Recruitment Of New Individuals Research Articles

Rodents mediate the relationship between seed rain, seed bank, and plant community with increased grazing disturbance.

Seed rain and the soil seed bank represent the dispersal of seeds in space and time, respectively, and can be important sources of recruitment of new individuals during plant community regeneration. However, the temporal dynamics of seed rain and the mechanisms by which the seed rain and soil seed bank may play a role in plant community regeneration with increased grazing disturbance remain unclear. Seed rain, soil seed bank, aboveground vegetation, and rodent density were sampled along a grazing gradient in an alpine marsh on the eastern Tibetan Plateau. We described the temporal dynamics of seed dispersal using Bayesian generalized mixed models, and nonmetric multidimensional scaling and the structural equation model were used to examine the effects of grazing disturbance on the relative role of seed rain and soil seed bank on aboveground plant community regeneration. The temporal dynamics of seed rain changed from a unimodal to a bimodal pattern with increased grazing disturbance. Both species diversity and seed density of the seed rain and seed bank increased significantly with increased grazing disturbance. Increased grazing disturbance indirectly increased the similarity of composition between seed rain, seed bank, and aboveground plant community by directly increasing species diversity and abundance of aboveground plant community. However, increased grazing disturbance also indirectly decreased the similarity of seed rain, soil seed bank, and aboveground plant community by directly increasing rodent density. The similarity between seed rain and aboveground plant community was greater than that of the soil seed bank and aboveground plant community with increased grazing disturbance. Grazing disturbance spreads the risk of seed germination and seedling establishment by changing the temporal dynamics of seed dispersal. Plants (positive) and rodents (negative) mediated the role of seed rain and soil seed bank in plant community regeneration. The role of seed rain in plant community regeneration is higher than the seed bank in disturbed alpine marshes. Our findings increase our understanding of the regeneration process of the plant community, and they provide valuable information for the conservation and restoration of alpine marsh ecosystems.

Structural diversity is better associated with forest productivity than species or functional diversity.

Understanding the relationship between biodiversity and productivity can be advanced by improving metrics used to quantify biodiversity. Structural diversity, that is, variation of size and form of plant organs, is an emerging biodiversity metric. However, compared with the other biodiversity metrics, its relative importance in specific components of forest productivity, for example, recruitment of new individuals, biomass net change after accounting for mortality, is largely unknown, particularly across a large spatial scale with multiple influential gradients. To address the knowledge gap, we used USDA Forest Service Forest Inventory and Analysis (FIA) data across the southcentral USA from 2008 to 2017. We calculated forest biomass increments due to recruitment and growth and net change in biomass. Then, we quantified the effects of a range of abiotic and biotic variables on the biomass increments and net change. Our results showed that (1) Structural diversity was negatively associated with the two biomass increments and net change in biomass. The negative effects were supported by increased occurrences of insects and diseases with greater structural diversity. (2) Compared with species and functional diversity, structural diversity showed a better association with biomass increments and net change, suggested by its larger absolute values of standardized coefficients, and the effects of structural diversity were negative in contrast to species diversity. (3) The effects of structural diversity, stand age, and elevation differed between natural and planted forests that may stem from the differences in stand development and species composition between the two forest types. Together, structural diversity may represent an important dimension of biodiversity impacts on plant productivity, which could be related to the exacerbated disturbances with greater structural diversity.

Age structure and climate sensitivity of a high Andean relict forest of Polylepis rodolfo-vasquezii in central Peru

