Large-scale land acquisitions aggravate the feminization of poverty - findings from a case study in MozambiqueMer info
GeoJournal 2018, : 1-22.
The local implications of large-scale land acquisitions (LSLAs), commonly referred to as land grabs, are at the center of an exponential production of scientific literature that only seldom focuses on gender. Our case study aims to contribute to filling this analytical gap. Based on structured interviews and focus groups, we investigate local experiences in the lower Limpopo valley in Mozambique, where a Chinese investor was granted 20,000 hectares in 2012. Our findings show that land access in the affected area varied prior to land seizure due to historical land use differences and after land seizure mainly due to non-universal compensation. Furthermore, we show that as farming conditions deteriorate, a trend toward both the feminization of smallholder farming and the feminization of poverty is consolidated. Succinctly, as available land becomes increasingly constricted, labor is allocated differently to alternative activities. This process is by no means random or uniform among households, particularly in a context in which women prevail in farm activities and men prevail in off-farm work. As men disengage further from smallholder farming, women remain directly dependent on fields that are smaller and of worse quality or reliant on precarious day labor in the remaining farms. We contend that the categories female-headed and male-headed households, although not inviolable, are useful in explaining the different implications of LSLAs in areas in which gender strongly substantiates individuals’ livelihood alternatives. © 2018 The Author(s)
Land Concessions and Rural Livelihoods in Mozambique - The Gap Between Anticipated and Real Benefits of a Chinese Investment in the Limpopo ValleyMer info
Journal of Southern African Studies 2017, 43 (6): 1181-1198.
In rural Mozambique, as in other African countries, large-scale land acquisitions are on the rise. This process is usually portrayed by host governments and investors as comprising win–win deals that can simultaneously boost agricultural productivity and combat poverty. This article focuses on one such investment, a large-scale Chinese land acquisition in the lower Limpopo valley, where attempts to modernise agriculture have occurred since colonial times. Based on an analysis of primary quantitative and qualitative data, this study explores livelihoods in the targeted area and local experiences and views regarding land loss and its implications. Our findings reveal a top-down process enabled by disregard for sound legislation, whereby land dispossession was followed by ‘take-it-or-leave-it’ opportunities that were unsuited to the most land-dependent livelihoods, particularly those of single-headed households. As the modernisation of the region is once again attempted through the promotion of large-scale agriculture, important historical continuities prevail. This study adds critical evidence to the discussion on the local development potential of land deals in Mozambique and other areas marked by similar democratic deficits.
Environmental Impacts of Rural Landscape Change During the Post-Communist Period in the Baltic Sea Region Mer info
The relationship between landscape configuration and plant species richness in forests is dependent on habitat p... Mer info
European Journal of Forest Research 2016, 135 (6): 1071-1082.
To assess the effects of landscape configuration on local plant species richness, we tested whether local species richness of forest understory plants is affected by the total forest area and forest edge length in the adjacent landscape. We also tested whether the landscape effect on species richness is different for forest and edge species. We estimated species richness from 113 forest sites in four regions in Northern Europe. At each site, we studied two plots, one at the edge and one in the core of the forest. Total forested area and forest edge length in circles with a 1-km radius, together with plot-specific variables of environmental conditions and temporal continuity of forests, were recorded at each plot. The amount of forest and the length of the forest edge in the adjacent landscape had a significant positive effect on local species richness of all understory plant species. As expected, edge species were positively affected by increasing length of the forest edge in the landscape, but surprisingly there was no effect of forest area on species richness of forest species. Temporal forest continuity had a negative effect on species richness of edge species but no effect on species richness of forest species. Our results suggest that forest edge length had a stronger landscape effect on understory plant species richness than forest area. Implications of these findings for the management of forest landscapes depend on priorities given to different species groups in biodiversity conservation, i.e. if emphasis is in total species richness or species richness of forest or edge species.
Forest succession and population viability of grassland plants - long repayment of extinction debt in Primula veris.Mer info
Oecologia 2016, 181 (1): 125-135.
