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Little is known about microhabitat use by Caribbean parrotfishes soon after settlement from the plankton. We monitored the abundance and distribution of recently settled Sparisoma spp. (likely mostly S. viride with some S. aurofrenatum) on 6 × 6 m quadrats (n = 9) on the fringing reef front in Barbados (West Indies) every 15 d for 6 mo. Each quadrat was divided into 1 m2 cells to examine associations between substrate composition and recruit (Stegastes diencaeus and threespot damselfish S. planifrons. Whereas Sparisoma recruits overlapped with longfins and to a lesser extent with threespots, small juveniles overlapped only with threespots. Some of the microhabitat associations with recruits and small juveniles at the cell scale were also found across quadrats. We suggest that the reef front is an important habitat for recently settled Sparisoma in Barbados, where they rely on being cryptic and solitary within turf algae gardens defended by damselfishes to minimize predation. After some growth, they perform a microhabitat shift, perhaps due to increased damselfish aggression. Thus, the early post-settlement dynamics of Caribbean Sparisoma might be strongly influenced by substrate modification by algal-gardening damselfishes.

Summary 1. Populations experiencing localized mortality can recover in the short term by net movement of individuals from adjacent areas, a process called compensatory immigration or spillover. Little is known about the factors influencing the magnitude of compensatory immigration or its impact on source populations. Such information is important for understanding metapopulation dynamics, the use of protected areas for conservation, management of exploited populations and pest control. 2. Using two small, territorial damselfish species (Stegastes diencaeus and S. adustus) in their naturally fragmented habitat, we quantified compensatory immigration in response to localized mortality, assessed its impact on adjacent source populations and examined the importance of potential immigrants, habitat quality and landscape connectivity as limiting factors. On seven experimental sites, we repeatedly removed 15% of the initial population size until none remained and immigration ceased. 3. Immigrants replaced 16–72% of original residents in S. diencaeus and 0–69% in S. adustus. The proportion of the source population that immigrated into depleted areas varied from 9% to 61% in S. diencaeus and from 3% to 21% in S. adustus. In S. diencaeus, compensatory immigration was strongly affected by habitat quality, to a lesser extent by the abundance of potential immigrants and not by landscape connectivity. In S. adustus, immigration was strongly affected by the density of potential migrants and not by habitat quality and landscape connectivity. On two control sites, immigration in the absence of creation of vacancies was extremely rare. 4. Immigration occurred in response to localized mortality and was therefore compensatory. It was highly variable, sometimes producing substantial impacts on both depleted and source populations. The magnitude of compensatory immigration was influenced primarily by the availability of immigrants and by the potential improvement in territory quality that they could achieve by immigrating and not by their ability to reach the depleted area.

There has been surprisingly little attention to adaptive variation in the locomotor speed and gaits used in antipredator behaviour. We investigated the relationship between body size and the use of two alternative gaits by three species of parrotfishes (princess, Scarus taeniopterus; queen, Scarus vetula; stoplight, Sparisoma viride) escaping an approaching snorkeller in their natural fringing reef habitat in Barbados. As body size increased from about 7 to 58 cm, the proportion of fish using an energetically more costly but relatively faster escape (body and caudal fin swimming) rather than a less costly and relatively slower escape (paired fin swimming) decreased from 100% to 0%. In contrast, the study confirmed previous research showing that larger fish fled at greater distances from the snorkellers, behaviour which would have increased safety but incurred higher opportunity costs. We conclude that small fish require a more expensive gait to attain an adequate escape speed. Thus, the gait used for escaping shows a compensatory relationship with body size because small individuals with lower swimming capacity use a higher proportion of that capacity. On the other hand, flight initiation distance shows cospecialization with body size because larger fish with higher swimming capacity further reduce their risk by fleeing sooner.

We present a protocol for using temperature records from external thermosensitive radiotransmitters recorded by data-logging receivers to identify bouts of rest and activity in mammals that sleep in a curled-up posture. We illustrate the protocol using eastern chipmunks (Tamias striatus) sampled in the Ruiter Valley Land Trust near Mansonville, Quebec, Canada. Temperatures recorded at intervals of 12–45 min, when chipmunks were in their burrows as well as above ground, displayed sequences of warmer, stable temperatures (assumed to be produced by curled-up, resting individuals) alternating with sequences of cooler, more variable temperatures (assumed to be produced by active individuals). By sampling points from typical sequences of rest and activity and using regression tree analyses to optimize the distinction between resting and active temperatures, we were able to define bouts of rest and activity. Torpor bouts were also identified by a distinct pattern of decreasing temperatures. Because curled-up rest did not occur outside the burrow, we were able to validate the assignment of bouts by independent determination of chipmunk locations using handheld telemetry. The proportion of observations of chipmunks outside the burrow correctly classified as active and the proportion of chipmunks classified as resting that were correctly located in their burrows were both high (approx. 96%). For the numerous mammalian species that curl up to rest, continuously recorded thermosensitive telemetry has the potential to provide more precise and reliable data on rest and activity over longer periods, including the night and time in burrows or dens, and with less effort per individual than most alternative techniques. © 2011 The Wildlife Society.

Nest predation is an important practical challenge for the conservation of egg-laying reptiles, with the potential to reduce hatchling recruitment and slow the recovery of threatened populations. Accurately forecasting where and when predation will occur has the potential to optimize predation management. Survival analysis, a set of statistical techniques recently popularized in studies of avian nest success, provides a unique approach for modelling variation in egg mortality risk throughout development. We used Cox proportional hazards regression to model the survival of sea turtle eggs from predation by the small Asian mongoose Herpestes javanicus, a widely introduced and destructive sea turtle nest predator in the Caribbean. We evaluated the ability of models to predict egg survival using 7 years of nest predation data for critically endangered hawksbill sea turtles Eretmochelys imbracata in Barbados. Daily predation risk was the highest for freshly laid nests, decreasing rapidly with nest age but increasing again near the end of development. Predation risk was the highest in and near patches of beach vegetation, increased over the nesting season and increased with nest density on the open beach but not in vegetation. Survival models calibrated using data from 2004 to 2005 showed excellent discrimination and ≥84% accuracy when predicting the fate of nests from previous years. Our study provides the first quantification of the daily variation in predation risk for incubating turtle eggs, revealing a narrow time window early in development during which the application of predation reduction measures is likely to have the greatest impact on nest survival. More generally, we demonstrate the utility of survival analysis for generating fine-scale predictions of spatiotemporal variation in turtle egg mortality, providing a flexible tool for the conservation of sea turtles and other egg-laying reptiles.

