Habitat structure

Physical features of the landscape may directly or indirectly influence effective resource distribution (e.g. Passiflora plants grow on earthen mounds in disturbed 

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Tybirk ef al. (2004) state that minimum standards on the extent of uncultivated areas should rather be implemented at the landscape level, where due consideration of landform and habitat structure could be taken. 

However, this does not answer the question of whether microcosms and meso-cosms are protective of the diversity of water bodies in the field. To answer this question, it would be necessary to relate biological monitoring data (e.g., population abundances, community structure) to chemical monitoring data. Due to the fact that in the field a number of factors might affect populations and communities (e.g., habitat structure, nutrient levels, other chemicals), it is important to find data sets that allow quantification of the effect of 1 specific substance. 

Indirect effect An effect resulting from the action of an agent on components of the ecosystem, which in turn affect the assessment endpoint or other ecological components of interest. Indirect effects of chemical contaminants include reduced abundance due to toxic effects on food species or on plants that provide habitat structure. See also direct effect. 

During stressor characterization, one considers not only the primary stressor but also secondary stressors that can arise as a result of various processes. For example, removal of riparian (stream-side) vegetation not only alters habitat structure directly, but can have additional ramifications such as increased siltation and temperature rise. For chemicals, secondary stressors can be produced by a range of environmental fate processes. 

In contrast, benthic community structure and processes in the NEPAP region are likely to be both extremely sensitive to, and have very little resistance to, physical perturbations (e.g. mining disturbance). This is because the natural ecosystem is relatively very stable (compared to virtually all other ecosystems), most animals are small and/or very delicately constructed, and critical habitat structure for the entire benthic fauna is concentrated within a few centimeters of the sediment-water interface. Thus, it would require very little physical energy to disrupt the animals and the thin veneer of surface sediments that define this ecosystem. The extremely low sediment accumulation rates, biotur-bation rates, nodule growth rates and macrofaunal recolonization rates of the NEPAP seafloor ecosystem, compared to other seafloor habitats (Smith Demopoulos, 2003), suggest that recovery from physical disturbance is likely to be extremely slow relative to other ecosystems. 

Rocha, P.L.B., Queiroz, L.R, and Pirani, J.R., Plant species and habitat structure in a sand dime field in the Brazilian caatinga a homogeneous habitat harbouring an endemic biota. Rev. Bras. Bot., 27,739,2004. 

Desjardine, X, Pereira, A., Wright, H., Matainaho, T, Kelly, M and Andersen, XJ. (2007) Taiiramamide, aUpopeptide antibiotic produced in culture by BrenbaciUus laterosporus isolated from a marine habitat structure elucidation and synthesis./. Nat. Prod., 70,1850-153. 

Responses of Aquatic Organisms. The interactions between aquatic organisms and the chemistry of their water habitats are extremely complex. If a species or a group of species increases or declines in numbers in response to acidification, then the biological structure of the entire water body is likely to be affected. Reactions of organisms to stress such as acidification can be termed a "dose-response" reaction (i.e. a certain dose of acidifying pollutant induces a certain response). 

The evolution of structures and mechanisms in plants to regulate water fluxes down these steep thermodynamic gradients and yet maintain the cellular conditions for biochemical activity was a major factor in the colonisation of the terrestrial habitat. Paradoxically, therefore, some water stress is completely normal , though some plants are better than others at accommodating large deviations. 

The morphological and physiological dissimilarities between mycorrhizal symbi-o.ses probably determine their success and their distinct patterns in different ecosystems (92). Nitrogen (N) available to both AM and ectomycorrhizal plants should not be regarded as a single pool open to free competition. Specialization of its acquisition and utilization in a given habitat is an important feature of plant and microbial community structure, while the fact that the ability to exploit its sources (and tho.se of other limited nutrients) is not the same in all species may result in niche differentiation (93). If habitat specialization is a reflection of differences between mycorrhizal types, ectomycorrhizal and AM species could cooccur because they exploit different niches in the. same ecosystem. 

Fattorusso s group, which earlier had discovered 48-50 in Axinella cannabina, reported the occurrence of another spiroaxane series, 51 and 52, from Acanthella acuta. The habitat of the latter sponge is the Bay of Naples. As was the case with other metabolites reported in their recent studies, the investigators deduced the structures of isonitrile 51 and iso thiocyanate 52 chiefly by 2D NMR methods. 

Marine mammals have adapted to an aquatic or semi-aquatic lifestyle with such features as reduced or eliminated limb structures, a blubber layer for thermoregulatory, nutritional, buoyancy and locomotory roles, and reproductive strategies conducive to fitness in a given biogeographic zone (habitat). The environmental challenges faced by newborn marine mammals at birth may explain there largely precocious nature and the apparent maturity of the immune system of newborn marine mammals [1],... 

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