Time lags in responses of organisms to deteriorating environmental conditions delay population declines and extinctions. We examined how local processes at the population level contribute to extinction debt, and how cycles of habitat deterioration and recovery may delay extinction. We carried out a demographic analysis of the fate of the grassland perennial Primula veris after the cessation of grassland management, where we used either a unidirectional succession model for forest habitat or a rotation model with a period of forest growth followed by a clear-cut and a new successional cycle. The simulations indicated that P. veris populations may have an extinction time of decades to centuries after a detrimental management change. A survey of the current incidence and abundance of P. veris in sites with different histories of afforestation confirmed the simulation results of low extinction rates. P. veris had reduced incidence and abundance only at sites with at least 100 years of forest cover. Time to extinction in simulations was dependent on the duration of the periods with favourable and unfavourable conditions after management cessation, and the population sizes and growth rates in these periods. Our results thus suggest that the ability of a species to survive is a complex function of disturbance regimes, rates of successional change, and the demographic response to environmental changes. Detailed demographic studies over entire successional cycles are therefore essential to identify the environmental conditions that enable long-term persistence and to design management for species experiencing extinction debts.
Trophic transfer of naturally produced brominated aromatic compounds in a Baltic Sea food chain Mer info
Chemosphere 2016, 144 : 1597-1604.
Brominated aromatic compounds (BACs) are widely distributed in the marine environment. Some of these compounds are highly toxic, such as certain hydroxylated polybrominated diphenyl ethers (OH-PBDEs). In addition to anthropogenic emissions through use of BACs as e.g. flame retardants, BACs are natural products formed by marine organisms such as algae, sponges, and cyanobacteria. Little is known of the transfer of BACs from natural producers and further up in the trophic food chain. In this study it was observed that total sum of methoxylated polybrominated diphenyl ethers (MeO-PBDEs) and OH-PBDEs increased in concentration from the filamentous red alga Ceramium tenuicorne, via Gammarus sp. and three-spined stickleback (Gasterosteus aculeatus) to perch (Perca fluviatilis). The MeO-PBDEs, which were expected to bioaccumulate, increased in concentration accordingly up to perch, where the levels suddenly dropped dramatically. The opposite pattern was observed for OH-PBDEs, where the concentration exhibited a general trend of decline up the food web, but increased in perch, indicating metabolic demethylation of MeO-PBDEs. Debromination was also indicated to occur when progressing through the food chain resulting in high levels of tetra-brominated MeO-PBDE and OH-PBDE congeners in fish, while some penta- and hexa-brominated congeners were observed to be the dominant products in the alga. As it has been shown that OH-PBDEs are potent disruptors of oxidative phosphorylation and that mixtures of different congener may act synergistically in terms of this toxic mode of action, the high levels of OH-PBDEs detected in perch in this study warrants further investigation into potential effects of these compounds on Baltic wildlife, and monitoring of their levels.
Tolerance to apical and leaf damage of Raphanus raphanistrum in different competitive regimes Mer info
Ecology and Evolution 2015, 5 (22): 5193-5202.
Tolerance to herbivory is an adaptation that promotes regrowth and maintains fitness in plants after herbivore damage. Here, we hypothesized that the effect of competition on tolerance can be different for different genotypes within a species and we tested how tolerance is affected by competitive regime and damage type. We inflicted apical or leaf damage in siblings of 29 families of an annual plant Raphanus raphanistrum (Brassicaceae) grown at high or low competition. There was a negative correlation of family tolerance levels between competition treatments: plant families with high tolerance to apical damage in the low competition treatment had low tolerance to apical damage in the high competition treatment and vice versa. We found no costs of tolerance, in terms of a trade-off between tolerance to apical and leaf damage or between tolerance and competitive ability, or an allocation cost in terms of reduced fitness of highly tolerant families in the undamaged state. High tolerance bound to a specific competitive regime may entail a cost in terms of low tolerance if competitive regime changes. This could act as a factor maintaining genetic variation for tolerance.
