Projected Population Growth Rates Research Articles

Population Dynamics of a Declining White-Tailed Deer Population in the Southern Appalachian Region of the United States

Although generally abundant, white-tailed deer (Odocoileus virginianus) populations in the southeastern United States have recently experienced several localized declines attributed to reduced fawn recruitment following the establishment of coyotes (Canis latrans). The Southern Appalachians is a mountainous region suggested to be experiencing white-tailed deer declines, as harvest numbers and hunter success rates have substantially decreased in northern Georgia since 1979. Low fawn survival (16%) was also recently documented in the Chattahoochee National Forest (CNF) in northern Georgia, necessitating further examination. We radio-collared 14 yearling and 45 adult female white-tailed deer along with 71 fawns during 2018–2020 in the CNF to estimate field-based vital rates (i.e., survival and fecundity) and parameterize stage-structured population models. We projected population growth rates (λ) over 10 years to evaluate the current rate of decline and various other management scenarios. Our results indicated that the observed population would decline by an average of 4.0% annually (λ = 0.960) under current conditions. Only scenarios including antlerless harvest restrictions in addition to improved fawn survival resulted in positive growth (λ = 1.019, 1.085), suggesting these measures are likely necessary for population recovery in the region. This approach can be applied by wildlife managers to inform site-specific management strategies.

Projecting wheat demand in China and India for 2030 and 2050: Implications for food security.

The combined populations of China and India were 2.78 billion in 2020, representing 36% of the world population (7.75 billion). Wheat is the second most important staple grain in both China and India. In 2019, the aggregate wheat consumption in China was 96.4 million ton and in India it was 82.5 million ton, together it was more than 35% of the world's wheat that year. In China, in 2050, the projected population will be 1294-1515 million, and in India, it is projected to be 14.89-1793 million, under the low and high-fertility rate assumptions. A question arises as to, what will be aggregate demand for wheat in China and India in 2030 and 2050? Applying the Vector Error Correction model estimation process in the time series econometric estimation setting, this study projected the per capita and annual aggregate wheat consumptions of China and India during 2019-2050. In the process, this study relies on agricultural data sourced from the Food and Agriculture Organization of the United States (FAO) database (FAOSTAT), as well as the World Bank's World Development Indicators (WDI) data catalog. The presence of unit root in the data series are tested by applying the augmented Dickey-Fuller test; Philips-Perron unit root test; Kwiatkowski-Phillips-Schmidt-Shin test, and Zivot-Andrews Unit Root test allowing for a single break in intercept and/or trend. The test statistics suggest that a natural log transformation and with the first difference of the variables provides stationarity of the data series for both China and India. The Zivot-Andrews Unit Root test, however, suggested that there is a structural break in urban population share and GDP per capita. To tackle the issue, we have included a year dummy and two multiplicative dummies in our model. Furthermore, the Johansen cointegration test suggests that at least one variable in both data series were cointegrated. These tests enable us to apply Vector Error Correction (VEC) model estimation procedure. In estimation the model, the appropriate number of lags of the variables is confirmed by applying the "varsoc" command in Stata 17 software interface. The estimated yearly per capita wheat consumption in 2030 and 2050 from the VEC model, are multiplied by the projected population in 2030 and 2050 to calculate the projected aggregate wheat demand in China and India in 2030 and 2050. After projecting the yearly per capita wheat consumption (KG), we multiply with the projected population to get the expected consumption demand. This study found that the yearly per capita wheat consumption of China will increase from 65.8 kg in 2019 to 76 kg in 2030, and 95 kg in 2050. In India, the yearly per capita wheat consumption will increase to 74 kg in 2030 and 94 kg in 2050 from 60.4 kg in 2019. Considering the projected population growth rates under low-fertility assumptions, aggregate wheat consumption of China will increase by more than 13% in 2030 and by 28% in 2050. Under the high-fertility rate assumption, however the aggregate wheat consumption of China will increase by 18% in 2030 and nearly 50% in 2050. In the case of India, under both low and high-fertility rate assumptions, aggregate wheat demand in India will increase by 32-38% in 2030 and by 70-104% in 2050 compared to 2019 level of consumption. Our results underline the importance of wheat in both countries, which are the world's top wheat producers and consumers, and suggest the importance of research and development investments to maintain sufficient national wheat grain production levels to meet China and India's domestic demand. This is critical both to ensure the food security of this large segment of the world populace, which also includes 23% of the total population of the world who live on less than US $1.90/day, as well as to avoid potential grain market destabilization and price hikes that arise in the event of large import demands.