Most wild animals show direct negative responses to human disturbance; however, disturbance may also have positive indirect effects by altering species interactions. In the Caribbean, introduced mongooses (Herpestes javanicus) are an important diurnal predator of the nests of critically endangered hawksbill sea turtles (Eretmochelys imbricata). We asked whether daytime visitor activity could benefit hawksbills by reducing mongoose activity in nesting habitat. We used track monitoring sites to measure how mongooses alter their space use in response to fluctuating human beach use and availability of hawksbill nests, and we estimated the indirect impact of human disturbance on nest predation for 5 years of hawksbill nesting. Human activity substantially decreased mongoose use of nesting habitat. Mongoose activity increased with abundance of nests and was lower at the edge than the interior of patches of beach vegetation, but neither factor altered relative sensitivity to disturbance. We estimated that, in addition to deterring mongooses from accessing nests on the open beach, human activity has the potential to reduce predation of nests in vegetation by up to 56% at our site, with the greatest per capita impact at low (

Flight initiation distance (FID), the distance at which an organism begins to flee an approaching threat, is an important component of antipredator behavior and a potential indicator of an animal’s perception of threat. In a field study on parrotfishes, we tested the predictions that FID in response to a diver will increase with body size, a correlate of reproductive value, and with experience of threat from humans. We studied a broad size range in four species on fringing reefs inside and outside the Barbados Marine Reserve. We used the Akaike's Information Criterion modified for small sample sizes (AICc) and model averaging to select and assess alternative models. Body size, reserve protection, and distance to a refuge, but not species, had strong support in explaining FID. FID increased with body size and generally remained two to ten times fish total length. FID was greater outside the reserve, especially in larger fish. Although we were not able to completely rule out other effects of size or reserve, this study supports predictions of an increase in FID with reproductive value and threat from humans.

Studies of coral reef fish recruitment have focused more on factors influencing the return of larvae to reefs and the process of settlement than on factors affecting survival in the plank- ton, despite the well-documented importance of the larval environment for temperate marine spe- cies. We examined the ability of environmental factors to explain temporal patterns of recruitment in 8 taxa of coral reef fishes, distinguishing variables associated with settlement from those associated with the pelagic larval stage. At 10 d intervals over a 17 mo period, we collected newly settled fishes from settlement units in Barbados (West Indies). We collected concurrent data on 3 settlement- associated variables, lunar darkness, wind speed, and tidal amplitude, and 5 larval environment vari- ables, sea-surface temperature, cloud cover, salinity, chlorophyll a concentration, and normalized water-leaving radiance at 555 nm. The last 3 were associated with low-salinity intrusions originating in the Amazon. We used hierarchical partitioning and Mallow's C(p) model selection to identify important variables for each taxon. Temporal patterns of recruitment differed among taxa of which 6 showed significant environmental correlations. Significant settlement variables included lunar darkness and tidal amplitude. Significant larval environment variables were diverse and varied in magnitude and sign across taxa. The effects of larval variables were generally strong relative to settlement variables. The temporal scale of the strongest environmental predictor differed across taxa. Our study supports the views that planktonic factors affecting larval survival substantially influ- ence recruitment in coral reef fishes and that different species are affected differently by a common, temporally variable, planktonic environment.

Predators are an important source of mortality for animals that lay their eggs in buried nests. We asked how depth alters the process of predation for buried prey. We outlined a general model of predation risk where depth may alter both prey detection and subsequent capture: deeper prey are detected less often because the strength of olfactory cues decreases with burial depth and, once detected, are further protected by the costs of digging. Using this framework, we examined how burial depth influenced egg predation for critically endangered hawksbill sea turtles (Eretmochelys imbricata) by introduced mongooses (Herpestes javanicus) in Barbados. We tested the effects of nest depth on detection and subsequent predation using observational data on hawksbill nests over a 2-year period and an experiment with artificial nests. For both real and artificial nests, depth had little effect on nest detection by mongooses, but once detected, shallower nests were much more likely to be preyed on. Mongooses appear to use depth-invariant surface cues to detect nests but increase digging persistence in response to olfactory cues. We argue that excavation cost is an important but overlooked mechanism protecting deeply buried resources. For reptiles with buried nests, the relationship between depth and predation risk leads to important predictions about how changes to nesting habitat or the predator community will affect egg survival and offspring sex ratio. More generally, identifying the mechanisms by which burial depth protects prey is essential for understanding how resource burial strategies evolved and are maintained in predator‐prey systems. Key words: cache recovery, conservation, hatching success, Herpestes auropunctatus javanicus, invasive species, temperature-dependent sex determination. [Behav Ecol]

We monitored the recruitment of 8 fish taxa at 10 d intervals for 1 yr on 5 fringing coral reefs along a 15 km stretch of the west coast of Barbados, using benthic standard monitoring units of recruitment of fishes (SMURFs). SMURFs are designed to sample taxa that settle onto coral rubble, including cryptic species, and to minimize post-settlement predation. We deployed SMURFs in reef habitat to separate meso-scale processes from the small-scale influences of benthic habitat. Recruit- ment of most taxa occurred year-round, but was highly variable, with on average more than 50% of recruits collected on only 14% of the sampling dates, indicating the importance of frequent sampling. Temporal patterns within taxa were concordant across reefs, indicating coast-wide synchronous set- tlement, but differed among taxa. Within reefs, 2 taxa settled more frequently on SMURFs sur- rounded by non-preferred substrate, 1 exhibited the opposite pattern, and the remaining 5 showed no substrate associations. Recruitment to individual SMURFs was seldom correlated among taxa. Among reefs, recruitment of 4 taxa was consistently lower on the central coast and higher at the north and south ends, consistent with a previously identified tidally induced flow regime that reduces onshore larval transport near the center of the west coast; the remaining taxa exhibited other spatial patterns, challenging the generality of the role of hydrodynamics. Overall, this study expands the tax- onomic range of recruitment studies, shows spatially coherent (over kilometers) but temporally vari- able (over tens of days) recruitment and reveals substantial diversity in patterns among concurrently settling taxa.

Foraging and vigilance conflict in animals that lower their head during food search and handling, but it is less clear whether these activities conflict in animals that handle food with the head raised. In these species, at least part of the foraging process is physically compatible with vigilance. Nevertheless, both vigilance and food handling require cognitive resources, so animals may not be vigilant whenever their head is raised. We tested whether grey squirrels are vigilant when they are handling food items held in their forepaws while in a semiupright posture. If vigilance occurs during handling, we predicted that squirrels finding food in a location with a partially blocked view would change location before handling to improve visibility. Because this test assumes that the benefit of vigilance during handling is greater than the cost of moving, we tested small food items (sunflower seeds) in which the temporal cost of changing position on the rate of food intake was relatively high and large items (crackers with peanut butter) in which the cost of changing position was relatively low. When handling crackers, squirrels that had their lateral view obstructed at the food presentation site changed to a position with a better view more often than controls or squirrels that had their overhead view obstructed. When handling sunflower seeds, squirrels never changed their position. These results support the view that squirrels are vigilant during semiupright handling, but that vigilance may be sacrificed if it leads to high foraging costs.

