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Persistence of aquatic insects across managed landscapes: effects of landscape permeability on re-colonization and population recovery
No full textHuman practices in managed landscapes may often adversely affect aquatic biota, such as aquatic insects. Dispersal is often the limiting factor for successful re-colonization and recovery of stressed habitats. Therefore, in this study, we evaluated the effects of landscape permeability, assuming a combination of riparian vegetation (edge permeability) and other vegetation (landscape matrix permeability), and distance between waterbodies on the colonization and recovery potential of weakly flying insects. For this purpose, we developed two models, a movement and a population model of the non-biting midge, Chironomus riparius, an aquatic insect with weak flying abilities. With the movement model we predicted the outcome of dispersal in a landscape with several linear water bodies (ditches) under different assumptions regarding landscape-dependent movement. Output from the movement model constituted the probabilities of encountering another ditch and of staying in the natal ditch or perishing in the landscape matrix, and was used in the second model. With this individual-based model of midge populations, we assessed the implications for population persistence and for recovery potential after an extreme stress event. We showed that a combination of landscape attributes from the movement model determines the fate of dispersing individuals and, once extrapolated to the population level, has a big impact on the persistence and recovery of populations. Population persistence benefited from low edge permeability as it reduced the dispersal mortality which was the main factor determining population persistence and viability. However, population recovery benefited from higher edge permeability, but this was conditional on the low effective distance that ensured fewer losses in the landscape matrix. We discuss these findings with respect to possible landscape management scenarios.
An integrated perspective to explain nitrogen mineralization in grazed ecosystems
No full textLarge herbivores are key drivers of nutrient cycling in ecosystems worldwide, and hence they have an important influence on the productivity and species composition in plant communities. Classical theories describe that large herbivores can accelerate or decelerate nitrogen (N) mineralization by altering the quality and quantity of resource input (e.g. dung, urine, plant litter) into the soil food web. However, in many situations the impact of herbivores on N mineralization cannot be explained by changes in resource quality and quantity.
In this paper, we aim to reconcile observations of herbivores on N mineralization that were previously regarded as contradictory. We conceptually integrate alternative pathways via which herbivores can alter N mineralization. We illustrate our new integrated perspective by using herbivore-induced soil compaction and subsequent changes in soil moisture and soil aeration as an example.
We show that the net effect of herbivores on mineralization depends on the balance between herbivore-induced changes in soil physical properties and changes in the quality and quantity of resource input into the soil food web. For example, soil compaction by herbivores can limit oxygen or water availability in wet and dry soils respectively, particularly those with a fine texture. This can result in a reduction in N mineralization regardless of changes in resource quality or quantity. In such systems the plant community will shift towards species that are adapted to waterlogging (anoxia) or drought, respectively. In contrast, soils with intermediate moisture levels are less sensitive to compaction. In these soils, N mineralization rates are primarily associated with changes in resource quality and quantity.
We conclude that our integrated perspective will help us to better understand when herbivores accelerate or decelerate soil nutrient cycling and improve our understanding of the functioning of grazed ecosystems
Does microbial stoichiometry modulate eutrophication of aquatic ecosystems?
No full textThe stoichiometry of prokaryotes (Bacteria and Archaea) can control benthic phosphorus (P) fluxes relative to carbon (C) and nitrogen (N) during organic matter remineralization. This paper presents the first experimental data on benthic microbial stoichiometry. We used X-ray microanalysis to determine C:N:P ratios of individual prokaryotes from C-limited Baltic Sea sediments incubated under oxic or anoxic conditions. At approximately 400:1, C:P ratios of prokaryotes from both oxic and anoxic incubations were higher than the Redfield ratio for marine organic matter (106:1), whereas prokaryotic C:N ratios (6.4:1) were close to the Redfield ratio. We conclude that high microbial C:P ratios contribute to the enhanced remineralization of P from organic matter relative to C and N observed in many low oxygen marine settings.
Effect of the aerenchymatous helophyte Glyceria maxima on the sulfate-reducing communities in two contrasting riparian grassland soils
No full textAims
The research aimed at studying the effect of flooding with sulfate-rich water on the activity, abundance and diversity of sulfate-reducing micro-organisms present in the root zone of an oxygen-releasing plant growing on two riparian grassland soils with contrasting amounts of iron.
Methods
A series of microcosms was used to investigate the effects. Plants were grown under controlled conditions in microcosms containing a rhizosphere and bulk soil compartment for a period of 12 weeks in the presence of sulfate-rich flood water. Molybdate-treated systems served as non-sulfate-reducing controls.
Results
At harvest, activity and numbers of sulfate-reducing micro-organisms were higher in the absence of molybdate, but a rhizosphere effect and an impact of the presence of high levels of iron were not observed on activity and numbers. Both soils had in common a diverse community of sulfate-reducing micro-organisms covering all major cultured bacterial taxa. The appearance of members of the Desulfovibrionaceae exclusively in the rhizosphere of G. maxima was the only unambiguous indication of a plant effect.
Conclusion
The presence of sulfate-rich flood water stimulated the activity and growth of a part of the sulfate-reducing community leading to a change in community composition. The proximity of aerenchymatous plant roots and the abundance of iron in the soil had a negligible effect on the sulfate-reducing community.
Nutrient amendment does not increase mineralisation of sequestered carbon during incubation of a nitrogen-limited mangrove soil
No full text
Introduction
Get PDFThis chapter will motivate why it is useful to consider the topic of derivations
and filtering in more detail. We will argue against the popular belief that
the minimalist program and optimality theory are incompatible theories in that the
former places the explanatory burden on the generative device (the computational
system) whereas the latter places it on the fi ltering device (the OT evaluator).
Although this belief may be correct in as far as it describes existing tendencies,
we will argue that minimalist and optimality theoretic approaches normally adopt
more or less the same global architecture of grammar: both assume that a generator
defines a set S of potentially well-formed expressions that can be generated on the
basis of a given input and that there is an evaluator that selects the expressions from
S that are actually grammatical in a given language L. For this reason, we believe
that it has a high priority to investigate the role of the two components in more detail
in the hope that this will provide a better understanding of the differences and similarities
between the two approaches. We will conclude this introduction with a brief
review of the studies collected in this book.
Great tits provided with ad libitum food lay larger eggs when exposed to colder temperatures
No full textThe amount of nutrients deposited into a bird egg varies both between and within clutches of the same female. Larger
eggs enhance offspring traits, but as a tradeoff, laying large eggs also infers energetic costs to the female. Income breeders
usually lay larger eggs later in the season, when temperatures and food availability are higher. Egg size is thus affected
by the daily amount of energy available to produce an egg under cold conditions, but it is less well known in how far
temperature exerts direct effects on egg size. We show that great tit females Parus major with access to ad libitum food
and breeding in climate-controlled aviaries varied their egg investments. The size of an individual egg was best predicted
by mean temperatures one week pre-laying, with females laying larger, rather than smaller, eggs under colder conditions.
Eggs increased in size over the season, but not significantly over the laying sequence. The degree of daily temperature
fluctuation did not influence egg size. In addition to a substantial between-female variation, sisters were more similar to
each other than unrelated females, showing that egg size does also reflect heritable intrinsic female properties. Natural
variation in egg size is thus not only determined by energy-limitation, but also due to females allocating more resources
to eggs laid in colder environments, thus increasing early survival of the chicks. That the positive correlation between
temperature and egg investments that is found in a natural population is reversed under ad libitum food conditions
demonstrates that wild great tits tradeoff own condition with survival prospects of their chicks as a function of available
food, not ambient temperature.