For a better understanding of forest ecology, tree-ring studies can provide information on climate sensitivity, tree growth patterns and population age structure that can inform about stand dynamics such as recruitment of new individuals, and other interspecific interactions related to competition and facilitation. Little is known about the ecology of the recently identified high Andean tree species Polylepis rodolfo-vasquezii. Here, we analyzed the relationship between tree size and age of two P. rodolfo-vasquezii forest stands located in the central Peruvian Andes at 11°S in latitude, and compared their growth patterns and climate sensitivity. We measured the height and diameter of each individual tree and collected tree core samples of living trees and cross sections of dead standing trees to generate two centennial tree-ring chronology at Toldopampa (1825–2015 CE) and at Pomamanta (1824–2014 CE) sites. The dendrochronological dates were evaluated by 14C analysis using the bomb-pulse methods analyzing a total of 9 calendar years that confirm the annual periodicity of this tree species. At the Toldopampa stand most trees ranged from 70 to 80 years old, with a 190-year old individual, being an older and better preserve forest than Pomamanta, with younger trees, probably because more human disturbances due to closer village proximity. No significant relationships were found between tree age and size in the oldest stand alerting that tree diameter should not be used as a metric for estimating tree ages as a general rule. The distinct growth patterns and the size-age relationship observed at the two forests may reflect distinct histories regarding human activities such as fire and logging. Nevertheless, both the Toldopampa and the Pomamanta tree-ring width chronologies exhibited common growth patterns and shared a similar positive response to temperature of the current growing season. Overall, our study confirmed the annual radial growth periodicity in P. rodofolfo-vasquezii trees using an independent method such as 14C analyses and a strong climate sensitivity of this tree species. These findings encourage the development of an extensive P. rodolfo-vasquezii tree-ring network for ecological and paleoclimate studies in the tropical Andes in South America.

Early development of two savanna tree species under simulated dry spells

The seedling stage represents a bottleneck in plants' life cycle, particularly in savanna environments, where the rainy season is the major window of opportunity for seedling development and recruitment of new individuals. However, an increase in the duration and frequency of dry spells (days without rain during the rainy season) is expected due to climate change, which may affect species recruitment and establishment. The aim of this study was to examine the effect of simulated dry spells on the growth performance and biomass of Qualea grandiflora and Tabebuia aurea seedlings. Seedlings (60 days old) were exposed to three irrigation treatments (daily irrigation, irrigation every 8 days, and irrigation every 15 days) for 130 days. We found no mortality in any of the irrigation treatments for both species. Although the growth parameters of Q. grandiflora were not significantly affected by the dry spells, the species invested more in shoot growth than in root growth. In contrast, there was a significant decrease in the root dry mass, root:shoot ratio, root biomass fraction, and relative growth rate of T. aurea seedlings exposed to dry spells of 15 days; but there was a significant increase in the specific taproot length and shoot biomass fraction. Overall, the plants showed species-specific responses to the dry spell treatments. Further, T. aurea seedlings invested more resources in taproot growth in response to dry spells. The development of deep-reaching taproots could be an effective physiological adaptation strategy for the survival and establishment of young plants and the resilience of native tree populations under future adverse climate scenarios.

Rarely naturalized, but widespread and even invasive: the paradox of a popular pet terrapin expansion in Eurasia

The North American terrapin, the red-eared slider, has globally recognized invasive status. We built a new extensive database using our own original and literature data on the ecology of this reptile, representing information on 1477 water bodies throughout Eurasia over the last 50 years. The analysis reveals regions of earliest introductions and long-term spatio-temporal dynamics of the expansion covering now 68 Eurasian countries, including eight countries reported here for the first time. We established also long-term trends in terms of numbers of terrapins per aquatic site, habitat occupation, and reproduction success. Our investigation has revealed differences in the ecology of the red-eared slider in different parts of Eurasia. The most prominent expression of diverse signs of invasion success (higher portion of inhabited natural water bodies, higher number of individuals per water body, successful overwintering, occurrence of juvenile individuals, successful reproduction, and establishment of populations) are typical for Europe, West Asia and East Asia and tend to be restricted to coastal regions and islands. Reproduction records coincide well with the predicted potential range based on climatic requirements but records of successful wintering have a wider distribution. This invader provides an excellent and possibly unique (among animals) example of wide alien distribution, without the establishment of reproducing populations, but through the recruitment of new individuals to rising pseudopopulations due to additional releases. Therefore, alongside the potential reproduction range, a cost-effective strategy for population control must take in account the geographical area of successful wintering.

