20 research outputs found
Resource heterogeneity and community structure: A case study in Heliconia imbricata Phytotelmata
Complex or non-additive differences in the distribution and abundance of arthropod species inhabiting the water-filled bracts of Heliconia imbricata can be created by simple manipulations of resource levels. The primary resources for these assemblages are the corollas of the flowers that accumulate in the bracts. Removing or adding corollas to individual bracts changes the pattern in the abundance of arthropod species within each bract such that bracts with different treatments ultimately differ in composition and numerical associations among species. These results suggest that direct and indirect resource-mediated factors can structure or significantly affect the distribution and abundance of species in these and perhaps other assemblages. Thus, in natural communities, if resources are heterogeneous among patches (such as among the bracts in this study) structure in a given patch may be a function of the resource level of that patch and can differ significantly from neighboring patches that provide different resource levels.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47788/1/442_2004_Article_BF00665591.pd
Modelling and experimental studies on the transfer of radionuclides to fruit
Although fruit is an important component of the diet, the extent to which it contributes to radiological exposure remains unclear, partially as a consequence of uncertainties in models
and data used to assess transfer of radionuclides in the food chain. A Fruits Working Group operated as part of the IAEA BIOMASS (BIOsphere Modelling and ASSessment) programme from 1997 to 2000, with the aim of improving the robustness of the models that are used for radiological assessment. The Group completed a number of modelling and experimental activities including: (i) a review of experimental, field and modelling information on the
transfer of radionuclides to fruit; (ii) discussion of recently completed or ongoing experimental studies; (iii) development of a database on the transfer of radionuclides to fruit; (iv)
development of a conceptual model for fruit and (v) two model intercomparison studies and a model validation study. The Group achieved significant advances in understanding the processes involved in transfer of radionuclides to fruit. The work demonstrated that further
experimental and modelling studies are required to ensure that the current generation of models can be applied to a wide range of scenarios
Estimating the biological half-life for radionuclides in homoeothermic vertebrates: a simplified allometric approach
The application of allometric, or mass-dependent,
relationships within radioecology has increased with the
evolution of models to predict the exposure of organisms
other than man. Allometry presents a method of addressing
the lack of empirical data on radionuclide transfer and
metabolism for the many radionuclide–species combinations
which may need to be considered. However, sufficient data
across a range of species with different masses are required to
establish allometric relationships and this is not always
available. Here, an alternative allometric approach to predict
the biological half-life of radionuclides in homoeothermic
vertebrates which does not require such data is derived.
Biological half-life values are predicted for four radionuclides
and compared to available data for a range of species.
All predictions were within a factor of five of the observed
values when the model was parameterised appropriate to the
feeding strategy of each species. This is an encouraging level
of agreement given that the allometric models are intended to
provide broad approximations rather than exact values.
However, reasons why some radionuclides deviate from what
would be anticipated from Kleiber’s law need to be determined
to allow a more complete exploitation of the potential
of allometric extrapolation within radioecological models
Effects of terrestrial isopods on the decomposition of woodland leaf litter
The indirect contribution terrestrial isopods make to decomposition processes by stimulating microbial activites has been quantified in laboratory experiments. The extent to which microbial metabolism is enhanced as a result of the passage of Betula pendula leaf litter through the alimentary system of isopods was measured for both freshly fallen and decayed leaves. Faeces derived from 1 g freshly fallen litter lost 75 mg g-1 D.W. more than did intact leaves, as a result of enhanced microbial metabolism. Faeces derived from 1 g of previously decayed leaves, which were shown to be the preferred food of isopods, lost only 17.5 mg g-1 D.W. more than intact decaying leaves. The isopod's direct contribution to soil metabolism was calculated to be 151 mg and 138 mg g-1 litter ingested when fed on freshly fallen and decayed leaves respectively. It is concluded that the physical and chemical changes in the leaf substrate which result from fragmentation and digestion by isopods do not necessarily accelerate the subsequent decomposition of the litter very significantly. Fungal propagule density was 3.2x and 3.6x higher in faeces derived from freshly fallen and decayed leaves respectively than in the intact litter. Numbers of viable bacteria were correspondingly 126x and 34x higher in faeces than in the freshly fallen and the decayed leaves. Levels of microbial inhibitors were lower in the faeces than in the leaves but levels of free amino acids stayed higher for longer in the faeces than they did in intact litter. In the field the physical removal of litter by the soil macrofauna from surface to deeper and moister microsites may be the most important indirect contribution that they make to decomposition processes