Biomarkers and mechanisms of natural disease resistance in dairy cows
Altena, S.E.C. van - \ 2016
Wageningen University. Promotor(en): Huub Savelkoul, co-promotor(en): Edwin Tijhaar. - Wageningen : Wageningen University - ISBN 9789462578005 - 158
dairy cows - biomarkers - disease resistance - immunity - antibodies - proteomics - immune response - dendritic cells - immunology - melkkoeien - biomarkers - ziekteresistentie - immuniteit - antilichamen - eiwitexpressieanalyse - immuniteitsreactie - dendritische cellen - immunologie
The aim of this thesis was to define and test biomarkers for disease resistance in dairy cows and to determine the underlying mechanism in natural disease resistance. The health status of the cows is an important issue in dairy farming. Due to the mandatory reduction in the use of antibiotics, alternatives are required to prevent the development and expression of illness in dairy cows. The identification of biomarkers associated with such disease offers the opportunity to adapt the management of cows at risk, and in this way, prevent them from developing overt disease. Previously, natural antibodies (NAbs) in serum and milk were used as candidate biomarkers for natural disease resistance in cows. In this thesis, we continue on the occurrence and mode of action of NAbs and also focus on their source: the B-1 cells. We performed a literature study on the identification and function of B-1 cells in different species and defined the limitations in the current identification of these cells in pigs, sheep and cows (Chapter 2). B-1 cells were described in cows by using widely accepted cell surface markers CD5 and CD11b. However, in literature several findings suggest that these cell surface markers are not unique markers for B-1 identification. The similarities between mice and veterinary animals in foetal B-cell development and antibody production, implies that B-1 cells are present in cows. In chapter 3, we carefully studied new markers to selectively identify B-1 cells in cows. The combination of B-1 cell markers IgM++ and pSYK++ (indicator constitutive intracellular signalling) identifies a distinct cell population with essential B-1 characteristics such as high CD80 expression. In addition, the development of these B-1 cells in calves before colostrum intake and 3 weeks afterwards shows the same kinetics as the development of NAbs represented by IgM antibodies binding to the well-accepted NAb-antigen phosphatidylcholine (PtC). In calves up to half a year of age, it is shown that the production of such NAbs increases from birth and stabilises from 6 weeks onwards. This implies an endogenous NAb production, which follows the same age-related kinetics as can be expected from B-1 cell development. In contrast, the development of total IgM antibody levels in calves shows a bimodal distribution, which is caused by the uptake and breakdown of maternally-derived IgM and simultaneous endogenous production of specific and natural IgM. Chapter 4 describes the role of such NAbs in bovine immunity. NAbs were represented by the binding of IgM to the naïve antigen keyhole limpet hemocyanin (KLH). Cows with high serum NAb levels were shown to have more IgM and IgG antibodies binding to common microbial structures LPS, LTA and PGN, than cows with low serum NAb levels. In addition, they also have more IgM antibodies binding to intact, fixed E. coli and S. Typhimurium bacteria. However, the killing of live E. coli and S. Typhimurium bacteria via antibody-mediated complement killing does not differ between cows with high and low NAb levels. The antibody-mediated complement killing was determined in a newly developed serum bactericidal test. Cows that performed less in the bactericidal test were more likely to develop mastitis in the future. This association was observed for the killing of E. coli and S. Typhimurium and the development of mastitis within the next one year. For S. Typhimurium the association was still present for the cases of mastitis occurring within four years after testing. Alternative biomarkers for disease resistance in cows were defined in chapter 5 by using a contemporary proteomics approach. Milk samples from high and low disease resistant cows were selected from the “Resilient Cattle” (Weerbaar Vee) biobank. Comparing the spectrum of milk proteins of high and low disease-resistant cows showed potential candidate biomarkers that were elevated in the milk of low-resistant cows. Two candidate marker proteins were validated with ELISA in a new and larger group of high- and low-resistant cows. Lactoferrin (LF) levels were significantly increased in milk of low-resistant cows. In addition, LF levels in milk were associated with clinical manifestations of lameness and had a predictive value for subsequent culling.
