enhanced by visibility near feeders, but only in forested habitats. The reverse effect of visibility in open habitats was more difficult to interpret as it was probably confounded by perch availability, from which a bird can defend its feeder. Our study is among the first to quantify the joint use of food resource by overlapping individuals unconstrained in their use of space. Our results show the importance of accounting for variation in space use among individuals as it translated into varying levels of defense and monopolization of feeders regardless of food resource distribution.
... Japanese medaka Oryzias latipes, Magnuson, 1961;Robb and Grant, 1998; chum salmon Oncorhynchus keta, Ryer and Olla, 1995; coho salmon Oncorhynchus kisutch, Ryer and Olla, 1996; Atlantic salmon Salmo salar, Cañon Jones et al., 2010). However, this is not always the case since in convict cichlid Archocentrus nigrofasciatus aggressive behaviour was low when food was limited, increased when food became abundant but decreased again when food was in excess (Grant et al., 2002). ...
Article
In intensive aquaculture, aggression among fish creates a disturbed social environment and leads to serious implications. Food is a resource of great importance for fish and its acquisition is an important enough reason for increased competition. Gilthead seabream Sparus aurata and European seabass Dicentrarchus labrax are the two main reared species of the Mediterranean aquaculture and known to exhibit aggressive behaviour. The present study aimed at investigating the effects of food quantity (low and high feeding ration, i.e. 1% and 3% of body mass) and method of food distribution (localised and dispersed) in the aggressive behaviour of these two species (mean initial body mass 39 g), before, during and after feeding. Analyses of data obtained showed that: a) Both species are most aggressive during feeding. b) In the case of gilthead seabream, aggression is intensified when fish are fed a low feeding ration, while the method of food distribution has no effect on aggression. However, a higher degree of social stress in feeding and non-feeding periods is indicated when the low feeding ration is distributed locally (i.e. appearance of dark vertical bands on the body). c) In the case of European seabass, aggression is intensified not only during feeding but also before and after feeding, especially at the low feeding ration under localised feeding. d) In both species aggressive acts are mainly biting and chasing, but the relative importance of each behavioural pattern is differently expressed in each species, especially before and after feeding. Present results add to a better understanding of gilthead seabream and European seabass aggression and could help towards an improved feeding practice in these species intensive rearing. Feeding an adequate amount of food and distributing it in a dispersed way can appease fish competition and spare energy for growth, thus providing for fish welfare and productivity.
... The present study is based on histochemical demonstration of glycoproteinic contents of the intestine of a popular aquarium fish Amatitlania nigrofasciata, which has also been used for behavioral studies (Townshend and Wootton, 1985;Budaev et al., 1999;Grant et al., 2002;Foam et al., 2005). For comparison of the content of mucosubstances of different parts of digestive tract, the cells oriented in anterior, mid and posterior parts of intestine were identified by their specific staining properties. ...
Article
Full-text available
In the present study, some histochemical features of goblet cells of the intestine of convict cichlid (A. nigrofasciata) were described. In order to reveal the main histological construction, transverse sections of different parts of intestine were firstly stained with hematoxylin eosin (HE). Sections of anterior, mid and posterior intestinal segments were also treated with different staining methods of alcian blue (AB) at pH 2.5, aldehyde fuchsin (AF), periodic acid-Schiff (PAS), KOH/PAS and PAS/AB (pH 2.5) and investigated. Goblet cells of anterior intestine were colored strongly by AB (pH 2.5), AF and PAS; and moderately by PAS/AB (pH 2.5) (AB dominant). In the mid part of the gastrointestinal tract, goblet cells were also stained strongly with AB, PAS and PAS/AB (pH 2.5) (AB dominant), however, their reactions to KOH/PAS treatment were recorded as negative. Because of numerous supranuclear vacuoles of the epithelial cells, only a few goblet cells could be differentiated in posterior parts of alimentary channel, with their weakly reaction to AB (pH 2.5), PAS and PAS/AB (pH 2.5). Moreover, these cells were not stained with AF and KOH/PAS. According to their affinities, goblet cells oriented in anterior and the mid intestine were mainly classified as acidic (AB-positive) and neutral (PAS-positive). Statistical analysis were confirmed that, the numbers of acidic and neutral cells of per unite square of epithelial area were significantly different.
... The present study is based on histochemical demonstration of glycoproteinic contents of the intestine of a popular aquarium fish Amatitlania nigrofasciata, which has also been used for behavioral studies (Townshend and Wootton, 1985;Budaev et al., 1999;Grant et al., 2002;Foam et al., 2005). For comparison of the content of mucosubstances of different parts of digestive tract, the cells oriented in anterior, mid and posterior parts of intestine were identified by their specific staining properties. ...
Article
Full-text available
In the present study, some histochemical features of goblet cells of the intestine of convict cichlid (A. nigrofasciata) were described. In order to reveal the main histological construction, transverse sections of different parts of intestine were frstly stained with hematoxylin eosin (H-E). Sections of anterior, mid and posterior intestinal segments were also treated with different staining methods of alcian blue (AB) at pH 2.5, aldehyde fuchsin (AF), periodic acid-Schiff (PAS), KOH/PAS and PAS/AB (pH 2.5) and investigated. Goblet cells of anterior intestine were colored strongly by AB (pH 2.5), AF and PAS; and moderately by PAS/AB (pH 2.5) (AB dominant). In the mid part of the gastrointestinal tract, goblet cells were also stained strongly with AB, PAS and PAS/AB (pH 2.5) (AB dominant), however, their reactions to KOH/PAS treatment were recorded as negative. Because of numerous supranuclear vacuoles of the epithelial cells, only a few goblet cells could be differentiated in posterior parts of alimentary channel, with their weakly reaction to AB (pH 2.5), PAS and PAS/AB (pH 2.5). Moreover, these cells were not stained with AF and KOH/PAS. According to their affnities, goblet cells oriented in anterior and the mid intestine were mainly classifed as acidic (AB-positive) and neutral (PAS-positive). Statistical analysis were confrmed that, the numbers of acidic and neutral cells of per unite square of epithelial area were signifcantly different.
... Artificial foliage consisting of green plastic strips attached to an inert glass weight in each tank was placed. Two segments of PVC tubing (10 cm long and 2.54 cm diameter) were placed to provide shelter for the fish at the possibility of the emergence of aggressive behavior typical of species in the cichlid family (Grant et al., 2002;Leiser et al., 2004;Arnott & Elwood, 2009;Heg, 2010;Lorenz et al., 2011). ...
Article
Full-text available
Wild populations of the green mojarra Cichlasoma beani, are being pressured by anthropogenic activities. It is possible to mitigate the deterioration of native species populations by developing culture techniques. Environmental factors such as light intensity and photoperiod may affect the development of fish under culture conditions. Therefore, the aim of the present study was to examine the effect of these factors on growth, survival, and condition of C. beani cultured in different light intensities and photoperiods. Light intensities of 1000, 1500 and 2000 lux and photoperiod 24:00, 16:08 and 08:16 Light:Dark (L:D) were tested in 40 L tanks (10 fish per tank, three replicates per treatment) during eight weeks. There were no significant differences in light intensity or photoperiod, which was associated with the natural adaptation of the species to these factors. The results also suggested the favorable overall growing conditions during the trial and he response of the life cycle stage of the specimens used in this study. The results of the present study indicate that the natural adaptations of C. beani, allow the favorable culture in various light conditions in juveniles, which can be advantageous for commercial culture as may imply low energy costs.
... Fish were fed with approximately 1% of the total biomass of the experimental tank. This single feed delivery point set-up is known to trigger territoriality and feeding competition among the individuals and dominant fish, at higher positions in the social hierarchical rank, tend to monopolise the feeding point [51][52][53][54]. The exact physical position of the fish in relation to the feeding point was recorded every 5 minutes before (1 hour = 12 frames) and every 5 minutes after (1 hour = 12 frames) feeding events (24 frames in total). ...
