Functional Ecology

Published by Wiley
Online ISSN: 1365-2435
Publications
Article
Commonly held views assume that ageing, or senescence, represents an inevitable, passive, and random decline in function that is strongly linked to chronological age. In recent years, genetic intervention of life span regulating pathways, for example, in Drosophila as well as case studies in non-classical animal models, have provided compelling evidence to challenge these views.Rather than comprehensively revisiting studies on the established genetic model systems of ageing, we here focus on an alternative model organism with a wild type (unselected genotype) characterized by a unique diversity in longevity - the honey bee.Honey bee (Apis mellifera) life span varies from a few weeks to more than 2 years. This plasticity is largely controlled by environmental factors. Thereby, although individuals are closely related genetically, distinct life histories can emerge as a function of social environmental change.Another remarkable feature of the honey bee is the occurrence of reverted behavioural ontogeny in the worker (female helper) caste. This behavioural peculiarity is associated with alterations in somatic maintenance functions that are indicative of reverted senescence. Thus, although intraspecific variation in organismal life span is not uncommon, the honey bee holds great promise for gaining insights into regulatory pathways that can shape the time-course of ageing by delaying, halting or even reversing processes of senescence. These aspects provide the setting of our review.We will highlight comparative findings from Drosophila melanogaster and Caenorhabditis elegans in particular, and focus on knowledge spanning from molecular- to behavioural-senescence to elucidate how the honey bee can contribute to novel insights into regulatory mechanisms that underlie plasticity and robustness or irreversibility in ageing.
 
Weaned northern elephant seal pups (Mirounga angustirostris). Photograph credit: S, Shen.
Percentage difference in breath-hold VO2 from resting VO2 (RMR) for all breath-holds (N = 275). The dotted line represents the mean RMR for each animal. (a) Filled circles are animals early in the developmental fast and open circles represent animals late in the developmental fast (F1,252 = 9·9, P = 0·002). (b) Filled circles are rest-associated apnoeas and close circles are voluntary submergences (P > 0·05).
Exponential coefficient (β) for rate of pO2 depletion across breath-holds (N = 70). (a) Filled circles are animals early in the PWF (2 weeks postweaned) and open circles represent animals late in the PWF (7 weeks postweaned) (P > 0·05). (b) Filled circles are rest-associated apnoeas and open circles are voluntary submergences (F1,64 = 4·5, P = 0·03).
Mean venous partial pressure of oxygen (pO2), partial pressure of carbon dioxide (pCO2), haematocrit (Hct) and pH at 30-s intervals combined across all breath-holds for all animals. Samples from breath-holds exceeding 10 min were not included in the figure. Black and white symbols (pO2, pCO2 and Hct) are associated with the left y-axis. Grey square symbols (pH) are associated with the right y-axis. Each point is represented by mean ± SE for every animal at that specific duration.
Article
Investigation into the development of oxygen storage capacity in air-breathing marine predators has been performed, but little is known about the development of regulatory factors that influence oxygen utilization. Strategies for efficiently using oxygen stores should enable marine predators to optimize time spent foraging underwater.We describe the developmental patterns of oxygen use during voluntary breath-holds in northern elephant seals (Mirounga angustirostris) at 2 and 7 weeks post-weaning. We measured 1) changes in oxygen consumption (VO2), and 2) changes in venous pH, partial pressure of oxygen (pO2), haemoglobin saturation (sO2), oxygen content (O2ct), partial pressure of carbon dioxide (pCO2), haematocrit (Hct) and total haemoglobin (tHb). To examine the effect of the dive response on the development of oxygen utilization, voluntary breath-hold experiments were conducted in and out of water.Suppression of VO2 during voluntary breath-holds increased significantly between 2 and 7 weeks post-weaning, reaching a maximum suppression of 53% below resting metabolic rate and 56% below Kleiber's standard metabolic rate. From 2 to 7 weeks post-weaning, breath-hold VO2 was reduced by 52%. Between the two age classes, this equates to a mean breath-hold VO2 reduction of 16% from resting VO2. Breath-hold VO2 also declined with increasing breath-hold duration, but there was no direct effect of voluntary submergence on reducing VO2.Age did not influence rates of venous pO2 depletion during breath-holds. However, voluntary submergence did result in slower pO2 depletion rates when compared to voluntary terrestrial apnoeas. The differences in whole body VO2 during breath-holds (measured at recovery) and venous pO2 (reflective of tissue O2-use measured during breath-holds), likely reflects metabolic suppression in hypoxic, vasoconstricted tissues.Consistent pCO2 values at the end of all voluntary breath-holds (59.0 ± 0.7 mmHg) suggests the physiological cue for stimulating respiration in northern elephant seal pups is the accumulation of CO2.Oxygen storage capacity and metabolic suppression directly limit diving capabilities and may influence foraging success in low-weaning weight seals forced to depart to sea prior to achieving full developmental diving capacity.
 
