Territorial vocalization in sympatric damselfish: acoustic characteristics and intruder discrimination

Damselfishes are well known for their aggressive, territorial behaviour during which the use of vocalization behaviour has been well documented. However, agonistic acoustic signalling has been understudied in particular when the vocalizations are interspecific. In this study, we characterize and compare the previously undescribed vocalization behaviour of longfin damselfish (Stegastes diencaeus), in an agonistic context, with the closely related and sympatric dusky damselfish (Stegastes adustus). Next, we examined if these congeneric species modulate their vocalizations in a similar pattern to previously described aggressive behaviour patterns. Audio field recordings of territorial males were obtained in response to three separate stimuli: (1) conspecific male damselfish, (2) heterospecific male damselfish and (3) a common intruder, the slippery dick wrasse (Halichoeres bivittatus). The vocal repertoires of both longfin and dusky damselfish comprised the same three distinct call types: chirps, pops and pulse trains. However, temporal measures of the calls showed significant differences between species. Additionally, dusky damselfish were more vocal overall, producing more calls and spending more time calling than longfin damselfish. These responses were stimulus and species dependent, as the two species modulated acoustic response by modulating pulse number based on intruder species. These results suggest that these closely related species of damselfish use vocalization behaviours that are both unique and context dependent.     

The effect of territorial damselfish (family Pomacentridae) on the space use and behaviour of the coral reef fish, Halichoeres bivittatus (Bloch, 1791) (family Labridae)

Most demersal species of damselfish (family Pomacentridae) are territorial herbivores that aggressively chase other fishes away from their nests. This study investigates whether the aggressive territorial damselfish, Stegastes leucostictus, modifies behaviours and home range area use in a less aggressive, non-territorial species, the slippery dick wrasse, Halichoeres bivittatus (family Labridae). Damselfishes and wrasses are ubiquitous and abundant members of coral reef fish assemblages around the world; hence, this study has broader implications beyond the two Caribbean species chosen for this study. A manipulative field experiment consisted of transplanting one or three S. leucostictus into artificial shelters positioned within adult or adjacent to juvenile H. bivittatus home ranges. The introduction of damselfish had little effect on the size of home range areas of juvenile or adult wrasses, but had a significant effect on the location of their home ranges. The damselfish also affected adult microhabitat use but did not affect use by juveniles. In addition, there was an increase in damselfish-wrasse interactions that resulted in a significant reduction in the amount of time adult wrasses could spend foraging or in a foraging assemblage. It was concluded that aggressive interactions with territorial damselfish affect individual H. bivittatus space use and may consequently affect the spatial distribution of H. bivittatus populations.     

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

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

Size assortment in mixed-species groups of juvenile-phase striped parrotfish (Scarus iserti) in The Bahamas

Striped parrotfish (Scarus iserti) often form heterospecific groups with other reef fishes. In this study, we examined the species and body size composition of these groups on reefs in The Bahamas. Groups averaged approximately 4 S.?iserti and 2 associated species, with surgeonfish (Acanthurus chirurgus and A.?bahianus), slippery dick (Halichoeres bivittatus), and bluehead wrasse (Thalassoma bifasciatum) as the most common associates. Fewer groups than expected had only 1 associate; groups with 3 or more associates were more common than expected. Both the S.?iserti and associated species tended to be closely size-matched within a group, perhaps due to benefits of size assortment in lowering predation risk. Likewise, the high frequency of groups with greater than a single associate species suggests that associates may benefit from not being the only phenotypically different individual in a group.     

Do cleaning stations affect the distribution of territorial reef fishes?