Article
Full-text available
Dominance is defined as the preferential access to limited resources. The present study aimed to characterise dominance in a non-aggressive flatfish species, the Senegalese sole (Solea senegalensis) by 1) identifying dominance categories and associated behaviours and 2) linking dominance categories (dominant and subordinate) with the abundance of selected mRNA transcripts in the brain. Early juveniles (n = 74, 37 pairs) were subjected to a dyadic dominance test, related to feeding, and once behavioural phenotypes had been described the abundance of ten selected mRNAs related to dominance and aggressiveness was measured in the brain. Late juveniles were subjected to two dyadic dominance tests (n = 34, 17 pairs), related to feeding and territoriality and one group test (n = 24, 4 groups of 6 fish). Sole feeding first were categorized as dominant and sole feeding second or not feeding as subordinate. Three social behaviours (i. ªResting the headº on another fish, ii. ªApproachingº another fish, iii. ªSwimming above anotherº fish) were associated with dominance of feeding. Two other variables (i. Total time occupying the preferred area during the last 2 hours of the 24 h test, ii. Organisms occupying the preferred area when the test ended) were representative of dominance in the place preference test. In all tests, dominant fish compared to subordinate fish displayed a significantly higher number of the behaviours ªRest the headº and ªApproachesº. Moreover, dominant sole dominated the sand at the end of the test, and in the group test dominated the area close to the feed delivery point before feed was delivered. The mRNA abundance of the selected mRNAs related to neurogenesis (nrd2) and neuroplasticity (c-fos) in dominant sole compared to subordinate were significantly different. This is the first study to characterise dominance categories with associated behaviours and mRNA abundance in Senegalese sole and provides tools to study dominance related problems in feeding and reproduction in aquaculture.
... We created territories for single individuals of both sexes and set out to alter territory value by the presence or absence of a nest site within a territory, as well as by supplementing territories with an abundant food source. Both the presence of nest sites and food availability have been shown to affect behavior in this species in certain contexts (Gumm and Itzkowitz 2007;Grant et al. 2002). ...
Article
Full-text available
Synopsis In animal contests, the value an individual assigns to limited resources can directly impact the level of aggression it demonstrates. For territorial species, individuals often assess their territory quality and appropriately modify the time and energy invested in its defense. In this study, male and female convict cichlids, Amatitlania nigrofasciata, were acclimated to one of three territorial treatments representing either a low, medium, or high resource value. Territories with a “Low Value” included substrate alone, “Medium Value” territories included substrate and a nest site, and a “High Value” territory included substrate, a nest site, and constant food source. After three days of acclimation, a size-matched intruder was introduced to elicit territorial aggression and behaviors were observed. Territory quality affected one measure of low-intensity aggression (displays) in residents but had no effect on high-intensity aggression (bites and chases). Moreover, there was a significant effect of sex, with males and females differing in the types of aggressive behaviors demonstrated across all treatments. Females showed more low-intensity aggressive behaviors toward intruders than males did. Additionally, a significant interaction of sex and territory quality was observed on two measures of high-intensity aggressive behavior (bites and chases), with females more likely than males to increase aggressive behaviors along with increasing territory quality. This suggests that females may be more sensitive and/or responsive to changes in the quality of a territory, possibly due to the necessity of a suitable nest site for egg deposition within a territory.
... Although much research has focused on advantages to the signaler within a communication network, it is important to also consider the receiver's response to a signal (Searcy and Nowicki 2005)-as the response to a signal may vary depending on the context in which that signal is displayed. Benefits of responding to a signal can depend on multiple factors, both social and environmental (Gill and Wolf 1975;Carpenter 1987;Grant et al. 2002;Johnson et al. 2004;Golabek et al. 2012;Queller and Murphy 2017). It is clear that individuals benefit through modifying their aggression based on social context (Clutton-Brock 1988). ...
Article
Full-text available
Status signals have evolved for individuals to avoid energetic and physical costs of resource defense. These signals reflect an individual’s competitive ability and therefore influence competitors’ decisions on how to invest in a fight. We hypothesized that the response of receivers to status signals will depend on the social context. During territorial defense, group members may provide support to a territory owner by participating in defense. We investigated whether the presence of juveniles—who group together with territorial males—alters the territorial male’s attack decisions and level of aggression in the black-crested titmouse (Baeolophus atricristatus). Crest-length in this species functions as status signal. We simultaneously presented two taxidermic male models in a territory: one with an unmanipulated crest and one with a modified shortened crest. Models were presented to males that had resident juveniles cohabiting on their territory, and to males without juveniles. During intrusions, juveniles actively defended against the simulated intruders by approaching and sometimes attacking. The presence of juveniles affected how territorial males responded to the status signals of the intruders: when juveniles were present, males were more likely to first attack the model with the unmanipulated crest (i.e., longer, and more threatening), compared to males residing without juveniles. This suggests that juvenile support alters the risk-taking decision of the territorial male. To our knowledge, this is the first indication that behavioral responses to a status signal depends on the presence of supportive group members. Significance statement Status signals can indicate relative quality of animals and can therefore be used to evaluate a competitor when deciding whether or not to fight over resources. The black-crested titmouse has been shown to use its crest length as a status signal during fights over food. In our study, we assessed if this status signal is also used in territorial defense, by conducting an experiment where we presented two taxidermic male models with different crest sizes to a territorial male. We also investigated whether juvenile presence influenced which model was attacked. In trials where juveniles were present, territorial males attacked the longer crested model significantly more often than in trials where territorial males were alone. This suggests that the presence of juveniles, which help the male defend the territory, allows the male to attack the more aggressive-appearing intruder.
... Although exceptions exist 95 , exposure to food shortages have been shown to generally increase aggression in other species 38,82,86,[96][97][98] , including ectotherms 93,99 . Thus, our finding that surviving pairs in our high-temperature treatment were generally more aggressive than those in our low-temperature treatment is supported by the literature and hints at behavioural adjustment or plasticity as a means to cope with stress (e.g., potential food www.nature.com/scientificreports/ ...
Article
Full-text available
Our understanding of how projected climatic warming will influence the world’s biota remains largely speculative, owing to the many ways in which it can directly and indirectly affect individual phenotypes. Its impact is expected to be especially severe in the tropics, where organisms have evolved in more physically stable conditions relative to temperate ecosystems. Lake Tanganyika (eastern Africa) is one ecosystem experiencing rapid warming, yet our understanding of how its diverse assemblage of endemic species will respond is incomplete. Herein, we conducted a laboratory experiment to assess how anticipated future warming would affect the mirror-elicited aggressive behaviour of Julidochromis ornatus, a common endemic cichlid fish in Lake Tanganyika. Given linkages that have been established between temperature and individual behaviour in fish and other animals, we hypothesized that water warming would heighten average individual aggression. Our findings support this hypothesis, suggesting the potential for water warming to mediate behavioural phenotypic expression through negative effects associated with individual health (body condition). We ultimately discuss the implications of our findings for efforts aimed at understanding how continued climate warming will affect the ecology of Lake Tanganyika fishes and other tropical ectotherms.
... When the resource is abundant, aggression is not necessary as all individuals can forage to satiation. Conversely, if the resource is too scarce, the cost of aggression exceeds the potential gain in foraging opportunities (Brown 1964), resulting in a decrease in aggression rates (Grant et al. 2002;Toobaie and Grant 2013). However, these patterns might be altered by predation risk as both the availability of resources and the risk of predation are known to affect aggression rates. ...
Article
Full-text available
Aggressive behaviour when competing for resources is expected to increase as the ratio of competitors to resource units (CRR) increases. Females are expected to be more aggressive than males when competing for food when body size is more strongly related to reproductive success in females than in males, whereas aggression is predicted to decrease under high ambient predation risk by natural selection. Under the risk allocation model, however, individuals under high ambient predation risk are expected to be more aggressive, and forage more in the absence of imminent risk than their low risk counterparts. An interaction between adult sex ratio (i.e. adult males/females), ambient predation risk (high vs. low), and sex on intrasexual competition for mates in Trinidadian guppies has been shown. The interaction suggested an increase in aggression rates as CRR increased, except for males from the high predation population. To compare the patterns of competition for food versus mates, we replicated this study by using food patches. We allowed four male or four female guppies from high and low predation populations to compete for 5, 3 or 1 food patches. The foraging rate was higher in a high rather than low ambient predation-risk population. Surprisingly, CRR, sex, and population of origin had no effect on aggression rates. Despite other environmental differences between the two populations, the effect of ambient predation risk may be a likely explanation for differences in foraging rates. These results highlight the importance for individuals to secure food despite the cost of competition and predation.
