Reduction In Population Growth Rate Research Articles

Fine mapping and characterization of BPH27, a brown planthopper resistance gene from wild rice (Oryza rufipogon Griff.)

The brown planthopper (Nilaparvata lugens Stål; BPH) is one of the most serious rice pests worldwide. Growing resistant varieties is the most effective way to manage this insect, and wild rice species are a valuable source of resistance genes for developing resistant cultivars. BPH27 derived from an accession of Guangxi wild rice, Oryza rufipogon Griff. (Accession no. 2183, hereafter named GX2183), was primarily mapped to a 17-cM region on the long arm of the chromosome four. In this study, fine mapping of BPH27 was conducted using two BC(1)F(2) populations derived from introgression lines of GX2183. Insect resistance was evaluated in the BC(1)F(2) populations with 6,010 individual offsprings, and 346 resistance extremes were obtained and employed for fine mapping of BPH27. High-resolution linkage analysis defined the BPH27 locus to an 86.3-kb region in Nipponbare. Regarding the sequence information of rice cultivars, Nipponbare and 93-11, all predicted open reading frames (ORFs) in the fine-mapping region have been annotated as 11 types of proteins, and three ORFs encode disease-related proteins. Moreover, the average BPH numbers showed significant differences in 96-120 h after release in comparisons between the preliminary near-isogenic lines (pre-NILs, lines harboring resistance genes) and BaiR54. BPH growth and development were inhibited and survival rates were lower in the pre-NIL plants compared with the recurrent parent BaiR54. The pre-NIL exhibited 50.7% reductions in population growth rates (PGR) compared to BaiR54. The new development in fine mapping of BPH27 will facilitate the efforts to clone this important resistant gene and to use it in BPH-resistance rice breeding.

Effects of a non-native biocontrol weevil, Larinus planus, and other emerging threats on populations of the federally threatened Pitcher’s thistle, Cirsium pitcheri

Larinus planus Frabicius (Curculionidae), is a seed-eating weevil that was inadvertently introduced into the US and was subsequently distributed in the US and Canada for the control of noxious thistle species of rangelands. It has been detected recently in the federally threatened Pitcher’s thistle (Cirsium pitcheri). We assayed weevil damage in a natural population of Pitcher’s thistle at Whitefish Dunes State Park, Door County, WI and quantified the impact on fecundity. We then estimated the impact of this introduced weevil and other emerging threats on two natural, uninvaded populations of Pitcher’s thistle for which we have long-term demographic data for 16yr (Wilderness State Park, Emmet County, MI) and 23yr (Miller High Dunes, Indiana Dunes National Lakeshore, Porter County, IN). We used transition matrices to determine growth rates and project the potential effects of weevil damage, inbreeding, goldfinch predation, and vegetative succession on Pitcher’s thistle population viability. Based on our models, weevil seed predation reduced population growth rate by 10–12%, but this reduction was enough to reduce time to extinction from 24yr to 13yr and 8yr to 5yr in the MI and IN population, respectively. This impact is particularly severe, given most populations of Pitcher’s thistle throughout its range hover near or below replacement. This is the first report of unanticipated ecological impacts from a biocontrol agent on natural populations of Cirsium pitcheri.

Native predators reduce harvest of reindeer by Sámi pastoralists

Contemporary efforts to protect biological diversity recognize the importance of sustaining traditional human livelihoods, particularly uses of the land that are compatible with intact landscapes and ecologically complete food webs. However, these efforts often confront conflicting goals. For example, conserving native predators may harm pastoralist economies because predators consume domestic livestock that sustain people. This potential conflict must be reconciled by policy, but such reconciliation requires a firm understanding of the effects of predators on the prey used by people. We used a long-term, large-scale database and Bayesian models to estimate the impacts of lynx (Lynx lynx), wolverine (Gulo gulo), and brown bear (Ursus arctos) on harvest of semi-domesticated reindeer (Rangifer tarandus) by Sami pastoralists in Sweden. The average annual harvest of reindeer averaged 25% of the population (95% credible interval = 19, 31). Annual harvest declined by 96.6 (31, 155) reindeer for each lynx family group (the surveyed segment of the lynx population) in a management unit and by 94.3 (20, 160) for each wolverine reproduction (the surveyed segment of the wolverine population). We failed to detect effects of predation by brown bear. The mechanism for effects of predation on harvest was reduced population growth rate. The rate of increase of reindeer populations declined with increasing abundance of lynx and wolverine. The density of reindeer, latitude, and weather indexed by the North Atlantic Oscillation also influenced reindeer population growth rate. We conclude that there is a biological basis for compensating the Sámi reindeer herders for predation on reindeer.