We examined the diurnal refuges occu- pied by the nocturnal squirrelfish, Holocentrus rufus, to describe refuges and the behavior associated with their use and to determine which, if any, refuge characteristics were selected. We tagged 21 H. rufus on two sites on a fringing reef in Barbados, West Indies, identified the refuges they used (n = 57), measured ten characteristics of each refuge and the surrounding microhabitat, and monitored their refuge use for 4 weeks. To evaluate refuge selection, we measured the same characteristics on a comparable number of unused potential refuges (n = 67) on the same reefs and used classification tree models to determine which characteristics separated used from unused refuges. Each fish used 1-9 refuges, which did not overlap among individuals and were defended against intrusion by conspecifics and some hetero- specifics. Fish with more than one refuge frequently moved among them. There was strong site fidelity with no immigration of untagged fish or emigration of tagged fish on either reef during the study period and no additional refuges being occupied over the 4-week period. Refuges were primarily holes, open at one or two ends, which varied in size, distance from the reef edge, entrance orientation, and vertical relief at the entrance. Holes used as refuges differed significantly from unused holes mainly in characteristics related to the vertical position of their entrance, but the classification tree models differed for the two sites. This study provides the first detailed information on characteristics of daytime refuges used by a noctur- nally active reef fish and the first evidence of selectivity of refuges. It suggests that the abundance and characteristics of holes on reefs could influence the density of H. rufus on natural reefs.

Although the importance of density-dependent dispersal has been recognized in theory, few empirical studies have examined how immigration changes over a wide range of densities. In a replicated experiment using a novel approach allowing within-site comparison, we examined changes in immigration rate following the gradual removal of territorial damselfish from a limited area within a much larger patch of continuous habitat. In all sites, immigration occurred at intermediate densities but did not occur before the start of removals and only rarely as density approached zero. In the combined data and in 5 of 7 sites, the number of immigrants was a hump-shaped function of density. This is the first experimental evidence for hump-shaped, density-dependent immigration. This pattern may be more widespread than previously recognized because studies over more limited density ranges have identified positive density dependence at low densities and negative density dependence at high densities. Positive density dependence at low density can arise from limits to the number of potential immigrants and from behavioral preferences for settling near conspecifics. Negative density dependence at high density can arise from competition for resources, especially high quality territories. The potential for non-linear effects of local density on immigration needs to be recognized for robust predictions of conservation reserve function, harvest impacts, pest control, and the dynamics of fragmented populations.

Home-range relocation occurs during natal and breeding dispersal, ontogenetic habitat shifts, and the maintenance of resourceor density-dependent patterns of distribution. Relocating animals are expected to change their behavior to compensate for limited familiarity with the new home range and with neighboring conspecifics; such changes may indicate some of the costs of relocation. Little is known, however, about the magnitude and duration of the changes or about the types of behavior affected. We investigated the short-term (2 day) behavioral changes associated with relocation in the highly territorial longfin damselfish, Stegastes diencaeus. We compared the behavior of newcomers settling into experimentally created vacancies in an established neighborhood with that of the original residents of the same territories. The greatest difference was an increase in the rate of agonistic interactions. Newcomers also used smaller territories, moved more, and fed less. Neighboring damselfishes were less aggressive toward neighbors that expanded into vacant territories than toward ‘‘strangers’’ that relocated from elsewhere. The behavior of newcomers approached that of original residents within 2 days but territory size did not. These observations suggest that relocating a territory increases energy expenditure and decreases energy intake. Such costs could explain the philopatry of reef fish when alternative locations are of uncertain quality or are only slightly better. Nevertheless, they are unlikely to outweigh the long-term benefits of obtaining a superior territory—especially for individuals from adjacent territories. Key words: aggression, dear‐enemy, dispersal, foraging, Pomacentridae, postsettlement movement. [Behav Ecol]

We developed a benthic standard monitoring unit for recruitment of fishes (SMURF) to sample fishes that settle in coral rubble and tested it on three fringing reefs on the west coast of Barbados, West Indies. These rubble SMURFs are inexpensive to construct and permit newly settled fishes, including cryptic, secretive and small species, to be quickly and fairly completely (> 83%) removed by divers without returning the unit to the surface. Over a 3-month period involving 9 collections, 32 units on 3 reefs yielded 948 newly settled fishes belonging to 28 taxa (3.3 ± 0.2 S.E. recruits per sample, n = 287) in addition to numerous crustaceans. Most specimens were Sparisoma spp. (Scaridae) (41.8%) and Stegastes partitus (Pomacentridae) (13.6%), with moderate numbers of Scarus spp. (Scaridae) (8.6%), Lythrypnus spp. (Gobiidae) (7.4%), and Pseudogramma gregoryi (Serranidae) (7.2%). Sampling SMURFs at 1-day rather than 11-day intervals yielded approximately twice as many fish, although some taxa were not affected by sampling frequency, indicating taxon-specific differences in post-settlement loss rates. Netting, intended to reduce predation on settlers, did not affect settlement estimates unless algae grew on it, suggesting that the SMURF design minimizes fish predation even in the absence of the netting. Over time, however, the netting resulted in substantial algal growth that was associated with an increase in abundance of Sparisoma spp. and a decrease in the abundance of S. partitus . This suggests that settler estimates are more affected by microhabitat changes from algal growth than by predation. During low settlement periods, SMURFs performed better than light-traps in assessing the daily input of new settlers of two abundant taxa. Eight SMURFs per reef were sufficient to demonstrate differences in settlement rates and temporal correlations in settlement within and among reefs. This study underscores the potential of benthic SMURFs to measure settlement of coral reef fishes at a range of spatio-temporal scales with moderate research cost and effort, and to facilitate the study of the settlement stage of several taxa.

When territory owners temporarily leave their territories, intrusion often increases. Periodic returns (revisits) may reduce intrusion, but not necessarily, because this tactic might increase total time away from the territory. The effectiveness of revisits also depends on a subsequent delay in the return of intruders. Adult female yellowtail damselfish briefly leave their territories in the early morning every 3 days to spawn. Some females make a single trip; others return to their territory several times before they finish spawning. To determine how much time females spent on revisits and whether it reduced intrusion, we observed revisits by multiple-trip females and compared intrusion on the territories of spawning and experimentally caged single-trip and multiple-trip females. If revisits reduce intrusions, multiple-trip females should have higher intrusions when caged than when spawning. If revisits show adaptive plasticity, caged single-trip females should have lower intrusion rates than caged multiple-trip females. Not counting the first trip to the male's nest and the final return trip, we estimated that spawning multiple-trip females averaged 86% of their time at the male's nest, 11% back in the territory and 3% travelling. When owners were spawning, territories of both single- and multiple-trip fish received about 5–7 min of intrusion. When owners were caged, intrusion increased significantly only on territories of multiple-trip females. We consider this the first direct evidence that revisits during temporary absences reduce intrusion on territories, suggesting that revisiting is a plastic trait that females may vary in response to intruder pressure.

