The temperature–productivity squeeze: constraints on brook trout growth along an Appalachian river continuum

We tested the hypothesis that brook trout growth rates are controlled by a complex interaction of food availability, water temperature, and competitor density. We quantified trout diet, growth, and consumption in small headwater tributaries characterized as cold with low food and high trout density, larger tributaries characterized as cold with moderate food and moderate trout density, and large main stems characterized as warm with high food and low trout density. Brook trout consumption was highest in the main stem where diets shifted from insects in headwaters to fishes and crayfish in larger streams. Despite high water temperatures, trout growth rates also were consistently highest in the main stem, likely due to competitively dominant trout monopolizing thermal refugia. Temporal changes in trout density had a direct negative effect on brook trout growth rates. Our results suggest that competition for food constrains brook trout growth in small streams, but access to thermal refugia in productive main stem habitats enables dominant trout to supplement growth at a watershed scale. Brook trout conservation in this region should seek to relieve the “temperature–productivity squeeze,” whereby brook trout productivity is constrained by access to habitats that provide both suitable water temperature and sufficient prey.     

Behavior of males in a reproductive aggregation of the banded demoiselle Calopteryx splendens (Insecta, Odonata)

The view according to which damselfly males practice two alternative reproductive tactics of access to females is critically discussed. It is widely accepted that some males (“territorial” ones) have priority as potential female partners, while others (“sneakers” or “wanderers”) are incapable of retaining an individual territory. They have a chance of mating only by intruding briefly into the area defended by a “territorial” male when a female is present there. Thus, the tactics of a “territorial” male consists in waiting for a female in its territory and copulating with it “by agreement,” whereas non-territorial males resort to forced copulations. By observation of individually marked males (48 out of 118) it was shown that every male could be regarded as “territorial” during a certain period and as a “wanderer” before and after it. Thus, no correlation between the modes of space use by a male (residence/mobility) and the characters of its external morphology and/or signal behavior appears to be possible in principle. According to the data obtained, a more plausible explanation is that the female chooses not the male but the best area for oviposition. In addition, it was ascertained that adherence to forced copulations cannot constitute successful “tactics” since they rarely result in insemination, neither by “territorial” nor “non-territorial” males. In other words, we are dealing not with certain alternative tactics (i.e., specialized adaptive mechanisms that have evolved in the species) but simply with the results of different sets of circumstances at a given moment.     

Environmental influences on territoriality of juvenile brook charr,Salvelinus fontinalis,in a stream environment

Synopsis Juvenile brook charr, Salvelinus fontinalis, defending territories in a laboratory stream channel changed their defensive tactics when fish numbers or water current velocity were increased. The associated increase in energy costs of territorial defense were apparently reduced by using relatively more lateral displays and fewer chases to repel intruders, and by decreasing territory size. Territory size tended to increase with food ration, although levels of aggression were not affected. These results emphasize the importance of energetic considerations in territoral defense in these fish, and are discussed in terms of current hypotheses regarding the resource base for territoriality.     

Territoriality and nutritional condition in Cynotilapia afra (Gunther) and Pseudotropheus zebra (Boulenger), cichlidae in Lake Malawi National Park, Malawi

The standard length, diurnal activities, territory sizes, and areas over which individuals foraged and the nutritional condition of territorial and non-territorial Cynotilapia afra and Pseudotropheus zebra were compared. Results show that territorial tenureship in these fishes does not depend on the male size, implying that aggressiveness, experience and motivation are more important in the maintenance of territory. However, terri-toriality in C. afra (t = 10.93, P < 0.05) and P. zebra (t = 3.31, P < 0.05) manifests itself in the reduction of nutritional condition because territorial males engage in energetically more demanding activities, e.g. courtship displays, fertilizing ripe females and chasing intruders that trespass into their territories. Territorial C. afra (t = 4.77; P < 0.05) and P. zebra (t = 5.89; P < 0.05) also fed over significantly smaller areas and spent significantly less time feeding than did non-territorial males. The biological significance of territoriality in these fish species is therefore not food intake, but mate attraction and reproductive success for which they trade off their nutritional condition. However, there might be a nutritional threshold below which the cost out-weighs the benefit. Hence, territorial males in poorer health abandon their territories in order to regain their condition.     