Article
1. Adaptive maternal programming occurs when mothers alter their offspring's phenotype in response to environmental information such that it improves offspring fitness. When a mother's environment is predictive of the conditions her offspring are likely to encounter, such transgenerational plasticity enables offspring to be better-prepared for this particular environment. However, maternal effects can also have deleterious effects on fitness.2. Here, we test whether female threespined stickleback fish exposed to predation risk adaptively prepare their offspring to cope with predators. We either exposed gravid females to a model predator or not, and compared their offspring's antipredator behaviour and survival when alone with a live predator. Importantly, we measured offspring behaviour and survival in the face of the same type of predator that threatened their mothers (Northern pike).3. We did not find evidence for adaptive maternal programming; offspring of predator-exposed mothers were less likely to orient to the predator than offspring from unexposed mothers. In our predation assay, orienting to the predator was an effective antipredator behaviour and those that oriented, survived for longer.4. In addition, offspring from predator-exposed mothers were caught more quickly by the predator on average than offspring from unexposed mothers. The difference in antipredator behaviour between the maternal predator-exposure treatments offers a potential behavioural mechanism contributing to the difference in survival between maternal treatments.5. However, the strength and direction of the maternal effect on offspring survival depended on offspring size. Specifically, the larger the offspring from predator-exposed mothers, the more vulnerable they were to predation compared to offspring from unexposed mothers.6. Our results suggest that the predation risk perceived by mothers can have long-term behavioural and fitness consequences for offspring in response to the same predator. These stress-mediated maternal effects can have nonadaptive consequences for offspring when they find themselves alone with a predator. In addition, complex interactions between such maternal effects and offspring traits such as size can influence our conclusions about the adaptive nature of maternal effects.
 
Article
Functional variability (FV) of populations can be decomposed into three main features: the individual variability of multiple traits, the strength of correlations between those traits and the main direction of these correlations, the latter two being known as 'phenotypic integration'. Evolutionary biology has long recognized that FV in natural populations is key to determining potential evolutionary responses, but this topic has been little studied in functional ecology.Here we focus on the arctico-alpine perennial plant species Polygonum viviparum L.. We used a comprehensive sampling of seven functional traits in 29 wild populations covering the whole environmental niche of the species. The niche of the species was captured by a temperature gradient, which separated alpine stressful habitats from species-rich, competitive sub-alpine ones. We seeked to assess the relative roles of abiotic stress and biotic interactions in shaping different aspects of functional variation within and among populations, that is, the multi-trait variability, the strength of correlations between traits, and the main directions of functional trade-offs.Populations with the highest extent of functional variability were found in the warm end of the gradient whereas populations exhibiting the strongest degree of phenotypic integration were located in sites with intermediate temperatures. This could reveal both the importance of environmental filtering and population demography in structuring FV. Interestingly, we found that the main axes of multivariate functional variation were radically different within and across population.Although the proximate causes of FV structure remain uncertain, our study presents a robust methodology for the quantitative study of functional variability in connection with species' niches. It also opens up new perspectives for the conceptual merging of intraspecific functional patterns with community ecology.
 