We developed a modified visual census technique suitable for fairly sedentary, hole-dwelling species and used it to determine the diversity, density, biomass, and habitat use of morays at four sites including fringing, patch, and bank reefs in Barbados, West Indies. The method involved a careful search during two passages over transects by day and by night, noting size and position of morays seen, and using the number of new observations on the second passage to estimate the proportion of morays not seen. First passage counts were generally higher than numbers of morays recorded in previous visual censuses. These estimates were raised when we used the time period (day or night) with the highest average density visible for each species, added different individuals from the two passages, and corrected for individuals not seen. We saw more goldentail morays (Gymnothorax miliaris) during the day but more spotted (G. moringa), viper (Enchelycore nigricans), and chestnut (E. carychroa) morays at night. Counts of chain morays (Echidna catenata) did not differ significantly between night and day. Relative abundance and size of moray species varied among sites and to a lesser extent among habitat types within sites, but spotted morays were generally the most important in numbers and biomass. Mean estimated moray density and biomass were much higher than in most previous visual censuses, but similar to rotenone samples on other reefs and comparable to those of other families of predatory fishes. Our findings confirm that morays are abundant and potentially important predators that should be the focus of more attention in ecological studies of coral reefs.

We examined the abundance of blue tang surgeonfish, Acanthurus coeruleus, in each of three social modes (schooling, territorial, and wandering) in relation to size class, ecological variables, population density and time of day to discern potential determinants of social organization. We found individuals from all three social modes in all four fringing reef habitats (back reef, flat, crest and spur and groove zones) at our main site. Territorial tang density was highest in the flat zone, lowest in the spur and groove zone and negatively related to adult damselfish density. A higher proportion of tangs formed schools in reef zones with the highest densities of territorial damselfishes (spur and groove, crest). In the back reef and flat zones, where damselfish densities were very low, tangs rarely formed schools. Tangs in the wandering mode were most abundant in the back reef. The density of territorial tangs did not change with time of day, but non-territorial tangs tended to wander more in the morning and to form schools more at midday. Small yellow-phase juveniles were always territorial, and the incidence of territoriality decreased in the larger size classes, while schooling and wandering increased. Among similar fringing reefs, the incidence of territoriality increased with increasing population density. These data suggest that life history stage, damselfish density, and conspecific population density are important determinants of blue tang social organization.

Marine reef fishes may spend a significant pro- portion of their daily activity budgets visiting cleaning sta- tions. Nevertheless, the roles of ectoparasites and of inter- actions with cleaners in shaping patterns of diel activity in these fishes have been largely ignored, possibly because the importance of cleaning for the hosts remains controversial. In diurnal species, a peak in ectoparasite infestation exists at dawn, suggesting that higher rates of cleaner-seeking dur- ing this time should be beneficial to hosts. In this study, we quantified the diel pattern of visitations to cleaners, as well as other major activities, in female yellowtail damselfish Microspathodon chrysurus on a Barbadian fringing reef. Females of this species leave their territories near dawn at 3 d intervals to spawn on male territories. On non-spawning days, cleaning peaked at dawn, when fish spent >20% of their time with cleaners, and declined thereafter, averaging over 11% of the time budget during the entire day. Supple- mental observations in Puerto Rico and the Virgin Islands also revealed dawn peaks in cleaner-seeking activity. Feed- ing and territory defense together occupied less than 3% of the time budget at dawn, and never seemed frequent enough to interfere with cleaning. On spawning days, 30% of females visited cleaners at male nests or while traveling back to their territories, and 24% visited cleaners on their own territories during revisitation trips before spawning was completed; nevertheless, they spent < 1 ⁄ as much time with cleaners as did non-spawning females. Reduced cleaner- seeking indicates that spawning competes with cleaner visitation in damselfish time budgets, producing a tradeoff between cleaning and reproduction. In the 30 min after spawning, females significantly increased their rate of inter- action with cleaners, compared with the same time on non- spawning days, and regained about 68% of the missed time with cleaners; feeding and aggression did not differ between spawning and non-spawning females. Compensatory post- spawning visiting of cleaners supports the hypothesis that cleaning at dawn is important, probably because of negative consequences of the dawn peak in parasite loads.

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 100 m2, but were much rarer on the reef flat. They were solitary and occupied stable home ranges (median=0.85 m2) 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 (

Movement of coral reef fishes across marine reserve boundaries subsequent to their initial settlement from the plankton will affect the ability of no-take reserves to conserve stocks and to benefit adjacent fisheries. However, the mobility of most exploited reef species is poorly known. We tagged 1443 individuals of 35 reef fish species captured in Antillean fish traps in the Barbados Marine Reserve and adjacent non-reserve over a two-month period. Trapping and visual surveys were used to monitor the movements of these fish during the trapping period and the subsequent two months. Estimates of distances moved were corrected for the spatial distribution of sampling effort and for the number of recaptures of individual fish. Recapture rates for individual species ranged from 0–100% (median=38%). Species mobility estimated by recapture and resighting were highly correlated. Most species were strongly site attached, with the majority of recaptures and resightings occurring at the site of tagging. However, only one of 59 tagged jacks (Caranx latus, C. ruber) was ever resighted, suggesting emigration from the study area. All species were occasionally recorded away from the sites where they had been tagged (20–500 m), and several species, including surgeonfish, Acanthurus bahianus, A. coeruleus, filefish, Cantherhines pullus, butterflyfish, Chaetodon striatus, angelfish Holocanthus tricolor and parrotfish, Sparisoma viride, ranged widely within reefs. In contrast, few movements were observed between reefs separated by more than 20 m of sand and rubble, and no emigration from the Reserve was recorded. Most reef fishes vulnerable to Antillean traps appear sufficiently site-attached to benefit from reserves. However, many species move over a wide enough area to take them out of small reserves on continuous reef. Use of natural home range boundaries could minimize exposure of fishes in reserves to mortality from adjacent fisheries.

