Demographic consequences of drought in the herbaceous perennial Cryptantha flava: effects of density,associations with shrubs,and plant size

The demographic consequences of a severe drought year were examined for two experimental plantings of the herbaceous desert perennial Cryptantha flava(Boraginaceae) in northeastern Utah, United States. A total of 6680 nutlets were planted individually or in clusters of four both under shrubs and in open microhabitats within two natural populations. Survival, growth, and flowering as a function of density and microhabitat were followed for 7 years, including 1 year when precipitation just before and during the growing season was 74.5% below normal. The design permitted assessment of how intraspecific density and shrub cover affect demographic response to drought. Mortality increased and flowering decreased dramatically during drought but neither varied with density or between shrub and open microhabitats. For plants growing under shrubs, survival (at Site 1) and growth (at Site 2) varied with shrub species. Average aboveground plant size also decreased during drought. Population size hierarchies were rearranged because larger plants lost leaf rosettes while many smaller plants grew. Density and microhabitat affected plant performance in non-drought years but more often at Site 1 than at Site 2. Individuals growing alone often were more likely to flower and/or produced more inflorescences when they did flower than did individuals growing with at least one other plant. However, for 2 years, survival rates at Site 1 were higher for plants growing in clumps than for single individuals. Shrubs also had mixed effects on plant performance. In some years, survival was higher under shrubs, but at Site 1 plants in the open often were more likely to flower and/or produced more inflorescences. Thus despite severe demographic consequences of drought, the study provided no evidence that intraspecific competition, interference by shrubs, or facilitation by shrubs increases under limited soil water.     

Demographic consequences of climate variation along an elevational gradient for a montane terrestrial salamander

Climate change represents a significant threat to amphibians. However, for many species, the relationship between demography and climate is unknown, which limits predictive models. Here, we describe the life history variation of Plethodon montanus using capture–recapture data over a period of 4 years, along an elevational gradient to determine how survival and growth vary with climate, and how these relationships vary with elevation. We used a hierarchical model to estimate asymptotic size and growth rate and a spatial Cormack-Jolly-Seber model to estimate the probability of capture and survival and dispersal variance. We found that during the active season, growth and survival rates are both positively affected by precipitation; however, while survival was positively affected by temperature at all elevations, higher temperatures led to a decrease in growth at lower elevations, while at higher elevations the opposite was true. During the inactive season, we found reduced growth rates, whereas survival was lower compared with the active at lower elevations but was higher at higher elevations. Increased inactive season temperatures resulted in decreased survival while we found that temperature, amount of snow, and elevation interacted to influence survival. At low elevations, which were warmer, survival decreased with increasing snowfall but at higher elevations, survival generally increased with increasing snowfall. Our results demonstrate that understanding how the environment can affect salamander demography to develop mechanistic models will require knowledge of the actual environmental conditions experienced by a given population as well as an understanding of the overall differences in climate at a given site.     

Dispersal biology of Liatris scariosa var. novae-angliae (Asteraceae), a rare New England grassland perennial

Propagule dispersal biology is a crucial avenue of research for rare plant species, especially those adapted to disturbance, such as northern blazing star (Liatris scariosa var. novae-angliae), a rare, early-successional New England grassland perennial. We examined the dispersal ability of northern blazing star propagules collected from 14 populations covering the entire latitudinal range of the taxon. Multiple regression demonstrated that dispersal ability, as measured by drop time in still air and flight distance in a low-speed wind tunnel, decreased significantly with propagule size and achene length, and increased with achene width and (for flight distance) pappus length. We used this multiple regression model to test for differences in predicted dispersal capability among maternal families, populations, and inland, coastal, and island habitats. Dispersal capability differed significantly among families and populations but not regions, and allometric relationships between morphological measurements were consistent across populations. Overall, dispersal capability was negatively correlated with germination success in a common greenhouse environment. However, germination success for a given dispersal ability, as well as achene shape, differed among populations. These results suggest specific populations to be targeted for management efforts promoting dispersal and establishment.     

Demographic variability in tiller populations of two perennial pampa grasses

Abstract. The general objectives of this study were: (1) to investigate the importance of internal influences in regulating the tiller dynamics in natural populations of the warm-season perennial grasses Paspalum dilatatum and Sporobolus indicus, coexisting in Argentine flooded pampa, in as much as they act independently of the underlying external environment, and (2) to evaluate the extent to which interactions between internal and external factors affect the variation in tiller dynamics within such populations. Within-population variation in seasonal development of plants and tillers with different neighbour composition was studied for an annual growth cycle. Tiller survival and tillering were significantly influenced by tiller size. Tiller age influenced tiller fate, as suggested by the additive effects of age and size of tillers. These relationships varied with season and with species. Size and age of tillers showed additive effects with their neighbouring species on the tiller fate of P. dilatatum, but the effects of age and size of S. indicus changed according their neighbourhood. Tiller survival of S. indicus during the early growth season was more size-dependent when the cold-season species Poa lanigera, was the principal neighbour. Flowering and tillering probabilities were positively related through their common positive responses to tiller size. Tiller survival and recruitment between different seasons were strongly related. Independently of neighbour composition, tiller survival was generally inversely related to tiller recruitment in previous seasons. Therefore, significant density-dependent mortality of tillers was found for both species during the early summer when tiller density was expressed by basal area units.     