THE SOCIAL BEHAVIOUR OF THE WHITE WAGTAIL MOTACILLA ALBA ALBA WINTERING IN ISRAEL

White Wagtails Motacilla alba wintering in Israel are partly territorial, mostly around human habitations, and partly live in flocks around temporary food sources. Individual birds may spend part of the season (or the day) in the territory and the other part with a flock. Experiments with artificial distribution of food, in a natural habitat, brought about a change from flocking to territorial behaviour. Preliminary observations suggest that in the natural situation the pattern of food distribution may be the proximate factor which regulates the birds' behaviour, by determining whether they have to fight for their food. Pairs are formed on many territories, and may last for long or short periods. Pair formation is initiated by females, who when seeking food appease the territorial males and are able to stay with them on their territories. Females also manifest territorial behaviour. Although pairing in winter territories is similar, in the behaviour involved, to sexual pairing, it is very unlikely that winter pairing continues into, or influences, pairing for breeding. It is suggested that the function of winter pair formation is that it allows two birds to exploit one territory, and that the main advantage is to the female which is the subordinate bird of the pair. This kind of pair-formation may be analogous to non-breeding group territories reported in some other birds.     

Hydrological Variation and Fish Assemblage Structure in the Middle Wabash River

We assessed the effect of a severe drought in 1999 upon stream morphology and brook trout (Salvelinus fontinalis) populations in seven headwater streams in the Greenbrier and Potomac River watersheds, West Virginia. During the drought, stream discharge was 96% lower than in years of normal precipitation. As a result, habitat availability and quality over all study streams was significantly lower. Riffle area was greatly reduced (?54%) relative to available pool area (?2%). Fine sediment levels (<0.063 mm) significantly increased within spawning substrate (p=0.01). Water temperature and dissolved oxygen were adequate (mean 15.8?°C, >6.0 mg l^?1, respectively) for brook trout survival in all streams during the drought. Brook trout populations were significantly reduced (adult 60%, Young-of-the-year 67%), and individual fish had significantly lower body condition during the drought relative to the post-drought period. Reductions in brook trout density and population condition during, and in the-post drought period, were related to spatially-limited food resources and/or increased fine sediment levels, but not to degraded water quality. Fisheries managers should consider the effect of periodic drought on brook trout populations and consider short-term harvest restrictions to abet recovery after such stochastic events.     

Mating Systems,Maternal and Biparental Care in Triggerfish (Balistidae)

Groups of the triggerfish Pseudobalistes fuscus and Odonus niger were studied from the underwater laboratory Neritica in Eilat, Gulf of Akaba, in the Red Sea. Mating and the roles of the sexes during broodcare seem to depend strongly on territory size, probably determined by shelter site and food availability, and territorial control- and defendability. The discussion considers why evolution has favoured maternal broodcare in the one case and biparental in the other.     

On Social Organization and Behaviour of the Gerenuk Litocranius walleri (Brooke 1878)

The social organization of the gerenuk in Tsavo East National Park, Kenya, is characterized by single adult ♂♂ on territories encompassing their entire home ranges, small ♀-groups of variable composition, often associated with territorial ♂♂, and small groups of subadult ♂♂. There appear to be no non-territorial adult ♂♂ (“bachelors”). Subadult ♂♂ wander about considerably, often alone, before they succeed in taking over a territory. Territorial ♂♂ perform linked urination/defecation and mark dry twigs with the antorbital gland secretion. Agonistic and courtship behaviour resemble those of other gazelles. Mother-young relations conform to the “hider type” among bovids.     

THE BIOLOGY OF THE MOURNING CHAT IN WINTER QUARTERS

Mourning Chats ( Enanthe lugens in the Helwan area in Lower Egypt winter along the lower spurs of the mountains. Each bird occupies a separate territory from which it excludes other Mourning Chats, and wherein it sings.
"Winter" song is most energetic in the months of July to October; at this season the main singing hours are in the early morning and early evening. In the period November to February song is less frequent, and is most often heard in the late afternoon.
In the hot weather of the autumn the birds select perches in shade during the mid-day hours.
Evidence is advanced that there is a measure of interspecific territorial competition between Mourning Chats, Hooded Chats ( Enanthe monacha and White-tailed Chats ( Enanthe leucopyga. The possible relevance of this interspecific territorial practice to the hypothesis of the "food value" of territory is discussed.     