Surgeonfish (Acanthuridae) are prominent, herbivorous members of coral reef communities that occur as dispersed individuals and small, loose groups ('non-schooling fish') or as members of large, highly aggregated, mixed-species schools ('schooling fish'). We examined the relationships among fish size, habitat use and schooling in two species of surgeonfish on a fringing reef in Barbados, West Indies. Both ocean surgeonfish, Acanthurus bahianus, and blue tangs, A. coeruleus, appeared to show ontogenetic habitat shifts. The density of juvenile ocean surgeonfish was highest in the back reef (inshore), lower on the reef crest (intermediate) and lowest in the spurs and grooves (offshore) zone, but schooling adults were most abundant in the spurs and grooves zone. In a multiple regression considering the effects of depth, algal cover, rugosity and distance from shore, the density of non-schooling ocean surgeonfish was positively associated with percent algal cover on the substratum and negatively with distance from shore. Newly settled blue tangs occurred only in the reef crest and spurs and grooves zones, but larger juveniles were more common in the back reef, while adults were more evenly distributed across zones. The density of non-schooling blue tang was positively associated with rugosity, distance from shore, and percent algal cover. In both species, schooling occurred primarily in adults; small juveniles never participated in the large, dense schools. The proportion of adults that were schooling increased from the back reef to the reef crest to the spurs and grooves zone. These results are consistent with the hypothesis that schooling permits adult surgeonfish access to higher quality food in the territories of damselfish (Pomacentridae) that predominate on the reef crest and spurs.

Juvenile pollock (Pollachius virens) school in open water at low tide and disperse in beds of intertidal algae at high tide. The goal of the present study was to determine whether both aggregation and use of algal habitat represent alternative antipred- ator tactics for pollock, and whether their occurrence depended on the number of fish present and the amount of algal habitat available. We systematically varied fish density and algal availability in large (8-M2) arenas and examined distributions before and after exposure to an avian predator model, a stuffed cormorant (Phalacrocorax auritus). Pollock preferred the algal habitat, and the proportion of fish in the algae increased as the amount of algal habitat increased. When density of fish in the arena increased, the number of fish in the algal habitat increased, but the proportion decreased. Following exposure to the predator model, the proportion of fish in the algae increased. Fish in the open were aggregated most of the time, but there was a trend toward increased aggregation of those fish remaining in the open following exposure to the predator. Thus, the use of two alternative antipredator tactics can produce very dynamic spatial distributions. Because the benefits of aggregations are positively density dependent while those of refuges are likely negatively density de- pendent, species that use both tactics are likely to show dramatic shifts in habitat distribution with changes in population size and refuge availability.

We examined how spatial distribution and the use of aggressive behavior by blue gouramis, Trichogaster trichopterus (Belontiidae), in the presence of a concentrated food source were affected by group size and by the short-term presence and absence of food. Gouramis aggregated in the area of the food source, and the frequency of aggressive acts per fish was higher for fish near the food source than for fish away from it. The frequency of aggressive acts per fish near the food source decreased with group size and was about 50 times higher in groups of 2 and 4 than it was in groups of 16 and 32. In group sizes 2 and 4, the frequency of aggression was unaffected by the presence and absence of food, but in larger group sizes aggression increased during short intervals without food. The mean proportion of time spent near the food source increased from group size 2 to group size 8 and decreased from group size 8 to group size 32 and was greater during intervals of food availability than during intervals in which food was not available. We suggest that gouramis adjust their relative use of contest and scramble competition according to the costs and benefits of aggression as determined by the number of competitors and by the potential for missed feeding opportunities. The average proportion of time spent in the vicinity of the food source appears to be influenced by both the rate of aggression and by the net rate of gain available.

We examined the relationship between the intestine length and the amount of plant material in the diet of 21 species of fish from forest streams in Panama. Alimentary tract analyses supplemented by literature reports showed that four loricariid catfish species and one poeciliid were specialized herbivores consuming almost exclusively periphyton and detritus. Four species, including one erythrinid, one characid, one trichomyctycterid and one eleotrid, were carnivores consuming almost entirely food of animal origin. Twelve species, including five characids, one lebiasinid, two pimelodelids, three cichlids and one poeciliid, were omnivores consuming food of both plant and animal origin, but the average proportion of food of plant origin (detritus and algae plus higher plant parts) varied from 4–60%. Most omnivores increased plant food consumption with increasing size. Because intestine length increases allometrically with body size and the pattern of increase differs considerably among species and is influenced by length:mass relationships, we compared species at the same size and took both length and mass into account. At a given size, intestine lengths of herbivores were longer than those of omnivores, and these were longer than those of carnivores. Differences in intestine length among the dietary categories were greater at larger body sizes and when the common size was defined by body mass than when it was defined by body length. There was no trend for the average proportion of plant material consumed to be related to intestine length among the omnivores, when confounding effects of body mass were taken into account. The slopes of the allometric equations relating log10 intestine length to log10 body size for herbivores tended to be higher than for omnivores and higher for omnivores than for carnivores, but both herbivores and omnivores showed extensive variation and overlap with the other dietary categories. Among the omnivores, there was no trend for slopes to be steeper for species consuming more plant material on average or for species showing larger ontogenetic increases in plant consumption. These results permit increased precision in describing diet-intestine length relationships, but indicate that the widely held belief that intestine length reflects diet in fishes should only be applied to broad dietary categories and not to finer divisions among omnivores.

We examined the ontogenetic allometry of intestine length in relation to body length and body mass in 21 species of fish from forest streams in Panama. The relationships between log10 intestine length and log10 body length and mass were well described by linear regressions, although some species showed slight curvilinearity. Slopes and intercepts of the linear regressions varied considerably among species. Intestine length was positively allometric in most species, with slopes of the intestine length:body length relationship ranging from 1.09 to 2.11. Relative intestine lengths (intestine length/body length) varied by two orders of magnitude (0.39–38.44) in the data set as a whole, but the variation was about one order of magnitude when species were compared at a common body size. Species in which body mass increased more rapidly with body length had more rapid increases in intestine length with body length. Among omnivorous and carnivorous species compared at the same body length, heavier species had longer intestines. Interspecific comparisons of relative intestine length may produce misleading conclusions unless comparisons are made at a common size and account for differences in relative mass.

Abstract. The adaptive significance of alternative patterns of dispersing hoarded food was examined by determining which factors influence the occurrence of scatter-hoarding in the eastern chipmunk a species that typically larder-hoards food to its burrow. A standardized food-provisioning test was used to determine the incidence of scatter-hoarding in relation to age, sex, reproductive condition, time of year, patch position and social context. Juveniles and females with young scatter-hoarded significantly more often than did other classes. Newly emerged juveniles scatter-hoarded both before and after they acquired a permanent burrow of their own, but decreased their frequency of scatter-hoarding as they grew older and more capable of defending their burrow. Females with young in the burrow did not appear to use scatter-hoarding to avoid revealing the location of the burrow, but may have been avoiding the risk that their young would consume all their hoarded food. The incidence of scatter-hoarding was not affected by the distance of the patch from the burrow nor by the number of competing sciurids at the patch. However, scatter-hoarding was more often performed by individuals that were harassed at the patch. This may have been a response to leaving the patch with an incomplete load; experimental exclusion of animals before they had completed loading demonstrated that possessing a small load increased the tendency to scatter-hoard. For juveniles and non-breeding adults, scatter-hoarding permitted more rapid removal of food from a patch than did larder-hoarding, but for females with young, scatter-hoarding trips took longer than larder-hoarding would have, largely because such females often made more than one hoard per trip. These results do not support the hypotheses that scatter-hoarding is a vestigial behaviour pattern of no adaptive significance or that is is simply a response to lack of larder space. They do, however, support the hypotheses that scatter-hoarding reduces pilferage of hoarded food by individuals unable to defend a larder and that it increases the rate at which subordinate individuals can sequester food from ephemeral patches.