... The occurrence of resource defense is predicted to be highest at intermediate levels of food abundance (Grant et al. 2002). When food is scarce the defended territory does not provide enough resources to cover the energetic costs of aggressive defense behavior whereas during high levels food abundance individuals that do not defend resources can obtain the same amount of food as territorial individuals without paying the costs of defense. ...
Thesis
Zahlreiche Forschungsarbeiten haben gezeigt, dass nicht nur Menschen, sondern auch Tiere konstante individuelle Unterschiede im Verhalten aufweisen. Zu verstehen warum sich diese Verhaltensunterschiede im Laufe der Evolution entwickelt haben, ist ein Ziel dieses Forschungsbereiches. In dieser Arbeit wurde untersucht wie verschiedene Modulatoren das Nahrungssuchverhalten von Blütenfledermäusen (Glossophaginae) beeinflussen um individuelle Verhaltensunterschiede zu quantifizieren und theoretische Vorhersagen zu testen. Alle Experimente wurden in naturnaher Umgebung mit programmierbaren, künstlichen Blüten durchgeführt. Es wird angenommen, dass die Plastizität von Verhalten ein generelles Merkmal ist in dem sich Tiere unterscheiden, da manche Individuen allgemein stärker auf Reize aus der Umwelt reagieren könnten als andere. Um diese Vorhersage zu testen, wurde die Nahrungsverfügbarkeit experimentell manipuliert und zwei Arten von Verhaltensplastizität in denselben Individuen gemessen. Die Ergebnisse unterstützen diese Annahme jedoch nicht, da die beiden Arten von Verhaltensplastizität nicht korrelieren. Neben Umwelteinflüssen können auch innere Merkmale wie die Stoffwechselrate das individuelle Nahrungssuchverhalten beeinflussen. Die Ergebnisse zeigen, dass sich die Individuen in ihrem täglichen Energieverbrauch unterscheiden und dass diese Unterschiede mit dem Explorationsverhalten während der Nahrungssuche korrelieren. Zusätzlich kann das individuelle Nahrungssuchverhalten auch von sozialen Faktoren beeinflusst werden. Bei limitierter Nahrungsverfügbarkeit verteidigen einzelne Männchen Blüten gegen andere Männchen, jedoch nicht gegenüber Weibchen. Individuelle Unterschiede in der Aggression und Aktivität werden dagegen nicht von der sozialen Gruppenzusammensetzung beeinflusst. In dieser Arbeit wurden nicht nur individuelle Unterschiede im Nahrungssuchverhalten von Blütenfledermäusen bestimmt, sondern auch Vorhersagen aus dem Bereich der Persönlichkeitsforschung bei Tieren überprüft.
... Time spent moving was recorded as the total time (in sec) that the focal fish was not stationary (Brown et al. 2006(Brown et al. , 2014. Foraging was recorded as pecking at the substrate, with the body at an angle >45°to the substrate (Grant et al. 2002). A reduction in time moving and foraging attempts is consistent with increased predator avoidance behaviour in juvenile cichlids (Brown et al. 2006(Brown et al. , 2014. ...
Article
Exposure to elevated levels of background predation risk is known to shape the behavioural response of prey organisms to known and unknown predation threats. However, less is known regarding the effects of background predation risk on predator recognition learning. Here, we test the potential effects of elevated background predation risk on the strength and retention of learned predator recognition in juvenile convict cichlids (Amatitlania nigrofasciata). In a series of laboratory trials, we exposed shoals of juvenile cichlids to conditions of elevated (vs. low) levels of background risk and then conditioned them to recognize a novel predator odour (rainbow trout, Oncorhynchus mykiss). The results of our first experiment demonstrate that despite showing reduced response intensities during initial conditioning (due to risk allocation), conditioned cichlids from high vs. low background risk show similar intensities of learned recognition when tested 24 h post-conditioning. Moreover, elevated levels of background risk induced a predator avoidance response among unconditioned cichlids (due to induced neophobia). Our second experiment demonstrates that while we find no difference in the strength of learning when tested 24 h post-conditioning, retention of acquired recognition is enhanced among cichlids from the high background predation risk treatment. Together, our results highlight the complex interacting effects past experience plays in shaping the response to acute predation threats.
... However, despite the extensive literature concerning resource value and contestant behaviour, there is limited information available concerning whether individuals alter their motivation if the availability of the resource fluctuates over time. In a series of experimental studies investigating how resource distribution affects decision making, No€ el, Grant, and Carrigan (2005; see also Grant, Girard, Breau, & Weir, 2002) showed that the number of chases between convict cichlids, Archocentrus nigrofasciatus, increased when the ratio between contestant density and defensible food patches increased from 1:1 to 2:1. However, as the ratio increased beyond 2:1 there was a significant decline in aggressive chases. ...
Article
Full-text available
Theory expects contestants to adjust their investment in fighting in line with the perceived value of a resource. Thus, we expect to see an increase in contest duration or aggressive actions if the subjective value of the resource is estimated to be high relative to occasions where the value is estimated to be low. Although this expectation is well established in theory, we know little about how contestants structure their contests over resources in the wild: in particular, how variation in resource availability affects how contestants invest in fights. The objectives of this study were twofold: to examine whether (1) the structure of male–male fights varied with presence and abundance of oestrous females in the population and (2) there was an association between investment in fighting and mating success, during fights between fallow deer, Dama dama. Subordinate but not dominant contestants increased their rate of attacking actions when there were oestrous females in the population. However, there was no association between dominant or subordinate contest actions and variation in the number of oestrous females on any single day. Regarding mating success, dominant males that increased their attack rate during fights were more likely to achieve a mating than those that did not, although this investment in attacks was not associated with the number of matings obtained. Conversely, mating success was associated with a reduction in the number of parallel walks for subordinate contestants. Therefore, subordinate males achieved more matings when ritualized display behaviour was reduced or omitted from the contest. These results suggest that a desperado effect may be present, and that contestants use an estimate of resource value rather than opponent quality when investing in contests.
... There are several studies demonstrating that aggression between individuals increases as the availability of food resources decreases (Grant et al., 2002;Lim et al., 2014), or as the time spent with individual conspecifics decreases (i.e., more aggressive towards unfamiliar as compared to familiar individuals; Utne-Palm & Hart, 2000). Similar results have been found when relatedness is considered, either on an individual level or in groups (Brown & Brown, 1996;Olsén & Järvi, 1997;Belisle & Chapais, 2001;Griffiths & Armstrong, 2002). ...
Article
Kin selection explains conditions under which closely related individuals should be less antagonistic towards one another. One benefit of kin selection is a reduction in aggression towards kin in various social contexts, such as foraging. In the gynogenetic Amazon molly, females have been shown to differentiate between clone types, preferring to associate with clonal sisters to non-sisters, regulating their aggressive behaviours accordingly. We ask if Amazon mollies in resource-limited environments retain the ability to regulate aggressive behaviours according to relatedness. We found that focal females regulated their aggressive behaviours depending on partner type. Females spent more time behaving aggressively towards the heterospecific females than either of the clonal lineages, and towards non-sister clones compared to clonal sisters. We are able to confirm that kin discrimination is maintained, resulting in females showing more aggression towards heterospecific females and non-sister clones in a food-limited environment, and that this aggression scales with relatedness.
... Although growth rates in rivers increase with the length of the territorial period (Katano & Iguchi, 1996), only c. 10% of Ryukyu-ayu establish feeding territories (Awata et al., 2012). This may be caused by the low food supply for this species in rivers, as the number of non-territorial individuals usually increases when the cost of defending territories exceeds the benefit of being territorial; that is, either the food is scarce or in excess (Grant et al., 2002). Considering this, Ryukyu-ayu that fail to gain territories (i.e., non-territorial individuals) may be better able to avoid competition for algal foods in rivers and visit estuaries to locate other food sources. ...