Dynamics of plant species during phytostabilisation of copper mine tailings and pyrite soils, Western Uganda Mer info
Journal of Environmental Engineering & Ecological Science 2014, 3 : -.
Introduction: Destruction of vegetation resources emanating from deposition of mine wastes is a serious environmental problem. Conventional plant species restoration methodologies are costly and feasible only on a small scale. The current study was focussed on developing phytostabilisation protocols involving the application of limestone, compost, selected tree species and assessing the re-establishment of plants in polluted soils.Methods: Early establishment of plant species under Eucalyptus grandis, Senna siamea and Leucaena leucocephala planted on mine tailings and pyrite soils amended with compost, limestone and limestone+compost was studied. Four plant inventories were conducted on the study plots and surrounding plant communities, involving enumeration of the plant species and estimation of their ground covers. Physico-chemical characteristics of the soils of the study plots were determined each time an inventory was conducted. Data were analysed using R statistical packages vegan and lme4.Results: Mine tailings and pyrite soils had extremely low pH, poor nutritional status, low organic matter content and elevated concentrations of heavy metals as compared to the unpolluted soils. Before treatment, species richness, diversity and plant cover were extremely low with most of the ground being completely bare. Treatment of the soils significantly improved the physico-chemical characteristics starting a plant succession that increased the number of species from 18 to 215 different species, belonging to 131 genera and 34 families. Plots of the leguminous tree species Senna siamea and Leucaena leucocephala had significantly more species than the non-leguminous Eucalyptus grandis. Early changes in species composition of the restoration plots were minimal. Correspondence analysis (CA) revealed significant differences in species composition between the experimental plots and the plots at the unpolluted site.Conclusion: Application of amendment material that significantly alters the physico-chemical characteristics of mine wastes is pre-requisite for their phytostabilisation. Leguminous tree species Senna siamea and Leucaena leucocephala have a higher potential for phytostabilisation of pyrite and copper tailings as their growth led to the establishment of understory plant communities with higher species diversity and cover.
Among-Population Variation in Tolerance to Larval Herbivory by Anthocharis cardamines in the Polyploid Herb Card... Mer info
PLoS ONE 2014, 9 (6): e99333-.
Plants have two principal defense mechanisms to decrease fitness losses to herbivory: tolerance, the ability to compensate fitness after damage, and resistance, the ability to avoid damage. Variation in intensity of herbivory among populations should result in variation in plant defense levels if tolerance and resistance are associated with costs. Yet little is known about how levels of tolerance are related to resistance and attack intensity in the field, and about the costs of tolerance. In this study, we used information about tolerance and resistance against larval herbivory by the butterfly Anthocharis cardamines under controlled conditions together with information about damage in the field for a large set of populations of the perennial plant Cardamine pratensis. Plant tolerance was estimated in a common garden experiment where plants were subjected to a combination of larval herbivory and clipping. We found no evidence of that the proportion of damage that was caused by larval feeding vs. clipping influenced plant responses. Damage treatments had a negative effect on the three measured fitness components and also resulted in an earlier flowering in the year after the attack. Tolerance was related to attack intensity in the population of origin, i.e. plants from populations with higher attack intensity were more likely to flower in the year following damage. However, we found no evidence of a relationship between tolerance and resistance. These results indicate that herbivory drives the evolution for increased tolerance, and that changes in tolerance are not linked to changes in resistance. We suggest that the simultaneous study of tolerance, attack intensity in the field and resistance constitutes a powerful tool to understand how plant strategies to avoid negative effects of herbivore damage evolve.
The association among herbivory tolerance, ploidy level, and herbivory pressure in Cardamine pratensis Mer info
Evolutionary Ecology 2010, 24 (5): 1101-1113.
