1,395 research outputs found

    Territorial status and survival in red grouse Lagopus lagopus scoticus: hope for the doomed surplus?

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    A previous study of survival in territorial and non-territorial red grouse Lagopus lagopus scoticus conducted between 1957 and 1967 found that territorial status in the autumn pre-determined over-winter survival. A very high proportion of territorial birds survived and virtually all non-territorial birds died or emigrated. We tested the hypothesis that over-winter survival was dependent on territorial status within four grouse populations in Scotland between 1986 and 1993. In contrast to the previous study, 66% of non-territorial birds survived over winter, compared to approximately 70% of territorial birds. There was no significant effect of territorial status on the survival estimates. Moreover, some of the birds considered to be non-territorial during autumn went on to successfully raise a brood. We suggest that on our study sites, territory ownership in autumn did not greatly influence over-winter survival, and territorial behaviour did not determine breeding density as previously supposed. We postulate differences with other studies may reflect variations in scale and predation pressure

    Differential impact of a shared nematode parasite on two gamebird hosts: implications for apparent competition

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    If the deleterious effects of non-specfic parasites are greater on vulnerable host species than on reservoir host species then exclusion of the vulnerable host through apparent competition is more likely. Evidence suggests that such a mechanism occurs in interactions between the ring-necked pheasant (Phasianus colchicus), the grey partridge (Perdix perdix), and their shared caecal nematode Heterakis gallinarum. Modelling of the system predicts that the reduced parasite impact on the pheasant compared to the partridge results in the force of infection transmitted from pheasants to partridges being sufficient to cause partridge exclusion. Since the parasite impacts are currently estimated from correlational work, controlled infections were conducted to experimentally compare the impact of H. gallinarum on the two hosts and verify cause and effect. While challenged partridges showed reduced mass gain, decreased food consumption, and impaired caecal activity, in comparison to controls, the only detectable effect of parasite challenge on the pheasant was impaired caecal activity. The impact ofH. gallinarum on challenged partridges conforms with previous correlational data, supporting the prediction that parasite-mediated apparent competition with the ring-necked pheasant may result in grey partridge exclusion. However, the observed decrease in the caecal activity of challenged pheasants could imply that H. gallinarum may also have an impact on the fecundity and survival of pheasants in the wild, particularly if food is limiting. If this is the case, the associated decrease in the force of infection to which the partridge is exposed may be sufficient to change the model prediction from partridge exclusion to pheasant and partridge coexistence

    A 240-Year Stable Oxygen and Carbon Isotopic Record in a Coral from South Florida: Implications for the Prediction of Precipitation in Southern Florida

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    This study reports on the δ18O and δ13C composition of the skeleton from a 240-year-old specimen of Montastraea faveolata growing in Biscayne National Park, South Florida. Annual variations in the δ18O of the skeleton deposited during the summer months show a bimodal correlation with summer rainfall. During wetter years, the δ18O of the coral skeleton and the amount of precipitation during the summer months are inversely correlated (r = -0. 7) reflecting dilution of the seawater by meteoric water lower in δ18O. During years in which summer rainfall is less than normal, increases in precipitation are positively correlated with skeletal δ18O (r = +0.6) reflecting the input of freshwater from the Everglades higher in δ18O. Based on this correlation the δ18O record of the coral skeleton suggests that the 19th and 18th centuries have been relatively dry compared to the 20th century. Carbon isotopic compositions of the skeleton are positively correlated with δ18O with the minimum in δ13C occurring several months after the minimum in δ18O. Since the mid 1930s there has been a decrease in δ13C of the skeleton. Explanations for this trend may be (1) it reflects the increased input of carbon derived from the destruction of terrestrial ecosystems, (2) its part of a long-term decrease in δ13C associated with increased addition of fossil fuel-derived CO2

    Chronicles of Oklahoma

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    Article recounts the events and experiences of the author, Peter J. Hudson, as he lived in and around the Choctaw Nation. Included are his memories of the roads, trails, settlements, names, mountains, streams, mining efforts, and events that happened within the region