Impact of genetic diversity and inbreeding on the life-history of Chironomus midges over consecutive generations

We report results of a multigenerational experiment with Chironomus riparius. Two strains with a high and a low level of genetic variability were exposed to a low, environmentally relevant TBT concentration of 80μgSnkg−1sedimentdw nominally (time weighted mean, based on measured concentrations: 4.5μgSnkg−1sedimentdw), and various life history traits as well as genetic diversity were monitored for eleven consecutive generations. While TBT effects are hardly visible in the outbred and genetically diverse strain, the inbred and genetically impoverished strain shows a clearly reduced population growth rate compared to the control. Moreover, the impoverished strain shows an increase in fitness over time. Analyses of variation at five microsatellite loci revealed that the level of genetic variation is strongly reduced in the inbred compared to the outbred strain. Moreover, genetic diversity increases over time in the inbred strain. This finding explains the observed increase in fitness in both inbred lineages (control and TBT exposed). The results document that inbreeding and the level of genetic diversity might be of crucial importance in populations under pollution stress. Furthermore, ecotoxicological bioassays have to consider genetic diversity if results between laboratories should be comparable. Our data provides evidence that genetic diversity strongly contributes to the survival of a population exposed to chemical pollution.

Modeling the interaction of physiological time, seasonal weather patterns, and delayed mating on population dynamics of codling moth,Cydia pomonella(L.) (Lepidoptera: Tortricidae)

AbstractThe effect of delaying female mating on population growth in codling moth (Cydia pomonella(L.)) was found to act on a physiological time (degree‐day) basis and was predictable using a simple quadratic equation. When combined with previous work on degree‐day based mortality, we were able to evaluate how the magnitude of population reduction and survival varied between sites, years, and generations at locations in California, Michigan, Pennsylvania and Washington states. In general, reductions in population growth associated with females mating 1–3 days after emergence were greater in warmer areas and during warmer times of the year. In any given year and location, the temperature profiles during peak flight were crucial in determining the population reductions, but over an 11‐year period, the average seasonal temperature profile was more important. During the overwintering generation, conditions were relatively mild in all locations and only minor differences were observed in population growth rates between locations. Populations experiencing 1–3 days delay in female mating were reduced 8, 19 and 32 % compared to populations experiencing no delay, respectively. During the first summer generation, population reductions doubled compared to those seen in the overwintering generation. During the second summer flight, reductions in population growth rate at the three cooler locations decreased, while they increased in the warmer California location. Overall, the results show delayed mating can help understand how population growth is related to environmental conditions experienced naturally by insect populations and will help guide studies of the mechanisms of mating disruption, a technique used for pest suppression in agricultural and forest systems.