In conclusion, we found that also in cows NAbs are produced by B-1 cells that can be identified based on the combined expression of cell surface IgM and internal pSYK. In addition, the frequency of these B-1 cells after birth follows a similar kinetics as described before in mice. These NAbs can be more precisely identified based on their PtC binding ability and their functional activity in a bactericidal test. However, the true predictive value of B-1 cells and NAbs for the health status and immunocompetence of dairy cattle remains to be established. Proteomics turned out to be a useful approach for identifying potential new biomarkers for health and disease in milk of cows. Application and further development of their predictive capacity is dependent on the availability of robust, sensitive and quantitative assays. This project was part of the “Resilient Cattle” project providing biological samples and essential data on the health status during respective lactation periods of individual dairy cows. The impact of this research now requires translation into management tools and principles for the individual farmer impacting on the overall health status and economic performance of his herd of dairy cattle.
The impact of bird herbivory on macrophytes and the resilience of the clear-water state in shallow lakes : a model study
Altena, Cassandra van; Bakker, Elisabeth S. ; Kuiper, Jan J. ; Mooij, Wolf M. - \ 2016
Hydrobiologia 777 (2016)1. - ISSN 0018-8158 - p. 197 - 207.
Alternative stable states - Ecosystem model - Eutrophication - Grazing - Top-down versus bottom-up control - Water quality management
Shallow lakes have the potential to switch between two alternative stable states: a clear macrophyte-dominated and a turbid phytoplankton-dominated state. Observational and experimental studies show that in some lakes herbivory by birds may severely decrease macrophyte biomass, while in other lakes, the removed biomass by herbivory is compensated by regrowth. These contradictory outcomes might arise because of interplay between top-down control by bird herbivory and bottom-up effects by nutrient loading on macrophytes. Here, we use the ecosystem model PCLake to study top-down and bottom-up control of macrophytes by coots and nutrient loading. Our model predicted that (1) herbivory by birds lowers the critical nutrient loading at which the regime shift occurs; (2) bird impact on macrophyte biomass through herbivory increases with nutrient loading; and (3) improved food quality enhances the impact of birds on macrophytes, thus decreasing the resilience of the clear-water state even further. The fact that bird herbivory can have a large impact on macrophyte biomass and can facilitate a regime shift implies that the presence of waterfowl should be taken into account in the estimation of critical nutrient loadings to be used in water quality management.
Searching for balance : stability and equilibria of food webs
Altena, C. van - \ 2016
Wageningen University. Promotor(en): Peter de Ruiter; J.A.P. Heesterbeek; Wolf Mooij, co-promotor(en): Lia Hemerik. - Wageningen : Wageningen University - ISBN 9789462576827 - 130
food webs - models - interactions - ecology - biocoenosis - ecological balance - voedselwebben - modellen - interacties - ecologie - biocenose - ecologisch evenwicht
How complexity of food webs relates to stability has been a subject of many studies. Often,
unweighted connectance is used to express complexity. Unweighted connectance is
measured as the proportion of realized links in the network. Weighted connectance, on the
other hand, takes link weights (fluxes or feeding rates) into account and captures the shape
of the flux distribution. Here, we used weighted connectance to revisit the relation between
complexity and stability. We used 15 real soil food webs and determined the feeding rates
and the interaction strength matrices. We calculated both versions of connectance, and
related these structural properties to food web stability. We also determined the skewness
of both flux and interaction strength distributions with the Gini coefficient. We found no
relation between unweighted connectance and food web stability, but weighted connectance
was positively correlated with stability. This finding challenges the notion that complexity
may constrain stability, and supports the ‘complexity begets stability’ notion. The positive
correlation between weighted connectance and stability implies that the more evenly flux
rates were distributed over links, the more stable the webs were. This was confirmed by the
Gini coefficients of both fluxes and interaction strengths. However, the most even
distributions of this dataset still were strongly skewed towards small fluxes or weak
interaction strengths. Thus, incorporating these distribution with many weak links via
weighted instead of unweighted food web measures can shed new light on classical
A proteomics-based identification of putative biomarkers for disease in bovine milk
Altena, S.E.C. van; Klerk, B. de; Hettinga, K.A. ; Neerven, R.J.J. van; Boeren, S. ; Savelkoul, H.F.J. ; Tijhaar, E.J. - \ 2016
Veterinary Immunology and Immunopathology 174 (2016). - ISSN 0165-2427 - p. 11 - 18.