Correlations in recruitment patterns of Atlantic reef fishes off the southeastern United States based on multi-decadal estimates from stock assessments

Atlantic reef fishes off the southeastern United States support a multispecies fishery important to both commercial and recreational fleets. Productivity of this reef-fish complex is driven to a large degree by recruitment of new individuals into their respective populations. In this study, we analyzed patterns in time series of annual recruitment of ten Atlantic reef-fish species, primarily snappers and groupers, that have been the subject of separate single-species stock assessments. Our focus was on identifying patterns in autocorrelation of recruitment within species and on uncovering patterns in correlation across species. We found that autocorrelation of recruitment deviations was evident in the majority (9/10) of species with a dominant lag of one year. Pairwise correlations between species were both positive and negative. Principal component analysis revealed two general groups of species: those that exhibited lower-than-expected recruitment in recent years and those that did not exhibit such low recruitment (either near expected or higher-than-expected). These results point toward common drivers of recruitment (e.g., environmental, ecological, exploitation) in this complex of reef-associated fishes, and they are a critical first step for developing hypotheses of underlying mechanisms. Additionally, they have practical importance for stock assessments that forecast recruitment when forming fishery management advice.

A Draft Reference Genome Assembly of the Critically Endangered Black Abalone, Haliotis cracherodii.

The once abundant black abalone, Haliotis cracherodii, is a large, long-lived grazing marine mollusk that inhabits the rocky intertidal along the coast of California. The species has experienced dramatic declines since the mid-1980s largely due to the fatal bacterial disease called withering syndrome, leading to the collapse of an economically important fishery and to its inclusion into the IUCN listing as a critically endangered species. In some places impacted by the disease, populations of black abalone have declined by more than 90%, prompting population crashes associated with very little recruitment of new individuals and changes to intertidal communities. Habitats that were dominated by crustose coralline algae and bare rock have become dominated instead by fleshy algae and sessile invertebrates. Here, we present the first high-quality black abalone reference genome, assembled with PacBio HiFi long-reads and assembled with Dovetail Omni-C data to generate a scaffold-level assembly. The black abalone reference genome will be an essential resource in understanding the evolutionary history of this species as well as for exploring its current levels of genetic diversity and establishing future management and restoration plans.

Highlighted articles for March 2022.

Highlighted articles for March 2022.

Variability in site characteristics linked to bay scallop abundance but not tethered survival: Implications for restoration

While predation impacts the abundance and distribution of prey species, the overall impact of predation varies with predator identity, predator density, and habitat complexity, among other factors. Numerous commercially and recreationally important prey species, such as bivalves, face intense predation that may affect management and restoration efforts. Therefore, predicting sites with elevated predation risk can be critical for successful restoration, although making predictions based on lab feeding assays may provide challenges. This study used bay scallops Argopecten irradians as a model organism to examine scallop abundance and survival in relation to predator density, habitat complexity, and predicted consumption, across multiple sites within the same estuary. Published predator-specific relationships between scallop consumption and habitat complexity were combined with field survey data to predict consumption potential at six sites in Shinnecock Bay, NY, USA. Using a series of Pearson correlations, the relationships between scallop abundance and tethered survival and site characteristics (habitat complexity, predator density, estimated consumption, scallop recruitment) were explored. Seagrass cover and recruitment of new individuals both strongly influenced scallop abundance, although tethered survival was not strongly correlated to any site metric (predator density, seagrass complexity, or estimated consumption). This study demonstrates potential issues when trying to link mesocosm studies to the field environment, such as sites with no seagrass but potentially confounding habitat complexity (i.e., Crepidula fornicata) and overestimates of consumption due to lack of realism in mesocosm studies. Overall, our study highlights the necessity of conducting field experiments to test mesocosm results, but also provides several valuable conclusions for shellfish restoration.

Biological Aspects and Movements of Neotropical Fruit-Feeding Butterflies.

