共查询到20条相似文献，搜索用时 15 毫秒
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Mekoya Mamo Abdella Gure Fanuel Kebede Kassahun Abie Addisu Asefa 《African Journal of Ecology》2019,57(3):404-410
This study was undertaken to determine the current population size, structure and habitat preference of Soemmerring's gazelle [Nanger soemmerringii (Cretzschmar 1828)] in the Alledeghi Wildlife Reserve, NE Ethiopia. Animals were counted, both during dry and wet seasons, along 12 line transects each in three habitat types (grassland, tree‐scattered grassland and bushland) in 2015/16. Habitat type had nonsignificant effect on mean population density of Soemmerring's gazelle, but wet season mean density was significantly higher than dry season mean density. Estimated weighted mean (±95% CI) population density of the species in the reserve was 1.90 (±0.17) and 5.99 (±0.370) individuals/km2 during the dry and wet seasons, respectively. Total population size of the species in the Alledeghi Wildlife Reserve was estimated at 826 ± 77 and 2,562 ± 158 individuals during the dry and wet seasons, respectively. Over half of the total population of Soemmerring's gazelle was represented by adult females during both seasons. Seasonal habitat preference of Soemmerring's gazelle was statistically significant, with greater preference for grassland habitat during wet season and for bushland habitat during dry season. In conclusion, this study has provided valuable data that will be used as a baseline for future population monitoring. 相似文献
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This article reviews the application of fluorescence correlation spectroscopy (FCS) and related techniques to the study of nucleic acid hairpin conformational fluctuations in free aqueous solutions. Complimentary results obtained using laser-induced temperature jump spectroscopy, single-molecule fluorescence spectroscopy, optical trapping, and biophysical theory are also discussed. The studies cited reveal that DNA and RNA hairpin folding occurs by way of a complicated reaction mechanism involving long- and short-lived reaction intermediates. Reactions occurring on the subnanoseconds to seconds time scale have been observed, pointing out the need for experimental techniques capable of probing a broad range of reaction times in the study of such complex, multistate reactions. 相似文献
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D. Carval V. Cotté M. Notaro P. Ryckewaert P. Tixier 《Journal of Applied Entomology》2015,139(7):510-518
The understanding of how environmental factors and agricultural practices affect population dynamics of insect pests is necessary for pest management. Here, we provide insight into the ecology of the banana rind thrips Elixothrips brevisetis (Bagnall) (Thysanoptera: Thripidae) by collecting and analysing a spatiotemporal database of population estimates in Martinique (West French Indies). We assessed the influence of climatic variables (which were rainfall and temperature) and biotic variables (which were banana and three weed species) on the adult thrips abundance for different components of the banana plant (sucker, mother plant and bunch) and evaluated the effect of thrips abundance and standard bunch covers on damages. The abundance of thrips on the sucker, the mother plant, and the bunch was significantly related to the abundance on neighbouring banana plants, and spatial autocorrelation indicated that E. brevisetis dispersed for only short distances. The number of thrips on the mother plant and on the bunch was positively related to the number of thrips on the sucker, suggesting that the thrips may disperse from the sucker to the mother plant and then to the bunch. The abundance of thrips on the sucker increased with sucker height and was positively correlated with the mean daily rainfall during the 17 days before sampling; the length of that period might correspond with the time required for an individual to complete its life cycle. Covered bunches had 98% fewer thrips than non‐covered bunches, and the damage caused by thrips was linearly related to the number of thrips present between the 2nd and 4th week after flowering. Finally, we found that the presence of Alocasia cucullata, Dieffenbachia seguine and Peperomia pellucida is significantly related with a decrease in thrips abundance on banana plants, suggesting the use of these weeds as potential trap plants. 相似文献
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Ebrahim Osdaghi S. Mohsen Taghavi Habiballah Hamzehzarghani Jay Ram Lamichhane 《Journal of Phytopathology》2016,164(10):722-734