Article
Body condition affects the timing and magnitude of life history transitions. Therefore, identifying proximate mechanisms involved in assessing condition is critical to understanding how these mechanisms affect the expression of life history plasticity. Nutrient storage is an important body condition parameter, likely playing roles in both attaining minimum body-condition thresholds for life history transitions and expression of life history traits.We manipulated protein availability for females of the flesh fly Sarcophaga crassipalpis to determine whether reproductive timing and output would remain plastic or become fixed. Liver was provided for 0, 2, 4, or 6 days of adult pre-reproductive development. Significantly, liver was removed after the feeding threshold had been attained and females had committed to producing a clutch.We also identified the major storage proteins and monitored their abundances, because protein stores may serve as an index of body condition and therefore may play an important role in life history transitions and plasticity.Flesh flies showed clear post-threshold plasticity in reproductive timing. Females fed protein for 2 days took ~30% longer to provision their clutch than those fed for 4 or 6 days. Observations of oogenesis showed the 2-day group expressed a different developmental program including slower egg provisioning.Protein availability also affected reproductive output. Females fed protein for 2 days produced ~20% fewer eggs than females fed 4 or 6 days. Six-day treated females provisioned larger eggs than 4-day treated females, followed by 2-day treated females with the smallest eggs.Two storage proteins were identified, LSP-1 and LSP-2. LSP-2 accumulation differed across feeding treatments. The 2- and 4-day treatment groups accumulated LSP-2 stores but depleted them during provisioning of the first clutch, whereas the 6-day group accumulated the greatest quantity of LSP-2 and had substantial LSP-2 stores remaining at the end of the clutch. This pattern of accumulation and depletion suggests that LSP-2 could play roles in both provisioning the current clutch and future clutches, making it a good candidate molecule for affecting reproductive timing and allotment. LSP-1 was not associated with post-threshold plasticity; it was carried over from larval feeding into adulthood and depleted uniformly across all feeding groups.
 
Bumblebee (Bombus terrestris audax) queen collecting legume pollen. Photograph by Nigel E. Raine.
Spatial configurations of flowers. Black circles (1–5) indicate the location of flowers (small circles = low rewarding value; large circles = high rewarding value), N is the nest-box (grey ellipse = entrance) and white bars (a–d) the geometric poster landmarks. Black arrows show examples of anticlockwise routes minimizing travel distance (the shortest possible route). Dashed arrows show examples of anticlockwise routes maximizing initial rate of food intake by visiting the most rewarding flower first (assuming a constant directionality of movement). Experiment 1: a bee minimizing travel distance would always maximize its initial rate of reward intake. Experiment 2: a bee maximizing its initial rate of reward intake would fly a route 18% longer than a bee minimizing travel distance. Experiment 3: a bee maximizing its initial rate of reward intake would fly a route 42% longer than a bee minimizing travel distance. Scale is in metres. Cartesian coordinates of all objects in the flight room are given in Table S1.
Directionality of bee movement between flowers. Plotting symbols represent values of directionality indices (DI) for each bee during phase 1 (circles) and phase 2 (diamonds) of observations. Negative DI values indicate a tendency for the bees to follow a clockwise route between flowers. Positive DI values indicate a tendency to move in an anticlockwise direction. Symbols in black illustrate significant biases in directionality compared with a null hypothesis that clockwise and anticlockwise routes are equally likely (binomial test with a random probability 0·5: P<0·05).
Frequency of route usage. In phases 1 and 2 of experiments, white columns represent the mean percentage of foraging bouts in which bees followed routes that minimized travel distance in relation to the cumulative number of foraging bouts completed (blocks of 20 successive bouts). In phase 2, grey columns represent the mean percentage of bouts in which bees followed routes that maximized initial rate of food intake and black columns the mean percentage of bouts in which bees followed routes that optimized both (minimized travel distance and maximized initial rate of food intake). P1: Generalized Linear Mixed Model (GLMM) with identity-link function (categorical variable: foraging bouts, random factor: individual). P2: GLMM with identity-link function (categorical variable: type of route, random factor: individual). Different letters (a, b, c) above columns indicate significant differences between percentages of foraging bouts within blocks of 20 bouts (t-tests).
Spatial geometry of routes. For each bee, diagrams represent the geometry of the most frequently used route (trapline) in the last 20 foraging bouts of phase 1 (i.e. bouts 21–40: upper rows) and phase 2 (i.e. bouts 61–80: lower rows) of experiments. Black circles indicate the spatial location of flowers (small circles = low rewarding value; large circles = high rewarding value), N is the nest-box and arrows the direction of bee movements. Numbers are the frequency with which the route was observed during the last 20 foraging bouts of each phase of experiments. *Routes minimizing travel distances (phases 1 and 2). †Routes maximizing initial rate of food intake (phase 2). Scale is in metres.
Article
1. Animals exploiting renewable resource patches are faced with complex multi-location routing problems. In many species, individuals visit foraging patches in predictable sequences called traplines. However, whether and how they optimize their routes remains poorly understood. 2. In this study, we demonstrate that traplining bumblebees (Bombus terrestris) make a trade-off between minimizing travel distance and prioritizing the most rewarding feeding locations. 3. Individual bees trained to forage on five artificial flowers of equal reward value selected the shortest possible route as a trapline. After introducing a single highly rewarding flower to the array, they re-adjusted their routes visiting the most rewarding flower first provided the departure distance from the shortest possible route remained small (18%). When routes optimizing the initial rate of reward intake were much longer (42%), bees prioritized short travel distances. 4. Under natural conditions, in which individual flowers vary in nectar productivity and replenish continuously, it might pay bees to prioritize highly rewarding locations, both to minimize the overall number of flowers to visit and to beat competitors. 5. We discuss how combined memories of location and quality of resource patches could allow bees and other traplining animals to optimize their routing decisions in heterogeneous environments.
 