Populations of a tropical epiphytic orchid are destabilized in its peripheral range by hurricane and an exotic herbivore

AbstractIn a time of global change, having an understanding of the nature of biotic and abiotic factors that drive a species' range may be the sharpest tool in the toolbox of conservation and management of threatened species. However, such information are lacking for most tropical and epiphytic species due to the complexity of life history, the roles of stochastic events, and the diversity of habitat across the span of a distribution. In this study, we conducted repeated census across the core and peripheral range of Trichocentrum undulatum, a threatened orchid that is found throughout the island of Cuba (species core range) and southern Florida (the northern peripheral range). We used demographic matrix modeling and stochastic simulations to investigate the impacts of herbivory, hurricanes, and logging (in Cuba) on projected population growth rates (λ and λs) among sites. Our study indicates that the Florida population is under high extinction risk and most populations in the core range show less interannual variability, but, with the exception of one population, are also in decline. The peripheral population experienced higher herbivory damage than did the core populations, by a native inflorescence‐crippling fly, Melanagromyza miamensis, and an invasive, mortality‐triggered scale, Diaspis boisduvalii. The latter was found in the Florida population only. Hurricanes increased levels of mortality and had a negative effect on λ. However, λ increased following hurricane events due to increased recruitment and decreased herbivory. Life table response experiments suggest that higher adult survival was the largest contributor to the higher λ observed in the growing Cuba populations, as compared with the population in Florida. Logging simulations in Cuba indicate that populations can maintain stability only if selective logging of host trees occurs at low frequency. Reintroduction of the species in its northern peripheral habitat is needed to ameliorate the threats from sea‐level rise and invasive herbivorous insects to secure the current species' northern, continental range margin. Our study exhibits how vital rates and ecological interactions vary across a species distribution and respond under differing stochastic events.

Site-specific temporal variation of population dynamics in subalpine endemic plant species

Endemic plants in high mountains are projected to be at high risk because of climate change. Temporal demographic variation is a major factor affecting population viability because plants often occur in small, isolated populations. Because isolated populations tend to exhibit genetic differentiation, analyzing temporal demographic variation in multiple populations is required for the management of high mountain endemic species. We examined the population dynamics of an endemic plant species, Primula farinosa subsp. modesta, in four subalpine sites over six years. Stage-based transition matrices were constructed, and temporal variation in the projected population growth rate (λ) was analyzed using life table response experiments (LTREs). The variation in λ was primarily explained by the site × year interaction rather than the main effects of the site and year. The testing sites exhibited inconsistent patterns in the LTRE contributions of the vital rates to the temporal deviation of λ. However, within sites, growth or stasis had significant negative correlations with temporal λ deviation. Negative correlations among the contributions of vital rates were also detected within the two testing sites, and the removal of the correlations alleviated temporal fluctuations in λ. The response of vital rates to yearly environmental fluctuations reduced the temporal variation of λ. Such effects manifested especially at two sites where plants exhibited higher plasticity than plants at other sites. Site-specific temporal variation implies that populations of high mountain species likely exhibit asynchronous temporal changes, and multiple sites need to be evaluated for their conservation.

Effects of habitat disturbance and rainfall on a dominant medicinal dry forest tree