Food partitioning between coexisting Atlantic salmon and brook trout in the Sainte‐Marguerite River ecosystem, Quebec

Food resource partitioning between similar‐sized, sympatric Atlantic salmon Salmo salar and brook trout Salvelinus fontinalis was examined as a possible mechanism enabling their coexistence in a stream (Allaire) of the Sainte‐Marguerite River ecosystem, Quebec, Canada. Fish stomach contents and invertebrate drift were collected concurrently during three diel cycles in August to September 1996. The food and feeding habits of an allopatric brook trout population in a nearby stream (Epinette) were studied for comparison. The diel feeding rhythms of the two coexisting fish species were similar. The composition of their diet, however, showed significant differences. Atlantic salmon predominantly (60–90%) fed on aquatic insects, mainly Ephemeroptera (35–60% of the diet). The brook trout mostly (50–80%) fed upon the allochthonous terrestrial insects (mainly adults of Coleoptera, Hymenoptera and Diptera) which comprised 5–40% of the stream drift. The allopatric brook trout fed opportunistically on the more abundant aquatic insects and terrestrial insects rarely formed 25% of its diet. The allopatric trout fed nearly twice as much as the sympatric brook trout during a day. The results suggest that the differences in feeding by brook trout in the two streams (with and without Atlantic salmon) are the result of inter‐specific interaction with Atlantic salmon and are not related to the differences in food availability between the two streams. Food resource partitioning between Atlantic salmon and brook trout may be viewed as an adaptive response resulting in a greater exploitation of available resources and coexistence.     

Resource-defense Polygyny and Male Territory Quality in the New Zealand Fur Seal

The polygynous New Zealand fur seal, Arctocephalus forsteri, breeds in densely-packed colonies with males defending exclusive territories. The distribution of individuals within a colony of these seals was monitored over three consecutive breeding seasons and behavioural thermoregulation was found to be an important factor influencing the site selection of both males and females. Shaded areas and pools of water were used by both sexes for cooling and use of these cooling substrates increased as rock surface temperature increased, resulting in a clumped distribution on hot days. Substrate preferences were tested experimentally by manipulating the availability of cooling substrates during two seasons. The number of females using an area increased significantly after shade or pools of water were added to that area. For males, pool additions resulted in increased use of those areas, while adding shade had no effect. Cooling substrates had a patchy distribution and could therefore be monopolised by territorial males. Using the number of females on a territory as a measure of male mating success, it was found that female numbers were most strongly positively correlated with the area of shaded substrate on a territory. Total territory area was also positively correlated with number of females. It is argued that thermoregulatory constraints are a major factor affecting female site choice, and that this in turn affects male mating success.     

Effects of Simultaneous vs. Sequential Settlement on the Territorial Behaviour of Juvenile Rainbow Trout (Oncorhynchus mykiss)

The aggression hypothesis predicts that territories will be smaller and more numerous when individuals arrive simultaneously rather than sequentially, because of the prior residency effect, whereas the attraction hypothesis predicts the opposite. In this study, we test the predictions of these contrasting hypotheses by releasing 12 juvenile rainbow trout (Oncorhynchus mykiss) either simultaneously, all on 1 d, or sequentially, two per day for 6 d, in artificial streams. After the fish spent an average of 1 wk in the streams, we quantified the number of territories established, territory size, aggression rate and growth rate. There was evidence of a prior residency effect – early arrivers were more aggressive and grew faster than late arrivers – but this effect did not alter the number or size of territories established. We concluded that the temporal patterns of arrival have no strong effects on the territorial dynamics of juvenile rainbow trout.     