We tested whether differences in ploidy level and previous exposure to herbivory can affect plant tolerance to herbivory. We conducted a common garden experiment with 12 populations of two ploidy levels of the perennial herb Cardamine pratensis (five populations of tetraploid ssp. pratensis and seven populations of octoploid ssp. paludosa). Earlier studies have shown that attack rates by the main herbivore, the orange tip butterfly Anthocharis cardamines, are lower in populations of octoploids than in populations of tetraploids, and vary among populations. In the common garden experiment, a combination of natural and artificial damage significantly reduced seed and flower production. We measured tolerance based on four plant-performance metrics: survival, growth, seed production and clonal reproduction. For three of these measurements, tolerance of damage did not differ between ploidy levels. For clonal reproduction, the octoploids had a higher tolerance than the tetraploids, although they experience lower herbivore attack rates in natural populations. Populations from sites with high levels of herbivory had higher tolerance, measured by seed production, than populations with low levels of herbivory. We did not detect any significant costs of tolerance. We conclude that high intensity of herbivory has selected for high tolerance measured by seed production in C. pratensis.
Spatial data replacing temporal data in population viability analyses - An empirical investigation for plantsMer info
Basic and Applied Ecology 2009, 10 (5): 401-410.
In conservation management, there is an urgent need for estimates of population viability and for knowledge of the contributions of different life-history stages to population growth rates. Collection of long-term demographic data from a study population is time-consuming and may considerably delay the start of proper management actions. We examined the possibility of replacing a long-term temporal data set (demographic data from several years within a population) with a short-term spatial data set (demographic data from different populations for the same subset of two continuous years) for stochastic estimates of population viability. Using matrix population models for ten perennial plant species, we found that the matrix elements of spatial data sets often deviated from those of temporal data sets and that matrix elements generally varied more spatially than temporally. The appropriateness of replacing temporal data with spatial data depended on the subset of years and populations used to estimate stochastic population growth rates (log lambda(s)). Still, the precision of log lambda(s) estimates measured as variation in the yearly change of logarithmic population size rarely differed significantly between the spatial and temporal data sets. Since a spatiotemporal comparison of matrix elements and their variation cannot be used to assess whether spatial and temporal data sets are interchangeable, we recommend further research on the topic.
Oikos 2007, 116 (12): 2071-2081.
To study mechanisms underlying plant tolerance to herbivore damage, we used apical and foliar damage as experimental treatments to study whether there are similar tolerance mechanisms to different types of damage. We also studied whether tolerance to different types of damage are associated, and whether there is a cost involved in plant tolerance to different types of herbivore damage. Our greenhouse experiment involved 480 plants from 30 full-sib families of an annual weed Raphanus raphanistrum, wild radish, which were subjected to control and two different simulated herbivore damage treatments, apex removal and foliar damage of 30% of leaf area. Apical damage significantly decreased seed production, whereas foliar damage had no effect. There was a significant genetic variation for tolerance to foliar, but not apical damage. No costs were observed in terms of negative correlation between tolerance to either damage type and fitness of undamaged plants. Tolerances to apical and foliar damage were not significantly correlated with each other. We observed a larger number of significant associations between tolerance and reproductive traits than between tolerance and vegetative traits. Plant height and leaf size of damaged plants interacted in their association to tolerance to foliar damage. Inflorescence number and pollen quantity per flower of damaged plants were positively associated with tolerance to apical damage. In late-flowering genotypes, petal size of undamaged plants and pollen quantity of damaged plants were positively associated with tolerance to foliar damage. In summary, traits involved in floral display and male fitness were associated with plant tolerance to herbivore damage.
Canadian Journal of Botany 2007, 85 (2): 160-166.
The evolution of flower size may be constrained by trade-offs between flower size and other plant traits. The aim of this study was to determine how selection on flower size affects both reproductive and vegetative traits. Raphanus raphanistrum L. was used as the study species. Artificial selection for small and large petal size was carried out for two generations. We measured the realized heritability of flower size and recorded flower production, time to flowering, plant size, and seed production in the two selection lines. The realized heritability was h(2) = 0.49. Our study, therefore, showed that R. raphanistrum has potential for rapid evolutionary change of floral size. The lines with large flowers produced smaller seeds and started to flower later than the lines with small flowers. There was no trade-off between flower size and flower number, but the lines selected for large flower size had more flowers and a larger plant size than lines selected for small flowers. Estimates of restricted maximum likelihood (REML) analysis of pedigrees also showed that flower size had a positive genetic correlation with start of flowering and plant height.