The interactive effects of anthropogenic disturbance and climatic variables can shape the demography of plant populations, but they remain poorly understood especially for long-lived species like tropical trees. Understanding these interactions is critical for designing forest management strategies in the face of both growing anthropogenic pressures and climate change. We explored the effects of habitat disturbance and interannual variation in rainfall on the population dynamics of Amphipterygium adstringens (Anacardiaceae), an ecologically dominant tree species endemic to the tropical deciduous forests of Mexico, that is heavily harvested for its medicinal bark. Specifically, we compared A. adstringens vital rates and long-term population growth rates of unharvested populations in a disturbed versus a protected tropical deciduous forest site; and explored the effects of inter-annual variation in annual rainfall on A. adstringens by comparing vital rates and population growth rates across three years with differing levels of rainfall. We established four plots in each of the two sites and monitored survival, growth and reproduction of 251 individuals over three years. We found that anthropogenic disturbance and rainfall differentially affected the vital rates of A. adstringens. Survival did not differ across sites or years. Growth tended to be lower and fecundity higher, in the protected site, but these effects varied across years and as a function of plant size. No seedlings were found in the disturbed site over the three years study period. Integral projection models showed that projected population growth rates (λ values) in the protected site were higher and much less variable over time than those of the disturbed site. Lambda values in the disturbed site were <1, indicating long-term population decline. In both sites, the rainiest year showed the highest population growth rate but the increase in λ was much higher in the disturbed site than in the protected site. These findings suggest that the population dynamics of A. adstringens are heavily affected by habitat disturbance forest management regime and that the impacts of interannual variability in rainfall or other environmental conditions may be exacerbated in disturbed conditions. The persistence of A. adstringens populations over time will require the exclusion of livestock as well as the implementation of silvicultural practices that will lead to seedling establishment and survival. This study provides key data for the management and conservation of A. adstringens, a highly valued medicinal species.

Female reproductive skew exacerbates the extinction risk from poaching in the eastern black rhino.

Variation in individual demographic rates can have large consequences for populations. Female reproductive skew is an example of structured demographic heterogeneity where females have intrinsic qualities that make them more or less likely to breed. The consequences of reproductive skew for population dynamics are poorly understood in non-cooperatively breeding mammals, especially when coupled with other drivers such as poaching. We address this knowledge gap with population viability analyses using an age-specific, female-only, individual-based, stochastic population model built with long-term data for three Kenyan populations of the Critically Endangered eastern black rhino (Diceros bicornis michaeli). There was substantial reproductive skew, with a high proportion of females not breeding or doing so at very low rates. This had a large impact on the projected population growth rate for the smaller population on Ol Jogi. Moreover, including female reproductive skew exacerbates the effects of poaching, increasing the probability of extinction by approximately 70% under a simulated poaching pressure of 5% offtake per year. Tackling the effects of reproductive skew depends on whether it is mediated by habitat or social factors, with potential strategies including habitat and biological management respectively. Investigating and tackling reproductive skew in other species requires long-term, individual-level data collection.

Pemodelan Geographically Weighted Logistic Regression dengan Fungsi Adaptive Gaussian Kernel Terhadap Kemiskinan di Provinsi NTT

The Geographically Weighted Logistic Regression (GWLR) model is a logistic regression model development that is applied to spatial data from non-stationary processes. This model is used to predict a model of the data set that has a binary response variable which takes into account the spatial factor. This study will discuss the use of the GWLR model using the adaptive weighting function of the Gaussian kernel in a poverty case study in East Nusa Tenggara Province in 2019.The parameter estimation of the Maximum Likelihood Estimation (MLE) method by giving different weights for each observation location. The weight used is the adaptive Gaussian kernel with the optimum bandwidth selection using the Cross-Validation (CV). Based on the results of testing the parameters of the GWLR model with a weighted adaptive Gaussian kernel, it can be concluded that the factors that influence poverty are local and vary in the 22 observation locations, including GRDP per capita, acceptance of smart Indonesian programs, and projected population growth rates, with a classification accuracy rate of 81,82%.

Searching for the causes of decline in the Dutch population of European Turtle Doves (Streptopelia turtur)

European Turtle Doves Streptopelia turtur have experienced a sharp decline in population numbers over past decades. Much uncertainty exists about the main cause or causes. Several pressures have been suggested, but because they affect different stages of the life cycle of the Turtle Dove, it is difficult to compare their contributions to the population decline. Here we applied a full life cycle approach to study how different pressures may have resulted in the decline. This was achieved by combining a review of existing literature on possible threats, pressures and the vital rates they concerned, with the analysis of an age‐structured matrix model. The population model was parameterized using estimates from a mark–recapture analysis and supplemented with vital rate estimates from the literature. Comparison with a Life Table Response Experiment (LTRE) was used to determine whether the Turtle Dove literature focuses on those vital rates in which the most important changes have taken place over time. The population model projected a similar decline to that observed in population counts. The LTRE analysis showed that declines in the number of clutches (halved since the 1960s) and in juvenile survival (relative annual rate of change of –1.33% since the 1950s) contributed most to the decline in the projected population growth rate. Although these vital rates are often reported as possible causes of population decline, the reviewed studies often focused on specific reproductive stages, such as egg survival or nestling survival, which did not show a large temporal change. Thus, there is a partial mismatch between our modelling results and the focus in the literature. Juvenile survival is thought to be affected by hunting, degradation of wintering habitat and infection with Trichomonas gallinae, and loss of foraging habitat seems to affect the number of clutches. The focus of conservation measures should therefore be on these threats and pressures. The first steps have already been taken with the completion of the international single species action plan for the conservation of the Turtle Dove and the implementation of the first conservation measures on the breeding grounds.

