دانلود ترجمه مقاله آنالیز ایزوتوپ پایدار برای پیش بینی کارایی های انتقال غذایی در شبکه غذایی

فهرست مطالب:

چکیده
مقدمه
مواد و روش ها
نتایج
بحث

بخشی از ترجمه:

آنالیز های اندازه محور را می توان با براورد های ایزوتوپ پایدار نیتروژن از سطح غذایی توسط نسبت وزن بدن ، نسبت وزن بدن شکار به شکارچی و نسبت متوسط تعداد گونه های شکار به شکارچی انجام داد.ما نشان دادیم که کارایی غذایی را می توان بدون براورد های انسبت اندازه و وزن بدن شکارچی به شکار براورد کرد و براورد های ما از کارایی غذایی مشابه با کارایی حاصله از مدل های اکوسیستم است((Christensen & Pauly 1993, Baumann 1995)).به علاوه رویکرد ما یک نسبت متوسط از وزن بدن شکارچی به شکار را به عنوان خروجی می دهد و این ها را می توان برای اعتبار سنجی نسبت های وزن بدن شکار چی به شکار پیش بینی شده از مطالعات رژیم غذایی مورد استفاده قرار داد(Hahm & Langton 1984, Jennings et al. 2001b).
آنالیز های ساختار و عملکرد اکوسیستم ها در بزرگ مقیاس به دلیل تفاوت در نمونه برداری، شناسایی مرز اکوسیستم ها، تعیین کمی مقدار تولید ورودی و خروجی و درک اثرات پیش بینی های لحاظ نشده در آنالیز ها سخت است( انسان، پرندگان دریایی پستانداران،Steele 1974, Mann & Lazier 1986, Sherman
& Alexander 1986, Bax 1991). رویکرد ما متکی به فرضیات تست نشده در خصوص کارایی نمونه برداری، از بین رفتن بیوماس و تولید ناشی از شیلات و میزان اثرات متقابل شکار و شکارچی در منطقه مورد مطالعه می باشد که مستقل از موارد دیده شده در خارج از منطقه و جز بندی است.براورد های کمی فراوانی بستکی به کارایی روش های نمونه برداری دارد و این کارایی برای بیشتر گونه ها شناخته نشده و و کلاس های اندازه ای در تورهای ماهیگیری مشخص نیست. این منجر به براورد های کم تر از مقدار واقعی و یا بیش تر از مقدار واقعی برای برخی کلاس های اندازه گونه ای می شود و از این رو اریبی در براورد های کارایی غذایی مشاهده خواهد شد. مدل های موجود گونه محور از نگرانی های مشابهی در خصوص براورد وفور برای گروه های جانوران باید با روش های مختلف نمونه برداری شود. عدم صید پذیری خوب و براورد های مربوط به بهترین روش های نمونه برداری می تواند موجب محدودیت در آنالیز اکوسیستم شود.

بخشی از مقاله انگلیسی:

