23 research outputs found

    Stable isotope mixing models elucidate sex and size effects on the diet of a generalist marine predator

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    We applied a 2-step clustering algorithm and Bayesian stable isotope mixing model to examine intraspecific differences in the contribution of prey sources to the diet and foraging habitat of harbor seals Phoca vitulina in the Salish Sea, USA. We analyzed stable isotopes of carbon and nitrogen collected from 32 seals and 248 prey samples representing 18 of 25 of the most common seal prey items identified in seal scat. Stable isotope analyses identified significant harbor seal sex- and size-based differences in diet and foraging habitat use. In comparison to males, female harbor seals had a higher contribution of prey items that were more 13C-enriched. This result may indicate that females derived more of their δ13C value from nearshore versus offshore food webs, an explanation supported by movement data on this population. However, large seals of both sexes displayed a greater offshore signal in their diet, indicating that seal mass effects on foraging habitat use were somewhat independent of sex. Our work contributes to understanding trophic linkages between these generalist consumers and their prey. The foraging differences that we detected between male and female harbor seals present complex challenges for fisheries management and for the design of marine reserves. Many marine reserves in the Pacific Northwest are located in close proximity to seal haul-out sites. By lowering the energetic costs of foraging of females, these reserves may ultimately have the unintended effect of increasing individual fitness, population growth rate, and influencing future predator-induced mortality on endangered species

    Variação do regime de umidade do solo durante o ciclo fenológico de plantas de batata

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    Neste trabalho foram analisadas as relações entre a produção, o desenvolvimento vegetativo e a evapotranspiração de uma cultura de batata (Solanum tuberosum L.) submetida à três regimes de umidade, definidos pelos valores assumidos pelo potencial matricial da água do solo antes de se proceder as irrigações (-0,5; -1,0 e -5,0 bares) em três estádios de desenvolvimento das plantas. Com respeito à produção de tubérculos, ficou evidenciado que por ocasião da tuberização e desenvolvimento de um grande número de tubérculos, as plantas revelaram uma maior sensibilidade à redução da umidade do solo. Assim, ocorrendo deficits moderados (-1,0 bar) no período inicial de desenvolvimento, a produção não foi significativamente afetada. Isto foi atribuído, em parte, à recuperação parcial do crescimento vegetativo no estádio subseqüente, quando foram restabelecidas condições mais adequadas de umidade no solo. O mesmo não se verificou no tratamento submetido a deficits mais severos (-5,0 bares) no estádio inicial. Neste caso, o crescimento foi quase irreversivelmente reduzido, contribuindo para diminuir a produção e a eficiência de utilização de água pelas plantas. A redução da umidade do solo, a partir dos 60 dias após a emergência das plantas, não afetou a produção de tubérculos. Este procedimento concorreu para aumentar significativamente a eficiência de utilização de água. Além disso, havendo suspensão total da irrigação neste período, a senescência foi antecipada em 16 dias, em relação aos tratamentos submetidos a níveis de umidade mais elevados. O desenvolvimento vegetativo e a produção não foram igualmente afetados pela redução da umidade do solo. Conseqüentemente, o crescimento das plantas não parece se constituir em um índice absoluto da produção de tubérculos de batata.Changes in soil water regime during vegetative growth and yield production of potato crop was not equally affected by soil water depletion. Concerning to yield production the results show that the soil water depletion effect are closely related to intensity and duration of water deficits and stage of plant growth in which they occurs. So, it was stablished that during the stage of tuberization and tuber development, the plant exhibited higher sensibility to water deficiency than in the initial or final stage of plant growth. On the other hand, moderate deficits (-1.0 bar of soil water matric potential) occurring in the initial stage of plant growth did not have any effect in tuber yield. This was attributed to the resumption of growth in the following stage. However, when a more severe water deficiency occurred (-5.0 bars of soil water matric potential), it was not observed the resumption phenomenon. In this case, an irreversible decrease in growth had the effect of decreasing yield. Soil moisture depletion in the final growth stage, about 60 days after plant emergence, did not decrease tuber yield, which increased plant water efficiency. When water supply was suppressed in this stage, the senescence was hastened in 16 days when compared to the other treatments with higher levels of soil moisture. As was evidenced, the vegetative growth is not an absolute index of the potato yield production
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