Differences in gill raker morphology between two local populations of a benthophagous filter-feeding fish, Goniistius zonatus (Cheilodactylidae)

Gill raker morphology of a benthophagous fish Goniistius zonatus (Cheilodactylidae) (10.9–29.2 cm SL), using a filter-feeding mode, was compared between two locations (Morode and Arakashi) in southern Japan. Although gill raker number and gill raker length at the two locations did not differ, gill raker spacing was narrower relative to overall fish size at Morode than at Arakashi, mainly because gill raker width was greater at Morode. The difference of gill raker spacing is unlikely to have a genetic or physiochemical explanation. Small invertebrates (≤1.0 mm) were dominant on the substrate at Morode but were less common at Arakashi. Such small animals were consumed by many fish at Morode but were rarely exploited at Arakashi. At Morode, the narrow gill raker spacing would be effective in retaining small prey, which should be an important energy resource in this population. The difference of interraker spacing at the two locations seems to be related to available prey size at each location. Received: November 14, 2000 / Revised: February 13, 2001 / Accepted: February 28, 2001     

Overlapping territory of the benthophagous cichlid fish, Lobochilotes labiatus, in Lake Tanganyika

Synopsis Feeding territories do not usually overlap in the same fish species. We studied overlapping territories and feeding behaviours of a benthophagous cichlid fish Lobochilotes labiatus Boulenger in a coastal area of Lake Tanganyika. Forty-four individuals of both sexes, 6–31 cm in total length, maintained territories in a 21 m × 25 m area. These could be regarded as feeding territories. The territories of similar-sized owners (usually different by less than 5 cm) did not overlap each other, but those of different-sized owners overlapped widely. Aggressive interactions were rarely observed between fish distinctly different in body size. Both large and small fish took benthic animals of the same kinds and of similar size. In contrast, the size of foraging sites (crevices) was different between them: the large fish foraged at large crevices and small fish at small crevices. This partitioning of foraging sites may enable the overlap of territories in this benthivore.     

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.     

Niche differentiation depends on body size in a cichlid fish: a model system of a community structured according to size regularities

1. Communities of different species are often structured according to niche differentiation associated with competitive interactions. We show that similar principles may apply on an ecological time-scale when individuals of a species having a wide size variation compete for resources, using the Lake Tanganyika cichlid Lobochilotes labiatus (5-30 cm). This species has a mouth especially adapted to suck up invertebrates from rock crevices. 2. Individuals defended feeding territories against similar-sized conspecifics, but not against different-sized ones. Thus, territories of similar-sized fish rarely overlapped, but up to a total of seven individuals (of seven size-ranks) had broadly overlapping territories with dissimilar-sized individuals. Comparison with expectation from the null model demonstrated clearly that observed size ratios between adjacent size rank were determined non-randomly regardless of sexual combinations. 3. Larger individuals took larger prey types of larger average size, but more importantly used wider rock crevices from which to suck food than smaller individuals. We calculated pairwise values of Schoener's index of diet overlap C(d) and the values of Levin's index of diet breadth B(d) (prey type and prey size) and the same for the width of the rock crevices used for foraging (C(r) and B(r)). C(d) remained high among all combinations of the seven ranks. In contrast, C(r) declined strongly in combinations of adjacent ranks (to 0.27), and was low or zero among further different size ranks. This shows that fish with overlapping territories divided the food resources largely through foraging site partitioning. Accordingly, B(d) did not depend on the size difference to the nearest two coinhabiting fish, whereas B(r) did. 4. We conclude that this L. labiatus community is structured non-randomly: body size-dependent effects on foraging site usage result in competition with, and territorial exclusion of, similar-sized individuals, but not of dissimilar-sized individuals that were accepted as coinhabitants. Accordingly, mean body size ratios (large/small) between two adjacent ranks were consistently approximately 1.28 [standard deviation (SD) = 0.07, n = 104], while approximately 1.34 from the null model (SD = 0.34, n = 10 400 simulations). We discuss our results as an example of Hutchinson's rule, applied originally to size ratios of different species.     

Depth-related differences in territory size and defense in the herbivorous cichlid,neolamprologus moorii, in lake tanganyika

Neolamprologus moorii, a small herbivorous cichlid of Lake Tanganyika, defends its territory against food competitors. Territory size and territorial defense were compared between two sites at different depths. In the shallow site, more fishes intruded into the territories than in the deep site, owing to the higher density fish population in the former. The territory holders in the shallow site attacked intruders more often, although the ratio of attacks to number of intruders was similar to that of the deep site. The territories in the deep site were larger and contained a greater amount of algae than the shallow site. The larger territory size in the deep site may have resulted from the lower cost of territory defense due to the lower competitor density and from the need to maintain a greater amount of food resources to compensate for lower algal productivity.     