The patterns of insect movement are the cumulate product of many individual decisions and can be shaped by the way morphology and behaviour interacts with landscape structure and composition. Hence, the ongoing process of habitat fragmentation increases the distance among suitable habitats and changes those in such a way that it may favour some movement behaviour. Our study described some biological traits (sex ratio, age structure and individual permanence in a population), as well as the movements of fruit-feeding butterflies along the horizontal dimension (among habitats: forest interior, natural forest transition - ecotone and anthropogenic forest transition - edge) and the vertical dimension (between canopy and understory). We sampled butterflies monthly over 1year in the Atlantic rainforest, South-eastern Brazil, following a standardized design using bait traps. We found that sex ratio was male biased for five out of the six more abundant species and the age structure showed an increase in recruitment of new individuals in the dry season followed by a noticeable aging of the populations in the wet season. In general, our results revealed an aggregated spatial distribution, in which few individuals travelled long distances while most individuals were recaptured in the same trap, suggesting that all studied habitats currently provide the necessary conditions for the maintenance of butterfly populations, favouring fewer movements and narrow home ranges for both sexes and species. Conservation of a set of heterogeneous habitats it is especially important for the maintenance of sedentary butterflies and of those that move large distances.

Water the odds? Spring rainfall and emergence‐related seed traits drive plant recruitment

Recruitment of new individuals from seed is a critical component of plant community assembly and reassembly, especially in the context of ecosystem disturbance and recovery. While frameworks typically aim to predict how communities will be filtered on the basis of traits influencing established plant responses to the environment, assembly from seed is more complex: the responses of seeds (affected by dormancy and germination function) and establishing plants (affected by root and leaf function) can both influence outcomes within a single growing season. This creates a potential role for a more diverse set seed and seedling traits, and for environmental variability on shorter timescales (e.g. seasonal versus annual dynamics), than are typically considered. We followed thousands of individual seeds comprising eleven herbaceous grassland species through the first growing season, seeking to uncover critical environmental (precipitation amount and timing) and trait‐based filters on seedling emergence and survival in assembling communities. We saw the biggest recruitment limitation when seeds failed to emerge, driven independently by a dry spring and interspecific variation in seed mass (positive effect) and seed dormancy (negative effect). Seedling survival rates were higher than emergence, with weaker predictive roles for traits like seedling root mass allocation (positive effect) and seed mass (positive under spring drought), and lesser impacts of summer rainfall on soil moisture and survival. Interestingly, most trait relationships were not conditional on rainfall, suggesting water‐independent mechanisms of their respective advantages. Although recruitment is a complex process, our findings suggest that trait‐based assembly frameworks can be a useful way to anticipate outcomes, particularly if dynamic early‐stage conditions (e.g. spring rainfall) and attributes (e.g. seed dormancy) receive greater attention. Given the importance of recruitment for community turnover in the context of global change and land management efforts, this is an area ripe for continued expansion in trait‐based and applied ecology.

Enigmatic Near‐Extirpation in a Boreal Toad Metapopulation in Northwestern Montana

ABSTRACTNorth America's protected lands harbor biodiversity and provide habitats where species threatened by a variety of stressors in other environments can thrive. Yet disease, climate change, and other threats are not limited by land management boundaries and can interact with conditions within protected landscapes to affect sensitive populations. We examined the population dynamics of a boreal toad (Anaxyrus boreas boreas) metapopulation at a wildlife refuge in northwestern Montana, USA, over a 16‐year period (2003–2018). We used robust design capture‐recapture models to estimate male population size, recruitment, and apparent survival over time and in relation to the amphibian chytrid fungus (Batrachochytrium dendrobatidis). We estimated female population size in years with sufficient captures. Finally, we examined trends in male and female toad body size and condition. We found no evidence of an effect of disease or time on male toad survival but detected a strong negative trend in recruitment of new males to the population. Estimates of male and female abundance decreased over time. Body size of males and females was inversely related to estimated population size, consistent with reduced recruitment to replace adults, but body condition of adult males was only weakly associated with abundance. Together, these results describe the demography of a near‐extirpation event, and point to dramatic decreases in the recruitment of new individuals to the breeding population as the cause of this decline. We surmise that processes related to the restoration of historical hydrology within the refuge adversely affected amphibian breeding habitat, and that these changes interacted with disease, life history, and other factors to restrict the recruitment of new individuals to the breeding population over time. Our results point to challenges in understanding and predicting factors that influence population change and highlight that current metrics for assessing population status can have limited predictive ability. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

