The macroecology of reef fish agonistic behaviour

Understanding the interplay between processes operating at large and small spatiotemporal scales in shaping biotic interactions remains challenging. Recent studies illustrate how phenotypic specialization, species life-history traits and/or resource partitioning recurrently underlie the structure of mutualistic interactions in terrestrial ecosystems along large latitudinal gradients of biodiversity. However, we know considerably less about how local processes interact with large-scale patterns of biodiversity in modulating biotic interactions in the marine realm. Considering agonistic behaviour as a proxy for contest competition, we empirically investigate whether the structure of reef fish agonistic interactions is conserved across a 34 000-km longitudinal gradient of biodiversity. By sampling coral reefs using standardized remote underwater video, we found recurrent patterns of fish agonistic behaviour in disparate communities distributed across five biogeographic provinces of the Pacific and Atlantic oceans. While the sheer number of species increases with regional richness, the number of aggressive disputes at the habitat scale is similar across communities. We then combined generalized linear models and network theory to reveal that, the emergent structure of local agonistic networks is not modular but instead recurrently display a nested structure, with a core of highly interactive site-attached herbivores of the Pomacentridae family. Therefore, despite the increase in the number of species involved in agonistic interactions toward speciose communities, the network structure is conserved along the longitudinal richness gradient because local disputes are mostly driven by closely-related, functionally-similar species. These findings suggest that evolutionary and local processes interact in modulating reef fish agonistic behaviour and that fine-scale niche-partitioning can structure the ecological networks in marine ecosystems.     

Metabolic consequences of agonistic behaviour: crab fights in declining oxygen tensions

The energetic consequences of fighting, which may depend on environmental conditions, can be an important factor shaping contest strategy and duration. Energy expenditure may be costly to fitness because it depletes reserves that could otherwise have been allocated to reproduction, and metabolites are produced that may constrain subsequent activities. We examined the variation in the metabolic consequences of fighting in relation to hypoxia. Contests were staged between pairs of size-matched male shore crabs Carcinus maenas L., under a range of water oxygen tensions (between 10 and 100% oxygen saturation) which crabs experience in their natural habitat. Fighting under normoxic and hypoxic conditions resulted in significantly elevated concentrations of haemolymph metabolites (L-lactate and glucose) compared with crabs at rest. However, these concentrations were much lower than in crabs that had been walking on a treadmill. Glycogen concentrations differed only under hypoxic conditions: glycogen stores were reduced in crabs after fighting and this reduction was similar to that after exercise on a treadmill. Contests were shorter when they were staged below a water P o2of 6.7 kPa ( approximately 30% normoxia). As water oxygen tensions were reduced, fighting crabs had greater concentrations of L-lactate and glucose in their blood and tissues whilst glycogen stores were reduced. Fights became shorter when crabs were exposed to severe hypoxia (P o2=2 kPa) for increasing lengths of time, and blood L-lactate concentrations increased. The results suggest that as fights progressed, crabs experienced an increasing metabolic debt, in the form of accumulation of L-lactate and a reduction in energy stores, which was amplified by hypoxic conditions. Copyright 1999 The Association for the Study of Animal Behaviour.     

Development of agonistic behaviour and vocalization in croaking gouramis

The development of agonistic behaviour and vocalization in the croaking gourami Trichopsis vittata was studied from hatching to sexual maturity (4 months of age). Initial interactions started when fry were 11 days old and consisted of approach and flight in a feeding context. More complex threat patterns appeared during dyadic encounters as fish grew older. Lateral display (spreading of median fins in a lateral position) first occurred during the third week, circling shortly afterwards and pectoral fin beating when fish were 7 weeks old. Rapid pectoral fin beating was first accompanied by sound emission at 8 weeks. Initially, croaking sounds were built up mainly of a series of single pulses, each one produced by one pectoral fin. Later, single pulses gave way to double pulses. Furthermore, pulse period and number of pulses increased, while the dominant frequency of croaks decreased significantly with age. After vocalization was established, frontal display, mouth biting and retreat behaviour occurred at the age of 10 weeks. Initially, young exhibited vertical bars which gave way to dots and horizontal bars at 8 weeks when fish started to vocalize. The order of appearance of behavioural patterns during ontogeny corresponds to the order of appearance in fights between adults. This is the first study demonstrating that the ontogenetic development of social signalling comprises characteristic changes in behaviour, vocalization and coloration in a teleost fish.     

