Intragroup social dynamics vary with the presence of neighbors in a cooperatively breeding fish

Conflict is an in here nt part of social life in group-living species. Group members may mediate conflict through submissive and affiliative behaviors, which can reduce aggression, stabilize dominance hierarchies, and foster group cohesion. The frequency and resolution of within-group conflict may vary with the presenee of neighboring groups. Neighbors can threaten the territory or resources of the whole group, promoting behaviors that foster within-group cohesion. However, neighbors may also foster conflict of interests among group members: opportunities for subordinate dispersal may alter conflict among dominants and subordinates while opportunities for extrapair reproduction may increase conflict between mates. To understand how neighbors mediate within-group conflict in the cooperatively breeding fish Neolamprologus pulcher, we measured behavioral dynamics and social network structure in isolated groups, groups recently exposed to neighbors, and groups with established neighbors. Aggression and submission between the dominant male and female pair were high in isolated groups, but dominant aggression was directly primarily at subordinates when groups had neighbors. This suggests that neighbors attenuate conflict between mates and foster conflict between dominants and subordinates. Further, aggression and submission between similarly sized group members were most frequent when groups had neighbors, suggesting that neighbors induce rank-related conflict. We found relatively little change in within-group affiliative networks across treatments, suggesting that the presence of neighbors does not alter behaviors associated with promoting group cohesion. Collectively, these results provide some of the first empirical insights into the extent to which intragroup behavioral networks are mediated by intergroup interactions and the broader social context.     

Seasonal crayfish activity as influenced by fluctuating water levels and presence of a fish predator

The diel rhythm of juvenile (0+) Astacus astacus was studied experimentally with constant and dielly fluctuating water levels. In the first case the diel rhythm was mainly crepescular, but with tendencies of a phase shift towards diurnal rhythm during low light conditions. The locomotor activity increased with temperature and with the length of the dark period. In presence of a crepescular predator the crayfish decreased their light period activity.
With fluctuating water levels the activity increased especially when the water level changes occurred during normal resting periods. Crayfish did not show any adaptation to fluctuating water levels by preferring covers constantly situated beneath the surface. The relative effect of the water level fluctuations increased with temperature.
As the main part of the juvenile crayfish population is concentrated to the litoral zone, diel water level regulations are thought to be detrimental to crayfish populations even if the regulation amplitude is small.     

Chemically mediated predator inspection behaviour in the absence of predator visual cues by a characin fish

Animals commonly approach (i.e. 'inspect') potential predators. Glowlight tetras, Hemigrammus erythrozonus, have previously been shown to inspect the combined chemical and visual cues originating from novel predators and to modify their inspection (approach) behaviour depending upon the predator's diet. We conducted two experiments to determine whether tetras would inspect the chemical cues of injured prey or the dietary cues of a novel predator in the absence of any visual cues. Shoals of glowlight tetras were exposed to either distilled water (control) or the skin extract of swordtail (lacking ostariophysan alarm pheromones) or the skin extract of tetra (with alarm pheromones). There was no significant difference in the frequency of predator inspection behaviour towards swordtail or tetra skin extract compared to the distilled water controls. In the second experiment, we exposed shoals of tetras to either distilled water or the odour of Jack Dempsey cichlids, Cichlasoma octofasciatum, which had been food deprived, or fed a diet of swordtails or tetras. There was no significant difference in the frequency of predator inspection behaviour towards the odour of the starved cichlids and the odour of the fed cichlids in either of the two diet treatments. However, when tetras were exposed to the odour of cichlids fed tetras, they took significantly longer to initiate an inspection visit, remained further from the source of the chemical cues and inspected in smaller groups, compared with the odour of a starved cichlid or a cichlid fed swordtails. These data strongly suggest that tetras will inspect chemical cues alone, but only if the cue contains information about the predator. Copyright 2000 The Association for the Study of Animal Behaviour.     

