One of the functions of chemical communication is territorial signalling. To achieve this, animals should mark their territories in a manner that increases the detectability of the marks, thereby maximising the probability that other animals detect the scent marks. In this study, we focused on the scent-marking behaviour of red foxes in relation to the abundance of their main prey, the European rabbit, in a suburban forest in Madrid, Spain. Our results reveal that foxes scent-marked more and increased the detectability of their marks in areas of higher rabbit density. It would appear that foxes defend food resources from competitors by increasing the number and the detectability of their scent marks.
Cannibalism is a common phenomenon among insects. It has raised considerable interest both from a theoretical perspective and because of its importance in population dynamics in natural ecosystems. It could also play an important role from an applied perspective, especially when using predatory species in biological control programmes. The present paper aims to study the cannibalistic behaviour of Nabis pseudoferus Remane and the functional response of adult females. In a non-choice experiment, adult females showed clear acceptance of immature conspecifics as prey, with relatively high mortality values (51.89 ± 2.69%). These values were lower than those occurring for heterospecific prey, Spodoptera exigua Hübner, under the same conditions (80.00 ± 2.82%). However, the main result was that the rate of predation on heterospecific prey was reduced to 59.09 ± 7.08% in the presence of conspecific prey. The prey-capture behaviour of adult females differed when they hunted conspecific versus heterospecific prey. This was shown in the average handling time, which was 23.3 ± 3.3 min in the first case (conspecific) versus 16.6 ± 2.5 min in the second (heterospecific). Furthermore, the values increased in the former case and declined in the latter according to the order in which the prey were captured. The difference in handling time was not significant when adjusting the adult female functional response to conspecific nymphs. We argue that these results likely indicate risk aversion and a fear of reprisal among conspecifics.
Many studies have documented that hatchery-reared salmonids generally have inferior survival after being stocked compared with wild conspecifics, hatchery and wild salmonids have been observed to differ in their antipredator responses. The response of brown trout (Salmo trutta) juveniles (0+) of differing backgrounds to a live predator was compared in two experiments. First, the antipredator behaviour of predator-na€ ıve hatchery-reared brown trout and wild-exposed brown trout were assessed in behavioural trials which lasted for eight days. Second, predator-na€ ıve and predator-conditioned hatchery-reared brown trout were assessed in identical behavioural trials. Brown trout were 'predator-conditioned' by being held in a stream-water aquarium with adult Atlantic salmon (Salmo salar) and adult brown trout for two days prior to behavioural trials. Predator-conditioned hatchery-reared brown trout spent more time in shelters in the trial aquaria than predator-na€ ıve hatchery-reared fish, but did not differ in time spent in the predator-free area. Predator conditioning may account for the increased time spent in the shelter, but does not appear to have affected time spent in the predator-free area. However, even if significant alteration in behaviour can be noted in the laboratory, the response might not be appropriate in the wild.
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