Differential plastic responses to temperature and nitrogen deposition in the subalpine plant species, Primula farinosa subsp. modesta.

Future environmental changes are projected to threaten plant populations near mountaintops, but plastic responses of plant traits that are related to demographic parameters may reduce the detrimental effects of altered environments. Despite its ecological significance, little is known about the intraspecific variation of plasticity in alpine plant species such as Primula farinosa subsp. modesta. In this study, we investigated the plastic responses of plants at the early developmental stage from four P. farinosa natural populations in response to temperature and nitrogen deposition under laboratory conditions. Measured traits included plant survival, leaf number, rosette diameter, carbon assimilation rate and leaf chlorophyll content. In addition, we conducted a demographic survey of the natural populations to assess the plant’s performance at the early developmental stage in the field and evaluate the ecological implications of our experimental treatments. The seedling stage contributed to the projected population growth rate in natural conditions, and the growth and survival of seedlings in the field were comparable to those grown in the control treatment. In response to high temperature, plants exhibited lower survival but produced larger rosettes with more leaves. Nitrogen deposition had little effect on plant survival and plant size; however, it increased plant survival in one population and altered the effect of temperature on the carbon assimilation rate. Populations exhibited differential plasticity indexes of measured traits in response to environmental treatments. These results suggest that even though the plants suffer from high early mortality under increasing temperature, stimulated growth at a high temperature potentially contributes to the persistence of P. farinosa natural populations. Natural populations might face differential extinction risks due to distinctive plastic responses to altered environments.

Climate change as an incentive for future human migration

Abstract. Human migration is both motivated and constrained by a multitude of socioeconomic and environmental factors, including climate-related factors. Climatic factors exert an influence on local and regional population density. Here, we examine the implications of future motivation for humans to migrate by analyzing today's relationships between climatic factors and population density, with all other factors held constant. Such “all other factors held constant” analyses are unlikely to make quantitatively accurate predictions, but the order of magnitude and spatial pattern that come out of such an analysis can be useful when considering the influence of climate change on the possible scale and pattern of future incentives to migrate. Our results indicate that, within decades, climate change may provide hundreds of millions of people with additional incentive to migrate, largely from warm tropical and subtropical countries to cooler temperate countries, with India being the country with the greatest number of people with additional incentive to migrate. These climate-driven incentives would be among the broader constellation of incentives that influence migration decisions. Areas with the highest projected population growth rates tend to be areas that are likely to be most adversely affected by climate change.

The ecology of human–carnivore coexistence

With a shrinking supply of wilderness and growing recognition that top predators can have a profound influence on ecosystems, the persistence of large carnivores in human-dominated landscapes has emerged as one of the greatest conservation challenges of our time. Carnivores fascinate society, yet these animals pose threats to people living near them, resulting in high rates of carnivore death near human settlements. We used 41 y of demographic data for more than 2,500 brown bears-one of the world's most widely distributed and conflict-prone carnivores-to understand the behavioral and demographic mechanisms promoting carnivore coexistence in human-dominated landscapes. Bear mortality was high and unsustainable near people, but a human-induced shift to nocturnality facilitated lower risks of bear mortality and rates of conflict with people. Despite these behavioral shifts, projected population growth rates for bears in human-dominated areas revealed a source-sink dynamic. Despite some female bears successfully reproducing in the sink areas, bear persistence was reliant on a supply of immigrants from areas with minimal human influence (i.e., wilderness). Such mechanisms of coexistence reveal a striking paradox: Connectivity to wilderness areas supplies bears that likely will die from people, but these bears are essential to avert local extirpation. These insights suggest carnivores contribute to human-carnivore coexistence through behavioral and demographic mechanisms, and that connected wilderness is critical to sustain coexistence landscapes.