The structure and context of alarm calls produced by chipmunks (Tamias striatus) at a field site in southern Quebec were recorded during opportunistic field observations and experimentally simulated hawk attacks. Chipmunks produced three call types in the presence of predators. Chipping consisted of a series of high frequency notes with a rapid downward frequency slope (9.6 to 2.8 kHz) and was given in the presence of mammalian predators by chipmunks perched on a raised vantage point. Chucking consisted of a series of lower frequency notes also sloping downwards (2.5 to 0.4 kHz), given in the presence of avian predators by perched animals. The trill was a lower amplitude, multi-note call usually given only once by animals before reaching a refuge while fleeing from either type of predator. The average trill contained 6–11 downward sloping notes (7.3 to 0.8 kHz). The alarm call types of eastern chipmunks appear to be similar to those reported for western chipmunks. However, they differ in the clear separation of the calls for aerial and terrestrial predators. Chipmunks differ from most other terrestrial sciurids in giving repeated calls for aerial as well as terrestrial predators and in using a call just before reaching a secure refuge.

Recently emerged brook trout (Salvelinus fontinalis) foraging is still-water pools varied considerably in the proportion of time they spent moving, speed while moving, and distance travelled during pursuit of prey. Trout that exhibited a high proportion of time spent moving, fast speeds while moving, and long pursuit distances directed more foraging attempts toward the upper portion of the water column, ate more insect prey and fewer crustaceans, and made more foraging attempts per minute than trout that exhibited a low proportion of time spent moving, slow speeds while moving, and short pursuit distances. The variation in movement was related less strongly to spatial heterogeneity in the locations (pool sizes, water depths) where individuals were observed. It was not significantly related to measures of temporal variation in the environment (date, time-of-day, water temperature), body size and shape, or hunger (the amount of food in the stomach). In these clear, shallow pools, differences in the spatial distribution and behaviour of prey types apparently facilitate divergent foraging behaviour and diet among the trout. Our findings are valuable for understanding the development and maintenance of the individual specializations in water-column use and diet reported previously for several salmonids.

Functional connectivity, the degree to which the landscape facilitates or impedes movement, depends on how animals perceive costs and benefits associated with habitat features and integrate them into a movement path. There have been few studies on functional connectivity in marine organisms, despite its importance for the effectiveness of Marine Protected Areas. In this study, we asked how open sand and conspecific distribution affected functional connectivity of longfin damselfish (Stegastes diencaeus) on fringing reefs in Barbados. We translocated 102 individuals to sites varying in sand gap width and in configuration: Continuous (solid reef between release site and territory); Detour (sand along the direct path between release site and territory, but an alternative, continuous solid U-shaped reef path); and Patch (sand between release site and territory, but an alternative stepping stone path). We visually tracked and mapped every homing path. We found no evidence of a barrier to movement in the Continuous configuration, but sand was a partial barrier in Detour and Patch configurations. The probability of crossing the sand gap dropped below 50% when its width was >1.85 m in Detour and >3.90 m in Patch configuration. Damselfish avoiding large gaps took detours that approximated the route maximizing travel over reef, but they crossed more short sand gaps and fewer conspecific territories, suggesting avoidance of agonistic interactions. This study quantifies for the first time the size and steepness of a barrier to movement in a marine organism, and it provides evidence for effects of both landscape configuration and conspecific distribution on functional connectivity.

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 min) 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.

Recently-emerged juvenile brook charr foraging in relatively homogeneous, clear, still-water pools displayed significant interindividual variation in the proportion of search time spent moving, the average speed during search, the average speed during periods of moving search, and the distance moved during pursuit of prey. The frequency distribution for interindividual variation in the proportion of time spent moving was bimodal, but distributions for the other movement parameters were not. Thus, in the field, young charr tended to specialize at one of two alternative movement patterns differing primarily in the proportion of time spent moving. The movement parameters were all positively correlated, but correlations between the proportion of time spent moving, the speed while moving, and pursuit distance were small enough (r2's < 0.30) to suggest that different aspects of search mode may vary relatively independently. Our findings have three implications for studies of search mode. First, intraspecific variation in search mode need not be only a response to environmental change, but can occur in the same environment at the same time. Second, frequency distributions of movement parameters offer a more objective base than do arbitrary classifications for determining how many types of foragers are present. Third, studies using different movement parameters to distinguish between alternative search modes (e.g. sitting-and-waiting and actively searching) may not be directly comparable.

Because species respond differently to habitat boundaries and spatial overlap affects encounter rates, edge responses should be strong determinants of spatial patterns of species interactions. In the Caribbean, mongooses ( Herpestes javanicus ) prey on hawksbill sea turtle ( Eretmochelys imbricata ) eggs. Turtles nest in both open sand and vegetation patches, with a peak in nest abundance near the boundary between the two microhabitats; mongooses rarely leave vegetation. Using both artificial nests and hawksbill nesting data, we examined how the edge responses of these species predict the spatial patterns of nest mortality. Predation risk was strongly related to mongoose abundance but was not affected by nest density or habitat type. The product of predator and prey edge response functions accurately described the observed pattern of total prey mortality. Hawksbill preference for vegetation edge becomes an ecological trap in the presence of mongooses. This is the first study to predict patterns of predation directly from continuous edge response functions of interacting species, establishing a link between models of edge response and species interactions.

We examined the old, but untested hypothesis that territory size limits the maximum population density of salmonids in streams. We used published data to derive an interspecific regression of territory size (m2) on fork length (cm) (log10 territory size = 2.61 log10 length—2.83, r2 = 0.87, n = 23). Growth and mortality trajectories of salmonid cohorts from eight experimental studies were compared to the maximum-density regression, the inverse of the territory–size regression. In shallow habitats, such as riffles and raceways, the cohort trajectories followed the maximum density regression quite closely and were consistent with the territory–size hypothesis. In addition, natural densities in eight other studies did not exceed the predicted maximum density and tended to fail within the 95% C.L. of the maximum-density regression. Data from shallow habitats, therefore, provide strong support for the territory–size hypothesis. A linear logistic response model showed that the probability of observing density-dependent growth, mortality, or emigration increased significantly with increasing values of an index of habitat saturation, developed from the territory–size regression. Our results suggest that the territory–size regression has practical value for predicting the maximum densities of stream-dwelling salmonids in shallow habitats and the occurrence of density-dependent population responses.

