Measuring specialization in species interaction networks

Background  

Network analyses of plant-animal interactions hold valuable biological information. They are often used to quantify the degree of specialization between partners, but usually based on qualitative indices such as 'connectance' or number of links. These measures ignore interaction frequencies or sampling intensity, and strongly depend on network size.     

Modelling the impact of climate change on woody plant population dynamics in South African savanna

Background

In Southern Africa savannas climate change has been proposed to alter rainfall, the most important environmental driver for woody plants. Woody plants are a major component of savanna vegetation determining rangeland condition and biodiversity. In this study we use a spatially explicit, stochastic computer model to assess the impact of climate change on the population dynamics of Grewia flava, a common, fleshy-fruited shrub species in the southern Kalahari. Understanding the population dynamics of Grewia flava is a crucial task, because it is widely involved in the shrub/bush encroachment process, a major concern for rangeland management due to its adverse effect on livestock carrying capacity and biodiversity.

Results

For our study we consider four climate change scenarios that have been proposed for the southern Kalahari for the coming decades: (1) an increase in annual precipitation by 30–40%, (2) a decrease by 5–15%, (3) an increase in variation of extreme rainfall years by 10–20%, (4) and increase in temporal auto-correlation, i.e. increasing length and variation of periodic rainfall oscillations related to El Niño/La Niña phenomena. We evaluate the slope z of the time-shrub density relationship to quantify the population trend. For each climate change scenario we then compared the departure of z from typical stable population dynamics under current climatic conditions. Based on the simulation experiments we observed a positive population trend for scenario (1) and a negative trend for scenario (2). In terms of the projected rates of precipitation change for scenario (3) and (4) population dynamics were found to be relatively stable. However, for a larger increase in inter-annual variation or in temporal auto-correlation of rainfall population trends were negative, because favorable rainfall years had a limited positive impact due to the limited shrub carrying capacity.

Conclusions

We conclude that a possible increase in precipitation will strongly facilitate shrub encroachment threatening savanna rangeland conditions and regional biodiversity. Furthermore, the negative effects found for positive auto-correlated rainfall support current ecological theory stating that periodically fluctuating environments can reduce population viability because species suffer disproportionately from poor environmental conditions.     

Early detection of Verticillium wilt resistance in a potato breeding program

Nine potato clones/cultivars selected for varying degrees of Verticillium wilt (VW) resistance based on degree of vascular colonization, were intercrossed and outcrossed to 13 uncharacterized clones. Based on growth characteristics of 3,535 seedling transplants and an assay quantifyingV. dahliae in potato vascular tissue, 404 clones were selected for further tests. The average number ofVerticillium dahliae colony forming units (CFU) expressed as Log₁₀(CFU + l)/0.1 ml of plant sap for the 404 clones was 2.3, and 1.3 and 3.7 for resistant Reddale and susceptible Kennebec checks, respectively. Thirty-five clones (8.66%) had CFU values equal to or less than Reddale suggesting that VW resistance is a readily transmitted trait.     

A possible genetic source for chipping potatoes from 40 F storage

An interspecific hybrid ofS. phureja x USW1, a haploid of Katahdin, produced acceptable potato chips when processed directly from 40 F (4.5 C) storage during 3 years of testing. It was crossed with 11 interspecific hybrids. Tubers from these progenies were stored for 5 weeks at 40 F and then chipped immediately for 55 seconds in vegetable oil maintained at 375 F (190 C). Of 645 seedlings tested, chip color was acceptable in 17 and variable in 18. A group of 600 seedlings fromS. tuberosum parents treated comparably produced black-colored chips without exception.     

Der Baobab (Adansonia digitata L.): Wildobst aus Afrika für Deutschland und Europa?!