Intermediate predator impact on consumers weakens with increasing predator diversity in the presence of a top-predator

Adding or removing a top-predator is known to affect lower trophic levels with potentially large, indirect effects on primary production. However, little is known about how predator diversity may affect lower trophic levels, or how adding or removing a top-predator influences the effects of predator diversity. Using aquatic mesocosms containing three and four trophic levels, we tested whether intermediate predator diversity affected predation on consumers and if top-predator presence influenced such effects. We found that the presence of intermediate predators suppressed the consumer population and that this suppression tended to increase with increased intermediate predator diversity when the top-predator was absent. However, with the top-predator present, increased intermediate predator diversity showed the opposite effect on the consumers compared to without a top-predator, i.e. decreased suppression of consumers with increased diversity. Hence, in our study, the loss of intermediate predator species weakened or strengthened predator–prey interactions depending on if the top-predator was present or not, while loss of the top-predator only strengthened the predator–prey interactions. Therefore, the loss of a predator species may render different, but perhaps predictable effects on the functioning of a system depending on from which trophic level it is lost and on the initial number of species in that trophic level.     

Retarded growth of cladoceran zooplankton in the presence of a copepod predator

Various instars of four different cladoceran species representing a wide spectrum of body size were grown at high food availability in the presence and in the absence of natural densities of an invertebrate predator, a cyclopoid copepod Acanthocyclops robustus (G.O. Sars). Daily weight increments calculated from individual weights at the end and at the beginning of each 1, 2 or 4 day experiment, showed that individual growth was more or less drastically retarded in the presence of the predator as well as when exposed to water in which the predator had been feeding. The data also showed that the effect of this invertebrate predator was more pronounced in small prey instars and small prey species that were more vulnerable to predation than large prey.     

Risk-sensitive resource defense in a territorial reef fish

As coral reefs are home to dense aggregations of a variety of species, aggressive territoriality is often a critical component of individual behavior. Identification and assessment of the risk posed by intruders is crucial to defending a territory, and fishes on coral reefs have been found to attend to body shape, body size, and coloration when responding to intruders. We examined the extent to which dusky damselfish (Stegastes adustus) discriminate among distinct categories of intruders by measuring the distance at which a fish attacks an intruder and the relative intensity and frequency of those attacks. We found that S. adustus discriminated among perceived threats, attacking conspecifics more intensely and more often than egg-predators and herbivores, and showing a trend of attacking those groups more often than invertebrate-feeders, which do not compete with damselfish for resources. Furthermore, territory holders attacked initial-phase wrasses from a farther distance than terminal-phase wrasses, suggesting that they can discriminate among classes of individuals within a species other than their own. Dusky damselfish thus exhibit the ability to make fine distinctions among intruders in a diverse ecosystem.     

Characterization of chemical defenses in ranid tadpoles against a fish predator

Tadpoles of some ranid species appear to possess chemical defenses against fish predators, but the chemicals have not been characterized. Here, we evaluated the vulnerability of three Japanese anuran tadpole species (Glandirana rugosa, Pelophylax nigromaculatus, and Hyla japonica) to a fish (Gnathopogon elongatus elongatus) and analyzed the defensive chemicals extracted from the unpalatable tadpoles. Additionally, we examined the defensive behavior of unpalatable tadpoles in response to fish chemical cues. The fish rejected both G. rugosa (83%) and P. nigromaculatus (48%), but not H. japonica (0%). Many of the rejected tadpoles survived (60–80%). Possible defensive chemicals were extracted by methanol from the skin of G. rugosa, but were not identifiable by gas chromatography–mass spectrometry because of small quantities. The chemicals have high polarity and non-volatility. When exposed to fish chemical cues, P. nigromaculatus decreased activity presumably as a defensive behavior, but G. rugosa did not. We demonstrated the presence of chemical defenses in at least two of these species and revealed that G. rugosa releases more effective or greater amounts of defense chemicals than P. nigromaculatus with respect to this fish predator. The increased efficacy of chemical defenses may correlate with decreasing defensive behavior.     

Juvenile exposure to predator cues induces a larger egg size in fish

When females anticipate a hazardous environment for their offspring, they can increase offspring survival by producing larger young. Early environmental experience determines egg size in different animal taxa. We predicted that a higher perceived predation risk by juveniles would cause an increase in the sizes of eggs that they produce as adults. To test this, we exposed juveniles of the mouthbrooding cichlid Eretmodus cyanostictus in a split-brood experiment either to cues of a natural predator or to a control situation. After maturation, females that had been confronted with predators produced heavier eggs, whereas clutch size itself was not affected by the treatment. This effect cannot be explained by a differential female body size because the predator treatment did not influence growth trajectories. The observed increase of egg mass is likely to be adaptive, as heavier eggs gave rise to larger young and in fish, juvenile predation risk drops sharply with increasing body size. This study provides the first evidence that predator cues perceived by females early in life positively affect egg mass, suggesting that these cues allow her to predict the predation risk for her offspring.     