Volcano plots showing the pairwise comparison of the differential expression of genes between mussels at three separate vertical positions on the shore during an emersion stress or after a 1-h recovery in ambient seawater. The red points indicate genes-of-interest that display both large-magnitude fold changes (FC ≥ 2, x-axis) as well as high statistical significance (P < 0·05, y-axis). Emersion stress: (a) Strawberry Hill (SH)-low vs. SH-mid, (c) SH-low vs. SH-high, (e) SH-mid vs. SH-high. 1 h recovery: (b) SH-low vs. SH-mid, (d) SH-low vs. SH-high, (f) SH-mid vs. SH-high.
Principal component analysis of the cumulative separation in gene expression between mussel populations located at Strawberry Hill (SH) and Boiler Bay (BB), OR. Mussels were sampled from the mid-intertidal zone at SH (squares) and two separate vertical positions on the shore at BB (mid – triangles and high – circles). Mussels were sampled during daily emersion (closed symbols) or after a 1-h recovery in ambient seawater (open symbols). Plot ordination was performed for the first 2 component loadings - Component 1: x-axis (35·13% of the variation); Component 2: y-axis (30·87% of the variation).
Article
1. The marine intertidal zone is characterized by large variation in temperature, pH, dissolved oxygen and the supply of nutrients and food on seasonal and daily time scales. These oceanic fluctuations drive ecological processes such as recruitment, competition and consumer–prey interactions largely via physiological mechanisms. Thus, to understand coastal ecosystem dynamics and responses to climate change, it is crucial to understand these mechanisms. 2. Here we utilize transcriptome analysis of the physiological response of the mussel Mytilus californianus at different spatial scales to gain insight into these mechanisms. We used mussels inhabiting different vertical locations within Strawberry Hill on Cape Perpetua, OR and Boiler Bay on Cape Foulweather, OR to study inter- and intra-site variation of gene expression. 3. The results highlight two distinct gene expression signatures related to the cycling of metabolic activity and perturbations to cellular homeostasis. Intermediate spatial scales show a strong influence of oceanographical differences in food and stress environments between sites separated by c. 65 km. 4. Together, these new insights into environmental control of gene expression may allow understanding of important physiological drivers within and across populations.
 