Semelparous or iteroparous: resource allocation tactics in the ayu, an osmeroid fish

Ayu Plecoglossus altivelis is an annual osmeroid fish with a single breeding season. Its reproductive mode tends to vary such that large females spawn once, while small females spawn twice with an interval of some 2 weeks. The hypothesis was examined that certain female reproductive modes are governed by adequate resource allocation according to maternal body size, to maximize lifetime reproductive success. A series of rearing experiments revealed that immediately before spawning, larger females had relatively higher diversion from the soma and higher investment into the gonad, in contrast to smaller females which maintained higher protein synthetic activity for further reproduction. It was concluded that the extant plasticity in the reproductive mode that occurred in P. altivelis was an outcome of different tactics on the semelparity-iteroparity continuum rather than maladaptive deviation from the optimum.     

Demographic consequences of sexual selection in the long-tailed manakin

Demographic divergence between the sexes is a major consequenceof sexual selection. Matrix-based demographic measures, includingthe sensitivity and elasticity of (population growth rate,fitness) to survival and fertility rates are powerful indexesof intersexual divergence. Many morphological, behavioral, andecological differences distinguish males and females in lekkinglong-tailed manakins (Chiroxiphia linearis), and none is moredramatic than the demographic divergence. Only 16 of 142 (8%)banded males copulated during an 8-year period. The mean estimatedage of male copulators was 10.1 years (SD = 2.2), and only 5of 166 copulations were by males 8 years old. Females probablybegin reproduction at age 1 or 2. The reproductive value curvereached a peak of 15.0 for 12th-year males, versus 2.7 for sixth-yearfemales. The matrix-based elasticity of X to survival rateswas greater in males (91% of total elasticity) than in females(80% of total). In a literature-based, interspecific comparison,the difference in elasticity to survival between the male andfemale manakins (91–80=11; ranks 2 and 9 of 16 species/sexcombinations) was greater than that between the sexes in northernelephant seals (90–84=6; ranks 3 and 8), which have thehighest variance of male mating success documented for mammals;red deer (88–87=1; ranks 4 and 5); Galapagos cactus finches(79–74=5; ranks 10 and 12); and acorn woodpeckers (76–74=2;ranks 11 and 13). In the face of continuing debate over appropriatemeasures of sexual selection, matrix-based demographic techniquesfacilitate quantitative, comparative analyses of the life-historyconsequences of sexual selection. Measures of intersexual demographicdivergence may provide insights into heretofore puzzling instancesof sexual selection in species with little dimorphism in sizeor ornament.     

Mechanistic,ecological, and evolutionary consequences of artificial light at night for insects: review and prospective

The alternation of light and dark periods on a daily or seasonal time scale is of utmost importance for the synchronization of physiological and behavioral processes in the environment. For the last 2 decades, artificial light at night (ALAN) has strongly increased worldwide, disrupting the photoperiod and its related physiological processes, and impacting the survival and reproduction of wild animals. ALAN is now considered as a major concern for biodiversity and human health. Here, we present why insects are relevant biological models to investigate the impact of ALAN. First the phenotypic responses to ALAN and their underpinning mechanisms are reviewed. The consequences for population dynamics, and the community composition and functioning are described in the second part. Because ALAN provides new and widespread selective pressure, we inventory evolutionary changes in response to this anthropogenic change. Finally, we identify promising future avenues, focusing on the necessity of understanding evolutionary processes that could help stakeholders consider darkness as a resource to preserve biodiversity as well as numerous ecosystem services in which insects are involved.     

Ecological consequences of interactions between ants and honeydew-producing insects

Interactions between ants and honeydew-producing hemipteran insects are abundant and widespread in arthropod food webs, yet their ecological consequences are very poorly known. Ant-hemipteran interactions have potentially broad ecological effects, because the presence of honeydew-producing hemipterans dramatically alters the abundance and predatory behaviour of ants on plants. We review several studies that investigate the consequences of ant-hemipteran interactions as 'keystone interactions' on arthropod communities and their host plants. Ant-hemipteran interactions have mostly negative effects on the local abundance and species richness of several guilds of herbivores and predators. In contrast, out of the 30 studies that document the effects of ant-hemipteran interactions on plants, the majority (73%) shows that plants actually benefit indirectly from these interactions. In these studies, increased predation or harassment of other, more damaging, herbivores by hemipteran-tending ants resulted in decreased plant damage and/or increased plant growth and reproduction. The ecological consequences of mutualistic interactions between honeydew-producing hemipterans and invasive ants relative to native ants have rarely been studied, but they may be of particular importance owing to the greater abundance, aggressiveness and extreme omnivory of invasive ants. We argue that ant-hemipteran interactions are largely overlooked and underappreciated interspecific interactions that have strong and pervasive effects on the communities in which they are embedded.     