Experimental analysis of territory size in a population of the fire ant Solenopsis invicta

Alternative models of territoriality are based on contrastingassumptions about the behavioral processes determining territorysize. In a series of controlled field experiments on the fireant Solenopsis invicta, I tested whether territory size is affectedby the availability of food, as predicted by most economic models,and whether territory size is affected by fighting ability,as predicted by models of competition among neighbors. Abundantfood was offered for 30–35 days to selected colonies eitherimmediately next to the nest (experiment 1) or at peripheralsites near the territory boundary (experiment 2). These foodsupplements had no detectable effect on territory size. Furthermore,food placed near the periphery of the territory did not significantlyalter local boundary positions. During both experiments, largecolonies lost more territory than did small colonies, reflectingtemporary declines in worker number due to the seasonal productionof reproductives. Such losses by large colonies during the summermonths create opportunities for newly founded colonies to expandterritories. In a third experiment, colonies from which workerswere removed lost significantly more territory than did unmanipulatedcontrols. These results show that territory areas in S. invictaare strongly affected by the relative fighting ability of neighboringcolonies but provide no evidence that colonies adjust territoryarea in response to short-term changes in the availability offood.     

Differences in Species Composition and Feeding Ecology of Catostomid Fishes in Two Distinct Segments of the Missouri River, North Dakota, U.S.A.

In 1997 and 1998, we sampled the Missouri River, North Dakota to determine if anthropogenic disturbances had influenced catostomid species composition and feeding ecology. We compared two distinct river segments, the Missouri River between the mouth of the Yellowstone River and Lake Sakakawea (the Yellowstone–Sakakawea segment (YSS)), a moderately altered segment and the Missouri River between Garrison Dam and Lake Oahe (the Garrison–Oahe segment (GOS)), a highly altered segment. The segments exhibited greatly different sucker communities. Bigmouth buffalo, Ictiobus cyprinellus, smallmouth buffalo, Ictiobus bubalus, and river carpsucker, Carpiodes carpio, represented 94% of the sucker catch in the YSS, whereas in the GOS, white sucker, Catostomus commersoni, and longnose sucker, Catostomus catostomus, constituted 98% of the sucker catch. In the YSS, high zooplankton densities led to greater sucker zooplanktivory and food niche overlap than in the GOS. Intense anthropogenic disturbances to the GOS are associated with the differences in sucker species composition, prey density and composition, and sucker feeding ecology between the two segments.     

Diet in one group of woolly spider monkeys,or muriquis (Brachyteles arachnoides)

Data on feeding behavior in one group of muriquis (Brachyteles arachnoides) were collected during a 14 month study at Fazenda Montes Claros, Minas Gerais, Brazil. Muriquis devoted an average of 51% of their annual feeding time to leaves, 32% to fruits, and 11% to flowers. The high proportion of leaves in their diet is consistent with predictions from the energetics of body size. However, they devoted a greater proportion of their feeding time to patchy fruit and flower resources than was expected from comparisons with smaller, sympatric howler monkeys. Muriqui diet varied with the availability of preferred food types across sample months. Fruit and flower consumption corresponded to the availability and abundance of these food resources in the forest. Leaves contributed substantially to muriqui diet throughout the year but appeared to be eaten primarily to provide necessary protein and/or necessary bulk. Male and female diets differed only in the greater proportion of feeding time females devoted to flowers.     

A comparative study of territoriality in intertidal and subtidal blennioids (Teleostei, Blennioidei)

This paper presents a comparative analysis of territoriality in three intertidal (Lipophrys pholis, Coryphoblennius galerita, Salaria pavo) and two subtidal (Tripterygion delaisi, Parablennius pilicornis) blennioid fishes. Focal-animal observations of males guarding eggs showed that: (i) intertidal species had smaller territories that were less frequently patrolled; (ii) in subtidal species feeding was limited to the territory, while in intertidal fishes a substantial proportion of the feeding acts occurred outside the defended area; (iii) intertidal species spent less time out of the nest and showed a lower level of locomotory activity; (iv) subtidal species were subjected to a higher number of territorial intrusions with more species intruding their territory, some of them potential egg predators; (v) subtidal species performed several water column displays that played a significant role in courtship, while in intertidal fishes these displays are almost absent. Signalling without the presence of a female was almost absent in intertidal species. It is argued that intertidal fishes minimize the time spent out of the nest and the loss of contact with the substrate, features that may be of high survival value in conditions of strong turbulence. Although intertidal species have a reduced time available for feeding, this may be compensated by lower levels of locomotory activity, territorial defense and risk of egg predation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Body shape evolution among ploidy levels of the Squalius alburnoides hybrid complex (Teleostei,Cyprinidae)