Article
Mammalian sleep is composed of two distinct states - rapid-eye-movement (REM) and non-REM (NREM) sleep - that alternate in cycles over a sleep bout. The duration of these cycles varies extensively across mammalian species. Because the end of a sleep cycle is often followed by brief arousals to waking, a shorter sleep cycle has been proposed to function as an anti-predator strategy. Similarly, higher predation risk could explain why many species exhibit a polyphasic sleep pattern (division of sleep into several bouts per day), as having multiple sleep bouts avoids long periods of unconsciousness, potentially reducing vulnerability.Using phylogenetic comparative methods, we tested these predictions in mammals, and also investigated the relationships among sleep phasing, sleep-cycle length, sleep durations and body mass.Neither sleep-cycle length nor phasing of sleep was significantly associated with three different measures of predation risk, undermining the idea that they represent anti-predator adaptations.Polyphasic sleep was associated with small body size, shorter sleep cycles and longer sleep durations. The correlation with size may reflect energetic constraints: small animals need to feed more frequently, preventing them from consolidating sleep into a single bout. The reduced daily sleep quotas in monophasic species suggests that the consolidation of sleep into one bout per day may deliver the benefits of sleep more efficiently and, since early mammals were small-bodied and polyphasic, a more efficient monophasic sleep pattern could be a hitherto unrecognized advantage of larger size.
 
Article
Adaptation can occur on ecological time-scales (contemporary evolution) and adaptive divergence can cause reproductive isolation (ecological speciation). From the intersection of these two premises follows the prediction that reproductive isolation can evolve on ecological time-scales. We explore this possibility in theory and in nature. Finding few relevant studies, we examine each in some detail. THEORY: Several models have demonstrated that ecological differences can drive the evolution of partial reproductive barriers in dozens to hundreds of generations. Barriers likely to evolve quickly include dispersal rate, habitat preference and selection against migrants/hybrids. PLANTS: Adjacent populations adapting to different fertilizer treatments or to mine tailings can develop reproductive barriers within at least 100 generations. These barriers include differences in flowering time and selection against migrants/hybrids. INVERTEBRATES: Populations on native and introduced host plants can manifest reproductive barriers in dozens to hundreds of generations. These barriers include local host preference and selection against migrants/hybrids. VERTEBRATES: Salmon adapting to divergent breeding environments can show restricted gene flow within at least 14 generations. Birds evolving different migratory routes can mate assortatively within at least 10-20 generations. Hybrid sculpins can become isolated from their ancestral species within at least 20-200 generations. Ecological speciation can commence within dozens of generations. How far it goes is an important question for future research.
 
Article
1. A graphic technique is presented in which data on age-specific reproduction of individuals are portrayed using: (i) a horizontal life line, the length of which is proportional to individual longevity; (ii) colour-coded segments depicting the level of reproduction at each age; and (iii) a cohort survival schedule created by rank-ordering individual life lines from shortest- to longest-lived. 2. The resulting graphic, referred to as an event history diagram, portrays data at the individual level and thus allows visual comparisons of detailed life-history patterns such as age of first reproduction, longevity, ages of high, medium, low and zero reproduction, and post-reproductive period. 3. Example graphs are shown for reproductive and longevity data gathered on 1000 medfly females. The average female lived 35·6 days and laid 759·3 eggs and therefore the graphs display information for 35 600 fly days and the age-distribution of laying for 759 300 eggs. 4. Because the graphics provide a means for visualizing large amounts of data precisely and efficiently, they reveal details and nuances in the data that are not apparent from conventional graphic methods. 5. The advantages of longitudinal data gathered on individuals and reasons why visualizing individual-level data is important are discussed.
 
