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Incorporation of unrelated eggs into a clutch by incubating females (egg retrieval), which has an obvious adaptive value when female retrieves her own egg, seems to be also a part of the reproductive tactics related to brood parasitism. In open nesting waterfowl, the parasitic egg remains frequently outside the nest bowl after the parasitic event. Using time-lapse video recorders, we described experimentally the behavioural reaction of the common pochard (Aythya ferina) females towards an egg lying beside the nest. We tested whether the females discriminate between conspecific and heterospecific eggs (brown chicken eggs). All 16 experimental females retrieved both conspecific and heterospecific eggs. We found no apparent differences in female responses towards either egg type. The retrieval of alien eggs can be a result of an imperfect recognition ability of the female, anti-predation defence, or sophisticated tactic related to the brood parasitism. The last explanation seems to be less likely due to imperfect egg recognition abilities in the species.
We conducted laboratory experiments (1) to confirm the existence of a non-injury released disturbance cue in juvenile convict cichlids and rainbow trout, and (2) to determine if cichlids and trout exhibit a graded threat-sensitive antipredator response to varying concentrations of disturbance cues. The results of our first experiment demonstrate that both cichlids and trout exhibit significant antipredator responses (reductions in time spent moving, foraging rate and area use) to the odour of conspecifics that had been exposed to a realistic predator model but not to the odour of undisturbed conspecifics. The results of our second experiment demonstrate that cichlids and trout exhibit reduced time spent moving and foraging rates proportional to the concentration of disturbance cue detected. Together, these results confirm the presence of disturbance cues in cichlids and trout and demonstrate that disturbance cues provide sufficient information to allow for graded threat-sensitive responses.
Fluctuating asymmetry (FA) of foramina as a measure of environmental stress was studied in polar bear (Ursus maritimus) skulls from East Greenland (n = 300, collected 1892–2004) and Svalbard (n = 388, collected 1950–2004). Levels of FA for each of the 11 traits used in the study were compared between sex/age groups (subadults, adult females, adult males), localities (East Greenland, Svalbard), and periods (≤ 1960 [prepollution] and > 1960, [pollution]) using general linear models (GLMs). The GLMs revealed that adult males had higher FA in two traits than other sex/age groups. Also, the Svalbard bears had higher FA in number of intracondylar foramina than had those from East Greenland, a trend corresponding well with skull differences found previously between the two subpopulations. No correlation was found between the bears' year of birth (n = 468) and FA or between levels of contaminants and FA (n = 65).
Predator-prey studies in streams have traditionally focused on mayfly-stonefly interactions in relatively constant flow conditions. In reality, however, lotic prey encounter multiple types of predators, most of which are restricted to low-velocity microhabitats. By contrast, some invertebrate prey may occur in very high current velocities. For example, many blackfly species are able to feed at velocities of 100 cm s-1, whereas even moderate currents reduce the hunting efficiency of their invertebrate predators. The caddisfly larvae of the genus Rhyacophila, however, may be an exception to the pattern of reducing predator efficiency with increasing velocity. Using a combination of laboratory and field experiments and behavioral field observations, we examined the interaction between predatory Rhyacophila caddis larvae and larval blackflies along a velocity gradient of 20–120 cm s-1. In laboratory experiments, Rhyacophila preferred currents slower than 50 cm s-1 while blackflies exhibited a wide tolerance of currents and frequently occurred in currents exceeding 100 cm s-1. In direct field observations, total activity and distance moved by Rhyacophila were similar at all current velocity regimes tested, but frequency of predation attempts on blackflies was lowest at the highest velocities (> 100 cm s-1). In a field colonization study, blackflies avoided substrates with the slowest velocities (< 40 cm s-1), as also did the caddis larvae. Only velocities approaching 100 cm s-1 provide blackflies with refuge from predation by Rhyacophila. Being able to maneuver across a wide range of velocities, Rhyacophila may have more pervasive effects on their prey than other lotic invertebrate predators.
We assessed the presence/absence and population size of a threatened beetle, Osmoderma eremita, inhabiting hollow oaks (Quercus robur). Population sizes varied widely between trees (10% of the hollow trees hosted two thirds of the individuals), and increased with the volume of wood mould (= loose material of dead wood) and the height of the entrances. Population density (number of adult beetles per litre of wood mould) increased with decreasing growth rate of the trees. Trees with the largest O. eremita populations were 300–400 years old. Among hollow trees, the population sizes increased with tree age. This is at least partly due to the fact that the volume of wood mould increased with tree age. Both the size of the largest entrance hole and tree diameter were positively correlated with the estimated wood mould volume, and could thus be used as easily measured proxies for wood mould volume.
Chrysomelid beetles inhabiting the herb, shrub and tree layers of two mixed forest ecosystems dominated by pine-oak-hawthorn were studied during April–October in 2005 and 2006 in Isparta province, Turkey. The leaf beetles of both sites were investigated in terms of species composition, dominance structure and vegetation preference. Frequency values and host plants were also provided for some species. A total of 127 Chrysomelidae species belonging to ten subfamilies were collected. Species composition similarity between the herb and tree layers was 3% at both sites, while similarity between the shrub and tree layers was 25% at site I and 44% at site II. In terms of vegetation structure, the herb layers of the two sites shared 60% of their chrysomelid species, the shrub layers shared 44% and the tree layers shared 50%, a result also reflected in a PCA analysis. The herb layer was the most diverse vegetation stratum in terms of leaf beetle diversity, and it appears that vegetation cover is the main factor influencing leaf beetle species composition at both forest stands studied.