Hybridization, ploidy level and genomic constitution may be important to respond to different environments, by producing different phenotypes and thus reducing competitive interaction. Through geometric morphometrics, we examined variation in body size and shape among biotypes of the Squalius alburnoides hybrid complex and their sperm donor (Squalius carolitertii). Results showed that S. carolitertii is significantly larger in size than the biotypes of the complex. No significant relationship was observed between ploidy and body size among S. alburnoides biotypes. Significant variation in body shape was found between S. carolitertii and S. alburnoides, and between tetraploids and the other biotypes. These differences in biotypes may reduce resource competition, highlighting the potential importance of resource availability favouring one biotype over another. In S. alburnoides, the adaptation to different trophic niches through modification of trophic morphology, body shapes, and feeding behaviour, may result from an increase in ploidy and genomic constitution. This adaptation may account also for the formation and maintenance of this nonsexual complex.     

Possible Causes of Variation in Territory Tenure in a Lekking Pompilid Wasp (Hemipepsis ustulata) (Hymenoptera)

Territorial males of the pompilid wasp Hemipepsis ustulata occupy their landmark territories for from less than 1 day to several weeks. Variation in territory tenure could arise if territories differ in their value and cost to defend (the tradeoff hypothesis). If superior sites attract more male competitors, raising the cost ofterritorial defense of these locations, we would expect (1) tenure times to be shorter at top-ranked sites and (2) tenure times to decline in years of high male density and competition. Although mean tenure times for males able to hold territories for at least 2 days were shorter at top-ranked sites, the difference was only statistically significant in one of three years. In the year of highest male density, a significantly higher proportion of all territorial males failed to hold the top-ranked sites for more than a single day; however, mean tenure duration at all occupied sites did not decline in this year. Thus, the tradeoff hypothesis received only partial support. An alternative hypothesis is that variation in male resource holding power, as reflected in male size or wing condition, contributes to differences in territorial tenure. However, although larger males were more likely to become territorial residents at the top-ranked sites, the duration of tenure at these locations was not positively correlated with body size. In addition, although wing condition declined throughout the flight season in concert with a sharp decrease in the duration of tenure at the top-ranked sites, males with fresher wings did not hold territories longer than males whose wings were in poorer condition when they assumed control of a site.     

黑卷尾繁殖期领域性的初步研究

鸟类的领域性是鸟类行为生态学研究的一个重要内容。在这方面国外进展很快,但国内工作较少,专文报道除三宝鸟之外,其它颇为罕见。1987年夏季,我们在太原市南郊对该地区的夏候鸟黑卷尾(Dicrurus macrocercus)的领域行为进行了观测。现将资料整理分析如下。一、工作区与工作方法太原盆地的自然环境和鸟类群落状况已有报道,在此不再赘述。工作区选在小马—加节两村之间约190ha的区域内(图1)。其     

The activity budget and use of territory by a tropical blenniid fish

Both sexes of Ophioblennius atlanticus (Valenciennes) maintain permanent territories, intermixed without pattern. They occur at a density of about 1.9 individuals per m² on shallow coral rock and comprise a significant portion of the benthic fish biomass. They are diurnal; about 60% of their time is spent resting, 15% swimming and 8.5% feeding. Feeding is concentrated in the afternoon and is time-minimized. Territory is used exponentially, about 50% of time being spent in about 15% of the territory. The relatively infrequent use of peripheral parts of a territory suggest that it is potentially compressible or expansible. This, in turn, leads to a conclusion that an optimum size can only be defined as a range and mat, normally, a territory includes more resources than the minimum for survival. Competition may be reduced between aegis corrivals of different species.     

Differential utilization of space and food by the inshore rockfishes (Scorpaenidae: Sebastes) of Carmel Bay,California

Synopsis Six rockfish species were found to be common in the Carmel Bay kelp forests. Five of these occupy spatial zones that are more or less distinct from one another. Three species (S. atrovirens, S. chrysomelas, and S. carnatus) occupy species-specific spatial zones while two others (S. serranoides and S. melanops), although spatially distinct from each other, occupy zones that overlap completely with a sixth species, S. mystinus. Food overlap values (PSI) indicate that S. mystinus has low competitive overlap with all other species, and hence can coexist with two species using the same habitat. Dietary arrays reflect the distinct spatial zones occupied by most of the rockfishes. Structural characteristics associated with feeding (maxillary, intestine, and gill raker length) suggest that these species are differentially adapted in regard to feeding morphology. The coexistence of these rockfishes appears to be the result of the partitioning of food and space resources, rather than the result of stochastic events which appear to be important in the structuring of some coral-reef fish communities. S. mystinus juveniles represent a major trophic link between adult piscivores and the planktonic organisms upon which the juveniles feed. A sustained crash in S. mystinus numbers might have a negative effect on abundance of kelp forest piscivorous species.     