We investigated the role of cleaning stations in determining the distribution of territorial reef species. Cleaner fish reduce their clients' ectoparasite loads and, therefore, proximity to cleaning stations should be advantageous for territorial fish. We focused on five damselfish species which hold permanent territories and cleaning stations occupied by cleaning gobies (Elacatinus spp.) on a Caribbean reef. Contrary to our predictions of higher densities near cleaning stations, we found that bicolor damselfish were less abundant near cleaning stations than at ecologically similar points without cleaning gobies whereas no effects were seen for longfin, dusky, yellowtail, and threespot damselfish. In addition, although damselfish densities were higher in the immediate vicinity of cleaning stations than 1.5-3 m away for most species, this was also the case at points without cleaners. Because cleaning stations are usually located on prominent coral heads or sponges, the overall significant attraction of damselfish to such structures, whether occupied by cleaning gobies or not, could reflect attraction to past or potential cleaning stations. However, it is more likely that interspecific competition and/or the low benefits of being cleaned at our study site prevent aggregation around cleaners. Cleaning stations may play only a minor role in determining the distribution of territorial reef fishes.     

Behaviour of the female beaugregory damselfish (Stegastes leucostictus)

Much less is known about the behaviour of female beaugregory damselfish than about males of the species. This study was initiated to determine behavioural patterns and interactions of female beaugregories on the back reef of Discovery Bay Marine Laboratory, North shore of Jamaica. Females fed, patrolled, and chased intruders in a significantly larger area and ate significantly more per 15-min observation period than did males. Males spent significantly more time patrolling their territories and chased significantly more total intruders than did females. However, this difference in total chases comes from the fact that males chased the bluehead wrasse, an egg predator, significantly more often than did females while all other species of intruder were chased the same by both sexes. The distance that females travelled from their homesite to court was significantly positively correlated to female body length. This increased distance travelled may relate to mate assessment. Female beaugregory damselfish may be able to be more selective in their choice of mate with increased size and distance travelled.     

Niche overlap among two species of coral dwelling fishes of the genus Dascyllus (Pomacentridae)

Synopsis The two damselfish, Dascyllus aruanus and D. marginatus are coral-dwelling species, occurring in separate groups or together in the corals Stylophora pistillata and Acropora spp. The two species, however, occur together more frequently than would be expected by chance. The niches of these species overlap in space, time and food. Looking for mechanisms that allow such coexistence, it was found that in such a bispecific group, no difference exists in agonistic acts between intra — or interspecific encounters. This phenomenon seems to be produced by two independent mechanisms — random settling of juveniles from the plankton and predation pressure that strongly limits the re-settling of the fish.     

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

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

Competitive interactions and the availability of sleeping sites for a diurnal coral reef fish

A field study was made to test whether the population size of a diurnal reef fish, the wrasse Thalassoma bifasciatum (Bloch), was limited by inter- or intraspecific competition for sleeping shelter. T. bifasciatum is often attacked at dusk by two small territorial damselfishes, Eupomacentrus dorsopunicans (Poey) and E. planifrons (Cuvier). Although these three species sleep in the same general habitats, there are qualitative differences in the types of holes they use and how they use them. Wrasse holes are usually in these damselfishes' territories, but damselfish attacks do not prevent wrasses entering holes. Wrasses infrequently defend their holes intraspecifically. They regularly change their holes, with little intra- or interspecific aggressive interaction. When its hole is removed, a wrasse is late in retiring but finds a hole near its old one with little aggressive interaction, and does not have a higher mortality rate. Empty wrasse holes are rarely refilled, and then only by conspecifics. Wrasses added to reefs find unoccupied holes and do not usurp other fishes' holes. Damselfish defend their eggs and food against the wrasse, but not their sleeping shelter, nor living space per se. Sleeping sites are not limiting the wrasse, but are present in a surplus. Intraspecific hole defense by a wrasse prevents a delay in its retiring that would increase the risk of crepuscular predation on it.     

