Duration of paternal care in the burying beetle Nicrophorus orbicollis Say is highly variable. Both parents bury and defend mouse‐sized vertebrate carcasses as food resources for their offspring, but males abandon their broods several days before females. Nests defended by single female parents were taken over by aggressive conspecifics in live of nine cases, whereas only six of 16 nests defended by both parents were taken over. In the event of a takeover, the intruding beetle replaced the resident beetle of the same sex, destroyed any eggs that were present, and paired with the remaining resident to produce a new clutch. Broods raised by usurpers following takeovers were less successful than broods raised by initial residents on unused carcasses. The majority of takeovers occurred 35 days after carcass burial. The occurrence of nest intrusions by conspecifics did not significantly influence duration of male parental care; when conspecific intruders were excluded from nests males remained with their broods (± S.E.) 11·2 ± 0·8 days (n= 15), and when intruders were added to nests males remained with their broods 12·2 ± 0·6 days (n= 8). Conflict for carcasses intensified in response to larger brood mass, but duration of male care was unaffected by brood mass. Overall. brood mass and the presence or absence of intruders explained only 5% of the variance associated with brood abandonment by males.

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Petal herbivory by chrysomelid beetles ( Phyllotreta sp.) is detrimental to pollination and seed production inLepidium papilliferum (Brassicaceae) Abstract . 1. Insect herbivory directed at flowers can decrease fruit and seed production by decreasing the attractiveness of a damaged flower to potential pollinators, by disrupting the transfer of pollen between pollinators and stigmas, or both.2. Effects of petal herbivory by a chrysomelid beetle ( Phyllotreta sp.) on pollination and seed production in Lepidium papilliferum (Brassicaceae) were examined.3. Under natural conditions, flowers with a hole chewed in a petal produced fruit and seed at a significantly lower rate than undamaged flowers (44% vs. 80% respectively). However, when damaged and undamaged flowers were hand pollinated, there was no significant difference in fruit or seed set (84% vs. 80% respectively).4. Petal herbivory in L. papilliferum disrupts the effectiveness of insect-mediated pollination, but it does not physically inhibit pollination or seed production.

2005. Crab spiders deter insect visitations to slickspot peppergrass flowers. Á/ Oikos 109: 577 Á/582.Insects visiting the flowers of slickspot peppergrass, Lepidium papilliferum (Brassicaceae), risk predation by crab spiders, Misumena vatia (Thomisidae). In a field study conducted at two sites in southwestern Idaho, 7.59/2.7% of L. papilliferum plants (range 0 Á/30%, N0/16 surveys of up to 40 randomly selected plants) harbored a crab spider. However, through 205 minutes of observations at plants with a spider, only 15 predation attempts were observed, with only 3 of those being successful. Despite the relatively low incidence of predation by crab spiders, an experiment revealed that the number of insects visiting L. papilliferum flowers was significantly lower at plants that harbored a crab spider than at plants free of spiders. In another experiment, floral visits increased significantly following the removal of crab spiders from individual plants. The deterrent effect of spiders was not due to a disproportionate avoidance response by certain types of insects; all insect families included in our analysis showed decreases in visitations to flowers when spiders were present, although none of these differences were statistically significant at the individual level. We found no significant change in the duration of visits to plants harboring a spider, implying either that the visitors were oblivious to the predator's presence, or that they were aware of the predator but kept their distance. Our study is one of a growing number to find a decrease in floral visits in response to predators, suggesting that the phenomenon is more widespread than was previously recognized.

We examined the influence of body temperature on swimming speed of northern water snakes (Nerodia sipedon) and determined how variation in water temperature influenced their escape response. In a laboratory experiment, swimming speed increased as a function of water temperature and body size. Swimming speed was less thermally dependent at temperatures approximating the snakes' normal range of activity, suggesting that selection has favoured increased performance breadth at this range. In the field, basking snakes retreated to water when approached. Despite a decrease in swimming speed at lower temperatures, and the cost associated with reduced metabolic rate due to loss of body temperature, however, flight distances were independent of water temperature. We found that basking snakes retreated to water sooner when perched at lower heights, possibly indicating that N. sipedon are more vulnerable to predators when on low perches. Predicting water snake escape behaviour may require not only knowledge of variation both among snakes and in their environment, but also a better understanding of the interaction between the snakes and their natural predators.

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