A parasitoid wasp induces overwintering behaviour in its spider host

Parasites and parasitoids control behaviors of their hosts. However, the origin of the behavior evoked by the parasitic organism has been rarely identified. It is also not known whether the manipulation is universal or host-specific. Polysphinctine wasps, koinobiont ectoparasitoids of several spider species that manipulate host web-spinning activity for their own protection during pupation, provide an ideal system to reveal the origin of the evoked behavior. Larva of Zatypota percontatoria performed species-specific manipulation of theridiid spiders, Neottiura bimaculata and Theridion varians, shortly before pupation. Parasitized N. bimaculata produced a dense web, whereas parasitized T. varians built a cupola-like structure. The larva pupated inside of either the dense web or the cupola-like structure. We discovered that unparasitized N. bimaculata produce an analogous dense web around their eggsacs and for themselves during winter, while T. varians construct an analogous 'cupola' only for overwintering. We induced analogous manipulation in unparasitized hosts by altering ambient conditions. We discovered that the behavior evoked by larvae in two hosts was functionally similar. The larva evoked protective behaviors that occur in unparasitized hosts only during specific life-history periods.     

Asymptotic behaviour of a model of hierarchically structured population dynamics

 A hierarchically structured population model with a dependence of the vital rates on a function of the population density (environment) is considered. The existence, uniqueness and the asymptotic behaviour of the solutions is obtained transforming the original non-local PDE of the model into a local one. Under natural conditions, the global asymptotical stability of a nontrivial equilibrium is proved. Finally, if the environment is a function of the biomass distribution, the existence of a positive total biomass equilibrium without a nontrivial population equilibrium is shown. Received 16 February 1996; received in revised form 16 September 1996     

Games spiders play. III: Cues underlying context-associated changes in agonistic behaviour

In this paper I consider the proximate cues underlying context-associated variation in the agonistic behaviour of the spider Agelenopsis aperta (Gertsch). At the initiation of a contest, individual opponents are shown to assess their relative weights; the subsequent behaviour of each is adjusted according to the result of the assessment. Escalation to potentially injurious behaviour early in the contest, for instance, is a threshold effect of weight bias. Several lines of evidence indicate, that only the territory Owner (resident) has information about the quality of a site at the initiation of a territorial dispute. (1) Owners of poor-quality sites that received food supplements exhibited significantly greater persistence and estimated energy expenditure in contests over these sites than unsupplemented individuals did over theirs. (2) A significant correlation was observed between web area and the behaviour of Owners, but not between web area and the behaviour of Intruders (individuals that encroach on occupied webs). (3) No correspondence was observed between spider body temperature and agonistic behaviour. (4) The presence or absence of prey on the web during the dispute did not affect the agonistic behaviour of either opponent. I conclude that the Intruder's behaviour is in some way adjusted to that of the Owner rather than directly to some aspect of the disputed site. Partial correlation analysis show site quality to have a greater influence on agonistic behaviour than weight bias, although both are important determinants of spider behaviour in territorial disputes.     

A spider diversity model for the Caucasus Ecoregion

Precise information on spatial patterns of species richness and endemic species distribution is important for effective species conservation. In the Caucasus Ecoregion such information is virtually non-existent for invertebrate taxa. Using occurrence data from a large database we calculated species distribution models with the GARP algorithm for 471 spider species to visualize the diversity distribution of spider species in this region. Overall species diversity was highest in mountain forests of the North Caucasus, east-central Georgia, the southern slopes of the eastern Great Caucasus and south-east Azerbaijan. A regression tree analysis Chi squared automatic interaction detector method revealed the mean temperature of the driest quarter and precipitation parameters to be the main environmental factors shaping these patterns. Diversity of endemic species was correlated with overall species diversity but hotspots of endemic species (10+ percent of all species) exists in high-mountain areas, suggesting post-glacial speciation events in the high mountains as the main sources of high endemism in Caucasus. Further information on the spatial distribution of species diversity of invertebrate taxa in the Caucasus Ecoregion is needed to improve conservation efforts in this biodiversity hotspot.     

