Kill Rate (kill + rate)

Distribution by Scientific Domains

Selected Abstracts

Vigilance and fitness in grey partridges Perdix perdix: the effects of group size and foraging-vigilance trade-offs on predation mortality

Summary 1Vigilance increases fitness by improving predator detection but at the expense of increasing starvation risk. We related variation in vigilance among 122 radio-tagged overwintering grey partridges Perdix perdix (L.) across 20 independent farmland sites in England to predation risk (sparrowhawk Accipiter nisus L., kill rate), use of alternative antipredation behaviours (grouping and use of cover) and survival. 2Vigilance was significantly higher when individuals fed in smaller groups and in taller vegetation. In the covey period (in early winter when partridges are in flocks), vigilance and use of taller vegetation was significantly higher at sites with higher sparrowhawk predation risk, but tall vegetation was used less by larger groups. Individuals were constrained in reducing individual vigilance by group size and habitat choice because maximum group size was determined by overall density in the area during the covey period and by the formation of pairs at the end of the winter (pair period), when there was also a significant twofold increase in the use of tall cover. 3Over the whole winter individual survival was higher in larger groups and was lower in the pair period. However, when controlling for group size, mean survival decreased as vigilance increased in the covey period. This result, along with vigilance being higher at sites with increasing with raptor risk, suggests individual vigilance increases arose to reduce short-term predation risk from raptors but led to long-term fitness decreases probably because high individual vigilance increased starvation risk or indicated longer exposure to predation. The effect of raptors on survival was less when there were large groups in open habitats, where individual partridges can probably both detect predators and feed efficiently. 4Our study suggests that increasing partridge density and modifying habitat to remove the need for high individual vigilance may decrease partridge mortality. It demonstrates the general principle that antipredation behaviours may reduce fitness long-term via their effects on the starvation,predation risk trade-off, even though they decrease predation risk short-term, and that it may be ecological constraints, such as poor habitat (that lead to an antipredation behaviour compromising foraging), that cause mortality, rather than the proximate effect of an antipredation behaviour such as vigilance. [source]

Inactivation of Mycobacterium avium ssp. paratuberculosis in milk by UV treatment

J. Donaghy
Abstract Aims:, To determine the effect of UV radiation on the viability of two strains of Mycobacterium avium ssp. paratuberculosis (Map) inoculated into milk. Methods and Results:,Mycobacterium avium ssp. paratuberculosis in a ultra heat treated milk matrix was subjected to increasing doses of UV-C radiation from 0 to 1836 mJ ml,1 using a pilot-scale UV reactor (20 l capacity). Survival of Map was monitored by culture on Herrold's egg yolk medium, Middlebrook 7H10 medium and the FASTPlaqueTBÔ phage assay. Differences in sensitivity to UV treatment were observed between strains, however, at 1000 mJ ml,1 a Map kill rate of 0·1,0·6 log10 was achieved regardless of strain used or method employed to enumerate Map. Although the inactivation trend was similar on the culture and phage assay, the former gave a consistently higher viable count. Conclusions:, The use of UV radiation alone does not represent an alternative to current pasteurization regimes for a large reduction in viable Map in milk. Significance and Impact of the Study:, To the authors' knowledge the work here represents the first pilot-scale UV treatment process used to assess UV efficacy to inactivate Map in milk. The results are similar to those obtained with a laboratory-scale process indicating the difficulties associated with UV treatment of an opaque liquid and the recalcitrance of Map towards inimical treatments. [source]

Could insecticide-treated cattle reduce Afrotropical malaria transmission?

Effects of deltamethrin-treated Zebu on Anopheles arabiensis behaviour, survival in Ethiopia
Abstract.,Anopheles arabiensis Patton (Diptera: Culicidae) is the most widespread vector of malaria in the Afrotropical Region. Because An. arabiensis feeds readily on cattle as well as humans, the insecticide-treatment of cattle , as employed to control tsetse (Diptera: Glossinidae) and ticks (Acari: Ixodidae) , might simultaneously affect the malaria vectorial capacity of this mosquito. Therefore, we conducted field experiments in southern Ethiopia to establish whether Zebu cattle (Bos indicus L.) treated with a pour-on pyrethroid formulation of 1% deltamethrin, widely used to control ticks and tsetse, would be effective against An. arabiensis or cause the female mosquitoes to feed more frequently on humans, due to behavioural avoidance of insecticide-treated cattle. Contact bioassays (3 min exposure) showed that the insecticide remained effective for about 1 month (kill rate > 50%) against mosquitoes feeding on the flanks of treated cattle. A novel behavioural assay demonstrated that An. arabiensis readily fed on insecticide-treated cattle and were not deflected to human hosts in the presence of treated cattle. DNA-fingerprinting of bloodmeals revealed that An. arabiensis naturally feeds most frequently on older animals, consistent with the established practice of applying insecticide only to older cattle, while allowing younger untreated animals to gain immunity against infections transmitted by ticks. These encouraging results were tempered by finding that > 90% of An. arabiensis, An. pharoensis and An. tenebrosus females feed on the legs of cattle, farthest from the site of pour-on application along the animal's back and where the treatment may be least residual due to weathering. Observations of mosquitoes feeding naturally on insecticide-treated cattle showed that the majority of wild female anophelines alighted on the host animal for less than 1 min to feed, with significantly shorter mean duration of feeding bouts on insecticide-treated animals, and the effective life of the insecticide was only 1 week. Thus the monthly application of deltamethrin to cattle, typically used to control tsetse and ticks, is unlikely to be effective against An. arabiensis populations or their vectorial capacity. Even so, it seems likely that far greater impact on anopheline mosquitoes could be achieved by applying insecticide selectively to the legs of cattle. [source]

The wolves of Isle Royale display scale-invariant satiation and ratio-dependent predation on moose

Summary 1The importance of two features of the predator functional response (satiation and predator dependence) is investigated in the wolf,moose interaction on Isle Royale National Park (Michigan, USA). This is done by fitting and comparing nine different functional response models to the observed kill rates. 2Three different observational scales (the whole island, the wolf packs, or a ,mixed' scale) are used to assess the sensitivity of the detected properties with respect to these spatial scales. 3Independently of the observational scale and of statistical assumptions on data structure, strong predator dependence and satiation of the wolf functional response are found. The ,mixed' scale gives the most consistent results, suggesting that predation should be measured for each pack, but that packs share all moose on the island. On this scale, the functional response is clearly ratio-dependent. [source]