Controlling a plant invader by targeted disruption of its life cycle

Summary1. Pest management strategies should be informed by research on a broad suite of biotic and abiotic interactions. We used a life table response experiment (LTRE) to assess the reliability of ragwortJacobaea vulgarismanagement recommendations based on interactions of (i) time of disturbance to initiate experimental units, (ii) herbivory from two biological control organisms, the cinnabar mothTyria jacobaeaeand ragwort flea beetleLongitarsus jacobaeaeand (iii) interspecific competition by perennial grasses.2. Our LTRE combines a factorial experiment with a linear, deterministic matrix model for ragwort populations representing transitions among three stages: 1st year juveniles, ≥2nd year juveniles and adults. Elasticity analysis identified potentially vulnerable ragwort transitions, and a contributions analysis confirmed which treatments influenced these transitions. Ultimate treatment effects were quantified as the reduction in population growth rates and time to local extinction.3. Elasticity analyses found the ragwort’s biennial pathway, juvenile to adult transition and fertility transition were most influential and most amenable to manipulation across all community configurations. The flea beetle and perennial grass competition had negative effects on survival and fertility, whereas the cinnabar moth only reduced fertility and induced the perennial pathway.4. All combinations of insects or increased plant competition reduced the growth rate of ragwort. Full interspecific competition and the flea beetle resulted in a significantly greater and faster decline in the ragwort populations than the cinnabar moth. Moreover, this pattern was consistent between two times of initial disturbance.5.Synthesis and applications.Maximizing plant competition provides the fastest way to control ragwort. If this option is unavailable, for example, grazed or disturbed land, the ragwort flea beetle provides excellent management to lower ragwort densities without the potential nontarget effects of the cinnabar moth. Factorial experiments and matrix models help to evaluate interacting factors that influence invasive species’ vulnerabilities, inform how to intervene in a weed life cycle to reduce weed abundance and confirm recommendations that are robust to community variation.

Evidence for source - sink dynamics in a regional population of arctic ground squirrels (Urocitellus parryii plesius)

Context Variable demographic rates can manifest themselves between habitat types in the form of source–sink dynamics where populations in sink habitats would not exist without the addition of migrants from source habitats. Aims Arctic ground squirrels (Urocitellus parryii pleisus (Osgood, 1900)) occupy a large geographic area in northern Canada and live in a variety of habitat types, including boreal forest, low-elevation meadows and alpine meadows, providing an opportunity to investigate the possible existence of source–sink dynamics. Methods We hypothesised that arctic ground squirrels in the south-western Yukon exhibit demographic characteristics indicative of source–sink dynamics. Boreal forest habitat could be a sink in spite of previous high squirrel densities, whereas meadows could be a source. We investigated this by mark–recapture live-trapping and radio-telemetry. Key Results In the boreal forest in the Kluane region, we found reduced recruitment, reduced population growth rates (λ), and reduced survivorship for radio-collared individuals that moved from low-elevation meadows into the boreal forest. There was no evidence from radio-collared juveniles of dispersal from high-density ground squirrel populations in alpine meadows down into boreal forest. Conclusions Boreal forest is a sink habitat for arctic ground squirrels. Source–sink dynamics observed between low-elevation meadow and boreal forest habitats appear to result from increased predation pressure in the boreal forest. The result has been a near extirpation of boreal forest arctic ground squirrels in the Kluane region since 1998. Implications Because the source areas of low-elevation meadows occupy only 7–9% of the lowland habitat, recolonisation of boreal forest sites has been very slow. Whereas alpine populations remain high in 2011, boreal forest populations remain near zero. Alpine populations do not appear to be a source for the boreal forest.