Differential effects of native vs. invasive predators on a common Caribbean reef fish

Predators may have consumptive (lethal) and non-consumptive (sub-lethal) effects on prey. Non-consumptive effects include altered behavior and reduced growth and fecundity. Native prey may not recognize non-native predators as a threat, and therefore may suffer pronounced effects. Additionally, non-native predators may elicit different behavioral responses from prey compared to native predators. Theory predicts that consumptive effects should be greater for non-native predators (due to prey naiveté), and non-consumptive effects should be greater for native predators (due to predator recognition). To test these hypotheses, I monitored bicolor damselfish (Stegastes partitus) in the presence of invasive predatory Pacific lionfish (Pterois spp.), a native predator (graysby, Cephalopholis cruentata), and an egg predator (bluehead wrasse, Thalassoma bifasciatum). Body size and location of lionfish and graysby were monitored on reefs in the Bahamas. Bicolor fecundity was measured as the number and size of egg-masses that individual fish laid. Bicolor fecundity was negatively correlated with lionfish density but not graysby or bluehead density. Neither predator had a detectable effect on bicolor body size, but lionfish density was negatively correlated with the size of mature adult damselfish. I observed behavioral responses of bicolors to the two piscivores, to bluehead wrasse, and to two herbivorous fishes (Acanthurus coeruleus, Scarus spp.) as non-aggressive controls. Bicolors changed behavior (feeding and aggression) in the presence of all native fishes, but not in the presence of lionfish. Thus, differential effects exist between native and non-native predators, and invasive lionfish pose a non-consumptive threat to bicolor damselfish via reduced growth and fecundity.     

Territorial boundaries of the male beaugregory damselfish

On six separate occasions during a two month period, there were no significant differences in mean attack distances by territorial male beaugregory damselfish Stregastes leucostictus against male conspecifics, bluehead wrasse Thalassoma bifasciatus and striped parrotfish Scarus iserti . Feeding areas and patrolling areas were typically smaller than attack distances. The presence or absence of eggs, or the quantity of eggs within the male's territory also was not significantly correlated with attack distances. © 2000 The Fisheries Society of the British Isles     

Post-settlement emigration affects mortality estimates for two Bahamian wrasses

Understanding the dynamics of open marine populations is inherently complex, and this complexity has led to decades of debate regarding the relative importance of pre- versus post-settlement processes in structuring these populations. Movement between patches may be an important modifier of patterns established at settlement, yet local immigration and emigration have received less attention than other demographic rates. I examined loss rates from tagged populations of juvenile wrasses (yellowhead wrasse Halichoeres garnoti and bluehead wrasse Thalassoma bifasciatum) at two sites in the Bahamas. Assuming that all losses were due solely to mortality would have significantly underestimated survivorship of yellowhead wrasse by 29% and bluehead wrasse by 14%. On average, per capita mortality and emigration rates were higher for yellowhead than bluehead wrasse, but neither demographic rate differed between sites for either species. With respect to within-species density, bluehead wrasse mortality was density-dependent at the patch reef site, but mortality rates of yellowhead wrasse were consistently density-independent. Evaluating the effects of between-species density, yellowhead wrasse mortality increased with a decrease in bluehead wrasse density, but this effect was limited to the patch reef site. Emigration rates were not a function of either within-species or between-species density, but instead varied inversely with isolation distance. Numerous previous studies of coral-reef fish, conducted on patch reefs separated by only a few meters of sand and often using untagged fish, may have confounded losses due to emigration with those due to mortality. A better understanding of the factors affecting emigration in marine fishes is important to their effective management using spatial tools such as marine protected areas.     

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.     

Field experiments on species recognition by the threespot damselfish, Eupomacentrus planifrons, (Pisces: Pomacentridae)

The threespot damselfish, Eupomacentrus planifrons, defends differently sized territories against individuals of different species. Tests were conducted in the field to determine the mechanism(s) by which this interspecific recognition occurs. It was found to be based largely on visual cues, the most important of which was body form. Both colour and movement had different effects for intra- and inter-specific intruders. Based on these data, it is proposed that different mechanisms underlie the recognition of and territorial defence against the two groups. Further, interspecific territoriality need not be an ‘accidental’ form of intraspecific territoriality nor a transitional phase in the divergence of already established species, but, rather, may be a stable system based on the simple need to defend an area against non-related competitors.     