Territory surveillance and prey management: Wolves keep track of space and time

Identifying behavioral mechanisms that underlie observed movement patterns is difficult when animals employ sophisticated cognitive‐based strategies. Such strategies may arise when timing of return visits is important, for instance to allow for resource renewal or territorial patrolling. We fitted spatially explicit random‐walk models to GPS movement data of six wolves (Canis lupus; Linnaeus, 1758) from Alberta, Canada to investigate the importance of the following: (1) territorial surveillance likely related to renewal of scent marks along territorial edges, to reduce intraspecific risk among packs, and (2) delay in return to recently hunted areas, which may be related to anti‐predator responses of prey under varying prey densities. The movement models incorporated the spatiotemporal variable “time since last visit,” which acts as a wolf's memory index of its travel history and is integrated into the movement decision along with its position in relation to territory boundaries and information on local prey densities. We used a model selection framework to test hypotheses about the combined importance of these variables in wolf movement strategies. Time‐dependent movement for territory surveillance was supported by all wolf movement tracks. Wolves generally avoided territory edges, but this avoidance was reduced as time since last visit increased. Time‐dependent prey management was weak except in one wolf. This wolf selected locations with longer time since last visit and lower prey density, which led to a longer delay in revisiting high prey density sites. Our study shows that we can use spatially explicit random walks to identify behavioral strategies that merge environmental information and explicit spatiotemporal information on past movements (i.e., “when” and “where”) to make movement decisions. The approach allows us to better understand cognition‐based movement in relation to dynamic environments and resources.     

Dominance hierarchies in group-living cleaning gobies: causes and foraging consequences

In species living in social groups, aggression among individuals to gain access to limiting resources can lead to the formation of stable social hierarchies. We tested whether dominance rank in social groups of sponge-dwelling cleaning gobies Elacatinus prochilos in Barbados was determined by physical attributes of individuals or by prior experience of dominance, and examined the foraging consequences of dominance rank. Intraspecific aggression within groups resulted in stable dominance hierarchies that were strongly correlated with fish length. Dominant individuals maintained exclusive territories while subordinate fish occupied broader home ranges. Larger, competitively dominant fish were able to monopolize areas inside the sponge lumen with the highest abundance of the polychaete Haplosyllis spp., a favoured prey item, and achieved the highest foraging rates. The removal of a territorial individual from large groups resulted in a domino-like effect in territory relocation of the remaining fish as individuals moved to the territory previously occupied by the individual just above them in the group hierarchy. Individuals added to existing groups generally failed to gain access to territories, despite being formerly dominant in their original groups. When given the opportunity to choose a location in the absence of larger competitors, gobies frequently preferred positions that were previously defended and that had abundant food. These results suggest that intraspecific competition for resources creates the observed dominance structures and provides support for the role of individual physical attributes in the formation and maintenance of dominance hierarchies.     

The adaptive significance of non-contact mate guarding by males of the dragonfly,Nannophya pygmaea Rambur (Odonata: Libellulidae)

InNannophya pygmaea, ovipositing females were frequently disturbed by conspecific males. Disturbed females often copulated with one of these males or flew away from the pool. Females which flew away from the pool due to male disturbance often returned later the same day and mated with different males. A territorial male would guard his ovipositing mate by hovering above her, presumably trying to prevent her from moving out of his territory. A non-territorial male would also guard his mate in a similar way, both at a vacant water area which was not occupied by any territorial males, or within the territory of a resident male. In addition, both territorial and non-territorial males chased intruding males in an attempt to prevent their mates from being stolen. Territorial males defended their mates better than non-territorial males. Both males and females often mated more than once in the course of a single day. Some territorial males copulated with a new female while another mate oviposited in their territories. This observation supported the “multiple mating hypothesis” proposed by Alcock (1979) and Uéda (1979) but other evidence suggested that this is an inadequate explanation for the non-contact guarding ofN. pygmaea.     

Feeding territoriality and the reproductive consequences in brown skuas<Emphasis Type="Italic"> Catharacta antarctica lonnbergi</Emphasis>

In the maritime Antarctic, brown skuas (Catharacta antarctica lonnbergi) show two foraging strategies: some pairs occupy feeding territories in penguin colonies, while others can only feed in unoccupied areas of a penguin colony without defending a feeding territory. One-third of the studied breeding skua population in the South Shetlands occupied territories of varying size (48 to >3,000 penguin nests) and monopolised 93% of all penguin nests in sub-colonies. Skuas without feeding territories foraged in only 7% of penguin sub-colonies and in part of the main colony. Females owning feeding territories were larger in body size than females without feeding territories; no differences in size were found in males. Territory holders permanently controlled their resources but defence power diminished towards the end of the reproductive season. Territory ownership guaranteed sufficient food supply and led to a 5.5 days earlier egg-laying and chick-hatching. Short distances between nest and foraging site allowed territorial pairs a higher nest-attendance rate such that their chicks survived better (71%) than chicks from skua pairs without feeding territories (45%). Due to lower hatching success in territorial pairs, no difference in breeding success of pairs with and without feeding territories was found in 3 years. We conclude that skuas owning feeding territories in penguin colonies benefit from the predictable and stable food resource by an earlier termination of the annual breeding cycle and higher offspring survivorship.Research licence: Umweltbundesamt Bonn 13.4-94003-1/5-7.     

