Attack intensity by two species of territorial damselfish (Pomacentridae) as estimates of competitive overlap with two species of wrasse (Labridae)

The intensity of interspecific territorial defense should be based upon the degree of competitive overlap. We tested this relationship in two territorial Caribbean damselfish (dusky, Stegastes adustus, and longfin, S. diencaeous) with intruders being the bluehead wrasse (Thalassoma bifascatus) and the slippery dick wrasse (Halichoeres bivittatus). Based on food habits, the slippery dick and the bluehead wrasse should have the same degree of competitive overlap to the two damselfish species. We also predicted that the larger slippery dick wrasse intruder would receive more aggression than the smaller bluehead wrasse intruder. Neither damselfish species distinguished between the two wrasses suggesting that they were ecologically equivalent. We also tested size differences within both species of wrasse and found that size had no influence on the aggression in the dusky damselfish. The longfin also did not show a size preference for the bluehead but did prefer to attack the larger slippery dick wrasse. In spite of the similarities between the dusky and the longfin damselfish and the similar food habits of the bluehead and the slippery dick wrasse, our results suggest that using intensity of interspecific territorial defense alone may not be an adequate measure of competitive overlap.     

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.     

Territorial behaviour of beaugregory damselfish (Stegastes leucostictus) in response to egg predators

To test the hypothesis that territorial male beaugregory damselfish (Stegastes leucostictus) can assess the degree of threat from egg predators, the aggressive behaviour of both males guarding eggs and males without eggs was recorded when they were presented with either one or five individuals of the wrasse egg predator Thalassoma bifasciatum. Presentations were made in a clear plastic bottle 0.5 m from artificial beaugregory breeding sites in the field. Two measures of aggressive behaviour (downhead threats and time spent within 10 cm of the presentation bottle) were significantly greater for multiple wrasse presentations than for single wrasse presentations, while a third measure (chase attempts) was not. In contrast, chase attempts were significantly greater for males guarding eggs than for males without eggs, but there was no significant difference in the level of downhead threats or bottle proximity time for this comparison. Levels of the three aggressive measures were not correlated with either the amount of eggs or the number of egg clutches present. These results indicate that territorial male beaugregories respond to an increase in the number of intruding egg predators by increasing the levels of low-cost threat behaviour, while the presence (but not the amount) of eggs results in an increase in the amount of higher cost attack behaviour. These experiments, therefore, support the hypothesis that male beaugregories can assess the degree of threat from egg predators, and indicate that they use this assessment to alter the strategies used in territorial defence.     

Distribution of behaviours and species interactions within home range contours in five Caribbean reef fish species (Family Labridae)

Synopsis This study investigated the distribution of behaviours and species interactions within home range contours in five Caribbean labrid species: Halichoeres bivittatus, H. garnoti, H. maculipinna, H. poeyi, and Thalassoma bifasciatum. For this study, contours were defined as: (a) 30%—the core use area, (b) 30–75%—the intermediate activity area, and (c) 75–95%—the peripheral activity area. Behaviours analyzed for this study included: (i) feeding (=biting the substrate or chewing), (ii) chased by pomacentrids, (iii) swimming alone, (iv) swimming with other fishes, and (v) all activities with other fishes. Fifty-nine percent of Halichoeres bivittatus observed showed a higher frequency than expected being chased by pomacentrids in the peripheral region of their home ranges. Halichoeres garnoti showed a lower frequency than expected swimming with other individuals in their core use area, and 64% of the individuals observed showed a higher frequency than expected being chased by pomacentrids in the peripheral region. In general, H. maculipinna exhibited a random distribution of behaviours throughout their home range areas, with a non-significant trend for more agonistic interactions with pomacentrids in peripheral regions. Halichoeres poeyi and T. bifasciatum showed higher frequencies than expected being chased by pomacentrids in the peripheral regions. Overall, the non-random distribution of agonistic interactions with pomacentrids throughout home range areas suggests that the presence or prior residence of territorial pomacentrids on coral reefs may modify the post-settlement selection of home range areas by these labrid species.     