Effect of brousse tigrée on the dynamics of nurse–protégé interactions of a cactus in the Chihuahuan Desert

AbstractA nurse–protégé relationship is a frequent facilitation interaction in deserts that allows the recruitment of new individuals of many species. Our aim was to evaluate the relationship of Echinocereus enneacanthus during its life cycle and its nurse plants in the brousse tigrée (tiger bush) vegetation of the Chihuahuan Desert. The population structure of the cactus is skewed toward adult stages, which are commonly found in the bare areas of the brousse tigrée, whereas juveniles are located in the vegetated bands. The vegetation structure and the nurse–protégé relationship were determined using censuses of 19 permanent plots monitored between 2008 and 2019. The differential association of E. enneacanthus with potential nurse plants was evaluated using an interaction network, under the hypothesis of strict association of the seedlings and juveniles with nurse species. In addition, χ2 tests and standardized residuals were fitted among likely nurse species, weighted by the cover of the nurse and of the areas without vegetation. The study species, as well as the nurse plants, had an aggregated distribution pattern. The interaction network showed that the frequency of the association with nurse plants decreased as the size of the protégé individuals increased. At the same time, there were differences in the establishment of E. enneacanthus under particular nurse plants; Prosopis glandulosa and Hilaria mutica were the most important. The nurse–protégé relationship for seeds and seedlings is integral to the vegetation bands of the brousse tigrée.

Long-Term Changes in Spatial Patterns and Life-Stage Structure in a Population of Senecio umbrosus Waldst. et Kit. Along With the Transformation of Grassland Vegetation

This paper was a part of studies conducted within an island population of the ragwort <em>Senecio umbrosus </em>(White Mt, southeastern Poland), a vulnerable element of xerothermic grasslands. Special attention was paid to the effects of expansive grass encroachment vs. grassland burning episodes on spatiotemporal patterns and life-stage structure of individuals in the population. The population traits were investigated nine times from 1990 to 2010, within three permanent patches differing in soil properties, initial floristic composition, grassland cover (particularly the cover of <em>Brachypodium pinnatum</em>), ragwort cover and density, shrub/tree cover influencing light intensity (full light–shadow), and grassland burning (zero–six episodes). There was a drastic decline in ragwort abundance within all the study patches accompanied by a decrease in the population clustering coefficient and a gradual equalization of the spatial distribution of ramets. The abundance was negatively correlated (PCA analysis) with an increase in <em>B. pinnatum </em>cover and positively correlated with the number of burning episodes, which temporarily delimited persistent litter cover and facilitated recruitment of new individuals. The decrease in ramet abundance ranged from 3.8 times (medium-high, moderately shadowed grassland; six cases of burning) to 8.3 times (high, dense, and shadowed grassland; four cases of burning). The patch of low, loose, sunlit, and never-burned grassland with the greatest initial density of ragwort (a 6.8-fold decrease in abundance) has evolved with time into a high and dense grassland with a greater coverage of <em>B. pinnatum </em>and <em>Calamagrostis epigejos</em>, additionally shaded by shrubs and young trees.

The role of fruits and fires in the germination of a rare subshrub, Amorpha georgiana (Fabaceae)1

Seed dormancy is a trait that has evolved to maximize germination when environmental conditions are optimal for successful recruitment of new individuals into a population. Physical dormancy is one such trait common in legumes and release from this condition is often associated with disturbance events, such as fire. Changes to the specific conditions (e.g., climate, fire regimes) that release seeds from dormancy can have negative effects on populations, especially of rare species. Therefore, understanding the species-specific requirements needed to release seeds from dormancy and induce germination provides insight into ecological processes, effects of changing environmental conditions, and potential conservation actions. Amorpha georgiana (Fabaceae) is a rare subshrub with indehiscent fruits (pods) found in fire-maintained longleaf pine habitats in the southeastern United States. The germination ecology of this species is largely unknown. The goals of this study were to determine the presence of physically dormant seed in A. georgiana and then, through a series of laboratory-based experiments, resolve the fire related factors that effectively overcome dormancy and promote germination. The seeds of A. georgiana exhibit physical dormancy and show significantly higher germination after brief exposure to hot water (94 °C) compared to all other temperatures and treatments assessed. Regardless of treatment, seeds have low germination when retained in their pods, but the pod is not the cause of physical dormancy. We found enclosure within an indehiscent pod and exposure to pyrogenic temperatures (> 80 °C) both affect dormancy release and germination of A. georgiana. The 3.5-fold increase in germination at pyrogenic temperatures suggests the response is highly fire-adapted and fits the definition of obligate pyrogenic dormancy release. While season of fire exposure was not significant in our study, we did find consistent negative effects on the germination response. Our results suggest pulses of heat from periodic growing season fires are likely necessary to promote recruitment and maintain populations of this rare species.

