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Rooted cuttings of clonal Sitka spruce (Picea sitchensis (Bong.) Carr.) were grown from April to October in 1 m long tubes sunk into the ground inside open top chambers. The same experiment was repeated in each of two consecutive years using a different clone of Sitka spruce each year. Air was either passed directly into the chambers (ambient air) or passed over charcoal filters which removed the majority of gaseous pollutants before entering the chambers (filtered air). Ambient pollution did not appear to influence the growth of Sitka spruce at least over the experimental period used. No significant differences were found between plants exposed to ambient or filtered air in terms of shoot and root dry mass, needle dry mass, root length, carbohydrate content of roots and needles, and in the percentage of meristematic cells close to the apex in each phase or interphase or undergoing mitosis. 相似文献
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Orb web spiders sit at the centre of their approximately circular webs when waiting for prey and so face many of the same
challenges as central-place foragers. Prey value decreases with distance from the hub as a function of prey escape time. The
further from the hub that prey are intercepted, the longer it takes a spider to reach them and the greater chance they have
of escaping. Several species of orb web spiders build vertically elongated ladder-like orb webs against tree trunks, rather
than circular orb webs in the open. As ladder web spiders invest disproportionately more web area further from the hub, it
is expected they will experience reduced prey gain per unit area of web investment compared to spiders that build circular
webs. We developed a model to investigate how building webs in the space-limited microhabitat on tree trunks influences the
optimal size, shape and net prey gain of arboricolous ladder webs. The model suggests that as horizontal space becomes more
limited, optimal web shape becomes more elongated, and optimal web area decreases. This change in web geometry results in
decreased net prey gain compared to webs built without space constraints. However, when space is limited, spiders can achieve
higher net prey gain compared to building typical circular webs in the same limited space. Our model shows how spiders optimise
web investment in sub-optimal conditions and can be used to understand foraging investment trade-offs in other central-place
foragers faced with constrained foraging arenas. 相似文献
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Elaine S. Fileman Penelope K. Lindeque Rachel A. Harmer Claudia Halsband Angus Atkinson 《Marine Biology》2014,161(11):2479-2494
Meroplankton are seasonally important contributors to the zooplankton, particularly at inshore sites, yet their feeding ecology is poorly known relative to holoplankton. While several studies have measured feeding in decapod larvae, few studies have examined the feeding rates of decapod larvae on natural prey assemblages throughout the reproductive season. We conducted 8 feeding experiments with Necora puber, Liocarcinus spp. and Upogebia spp. zoea larvae collected from the L4 monitoring site off Plymouth (50°15.00′N, 4°13.02′W) during spring–summer 2009 and 2010. This period spanned moderate-to-high food availability (0.5–1.6 µg chl-a L?1), but a great range in food composition with small cells <20 µm dominating in 2010. Daily rations averaged 17, 60 and 22 % of body C for the 3 respective decapod species. Clearance rates differed according to prey type, and all 3 decapod genera showed evidence of selection of dinoflagellates. Importantly, small cells including nano- and pico-plankton were ingested, this being demonstrated independently by flow cytometric analysis of the feeding experiments and molecular analysis. PCR-based analysis of the haptophyte portion of the diet revealed ingestion of Isochrysis galbana by decapod larvae in the bottle incubations and Isochrysis galbana and Phaeocystis globosa by decapod larvae collected directly from the field. This study has shown that pico- and nano-sized plankton form an important supplement to the diverse and variable diet of decapod larvae. 相似文献
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