Acquisition of a defended resource: a benefit of group foraging for the neotropical wrasse,Thalassoma lucasanum

Synopsis The neotropical Pacific wrasse, Thalassoma lucasanum, forms groups of 30 to 300 individuals that overwhelm the defense of embryos by the Pacific sergeant major, Abudefduf troschelii, and thereby gain access to a food resource from which solitary individuals are effectively excluded by paternal defense. The duration of feeding by the wrasse groups and the fraction of embryos eaten in a nest are positively correlated with group size. The benefit of group foraging is probably derived from a reduction in the frequency with which group members experience attack by defending sergeant majors, as reflected in the positive correlation of group size with feeding duration. Large foraging groups only form when sergeant major embryos are present in nests, indicating that this is a primary benefit of participation in these groups for this wrasse. In contrast, in the Caribbean large foraging groups of the congeneric bluehead wrasse, T. bifasciatum, fail to form despite the presence of defended embryos of the Caribbean sergeant major, A. saxatilis. This might be due to the relatively low population densities of the Caribbean wrasse in comparison to those of the Pacific wrasse or to the relatively low densities of Caribbean sergeant major nests containing embryos at any time.     

Effects of depth and bottom communities on the distribution of highly territorial reef fish in the northwestern region of Cuba

The main goal of the study was to investigate changes in reef fish species abundance and its correlation with selected environmental variables. Three main questions guided the analyses: (i) Do the analytical methods have a significant influence on the results; (ii) What are the main assemblage variation axes; and (iii) What are the factors correlating best with assemblage composition. Highly territorial fish assemblages of several coral reefs along the northwestern region of Cuba were assessed using a stationary point visual census technique. A total of 39 701 individuals of 26 species from the families Chaetodontidae, Labridae and Pomacentridae were counted in 841 censuses; almost 80% of the fish belonged to just four species: bluehead (Thalassoma bifasciatum), bicolor damselfish (Stegastes partitus), slippery dick (Halichoeres bivittatus) and blue chromis (Chromis cyanea). Several multivariate techniques (cluster analysis, non‐metric multidimensional scaling and canonical correspondence analysis) were used to explore main patterns in assemblage composition variation. It was found that the results did not differ significantly when analyzing the same data set. Furthermore, it was shown that the combined use of different multivariate techniques enhanced the interpretation of fish assemblage composition changes. Depth was the main variable explaining variation in the composition of fish assemblages in the studied reefs. The densities of corals and gorgonians were also strongly associated with depth. Sponge density made an additional significant contribution to the explanatory model. Results of this research could be used as a baseline reference for future analyses of the impact of human actions in the study area. (e.g. oil spills, change in fishing intensity, other pollution events, tourism development).     

Size-dependent territory defense by a damselfish

Summary Three adult size classes of the territorial Caribbean dusky damselfish,Stegastes dorsopunicans, are differently distributed with respect to habitat, and with respect to the biomass of filamentous algal turfs in the areas they defend. The density of large individuals is positively correlated with the decalcified dry biomass of these turfs, whereas the densities of medium and small individuals are inversely related to algal biomass. Density of the urchin,Diadema, is also inversely correlated with algal biomass. The high density of large dusky damselfish in sites with algal turfs of relatively high biomass probably results from preferences of dusky damselfish for sites in which algal turfs are thick, and superior abilities of large individuals to defend these sites.Because both rate of attacks and the effectiveness of attacks on territory invaders by dusky damselfish increases with increasing size, sites with relatively high biomass algal turfs are typically better defended than those with lower biomass turfs. Apparently as a result of this, small foraging groups of the blue tang surgeonfish,Acanthurus coeruleus, feed less on high biomass algal turfs than do larger foraging groups, the members of which experience attacks by defending damselfishes less frequently. The relatively low proportionate use of high biomass feeding sites by solitary blue tangs and members of small foraging groups is caused by dusky damselfish. When the density of this damselfish was reduced artificially, use of high biomass algal turfs by solitary blue tangs increased to a level indistinguishable from that of participants in large foraging groups.     