We report in this study for the first time the occurrence of bacterial spot of pepper in Iran and both phenotypic and genetic characterization of its causal agent, Xanthomonas euvesicatoria. Pepper plants grown in 15 of 30 surveyed private gardens and commercial fields were infected by the pathogen in Marand County, East Azerbaijan Province, north‐western Iran. The obtained strains of X. euvesicatoria had different amylolytic and pectolytic activities compared with those reported for this species elsewhere. Pathogenicity tests showed that strains isolated from diseased pepper are able to infect tomato, in addition to pepper. Host range of the pathogen was assessed on eight annual plant species including crops and weeds by measuring the population dynamics. The host range assessment showed that in addition to pepper and tomato, known hosts of X. euvesicatoria, the Iranian strains were able to colonize a number of new hosts such as nightshade and common bean. In contrast, none of them were able to build up their population on cowpea, eggplant, bindweed and zucchini. All X. euvesicatoria strains obtained in this study were sensitive to copper sulphate and streptomycin at concentrations higher than 20 and 50 mg/l, respectively. Phylogenetic analyses of the strains using the sequences of gyrB and hrpB genes confirmed their species as X. euvesicatoria. Given a direct commercial trade of fresh solanaceous vegetables between Iran and Turkey, it is hypothesized that the pathogen entered north‐western Iran from eastern parts of Turkey through infected plant materials. Finally, the role of prevention – based on the use of healthy planting materials and resistant and/or tolerant plant varieties – to contain the potential disease epidemics is discussed. 相似文献
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- Climate change and human population growth threaten the supply of fresh water for human use and freshwater biodiversity. Long‐term studies are necessary to identify the effects of such temporal trends on biological and ecological phenomena; however, the collection of long‐term data can be costly and time‐consuming.
- We investigated the effect of hydrological variation over time on population dynamics in a perennial river of the northern Chihuahuan Desert, using an imperilled freshwater mussel (Popenaias popeii) as a model. We conducted a 15‐year mark‐and‐recapture study, and distance sampling, to estimate demographic parameters while accounting for habitat heterogeneity and changes in river discharge.
- Recapture probability varied between microhabitats, and survival was positively correlated with river discharge. Survival and the finite rate of population growth were relatively stable over time. Over 60% of individuals were found at relatively high density in riffle habitats, which compose c. 16% of the total study area.
- Mean monthly temperature in the region increased over the past 100 years, and mean monthly discharge of the Black River declined over the past 65 years. With no significant trends in total monthly precipitation, declines in discharge suggest that reduction of stream flow is likely due to lowering of the water table and decreased groundwater recharge.
- Significant changes in climate and hydrological regimes, and increases in anthropogenic threats (increased water demand, degraded water quality) in the region, may induce significant declines in population size of this imperilled mussel. We demonstrated the importance of considering habitat heterogeneity and hydrological cycles over time to examine population dynamics. Survival of benthic invertebrates in desert streams is sensitive to hydrological cycles, which are expected to be altered via climate change and extensive water use. Species recovery plans need to incorporate knowledge of spatial distributions when designing strategies for habitat assessment and making conservation decisions.
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Jeffrey P. Bibeau Erkan Tüzel Luis Vidali 《The Plant journal : for cell and molecular biology》2013,73(3):417-428
Tip growth is essential for land colonization by bryophytes, plant sexual reproduction and water and nutrient uptake. Because this specialized form of polarized cell growth requires both a dynamic actin cytoskeleton and active secretion, it has been proposed that the F‐actin‐associated motor myosin XI is essential for this process. Nevertheless, a spatial and temporal relationship between myosin XI and F‐actin during tip growth is not known in any plant cell. Here, we use the highly polarized cells of the moss Physcomitrella patens to show that myosin XI and F‐actin localize, in vivo, at the same apical domain and that both signals fluctuate. Surprisingly, phase analysis shows that increase in myosin XI anticipates that of F‐actin; in contrast, myosin XI levels at the tip fluctuate in identical phase with a vesicle marker. Pharmacological analysis using a low concentration of the actin polymerization inhibitor latrunculin B showed that the F‐actin at the tip can be significantly diminished while myosin XI remains elevated in this region, suggesting that a mechanism exists to cluster myosin XI‐associated structures at the cell's apex. In addition, this approach uncovered a mechanism for actin polymerization‐dependent motility in the moss cytoplasm, where myosin XI‐associated structures seem to anticipate and organize the actin polymerization machinery. From our results, we inferred a model where the interaction between myosin XI‐associated vesicular structures and F‐actin polymerization‐driven motility function at the cell's apex to maintain polarized cell growth. We hypothesize this is a general mechanism for the participation of myosin XI and F‐actin in tip growing cells. 相似文献