Demographic effects of warming,elevated soil nitrogen and thinning on the colonization of a perennial plant

Global change is causing significant modifications to native plant communities. These effects can be direct through changes in productivity, or indirect through the spread of invading species. Identifying vital traits important for individual species’ response to environmental variation could be useful for making predictions about how entire communities may respond to global change. I studied the effects of factors associated with global change on the demography of an experimentally introduced species, Pityopsis aspera. In a Florida old-field, I investigated how warming, increased soil nitrogen and thinning of the extant plant community affected survival, growth and reproduction of P. aspera using a life table response experiment. The estimated population growth rate (λ) of P. aspera was reduced by nitrogen addition, as a result of decreased fecundity. However, λ increased in response to the warming treatment, as a result of increased fecundity. In the presence of thinning, both warming and nitrogen served to increase λ as a result of an increase in the growth of young individuals. This experiment illustrates how different vital rates contribute to the population level responses of an experimentally introduced plant to warming, and nitrogen deposition. Results also show how these demographic responses may occur via indirect effects through established species. This work highlights the importance of studying interactions among temperature, soil nitrogen and demography across the entire life cycle in order to capture the complex and, often, non-additive relationships mediating global change effects.     

Demographic consequences of drift in contiguous hives of Bombus terrestris

The objective of this experiment was 1) to quantify drift between bumblebee, Bombus terrestris L., colonies when hives are vertically stacked; and 2) to measure the impact of drift on the colony growth. The experiment was conducted outside, in an open area, at three sites with one stack of three colonies per site. Observations were made from the 28th to the 58th d of the colony development, before the competition point. Bumblebees were regularly marked with a colony-specific color to access the migrations and the cumulative births in colonies. The population size and the colony composition were analyzed by dissection at the end of the experiment. The results showed that approximately equal to 50% of the individuals observed at a hive entrance (entering and exiting individuals) were foreigners. The cumulative births became significantly lower on the lowest floor after one week of experiment. At the end of the experiment, colonies were composed of 20.58% drifters (resident since at least 1 d), and a mean migration rate of 19.82% was determined. Globally, the lowest floor seemed to be progressively abandoned by resident workers for the benefit of the other floors. Because drift induces modifications of the colony growth (potentially on the number of foragers produced and likely on pollination), we suggest to greenhouse growers not to stack colonies but to distribute them throughout the greenhouse.     

Demographic consequences of changing body size in a terrestrial salamander

Changes in climate can alter individual body size, and the resulting shifts in reproduction and survival are expected to impact population dynamics and viability. However, appropriate methods to account for size‐dependent demographic changes are needed, especially in understudied yet threatened groups such as amphibians. We investigated individual‐ and population‐level demographic effects of changes in body size for a terrestrial salamander using capture–mark–recapture data. For our analysis, we implemented an integral projection model parameterized with capture–recapture likelihood estimates from a Bayesian framework. Our study combines survival and growth data from a single dataset to quantify the influence of size on survival while including different sources of uncertainty around these parameters, demonstrating how selective forces can be studied in populations with limited data and incomplete recaptures. We found a strong dependency of the population growth rate on changes in individual size, mediated by potential changes in selection on mean body size and on maximum body size. Our approach of simultaneous parameter estimation can be extended across taxa to identify eco‐evolutionary mechanisms acting on size‐specific vital rates, and thus shaping population dynamics and viability.     

Herbivore-mediated ecological costs of reproduction shape the life history of an iteroparous plant

Plant reproduction yields immediate fitness benefits but can be costly in terms of survival, growth, and future fecundity. Life-history theory posits that reproductive strategies are shaped by trade-offs between current and future fitness that result from these direct costs of reproduction. Plant reproduction may also incur indirect ecological costs if it increases susceptibility to herbivores. Yet ecological costs of reproduction have received little empirical attention and remain poorly integrated into life-history theory. Here, we provide evidence for herbivore-mediated ecological costs of reproduction, and we develop theory to examine how these costs influence plant life-history strategies. Field experiments with an iteroparous cactus (Opuntia imbricata) indicated that greater reproductive effort (proportion of meristems allocated to reproduction) led to greater attack by a cactus-feeding insect (Narnia pallidicornis) and that damage by this herbivore reduced reproductive success. A dynamic programming model predicted strongly divergent optimal reproductive strategies when ecological costs were included, compared with when these costs were ignored. Meristem allocation by cacti in the field matched the optimal strategy expected under ecological costs of reproduction. The results indicate that plant reproductive allocation can strongly influence the intensity of interactions with herbivores and that associated ecological costs can play an important selective role in the evolution of plant life histories.     