International journal of plant sciences 2007, 168 (7): 1013-1019.
Maternal plant responses to different levels of pollination vary and are of importance for the total fitness of the plant. We studied how varying pollen load affects late flowering, reproduction, and growth of maternal plants. Raphanus raphanistrum, Sinapis arvensis, and Brassica napus were used as study species. We conducted hand- pollination experiments with different pollen loads for early flowers in the inflorescence and measured responses on vegetative traits, floral traits of late flowers, and seed production. There were no effects on vegetative traits, but floral traits were affected by treatments in two of the study species. The high pollen load treatment in S. arvensis resulted in longer petals on late flowers compared with the low pollen load treatment. In R. raphanistrum, the high pollen load treatment resulted in a higher number of flowers, with narrower petals, than the low pollen load treatment. Total seed production was similar in both treatments in all species. Our results suggest that plants that received a high pollen load were able to allocate resources to high seed production of early flowers and to increased pollen dispersal of late flowers, thereby achieving higher total fitness than plants that received a lower pollen load.
Conservation Biology 2006, 20 (3): 833-843.
Although the effects of deterministic factors on population viability often are more important than stochasticity, few researchers have dealt with the effect of deterministic habitat changes on plant population demography We assessed population viability for the perennial herb Primula veris L. and identified targets for management based on demographic data from five different habitat types representing different degrees of canopy closure. We conducted replicate studies at the border of the distribution area and in more central parts. Demographic patterns were similar between the two regions. Most study populations had a positive population growth, and only populations in late phases of forest succession showed consistently negative trends. The populations of open habitats had high seedling recruitment, and the populations of early and middle forest succession had high seed production. The importance of survival for population growth rate increased with increasing habitat closure, whereas the importance of growth and reproduction decreased. Results of the elasticity analysis suggested that the best method to manage decreasing late-successional populations is to increase survival of the largest individuals. The life-table response experiment (LTRE) analysis, however, showed that survival of the largest individuals contributed little to differences in population growth rates of different habitats, whereas seed production and growth of small individuals were more important. Moreover, direct perturbation of the performance of the largest stages showed that late-successional populations would not attain positive population growth even if the largest stages had no mortality at all. We conclude that restoration of recruitment is the only possibility for positive population growth in late-successional populations of P. veris, although the elasticities of recruitment transitions are low. Our results also suggest that retrospective demographic methods such as LIRE constitute an important and necessary complement to prospective methods such as elasticities in identifying management targets.
Basic and Applied Ecology 2006, 7 (3): 224-235.
The joint effects of multiple herbivores on their shared host plant have received increasing interest recently. The influence of herbivores on population dynamics of their host plants, especially the relative roles of different types of damage, is, however, still poorly understood. Here, we present a modelling approach, including both deterministic and stochastic matrix modelling, to be used in estimating fitness effects of multiple herbivores on perennial plants. We examined the effects and relative roles of two specialist herbivores, a pre-dispersal seed predator, Euphranta connexa, and a Leaf-feeding moth, Abrostola asclepiadis, on the population dynamics and long-term fitness of their shared host plant, a Long-lived perennial herb Vincetoxicum hirundinaria (Asclepiadaceae). We collected demographic data during 3 years and combined these data with the effects of natural levels of herbivory measured from the same individuals. We found that both seed predation and leaf herbivory reduced population growth of V. hirundinaria, but only very high damage levels changed the growth trend of the vigorously growing study populations from positive to negative. Demographic modelling indicated that seed predation had a greater impact on plant population growth than leaf herbivory. The effect of leaf herbivory was weaker and diminished with increasing level of seed predation. Evaluation of individual fitness components, however, suggested that leaf herbivory contributed more strongly to host plant fitness than seed predation. Our results emphasize that understanding the effects of a particular herbivore on plant population dynamics requires also knowledge on other herbivores present in the system, because the effect of a particular type of herbivory on plant population dynamics is likely to vary according to the intensity of other types of herbivory. Furthermore, evaluating herbivore impact from using individual fitness components does not necessarily reflect the long-term effects on total plant fitness.