Increasing aridity threatens the sexual regeneration of Quercus ilex(holm oak) in Mediterranean ecosystems.

Knowledge of the recruitment of dominant forest species is a key aspect for forest conservation and the ecosystem services they provide. In this paper, we address how the simultaneous action of climate change and the intensity of land use in the past influence the recruitment of a forest species that depends on the provision of nurse plants to recruit. We compared the number of saplings (up to 15 years old) and juveniles (16 to 50 years old) of Quercus ilex in 17, 5.3 ha plots in the Iberian System (eastern Spain). We used a gradient of past deforestation intensity crossed with two levels of average annual precipitation, one of them at the lower limit of the species' precipitation niche (semi-arid) and the other at the optimum (sub-humid). We also examined the association between recruits and nurse plants and the effect on this association of plot-scale factors, such as seed abundance (reproductive Q. ilex), microsites (nurse species and soil availability), and large herbivores. The increase in aridity in the last decades has drastically reduced the recruitment of new individuals in the forests of Q. ilex located in the lower limit of their precipitation niche, regardless of the intensity of past deforestation that they suffered. Recruitment in these climatic conditions depends almost exclusively on large trees and shrubs whose abundance may also be limited by aridity. The lack of regeneration questions the future of these populations, as the number of individuals will decrease over time despite the strong resistance of adult trees to disturbance and drought.

Burning grasses, poor seeds: post-fire reproduction of early-flowering Neotropical savanna grasses produces low-quality seeds

Fire is a key factor triggering ecological processes in old-growth grasslands and savannas and could have strong implications for reproduction via seeds for the herbaceous layer. In the Neotropical savannas, grasses show strong synchronous post-fire flowering, and their reproduction is often considered fire-dependent, with their massive post-fire seed production being suggested as a source of population maintenance. However, literature lacks studies to provide evidence of fire-dependent flowering and no study has assessed the quality of the post-fire seed production. Therefore, we aimed to describe a phenological pattern across early-flowering Neotropical savanna grasses in both recently burnt and unburnt cerrado communities addressing three questions: (1) Do the early-flowering species rely on fire for reproduction via seeds? (2) If no, what are the effects of fire on their reproductive phenology? (3) Does the massive seed production in post-fire cerrado communities lead to high-quality seeds? We recorded the reproductive phenology of nine early-flowering grasses for 17 weeks in unburnt and recently burnt cerrado communities. We collected the seeds, estimated the production of fertile seeds, and tested germination. No species showed a pattern of fire-dependent reproduction. Fire stimulated earlier flowering while reproduction in the unburnt community was related to continuous rainfall. Seed production following fire was of low quality, and no species produced > 7% fertile seeds. Seed germination remained below 50% for most species. Post-fire seed production of early-flowering species led to poor seed quality, suggesting a constraint to the recruitment of new individuals of early-flowering Neotropical savanna grasses in recently burnt cerrados.