In many animal species, locomotion is frequently interrupted by brief pauses. This intermittent locomotion is usually considered a mode of prey search, but other possible functions include reduced detection or attack by predators and improved endurance. We tested the hypothesis that pauses also serve to improve vigilance for predators in two species of sciurid rodent. Videotaping animals travelling between food-collecting and food-hoarding sites revealed that numerous short pauses comprise 5-38% of the time spent 'moving' in grey squirrels, Sciurus carolinensis, and 0-41% in eastern chipmunks, Tamias striatus. In this situation, search for food items did not occur, and pausing did not reduce the total time spent as a moving stimulus for predators. It also appeared that speed while running was too slow and the pauses too brief to provide an endurance advantage. As predicted by the vigilance hypothesis, both species spent more time pausing when moving away from forest cover (presumably towards areas of higher risk) than when travelling back towards forest cover. In control trials within forest cover, squirrels did not differ in time pausing when approaching and leaving patches, but chipmunks paused more when approaching patches than when leaving them. We conclude that one function of pausing in squirrels is to improve anti-predator vigilance. The occurrence of pausing by chipmunks did not match a priori predictions of the vigilance hypothesis. Because it also failed to match predictions of previous alternative hypotheses, we suggest that studies are needed to examine whether the risk of attacks by conspecifics and predators is higher for chipmunks approaching than leaving food patches in forest habitat. Copyright 1998 The Association for the Study of Animal Behaviour.

We studied the rainy season dispersal of the fish Poecilia gillii (Poeciliidae) from pools in a steepgradient, intermittent stream in Santa Rosa National Park, Costa Rica. The stream consisted of about 20 pools separated by dry streambed except during two floods and subsequent brief periods of flow. Individually recognizable tags permitted mark-recapture estimates of population size and information on individual movements. The first flood was very severe, with pools losing an average of 75% of their populations (range 12-99%). Most of the lost fish died by becoming trapped in desiccating pools. Males and juveniles were more likely to be lost than were females. Population loss was negatively related to pool volume and positively related to streambed slope. In addition, population loss was positively related to preflood population size when the effects of pool volume and slope were removed indicating that pools with higher densities lost more fish. Of the fish recaptured after the flood, the average proportion found in the pool in which they had been tagged varied from 16%-96%, depending on the area of the stream. Of fish that moved, 92% went downstream. The second flood was less severe though stream flow lasted as long, and there was little effect on the pool populations. Involuntary flushing during the flood and voluntary departure apparently interacted to produce the observed patterns.

To investigate the effect of familiarity'with the local terrain on the ability to escape predators, we recorded the type of refuge chosen and the distance and time required to reach it, for chipmunks escaping a pursuing human at different distances from their burrows. Chipmunks never used their burrow as a refuge unless the chase was initiated within 2.5 m of the burrow entrance. The final refuge was commonly farther than the burrow entrance. Chipmunks were most likely to take refuge in holes other than their burrow when chased within their home range, whereas they were most likely to flee up trees when chased outside their home range. Chipmunks released within their home range (10 m from burrow) took only half as much time and travelled only half as far to reach a refuge as they did when released outside their normal home range (100 m from burrow)

SUMMARY (1) This study examines the population ecology of Poecilia gillii (Kner & Steindachner, 1863), a small algae- and detritus-feeding fish, inhabiting sixteen isolated, residual pools of a high-gradient, intermittent stream in Costa Rica following floods which severely reduced the number of fish in the stream. (2) Immediately after the floods, population sizes averaged 20% and pool surface areas 130% of their pre-flood values, periphyton production was relatively low and dissolved oxygen was relatively high. Among pools, population densities were not correlated with their pre-flood values, and the population growth rates showed a weak negative correlation with density, a marginal positive correlation with periphyton production and no correlation with oxygen. (3) Near the end of the 153-day post-flood study period, population sizes had risen to 50% of their pre-flood values, while pool areas had fallen to 73% of their preflood values. Periphyton production was relatively high and dissolved oxygen was very low. Among pools, population densities were correlated with their pre-flood values, and the population growth rate showed a strong negative correlation with population density and strong positive correlations with periphyton production and dissolved oxygen level. (4) These results suggest that in highly seasonal tropical environments, temporal patterns of population abundance in high-gradient streams will be very different from those in floodplains, where the rainy season is a time of increase and the dry season a time of decline. Spatial variation in environmental characteristics which control periphyton, detritus and oxygen availability may produce characteristic population densities in different pools. An increase in the proportion of males and a decrease in their size after the floods suggest social inhibition of sexual maturation during the late dry season.

Cinematographic analysis of the air-gulping behavior used by Hoplerythrinus to ventilate its respiratory gas bladder showed that this action requires about 0.8 s and that inspiration precedes expiration. Expired breaths contain 15–35 ml gas per kilogram body weight, while the gas bladder contains 30–80 ml/kg. Tidal volume may range from 19 to 130% of the gas bladder volume with a mean of 50%. Newly inspired air is mixed with the gas expired in the same breath. However, there is partial separation of inspired and expired gas. Tying off various parts of the gas bladder showed that the nonrespiratory anterior chamber plays an important role in this separation. X-ray cinematography confirmed these conclusions and demonstrated that the anterior chamber expands greatly to accommodate the newly inspired air.

The respiration physiology of Piabucina festae, an air-breathing characin fish in the family Lebiasinidae, has been compared with that of P. panamensis, a closely related non-air-breathing species. The gas bladder of P. festae is highly modified for rapid O₂ absorption through the presence of a specialized region in the posterior chamber. In P. panamensis this organ has no respiratory specializations, but low rates of O₂ absorption do occur. Piabucina festae has a higher metabolic rate than P. panamensis and can maintain its routine $\dot{V}O_{2}$ without air breathing in normoxic water. The capacity for aquatic respiration of P. festae is reduced compared with that of P. panamensis. Piabucina festae has a lower resistance to aquatic hypoxia. It cannot greatly increase its rate of gill ventilation and has a critical oxygen tension (PCO₂) of 70 torr. By contrast, P. panamensis can increase gill ventilation by five times and has a critical PCO₂ of 25 torr. Air-breathing characins occur only in the Neotropic...

The interbreath interval for aerial and aquatic ventilation was determined for seven Florida gars (Lepisosteus platyrhincus, Pisces, Lepisosteidae) before, during, and after exposure to the simulated threat of predation by a mounted great blue heron (Ardea herodius, Aves, Ardeidae). During exposure to the heron, air-breath interval increased by 118% while water-breath interval decreased by 13% as compared with the pre-heron period. This provides evidence that ecological factors not directly involved in the physiology of gas exchange can influence respiratory partitioning in fishes. It also supports the hypothesis that retention of water-breathing capacity in air-breathing fish can reduce the risk of aerial predation in these species.