    Evolutionary History and Attenuation of Myxoma Virus on Two Continents

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    The attenuation of myxoma virus (MYXV) following its introduction as a biological control into the European rabbit populations of Australia and Europe is the canonical study of the evolution of virulence. However, the evolutionary genetics of this profound change in host-pathogen relationship is unknown. We describe the genome-scale evolution of MYXV covering a range of virulence grades sampled over 49 years from the parallel Australian and European epidemics, including the high-virulence progenitor strains released in the early 1950s. MYXV evolved rapidly over the sampling period, exhibiting one of the highest nucleotide substitution rates ever reported for a double-stranded DNA virus, and indicative of a relatively high mutation rate and/or a continually changing selective environment. Our comparative sequence data reveal that changes in virulence involved multiple genes, likely losses of gene function due to insertion-deletion events, and no mutations common to specific virulence grades. Hence, despite the similarity in selection pressures there are multiple genetic routes to attain either highly virulent or attenuated phenotypes in MYXV, resulting in convergence for phenotype but not genotype. © 2012 Kerr et al

    Breeding losses of red grouse in Glen Esk (NE Scotland): Comparative studies, 30 years on

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    Hatching success, brood survival and predation rates of red grouse chicks were examined at four sites in north-east Scotland over two years (1994--1995). Two of these sites have previously been the focus of a large-scale population study on grouse during the late 1950s enabling a comparison to be made. A total of 85 hens were radio-tracked and their breeding success monitored over the two years. Compared with studies undertaken in the 1950s, mean clutch size had risen from 7.2 to 8.6 eggs. Of the 76 nests monitored, 17 (22.4%) broods were lost either through egg or chick predation or by the adult being taken by a predator during incubation. Stoats appeared to be responsible for the largest amount of egg predation. There was a significant increase in predation levels, although hatching success was not significantly different from the 1950s. Chick mortality was highest within the first ten days, a similar result to that found in the 1950s. Overall, mean brood survival from hatching to 20 days was 55.1%. Possible reasons for larger clutch sizes, and the apparent increase in predation levels, are discussed

    Re-assessing the infection strategies of the entomopathogenic nematode Steinernema feltiae (Rhabditidae; Steinernematidae)

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    Previous studies have indicated that between 60 and 80% of a population of entomopathogenic nematodes do not infect their insect hosts at any one period in time. Two hypotheses explain this behaviour: the first that there is a subpopulation of non-infectious nematodes and the second that the non-infectious group is created by inhibitory cues derived from infected insects. Through an experimental approach with the Galleria mellonella-Steinernema feltiae system we show that both mechanisms operate together. When conditions for infection were optimized, the sum of individual infection behaviours was similar to the number infecting as a population, implying observed infection rates are driven by intrinsic mechanisms. In addition, there was evidence that an infected host released a chemical cue into the environment which inhibited subsequent levels of infection. This degree of inhibition was independent of the number of infecting nematodes. Both these mechanisms are dynamic, so the observed proportion of infectious nematodes depended heavily on the time of exposure. The implications of these findings for both the design of laboratory trials and the use of entomopathogenic nematodes in biological control are discussed

    Evaluating the efficacy of entomopathogenic nematodes for the biological control of crop pests: A nonequilibrium approach

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    The efficacy of entomopathogenic nematodes for biological control is assessed using deterministic models. Typically, the examination of such models involves stability analyses to determine the long‐term persistence of control. However, in agricultural systems, control is often needed within a single season. Hence, the transient dynamics of the systems were assessed under specific, short‐term control scenarios using stage‐structured models. Analyses suggest that preemptive application may be the optimum strategy if nematode mortality rates are low; applying before pest invasion can result in greater control than applying afterward. In addition, repeated applications will suppress a pest, providing the application rate exceeds a threshold. However, the period between applications affects control success, so the economic injury level of the crop and the life history of the pest should be evaluated before deciding the strategy. In all scenarios, the most important parameter influencing control is the transmission rate. These findings are applicable to more traditional biological control agents (e.g., microparasites and parasitoids), and we recommend the approach adopted here when considering their practical use. It is concluded that it is essential to consider the specific crop and pest characteristics and the definition of control success before selecting the appropriate control strategy
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