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Effects of patch connectivity and heterogeneity on metacommunity structure of planktonic bacteria and viruses
No full textDispersal limitation is generally considered to have little influence on the spatial structure of biodiversity in microbial metacommunities. This notion derives mainly from the analysis of spatial patterns in the field, but experimental tests of dispersal limitation using natural communities are rare for prokaryotes and, to our knowledge, non-existent for viruses. We studied the effects of dispersal intensity (three levels) and patch heterogeneity (two levels) on the structure of replicate experimental metacommunities of bacteria and viruses using outdoor mesocosms with plankton communities from natural ponds and lakes. Low levels of dispersal resulted in a decrease in the compositional differences (beta diversity) among the communities of both bacteria and viruses, but we found no effects of patch heterogeneity. The reductions in beta diversity are unlikely to be a result of mass effects and only partly explained by indirect dispersal-mediated interactions with phytoplankton and zooplankton. Our results suggest that even a very limited exchange among local communities can alter the trajectory of bacterial and viral communities at small temporal and spatial scales.
Faltering lemming cycles reduce productivity and population size of a migratory Arctic goose species
No full text1. The huge changes in population sizes of Arctic-nesting geese offer a great opportunity to
study population limitation in migratory animals. In geese, population limitation seems to have
shifted from wintering to summering grounds. There, in the Arctic, climate is rapidly changing,
and this may impact reproductive performance, and perhaps population size of geese, both
directly (e.g. by changes in snow melt) or indirectly (e.g. by changes in trophic interactions).
2. Dark-bellied brent geese (Branta bernicla bernicla L.) increased 20-fold since the 1950s. Its
reproduction fluctuates strongly in concert with the 3-year lemming cycle. An earlier analysis,
covering the growth period until 1988, did not find evidence for density dependence, but thereafter
the population levelled off and even decreased. The question is whether this is caused by
changes in lemming cycles, population density or other factors like carry-over effects.
3. Breeding success was derived from proportions of juveniles. We used an information-theoretical
approach to investigate which environmental factors best explained the variation in
breeding success over nearly 50 years (1960–2008). We subsequently combined GLM predictions
of breeding success with published survival estimates to project the population trajectory
since 1991 (year of maximum population size). In this way, we separated the effects of lemming
abundance and population density on population development.
4. Breeding success was mainly dependent on lemming abundance, the onset of spring at the
breeding grounds, and the population size of brent goose. No evidence was found for carryover
effects (i.e. effects of conditions at main spring staging site). Negative density dependence
was operating at a population size above c. 200 000 individuals, but the levelling off of
the population could be explained by faltering lemming cycles alone.
5. Lemmings have long been known to affect population productivity of Arctic-nesting
migratory birds and, more recently, possibly population dynamics of resident bird species,
but this is the first evidence for effects of lemming abundance on population size of a migratory
bird species. Why lemming cycles are faltering in the last two decades is unclear, but this
may be associated with changes in winter climate at Taimyr Peninsula (Siberia).
Testing the Australian Weed Risk Assessment with different proxies for invasiveness
No full textThe Weed Risk Assessment (WRA) has become an effective tool in predicting invasiveness of exotic plant species. In studies testing the WRA, exotic plant species are usually divided into major weeds, minor weeds and non-weeds. However, these divisions are qualitative, as the categories are assigned by experts. Many studies searching for plant traits that are indicative of plant invasiveness use quantitative estimates to measure invasiveness. We compared how quantitative and qualitative estimates of invasiveness may relate to WRA scores. As quantitative estimates we used regional frequency (spread), change in regional frequency and local dominance of naturalized exotic plant species in The Netherlands. To obtain a qualitative estimate we determined if the exotic plant species occurred on a black list in neighbouring regions. We related WRA scores of the exotic plant species to these qualitative and quantitative estimates of invasiveness. Our results reveal that the WRA predicted the qualitative (black list) estimate more accurately than the quantitative (dominance and spread) ones. The black list estimate matches with the overall impact of exotic species, which is assumed to incorporate regional spread, local dominance and noxiousness. Therefore, the WRA predicts the noxiousness component, but to a lesser extent the spatial components of impact of exotic species. On the other hand, studies that use regional spread and other quantitative estimates of invasiveness tend not to include the noxiousness component of impact. We propose that our analyses may also help to further solve the recent debate on whether or not performing research on exotic species.
Dog Poisonings Associated with a Microcystis aeruginosa Bloom in the Netherlands
No full textIn early autumn 2011, three dogs died after they had been exposed to a Microcystis aeruginosa bloom on Lake Amstelmeer, The Netherlands. The cyanobacterial scum from the lake contained up to 5.27 x 10(3) mu g g(-1) dry-weight microcystin, the vomit of one of the dogs contained on average 94 mu g microcystin g(-1) dry-weight. In both cases, microcystin-LR was the most abundant variant. This is the first report of dog deaths associated with a Microcystis bloom and microcystin poisoning in The Netherlands. [KEYWORDS: bathing water cyanobacterial scum cyanotoxins microcystin LC-MS/MS swimming ban blue-green-algae cyanobacterial toxins 1st report benthic cyanobacteria anatoxin-a lake neurotoxicosis diversity identification heptapeptides]
The way forward in soil biochar research: targeting trade-offs between the potential wins
No full textBiochar application to soil is currently widely advocated for a variety of reasons related to sustainability. Typically, soil amelioration with biochar is presented as a multiple-‘win’ strategy, although it is also associated with potential risks such as environmental contamination. The most often claimed benefits of biochar (i.e. the ‘wins’) include (i) carbon sequestration; (ii) soil fertility enhancement; (iii) biofuel/bioenergy production; (iv) pollutant immobilization; and (v) waste disposal. However, the vast majority of studies ignore possible trade-offs between them. For example, there is an obvious trade-off between maximizing biofuel production and maximizing biochar production. Also, relatively little attention has been paid to mechanisms, as opposed to systems impacts, behind observed biochar effects, often leaving open the question as to whether they reflect truly unique properties of biochar as opposed to being simply the short-term consequences of a fertilization or liming effect. Here, we provide an outline for the future of soil biochar research. We first identify possible trade-offs between the potential benefits. Second, to be able to better understand and quantify these trade-offs, we propose guidelines for robust experimental design and selection of appropriate controls that allow both mechanistic and systems assessment of biochar effects and trade-offs between the wins. Third, we offer a conceptual framework to guide future experiments and suggest guidelines for the standardized reporting of biochar experiments to allow effective between-site comparisons to quantify trade-offs. Such a mechanistic and systems framework is required to allow effective comparisons between experiments, across scales and locations, to guide policy and recommendations concerning biochar application to soil.