Heart structure of some deep-sea fish (Teleostei: Macrouridae)

The hearts of 29 species of macrourid teleosts were examined in this study. For the one species for which a length range was available ( Coryphaenoides (C.) rupestris ), the heart weight as a percentage of body weight was 0·059. This is similar to values for relatively inactive fish. The atrial myocardium was reduced and had only a sparse trabecular network. In some species it was surrounded by a highly developed epicardium, but in others there was interstitial connective tissue in the myocardium that may serve to strengthen this chamber. The ventricle was entirely spongy, and all species lacked an outer compact layer of myocardium and associated coronary vasculature. All the ventricles were sac-like in form. The bulbus arteriosus was highly complex, and in its proximal portion there was an endothelially-lined, inner tube surrounded by a spongy network of blood-filled spaces, outside which was an outer compact layer of smooth muscle and elastica. These features of the bulbus may prevent backflow of blood after ventricular systole. The endothelial cells lining the bulbus were usually PAS-positive and in some species contained acid mucopolysaccharides.     

Diurnal periodicity of spawning activity of permanently territorial damselfishes (Teleostei: Pomacentridae)

Synopsis Like other congeneric damselfishes, the herbivorous Stegastes altus defends individual feeding territories from heterospecific food competitors, regardless of sex. Females spawned demersal eggs for 31.4 min (n = 25) at the nest in territories of males 0–75 m away from theirs. Throughout the spawning season (June to September), spawning occurred only at dawn, mainly just after sunrise. Daily activity of the fish community showed that potential diurnal food competitors were few or inactive only at dawn and dusk. The frequency of intrusions into the female's territory by heterospecific competitors were as low when she left her territory to spawn at dawn, as they were in the daytime when she defended it. Removal of the female in the daytime resulted in a significant increase in intrusion frequency. An ‘anti-competitor hypothesis’, whereby dawn spawning ensures the food resource in the female's territory seems to explain not only the spawning periodicity in S. altus but also the timing of spawning of other permanently territorial damselfishes. Contribution from the Laboratory of Animal Ecology, Kyoto University, No. 492.     

Biology of the western minnow,Galaxias occidentalis Ogilby (Teleostei : Galaxiidae), in a south-western Australian river

The size and age composition, growth and diet of the western minnow, Galaxias occidentalis, in the southern branch of the Collie River in south-western Australia were determined from samples collected at approximately monthly intervals between January 1984 and December 1986. The prominent, narrow hyaline zone on otoliths was shown to be formed annually and thus valid for ageing these fish. An examination of the otoliths of 4711 fish indicated that 69.2 and 26.8% of the fish caught belonged to the 0 + and I + age classes, respectively. While the vast majority of the remaining fish represented the II + age class, a few III + and IV + and one V + fish were also recorded. Growth was seasonal, being greatest in spring and autumn and effectively ceasing in winter. Females began to grow faster than males during their first autumn of life. The respective mean lengths of males and females were 70 and 75 mm at the end of the first year and 90 and 100 mm at the end of the second year. The largest fish caught was a III + female measuring 163 mm and weighing 32.0 g. The respective von Bertalanffy growth curve parameters for L, K and t₀ were 109, 0.758 and - 0.338 for males, and 124, 0.762 and - 0.223 for females. Although the diet of G. occidentalis was always dominated by small terrestrial fauna, and particularly insects, conspicuous seasonal differences were found between the more important of the other components. Data on body size, growth and diet of G. occidentalis are compared with those recorded for other galaxiids.     

The use of territorial gardening versus kleptoparasitism by a subtropical reef fish (Kyphosus cornelii) is influenced by territory defendability

Many territorial herbivorous animals increase the productivityor quality of the prey community on their territory. However,this gardening tactic may be vulnerable to kleptoparasitismunless gardeners can exclude others from the patch. We investigatedthe influence of territory defendability on the decision ofwestern buffalo bream (Kyphosus cornelii) to defend an algalgarden or to leave their territories and invade those of conspecifics.Fish monitored while away from their territories did kleptoparasitizethe gardens of conspecifics. We manipulated the structural complexityof territories through the addition of short or tall simulatedvegetation. Increasing the height of simulated vegetation onthe territory decreased the defendability of territories butincreased their safety for fish; territories with tall vegetationwere more easily invaded by conspecifics, but fish returnedmore rapidly to these territories after being disturbed. Ina paired experiment, fish spent more time away from their territories(roving) when tall vegetation was added than when short vegetationwas added. However, this effect was influenced by depth, witha greater difference between treatments on deeper territories,and by body size, with a greater difference for larger fish.These results support the prediction that territory-holdingindividuals faced with a trade-off between defending their owngarden or kleptoparasitizing from others adjust their use ofthese tactics based on the defendability of resources.