In Germany and Europe exotic fruits from distant places are becoming more and more important. In the tropics and subtropics an enormous variety of edible fruits exists. In 2008 the dry fruit pulp of the baobab (Adansonia digitata L.) was approved as novel food for the EU and thus entered the formal food market. Hence, an increasing number of products became available in Europe. The baobab is an impressive tree in the savannas of Africa. Due to its dense and wide spreading root system and its enormous water storing capacity in the stem, the tree can grow under very dry environmental conditions. In many regions of Africa it is a multipurpose indigenous fruit tree species which offers shelter and provides food, fodder and medicine as well as raw material for many purposes. However, even in Europe a wide range of products is now available as shown in the present study, which identified more than 300 baobab products or products with baobab as an ingredient. In Germany, not only the natural baobab pulp but also ready-made foodstuffs such as soft drinks, sandwich spreads, cereal bars, sweets and chocolates are available. Furthermore, a diverse range of pharmaceutical and cosmetic products with extracts from the baobab is available in the market. The products range from after shave and perfume to shampoo and shower gel to leg lotion and foot spray. In Germany baobab saplings and seeds are offered for planting and cultivation as an indoor pot plant. Commercially marketed baobab bonsai seedlings for the European market are produced in Senegal. In Africa the baobab fruits are mainly harvested from wild stands. However, the commercial production of baobab fruits in orchards could be an important future opportunity for income generation to many local households. More research on baobab, including the domestication of this wild fruit tree species, and the conservation of its natural stands as important genetic resource are prerequisites for sustainably increased fruit production.     

Detection of exotic QTLs controlling nitrogen stress tolerance among wild barley introgression lines

Nitrogen (N) is one of the most important plant nutrients, controlling growth and, ultimately, yield of a cultivar. Hordeum vulgare ssp. spontaneum, the wild barley progenitor of cultivated barley, is known to possess genes that can improve tolerance against biotic and abiotic stresses. A quantitative trait locus (QTL) study with two levels of N fertilization was conducted under glasshouse in order to locate wild barley alleles that improve N stress tolerance in the genetic background of an elite barley cultivar. For this, a set of 28 barley introgression lines (S42ILs), which originate from the cross ??Scarlett???×???ISR42-8??, was studied. The S42ILs, containing single or multiple wild barley introgressions, and ??Scarlett?? were evaluated in regard to a total of 15 traits, related to morphological parameters, grain parameters as well as to carbon (C) and N content parameters. A mixed model analysis and a subsequent Dunnett test was conducted to identify S42ILs that significantly deviate from the recurrent parent ??Scarlett??, either tested separately for each N level, or simultaneously across both N levels. In total, 65 QTLs were detected for the S42IL set. Most QTLs were found for chlorophyll content during heading (10 QTLs) and the fewest for C/N ratio of straw (1 QTL). The individual S42ILs possessed different numbers of QTLs. For S42IL-108, a maximum of eight QTLs were found whereas S42IL-145 did not show any significant difference from ??Scarlett??. Wild barley alleles revealed decreasing effects at 32 QTLs and increasing effects at 33 QTLs. Although 25 QTLs exhibited similar effects across both N levels, 18 and 22 QTLs exhibited effects that were only detected under N0 or N1, respectively. We, thus, conclude that it may be worth to select improved barley cultivars for N stress tolerance separately under low N fertilization, rather than extrapolating trait performances from experiments carried out under standard N fertilization conditions. A number of wild barley QTL alleles improved N stress tolerance. For example, a wild barley QTL allele on chromosome 4H, present in the Hsp introgression of S42IL-119, was associated with a 13.0?% increase of thousand grain weight across both N levels and a 20?% increase under low N supply. QTLs detected in the present study were compared with those of previous field studies of the same cross and with other QTL studies in barley and other small grains. Accordance between QTL studies (QTLs showing similar effects at the same map location) is documented and discussed. Based on our study, promising wild barley QTL alleles are available in S42ILs, which can be readily utilized to select for improved N use efficiency in barley breeding.     