Article
Summary • Theoretical models predict that large-seeded species should germinate more rapidly than small-seeded species, since large seeds are more likely to have higher post-dispersal seed predation than small seeds. A prompt germination strategy would therefore enable large seeds to reduce risks of mortality. • To assess this predicted relationship between seed mass and mean time to germination (MTG), we used a meta-analysis of published data sources. Our data base contained information for these two traits for 1037 tree species from five tropical areas worldwide (Brazil, India, Ivory Coast, Malaysia and Panama). Both cross-species analyses and phylogenetically independent contrasts (PIC) were conducted on the log-transformed values of seed mass and MTG. • Log-seed mass was a significantly phylogenetically conserved trait in all five data sets. Log-MTG was significantly phylogenetically conserved in all sites except for Malaysia and India. • Log-MTG and log-seed mass were significantly positively correlated in all sites except for Malaysia. PIC analyses showed a significantly positive relationship in Brazil, India and Ivory Coast but not in Malaysia and Panama. When all sites were combined, PIC analyses indicated a significant positive relationship between these two traits. • Our findings do not support the hypothesis that large seeds germinate faster than small seeds, but rather that small seeds germinate faster. We interpret our results in light of phylogenetic and biophysical constraints. We propose four alternative mechanisms that could account for the observed pattern, including developmental constraints, water absorption and investment to physical defences.
 
Article
1. There is limited understanding of patterns of variation that exist among root traits of different species, especially under field conditions. We contrasted 11 fast- and slow-growing species paired within five evolutionary lineages to investigate whether root traits associated with soil resource acquisition were related to species’ potential growth rate. 2. Measurements of root morphology, architecture, nitrogen and phenolic concentration, respiration and phosphorus uptake were taken on fine, non-woody roots sampled from forest stands in central Pennsylvania, USA. 3. Across all five contrasts, roots of fast-growing species generally had higher specific root length, smaller diameters, greater degree of branching, and lower phenolic concentrations than those of slow-growing species. This suggests differences in potential soil exploration and root defences among species differing in potential growth rate. 4. There were no significant differences between fast- and slow-growing species in root tissue density, respiration or P uptake. Lack of root physiological differences between species differing in growth rate contrasted with previous research on chamber-grown seedlings. 5. These results imply that, while roots of fast-growing species may be constructed for more rapid soil exploration and shorter life span than those of slow-growing species, root physiology is either more closely tied to overall plant physiology, which is more similar among mature trees, or masked by variation in soil microsites, root age or interactions with mycorrhizal fungi.
 
Article
1. Clearcut logging results in major changes in ectomycorrhizal fungal communities, but whether this results in the loss of key functional traits, such as those associated with nutrient acquisition from soil organic matter, is unknown. Furthermore, little is known about the importance of resource partitioning in structuring ectomycorrhizal fungal communities following disturbance because most research on these communities has focussed on life history strategies. By studying functional traits, such as activities of enzymes involved in the catabolism of organic macromolecules in soil, we can determine whether a physiological potential for resource partitioning exists in pioneer ectomycorrhizal communities and whether severe disturbance affects these important ecosystem services.
 
Article
Summary • Although plant nitrogen (N) strategies may play an important role for community structure and ecosystem functioning, there is not a clear understanding of the link between N acquisition by roots and N utilization by shoots. Particularly, it is unclear how the co-variations between size- and physiology-related traits determine N acquisition and N utilization at the plant scale. • We used 13 co-occurring temperate pasture grasses to study inter-specific variations in above-ground N yield and in root N acquisition and shoot N utilization traits. N acquisition traits concerned root influx capacities for and , root mass and specific root area in ingrowth cores. N utilization traits concerned leaf life span, leaf N content, leaf N resorption, mean residence time of N and leaf N use efficiency. • We found evidence for three trade-offs across species concerning root N acquisition: (i) root mass increased when specific root area declined; (ii) an increase in root area was observed when total N influx capacity decreased; and (iii) root influx capacity increased when capacity declined. • High total root uptake capacity gave rise to high leaf N content and was associated across species to low leaf N use efficiency. Tall grasses were characterized by high shoot N yield, high root biomass and high leaf N use efficiency. Physiology-related traits and size-related traits were generally found independent. • Our study demonstrates how size and N uptake related root traits are associated to major axes of plant specialization ((i) plant size and (ii) conservation vs. exploitation of N) which were previously identified based on shoot traits. Contrasted N strategies were segregated across species according to four combinations along these two axes.
 