Variações temporais na estrutura em fitofisionomias de Cerrado e Floresta Estacional Semidecidual em Curvelo, MG

Este estudo teve como objetivo analisar a dinâmica da estrutura de espécies arbóreas e relacionar as mudanças com as condições edáficas em fitofisionomias de cerrado stricto sensu (de 2010 a 2015), cerradão (de 2010 a 2015) e floresta estacional semidecidual (de 2011 a 2015) em Curvelo, Minas Gerais. O inventário florestal considerou amostragens do tipo sistemática em 15 unidades amostrais de 20 × 50 metros no cerrado stricto sensu (CSS), 10 unidades amostrais 20 × 50m no cerradão (CD), CAS ≥ 15,7cm) e 25 unidades amostrais de 10 × 40m na floresta estacional semidecidual (FES - CAP ≥ 15,7 cm). Amostras de solo foram coletadas em todas as unidades amostrais para caracterização química e granulométrica. Nas três fitofisionomias, o número de indivíduos ingressantes foi inferior ao de egressos. No CSS, a área basal no inventário final foi superior à área basal inicial (23,675 – 25,845m2/ha), devido ao incremento expressivo dos sobreviventes. Ocorreram reduções na área basal no CD (19,322 – 17,008 m2/ha) e na FES (28,183 – 28,148 m2/ha), decorrente da alta taxa de mortalidade. Nas três fitofisionomias, a mortalidade foi maior nas primeiras classes diamétricas. De forma lenta, o CSS e CD estão se recuperando pós-distúrbio (fogo), estão surgindo novos indivíduos (recrutas) e crescimento diamétrico dos sobreviventes. Durante o intervalo de 5 anos, não foi possível identificar a recuperação do número de indivíduos, enquanto que a FES sem distúrbio do fogo, a perda de indivíduos pela mortalidade e a inclusão de novos indivíduos pelo recrutamento foram mais equilibradas.

Novel parasite invasion leads to rapid demographic compensation and recovery in an experimental population of guppies

The global movement of pathogens is altering populations and communities through a variety of direct and indirect ecological pathways. The direct effect of a pathogen on a host is reduced survival, which can lead to decreased population densities. However, theory also suggests that increased mortality can lead to no change or even increases in the density of the host. This paradoxical result can occur in a regulated population when the pathogen's negative effect on survival is countered by increased reproduction at the lower density. Here, we analyze data from a long-term capture-mark-recapture experiment of Trinidadian guppies (Poecilia reticulata) that were recently infected with a nematode parasite (Camallanus cotti). By comparing the newly infected population with a control population that was not infected, we show that decreases in the density of the infected guppy population were transient. The guppy population compensated for the decreased survival by a density-dependent increase in recruitment of new individuals into the population, without any change in the underlying recruitment function. Increased recruitment was related to an increase in the somatic growth of uninfected fish. Twenty months into the new invasion, the population had fully recovered to preinvasion densities even though the prevalence of infection of fish in the population remained high (72%). These results show that density-mediated indirect effects of novel parasites can be positive, not negative, which makes it difficult to extrapolate to how pathogens will affect species interactions in communities. We discuss possible hypotheses for the rapid recovery.

Genetic monitoring of translocated plant populations in practice.

Plant translocations allow the restoration of genetic diversity in inbred and depauperate populations and help to prevent the extinction of critically endangered species. However, the successes of plant translocations in restoring genetically viable populations and the possible associated key factors are still insufficiently evaluated. To fill this gap, we carried out a thorough genetic monitoring of three populations of Arnica montana that were created or reinforced by the translocation of plants obtained from seeds of two large natural source populations from southern Belgium. We genotyped nine microsatellite markers and measured fitness quantitative traits over two generations (transplants, F1 seed progeny and newly established F1 juveniles). Two years after translocation, the genetic restoration had been effective, with high genetic diversity and low genetic differentiation across generations, extensive contemporary pollen flow, admixture between seed sources in the F1 generation and recruitment of new individuals from seeds. We detected site, seed source and maternal plant effects on plant fitness. The results also suggest that phenotypic plasticity may favour short-term individual survival and long-term adaptive capacity and enhance the evolutionary resilience of the populations to changing environmental conditions. We found no sign of heterosis or outbreeding depression at early life stages in the F1 generation. Our findings emphasize the importance of the translocation design (700 transplants of mixed sources, planted at high density) as well as the preparatory site management for the successful outcome of the translocations, which maximized flowering, random mating, and recruitment from seeds in the first years after translocation.