Influence of Reproductive Status: Home Range Size in Water Voles (Arvicola amphibius)

The relationship between home range and reproductive status of water voles (Arvicola amphibius) was studied by radio-tracking on an island off the coast of northern Norway in 2006–2009. The aim was to test assumptions about the species’ social structure relative to other microtines. Juveniles used fairly small ranges (about 400 m²), with no difference between males and females. Subadults, overwintered voles in April, had ranges similar to juveniles. Reproductively active males (mean 2774.0 m²) increased their range seven-fold relative to juvenile males, with ranges on average 3.3 times larger than adult females (mean 848.3 m²), which also expanded their range. Most litters were born in May and June, and as reproduction ceased in July adult males reduced their range whilst females did not. Body mass or year did not influence home range size. Overlap of home ranges varied, but could be extensive in both adult males and females. The water vole had a social structure similar to some Microtus species, but females appeared to be non-territorial and males perhaps conditioned territorial and non-territorial.     

Social organization,survival, and dispersal of cape foxes (Vulpes chama) in South Africa

We monitored 20 cape foxes (Vulpes chama) to determine the social organization, survival, and dispersal of this species on two sites in South Africa from 2005 to 2008. Cape foxes were socially monogamous and territorial, with annual home ranges of mated pairs (n = 8) overlapping 80% on average, compared to a mean overlap of 3% between foxes in adjacent ranges. At least 2 pairs remained associated for >1 breeding season, and both sexes exhibited strong site fidelity, as home ranges in consecutive years overlapped 58–98%. Members of mated pairs never foraged together, however they used the same or nearby (<100 m apart) day rests 81% of the time when pups were 0–4 months of age, but only 28% of the time during other months of the year. Dispersal was male biased, as all juvenile males (n = 6) dispersed when 9–11.5 months old, whereas 3 of 4 juvenile females remained philopatric as either breeders or non-breeding associates. At least 6 foxes bred as yearlings (3 F, 3 M), indicating cape foxes have high reproductive potential. Two adult females maintained their territories after their mates died, whereas two adult males dispersed soon after their mates died, indicating cape foxes likely have a female-based social organization. Annual survival was 0.64, and predation from larger carnivores, primarily black-backed jackals (Canis mesomelas), was responsible for 71% of mortalities. Our results provided empirical support for previous hypotheses regarding the relationship between body size and life-history patterns in Canidae, as several ecological parameters of cape foxes were similar to that of other small (<6 kg) canid species, especially Vulpes species inhabiting arid and semi-arid environments.     

Experimental analysis of resource sharing between herbivorous damselfish and blennies on the Great Barrier Reef

Competition theory suggests that species with very similar resource requirements should not be able to coexist when resources are limiting. However, on coral reefs, territorial herbivorous fishes which use apparently very similar resources often coexist without competitive exclusion. This study investigates patterns of resource use by damselfish Pomacentrus flavicauda Whitley and blennies, primarily Salarias fasciatus Bloch, living in rubble habitats on the Great Barrier Reef. These species feed mainly on turf algae and have overlapping territories and home ranges. I ask two questions:

• 1.(1) is there any evidence of resource partitioning between these species; and
• 2.(2) do they compete for food or space? It is highly unlikely that damselfish and blenny species partition food resources by eating different species of algae, since species are intermixed at a very small scale in the algal turf. Instead, differences in food use were looked for by counting the numbers of bites fish of each species took from different parts of the rubble habitat.

Little difference in food use was found between Pomacentrus flavicauda and Salarias fasciatus except that the former fed on plankton to some extent whilst the latter did not. A manipulation experiment was performed to assess whether blennies inhabiting damselfish territories competed with damselfish for algae. Damselfish territories were used as experimental units and two manipulations performed:

• 1.(1) S. fasciatus removal, and
• 2.(2)Pomacentrus flavicauda removal.