Biomarker - Dairy cattle - Lactoferrin - Milk
The objective of this study was to identify and characterize potential biomarkers for disease resistance in bovine milk that can be used to indicate dairy cows at risk to develop future health problems. We selected high- and low-resistant cows i.e. cows that were less or more prone to develop diseases according to farmers' experience and notifications in the disease registration data. The protein composition of milk serum samples of these high- and low-resistant cows were compared using NanoLC-MS/MS. In total 78 proteins were identified and quantified of which 13 were significantly more abundant in low-resistant cows than high-resistant cows. Quantification of one of these proteins, lactoferrin (LF), by ELISA in a new and much larger set of full fat milk samples confirmed higher LF levels in low- versus high-resistant cows. These high- and low-resistant cows were selected based on comprehensive disease registration and milk recording data, and absence of disease for at least 4 weeks. Relating the experienced diseases to LF levels in milk showed that lameness was associated with higher LF levels in milk. Analysis of the prognostic value of LF showed that low-resistant cows with higher LF levels in milk had a higher risk of being culled within one year after testing than high-resistant cows. In conclusion, LF in milk are higher in low-resistant cows, are associated with lameness and may be a prognostic marker for risk of premature culling.
Bovine natural antibodies in antibody-dependent bactericidal activity against Escherichia coli and Salmonella Typhimurium and risk of mastitis
Altena, S.E.C. van; Peen, M.A. ; Linden, F.H. van der; Parmentier, H.K. ; Savelkoul, H.F.J. ; Tijhaar, E.J. - \ 2016
Veterinary Immunology and Immunopathology 171 (2016). - ISSN 0165-2427 - p. 21 - 27.
Antibody-mediated complement killing - Dairy cattle - Natural antibodies
Natural antibodies (NAbs) are mostly IgM antibodies produced without antigenic stimulation and serve as a first line of defence of the immune system. As both natural and specific antibodies are present in animals, NAbs are studied by determining the IgM response to naïve antigens like keyhole limpet hemocyanin (KLH). In this study, we selected cows based on high and low anti-KLH IgM titers, reflecting high and low NAb titers, and determined if the anti-KLH IgM titers were indicative for the recognition of common microbial structures (lipopolysaccharide, lipoteichoic acid and peptidoglycan) and intact bacteria (Escherichia coli and Salmonella Typhimurium). Sera with high NAbs titers showed more IgM and IgG binding to common microbial structures and S. Typhimurium bacteria than sera with low NAbs titers. The same association was observed for IgM binding to E. coli, but not for IgG binding to E. coli. Antibody-mediated complement killing of E. coli and S. Typhimurium in a newly developed bactericidal test was equal between high and low NAb cows. However, relating the outcome of the bactericidal test to the development of mastitis within one and even four years after sampling showed a significant negative correlation implying cows that were less potent in bacterial killing had a higher chance on developing mastitis. In conclusion, sera with high NAbs titers had more antibodies binding to common microbial structures and intact bacteria. Furthermore, the bactericidal test might provide a useful prognostic tool for the development of mastitis.