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Anna Tammilehto Phillip C. Watts Nina Lundholm 《The Journal of eukaryotic microbiology》2017,64(2):248-256
The arctic phytoplankton spring bloom, which is often diatom‐dominated, is a key event that provides the high latitude communities with a fundamental flux of organic carbon. During a bloom, phytoplankton may increase its biomass by orders of magnitude within days. Yet, very little is known about phytoplankton bloom dynamics, including for example how blooming affects genetic composition and diversity of a population. Here, we quantified the genetic composition and temporal changes of the diatom Fragilariopsis cylindrus, which is one of the most important primary producers in the Arctic, during the spring bloom in western Greenland, using 13 novel microsatellite markers developed for this study. We found that genetic differentiation (quantified using sample‐specific FST) decreased between time points as the bloom progressed, with the most drastic changes in FST occurring at the start of the bloom; thus the genetic structure of the bloom is characterized by isolation by time. There was little temporal variation in genetic diversity throughout the bloom (mean HE = 0.57), despite marked fluctuations in F. cylindrus cell concentrations and the temporal change in sample‐specific FST. On the basis of this novel pattern of genetic differentiation, we suggest that blooming behavior may promote genetic diversity of a phytoplankton population. 相似文献
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Species interactions change when the external conditions change. How these changes affect microbial community properties is an open question. We address this question using a two‐species consortium in which species interactions change from exploitation to competition depending on the carbon source provided. We built a mathematical model and calibrated it using single‐species growth measurements. This model predicted that low frequencies of change between carbon sources lead to species loss, while intermediate and high frequencies of change maintained both species. We experimentally confirmed these predictions by growing co‐cultures in fluctuating environments. These findings complement more established concepts of a diversity peak at intermediate disturbance frequencies. They also provide a mechanistic understanding for how the dynamics at the community level emerges from single‐species behaviours and interspecific interactions. Our findings suggest that changes in species interactions can profoundly impact the ecological dynamics and properties of microbial systems. 相似文献
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G. K. Awudzi A. R. Cudjoe P. Hadley P. E. Hatcher A. J. Daymond 《Journal of Applied Entomology》2017,141(4):247-255
Mirids (Sahlbergella singularis and Distantiella theobroma) are the most important insect pests affecting cocoa production across West Africa. Understanding the population dynamics of mirids is key to their management; however, the current recommended hand‐height assessment method is labour intensive. The objective of the study was to compare recently developed mirid sex pheromone trapping and visual hand‐height assessment methods as monitoring tools on cocoa farms and to consider implications for a decision support system. Ten farms from the Eastern and Ashanti regions of Ghana were used for the study. Mirid numbers and damage were assessed fortnightly on twenty trees per farm, using both methods, from January 2012 to April 2013. The mirid population increased rapidly in June, reached a peak in September and began to decline in October. There was a significant linear relationship between numbers of mirids sampled to hand‐height and mirid damage. High numbers of male mirids were recorded in pheromone traps between January and April 2012 after which there was a gradual decline. There was a significant inverse relationship between numbers of trapped adult mirids and mirids sampled to hand‐height (predominantly nymphs). Higher temperatures and lower relative humidities in the first half of the year were associated with fewer mirids at hand‐height, but larger numbers of adult males were caught in pheromone traps. The study showed that relying solely on one method is not sufficient to provide accurate information on mirid population dynamics and a combination of the two methods is necessary. 相似文献
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Liselotte Wesley Andersen Ronja Dirksen Elena A. Nikulina Hans J. Baage Gunars Petersons Pter Estk Oleg L. Orlov Maria V. Orlova Florian Gloza‐Rausch Matthias Gttsche Esben Terp Fjederholt Frauke Krüger Morten Elmeros 《Ecology and evolution》2019,9(9):5292-5308