There were four replicates of each with four undisturbed controls. Territory sizes, feeding rates and attack rates on other fishes of P. flavicauda were measured before and after blenny removal. Blenny density and biomass were measured before and after P. flavicauda removal. None of these measures provided evidence of exploitation competition between these species or of changes in levels of interference competition by damselfish after blenny removal. Blenny densities and biomass did not change significantly after damselfish removal. Damselfish appear to tolerate blennies within their territories because they cannot economically exclude them. However, the intermittent availability of an alternative source of algae outside damselfish and blenny territories and home ranges may mean that algae are not normally a limiting resource.     

The social organization of adult blue tangs, <Emphasis Type="Italic">Acanthurus coeruleus</Emphasis>, on a fringing reef,Barbados, West Indies

Blue tangs in Barbados exhibit three distinct social modes: territorial, schooling and wandering. We compared the mobility, foraging, aggression performed and received and the use of cleaning stations of adult blue tangs among modes and among habitats within a single fringing reef in Barbados. Evidence from observed switches during focal observations and multiple observations of tagged individuals indicate that fish are either territorial or non-territorial. Non-territorial fish formed schools and wandered. However, wandering can be used during solitary movements by fish in either type. Fish in the territorial mode, not previously described in adults of this species, restricted activity to a small area overlapping the territories of other tangs. They actively chased conspecifics and were chased mostly by damselfishes. They swam more slowly and fed at higher rates than other modes. Fish in the schooling mode ranged widely in compact, polarized groups of conspecifics, congeners and other species. They were not aggressive and were attacked mostly by damselfishes. They swam rapidly and fed at intermediate rates. Fish in the wanderer mode showed neither aggression nor association with other individuals. They swam rapidly, well above the substrate, fed little, were chased by conspecifics, ocean surgeonfish, A. bahianus, and damselfish and visited cleaning stations more often then other modes. All three modes were observed in all four main zones of the reef, and their behaviour changed quantitatively with habitat type. We suggest that territoriality reduces competition for algal food, schooling allows fish to overcome the food defence by damselfish, tangs and ocean surgeonfish, and wandering permits solitary movement over the reef to cleaning stations, feeding sites and other resources.     

Site fidelity and homing in juvenile rabbitfishes (Siganidae)

The behaviour of juvenile fishes is critical in establishing the link between recruitment and subsequent adult populations. If juvenile fishes move, they can respond to variation in local conditions before adult home ranges are established. Alternatively, if juveniles establish fixed home ranges at settlement, their decisions may determine future population densities at small spatial scales. Field observations and translocations revealed that juvenile rabbitfishes (Siganus corallinus and S. doliatus) have small home ranges and strong homing abilities (covering 6 m in 1 h or 36 m within 24 h). Only four of 22 individuals failed to return; all were transferred up-current, suggesting that olfaction is important in homing. Small home ranges and strong homing tendencies in juvenile herbivores suggest that decisions made by recruits will impact the spatial extent of both adult fishes and the functional roles they play within ecosystems.     

Benefits of heterospecific foraging by the Caribbean wrasse,Halichoeres garnoti (Pisces: Labridae)

Synopsis Terminal-phase yellowhead wrasses, Halichoeres garnoti, foraged alone or in association with foraging goatfish, Pseudupeneus maculatus and Mulloides martinicus. Whereas H. garnoti did not dig for benthic infauna, the goatfish foraged almost exclusively on and in sand substrata. Wrasses in the company of goatfish made significantly more strikes on sand substrata than did solitary wrasses, although there were no significant differences in the frequency of strikes on sand and hard substrata combined. The frequencies of other behaviors (searches, scratches, flights, chases, rests, yawns, and cleanings) were not significantly different between solitary and associated wrasses. H. garnoti are attracted to foraging goatfish, which provide access to an otherwise unavailable food resource. To whom reprint requests should be sent     

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.     