In: Reproductive Allocation in Plants. Burlington : Elsevier Academic, 2005. 51-75.
Oikos 2005, 111 (3): 563-573.
Large data requirements may restrict the use of matrix population models for analysis of population dynamics. Less data are required for a small population matrix than for a large matrix because the smaller matrix contains fewer vital rates that need to be estimated. Smaller matrices, however, tend to have a lower precision. Based on 37 plant species, we studied the effects of matrix dimensionality on the long-term population growth rate (lambda) and the elasticity of lambda in herbaceous and woody species. We found that when matrix dimensionality was reduced, changes in lambda were significantly larger for herbaceous than for woody species. In many cases, lambda of woody species remained virtually the same after a substantial decrease in matrix dimensionality, suggesting that woody species are less susceptible to matrix dimensionality. We demonstrated that when adjacent stages of a transition matrix are combined, the magnitude of a change in lambda depends on the distance of the population structure from a stable stage distribution, and the difference in the combined vital rates weighted by their reproductive values. Elasticity of lambda to survival and fecundity usually increased, whereas elasticity to growth decreased both in herbaceous and in woody species with reduced matrix dimensionality. Changes in elasticity values tended to be larger for herbaceous than for woody species. Our results show that by reducing matrix dimensionality, the amount of demographic data can be decreased to save time, money, and field effort. We recommend the use of a small matrix dimensionality especially when a limited amount of data is available, and for slow-growing species having a simple matrix structure that mainly consists of stasis and growth to the next stage.
Importance of correlations among matrix entries in stochastic models in relation to number of transition matrices Mer info
Oikos 2005, 111 (1): 9-18.
Stochastic matrix models are used to predict population viability and the risk of extinction. Different stochastic methods require different amounts of estimation effort and may lead to divergent estimates. We used 16 transition matrices collected from ten populations of the perennial herb Primula veris to compare population estimates produced by different stochastic methods, such as selection of matrices, selection of vital rates, selection of matrix elements, and Tuljapurkar's approximation. Specifically, we tested the reliability of the methods using different numbers of transition matrices, and examined the importance of correlations among matrix entries. When correlations among matrix entries were included in the models, selection of vital rates produced the lowest and Tuljapurkar's approximation produced the highest estimates of mean population growth rates. Selection of matrices and matrix elements often produced nearly similar population estimates. Simulations based on incompletely estimated correlations among matrix entries considerably differed from those based on all correlations estimated, particularly when correlations were strong. The magnitude of correlations among matrix entries depended on the number of matrices, which made it difficult to generalize correlations within a species. Given that selection of vital rates or matrix elements is used, correlations among matrix entries should usually be included in the model, and they should preferably be estimated from the present data rather than according to other information of the species.
Acta Oecologica 2005, 28 (3): 207-212.
Seed size is a widely accepted measure of seed quality, because many earlier studies have shown that large seeds have high seedling survival, growth and establishment. We tested whether ovule loss increases size of the remaining seeds and whether such size increase affects seedling establishment. We removed all except one flower from inflorescences of Primula veris L. (Primulaceae), a perennial hemicryptophyte herb, at a late stage of flowering. Flower removal (FR) increased seed size by 33% compared to the control plants. We then divided the seeds within each treatment to small, middle-sized and large seeds and carried out a sowing experiment in the field, Within each experimental group, seedling establishment was positively associated with seed size. However, despite size differences, seeds from the FIR and control groups had the same seedling establishment probability. Seeds from FR plants had a higher seedling emergence in May than those from control plants, but the number of seedlings alive per sowing plot in the late summer was the same in both experimental groups. Increase in seed mass after partial FR thus did not enhance seedling performance, although seed size variation due to other causes was positively correlated with seedling establishment. Further studies are needed to show whether plastic changes of seed size are usually adaptive or not.