双酚A对萼花臂尾轮虫毒性及生活史的影响

应用生态毒理学研究方法,研究了双酚A(BPA)对萼花臂尾轮虫毒性及生活史影响。结果表明:BPA对萼花臂尾轮虫24 h急性毒性LC₅₀为13.76 mg/L,95%置信限为10.97-17.10 mg/L。生活史研究显示:与对照组相比,0.25-4.0 mg/L的BPA对轮虫胚胎发育历时影响不显著;2.0-4.0 mg/L的BPA显著延迟了轮虫幼体发育时间;当BPA为0.5 mg/L时,轮虫净生殖率(<em>R₀</em>)显著上升,但BPA浓度为2.0和4.0 mg/L时<em>R₀</em>显著降低;4.0 mg/L的BPA显著缩短世代时间(<em>T</em>);BPA浓度为2.0、4.0 mg/L时,轮虫生命期望值(<em>e</em>₀)显著下降;BPA浓度为1.0、2.0、4.0 mg/L时,轮虫内禀增长率(<em>r_m</em>)显著下降;BPA浓度为0.5、1.0 mg/L时轮虫所产后代混交率(MR)显著增长。研究结果表明BPA对轮虫的生殖具有干扰作用,其中<em>R₀</em>和MR受BPA影响最为显著。;The presence of toxic agents in aquatic environments has increased in recent years. Some of them that are released into the aquatic environment interfere with the endocrine system of organisms by affecting development time, causing reproductive abnormalities and reducing population growth rates in zooplankton including rotifers. Bisphenol A (BPA, 4,4¹-isopropylidine diphenol) is a commercially important chemical with an estimated worldwide production capacity of 3.7 million metric tons per year and demonstrates estrogenic activity. Many acute and chronic toxicity studies under controlled conditions have used either fish or the cladoceran<em> Daphnia magna.</em> However there is little information using rotifers with BPA. With short life spans and high reproductive abilities, rotifers such as <em>Brachionus calyciflorus</em> are particularly useful for environmental toxicology because of their higher sensitivities to most toxicants. Moreover, rotifers are important trophic components of aquatic food webs constituting a major food source for fish and invertebrate predators and thus play a vital role in transporting energy and nutrients in aquatic ecosystems. The aim of the present work was therefore to use <em>B. calyciflorus</em> to study the effect BPA on the life history characteristics and mixis.<br> Population of <em>B.calyciflorus</em> was (0-2 h old) obtained by hatching resting eggs in EPA medium. Resting eggs were endowed by professor T W. Snell. Test toxicant solutions were prepared by US EPA medium. The rotifers were fed using unicellular green algae <em>Chlorella pyrenoidosa</em> at 1.0×10⁶cells/mL,the alga was cultured in a semi-continuous culture using HB-4 medium in 3 L transparent flasks under a light intensity of 4000 lux and photo period was 12∶12 (L∶D). The results showed that 24 h median lethal concentration (24 h LC₅₀) value of BPA for <em>B. calyciflorus</em> was 13.76 mg/L, and 95% limits was 10.97-17.10 mg/L. In the tested concentration range of 0.25-4.0 mg/L, BPA at 2.0 and 4.0 mg/L extended significantly the durations of juvenile development and total eggs production. At 2.0-4.0 mg/L BPA did not affect significantly the durations of embryonic development. BPA concentration at 0.5 mg/L increased markedly net reproductive rate (<em>R₀</em>), 2.0-4.0 mg/L decreased <em>R</em>₀. BPA concentration had no effect on generation time (<em>T</em>) except at 4.0 mg/L. BPA concentration from 1.0 to 4.0 mg/L decreased the intrinsic rate of population increase (<em>r_m</em>), 0.5, 1.0 mg/L increased significantly mixis rate of<em> B.calyciflorus.</em> The results showed that different endpoints of both development and reproduction had different sensitivity to BPA. <em>R₀</em> and mixis rate endpoint of the rotifers appeared to be more sensitive than other endpoints.

Impacts of salinity and fish-exuded kairomone on the survival and macromolecular profile of Daphnia pulex

Global warming is already causing salinization of freshwater ecosystems located in semi-arid regions, including Turkey. Daphnids, which are important grazers on phytoplankton and a major food source for fish and invertebrates, are sensitive to not only changes in salinity levels, but also presence of predators. In this study, the interactive effect of salinity toxicity (abiotic factor) with predation pressure mimicked by the fish-exuded kairomone (biotic factor) and the effect of salt acclimation on daphnids were investigated. Impacts of these stressors on daphnid survival, life history and molecular profile were observed. The presence of the kairomone antagonistically alters the effect of salinity, as observed from the 24- and 48-h LC(50) values and survival results. Molecular findings provided solid evidence to this antagonism at even lower salt concentrations, for which antagonism was not evident with organismal data. Fish predation counterbalances the negative effect of salinity in terms of reserve energy density. Therefore, it is important to investigate multiple stressor effects in ecotoxicological bioassays complemented with molecular techniques. The single effect of increasing salinity resulted in increased mortality, decreased fecundity, and slower somatic growth in Daphnia, despite their acclimation to salinity. This insignificance of acclimation indicates that Daphnia do not have any physiological mechanisms to buffer the adverse effects of salinity, making it a very crucial factor. Salinity-induced reduction in population growth rate of freshwater keystone species Daphnia-despite acclimation-indicates that global warming-induced salinity may cascade through the food web and lead to dramatic environmental consequences in the structure of lake ecosystems.