Introduced predator elicits deficient brood defence behaviour in a crater lake fish

Introduced species represent one of the most serious global threats to biodiversity. In this field-based study, we assessed behavioural responses of brood tending cichlid fish to an invasive predator of their offspring. This was achieved by comparing parental defence responses of the endangered arrow cichlid (Amphilophus zaliosus), a fish species endemic to the crater lake Apoyo in Nicaragua, towards the bigmouth sleeper (Gobiomorus dormitor), a formidable predator of cichlid fry, and all other potential fish predators of offspring. The bigmouth sleeper was recently introduced into Apoyo but naturally co-exists with cichlids in a few other Nicaraguan lakes. Arrow cichlid parents allowed bigmouth sleepers to advance much closer to their fry than other predators before initiating aggressive brood defence behaviours. Interestingly, parents of a very closely related species, A. sagittae, which has coevolved with bigmouth sleepers in crater lake Xiloá, reacted to approaching bigmouth sleepers at comparable distances as to other predators of cichlid fry. These results provide a novel demonstration of the specific mechanism (i.e. naive parental behaviour) by which invasive predators may negatively affect species that lack the adequate behavioural repertoire.     

Interpopulation variation in a fish predator drives evolutionary divergence in prey in lakes

Ecological factors are known to cause evolutionary diversification. Recent work has shown that evolution in strongly interacting predator species has reciprocal impacts on ecosystems. These divergent impacts of predators may alter the selective landscape and cause the evolution of prey. Yet, this link between intraspecific variation and evolution is unexplored. We compared the life history of a species of zooplankton (Daphnia ambigua) from lakes in New England in which the dominant planktivorous predator, the alewife (Alosa pseudoharengus), differs in feeding traits and migratory behaviour. Anadromous alewife (seasonal migrants) exhibit larger gapes, gill-raker spacing and target larger prey than landlocked alewife (year-round freshwater resident). In 'anadromous' lakes, Daphnia are abundant in the spring but extirpated by alewife predation in summer. Daphnia are rare year-round in 'landlocked' lakes. We show that Daphnia from lakes with anadromous alewife grew faster, matured earlier but at the same size and produced more offspring than Daphnia from lakes with landlocked or no alewife across multiple temperature and resource treatments. Our results are inconsistent with a response to size-selective predation but are better explained as an adaptation to colder temperatures and shorter periods of development (countergradient variation) mediated by seasonal alewife predation.     

Long-term cleaner fish presence affects growth of a coral reef fish

Cleaning behaviour is considered to be a classical example of mutualism. However, no studies, to our knowledge, have measured the benefits to clients in terms of growth. In the longest experimental study of its kind, over an 8 year period, cleaner fish Labroides dimidiatus were consistently removed from seven patch reefs (61-285 m(2)) and left undisturbed on nine control reefs, and the growth and parasite load of the damselfish Pomacentrus moluccensis determined. After 8 years, growth was reduced and parasitic copepod abundance was higher on fish from removal reefs compared with controls, but only in larger individuals. Behavioural observations revealed that P. moluccensis cleaned by L. dimidiatus were 27 per cent larger than nearby conspecifics. The selective cleaning by L. dimidiatus probably explains why only larger P. moluccensis individuals benefited from cleaning. This is the first demonstration, to our knowledge, that cleaners affect the growth rate of client individuals; a greater size for a given age should result in increased fecundity at a given time. The effect of the removal of so few small fish on the size of another fish species is unprecedented on coral reefs.     

Species segregation during predator evasion in cyprinid fish shoals

SUMMARY. 1. When a predator attacks a mixed-species group, individual prey arc faced with a conflict between retaining the advantages of large group size and the disadvantages of remaining among aliens. Experiments were designed to show how this conflict is resolved in fish shoals.
2. Simulated attacks with a model predator were made upon mixed and single species shoals of three cyprinid species under semi-natural conditions in a fluvarium.
3. Measurements of elective group size, neighbour identity and distance, and encounters within and between species revealed behaviour which sorted fish into species at the onset of predator attack.
4. A control experiment demonstrated the same effect for fish of matched size.
5. The value to the individual of segregative behaviour in response to predator threat is discussed.     