How climate change and wildlife management affect population structure in wild boars

Global climate change affects many species and contributes to the exceptional population growth of wild boar populations and thus to increasing human-wildlife conflicts. To investigate the impact of climate change on wild boar populations we extended existing models on population dynamics. We included for the first time different juvenile conditions to account for long-lasting effects of juvenile body mass on adult body mass and reproductive success. Our analysis shows that incorporating phenotypes, like body mass differences within age classes, has strong effects on projected population growth rates, population structures and the relative importance of certain vital rates. Our models indicated that an increase in winter temperatures and food availability will cause a decrease in mean body mass and litter size within Central European wild boar populations. We further analysed different hunting regimes to identify their effects on the population structure as well as their efficiency in limiting population growth. While targeting juveniles had the lowest effect on population structure, such strategies are, however, rather ineffective. In contrast, culling predominantly yearlings seems very effective. Despite being equally effective, only focusing on adults will not result in a reduction of population size due to their low proportion within populations.

Modeling the combined impacts of host plant resistance and biological control on the population dynamics of a major pest of wheat.

Single-tool approaches often fail to provide effective long-term suppression of pest populations, such that combining several tools into an integrated management strategy is critical. Yet studies that harness the power of population models to explore the relative efficacy of various management tools and their combinations remain rare. We constructed a Leslie matrix population model to evaluate the potential of crop resistance, acting alone or in combination with biological control, to reduce populations of the wheat stem sawfly, Cephus cinctus Norton, a major pest of wheat in North America. Our model projections indicated that crop resistance reduced, but did not stop, C. cinctus population growth, suggesting that implementing multiple management tools will be necessary for longer term control of this pest. The levels of parasitism needed to curtail population growth were much lower in model projections for resistant solid-stemmed compared with susceptible hollow-stemmed cultivars (22% versus 86%). Furthermore, even when accounting for the reduced levels of parasitism observed in resistant cultivars, projected population growth rates for C. cinctus were always lower in resistant compared with susceptible wheat cultivars. Despite some empirical evidence for antagonistic interactions between resistance and biological control, our models suggest that combining these two approaches will always reduce population growth rates to lower levels than implementing either strategy alone. More work focused on integrating biological control into crop resistance breeding programs, and determining how these approaches affect performance of limiting life stages, will be important to optimize sustainable approaches to integrated pest management in this system and more broadly. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

Pre‐dispersal seed predation and pollen limitation constrain population growth across the geographic distribution of Astragalus utahensis

Abstract A central focus of ecology is to understand the conditions under which biotic interactions affect species’ abundance and distribution. Classic and recent studies have shown that biotic interactions can strongly impact local or regional patterns of species abundance, but two fundamental questions remain largely unaddressed for non‐competitive biotic interactions. First, do the effects of these interactions on population performance change predictably with environmental context? Second, to what extent do population‐scale effects contribute to limiting species’ geographic distributions? To address these questions, we experimentally assessed the extent to which pollen limitation and insect seed predators affected the fecundity and projected population growth rate (λ) of the native forb Astragalus utahensis. We studied populations at the centre and northern edge of the latitudinal range of A. utahensis that occur across a gradient in abiotic harshness characterized primarily by declining mean annual precipitation. Supplementing pollen and suppressing pre‐dispersal seed predators increased seed production similarly within A. utahensis populations at the centre and northern edge of the range. Integral projection population models revealed that relaxing these checks on seed production tended to increase λ in most populations, regardless of their location within the range. Synthesis. Our results suggest that pollen limitation and insect herbivores limit population growth in A. utahensis similarly across the centre‐to‐north portion of its latitudinal distribution. However, because A. utahensis population growth barely reaches the level of replacement at the northern range edge, the reduction in λ resulting from these interactions may contribute to limiting expansion at the northern edge of A. utahensis’ latitudinal range.