The behavior of dwarf gouramis (Colisa lalia, Pisces, Belontiidae) and their vulnerability to predation by snakeheads (Channa micropeltes, Pisces, Channidae) were observed at four dissolved oxygen concentrations. When the oxygen level was near saturation (8 ppm) or only moderately reduced (3 ppm), the gouramis rarely breathed air and spent most of their time in a patch of artificial vegetation. At extremely low oxygen concentrations (1 and 0 ppm) the gouramis increased their air-breathing frequency and spent less time in cover. Gouramis were more likely to be captured by the snakeheads when out of the vegetation, and thus were caught more quickly at lower oxygen levels, even though their air-breathing frequency declined and use of cover increased in the presence of the predators. These results indicate that dissolved oxygen concentration, which varies considerably in many fish habitats, can affect use of cover and risk of predation in fishes.

Use of the surface water for aquatic respiration (aquatic surface respiration, ASR) is one of the few alternatives to aerial respiration which allow fish to survive extreme hypoxia, yet it has received very little attention. This report examines three generalizations concerning ASR on a phylogenetically and geographically diverse range of tropical freshwater fishes. It demonstrates that ASR greatly enhances survival in hypoxic water, even in fish not morphologically specialized to use the surface film, that ASR is initiated at a distinct threshold oxygen concentration, with time spent at the surface increasing rapidly as O2 declines, and that with extreme deoxygenation fish perform ASR over 90% of the time. Ninety-four percent of the 31 species of non-air breathing fish tested showed ASR., with the threshold oxygen concentration ranging from 6 to 40 torr.

Six bimodal and six water-breathing species of fish were exposed to predation by a green heron (Butorides striatus) in a laboratory experiment to examine the hypothesis that aerial predation selects against the evolution and use of air breathing. Tests were performed at 1.6 and 0.5 mg O2∙L−1 ([Formula: see text] and 9 Torr, respectively; 1 Torr = 133.322 Pa). Most water breathers avoided the surface at 1.6 mg∙L−1 but not at 0.5 mg∙L−1, where they performed aquatic surface respiration. Most bimodal species breathed air at both oxygen concentrations. The risk of capture increased with proximity to the surface. The prey species responded to the predator by increasing mean depth, decreasing the rate of air breathing or aquatic surface respiration, and avoiding the vicinity of the predator when surfacing. Despite these and other antipredator characteristics, all species were vulnerable to capture in the test situation. Overall, the survivorship of water-breathing fishes was significantly higher than that of bimodal species at 1.6 mg∙L−1 and similar to that of bimodal species at 0.5 mg∙L−1. Aerial predation pressure should favor water breathing over air breathing except at oxygen concentrations lower than 0.5 mg∙L−1.

The ‘ideal free distribution’ predicts the proportion of a population in each of several adjacent habitats with different resource levels. Previous tests of this model have ignored the effect of population size, although both theoretical and empirical studies of interference suggest that population size may have important effects on individuals' rates of resource gain. The ability of the ideal free distribution to predict how groups of 30, 60, 120 and 240 zebrafish, Brachydanio rerio, would distribute themselves among renewing resource patches in the laboratory was tested. Fish foraging in a pool 1·8 m in diameter received brine shrimp, Artemia, in three distinct patches with a 1:2:4 profitability ratio, keeping the arrival rate of food per fish constant for all group sizes. Deviations from the ideal free distribution were found with groups of 120 and 240 fish. These deviations were similar to the ‘ideal despotic distribution’, but occurred in the groups that had the lowest rate of chasing and the lowest proportion of fish outside food patches. It is hypothesized that at high densities ‘ideal interference distributions’ were formed, due not to aggression but to other density-related reductions in foraging efficiency.

Digestive tracts of wild guppies, Poecilia reticulata (Pisces: Poeciliidae), contained mainly benthic algae and aquatic insect larvae. In the laboratory, guppies matured on diets consisting solely of Chlorococcum (Chlorophyceae), but growth rates were slower than those of fish raised on Daphnia or commercial dried food. Fish grazing benthic algae performed rapid pecks in which the jaws were maximally protracted to cover a relatively large area. Pecks were performed in series at mean intervals of 0.55 s. Jaw movements required 0.17 s, while substrate contact lasted 0.03 s. Ingestion per peck increased with fish size and algal density. Males fed at lower food densities and ingested more per peck than females of similar weight. Females had longer feeding bouts than males. The fish ingested 16–25% of their body weight in dry weight of algae daily when they were fed ad libitum.

When dissolved oxygen concentration was near saturation in a laboratory experiment, guppies that spent (a) more time at the surface and (b) more time moving had a higher probability of being captured by a predatory cichlid fish. With decreasing oxygen concentration surface time and percent time moving increased, but prey risk decreased. In addition, the qualitative correlates of risk changed; under hypoxic conditions, predation risk was lower for prey which spent more time at the surface and in motion. Thus, dissolved oxygen concentration influences both quantitative and qualitative aspects of risk from water-breathing predators.

Chipmunks filling their cheek pouches with sunflower seeds decrease their rate of loading as their cheek pouches fill. Under these conditions, Charnov's (1976) marginal value theorem, as adapted for load size in ‘central place foragers’ by Orians & Pearson (1979) , predicts an increase in load size with increased travel time between the foraging site and burrow. This prediction was verified. However, the quantitative predictive value of the theory is questioned because it failed to predict accurately either the actual loads or the trend in load size with distance.

The bimodally respiring catfish Clarias macrocephalus Gunther responded to a toxic extract of Croton tiglium (Euphorbiaceae) seeds by increased air breathing under both normoxic (8.1 ± 0.4 mgO2 l−1) and hypoxic (0.7 ± 0.1 mgO2l−1) conditions. Fish in hypoxia survived longer than those in normoxia when surface access was provided. When air breathing was prevented, survival time in toxin was greatly reduced at both levels of dissolved oxygen, and fish in normoxia survived longer than those in hypoxia. Non-toxin controls without surface access survived in normoxia but in hypoxia died at the same time as the fish in toxin. These results suggest that air breathing increases the resistance offish to toxins by permitting a decrease in the rate of gill ventilation and hence the rate at which toxins are absorbed.

Corydoras aeneus uses the posterior intestine for aerial respiration. Ventilation takes place in a rapid dash to the surface. Air is inspired during the 0.06–0.07 s that the mouth is exposed; expiration occurs via the anus as the fish begins to dive. Air breathing occurs at all dissolved oxygen partial pressures [Formula: see text] from 0 Torr (1 Torr = 133.322 Pa) to at least 140 Torr, but frequency, ranging from 1–45 breaths∙h−1, is negatively correlated with [Formula: see text]. Corydoras aeneus survive at least 9 days without air breathing under normoxic conditions [Formula: see text] but below 15 Torr, only fish able to reach the surface survive. Air-breathing rates are significantly influenced by variations in depth between 10–120 cm but the pattern of response depends on [Formula: see text] and involves changes in activity.