Food web stability and weighted connectance : the complexity-stability debate revisited
Altena, Cassandra van; Hemerik, Lia ; Ruiter, Peter C. de - \ 2016
Theoretical Ecology (2016). - ISSN 1874-1738 - p. 49 - 58.
Jacobian matrix - Link distribution - Weighted connectance
How the complexity of food webs relates to stability has been a subject of many studies. Often, unweighted connectance is used to express complexity. Unweighted connectance is measured as the proportion of realized links in the network. Weighted connectance, on the other hand, takes link weights (fluxes or feeding rates) into account and captures the shape of the flux distribution. Here, we used weighted connectance to revisit the relation between complexity and stability. We used 15 real soil food webs and determined the feeding rates and the interaction strength matrices. We calculated both versions of connectance, and related these structural properties to food web stability. We also determined the skewness of both flux and interaction strength distributions with the Gini coefficient. We found no relation between unweighted connectance and food web stability, but weighted connectance was positively correlated with stability. This finding challenges the notion that complexity may constrain stability, and supports the ‘complexity begets stability’ notion. The positive correlation between weighted connectance and stability implies that the more evenly flux rates were distributed over links, the more stable the webs were. This was confirmed by the Gini coefficients of both fluxes and interaction strengths. However, the most even distributions of this dataset still were strongly skewed towards small fluxes or weak interaction strengths. Thus, incorporating these distribution with many weak links via weighted instead of unweighted food web measures can shed new light on classical theories.
Patterns in intraspecific interaction strengths and the stability of food webs
Altena, C. van; Hemerik, L. ; Heesterbeek, J.A.P. ; Ruiter, P.C. de - \ 2016
Theoretical Ecology 9 (2016)1. - ISSN 1874-1738 - p. 95 - 106.
A common approach to analyse stability of biological communities is to calculate the interaction strength matrix. Problematic in this approach is defining intraspecific interaction strengths, represented by diagonal elements in the matrix, due to a lack of empirical data for these strengths. Theoretical studies have shown that an overall increase in these strengths enhances stability. However, the way in which the pattern in intraspecific interaction strengths, i.e. the variation in these strengths between species, influences stability has received little attention. We constructed interaction strength matrices for 11 real soil food webs in which four patterns for intraspecific interaction strengths were chosen, based on the ecological literature. These patterns included strengths that were (1) similar for all species, (2) trophic level dependent, (3) biomass dependent, or (4) death rate dependent. These four patterns were analysed for their influence on (1) ranking food webs by their stability and (2) the response in stability to variation of single interspecific interaction strengths. The first analysis showed that ranking the 11 food webs by their stability was not strongly influenced by the choice of diagonal pattern. In contrast, the second analysis showed that the response of food web stability to variation in single interspecific interaction strengths was sensitive to the choice of diagonal pattern. Notably, stability could increase using one pattern and decrease using another. This result asks for deliberate approaches to choose diagonal element values in order to make predictions on how particular species, interactions, or other food web parameters affect food web stability.
Rooting area and drinker affect dunging behaviour of organic pics
Vermeer, H.M. ; Altena, H. ; Vereijken, P.F.G. ; Bracke, M.B.M. - \ 2015
Applied Animal Behaviour Science 165 (2015). - ISSN 0168-1591 - p. 66 - 71.