Intestinal metabolism of two A-type procyanidins using the pig cecum model: detailed structure elucidation of unknown catabolites with Fourier transform mass spectrometry (FTMS)

Procyanidins, as important secondary plant metabolites in fruits, berries, and beverages such as cacao and tea, are supposed to have positive health impacts, although their bioavailability is yet not clear. One important aspect for bioavailability is intestinal metabolism. The investigation of the microbial catabolism of A-type procyanidins is of great importance due to their more complex structure in comparison to B-type procyanidins. A-type procyanidins exhibit an additional ether linkage between the flavan-3-ol monomers. In this study two A-type procyanidins, procyanidin A2 and cinnamtannin B1, were incubated in the pig cecum model to mimic the degradation caused by the microbiota. Both A-type procyanidins were degraded by the microbiota. Procyanidin A2 as a dimer was degraded by about 80% and cinnamtannin B1 as a trimer by about 40% within 8 h of incubation. Hydroxylated phenolic compounds were quantified as degradation products. In addition, two yet unknown catabolites were identified, and the structures were elucidated by Fourier transform mass spectrometry.     

Apigenin-induced suicidal erythrocyte death

Apigenin, a flavone in fruits and vegetables, stimulates apoptosis and thus counteracts cancerogenesis. Erythrocytes may similarly undergo suicidal cell death or eryptosis, characterized by cell shrinkage and phosphatidylserine exposure at the cell surface. Triggers of eryptosis include increase of cytosolic Ca(2+) activity ([Ca(2+)](i)), ceramide formation and ATP depletion. The present study explored the effect of apigenin on eryptosis. [Ca(2+)](i) was estimated from Fluo3-fluorescence, cell volume from forward scatter, phosphatidylserine exposure from annexin V binding, hemolysis from hemoglobin release, ceramide utilizing antibodies, and cytosolic ATP with luciferin-luciferase. A 48 h exposure to apigenin significantly increased [Ca(2+)](i) (≥ 1 μM), increased ceramide formation (15 μM), decreased ATP concentration (15 μM), decreased forward scatter (≥ 1 μM), and increased annexin V binding (≥ 5 μM) but did not significantly modify hemolysis. The effect of 15 μM apigenin on annexin V binding was blunted by Ca(2+) removal. The present observations reveal novel effects of apigenin, i.e. stimulation of Ca(2+) entry, ceramide formation and ATP depletion in erythrocytes with subsequent triggering of suicidal erythrocyte death, paralleled by cell shrinkage and phosphatidylserine exposure.     

Smart spatial incentives for market-based conservation

Market-based instruments such as payments, auctions or tradable permits have been proposed as flexible and cost-effective instruments for biodiversity conservation on private lands. Trading the service of conservation requires one to define a metric that determines the extent to which a conserved site adds to the regional conservation objective. Yet, while markets for conservation are widely discussed and increasingly applied, little research has been conducted on explicitly accounting for spatial ecological processes in the trading. In this paper, we use a coupled ecological-economic simulation model to examine how spatial connectivity may be considered in the financial incentives created by a market-based conservation scheme. Land use decisions, driven by changing conservation costs and the conservation market, are simulated by an agent-based model of land users. On top of that, a metapopulation model evaluates the conservational success of the market. We find that optimal spatial incentives for agents correlate with species characteristics such as the dispersal distance, but they also depend on the spatio-temporal distribution of conservation costs. We conclude that a combined analysis of ecological and socio-economic conditions should be applied when designing market instruments to protect biodiversity.     

Remaining questions in the case for balanced harvesting

Balanced harvesting – harvesting all species and sizes in an ecosystem in proportion to their productivity – is a fisheries management strategy that has been suggested recently to increase yields, while reducing overall ecosystem impact. However, some aspects of balanced harvesting are controversial, including its call for extensive harvesting of juveniles and forage fish. Balanced harvesting also calls for targeting species and size‐classes that are not currently marketable, possibly at a significant economic cost. Some have argued that this cost is outweighed by the ecological benefits of maintaining the ecosystem size and trophic structures and by the benefits of extra yield for food security. There is broad consensus that balanced harvesting would require major changes to fishery management institutions and consumer behaviour, and it is unclear to what extent it is physically possible with current technologies. For this reason, we argue that steps to implement balanced harvesting are difficult to justify until the case for it is more clearly resolved. We outline some of the pivotal questions that must be answered to make a convincing case for or against balanced harvesting, many of which can be answered empirically. In identifying these questions, we hope to offer a constructive path forward in resolving some of the key issues in the balanced harvesting debate.