Characterising demographic contributions to observed population change in a declining migrant bird

Populations of Afro‐Palearctic migrant birds have shown severe declines in recent decades. To identify the causes of these declines, accurate measures of both demographic rates (seasonal productivity, apparent survival, immigration) and environmental parameters will allow conservation and research actions to be targeted effectively. We used detailed observations of marked breeding birds from a ‘stronghold’ population of whinchats Saxicola rubetra in England (stable against the declining European trend) to reveal both on‐site and external mechanisms that contribute to population change. From field data, a population model was developed based on demographic rates from 2011 to 2014. Observed population trends were compared to the predicted population trends to assess model‐accuracy and the influence of outside factors, such as immigration. The sensitivity of the projected population growth rate to relative change in each demographic rate was also explored. Against expectations of high productivity, we identified low seasonal breeding success due to nocturnal predation and low apparent first‐year survival, which led to a projected population growth rate (λ) of 0.818, indicating a declining trend. However, this trend was not reflected in the census counts, suggesting that high immigration was probably responsible for buffering against this decline. Elasticity analysis indicated λ was most sensitive to changes in adult survival but with covariance between demographic rates accounted for, most temporal variation in λ was due to variation in productivity. Our study demonstrates that high quality breeding habitat can buffer against population decline but high immigration and low productivity will expose even such stronghold populations to potential decline or abandonment if either factor is unsustainable. First‐year survival also appeared low, however this result is potentially confounded by high natal dispersal. First‐year survival and/or dispersal remains a significant knowledge gap that potentially undermines local solutions aimed at counteracting low productivity.

Greater sexual reproduction contributes to differences in demography of invasive plants and their noninvasive relatives

An understanding of the demographic processes contributing to invasions would improve our mechanistic understanding of the invasion process and improve the efficiency of prevention and control efforts. However, field comparisons of the demography of invasive and noninvasive species have not previously been conducted. We compared the in situ demography of 17 introduced plant species in St. Louis, Missouri, USA, to contrast the demographic patterns of invasive species with their less invasive relatives across a broad sample of angiosperms. Using herbarium records to estimate spread rates, we found higher maximum spread rates in the landscape for species classified a priori as invasive than for noninvasive introduced species, suggesting that expert classifications are an accurate reflection of invasion rate. Across 17 species, projected population growth was not significantly greater in invasive than in noninvasive introduced species. Among five taxonomic pairs of close relatives, however, four of the invasive species had higher projected population growth rates compared with their noninvasive relative. A Life Table Response Experiment suggested that the greater projected population growth rate of some invasive species relative to their noninvasive relatives was primarily a result of sexual reproduction. The greater sexual reproduction of invasive species is consistent with invaders having a life history strategy more reliant on fecundity than survival and is consistent with a large role of propagule pressure in invasion. Sexual reproduction is a key demographic correlate of invasiveness, suggesting that local processes influencing sexual reproduction, such as enemy escape, might be of general importance. However, the weak correlation of projected population growth with spread rates in the landscape suggests that regional processes, such as dispersal, may be equally important in determining invasion rate.

Accuracy of Short‐Term Demographic Data in Projecting Long‐Term Fate of Populations

Short-term surveys are useful in conservation of species if they can be used to reliably predict the long-term fate of populations. However, statistical evaluations of reliability are rare. We studied how well short-term demographic data (1999-2002) of tartar catchfly (Silene tatarica), a perennial riparian plant, projected the fate and growth of 23 populations of this species up to the year 2010. Surveyed populations occurred along a river with natural flood dynamics and along a regulated river. Riparian plant populations are affected by flooding, which maintains unvegetated shores, while forest succession proceeds in areas with little flooding. Flooding is less severe along the regulated river, and vegetation overgrowth reduces abundance of tartar catchfly on unvegetated shores. We built matrix models to calculate population growth rates and estimated times to population extinction in natural and in regulated rivers, 13 and 10 populations, respectively. Models predicted population survival well (model predictions matched observed survival in 91% of populations) and accurately predicted abundance increases and decreases in 65% of populations. The observed and projected population growth rates differed significantly in all but 3 populations. In most cases, the model overestimated population growth. Model predictions did not improve when data from more years were used (1999-2006). In the regulated river, the poorest model predictions occurred in areas where cover of other plant species changed the fastest. Although vegetation cover increased in most populations, it decreased in 4 populations along the natural river. Our results highlight the need to combine disturbance and succession dynamics in demographic models and the importance of habitat management for species survival along regulated rivers.