Land-use changes, forest/soil conditions and carbon sequestration dynamics: A bio-economic model at watershed level in Nepal

A dynamic bio-economic model has been used at watershed level in Nepal to analyze the land-use changes, forest and soil conditions and their resultant impacts on carbon (C) sequestration. Planning horizon of the model extends over a period of 25 years. The objective function is maximization of the sum of discounted net income flows from agriculture, livestock and forestry productions; imputed value of leisure and labour hiring out activities subject to annual constraints on land, labour and capital availability along with the fulfilment of minimum cash and consumption requirements. The seven scenarios analyzed by the model are: business as usual (BAU), reduction in population growth rate from 2 to 1.5% p.a., increased prices of major crops by 10 and 20%, reduction in emigration of active labour force from the watershed from the current rate of 20–15 and 10%, and increase in discount rate from 5 to 10%. The results indicate that reduced labour emigration rates and increase in the prices of major crops lead to expansion of cultivated area and shift from one land use to the others. Land clearing becomes more severe with decline in labour emigration rate. Up to 10% increase in the prices of agricultural crops does not have noticeable effect on total land clearing. Increase in discount rate leads to less land clearing, more biomass harvesting and higher net C sequestration as compared to the BAU scenario. Assuming a C price of 10 USD per MgC and 5% discount rate, the net present value of C sequestration for the first 25 years is estimated at 1.83 mill USD in the BAU scenario, varying from 0.16 mill USD to 2.26 mill USD, as respectively the lowest and highest values for the seven scenarios analysed. A reduction in population growth and maintenance of current rate of off-farm employment are suggested for slowing down the expansion of cultivated land area, and thereby reducing the forest/soil degradation and C emissions. This in turn would enhance the income potential from C sequestration.

Development and characterization of japonica rice lines carrying the brown planthopper-resistance genes BPH12 and BPH6

The brown planthopper (Nilaparvata lugens Stål; BPH) has become a severe constraint on rice production. Identification and pyramiding BPH-resistance genes is an economical and effective solution to increase the resistance level of rice varieties. All the BPH-resistance genes identified to date have been from indica rice or wild species. The BPH12 gene in the indica rice accession B14 is derived from the wild species Oryza latifolia. Using an F(2) population from a cross between the indica cultivar 93-11 and B14, we mapped the BPH12 gene to a 1.9-cM region on chromosome 4, flanked by the markers RM16459 and RM1305. In this population, BPH12 appeared to be partially dominant and explained 73.8% of the phenotypic variance in BPH resistance. A near-isogenic line (NIL) containing the BPH12 locus in the background of the susceptible japonica variety Nipponbare was developed and crossed with a NIL carrying BPH6 to generate a pyramid line (PYL) with both genes. BPH insects showed significant differences in non-preference in comparisons between the lines harboring resistance genes (NILs and PYL) and Nipponbare. BPH growth and development were inhibited and survival rates were lower on the NIL-BPH12 and NIL-BPH6 plants compared to the recurrent parent Nipponbare. PYL-BPH6 + BPH12 exhibited 46.4, 26.8 and 72.1% reductions in population growth rates (PGR) compared to NIL-BPH12, NIL-BPH6 and Nipponbare, respectively. Furthermore, insect survival rates were the lowest on the PYL-BPH6 + BPH12 plants. These results demonstrated that pyramiding different BPH-resistance genes resulted in stronger antixenotic and antibiotic effects on the BPH insects. This gene pyramiding strategy should be of great benefit for the breeding of BPH-resistant japonica rice varieties.