Journal of Applied Ecology 2005, 42 (2): 317-326.
1. Changes in land use are the primary cause of decline for many plant species. Efficient management actions for such species must be based on knowledge of the key phases of the plant life cycles that respond most to changes in environmental factors. 2. To assess how grazing influences population viability of the perennial rosette herb Primula veris, we applied four experimental treatments to abandoned grasslands and recorded the demographic response in permanent plots and seed sowing experiments over 3 years. 3. Treatments had strong effects on population viability. Transition matrix models showed that cutting the surrounding vegetation had no effect on population growth rate (lambda). However, when this was combined with litter removal lambda increased to 1.46, compared with 1.11 in controls. With disturbance and complete removal of the surrounding vegetation the effect was even stronger, and lambda increased to 1.60. 4. Increases in lambda were primarily a result of increased growth of the smallest rosettes, and increased seedling production. In contrast, the performance of larger P. veris individuals was not affected by experimental treatments. 5. The higher the elasticity of a particular life cycle transition, the less the change in the transition rate caused by treatments. This suggests that plants are able partly to buffer the effects of environmental variation by minimizing changes in the life cycle transitions that are most important to population growth rate. 6. Synthesis and applications. Experimental demographic approaches provide an important tool for assessing how grazing and other types of management influence species viability, and help to unravel the mechanisms underlying such relationships. With such information it is possible to predict the effects of novel types of management and land-use scenarios on population viability. For P. veris, we identified seedling establishment as a key phase in the life cycle, and litter accumulation as a key environmental factor, suggesting that these should be prime targets for management. One practice that is likely to favour as well as seedling establishment preventing litter accumulation is late summer grazing.
In: Insects and ecosystem function. Berlin : Springer, 2004. 257-275.
Journal of Evolutionary Biology 2004, 17 (6): 1167-1177.
An increasing number of studies have recently detected within-organism genetic heterogeneity suggesting that genetically homogeneous organisms may be rare. In this review, we examine the potential costs and benefits of such intraorganismal genetic heterogeneity (IGH) on the fitness of the individual. The costs of IGH include cancerous growth, parasitism, competitive interactions and developmental instability, all of which threaten the integrity of the individual while the potential benefits are increased genetic variability, size-specific processes, and synergistic interactions between genetic variants. The particular cost or benefit of IGH in a specific case depends on the organism type and the origin of the IGH. While mosaicism easily arise by genetic changes in an individual, and will be the more common type of IGH, chimerism originates by the fusion of genetically distinct entities, and is expected to be substantially rare in most organisms. Potential conflicts and synergistic effects between different genetic lineages within an individual provide an interesting example for theoretical and empirical studies of multilevel selection.
Journal of Evolutionary Biology 2004, 17 (6): 1192-1194.
Evolution 2003, 57 (3): 677-680.
Tiffin and Inouye (2000) discussed the use of natural and imposed (controlled) damage in experiments of herbivore tolerance. They constructed a statistical model of the effect of herbivory on plant fitness, including damage level and an environmental factor as the independent factors, in which tolerance is defined as a slope of the regression line when damage level is regressed with plant fitness. They claim that while experiments with imposed damage are more accurate (i.e., they give a more correct estimate of tolerance), experiments with natural damage are more precise under a wide range of parameter values (i.e., tolerance estimates explain a larger part of variation in fitness). I show, however, that experiments with imposed damage are less precise only when an experimenter uses an experimental design that has weaker statistical power than in experiments with natural herbivory. The experimenter can nevertheless control the damage levels to optimize the experimental designs. For instance, when half of the experimental plants are left undamaged and the other half treated with maximal relevant damage level, experiments with imposed damage are almost always much more precise than experiments with natural damage.
Journal of Theoretical Biology 2002, 219 (4): 495-505.