Conservation genetics is important in the management of endangered species, helping to understand their connectivity and long‐term viability, thus identifying populations of importance for conservation. The pond bat (Myotis dasycneme) is a rare species classified as “Near Threatened” with a wide but patchy Palearctic distribution. A total of 277 samples representing populations in Denmark, Germany, Latvia, Hungary, and Russia were used in the genetic analyses; 224 samples representing Denmark, Germany, and Russia were analyzed at 10 microsatellite loci; 241 samples representing all areas were analyzed using mitochondrial D‐loop and cytochrome B sequences. A Bayesian clustering approach revealed two poorly resolved clusters, one representing the Danish and German groups and the other the Russian group. However, significantly different pairwise FST and DEST estimates were observed between the Danish and German groups and between the Danish and Russian groups suggesting a recent population structure. These conflicting results might be attributed to the effect of migration or low resolution due to the number of microsatellite markers used. After concatenating the two mitochondrial sequences, analysis detected significant genetic differentiation between all populations, probably due to genetic drift combined with a founder event. The phylogenetic tree suggested a closer relationship between the Russian and Northern European populations compared to the Hungarian population, implying that the latter belongs to an older ancestral population. This was supported by the observed haplotype network and higher nucleotide diversity in this population. The genetic structuring observed in the Danish/German pond bat stresses the need for a cross‐border management between the two countries. Further, the pronounced mtDNA structuring, together with the indicated migration between nearby populations suggest philopatric female behavior but male migration, emphasizes the importance of protecting suitable habitat mosaics to maintain a continuum of patches with dense pond bat populations across the species' distribution range. 相似文献
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Exposure of plants to UV‐C irradiation induces gene expression and cellular responses that are commonly associated with wounding and pathogen defence, and in some cases can lead to increased resistance against pathogen infection. We examined, at a physiological, molecular and biochemical level, the effects of and responses to, sub‐lethal UV‐C exposure on Arabidopsis plants when irradiated with increasing dosages of UV‐C radiation. Following UV‐C exposure plants had reduced leaf areas over time, with the severity of reduction increasing with dosage. Severe morphological changes that included leaf glazing, bronzing and curling were found to occur in plants treated with the 1000 J·m?2 dosage. Extensive damage to the mesophyll was observed, and cell death occurred in both a dosage‐ and time‐dependent manner. Analysis of H2O2 activity and the pathogen defence marker genes PR1 and PDF1.2 demonstrated induction of these defence‐related responses at each UV‐C dosage tested. Interestingly, in response to UV‐C irradiation the production of callose (β‐1,3‐glucan) was identified at all dosages examined. Together, these results show plant responses to UV‐C irradiation at much lower doses than have previously been reported, and that there is potential for the use of UV‐C as an inducer of plant defence. 相似文献
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Harbor seal breeding behavior and habitats constrain opportunities for individual‐based studies, and no current estimates of both survival and fecundity exist for any of the populations studied worldwide. As a result, the drivers underlying the variable trends in abundance exhibited by harbor seal populations around the world remain uncertain. We developed an individual‐based study of harbor seals in northeast Scotland, whereby data were collected during daily photo‐identification surveys throughout the pupping seasons between 2006 and 2011. However, a consequence of observing seals remotely meant that information on sex, maturity‐stage, or breeding status was not always available. To provide unbiased estimates of survival rates we conditioned initial release of individuals on the first time sex was known to estimate sex‐specific survival rates, while a robust design multistate model accounting for uncertainty in breeding status was used to estimate reproductive rate of multiparous and ≥3‐yr‐old females. Survival rates were estimated at 0.95 (95% CI = 0.91–0.97) for females and 0.92 (0.83–0.96) for males, while reproductive rate was estimated at 0.89 (0.75–0.95) for multiparous and 0.69 (0.64–0.74) for ≥3‐yr‐old females. Stage‐based population modeling indicated that this population should be recovering, even under the current shooting quotas implemented by the recent management plan. 相似文献
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Katri Korpela Maria Delgado Heikki Henttonen Erkki Korpimäki Esa Koskela Otso Ovaskainen Hannu Pietiäinen Janne Sundell Nigel G Yoccoz Otso Huitu 《Global Change Biology》2013,19(3):697-710