Article
In the Yakugachi River, Amami‐Oshima Island, southern Japan, low nutrient concentrations in the river suggest that food availability is limited for the subtropical ayu sweetfish Plecoglossus altivelis ryukyuensis. Since sweetfish is an amphidromous fish that mainly grows in rivers after spending 2 months in the sea, limited food availability in rivers would force this species to migrate to other habitats with better food availability. Otolith increment and Sr–Ca analyses of 48 adult sweetfish collected from the Yakugachi River revealed that all individuals visited estuaries more than three times after moving upstream. Although the specific growth rates of this species in the river had no correlation with the salinity profile in the fluvial period, this movement may be an adaptive choice because the salinity profile significantly affected the body size at maturity. Our results highlighted individual‐based variations in amphidromous migration for utilising estuaries, which could be explained by relatively higher productivity in estuarine than in freshwater and marine habitats. This article is protected by copyright. All rights reserved.
Conference Paper
Full-text available
One of the most popular tropical fish kept in the aquariums is the Angelfish. Angelfish belongs to the Cichlidae family and especially the species Pterophyllum scalare were found in the Amazone river and in the coastal rivers of Guinea. It distinguishes itself from other tropical species by its breeding behavior which involves competition for territory sexual partners courtship and parental care. This research paper examines the spawning technique for the production of Angelfish, Pterophyllum scalare. The reproduction experiments were carried out at the laboratory of Ornamental fish culture in the Technological Educational Institution of Messolonghi in West Greece. Six pair of mature angelfish Pterophyllum scalare were kept in captivity for 120 days in 75 L aquarium tanks and natural photoperiod. The aquarium was filled with 4 o dH soft water, which is taken from a Reverse osmosis unit. There is a continuous aeration flow rate supported by an external aeration system. Flirtation was accomplished with an external biological filter, including as substrate siphorax and zeolite for removing ammonia from aquarium. The water temperature was kept between 28 and 30 o C with a 100 W heater placed in the one corner of the aquarium. pH is between 6.5 and 6.8 and dissolved oxygen range from 7,7 to 8,0 mg/lt. The physical-chemical parameters such as pH, temperature, hardness, ammonia, nitrite and nitrate level were monitored every two days. They were fed to satiation three times per day. The diet was a mixture of pellets, flakes, bloodworms, daphnia, Cyclops, tubifex worms and mosquito larvae. At the end of the experiment 120 fry of the same age were produced. The survival rate was 60%. INTRODUCTION The fresh water Angelfish is found in the central Amazon River of Brazil and tributaries into Peru, Colombia, French Guinea and eastern Ecuador. They inhabit swamps or flooded grounds where the aquatic vegetations are dense and the water is clear or silty. Pterophyllum scalare, are members of the Cichlidae family and they have hold a unique position in the world fish keeping in Aquariums. Angelfish have been called the « King of the aquariums» because they are extremely beautiful animals, with highly varied finnage and color schemes. The adults have a length up to 15cm and their colors may be gold silver, black or marbled. The most common coloring of the wild species is silver with dark vertical bars. Juvenile have 7 stripes on their side and the adults have 4 stripes. Their body is compressed and disc-shaped. The dorsal (top) and the anal (bottom) spiny rays increase in length from anterior (front) to posterior (back) of the fin.
Article
Individual spatial positioning plays an important role in mediating the costs and benefits of group living and, as such, shapes different aspects of animal social systems including group structure and cohesiveness. Here, we aim to quantify variation in individual spacing behaviour and its correlates in a group of wild Assamese macaques (Macaca assamensis) in north-eastern Thailand, which experiences both predation pressure and within-group feeding competition. Data on individual spatial positions were collected during group scans using GPS devices and results suggest that both group cohesiveness and individual spatial positions within a group can be adjusted to mediate the costs and benefits of group living. Individuals had greater nearest neighbour distances and lower numbers of close neighbours when the group was feeding, compared to when the main group activity was resting/social or moving. This is likely due to the high costs of proximity associated with feeding competition. Immature individuals and females with young infants which are more vulnerable to predation were located closer to the centre of the group than both adult males and females without infants. This indicates the importance of predation risk in driving individual spatial position. Among adults, higher ranking individuals occupied more central positions within the group while lower ranking individuals were more peripheral. It appears that low ranking individuals trade reduced feeding interference and improved feeding success for increased predation risk. This could help explain why females in the study population do not display a rank related skew in energy intake.
Thesis
Full-text available
Global Climate Change will increase precipitations in the temperate and Northern coast of Europe during winter and spring. In riverine ecosystems, precipitations affect strongly the discharge of running waters and, thus, it is predicted that streams will face more severe floods. Additionally, air and water temperature will increase all over the world. These new environmental conditions can alter the phenology of species and predator/prey interactions. Newborns of brown trout (Salmo trutta L.) start their exogenous feeding in March/April. This stage is a critical step as individuals undergo huge physiological and behavioral changes. To allow a good development and a high survival rate, preys have to be abundant, particularly during early ontogenesis when fish are most vulnerable to food scarcity and predation. In this thesis, experiments in controlled-environment were conducted to estimate the effect of water velocity on the drift of preferred prey taxa for salmonids and to understand the effect of temperature on the metabolism of alevins facing starvation. Experiments in semi-natural conditions were set up to better understand the effects of floods on invertebrate communities and on survival, behavior and growth of first-feeding alevins. Our data support that floods affect trout differently depending on when they start feeding (early or late spring) and the availability of prey in their environment.
Article
Competition is a fact of life. It can take many forms, but biologists usually recognize two broad categories. In the first one, called exploitative or scramble competition, the contests are like races. The most food goes to the animal that eats the fastest, the best shelter is occupied by whoever reaches it first, and the largest share of eggs are fertilized by those males which produce the most sperm. There is usually little aggression displayed in such cases. However, in the second category, which is called interference or defense competition, animals fight among themselves for the right to monopolize food, to occupy alone a shelter or a territory, or to secure exclusive access to a mate. Following are some concepts and examples dealing with interference competition in fishes. Dominance hierarchies Aggression allows some social fishes to sort out their relative ranks within a dominance hierarchy. Thus, when a few individuals from a social yet slightly aggressive species are placed together for the first time into a tank, a lot of nipping and chasing commonly occurs. After a while however, this aggression subsides. A pecking order has developed, every individual having figured out its place in the hierarchy. Researchers can determine the ranking of each fish by carefully observing the outcome of the initial skirmishes. The more bites an individual delivers, the more chases it initiates, and the more adversaries it wins against, then the more dominant it is. Often a linear hierarchy emerges, going from the so-called "alpha" fish at the top, to "beta" and "gamma" just below, and so on down the Greek alphabet until we reach poor "omega" at the bottom of the heap. Such a phenomenon can be observed in many salmonids, poeciliids, and centrarchids. Alternatively, the hierarchy can be despotic rather than linear. In such a case a single individual, the despot, is dominant over the other fish, who are all equally miserable. Captive eels and catfishes sometimes show this pattern. Development of a stable and peaceful dominance hierarchy benefits everyone because fighting is energetically costly, potentially injurious, and therefore not to be done on a regular basis. However, it goes without saying that the low-ranking subordinates are not necessarily living the happiest existence. Typically their access to food is limited, as suggested by the fact that their growth rate is slower than that of dominants. For the experimenter, the challenge here resides in showing that poor growth is indeed caused directly by interference from bossy dominants, rather than poor growth and subordinate status both being caused by a third factor, such as inefficient physiology.