Density‐dependence in the survival and reproduction of Bald Eagles: Linkages to Chum Salmon

AbstractDuring the late 20th Century, due to decreases in both contamination and persecution, bald eagle (Haliaeetus leucocephalus) populations increased dramatically. Currently, mechanisms regulating eagle populations are not well understood. To examine potential regulating processes in the Pacific Northwest, where eagles are no longer primarily regulated by contaminants or direct persecution, we examined bald eagle reproductive success, breeding populations, winter populations, mortality, and salmon stream use. Wintering and breeding eagle populations in south‐coastal British Columbia (BC) quadrupled between the early 1980s and the late 1990s, and have since stabilized. Density‐dependent declines in reproduction occurred during 1986–2009, but not through changes in site quality. Mid‐winter survival was crucial as most mortality occurred then, and models showed that density‐dependent reductions in population growth rates were partially due to reduced survival. Wintering eagles in British Columbia fed heavily on chum salmon (Oncorhynchus keta) runs, and then switched to birds in late winter, when mortality was highest. Eagles tended to arrive after the peak in salmon availability at streams in BC as part of a migration associated with salmon streams from Alaska to northern Washington. Eagles were most abundant in southern BC during cold Alaskan winters and in years of high chum salmon availability. We suggest that eagle populations in the Pacific Northwest are currently partially limited by density on the breeding grounds and partially by adult mortality in late winter, likely due to reduced late winter salmon stocks forcing eagles to exploit more marginal prey supplies. Larger eagle populations have affected some local prey populations. © 2011 The Wildlife Society.

A Flow Cytometry Based Oligotrophic Pollutant Exposure Test To Detect Bacterial Growth Inhibition and Cell Injury

Toxicity of chemical pollutants in aquatic environments is often addressed by assays that inquire reproductive inhibition of test microorganisms, such as algae or bacteria. Those tests, however, assess growth of populations as a whole via macroscopic methods such as culture turbidity or colony-forming units. Here we use flow cytometry to interrogate the fate of individual cells in low-density populations of the bacterium Pseudomonas fluorescens SV3 exposed or not under oligotrophic conditions to a number of common pollutants, some of which derive from oil contamination. Cells were stained at regular time intervals during the exposure assay with fluorescent dyes that detect membrane injury (i.e., live-dead assay). Reduction of population growth rates was observed upon toxicant insult and depended on the type of toxicant. Modeling and cell staining indicate that population growth rate decrease is a combined effect of an increased number of injured cells that may or may not multiply, and live cells dividing at normal growth rates. The oligotrophic assay concept presented here could be a useful complement for existing biomarker assays in compliance with new regulations on chemical effect studies or, more specifically, for judging recovery after exposure to fluctuating toxicant conditions.

Assessment of indirect pesticide effects on worm‐eating warbler populations in a managed forest ecosystem

Ecological risk assessments rarely evaluate indirect pesticide effects. Pesticides causing no direct mortality in wildlife can still reduce prey availability, resulting in a lower reproductive rate or poor juvenile condition. Few studies have examined these consequences at the population level. We use a four-year data set from a forest ecosystem in which Bacillus thuringiensis kurstaki (Btk) was applied to control gypsy moths (Lymantria dispar L.). Lower worm-eating warbler (Helmitheros vermivorus) productivity on Btk plots contributed to an intrinsic growth rate <1. Altered provisioning behavior by adults led to lower nestling mass in Btk-treated plots, and simulations of reduced juvenile survival expected as a result further reduced population growth rate. The present study explored different spatial representations of treated areas, using a two-patch matrix model incorporating dispersal. Minimal migration from areas with increasing subpopulations could compensate for detrimental reductions in reproductive success and juvenile survival within treated subpopulations. We also simulated population dynamics with different proportions of treated areas to inform management strategies in similar systems. Nontoxic insecticides are capable of impacting nontarget populations with consistent, long-term use and should be evaluated based on the spatial connectivity representative of habitat availability and the time period appropriate for risk assessment of pesticide effects in wildlife populations.