Small rodents are key species in many ecosystems. In boreal and subarctic environments, their importance is heightened by pronounced multiannual population cycles. Alarmingly, the previously regular rodent cycles appear to be collapsing simultaneously in many areas. Climate change, particularly decreasing snow quality or quantity in winter, is hypothesized as a causal factor, but the evidence is contradictory. Reliable analysis of population dynamics and the influence of climate thereon necessitate spatially and temporally extensive data. We combined data on vole abundances and climate, collected at 33 locations throughout Finland from 1970 to 2011, to test the hypothesis that warming winters are causing a disappearance of multiannual vole cycles. We predicted that vole population dynamics exhibit geographic and temporal variation associated with variation in climate; reduced cyclicity should be observed when and where winter weather has become milder. We found that the temporal patterns in cyclicity varied between climatically different regions: a transient reduction in cycle amplitude in the coldest region, low‐amplitude cycles or irregular dynamics in the climatically intermediate regions, and strengthening cyclicity in the warmest region. Our results did not support the hypothesis that mild winters are uniformly leading to irregular dynamics in boreal vole populations. Long and cold winters were neither a prerequisite for high‐amplitude multiannual cycles, nor were mild winters with reduced snow cover associated with reduced winter growth rates. Population dynamics correlated more strongly with growing season than with winter conditions. Cyclicity was weakened by increasing growing season temperatures in the cold, but strengthened in the warm regions. High‐amplitude multiannual vole cycles emerge in two climatic regimes: a winter‐driven cycle in cold, and a summer‐driven cycle in warm climates. Finally, we show that geographic climatic gradients alone may not reliably predict biological responses to climate change. 相似文献
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Mit mutations that disrupt function of the mitochondrial electron transport chain can, inexplicably, prolong Caenorhabditis elegans lifespan. In this study we use a metabolomics approach to identify an ensemble of mitochondrial‐derived α‐ketoacids and α‐hydroxyacids that are produced by long‐lived Mit mutants but not by other long‐lived mutants or by short‐lived mitochondrial mutants. We show that accumulation of these compounds is dependent on concerted inhibition of three α‐ketoacid dehydrogenases that share dihydrolipoamide dehydrogenase (DLD) as a common subunit, a protein previously linked in humans with increased risk of Alzheimer's disease. When the expression of DLD in wild‐type animals was reduced using RNA interference we observed an unprecedented effect on lifespan – as RNAi dosage was increased lifespan was significantly shortened, but, at higher doses, it was significantly lengthened, suggesting that DLD plays a unique role in modulating length of life. Our findings provide novel insight into the origin of the Mit phenotype. 相似文献
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Capture–mark–recapture (CMR) approaches are the backbone of many studies in population ecology to gain insight on the life cycle, migration, habitat use, and demography of target species. The reliable and repeatable recognition of an individual throughout its lifetime is the basic requirement of a CMR study. Although invasive techniques are available to mark individuals permanently, noninvasive methods for individual recognition mainly rest on photographic identification of external body markings, which are unique at the individual level. The re‐identification of an individual based on comparing shape patterns of photographs by eye is commonly used. Automated processes for photographic re‐identification have been recently established, but their performance in large datasets (i.e., > 1000 individuals) has rarely been tested thoroughly. Here, we evaluated the performance of the program AMPHIDENT, an automatic algorithm to identify individuals on the basis of ventral spot patterns in the great crested newt (Triturus cristatus) versus the genotypic fingerprint of individuals based on highly polymorphic microsatellite loci using GENECAP. Between 2008 and 2010, we captured, sampled and photographed adult newts and calculated for 1648 samples/photographs recapture rates for both approaches. Recapture rates differed slightly with 8.34% for GENECAP and 9.83% for AMPHIDENT. With an estimated rate of 2% false rejections (FRR) and 0.00% false acceptances (FAR), AMPHIDENT proved to be a highly reliable algorithm for CMR studies of large datasets. We conclude that the application of automatic recognition software of individual photographs can be a rather powerful and reliable tool in noninvasive CMR studies for a large number of individuals. Because the cross‐correlation of standardized shape patterns is generally applicable to any pattern that provides enough information, this algorithm is capable of becoming a single application with broad use in CMR studies for many species. 相似文献