Predicting climate-induced changes in population dynamics of invasive species in a marine epibenthic community

As climate change and invasive species, both individually and in concert, continue to elicit responses in native communities, we are challenged with finding strategies for predicting the strength of such impacts. The effects of invasive species are often determined by their abundance, and warming temperatures can alter species' demographic rates and, thus, population growth rates. Here, we combined lab experiments, field experiments and observations, and population modeling to predict the population dynamics of three marine invaders in response to climate warming. We projected population growth rate at an ambient and an increased temperature predicted by climate-change scenarios (+4°C) for three invasive species in the epibenthic fouling community of Bodega Harbor, California, USA: the tunicates Botrylloides violaceus and Botryllus schlosseri and the bryozoan Watersipora subtorquata. There was a positive effect of temperature on population growth rate for B. schlosseri, and further analysis revealed that this predicted increase was driven by warming effects on settler growth rate and adult fecundity. Increases indicated for non-native marine fouling species are especially pertinent when considering the potential cascading effects on community composition and functioning that can result from species invasions. Our results highlight the potential for marked increases in an invasive species in response to climate change, as well as the promising role that population modeling can play in elucidating the mechanisms of such responses.

Strong persistent growth differences govern individual performance and population dynamics in a tropical forest understorey palm

Summary Persistent variation in growth rate between individual plants can have strong effects on population dynamics as fast growers reach the reproductive size at an earlier age and thus potentially contribute more to population growth than slow growers. In tropical forests, such persistent growth differences have so far been documented for canopy tree species, where they are primarily associated with forest gap dynamics, but not for forest understorey species which are less responsive to gaps. Here, we study persistent growth differences and their demographic consequences for a tropical forest understorey palm, Chamaedorea elegans. We measured internodes along stems and annual leaf production rates to reconstruct lifetime growth trajectories. Using regression analysis, we determined the relative effect of stem length and past growth rate on vital rates (survival, growth and reproduction). We then simulated population dynamics using integral projection models (IPMs), in which individuals were categorized by both stem length and lifetime past growth rate. Stem growth differences among individual palms persisted over most of their lifetime. Past growth rate averaged over the palm's lifetime proved to be a very good predictor of growth, reproduction probability and seed production, often much better than stem length or age. The effects of past growth rate were positive, indicating that fast growers maintain high rates of growth and reproduction. Projected population growth rate (λ) was 1.056, and stable stage distributions closely resembled observed population structures. Separating individuals with above‐median and below‐median past growth rates in IPMs revealed substantial differences in elasticity values. The 50% fastest growers had a 1.8 times higher elasticity, and thus a 1.8 times higher contribution to population growth, compared to slow growers. Synthesis. Strong and persistent growth differences that are probably associated with environmental (edaphic) and/or genetic factors govern individual performance and population dynamics of a tropical forest understorey palm. Overall, our study shows that strong inter‐individual growth variation is not limited to canopy trees and that it can be generated by other factors than canopy dynamics. It is likely that persistently fast‐growing ‘super performers’ govern population growth of many long‐lived species.

Postdispersal seed predation limits the abundance of a long‐lived perennial forb (Lithospermum ruderale)

Loss of seeds to consumers is common in plant communities, but the degree to which these losses influence plant abundance or population growth is often unclear. This is particularly the case for postdispersal seed predation by rodents, as most studies of rodent seed predation have focused on the sources of spatiotemporal variation in seed loss but not quantified the population consequences of this loss. In previous work we showed that seed predation by deer mice (Peromyscus maniculatus) substantially reduced seedling recruitment and establishment of Lithospermum ruderale (Boraginaceae), a long-lived perennial forb. To shed light on how rodent seed predation and the near-term effects on plant recruitment might influence longer-term patterns of L. ruderale population growth, we combined experimental results with demographic data in stage-based population models. Model outputs revealed that rodent seed predation had a significant impact on L. ruderale population growth rate (lambda). With the removal of postdispersal seed predation, the projected population growth rates increased between 0.06 and 0.12, depending on site (mean deltalambda across sites = 0.08). Seed predation shifted the projected stable stage distribution of populations from one with a high proportion of young plants to one in which larger adult size classes dominate. Elasticities of vital rates also changed, with germination and growth of seedlings and young plants becoming more important with the removal of seed predation. Simulations varying the magnitude of seed predation pressure while holding other vital rates constant showed that seed predation could lower lambda even if only 40% of available seeds were consumed. These results demonstrate that rodent granivory can be a potent force limiting the abundance of a long-lived perennial forb.