The consequences of short-term cortisol elevation on individual physiology and growth rate in wild largemouth bass (Micropterus salmoides)

In this study, we explored the growth, survival, and potential population-level effects of short-term experimentally induced stress in largemouth bass ( Micropterus salmoides ). Cortisol implants [50 mg·(kg body mass)–1] were used to increase circulating stress hormones in a group of wild fish in a research lake for ∼6 d in June 2007. Through mark-and-recapture, we compared survival, growth, and plasma biochemistry of cortisol-treated, sham-treated, and control fish at liberty until October 2007. Cortisol-treated fish displayed persistent growth rate depression compared with other groups. However, neither plasma biochemistry nor mortality rates differed among treatments. In a complementary study, we found that the standard metabolic rates (SMR) of cortisol-treated fish were higher than control fish ∼56 h following treatment. Bioenergetics modelling revealed that a transient elevation in SMR alone was insufficient to explain the observed growth depression. Finally, we constructed a simple population model to explore the potential consequences of growth depression. We found that a 10% reduction in population growth rate is conceivable when 39% of the population experiences a stress causing the growth rate depression documented in this study. Our study is novel in highlighting that individual and potentially population-level growth depression can result from a single stress event of short duration.

Assessing toxicity of nanoparticles using Brachionus manjavacas (Rotifera)

Rotifers are major components of zooplankton in freshwater and coastal marine ecosystems throughout the world and could be useful indicator species, providing valuable insight into the effects of nanoparticles on microinvertebrate grazers. Here we report initial efforts to characterize the immediate and longer-term effects of nanoparticle exposure on the reproduction of the coastal marine and salt lake rotifer Brachionus manjavacas. We used chemically unreactive fluorescent nanoparticles to probe how size and concentration affects the mode of uptake, distribution within the rotifer body, reproductive rate, feeding behavior, and offspring fitness. Population growth rate (r) was depressed 50% in rotifer populations exposed to 0.30 μg mL(-1) of 37-nm particles, and 89% in populations exposed to 1.1 μg mL(-1). Larger particles of identical chemical composition, but with diameters up to 3000 nm, caused no reduction in population growth rate. These larger particles remain confined in the gut, implicating nanoparticle size as a critical factor in the ability to penetrate the gut wall and enter tissues. Transfer of the F1 offspring from nanoparticle exposed maternal females into nanoparticle-free media demonstrated that nanoparticles are rapidly cleared from the animals with no significant residual adverse effects.

Food insecurity: challenges of agricultural extension in developing countries

The emphasis on accelerated agricultural development by developing countries was meant to achieve food security. However, food insecurity has remained a problem throughout much of the developing world and is the result of such factors as slow (as well as highly variable) growth in domestic food production, rapid population growth rates, limited financial capacity to import food and inadequate external assistance. Agricultural extension, on the other hand, plays an important role in development by assuring adequate and timely access by farmers to relevant advice, with appropriate incentives to adopt new technologies if it suits their socio-economic and agroecological circumstances. This paper discusses: the concepts of food security and food insecurity; the causes and consequences of food insecurity; the short-run and long-run measures for alleviating food insecurity; the strengths and weaknesses of some extension modalities; and the modifications to existing extension systems for the achievement of food security. The conclusions drawn are that: (a) improvements in nutritional standards and food security will involve not just a certain rate of agricultural growth, but reduction in population growth rates; and (b) modifications to extension services have the potential to improve agricultural productivity, increase farmers’ incomes, and improve food security. Key words: Food insecurity, food security, agricultural extension, developing countries

