Competitive hierarchies among three species of juvenile coral reef fishes

Interspecific competition is often asymmetric, and it can limit the spatial distributions of competitively inferior species within a community. When asymmetric competition involves 2 or more component species, the ranking of species' competitive abilities may form competitive hierarchies (all species of higher rank out-compete all species of lower rank) or competitive networks (at least 1 species of lower rank out-competes =1 species of higher rank). Expectations of resource monopolization and patterns of distribution and abundance among species in competitive networks are expected to differ from those in competitive hierarchies. We conducted a field experiment to evaluate the relative competitive abilities of juveniles of 3 closely related species of reef fish (bird wrasse Gomphosus varius, fivestripe wrasse Thalassoma quinquevittatum and the sixbar wrasse T. hardwicke) on Moorea, French Polynesia. We controlled for intrinsic variation in survivorship among species and found that competition among these 3 species was highly asymmetric, resulting in a simple competitive hierarchy (sequence of competitive ability from superior to inferior competitors): fivestripe wrasse > bird wrasse > sixbar wrasse. We surveyed densities of the 3 reef fish species on 55 patch reefs and observed significant negative spatial covariation between superior and inferior competitors, consistent with competitive hierarchies that limit the spatial distributions of the inferior species (sixbar wrasse). Our work demonstrates that intense asymmetric competition and the formation of competitive hierarchies may be an important determinant of resource monopolization and patterns of distribution and abundance in reef fishes. © Inter-Research 2013.

Competitive hierarchies among three species of juvenile coral reef fishes

Interspecific competition is often asymmetric, and it can limit the spatial distributions of competitively inferior species within a community. When asymmetric competition involves 2 or more component species, the ranking of species' competitive abilities may form competitive hierarchies (all species of higher rank out-compete all species of lower rank) or competitive networks (at least 1 species of lower rank out-competes =1 species of higher rank). Expectations of resource monopolization and patterns of distribution and abundance among species in competitive networks are expected to differ from those in competitive hierarchies. We conducted a field experiment to evaluate the relative competitive abilities of juveniles of 3 closely related species of reef fish (bird wrasse Gomphosus varius, fivestripe wrasse Thalassoma quinquevittatum and the sixbar wrasse T. hardwicke) on Moorea, French Polynesia. We controlled for intrinsic variation in survivorship among species and found that competition among these 3 species was highly asymmetric, resulting in a simple competitive hierarchy (sequence of competitive ability from superior to inferior competitors): fivestripe wrasse > bird wrasse > sixbar wrasse. We surveyed densities of the 3 reef fish species on 55 patch reefs and observed significant negative spatial covariation between superior and inferior competitors, consistent with competitive hierarchies that limit the spatial distributions of the inferior species (sixbar wrasse). Our work demonstrates that intense asymmetric competition and the formation of competitive hierarchies may be an important determinant of resource monopolization and patterns of distribution and abundance in reef fishes. © Inter-Research 2013.

Sea turtle symbiosis facilitates social monogamy in oceanic crabs via refuge size

The capacity for resource monopolization by individuals often dictates the size and composition of animal groups, and ultimately, the adoption of mating strategies. For refuge-dwelling animals, the ability (or inability) of individuals to monopolize refuges should depend on the relative size of the refuge. In theory, groups should be larger and more inclusive when refuges are large, and smaller and more exclusive when refuges are small, regardless of refuge type. We test this prediction by comparing the size and composition of groups of oceanic crabs ( Planes minutus ) living on plastic flotsam and loggerhead sea turtles. We found that (i) surface area of refuges (barnacle colonies on flotsam and supracaudal space on turtles) is a better predictor of crab number than total surface area and (ii) flotsam and turtles with similar refuge surface area host a similar number (1–2) and composition (adult male–female pairs) of crabs. These results indicate that group size and composition of refuge-dwelling animals are modulated by refuge size and the capacity for refuge monopolization. Moreover, these results suggest that sea turtle symbiosis facilitates social monogamy in oceanic crabs, providing insights into how symbiosis can promote specific mating strategies.

The “Lessepsian invasion” – a case study revisited

A case study of the Lessepsian invasion of the Mediterranean Sea was carried out during the 1970s by a Hebrew University of Jerusalem team that included Uzi Ritte and his research students. The study zoomed on two mollusk “trios” of mytilid bivalves and cerithiid gastropods, each including an invader, a closely related and ecologically similar indigenous Red Sea species and a Mediterranean indigenous competitor. This paper revisits the results, conclusions and projections made by the 1970s study in the context of a recent unified invasion biology framework, and in the view of the dynamic development of the Lessepsian invasion and research into it throughout the more than 30 years since the case study took place. The approach of studying “trios” to detect potential invaders and project the course of invasions has not been repeated in the Lessepsian system since the 1970s case study. But the findings that opportunistic life history traits linked with a match of habitat in the invaded range to a species’ ecological niche make this species a potential invader and enable it to coexist with an encountered competitor remain robust. Recent human-induced and other environmental changes in the Mediterranean have however highlighted a potential significance of propagule pressure in intensifying competitive exclusion and resource monopolization by the invader, to the point of potentially impacting the invaded ecosystem.

Spyware

There is a potent threat to computer security represented by the emerging class of applications commonly known as “spyware,” designed to remotely monitor and report on user activity. The threat manifests itself indirectly, unlike hacker intrusions and many virus infections. These remote monitoring applications record and transmit information on computer user behaviors to third parties, who then utilize monitored customer data for marketing segmentation and targeting, or for more nefarious violations of user computer security. Most spyware is legal, having typically been installed during free software downloads online. Some spyware is illegal, having been remotely installed by bots on visited Web sites, and can remotely monitor for illegitimate purposes such as keystroke logging and password theft and account access. Spyware is often defended by its sponsors as a means of more effectively targeting the Internet experience to users, but users typically find the costs of this purportedly customer-centric monitoring process objectionable in terms of subsequent advertising distraction and system resource monopolization.

Monopolization of food by zebrafish (Danio rerio) increases in risky habitats

Dominant zebrafish (Danio rerio) previously have been shown to reduce their monopolization of food when foraging in structurally complex habitats compared with open habitats. Complex habitats may be more difficult to defend but may also be safer. To decouple these effects, we compared aggression and monopolization of food in groups of zebrafish foraging in an open habitat and one with overhead cover, as well as in an open habitat and a complex (vegetated) habitat. Covered and open habitats should have been equally defendable. In our experiments, fish used covered habitats more than open ones, suggesting that the perceived risk of predation was lower in covered habitats. There was no difference in use of vegetated and open habitats, suggesting that these habitats, which should differ in defendability, did not differ in safety. We found that the degree of food monopolization (expressed in the coefficient of variation within groups) at risky feeders was significantly greater in open habitats than in covered, but not vegetated, habitats. We did not find a difference in aggression between habitats. These results indicate that resource monopolization in groups of zebrafish is greater in risky habitats and support the hypothesis that the lower monopolization of food in complex habitats could result from greater safety in those habitats rather than, or in addition to, the reduction in defendability.