Average number of flowers that opened per cyme per hour (n = 30). The average was calculated by adding data for the 30 plants over 4 days.
Increase in the number of pollen grains on the body of workers of Bombus pascuorum after different numbers of virgin flowers visited.
Relationship between the percentage selfing predicted with the model and the flower sequence position when bumble-bees visit virgin flowers. Parameters were estimated by Rademaker et al. (1997) for B. terrestris under controlled conditions: A = 4448, k1 = 0·0015, k2 = 0·16, k3 = 0·5, k4 = 0·061, B = 55000. The solid line gives results with these parameters. The dotted line with reduced k3 (k3 = 0·25), the broken line with reduced k4 (k4 = 0·04), and the broken, dotted line with increased A (A = 8000). For further explanation see text. The maximum percentage selfing estimated with RAPDs from the plants on which bees visit a sequence of virgin flowers is plotted in the figure (open dots).
Relationship between the percentage selfing predicted with the model and the number of flowers visited per approach. Parameters were estimated by Rademaker et al. (1997) for B. terrestris under controlled conditions: A = 4448, k1 = 0·0015, k2 = 0·16, k3 = 0·5, k4 = 0·061, B = variable as in Table 1. The solid line gives results with these parameters and the identical results if B = 13 400, which is the average amount of pollen encountered in the flowers visited by the bee. The dotted line gives results with reduced k3 (k3 = 0·25) and the broken line with k3 = 0·15. For further explanation see text. The maximum percentage selfing obtained with RAPDs from the field population is plotted in the figure (solid dots). (b) Effect of A (A = 4448 solid line, A = 6000 broken line, A = 8000 dotted line), which is the number of pollen grains on the bee at arrival at the plant, on the predicted percentage selfing for plants with flowers with on average B=13 400 pollen grains.
Article
1. We quantified geitonogamous selfing in Echium vulgare, a self-compatible, bumble-bee pollinated plant. A maximum estimate of selfing was determined using a paternity analysis with RAPDs. In the first experiment, bumble-bees visited a sequence of virgin flowers. The percentage selfing increased rapidly from 12% in the first flower visited, up to 50% in the 15th flower visited in the sequence. In the second experiment, when bees visited plants in a natural population, the average selfing of plants increased with the number of open flowers from 0% to maximally 33%. 2. The results obtained in both experiments are consistently lower than predicted by our model on pollen dynamics (Rademaker, de Jong & Klinkhamer 1997). We modified the model on pollen dynamics to link it more to the field situation with observations on flower stage, flower opening and bumble-bee preference, so that the bumble-bees encounter a variable number of pollen grains per flower. We also adjusted the parameters. If less pollen adheres to the bee (25% instead of 50%) after removal from the anthers, or if bees arrive at a plant with more pollen grains (6000 instead of 4448), the predictions of the model in regard to selfing could be improved but were still high compared with the observed selfing rates measured with RAPDs. 3. We suggest that the model is consistent with pollen dynamics in the field. However, post-pollination processes like selective abortion could play a role in E. vulgare.
 
Leaf thickness and leaf mass per unit area (LMA) of the different species plotted vs. leaf life span. Deciduous and evergreen species are separated by a broken vertical line. Error bars are omitted for clarity.
anova table for the interspecific d ifferences in leaf traits
Correlation coefficients between leaf longevity and other leaf attributes (log-transformed) All species Evergreen species only Evergreen Quercus and Pinus species only
Article
Summary • It has been proposed that in longer-living leaves the allocation of biomass to structural components is greater than in shorter-living leaves, leading to a greater leaf mass per area (LMA) and to lower assimilation rates. However, direct evidence in support of this hypothesis is very scarce. • In the present work we investigated the relationships between leaf duration and LMA, leaf thickness and fibre concentrations (cellulose, hemicellulose and lignin) in five oak species, five pine species and three additional tree species, differing in leaf life spans. Correlations among leaf life span and the other leaf traits were obtained both across species (TIPs) and as phylogenetically independent contrasts (PICs). • Leaf thickness and LMA increased steadily with leaf longevity. No relationship was found between leaf longevity and the lignin concentration per unit leaf mass. Evergreen leaves were found to have higher mean concentrations of cellulose and hemicellulose than deciduous ones. However, no relationship was observed between leaf longevity and the concentration of structural carbohydrates across the set of evergreen species, although PIC correlations revealed increases in cellulose with leaf longevity within particular lineages. • Our findings reveal that leaf reinforcement by structural carbohydrates depends on leaf habit (deciduous vs. evergreen) and, within a given lineage, also on leaf longevity. However, among the evergreen species co-occurring in a particular environment, leaf duration may apparently be increased, with no need for increases in the concentration of structural components per unit leaf mass.
 