Article
Full-text available
Traits used in communication, such as colour signals, are expected to have positive consequences for reproductive success, but their associations with survival are little understood. Previous studies have mainly investigated linear relationships between signals and survival, but both hump-shaped and U-shaped relationships can also be predicted, depending on the main costs involved in trait expression. Furthermore, few studies have taken the plasticity of signals into account in viability selection analyses. The relationship between signal expression and survival is of particular interest in melanin-based traits, because their main costs are still debated. Here, we first determined the main factors explaining variability in a melanin-based trait linked to dominance: the bib size of a colonial bird, the sociable weaver Philetairus socius. We then used these analyses to obtain a measure representative of the individual mean expression of bib size. Finally, we used capture–recapture models to study how survival varied in relation to bib size. Variation in bib size was strongly affected by year and moderately affected by age, body condition and colony size. In addition, individuals bearing small and large bibs had higher survival than those with intermediate bibs, and this U-shaped relationship between survival and bib size appeared to be more pronounced in some years than others. These results constitute a rare example of disruptive viability selection, and point towards the potential importance of social costs incurred by the dominance signalling function of badges of status.
Conference Paper
Full-text available
Breeding ornamental tropical fishes is a unique experience that in majority abuts in the problems of feeding. Aquarist often overlooks the importance of feeding of a balanced diet for fish health and maintenance of water quality in the aquarium. Most hobbyists apply techniques which based on their experience or in the on-package feeding guide, without they knowing the feeding importance. Such methods leads in overfeeding. The overfeeding of fish in an aquarium results in increased pollution (ammonia and nitrite). The quantity and the quality of food is the most important step because allowed to management techniques for commercial scale culture protocols for ornamental and tropical fishes. One of the most and popular tropical fish that have hold the one and only position in the world aquarium fish keeping is Angelfish. The study of this paper is to examine the effect of different temperatures and different types of feed on the growth of a cichlid fish, pterophyllun scalare. The experiments were carried out at the Laboratory of Ornamental fish Culture in Technological Educational Institution of Messolonghi in West Greece. Angelfish larvae are hatched from females that have been maturated in captivity. Pterophyllum scalare fry, 1.00 gr in total weigh and 4.02 cm in total length are kept into 40 lt aquariums. The animals were divided into 4 groups of 10 individual and they were kept in two different temperatures for growth, the optimal temperature of growth 29 o C and the minimum temperature of growth 25 o C. Juvenile Pterophyllum scalare grow in the aquariums over a period of 60 days. All fishes are fed with 4 experimental diets which are a combination of pellets-flakes and frozen food with different percentages of protein and lipids. Food availability, food consumption and food composition can be an important factor affecting reproduction and fish growth. Preliminary results show that Angelfish, Pterophyllum scalare introduce a high growth rate in high temperatures than in low.
Article
Aggressive behavior can be an important factor in determining how animals use and divide space and resources. Previous studies have shown that aggression in fishes can be influenced by a variety of factors, including water temperature and resource levels. In this study, we tested if the amount of habitat structure in the environment affected aggression levels in female convict cichlids Archocentrus nigrofasciatus. We performed a laboratory experiment in which we placed female convict cichlids into an aquarium with low or high amounts of habitat structure and monitored the dominant female's behavior toward the subordinate female. Aggressive behavior in convict cichlids primarily consists of chases and bites. We found that the total time the dominant female spent chasing the subordinate female was greater when there was a low amount of habitat structure as compared to when there was a high amount of habitat structure. We also found that both the average duration of a chasing bout and the number of bites directed at the subordinate fish increased when there was a low amount of structure, but the number of chases did not. These results indicate that increased habitat structural complexity decreases aggressive behavior in convict cichlids [Current Zoology 56 (1): 52-56, 2010].
Conference Paper
Full-text available
Farming ornamental fish in aquariums and especially the tropical egg-layer with parental care is now an establish industry in several countries including Europe. The success of farming ornamental fish depends on their fish nutrition and the composition and type of the fish diets. This paper examines the growth rate and survival rate of cichlid Archocentrus nigrofasciatus species under different temperatures and different types of food. The experiments were carried out at the Laboratory of ornamental fish culture in the Technological Educational Institution of Messolonghi, in West Greece. Two hundred fish (1,3gr wet weight and 2,6cm total length) were reproduced from females that have been matured in captivity. The fish were kept in 40 lt aquariums and were divided into 5 treatments (starvation, Food 1, Food 2, Food 3, Food 4) of 20 individuals, respectively. They were kept in two different temperatures: 27 o C for optimal growth and 20 o C for minimum growth. They were fed 4 different diets which are a combination of pellets, flakes and frozen food with different percentages of protein and lipids three times per day, for a period of 60 days. Archocentrus nigrofasciatus grow well (SGR= 1.25% of growth per day) when fed the pelleted feed at the optimal temperature of 27 o C. Food consumption is measured 0.062 g or 38 pellets per fish. Preliminary results show that there is low growth rate in low temperatures.
Article
Full-text available
The role and consequences of aggressive behavior in competition for food and space were studied among laboratory populations of juvenile medaka. Growth rate, used to measure the success of an individual fish in different competitive situations, was followed for 648 fish in populations of 1, 2, 4, 8, or 16 fish in 1-, 4-, or 8-liter baskets.Aggressive behavior was initiated by internal state of "hunger" and the presence of food stimuli and smaller medaka. Aggression was at a low level when food was supplied in excess and large fish had no competitive advantage over small fish. Reducing the amount of space from 1 to 1/16 liter per fish did not alter the growth consequences of competition as long as the accumulation of waste products was prevented and food was supplied in excess.When food supply was limited, large medaka were socially dominant, chased small fish away from food, and grew faster than small fish. If food was spatially localized the social hierarchical societies changed into territorial societies in which the dominant defended the food area, but aggression only dispersed the subordinates throughout the habitat when food was evenly distributed. The advantage of social dominance was less if population size was large, if food was evenly distributed, and visual isolation between competitors was great. The advantage was high if food was contagiously distributed and visual isolation between competitors was great.
Article
Full-text available
Operational sex ratio (OSR), the number of potentially mating males divided by the number of fertilizable females, plays a central role in the theory of mating systems by predicting the intensity of intra-sexual competition and sexual selection. We introduce a general version of OSR, competitor-to-resource ratio (CRR, the number of potential competitors divided by the number of resource units), as a potential way of predicting the intensity of competition for any resource. We manipulated CRR over a broad range (0.5-8) by varying both the number of competing male Japanese medaka fish (Oryzias latipes) and the number of resources, either females or food items. We tested whether the rate of male-male aggression differed depending on resource type and whether it increased monotonically or followed a dome-shaped relationship with increasing CRR. The patterns of competitive aggression in relation to CRR did not differ significantly between resource types. In addition, the per capita rate of aggression followed a dome-shaped curve; it was low when CRR was less than one, initially increased as CRR increased, was highest at a CRR of about two, and then decreased when CRR was greater than two. However, competitor number, independent of CRR, had a significant and negative effect on rate of aggression. We suggest that CRR is a valuable predictor of the rate of competitive aggression and may be a useful concept for synthesizing ideas about resource competition and monopolization that are currently dispersed in the separate bodies of literature on mating systems, social foraging and territoriality. Key words: aggression, competitor-to-resource ratio, Japanese medaka, mating systems, operational sex ratio, Oryzias latipes, resource com- petition, territoriality. (Behav Ecol 11:670-675 (2000))
Article
Full-text available
There is widespread concern that artificial selection for rapid growth will indirectly select for aggressive fish, thus nullifying genetic stock improvement programs based on selection. We show that this unfortunate result is highly unlikely. The argument is based on a game-theoretic analysis of two general features of fish competition: (1) the growth of some individuals is often suppressed even when food is abundant and (2) the behaviour of a fish towards other members of a population depends on its relative size. The commonsense view that growth rate selection favours aggressive fish is shown to be correct only when aggressive behaviour is independent of relative size and resources are severely limited. In experimental and aquaculture environments, growth rate selection is shown to favour a decrease in the value of both aggressive and submissive behaviour, i.e. fish which ignore each other. Artificial selection for rapid growth will therefore indirectly select for tameness, not aggression.
Article
Full-text available
Feeding territories of Golden-winged Sunbirds contain enough energy to sup- port an individual's daily energy requirements, and the amount of nectar per flower inside a territory tends to average higher than in adjacent undefended flowers. When undefended nectar levels are low (especially below 2 /ul per flower) the costs of territorial defense can easily be offset by energy saved from shortened foraging time budgets made possible by feeding at the higher average nectar levels. At higher undefended nectar levels the costs of territorial defense should not be recoverable. The balance between these costs and gains appears to define the conditions when territorial defense in this species is advantageous.