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Spatial synchrony of population fluctuations is ubiquitous in nature. Theoretical models suggest that correlated environmental stochasticity, dispersal, and trophic interactions are important promoters of synchrony in nature to leave characteristic signatures of distance‐dependent decays in synchrony. Recent refinements of this theory have clarified how distance‐decay curves may steepen if local dynamics are governed by different density‐dependent feedbacks and how synchrony should vary regionally if the importance and correlation of environmental stochasticity is location‐specific. We analysed spatiotemporal data for the common vole, Microtus arvalis from 49 districts in the Czech Republic to examine the pattern of population synchrony between 2000 and 2014. By extending the nonparametric covariation function, we develop a quantitative method that allows a dissection of the effects of distance and additional variables such as altitude on synchrony. To examine the pattern of local synchrony, we apply the noncentered local‐indicators of spatial association (ncLISA) which highlights areas with different degrees of synchrony than expected by the region‐wide average. Additionally, in order to understand the obtained pattern of local spatial correlations, we have regressed LISA results against the proportion of forest in each district. The common vole abundances fluctuated strongly and exhibited synchronous dynamics with the typical tendency for a decline of synchrony with increasing distance but, not with altitude. The correlation between the neighbor districts decreases as the proportion of forest increases. Forested areas are suboptimum habitats and are strongly avoided by common voles. The investigation of spatiotemporal dynamics in animal populations is a key issue in ecology. Although the majority of studies are focused on testing hypotheses about which mechanisms are involved in shaping this dynamics it is crucial to understand the sources of variation involved in order to understand the underlying processes. 相似文献
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Pradeep Sharma Shefali Bharati Pandey Senthilkumar K. Muthusamy Satish Kumar Mahender Singh Saharan Sudheer Kumar Garima Singroha Indu Sharma Gyanendra Pratap Singh 《Journal of Phytopathology》2018,166(10):729-738
Simple sequence repeats (SSRs) are preferred molecular markers because of their abundance, robustness, high reproducibility, high efficiency in detecting variation and suitability for high‐throughput analysis. In this study, an attempt was made to mine and analyse the SSRs from the genomes of two seed‐borne fungal pathogens, viz Ustilago maydis, which causes common smut of maize, and Tilletia horrida, the cause of rice kernel smut. After elimination of redundant sequences, 2,703 SSR loci of U. maydis were identified. Of the remaining SSRS, 44.5% accounted for di‐nucleotide repeats followed by 29.8% and 2.7% tri‐ and tetranucleotide repeats, respectively. Similarly, 2,638 SSR loci were identified in T. horrida, of which 20.2% were di‐nucleotide, 50.4% tri‐ and 20.5% tetra‐nucleotide repeats. A set of 65 SSRs designed from each fungus were validated, which yielded 23 polymorphic SSRs from Ustilago and 21 from Tilletia. These polymorphic SSR loci were also successfully cross‐amplified with the Ustilago segetum tritici and Tilletia indica. Principal coordinate analysis of SSR data clustered isolates according to their respective species. These newly developed and validated microsatellite markers may have immediate applications for detection of genetic variability and in population studies of bunt and smut of wheat and other related host plants. Moreover, this is first comprehensive report on molecular markers suitable for variability studies in wheat seed‐borne pathogens. 相似文献
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For many species of reptile, crucial demographic parameters such as embryonic survival and individual sex (male or female) depend on ambient temperature during incubation. While much has been made of the role of climate on offspring sex ratios in species with temperature‐dependent sex determination (TSD), the impact of variable sex ratio on populations is likely to depend on how limiting male numbers are to female fecundity in female‐biased populations, and whether a climatic effect on embryonic survival overwhelms or interacts with sex ratio. To examine the sensitivity of populations to these interacting factors, we developed a generalized model to explore the effects of embryonic survival, hatchling sex ratio, and the interaction between these, on population size and persistence while varying the levels of male limitation. Populations with TSD reached a greater maximum number of females compared to populations with GSD, although this was often associated with a narrower range of persistence. When survival depended on temperature, TSD populations persisted over a greater range of temperatures than GSD populations. This benefit of TSD was greatly reduced by even modest male limitation, indicating very strong importance of this largely unmeasured biologic factor. Finally, when males were not limiting, a steep relationship between sex ratio and temperature favoured population persistence across a wider range of climates compared to the shallower relationships. The opposite was true when males were limiting – shallow relationships between sex ratio and temperature allowed greater persistence. The results highlight that, if we are to predict the response of populations with TSD to climate change, it is imperative to 1) accurately quantify the extent to which male abundance limits female fecundity, and 2) measure how sex ratios and peak survival coincide over climate. 相似文献