Observations on the agonistic behaviour of Lepadogaster lepadogaster purpurea (Pisces: Gobiesocidae)

Agonistic behaviour of captive Lepadogaster lepadogaster purpurea , was described, forming the first record of such behaviour in the family Gobiesocidae. Both male and female engaged in similar behaviours. The agonistic interactions were related mainly to the control of shelter sites and larger fish tended to chase away and take over the shelter of smaller fish.     

Predictability of feeding: Its effect on agonistic behaviour and growth in grower pigs

Predictability of feeding was experimentally manipulated in Experiment I by changing the reliability of signals announcing the arrival of food for 32 female grower pigs. Results indicated that competition for places at the feed-pan increased when feeding time was unreliably signalled. Experiment II offered a total of 36 pigs, the R group, reliable signals throughout a 13-week period, and another 36 pigs, the UNR group, only unreliable signals. The frequency of aggression in the latter group was higher between meals when no signals were given, mainly after disturbances from in or outside of the pig-shed. Analysis of the behaviour of individual pigs indicates that the higher aggression is frustration-induced. The UNR group also showed a trend for greater variation in weight gain than the R group. The behavioural mechanisms through which unpredictable management practices affect the behaviour and growth of grower pigs are discussed.     

Mating behaviour of Dacus ciliatus (Loew) [Diptera:Tephritidae]: comparisons between a laboratory and a wild population

As part of the development of a sterile insect technique (SIT) application for the Ethiopian fruit fly, Dacus ciliatus, we studied the mating behaviour of a laboratory‐adapted strain (a 4‐year‐old colony kept for more than 40 generations) and a wild population. Effects of laboratory rearing and irradiation were assessed by carrying out mating compatibility and male mating competitiveness tests using a 1:1 ratio between irradiated (120 Gy) laboratory males and non‐irradiated wild males. Mating behaviour was studied on host and non‐host plants under field cage conditions. To assess the effect of mass rearing upon male performance, we repeated the mating competitiveness test using non‐irradiated laboratory insects. The findings indicated a high degree of compatibility among the two populations and satisfactory competitiveness of the irradiated laboratory males (ca. 35%). The competitiveness of non‐irradiated laboratory males was also ca. 35%, suggesting that no adverse effects resulted from their irradiation. Mating occurred only at twilight and mainly on the underside of leaves of non‐host plants (lemon trees). Findings are discussed in view of their implications for a future application of SIT against this fruit fly pest.     

A population model for two-spotted spider mite Tetranychus urticae and its predator Metaseiulus occidentalis

A population simulation model that was developed for the fruit tree red spider mite (Panonychus ulmi Koch) and its phytoseiid predator (Amblyseius potentillae Garman) (Rabbinge, 1976) was adapted to Metaseiulus occidentalis Nesbitt and Tetranychus urticae Koch. The model uses life-table data for T. urticae and M. occidentalis and M. occidentalis' numerical and functional responses. The assumptions made in the model were tested by comparing the model outcome with the results of an independent greenhouse experiment. Sensitivity analyses were also done to evaluate the implicit assumptions of the model and to determine the relative importance of the rates and parameters used. Results of the sensitivity analysis showed that time of release is critical for rapid control of the prey population. Predator-prey release ratios and frequency of releases are relatively less important. Differences in functional and numerical response and predator dispersal rate also seem relatively less important than proper timing of releases.

---

Zusammenfassung Ein Simulationsmodell, das für die Populationen der Obstbaumspinnmilbe (Panonychus ulmi Koch) und ihren Feind (Amblyseius potentillae Garman) entwickelt worden war (Rabbinge, 1976), wurde Metaseiulus occidentalis Nesbitt und Tetranychus urticae Koch angepasst. Das Modell verwendet Life-table Daten für T. urticae und M. occidentalis sowie die numerischen und funktionalen Reaktionen von M. occidentalis. Die im Modell gemachten Annahmen wurden getestet, indem das Modellergebnis mit den Resultaten eines unabhängigen Gewächshausversuchs verglichen wurde. Die Sensitivitätsanalyse zeigte, dass der Zeitpunkt der Freilassung entscheidend ist für eine rasche Begrenzung der Wirtspopulation. Das Räuber-Wirtverhältnis und die Häufigkeit der Freilassung sind weniger wichtig. Unterschiede in der numerischen und funktionalen Reaktion und die Ausbreitungsgeschwindigkeit scheinen ebenfalls weniger wichtig zu sein als der richtige Zeitpunkt der Freilassung.