Demography and habitat availability in territorial occupancy of two competing species

Although metapopulation dynamics have become the focus of considerable theoretical research, little attention has been paid to its role when examining the coexistence of species. When two or more species live in the same patch network, interspecific interactions may affect their dispersal, colonization and extinction rates, and it may be possible to incorporate competition affecting these parameters in metapopulation models. Here, we extend the territorial occupancy model proposed by Lande to competing species. Our model estimates an equilibrium proportion of habitat occupancy as a function of life‐history parameters, dispersal behavior, habitat suitability and interspecific interactions. Moreover, it could prove to be useful as a tool in the assessment of potential management decisions. We apply the model to the golden Aquila chrysaetos and the Bonelli's eagle Hieraaetus fasciatus, two territorial raptors that coexist in the Mediterranean region, sharing food and nesting habitats. Over the last twenty years, while the golden eagle has maintained and, in some cases, increased its breeding numbers, Bonelli's eagle has suffered a marked decline, with many territories abandoned by the latter now occupied by the former. This suggests that the dynamics of these species could be influenced by interspecific competition. The model identified the relative importance of competition (stable equilibrium that allows long‐term coexistence) and predicted that, when habitat overlap is slight as in the study area, intraspecific dynamics are much more important for the persistence of each species than interspecific ones. Our results suggest that the improvement of territorial bird survival and productivity are the most urgently needed actions to be undertaken in the case of the golden eagle, while for Bonelli's eagle efforts should be focused on improving territorial and non‐territorial bird survival. As habitat conservation measures, the proportion of suitable exclusive habitat should be increased for both species.     

Use and partition of space and resources by two coexisting Rhyacophila species (Trichoptera) in a high mountain stream

Life history, distribution, drift and food habits of two coexisting Rhyacophila species, Rhyacophila evoluta and Rhyacophila intermedia were studied in a high mountain stream in the Pyrénées.The life histories of both species took two years downstream and three years upstream. Several generations and a large range of larval instars permanently coexisted in the river.Slight temporal segregation of the life histories and differences in size and food habits of the coexisting larvae partially reduced the interspecific competition and allowed an optimal use of space. Instars IV of R. evoluta and V of R. intermedia, which had the most similar biological characteristics had the same microdistribution when they lived alone but used different habitats when they coexisted.     

Comparative feeding ecology of two herbivorous damselfishes (Pomacentridae: Teleostei) from the Gulf of California,Mexico

Two species of benthic damselfishes from the Gulf of California, Mexico, use contrasting behaviors when feeding on benthic algal communities. The small (±70 g) Cortez damselfish, Eupomacentrus rectifraenum (Gill, 1862), feeds selectively from a multi-species algal mat, eats fleshy red and green algae and ignores brown and calcareous algae. The giant blue damselfish, Microspathodon dorsalis (Gill, 1862), is a large (±450 g), lethargic, nonselective feeder which grazes on a near monoculture of a fleshy red alga, Polysiphonia sp. Feeding activity for both species is low in the morning peaks during late afternoon, and drops sharply as night approaches. Based on feeding rates, gut-filling times, and weights of gut contents, Cortez damselfish process six to eight full guts of food and giant blue damselfish three full guts of food per day. The algal mat exhibits high standing crops (291–618 g dry wt · m^?2) and low productivity, but the preferred food of the Cortez damselfish (Ulva) appears to colonize the mat frequently and grow rapidly. The Polysiphonia dominated community on giant blue damselfish territories exhibits low standing crops (23 g · m^?2) and high productivity (34–47 times that of the mat per gram algae). Even though the feeding behaviors and resources used by the two damselfishes differ, both species eat similar food (delicate red and green fleshy algae, and depend on rapid colonization and/or high productivity to maintain their primary foods in the grazed algal community.