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Biology Letters (4)
Bilde, Trine (1)
Bressendorff, Berith B. (1)
Elsayed, Rehab (1)
Fuchs, Thomas (1)
Hammel, Jörg U. (1)
Høye, Toke Thomas (1)
Mayntz, David (1)
Pekár, Stano (1)
Tuni, Cristina (1)
Vollrath, Fritz (1)
Year of Publication
Dome-shaped functional response induced by nutrient imbalance of the prey
Bressendorff, Berith B.
Nutritional ecological theory predicts that predators should adjust prey capture and consumption rates depending on the prey's nutritional composition. This would affect the predator's functional response, at least at high prey densities, i.e. near predator satiation. Using a simple fruitfly-wolf spider laboratory system in Petri dishes, we found that functional responses changed from day to day over a 7 day period. After 1 to 2 days of feeding, dome-shaped functional responses (i.e. reduced predation at highest prey densities) appeared in spiders fed nutritionally imbalanced prey, compared with steadily increasing or asymptotic functional responses with nutritionally near-optimal prey. Later again (days 5–7), the difference disappeared as the level of the functional response was reduced in both treatments. Experiments with adult females in spring and subadult spiders in autumn revealed opposite patterns: a dome-shaped response with high-lipid prey for reproductive females, for which protein-rich prey are optimal, and a dome-shaped (or simply reduced) response with high-protein prey for pre-winter subadults, for which high-lipid flies are the optimal prey. Our results have implications for predation theory and models of biological control that have, so far, neglected nutritional aspects; in particular, the dynamic nutritional state of the predators should be incorporated.
Araneae; biological control; geometric framework; Lycosidae; predation; nutrient composition
Nutrient balance affects foraging behaviour of a trap-building predator
Predator foraging may be affected by previous prey capture, but it is unknown how nutrient balance affects foraging behaviour. Here, we use a trap-building predator to test whether nutrients from previous prey captures affect foraging behaviour. We fed orb-weaving spiders (Zygiella x-notata) prey flies of different nutrient composition and in different amounts during their first instar and measured the subsequent frequency of web building and aspects of web architecture. We found that both the likelihood of web building and the number of radii in the web were affected by prey nutrient composition while prey availability affected capture area and mesh height. Our results show that both the balance of nutrients in captured prey and the previous capture rate may affect future foraging behaviour of predators.
foraging behaviour; prey quality; trap construction
Climate change and sexual size dimorphism in an Arctic spider
Høye, Toke Thomas
Hammel, Jörg U.
Climate change is advancing the onset of the growing season and this is happening at a particularly fast rate in the High Arctic. However, in most species the relative fitness implications for males and females remain elusive. Here, we present data on 10 successive cohorts of the wolf spider Pardosa glacialis from Zackenberg in High-Arctic, northeast Greenland. We found marked inter-annual variation in adult body size (carapace width) and this variation was greater in females than in males. Earlier snowmelt during both years of its biennial maturation resulted in larger adult body sizes and a skew towards positive sexual size dimorphism (females bigger than males). These results illustrate the pervasive influence of climate on key life-history traits and indicate that male and female responses to climate should be investigated separately whenever possible.
body size; carapace width; life cycle; Pardosa glacialis; sexual size dimorphism
Death feigning in the face of sexual cannibalism
Pre-copulatory sexual cannibalism by females affects male and female reproductive success in profoundly different ways, with the females benefiting from a meal and the male facing the risk of not reproducing at all. This sexual conflict predicts evolution of traits to avoid cannibalism and ensure male reproductive success. We show that males of the nuptial gift-giving spider Pisaura mirabilis display a remarkable death feigning behaviour—thanatosis—as part of the courtship prior to mating with potentially cannibalistic females. Thanatosis is a widespread anti-predator strategy; however, it is exceptional in the context of sexual selection. When the female approached a gift-displaying male, she usually showed interest in the gift but would sometimes attack the male, and at this potentially dangerous moment the male could ‘drop dead’. When entering thanatosis, the male would collapse and remain completely motionless while retaining hold of the gift so it was held simultaneously by both mates. When the female initiated consumption of the gift, the male cautiously ‘came to life’ and initiated copulation. Death feigning males were more successful in gaining copulations, but did not have prolonged copulations. We propose that death feigning evolved as an adaptive male mating strategy in conjunction with nuptial gift giving under the risk of being victimized by females.
sexual cannibalism; sexual conflict; cannibalism avoidance; thanatosis; male mating strategy
Results 1-4 (4)
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