Hygiene is a common problem on outdoor runs of growing organic pigs. Manure and urine are mainly excreted outdoors and tend to spread all over the run. Reducing the soiled surface area may be beneficial to animal welfare, hygiene, ammonia emissions and labour, not only in organic but also in conventional systems. The objective was to reduce the soiled surface area in the pen and to make the outdoor run more attractive for pigs. Introduction of a rooting area and drinker in the outdoor run was tested in a 2 × 2 factorial design. In total, four replicates were studied in a room with two rows of four pens containing 14 pigs each. More pigs went outdoors in pens with rooting area access than in pens without a rooting area (11.2 vs. 8.5%, P = 0.003). This was due to more pigs entering the rooting area and an adjacent slatted floor. Addition of a drinker did not attract more pigs outdoors (P = 0.53). The rooting area improved the cleanliness of the whole pen (P < 0.001). However, in some cases the rooting area was also used as a dunging area. The area around the additional outdoor drinker was cleaner, but on the whole, pens were dirtier (P = 0.011). Introduction of an outdoor drinker resulted in more indoor pen fouling, especially around the indoor drinker (P < 0.001). An outdoor rooting area makes the outdoor run more attractive for pigs and reduces the dunging area. This study contributes to the knowledge base on how to reduce the dunging surface in pens for organic pigs
|Identification of putative B1 B-cells in cows
Altena, S.E.C. van; Meijer, B. ; Savelkoul, H.F.J. ; Tijhaar, E.J. - \ 2015
- p. 82 - 82.
Food-web stability signals critical transitions in temperate shallow lakes
Kuiper, J.J. ; Altena, Cassandra Van; Ruiter, P.C. De; Gerven, L.P.A. Van; Janse, J.H. ; Mooij, W.M. - \ 2015
Nature Communications 6 (2015). - ISSN 2041-1723
A principal aim of ecologists is to identify critical levels of environmental change beyond which ecosystems undergo radical shifts in their functioning. Both food-web theory and alternative stable states theory provide fundamental clues to mechanisms conferring stability to natural systems. Yet, it is unclear how the concept of food-web stability is associated with the resilience of ecosystems susceptible to regime change. Here, we use a combination of food web and ecosystem modelling to show that impending catastrophic shifts in shallow lakes are preceded by a destabilizing reorganization of interaction strengths in the aquatic food web. Analysis of the intricate web of trophic interactions reveals that only few key interactions, involving zooplankton, diatoms and detritus, dictate the deterioration of food-web stability. Our study exposes a tight link between food-web dynamics and the dynamics of the whole ecosystem, implying that trophic organization may serve as an empirical indicator of ecosystem resilience.
|Identification of natural antibody producing B1 B-cells in cows
Altena, S.E.C. van - \ 2015
Biomarkers voor weerstand : Perspectief voor de toekomst
Altena, Christine van - \ 2015
|UVb radiation impacts vitamin D3 status but not growth in the nocturnal leopard gecko
Diehl, E. ; Oonincx, D.G.A.B. ; Kik, M.J.L. ; Baines, F.M. ; Hendriks, W.H. ; Bosch, G. - \ 2015
In: Proceedings of the 8th European Zoo Nutrition Conference. - - p. 37 - 37.
|Does foraging ecology of terrestrial carnivores impact digestive physiology and metabolism?
Bosch, G. ; Hendriks, W.H. - \ 2015
In: Proceedings of the 8th European Zoo Nutrition Conference. - - p. 23 - 23.
Maturation of the immune response
Altena, S.E.C. van; Meijer, B. ; Savelkoul, H.F.J. - \ 2014
In: Encyclopedia of Immunotoxicology / Vohr, H.W., Springer - ISBN 9783642277863 - p. 1 - 11.
The innate immune system depends on features like extracellular and intracellular pattern recognition receptors (PRR) that recognize general molecular patterns. Different types of PRR have been described, identifying microbe-, pathogen-, and danger-associated molecular patterns (abbreviated as MAMP, PAMP, and DAMP, respectively). PRR enhance ligation and phagocytosis of microbes or have signaling ability allowing activation of the cell. Ligation of extracellular toll-like receptors (TLR) by bacterial ligands like lipopolysaccharide (LPS) (binds to TLR4), peptidoglycan (PGN) (TLR2), and flagellin (TLR5) results in MyD88-dependent production of inflammatory cytokines like interleukin (IL)-1ß, IL-6, IL-8, and partly TNF-a. The expression of TLRs is vast as they are found on the cell membranes of innate immune cells (dendritic cell (DC), macrophages, natural killer cells), cells of the adaptive immunity (T and B lymphocytes), and nonimmune cells (epithelial and en ...