Size-dependent feeding association of two wrasses (genusPseudolabrus) with the morwong,Goniistius zonatus

While foraging on the substrate, two closely-related wrasses,Pseudolabrus eoethinus andP. sieboldi, which occur sympatrically in the Uwa Sea, Shikoku Island, Japan, often accompanied the morwong,Goniistius zonatus, eating benthic invertebrates flushed out by the latter's feeding activities. Both wrasses tended to feed more frequently in such an association than when solitary.Pseudolabrus eoethinus (9–17 cm TL) accompaniedG. zonatus more frequently than the smallerP. sieboldi (7.5–12 cm TL), large individuals of the former attending the host more often than smaller ones. This tendency was not apparent inP. sieboldi. The size-dependent association frequency was determined by 1) the chances of encountering a host, and 2) interference among the wrasses. The frequency of encounter of wrasses with a host depended on the home range size of the former, such being positively correlated with body size. Interference among the wrasses resulted in smaller individuals being repelled by larger ones, irrespective of species, when they were approaching or attending a host.     

Territoriality and Habitat Use by Juvenile Blue Tangs, Acanthurus coeruleus

We studied territoriality and habitat use by yellow phase juvenile blue tangs, Acanthurus coeruleus, on a small fringing reef in Barbados, West Indies. Juvenile blue tangs occurred on the reef crest, spurs, and a transition zone between the reef crest and reef flat at a density of about 8 individuals per 100m², but were much rarer on the reef flat. They were solitary and occupied stable home ranges (median=0.85m²) that increased with body size. Observational and experimental data documented aggressive defense of home ranges against conspecific and to a lesser extent congeneric, A. bahianus, juveniles (about 7.5 approaches and attacks per hour directed at intruders). Home range locations were structurally more complex and closer to a vertical face than expected by chance. Although juvenile blue tang territories overlapped considerably with those of larger and more aggressive Stegastes damselfish, which are believed to exclude solitary adult Acanthurus spp. from reef crest and spurs, the tangs avoided Stegastes and were rarely chased (<0.3 fleeing events per hour). Space use and social organization of yellow juvenile blue tangs contrast strikingly with that of both conspecific adults and congeneric juveniles.     

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.     

Spatial Dispersion and Nonmigratory Spawning in the Bluehead Wrasse (Thalassoma bifasciatum)

Earlier studies of the behavior of the bluehead wrasse Thalassoma bifasciatum have shown it to be a migratory spawner with large terminal-phase males defending temporary spawning territories. We describe a variant social structure where fish occupy permanent home ranges, spawn within or near these home ranges, and are not territorial. Movements of identified terminal-phase and intermediate males and females were mapped in the backreef areas of three coral reefs in Puerto Rico. Locations of spawns were then compared with these home-range maps. All fish used most or all of their morning home range during the afternoon spawning period. Both terminal-phase males and females spawned within or near their home ranges. Males were relatively tolerant of other males during the afternoon spawning period: only one in five encounters between large males resulted in aggressive chases. The location of chases bore no relation to spawning sites, areas of morning foraging, or to home-range borders. A Monte Carlo computer simulation was used to measure home-range dispersion of terminal-phase and intermediate males at our main site. If males were territorial, we should expect their home ranges to be significantly overdispersed within the cumulative area they occupied. During the first year male home ranges were overdispersed but during the second year they were randomly dispersed, even though the same number of terminal-phase males occupied the same study site both years. Differences in social behavior between backreef areas and other areas reported in the literature, and found in other portions of our reefs, may be related to differences in feeding ecology between populations and between different portions of the same reef.     

A new heterospecific foraging association between the puddingwife wrasse,Halichoeres radiatus,and the bar jack,Caranx Tuber: evaluation of the foraging consequences

Synopsis The bar jack,Caranx Tuber, was commonly observed to follow individual puddingwife wrasses,Halichoeres radiatus, that were foraging on the substrate. Individuals of both species actively pursued the other to maintain these heterospecific foraging teams, were sometimes attracted to feeding acts initiated by team partners, and the foraging rates of teamed jacks and wrasses were positively correlated. Pilfering of food items was rare, suggesting little, if any, competition cost of this foraging association. The ratio of bites to search in teamed jacks was over three times that when solitary, and jacks were sometimes aggressive to conspecifics attempting to join their team, suggesting that the association is beneficial to the jacks. Both bite and search rates were higher in puddingwifes when teamed with a jack, indicating that the association also benefits the wrasses. Benefits to puddingwifes may be derived directly from attendants because wrasses were sometimes attracted to jack foraging acts. However, increased foraging in wrasses may also be a consequence of heightened motivation to feed owing to heterospecific social facilitation.     