Seasonal variation in the invertebrate community and diet of a top fish predator in a thermally stable spring

Hydrobiologia - Many life-history events in aquatic invertebrates are triggered by seasonal changes in water temperature, but other ecological factors may be important as well. To rule out the...     

Reconstructing the introduction history of an invasive fish predator in South Africa

The Largemouth Bass (Micropterus salmoides) is a global invader with demonstrated ecological impacts on native fish communities. Introductions of fishes in freshwater ecosystems are often characterized as complex processes, yet an understanding of the nature of the introduction can inform management and conservation actions. Early in the twentieth century, two introductions of Largemouth Bass were made into South Africa for the establishment of a recreational fishery, and subsequent translocations have expanded their distribution to include much of southern Africa. In this study we quantified neutral genetic variation, modeled potential introduction scenarios, and identified potential source regions from within the native range. We documented limited levels of genetic diversity in nuclear microsatellite genotypes across populations (mean allelic richness = 1.80 and mean observed heterozygosity = 0.16) and observed low levels of genetic differentiation among four of the five focal populations (mean pairwise fixation index = 0.09), with a fifth population displaying greater levels of genetic divergence (mean pairwise fixation index = 0.27). A total of three cytochrome b haplotypes were recovered from South Africa samples and the single most common haplotype (93% of individuals) was identical to a haplotype from a population of Largemouth Bass in Maryland, USA. Using limited available stocking data along with outputs from Principal Component Analysis and approximate Bayesian evaluation of competing introduction scenarios we confirm the presence of multiple introductions. Despite evidence for multiple introductions, Largemouth Bass in South African water bodies harbor extremely low neutral genetic diversity, suggesting that even a very limited number of propagules can experience a high likelihood of success in invading nonnative waters.     

N-person games and the evolution of co-operation: a model based on predator inspection in fish

Two N-person game theoretical models examining the evolution of co-operation during predator inspection in fish are presented. Predator inspection occurs in small shoals of fish, in which one to a few individuals, the "inspectors" (co-operators) break away from the shoal and cautiously approach a predator to obtain information on this potential danger. In the models presented here, remaining with the shoal and not inspecting is considered an act of defection. Both model I and II produce a stable internal polymorphism of inspectors and noninspectors. While the equilibrial frequency of inspectors can be low (i.e. less than 10%) at large shoal size, the proportion of shoals containing any inspectors--and therefore exhibiting the inspection behavior--is much greater. Both models presented here, and N-person games in general are equivalent to intrademic group selection models of evolution in structured populations, in which shoals are trait groups and co-operation evolves by between-shoal selection. While the results are cast in terms of predator inspection, the model itself is general and applies to any multi-group scenario where co-operators benefit entire groups at their own expense. The results presented here add to the mounting theoretical and empirical evidence that co-operation is frequently not a pure evolutionarily stable strategy, and that many metapopulations should be polymorphic for both co-operators and defectors.     

Summer diapause in Daphnia as a reaction to the presence of fish

A chemical signal, released by a fish predator under summer-likehigh water temperature and long-day photoperiod, caused theformation of resting eggs in a clone of Daphnia magna. No ephippialfemales were recorded and no ephippia were released in the controltreatment during 45 days of the experiment. When exposed tofish water, the fraction of ephippial females reached a maximumof 3.7%, a value comparable to that registered in summer inthe GroBer Binnensee (Northern Germany), a hypertrophic lakeinhabited by fish, which was the source lake for our experimentalclone. The number of ephippia released within 45 days was onaverage 34 ± 22. Ephippia formation could not resultfrom the between-treatment differences in population density,and related patterns of food depletion, since no substantialdifference between control and fish treatment was observed.Instead, specific information on the presence of a predatorprovided a cue which induced the formation of resting eggs inDaphnia. Under heavy predation and very low survival probabilityof parthenogenetic females, ephippia formation in summer canbe adaptive, i.e. higher fitness can be achieved through survivalin the diapausing state than through the immediate reproductivegain via parthenogenesis.     

A focus on long-run sustainability of a harvested prey predator system in the presence of alternative prey

Within the framework of a general equilibrium model we study the long-run dynamics of a prey-predator model in the presence of an alternative prey. Our results show that sustainability, i.e. a positive value of the population in the long run, essentially depends on individual harvesting efforts and digesting factors relative to alternative prey. A detailed bifurcation analysis evidences the richness of possible long-run dynamics. Our model clearly shows that the role of an alternative prey must be taken into consideration when studying prey-predator dynamics.