Article
Full-text available
White Wagtails Motacilla alba wintering in Israel are partly territorial, mostly around human habitations, and partly live in flocks around temporary food sources. Individual birds may spend part of the season (or the day) in the territory and the other part with a flock.Experiments with artificial distribution of food, in a natural habitat, brought about a change from flocking to territorial behaviour. Preliminary observations suggest that in the natural situation the pattern of food distribution may be the proximate factor which regulates the birds' behaviour, by determining whether they have to fight for their food.Pairs are formed on many territories, and may last for long or short periods. Pair formation is initiated by females, who when seeking food appease the territorial males and are able to stay with them on their territories. Females also manifest territorial behaviour.Although pairing in winter territories is similar, in the behaviour involved, to sexual pairing, it is very unlikely that winter pairing continues into, or influences, pairing for breeding. It is suggested that the function of winter pair formation is that it allows two birds to exploit one territory, and that the main advantage is to the female which is the subordinate bird of the pair. This kind of pair-formation may be analogous to non-breeding group territories reported in some other birds.
Article
Full-text available
Thirteen territorial male Anna's Hummingbirds, Calypte anna, were observed during the 1981 and 1982 breeding seasons. Breeding territories were large, but size was not determined by energy availability. When a food source (sucrose solution in feeders) was present, the degree to which it was defended was a function of food quality. If a high-quality food source was absent, males did not exhibit the behaviors associated with defending a food source, but breeding territoriality remained intact. Territories were maintained for the entire breeding season even when food quality was varied. The lack of a relationship between the number of chases involving females and dive displays with variations in food quality, along with observations of long territory tenure, suggest that the primary function of the territory is reproductive and that an internal food source is not necessary for its maintenance.
Article
Full-text available
Cichlids are unusual among fishes because they have prolonged care of their young. Convict cichlids,Cichlasoma nigrofasciatum, are monogamous and have biparental care of their young. This species has been studied extensively in the laboratory, however, little is known of their reproductive habits in nature. Four populations of convict cichlids were studied in Costa Rican streams during the long dry season in 1990 and 1991. Basic physical and chemical parameters of the study sites are described. In the study area breeding fish paired size assortatively; large males with large females and small males with small females. A comparison of the size distribution of breeding fish to that of non-breeding fish showed that small males and in some cases, small females were excluded from breeding. This suggests competition among males for nest sites and mates or female-female competition. Further evidence of intrasexual competition in females is provided by the black colour phase adopted by some females. Some of these females were active in courtship and had mature ova. Cave guarding behaviour and reuse of caves show that a ready-made spawning site is an important resource shaping the mating system of this species. This description of basic natural history can serve as a source of testable hypotheses for future research and allow the results from laboratory studies on this and related species to be interpreted within the ecological context of the natural habitat.
Article
Full-text available
On the east coast of Australia, new holland and white-cheeked honeyeaters experience huge seasonal changes in nectar availability over their breeding periods. I observed breeding males of both species to determine whether levels of territorial aggressiveness varied with these changes in nectar availability. I watched individual males repeatedly and assessed their aggressiveness by recording their responses to birds that came within 30 m of them. Almost all attacks were on unfamiliar birds; males never attacked their mates or offspring and rarely attacked other birds that were resident in the area. Intruders were most likely to be attacked if they were conspecifics, if they landed rather than flying by, and if they came near the centers of males' territories. Taking into account the types, behaviors, and locations of intruders, there were pronounced seasonal changes in the probability of an intruder being attacked by a territorial male. Males were least aggressive when nectar was abundant, suggesting that territorial aggression could be at least partially a response to scarcity of nectar. Seasonal changes in aggressiveness were not accounted for by breeding cycles or by changes in frequency of intrusions.
Article
Full-text available
Animals searching for food in groups display highly variable degrees of aggressiveness. In this paper I present an individual-based game theoretical model of how gregarious animals should adjust their level of aggressiveness to their environmental conditions. In accordance with behavioral observations, the predicted level of aggressiveness increases progressively with decreasing food availability and increasing animal density. The proposed model also predicts a positive influence of food energy value and handling time on the level of aggressiveness within the group. In addition, the model provides information about the influence of aggressive behavior on individual foraging success, interference, and population dynamics. Adaptive behavioral rules for aggressiveness in consumers are predicted to respond to both competitors and food density in a way that contributes to stabilization of the dynamics of population systems.
Article
Full-text available
The fact that most female primates (and many other mammals) live in groups is paradoxical, given that the presence of others presumably increases competition for foods and may, for some, reduce reproductive success. Competition for food resources is generally inferred from any of the following observations: (1) female dominance hierarchies within groups; (2) female aggression between groups; (3) increasing home-range size with increasing group size; (4) longer day-range length with increasing group size; and (5) lower reproductive rates in larger groups. Both female aggression (interference competition) and adjustments of ranging behavior to group size (exploitative competition) have been linked in the past to patterns of food distribution and abundance. Using data largely from the literature, this paper examines the covariance of female aggression and ranging behavior among 20 species of primates in an attempt to better explain the variation in female relationships within and between groups of primates. Results show that groups of females are aggressive toward other groups and that home-range size increases with increasing group size in most species. In addition, in those species with strong dominance hierarchies within groups, day-range length increases as a function of group size. However, in those species that do not have strong dominance hierarchies within groups, dayrange length does not increase as a function of group size. The implications of these results are presented in a model that suggests that intergroup competition is determined by food abundance, whereas intragroup competition is determined by food distribution. This model differs from earlier models in its explanation of the ecological conditions that influence female relationships within and between groups of primates. [Behav Ecol 1991;2:143–155]
Article
Blackfly larvae are sometimes evenly spaced on a substrate, suggesting that individuals may react negatively to the presence of other larvae. Direct observations indicate that larvae often behave aggressively towards neighbors. Three kinds of evidence support the hypothesis that this aggressive behavior is associated with the defense of filterable food resources. 1) Aggressive behavior is initiated almost exclusively towards upstream neighbors, which are the only larvae capable of altering the availability of filterable particles being delivered to an individual by the current. If an individual succeeds in aggressively displacing its upstream neighbor(s), it ceases to behave aggressively, and returns to its normal filter-feeding behavior. 2) Following successful displacement of such neighbors, the individual's short-term ingestion rate (measured indirectly) increases significantly. 3) Frequency of territorial behavior declines when the availability of filterable particles is increased. -from Author
Article
The hypothesis that spatially predictable resources are more easily monopolized and defended than spatially unpredictable resources was tested by allowing groups of six juvenile convict cichlids, Cichlasoma nigrofasciatum, to compete for Daphnia magna prey. One prey appeared every 15 s in one of four patches defined by their probability (0·667, 0·167, 0·083, 0·083) of receiving the prey. Spatial predictability was manipulated by varying how often these probabilities were randomly assigned to the patches over a 3-day experimental period: once (Predictable), six times (Intermediate), or 36 times (Unpredictable). With increasing resource predictability, dominant fish became significantly more aggressive, more sedentary, and monopolized a greater share of the food. The number of prey eaten by individual fish was positively correlated with body mass and aggressiveness (the proport on of encountered conspecifics that were chased) in the Predictable treatment, with body mass in the Intermediate treatment, and with body mass and mobility (the frequency of patch switching) in the Unpredictable treatment. These results suggest that interference competition, via resource defence, is effective in spatially predictable environments, whereas exploitative competition, via scrambling, is effective in spatially unpredictable environments.
Article
The behaviour of juvenile (0+) Pseudolabrus celidotus was examined in thirteen shallow reef habitats in northeastern New Zealand, with the aim of assessing the influence of density on the frequency of encounters between individuals and the time allocated to agonistic and foraging behaviour. Local density and the frequency of encounters both differed significantly among habitats, and were positively correlated. The frequency and the mean proportion of the time budget spent on intraspecific agonistic encounters differed among habitats, and exhibited bell-shaped relationships to density; aggressive behaviour was frequent at intermediate densities, but rare in very low or high density populations. This was explained by an inverse relationship between density and the proportion of encounters resulting in aggressive behaviour. There were significant differences among the habitats in the amount of time spent foraging, the high level of aggression at intermediate densities being associated with decreased time spent foraging. Juveniles in the three highest density habitats foraged mainly on plankton, whereas juveniles at densities lower than 100 per 500 m2 foraged on micro-crustaceans associated with algae.