|Identification of putative B1 B-cells in cows
Altena, S.E.C. van; Meijer, B. ; Savelkoul, H.F.J. ; Tijhaar, E.J. - \ 2014
Natural antibodies (Nabs) are antibodies spontaneously produced by B1 B-cells, without prior antigenic stimulation and are considered part of the innate immune system. They are primarily of the IgM isotype and are often directed to conserved microbial components. In contrast, specific antibodies (Spabs) are produced by B2 B-cells that do need antigenic specific stimulation to induce antibody production. Nabs levels might be related with disease resistance in dairy cows. However, defining the exact contribution of natural and specific antibodies is difficult, because they cannot be easily discriminated in serum. We therefore tried to identify the Nabs-producing bovine B1 B-cells. This will enable us to determine the relationship of these cells with disease resistance of dairy cows. Peripheral blood mononuclear cells (PBMCs) of cows were tested by flow cytometry for markers and functional characteristics of B1 B cells, described earlier for B1 B cells in other species. The combination of one extracellular and one intracellular marker stained a population with characteristics of B1 B cells. Additionally experiments are performed on FACS sorted cells to confirm these results.
The mucosal factors retinoic acid and TGF-B induce phenotypically and functionally distinct dendritic cell types
Hartog, C.G. den; Altena, S.E.C. van; Savelkoul, H.F.J. ; Neerven, R.J.J. van - \ 2013
International Archives of Allergy and Immunology 162 (2013)3. - ISSN 1018-2438 - p. 225 - 236.
bronchial lymph-node - t-cells - tgf-beta - intestinal inflammation - vitamin-a - tolerance - generation - expression - responses - outcomes
Non-inflammatory dendritic cell (DC) subsets play an essential role in preventing massive inflammation in mucosal tissues. We investigated whether mucosa-related factors, namely retinoic acid (RA) and transforming growth factor-ß (TGF-ß1), can induce such DC types. DCs were differentiated from monocytes in the absence or presence TGF-ß1 and RA. The phenotype as well as responsiveness to bacterial ligands was studied in detail. Compared to monocyte-derived DCs (moDCs), the expression of co-stimulatory molecule CD86 and DC maturation marker CD83 were strongly reduced by RA and TGF-ß1. In addition, both RA- and TGF-ß1-induced DCs showed strongly decreased responsiveness to stimulation with the bacterial ligands lipopolysaccharide and peptidoglycan, and produced significantly lower levels of the pro-inflammatory cytokines IL-12 and TNF-a compared to moDCs, whilst IL-10 production was not significantly reduced. DCs differentiated under the influence of RA uniquely expressed markers related to intestinal homing (CD103 and integrin ß7). In addition, CCR7, which mediates homing to lymph nodes, was expressed by DCs differentiated in the presence of RA, and also to a lesser extent by the other DC types. Furthermore, whereas moDCs and TGF-ß1-derived moDCs expressed high levels of CD32, RA-derived DCs lacked CD32 expression but expressed high levels of CD64, suggesting that RA-DCs may primarily respond to soluble proteins and moDCs, and TGF-ß DCs to immune complexes. The data presented here support the hypothesis that the mucosal factors TGF-ß1 and RA, which can also be provided through dietary intake of dairy products, result in functionally and phenotypically distinct DC types with non-inflammatory properties.