Territory Area as a Determinant of Mating Systems

Territoriality is an integral part of breeding behavior in manyanimals. Because the reproductive success of territorial malesis often limited by access to females, breeding males shouldbehave as "area maximizers" when the basis of female choiceis either the abundance of resources within the territory orterritory area per se. Being reproductively more limited byenergy, territorial females should be "energy maximizers." Aseries of simple analytical models of territory area for suchforagers is developed to explore how changes in local food productionand/or local competitor density affect both the probabilityof a territorial male securing more than one mate (polygyny)and the probability of his and his mates' reproductive successincreasing. Two cases are modeled (only males territorial vs.both sexes territorial), each for various sets of assumptionsregarding interactions between food production, feeding efficiency,and competitor density. Concurrent responses in territory area,territory food reserves, net energy gain, and time budgetingprovide testable sets of predictions for each scenario. Whereonly males are territorial (Case I), changes in food productioncan have different (indeed, opposite) effects upon an individualmale's probability of becoming polygynous, depending upon whetherthe basis of female choice is the abundance of food within theterritory or another factor positively correlated with territoryarea. Increases in competitor density usually decrease the probabilityof polygyny regardless of the basis of female choice. Whereboth sexes are territorial and territories overlap intersexually(Case II), the mating system becomes a function of the numberof female territories within each male's territory, which varieswith the ratio of male to female territory areas. In this case,the probability of polygyny occurring will increase if foodproduction for both sexes increases without concurrent increasesin competitor density, and will decrease if competitor densityfor both sexes increases without concurrent increases in feedingefficiency. Few data are presently available to test eitherthese general predictions or numerous sets of secondary predictionstabulated in the text. Available evidence is largely consistentwith the models, but mostly circumstantial. This is becausethe predictions of these and other models of territory areaare strongly assumption dependent, and few published studieshave investigated these assumptions. These analyses demonstratethat to accurately assess the mechanisms by which environmentalfactors affect territory area, and thus mating systems, testsof the underlying assumptions of models are essential.     

Importance of terrestrial subsidies for native brook trout in Appalachian intermittent streams

相似文献   

Recruiting juvenile damselfish: the process of recruiting into adult colonies in the damselfish Stegastes nigricans

Juveniles of Stegastes nigricans occur in adult colonies, solitarily, and occasionally in juvenile colonies. We concentrated on solitary juveniles and those in adult colonies. We examined the costs and benefits of different settlement strategies, quantified the territory requirements of adults, and investigated the process of how juveniles make the transition to adult territorial fish. An adequate adult territory lies next to those of other adults, is proportional in area to the size of the adult, and contains a refuge tunnel whose entrance is sufficiently large. Compared with solitary juveniles, those <4 cm total length inhabiting adult colonies experienced reduced heterospecific competition for algal food and consequently benefited from a greater density of algae. A cost of recruiting into an adult colony, however, was increased attacks by adults. Juveniles that settled in adult colonies avoided attacks by retreating into small holes inaccessible to adults. As juveniles in adult colonies grew, they were chased less often by adults, whereas they themselves chased adults and heterospecific fish more often. Because territory size correlated with fish size in adult colonies, its area had to expand as the young fish grew, and that expansion was done at the expense of neighbors. Obtaining the space needed by an adult may be possible only when the juvenile settles directly into an adult colony. Juveniles that first settle down solitarily, or in juvenile colonies, may later attempt to enter adult colonies. However, because they do so as larger juveniles, they would have difficulty insinuating themselves into small refuges, which is essential for retreat from the adults. Received in revised form: 4 January 2001 Electronic Publication     

Shade as enrichment: testing preferences for shelter in two model fish species

We compared preferences shown by zebrafish Danio rerio and three-spined stickleback Gasterosteus aculeatus for shelter provided by above-tank shade and artificial plants. Zebrafish showed no preference for either shelter, whereas sticklebacks showed a preference for both shelter types over open areas and for shade over plants. Our results suggest shade may be used as enrichment for captive fish and re-emphasise the importance of species-specific welfare considerations.