Fish habitat suitability and community structure in the equatorial Lake Naivasha,Kenya

Habitat suitability indices indicate how fish species respond to different habitat types. We assessed effects of habitat characteristics on fish distribution in an equatorial lake, Lake Naivasha, Kenya, where habitats vary according to substrate, depth and turbidity. Using monthly data between 2008 and 2010 using multi-mesh gill nets, catch per unit effort was used as a relative abundance measure to identify how habitat variables drive fish distribution. The focus was on commercial fishes: two introduced species (Cyprinus carpio and Micropterus salmoides) and two naturalised species (Oreochromis leucostictus and Tilapia zillii). Analyses revealed distinct preferences for different habitat variables by all commercial species except for C. carpio. For example, O. leucostictus preferred shallow waters with silt–clay substrates whilst M. salmoides preferred deeper waters with sandy/rocky substrates. Conversely, C. carpio showed no specialised habitat requirements. Niche overlaps were significantly lower between O. leucostictus and its respective sympatric species than between other species, a likely result of its territorial behaviour. The continued environmental degradation of Lake Naivasha may imperil the preferred habitats of the niche restricted M. salmoides, O. leucostictus and T. zillii. By contrast, the ubiquity of C. carpio may facilitate their invasion, and consequently sustain their dominance in the lake’s commercial fishery.     

Diet, foraging, and use of space in wild golden-headed lion tamarins

Lion tamarins (Callitrichidae: Leontopithecus) are small frugi-faunivores that defend large home ranges. We describe results from the first long-term investigation of wild golden-headed lion tamarins (L. chrysomelas; GHLTs). We present data about activity budgets, daily activity cycles, diet, daily path length, home range size, home range overlap, and territorial encounters for three groups of GHLTs that were studied for 1.5-2.5 years in Una Biological Reserve, Bahia State, Brazil, an area characterized by aseasonal rainfall. We compare our results to those from other studies of lion tamarins to identify factors that may influence foraging and ranging patterns in this genus. Ripe fruit, nectar, insects, and small vertebrates were the primary components of the GHLT diet, and gums were rarely eaten. Fruit comprised the majority of plant feeding bouts, and the GHLTs ate at least 79 different species of plants from 32 families. The most common foraging sites for animal prey were epiphytic bromeliads. The GHLTs defended large home ranges averaging 123 ha, but showed strong affinities for core areas, spending 50% of their time in approximately 11% of their home range. Encounters with neighboring groups averaged two encounters every 9 days, and they were always aggressive. Data about time budgets and daily activity cycles reveal that the GHLTs spent most of their time foraging for resources or traveling between foraging sites distributed throughout their home ranges. The GHLTs spent much less time consuming exudates compared to lion tamarins in more seasonal environments. Additionally, the GHLTs had much larger home ranges than golden lion tamarins (L. rosalia), and did not engage in territorial encounters as frequently as L. rosalia. GHLT ranging patterns appear to be strongly influenced by resource acquisition and, to a lesser extent, by resource defense.     

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.     

Effects of the Caribbean threespot damselfish,Stegastes Planifrons (Cuvier), on algal lawn composition

Algal lawn communities within territories of herbivorous threespot damselfish, Stegastes planifrons (Cuvier) were studied in a shallow back-reef environment at La Parguera, Puerto Rico. Caging exclusion experiments, monitoring of non-manipulated lawns and gut content analyses were used to determine the effect of S. planifrons on algal species composition of the lawn. An average of 40 algal species per sampling period were found in naturally occuring lawns, with a total of 53 species being recorded throughout the course of study. Examination of algal species found in damselfish guts and comparison with natural lawns indicate that damselfish feed primarily on their algal lawns and graze the algae present in proportion to abundance. Caged algal lawns showed significant decline in algal species number and abundance over time. Non-selective feeding by Stegastes planifrons within their territorial lawns appears to result in an “intermediate disturbance” which maintains a greater algal species richness than is found in their absence.