Food Insecurity: Challenges of Agricultural Extension in Developing Countries

The emphasis on accelerated agricultural development by developing countries was meant to achieve food security. However, food insecurity has remained a problem throughout much of the developing world and is the result of such factors as slow (as well as highly variable) growth in domestic food production, rapid population growth rates, limited financial capacity to import food and inadequate external assistance. Agricultural extension, on the other hand, plays an important role in development by assuring adequate and timely access by farmers to relevant advice, with appropriate incentives to adopt new technologies if it suits their socio-economic and agroecological circumstances. This paper discusses: the concepts of food security and food insecurity; the causes and consequences of food insecurity; the short-run and long-run measures for alleviating food insecurity; the strengths and weaknesses of some extension modalities; and the modifications to existing extension systems for the achievement of food security. The conclusions drawn are that: (a) improvements in nutritional standards and food security will involve not just a certain rate of agricultural growth, but reduction in population growth rates; and (b) modifications to extension services have the potential to improve agricultural productivity, increase farmers’ incomes, and improve food security.

Accommodating environmental variation in population models: metaphysiological biomass loss accounting

1. There is a pressing need for population models that can reliably predict responses to changing environmental conditions and diagnose the causes of variation in abundance in space as well as through time. In this 'how to' article, it is outlined how standard population models can be modified to accommodate environmental variation in a heuristically conducive way. This approach is based on metaphysiological modelling concepts linking populations within food web contexts and underlying behaviour governing resource selection. Using population biomass as the currency, population changes can be considered at fine temporal scales taking into account seasonal variation. Density feedbacks are generated through the seasonal depression of resources even in the absence of interference competition. 2. Examples described include (i) metaphysiological modifications of Lotka-Volterra equations for coupled consumer-resource dynamics, accommodating seasonal variation in resource quality as well as availability, resource-dependent mortality and additive predation, (ii) spatial variation in habitat suitability evident from the population abundance attained, taking into account resource heterogeneity and consumer choice using empirical data, (iii) accommodating population structure through the variable sensitivity of life-history stages to resource deficiencies, affecting susceptibility to oscillatory dynamics and (iv) expansion of density-dependent equations to accommodate various biomass losses reducing population growth rate below its potential, including reductions in reproductive outputs. Supporting computational code and parameter values are provided. 3. The essential features of metaphysiological population models include (i) the biomass currency enabling within-year dynamics to be represented appropriately, (ii) distinguishing various processes reducing population growth below its potential, (iii) structural consistency in the representation of interacting populations and (iv) capacity to accommodate environmental variation in space as well as through time. Biomass dynamics provide a common currency linking behavioural, population and food web ecology. 4. Metaphysiological biomass loss accounting provides a conceptual framework more conducive for projecting and interpreting the population consequences of climatic shifts and human transformations of habitats than standard modelling approaches.

Adapting conservation efforts to face climate change: Modifying nest-site provisioning for lesser kestrels

Adaptation to climate change has recently become a crucial element on the climate change policy agenda as it is now recognized that even the most stringent mitigation efforts may not arrest the effects of climate warming. The ecological impacts and costs of predicted weather-related extreme events, such as extreme temperatures, are not fully understood and may present unexpected challenges to conservationists that require solutions. In Portugal, provisioning of artificial nests has been the main driver of the spectacular increase in the endangered lesser kestrel population. Nevertheless, atypically high temperatures recorded during the 2009 breeding season coincided with a mortality of 22% of surveyed chicks in provided nests. Hot days did not affected prey delivery rates to the nestlings, suggesting that the die-off was due to chicks’ acute dehydration. Chick mortality was significantly higher amongst younger individuals. Within survivors, physiological costs of high temperatures significantly affected chick growth and body condition at fledging. Nest-site microclimate was influenced by nest-type and compass orientation: wooden nest-boxes attained the highest temperatures, exceeding 55 °C when facing south, so explaining the recorded higher mortality, lower growth rates and lower fledging body condition among broods in these nests. Simulated scenarios of global warming with increasing occupation rate of artificial nests due to reductions in alternatives predicted a reduction in population growth rate. In the worst scenario, with a 100% occupancy of nest-boxes, the population growth would decline on average 7% per year. The impact of high temperatures on lesser kestrel breeding success highlights a need for actions to modify and research to adapt conservation efforts and future planning to account for climate change.