Article
Aerobic swimming performance (critical swimming speed, U-crit), food consumption per meal (by X-ray radiography), specific growth rate (SGR), haematocrit, and fin condition were monitored in individual juvenile rainbow trout (Oncorhynchus mykiss). The fish were held in groups over a 9-week period and fed daily group rations (dry food) of 2.0, 1.5, 1.0, and 0.5% wet body mass (BM). day(-1). SGR declined and competition increased at lower ration levels, as reflected by greater fin damage, reduced haematocrits and condition factors, and, at 0.5% BM . day(-1), a substantial increase in the coefficient of variation among individual meals. Absolute U-crit, also declined at lower ration levels. However, there was no relationship between U-crit and haematocrit, fin damage, or condition factor in any of the ration groups. A negative correlation was found between U(cri)t and SGR in individual trout fed a group ration of 2.0% BM . day(-1), but a positive correlation was seen at 0.5% BM . day(-1) and no relationship at 1.0 and 1.5% BM . day(-1). There was a positive relationship between individual SGR and food consumption only among fish fed a ration of 2.0% BM . day(-1). A significant negative relationship between U-crit and individual food consumption was also found among fish in this ration group.
Article
Field studies have shown that animals often abandon territorial defense when food is abundant, but the causes of this behavior are controversial. Sometimes the cessation of defense is attributed to the food supply being so abundant that monopolization of the resource gains the defender nothing, even though defense would be energetically feasible. Other studies show that when the food supply is rich, such large numbers of competitors are attracted that defense is overwhelmed. Knowledge of the amount of food available relative to the numbers of consumers in the region can resolve the controversy. When food is limited throughout a region, a localized rich foraging area will attract competitors.Defense of such an area therefore may yield a large increase in net benefit to the defender, depending on whether or not so many competitors recruit that defense is too costly. However, when a localized foraging area is rich but food is also superabundant throughout the region, intruders may not recruit even if the area is undefended. Therefore the benefits of defense, if it were to occur, would be low. Field studies of nectar-feeding birds show that defense continued on rich foraging areaswhen floral nectar was limited to the population regionally, and resulted in enhanced food availability relative to that in undefended areas. However, under conditions of artificially rich food supplies (sugar-water feeders) and extremely limited food regionally, defense was sometimes overwhelmed by competitors. Cessation of defense on locally rich foraging areas also occurred when nectar was regionally superabundant. Therefore, both proposed causes of cessation of defense occurred in these systems and were easily distinguished by examining the degree to which food was limited in the surrounding region relative to localized foraging areas. I show that animals potentially can assess whether or not food supply is limited in the surrounding region by sampling and comparing standing crops in defended and undefended situations.
Article
The hypothesis that resource monopolization and defense increase as the spatial clumping of resources increases was tested using groups of three convict cichlids competing for 120 Daphnia magna prey. Spatial clumping was manipulated by varying the distance (3, 20, or 40 cm) between three tubes through which the prey appeared. As predicted, monopolization of prey (percentage eaten by the dominant fish) and frequency of aggression (chases per minute) by dominant fish increased significantly as the distance between the tubes decreased. However, there was no evidence of individual flexibility in the aggressiveness (percentage of conspecifics chased) of dominant fish across treatments. Differences among dominant fish in aggressiveness were positively correlated with their ability to monopolize prey, but the strength of the correlation decreased as the distance between the tubes increased. Aggression appears to be a more effective mechanism of interference competition when resources are clumped than when resources are dispersed.
Article
The hypotheses that variation in male mating success and use of aggression by competing males increase with decreasing synchrony of female arrival were experimentally tested. Groups of three male Japanese medaka,Oryzias latipes(Pisces, Oryziidae) were allowed to compete for females that were placed in the tank either simultaneously (synchronous treatment, male-to-female operational sex ratio=0·5) or sequentially (asynchronous treatment, operational sex ratio=3). In these experiments, the mating system of medaka was scramble-competition polygyny because male mating success was primarily determined by their persistence in following and courting females rather than by dominance and aggression. As predicted, the coefficient of variation of male mating success and the rate of aggression by males was higher in the asynchronous than in the synchronous treatment. In addition, the percentage of matings in which a sneaker participated was also higher in the asynchronous than in the synchronous treatment. Operational sex ratio, mediated by female synchrony, seems to be an important proximate factor influencing the intensity of male-male competition. These results suggest that differences between males in their ability to scramble for females can generate important variance in mating success, a mechanism that is often overlooked in the literature on mating systems.
Article
Nest and offspring defence by birds can be treated as an optimization problem wherein fitness benefits are determined by the survival of the current brood and fitness costs depend upon the probability that the parent will survive to breed again. At the optimal intensity of defence, net fitness benefits are maximized. Most research has focused on seasonal patterns of nest defence to test the prediction that intensity of nest defence should increase through the nesting cycle either because renesting potential declines or because the probability of offspring survival increases rapidly relative to that of the parents. Intensity of nest defence is predicted to increase with parental experience and confidence of parenthood; offspring number, quality and vulnerability; and nest accessibility and conspicuousness. The response of parents is also expected to vary with the relative armament and mobility of parent and predator and the relative roles of the parents in caring for their offspring. -from Authors
Article
The hypothesis that monopolization and defence of resources decreases as the temporal clumping of resource arrival increases was tested using groups of six zebrafish competing for 300 Daphnia pulex prey. Clumping was varied by controlling the duration of the period (3, 10, 30, 100 or 300 rain) over which the prey arrived through a single, centrally located feeding tube, which was vigorously defended by the dominant fish in each group. Resource monopolization, measured by the variance/mean ratio of prey eaten per individual per trial within a group, increased as trial duration increased. The share going to the most successful fish also increased with trial duration. Resource defence by the dominant fish, measured as total chases per trial, increased as trial duration increased, but number of chases per min reached a peak in the 30-min trial. The number of competitors near the feeding tube decreased with trial duration, suggesting that defence became more effective in longer trials. In short trials, dominant fish were not necessarily the most successful individuals, but with increasing trial length the proportion of groups in which dominant fish were the most successful and the proportion of prey taken by the dominant fish in each group increased. This is the first direct evidence that an increase in monopolization produced by a decrease in clumping of resource arrival occurs because of more effective defence.
Article
I argue that a net benefit model of aggressive social organization is consonant with observed variation between territorial and dominance systems. For nectarivores net benefits are associated with obtaining nectar. Costs are time and energy associated with aggression and possible risks of injury. The fitness criterion probably varies across situations and may be long or short-term. An important problem for behaviorists is to understand the position in a time hierarchy at which particular social interactions are important.
Article
Chum salmon (Oncorhynchus keta) were grown in groups of 10 for 40 d on three limiting ration levels, and weight and fork length were measured at day 0 and day 40. Variation in growth of fish within a cohort was estimated from calculation of coefficients of variation for weight, fork length, condition factor, and growth rate. Average growth was significantly less at the lowest ration level than at the two higher levels, where average growth did not differ significantly. However, variation in growth (growth depensation) was significantly higher at the lowest and intermediate ration levels than at the highest ration level; we surmise that this higher variation is associated with increased competition and the disproportionate acquisition of food by larger fish. Aggressive behavior was most intense at the highest ration level. Chum salmon apparently show characteristics of a schooling fish while showing aggression, behaviors that are generally viewed as mutually exclusive.