INTRODUCTION The principle primary producers in marine ecosystems are small unicellular algae (Duarte & Cebrián 1996), and these support strongly size-structured foodchains where most predators are larger than their prey (Pope et al. 1994). Since many marine species will grow in mass by 5 or more orders of magnitude during their life cycle (Cushing 1975), and since cannibalism, cross-predation and transient predator-prey relationships are common (Pope et al. 1994, Boyle & Bolettzky 1996), there are compelling reasons to adopt size rather than species-based analyses of marine food webs (Sheldon et al. 1972, Kerr 1974). Body size determines potential predators and prey (Cohen et al. 1993), rates of production and natural increase (Banse & Moser 1980, Brey 1999), energy requirements (Boudreau et al. 1991) and vulnerability to mortality (Jennings et al. 1998). Biomass size-spectra (plots of biomass as log bodymass class vs log body-mass class) have been used to describe the structure of aquatic ecosystems (Sheldon et al. 1972, Kerr 1974, Pope et al. 1988, Duplisea & Kerr 1995, Rice & Gislason 1996), and models of these sizespectra assume that biomass and production decrease in progressively heavier body-mass classes due to the inefficient transfer of carbon from prey to predators (Dickie et al. 1987, Thiebaux & Dickie 1992). This implies that heavier size-classes are higher in the trophic continuum, a pattern demonstrated empirically for plankton (Fry & Quinones 1994), benthic invertebrate (France et al. 1998) and fish (Jennings et al. 2002) communities. The trophic continua across body sizeclasses also show that fixed (integer) trophic levels do not appropriately describe the structure of aquatic food webs, and trophic level can thus refer to any point on the continuum. Estimates of trophic transfer efficiency are needed to estimate unknown fluxes in production models, the potential yields of fisheries and the proportion of primary production required to sustain them (e.g. Pauly & Christensen 1995). Trophic transfer efficiency (TE) describes the proportion of prey production that is converted to predator production (TE = Pc/Pp, where Pc is predator production and Pp is prey production). Since body mass is correlated with specific production (Banse & Moser 1980), biomass size-spectra can be parameterised to give production by body-mass class (Platt & Denman 1978, Gaedke & Straile 1994, Duplisea & Kerr 1995). If mean predator-to-prey mass ratios can be estimated, then trophic transfer efficiency can be determined from the slope of the production size spectrum (e.g. Gaedke & Straile 1994). However, if trophic level at body mass is known, TE could be calculated without knowing the mean predator-prey body-mass ratio. This is because the slope of the relationship between trophic level and production at body size is the TE and the slope of the relationship between trophic level and body mass is the mean predator-prey body-mass ratio (as an output). Trophic level can be estimated using nitrogen stable isotope analysis (Owens 1987), because the abundance of δ۱۵N in the tissues of predators is enriched relative to their prey (Minagawa & Wada 1984, Peterson & Fry 1987, Cabana & Rasmussen 1996, Post et al. 2000, Post 2002). Indeed, Fry & Quinones (1994), France et al. (1998) and Jennings et al. (2002) have already used nitrogen stable isotope analysis to show that the trophic levels of plankton, invertebrates and fishes in biomass size-spectra increase continuously with increasing body size. Nitrogen stable isotope analysis is preferable to diet analysis for estimating trophic levels in many marine food webs because most species switch their diet frequently, prey on species that are digested at different rates, have gut contents that cannot be identified, or regurgitate gut contents on capture (Staniland et al. 2001, Polunin & Pinnegar 2002). The abundance of δ۱۵N reflects the composition of the assimilated diet and integrates differences in assimilated diet over time (Minagawa & Wada 1984, Hobson & Welch 1992, Post 2002). Broadly constant ratios of the number of predator to prey species may be a general property of parts of some food webs (Briand & Cohen 1984, Jeffries & Lawton 1985). While such ratios cannot be determined accurately in food webs with taxonomic aggregation (Pimm 1982, Link 2002), ratios have been determined from species lists and knowledge of diet (Jeffries & Lawton 1985). In freshwater communities, these ratios range from 0.48 in species-poor collections to 0.29 in species-rich collections, with a mean of 0.36 (Jeffries & Lawton 1985). If relationships between body size, diversity and trophic structure can be described, then the slope of the relationship between trophic level and species richness at a given body size is the ratio of the mean number of predator to prey species. In a previous paper, we used isotope analyses and size-spectra to describe trophic relationships within and among species and to describe the relationship between the size and trophic structure of a benthic fish and invertebrate community (Jennings et al. 2002). However, in this analysis, it was not possible to consider all pathways of energy flow through the food web, since some species of infauna and pelagic fish that interact with the benthic community, and contribute to production, were excluded. Here, we extend the population- and community-based approaches of Jennings et al. (2002) to the ecosystem, and quantify the abundance, diversity and δ۱۵N of all major groups of animals within a defined size range. We use these new data to integrate size-based production, diversity and stable isotope analyses and to establish relationships between production, diversity and trophic structure. We show that estimates of TE and predator-prey mass ratios derived from size-based analyses are comparable with those based on more data-intensive methods.