Demographic consequences of a food and water shortage to desert Chacma Baboons,Papio ursinus

The age-sex composition of a chacma baboon (Papio ursinus)population changed following a 5-month interval of extreme food and water shortages. Mortality was significantly greater among adult females, juveniles, and infants than among adult males. The probable basis of 19 of 22 deaths during the interval of food and water shortage was starvation caused by drought conditions which localized water sources, reducing access to food resources. This resulted in a long-term (> 6-year) shift in adult sex ratios within this three-troop population, from 1.04 to 1.42-1.58 adult and subadult males per adult female. Patterns of intertroop interaction were also influenced by food scarcity, which determined which troop was most seriously affected.     

Using genomic information for management planning of an endangered perennial,Viola uliginosa

Species occupying habitats subjected to frequent natural and/or anthropogenic changes are a challenge for conservation management. We studied one such species, Viola uliginosa, an endangered perennial wetland species typically inhabiting sporadically flooded meadows alongside rivers/lakes. In order to estimate genomic diversity, population structure, and history, we sampled five sites in Finland, three in Estonia, and one each in Slovenia, Belarus, and Poland using genomic SNP data with double‐digest restriction site‐associated DNA sequencing (ddRAD‐seq). We found monophyletic populations, high levels of inbreeding (mean population F_SNP = 0.407–0.945), low effective population sizes (N_e = 0.8–50.9), indications of past demographic expansion, and rare long‐distance dispersal. Our results are important in implementing conservation strategies for V. uliginosa, which should include founding of seed banks, ex situ cultivations, and reintroductions with individuals of proper origin, combined with continuous population monitoring and habitat management.     

Demographic consequences of adult sex ratio in a reintroduced hihi population

1.?Male-biased adult sex ratios are frequently observed in free-ranging populations and are known to cause changes in mating behaviours including increased male harassment of females, which can cause injury to females and/or alter female behaviour during breeding. 2.?Although we can explain why such behaviours may evolve and have studied their impacts on individuals when it does, we know very little about the demographic consequences of harassment caused by changes in adult sex ratio. 3.?Using a 12-year longitudinal data set of a free-living and endangered New Zealand passerine, the hihi (Notiomystis cincta), we show that a changing adult sex ratio has little or no effect on adult female survival or the number of fledglings produced per female. This is despite clear evidence of male harassment of breeding females when the sex ratio was male biased (up to three males per female). 4.?The length of the study and major fluctuations in sex ratio observed made it possible to obtain narrow confidence or credible intervals for effect sizes, showing that any effect of sex ratio on demographic rates were small. 5.?Our results provide rare empirical evidence for the demographic consequences of biased adult sex ratios in the wild and particularly in a conservation context.     

Demographic consequences of age-structure in extreme environments: population models for arctic and alpine ptarmigan

Organisms living in arctic and alpine environments are increasingly impacted by human activities. To evaluate the potential impacts of global change, a better understanding of the demography of organisms in extreme environments is needed. In this study, we compare the age-specific demography of willow ptarmigan (Lagopus lagopus) breeding at arctic and subalpine sites, and white-tailed ptarmigan (L. leucurus) breeding at an alpine site. Rates of egg production improved with age at the alpine and subalpine sites, but the stochastic effects of nest and brood predation led to similar rates of annual fecundity among 1-, 2-, and 3+-year-old females. All populations had short generation times (T<2.7 years) and low net reproductive rates (R ₀<1.2). Stable age distributions were weighted towards 1-year-old females in willow ptarmigan (>59%), and to 3+-year-old females in white-tailed ptarmigan (>47%). High damping ratios (ρ>3.2) indicated that asymptotic estimates were likely to match natural age distributions. Sensitivity and elasticity values indicated that changes in juvenile survival would have the greatest impact on the finite rate of population change (λ) in willow ptarmigan, whereas changes to the survival of 3+-year-old females would have a greater effect in white-tailed ptarmigan. High survivorship buffers white-tailed ptarmigan in alpine environments against the potential effects of climate change on annual fecundity, but may make the species more sensitive to the effects of pollutants or harvesting on adult survival. Conversely, processes that reduce annual fecundity would have a greater impact on the population viability of willow ptarmigan in arctic and subalpine environments. If these same demographic patterns prove to be widespread among organisms in extreme environments, it may be possible to develop general recommendations for conservation of the biological resources of arctic and alpine ecosystems.