Article
Models of optimal territory size are usually tested only by demonstrating that territory size is inversely related to food abundance or intruder number. The most fundamental predictions of the models, however, have rarely been tested: i.e. the fitness of the defender is a function of territory size and the optimal territory is one of intermediate size. We tested these predictions by measuring the growth rate of large convict cichlids (Archocentrus nigrofasciatus, formerly Cichlasoma nigrofasciatum) while defending food patches against smaller intruders over a 10-day period. Food patches differed in area by more than two orders of magnitude. We manipulated food abundance so that it increased with patch size in a decelerating way. As assumed, the realized benefits of defence (weight of food eaten by the defender) and the costs of defence (chase rate and chase radius) both increased in a decelerating way with increasing patch area. As predicted, the growth rate of the defender first increased and then decreased with increasing patch size. The initial increase in defender growth rate with increasing patch size was related to an increase in food eaten, but the decrease in growth rate for fish defending the largest patches was related to the costs of defence. Fish defending large patches had a low growth efficiency, apparently because of the social stress caused by intruders in their territories. Taken together, these results support the assumptions and predictions of optimal territory size models.
Article
Investigated the effect of asymmetries in the expected value of food on the outcome of contests among 48 convict chichlids (12 pairs of contestants of each sex). Fish were trained to expect a greater or lesser amount of food when fed individually; during contests, food was released into a central area, and both contestants were released simultaneously. The asymmetry that had been created during training had little effect on the outcome of the contests. Rather, body size had a significant effect. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
Brown trout of different weights (range 8-358 g) were fed to satiation at fifteen different water temperatures (range 3.8–21.6°C. Both the weight of the trout (Wg) and the water temperature (T°C) affected the maximum weight of food (Q mg) consumed in a meal, and the relationship between the three variables was well described by a multiple regression equation which can be used to estimate the value of Q (with 95% confidence limits) for trout of different weights at different temperatures between 3.8°C and 21.6°C. The satiation time (with 95% confidence limits) can also be estimated from a multiple regression equation for trout of different weights at temperatures between 6.8°C and 18.1°C. Estimates from the multiple regression equations were applicable to a wide range of food organisms with the exception of larvae ofTenebrio molitor (mealworms). Appetite (measured by voluntary food intake) varied with temperature and was greatest between 13.3°C and 18.4°C. From comparisons with the results of other workers, it was concluded that the maximum amount of food consumed in a meal may provide sufficient calories for both the daily metabolic requirements and the daily maintenance requirements of a trout at temperatures between 3.8°C and 18.4°C, but not at temperatures above 18.4°C.
Article
HAT are the conditions which facilitate or hinder the evolution of ter- ritoriality? No generally accepted solution to this problem has yet been found-perhaps because too specific an answer has been sought for too general a question. Instead, the diversity of systems of territorial and other aggressive behavior has come to be well appreciated, as evidenced in recent reviews of territoriality (e.g., Kuroda, 1960; Carpenter, 1953; Hinde, 1956), and the impossibility of providin g a specific answer applicable to all types of territoriality is now realized. Arguments over which are the primary selection pressures leading to cer- tain types of territoriality continue, however, as shown in the recent contribu- tions bearing on the "function" of territoriality by Stenger (1958)) Wynne- Edwards (1962), Kalela (1958)) Kuroda (1960), Peters (1962)) and others. The present paper offers a new orientation to the problem by presenting a general theory for the evolution of territoriality with special reference to its diversity among species. Since most of the previous theories have already been shown to be untenable or severely limited (see especially Carpenter, 1958; Tinbergen, 1957; and Hinde, 1956, for criticism of them), little attention will be given to them here. A theoretical framework for the consideration of some of the mechanisms promoting and limiting the evolution of territorial behavior is outlined in Fig. 1. Aggressive behavior is generally employed by individuals in the acquisition of goals which tend to maximize individual survival and reproduction. Natu- ral selection should favor aggressive behavior within a population when these goals are consistently and easily accessible to individuals through aggression but should not favor it when they are not accessible. For example, when a food supply cannot be feasibly defended, because of its mobility or transient nature , generally no territorial system is evolved to defend it; and the terri- tory, if present, may be restricted only to the nest and the area reachable by the parents on the nest. Such cases are found in colonial sea birds, nomadic and social feeding passerine species, and aerial feeders. In these species the goal of increased or guaranteed food supply is unlikely to be attained through aggression. On the other hand, if the individual depends for its nesting requirements,
Article
A continuum concept of spatial organization linking territoriality and social hierarchy suggests that individuals will alter their degree of exclusiveness and priority of access to resources in accord with the net benefits of aggression. Thus changes in resource distribution will produce changes in the control of resource space for any one individual. Similarly when comparing among individuals, responses will change in accord with their aggressive abilities when compared to those of possible opponents. The existence of such a continuum model of spacing was investigated in a nectar feeder, the New Zealand bellbird (Anthornis melanura: Meliphagidae). A natural change in spatial distribution of resources from highly concentrated to dispersed provided an opportunity to follow changes in access for known individuals. Comparison of individuals of different hierarchical status, sex and residential status was also possible within each system as was an estimate of comparative rewards. At the concentrated resource, individuals could be ranked in a dominance hierarchy although spatial separation between more dominant individuals did occur. At the more spatially dispersed resource, most individuals obtained a level of exclusive use. Access to both resources varied for different individuals but the asymmetries that related to greater access in one system also produced greater access in the other resource.
Article
Territorial activity in the Anna hummingbird (Calypte anna) was measured while energy availability on the territory was varied. On days when energy availability was unlimited, residents defended highly exclusive territories primarily by energetically expensive defense behaviors. As energy availability decreased, exclusiveness declined gradually, relative use of energetically inexpensive defense increased, and owners spent less time on the territory.Territorial behavior also varied with short term depressions in energy availability: A lower percentage of intruders was chased and departures of an owner from its territory were more frequent shortly after feeding.When resource dispersion was increased without changing substantially total rewards per territory, chasing by owners increased.
Article
Young-of-the-year brook charr in streams use either an active or a sit-and-wait foraging tactic and exhibit a range of resource defense from territoriality to tolerating conspecifics. We use simple graphical models, based on encounter rate with drift and the theory of economic defendability, to predict qualitative changes in the aggressiveness and mobility of brook charr in relation to current velocity. Aggressiveness (percent of conspecifics eliciting an overt response) initially increases with increasing current velocity, as does drift rate and foraging rate. However, aggressiveness decreases at high current velocities, probably because of increased costs of defense at these velocities. In standing water areas, brook charr use primarily an active foraging tactic, but mobility (percent time spent moving) decreases rapidly as current velocity increases. These results are generally consistent with the simple graphical models. A literature survey suggests that the models can be generalized for most species of stream salmonids.
Article
Summer generation 3rd, 4th and 5th instar nymphs plus adults of Gerris remigis were satiated for 2 days in a laboratory tray then deprived of food. Within 1/2–2 days, 19 of 27 nymphs and 10 of 30 adults began to exhibit territoriality, continued being so for 3–9 days, then ceased shortly before becoming quiescent. In the field, muscid flies fed to different territorial striders at a rate of 0, 1, 2, or 3 flies/day, resulted in 8 of 10 striders (at 2 flies/day) and 10 of 10 striders (at 3 flies/day) ceasing territoriality, whereas 5 of 8 controls (at 0 flies/day) remained territorial. Thus, lower and upper food thresholds were demonstrated, the upper threshold approached both from above (laboratory study) and below (field study).
Article
YoungEtroplus maculatus andPelmatochromis subocellatus kribensis were reared on diets of low, medium, or high quantities of food and the ontogeny of behavior documented until fish matured. Data were categorized into: (1) from the beginning of the experiment to the midpoint (100 days forE. maculatus and 118 days forP. s. kribensis); and (2) from the midpoint to maturity. For both species the tendency to be territorial, as deduced by the numbers of territories defended, or number of charges or rams performed, was explained by a unimodal relationship between territorial tendency and food available per gram of fish. Young fish receiving low quantities of food were highly territorial, but as they grew and food available per gram of fish decreased, they gave up territorial behavior. Young fish receiving high quantities of food were not territorial initially, but as they grew became increasingly territorial. Fish receiving intermediate quantities of food always defended territories. Lateral displays were performed most often by fish receiving intermediate quantities of food apparently because they were ambivalent being close to either the lower or upper thresholds for territoriality.