Extraction efficiency of J2 of M. chitwoodi from roots and potato peels using the Seinhorst spray mist-chamber
Teklu, M.G. ; Been, T.H. ; Schomaker, C.H. ; Beniers, Annelies ; Altena, L. ; Beers, T.G. van; Boomsma, D. ; Molendijk, L.P.G. - \ 2013
Culicoides obsoletus extract relevant for diagnostics of insect bite hypersensitivity in horses
Meide, N.M.A. van der; Meulenbroeks, C. ; Altena, S.E.C. van; Schurink, A. ; Ducro, B.J. ; Wagner, B. ; Leibold, W. ; Rohwer, J. ; Jacobs, F. ; Sloet van Oldruitenborgh-Oosterbaan, M.M. ; Savelkoul, H.F.J. ; Tijhaar, E. - \ 2012
Veterinary Immunology and Immunopathology 149 (2012)3-4. - ISSN 0165-2427 - p. 245 - 254.
dermatitis sweet itch - dermal hypersensitivity - icelandic horses - british-columbia - summer eczema - equine ige - antibodies - ceratopogonidae - identification - netherlands
Insect bite hypersensitivity (IBH) is an allergic dermatitis in horses caused by the bites of Culicoides species. The aim of the present study was to evaluate the applicability of whole body extracts of C. obsoletus (the main species found feeding on horses in the Netherlands), C. nubeculosus (rarely found in The Netherlands) and C. sonorensis (typical for North America) for diagnosis of IBH in horses in The Netherlands. Blood and serum samples of 10 clinically confirmed IBH affected and 10 healthy control horses were used to evaluate the IgE titers (ELISA) against the Culicoides whole body extracts of the three Culicoides species. Basophil degranulation was assessed by histamine release test (HRT) after stimulation with these extracts at 5, 0.5 and 0.05 µg/ml. IBH affected horses had significantly higher IgE titers against C. obsoletus than against C. nubeculosus and C. sonorensis. Furthermore, C. obsoletus induced significantly higher histamine release in whole blood of IBH affected horses compared to the other extracts at 0.5 µg/ml. Western blot data revealed IgE binding to many proteins in C. obsoletus extract. This interaction was absent or weak in C. nubeculosus and C. sonorensis extracts for IBH affected horses. Results on individual level indicate that the HRT is more sensitive than ELISA in diagnosing IBH. However, ELISA is more practical as a routine test, therefore the ELISA was further evaluated using C. obsoletus extract on 103 IBH affected and 100 healthy horses, which resulted in a test sensitivity and specificity of 93.2% and 90.0%, respectively. The IgE ELISA readings enabled the analysis of the predicted probability of being IBH affected. From an optical density 450 nm value of 0.33 onwards, the probability of IBH affected was more than 0.9. The results presented in this paper show that the use of native Culicoides spp. that feed on horse, is important for improved diagnosis and that the described ELISA based on C. obsoletus can be used routinely to diagnose IBH in countries where this species is the main Culicoides feeding on horses
Species composition and fire: non-additive Mixture effects on ground fuel flammability.
Altena, C. ; Logtestijn, R.S.P. ; Cornwell, W.K. ; Cornelissen, J.H.C. - \ 2012
Frontiers in Plant Science 3 (2012). - ISSN 1664-462X - 10 p.
Diversity effects on many aspects of ecosystem function have been well documented. However, fire is an exception: fire experiments have mainly included single species, bulk litter, or vegetation, and, as such, the role of diversity as a determinant of flammability, a crucial aspect of ecosystem function, is poorly understood. This study is the first to experimentally test whether flammability characteristics of two-species mixtures are non-additive, i.e., differ from expected flammability based on the component species in monospecific fuel. In standardized fire experiments on ground fuels, including monospecific fuels and mixtures of five contrasting subarctic plant fuel types in a controlled laboratory environment, we measured flame speed, flame duration, and maximum temperature. Broadly half of the mixture combinations showed non-additive effects for these flammability indicators; these were mainly enhanced dominance effects for temporal dynamics – fire speed and duration. Fuel types with the more flammable value for a characteristic determined the rate of fire speed and duration of the whole mixture; in contrast, maximum temperature of the fire was determined by the biomass-weighted mean of the mixture. These results suggest that ecological invasions by highly flammable species may have effects on ground-fire dynamics well out of proportion to their biomass.