We devise a stochastic and spatially explicit model for the dynamics of the initials cells in a stratified shoot apical meristem (SAM). The meristem is composed of three layers with seven initials per layer. We investigate the probability and number of divisions for a mutant lineage to either reach fixation or becoming purged through selection or drift. In contrast to previous studies our results show that the functional organization of the initials in stratified SAMs acts as an efficient purging mechanism particularly of deleterious mutations. All mutants are rapidly purged when deleterious. The probability of fixation for mutants with a higher fitness than the wild type increases linearly up to 70%. The median number of divisions to fixation of both genotypes is insensitive to the mutant's fitness. The median number of divisions to wildtype fixation is less than 100, with the upper quartile below 200. The largest number of divisions to wild-type fixation are in the order of 100 000 divisions. Our results indicate that the spatial organization of SAM enables the efficient purging of mutant lineages, particularly if they are deleterious. On the other hand, long-lived chimeric stages are common when mutant lineages succeed to overcome the initial numerical disadvantage.
Oikos 2002, 98 (2): 308-322.
Trade-offs involving life span are important in the molding of plant life histories. However, the empirical examination of such patterns has so far been limited by the fact that information on life span is mainly available in terms of discrete categories; annuals, semelparous perennials and iteroparous perennials. We used transition matrix models to project continuous estimates of conditional life spans from published information on size- or stage-structured demography for 71 perennial plant species. The projected life span ranged from 4.3 to 988.6 years and more than half of the species had a life span of more than 35 years. Woody plants had on average a projected life span more than four times as long as non-woody plants. Life spans were higher in forests than in open habitats and individuals of non-clonal species tended to have a longer life span than ramets of clonal species. Self-incompatible plants on average lived longer than self-compatible plants. There were no clear relations between life span and geographical region, dispersal syndrome, pollination mode, seed size or the presence of a seed bank. We conclude that accurate estimates of life span are central to understand how longevity is correlated to other traits within the group of perennial plants.
Pre-dispersal seed predation in Primula veris - among-population variation in damage intensity and selection on flower numberMer info
Oecologia 2002, 133 (4): 510-516.
The geographic mosaic theory of co-evolution states that evolution of interactions is driven by geographical variation in interactions between species. We investigated whether the intensity of pre-dispersal seed predation differed among nine Primula veris populations over 5 years, and whether such differences lead to geographical variation in selection on flower number. Seed predation intensity differed significantly among years and populations, and it increased with canopy closure and decreased with the density of the field layer vegetation. Individuals in open habitats also produced the highest number of flowers. Moreover, the phenotypic selection on flower number differed among years and populations. In populations of closed habitats, with high seed predation pressure, the increased number of flowers was often correlated with an increased number of damaged capsules. However, an increased flower number did not result in fewer intact fruits due to seed predation in any population.
Effects of foliar herbivory by insects on the fitness of Raphanus raphanistrum - damage can increase male fitness.Mer info
American Naturalist 2001, 158 (5): 496-504.
Generally, effects of herbivory on plant fitness have been measured in terms of female reproductive success (seed production). However, male plant fitness, defined as the number of seeds sired by pollen, contributes half of the genes to the next generation and is therefore crucial to the evolution of natural plant populations. This is the first study to examine effects of insect herbivory on both male and female plant reproductive success. Through controlled field and greenhouse experiments and genetic paternity analysis, we found that foliar damage by insects caused a range of responses by plants. In one environment, damaged plants had greater success as male parents than undamaged plants. Neither effects on pollen competitive ability nor pollinator visitation patterns could explain the greater siring success of these damaged plants. Success of damaged plants as male parents appeared to be due primarily to changes in allocation to flowers versus seeds after damage. Damaged plants produced more flowers early in the season, but not more seeds, than undamaged plants. Based on total seed production, male fitness measures from the first third of the season, and flower production, we estimated that damaged and undamaged plants had equal total reproductive success at the end of the season in this environment. In a second, richer environment, damaged and undamaged plants had equal male and female plant fitness, and no traits differed significantly between the treatments. Equal total reproductive success may not be ecologically or evolutionarily equivalent if it is achieved differentially through male versus female fitness. Genes from damaged plants dispersed through pollen may escape attack from herbivores, if such attack is correlated spatially from year to year.