Article
1. Carbon stable isotopes are commonly used as a research tool in physiological ecology. When elements are consumed, they are naturally enriched or depleted as the consumer processes them. The difference in isotopic composition between the consumer and the diet is known as the discrimination factor (Δ13C). 2. Mixing models are used to estimate the contribution of multiple dietary components to a consumer’s tissues and discrimination must be estimated in the model. Often, discrimination factors vary depending on multiple factors, yet in many models the discrimination factor is assumed to be constant for each dietary component. 3. Few studies have evaluated the mechanistic basis of stable isotope metabolism and discrimination during macromolecule biosynthesis, despite the potential to improve estimations of discrimination factors. We tested whether 13C discrimination depends on the dietary concentration of 13C by culturing the bacterium Bacillus subtilis in a gradient of broths ranging from a δ13C of −11·8‰ to −25·3‰. We found an increase in discrimination in whole bacterial tissue, bulk lipid, and lipid-extracted fractions as dietary the concentration of 13C increased, with lipids showing the greatest discrimination ranging from 2·72‰ in the low 13C broths to 15·5‰ in the high13C broths. 4. These findings contrast with the majority of isotopic ecology data that typically show a moderate enrichment of 13C as trophic level increases. This discrepancy is attributed to the de novo biosynthesis of the majority of cellular components in this study as opposed to the effects of isotopic routing seen in more metabolically complex taxa.
 
Box and whisker plots illustrate plant functional type variation along the (a) leaf economics spectrum (PC1), (b) seed mass and SRL spectrum (PC2), and (c) height and phenology spectrum (PC3). The three shrubs and two trees were combined into a ‘C3 woody plants’ group for simplicity. Each of the three anova tests were significant (P < 0·05), and significantly different pairwise contrasts (Tukey’s HSD) are indicated by different lowercase letters.
Simple linear relationships between fine root Nmass (%) and (a) leaf Nmass (%), (b) the leaf economics spectrum (represented by the first principal component), and (c) specific root length (g m−2), and between (d) specific leaf area (mm2 mg−1) and specific root length.
Simple linear relationships between litter decomposition rate (measured as the proportion of litter mass loss after decomposing in the forest for 1 year) and (a) leaf Nmass (%), (b) leaf dry matter content (mg mg−1), (c) the leaf economics spectrum (represented by the first principal component), and (d) the height and phenology spectrum (represented by the third principal component). The outlier in panels b and d represents ponderosa pine, and both relationships were still significant if this species was removed from the regression analysis.
Article
1. Westoby’s [Plant and Soil (1998), 199, 213] Leaf-Height-Seed (LHS) plant strategy scheme quantifies the strategy of a plant based on its location in a three-dimensional space defined by three functional traits: specific leaf area (SLA), height, and seed mass. This scheme is based on aboveground traits and may neglect strategies of belowground resource capture if root functioning is not mirrored in any of the axes. How then do fine roots fit into the LHS scheme? 2. We measured 10 functional traits on 133 plant species in a ponderosa pine forest in northern Arizona, USA. This data set was used to evaluate how well the LHS scheme accounts for the variation in above and belowground traits. 3. The three most important plant strategies were composed of multiple correlated traits, but SLA, seed mass, and height loaded on separate principle components. The first axis reflected the widely observed ‘leaf economics spectrum’. Species at the high end of this spectrum had high SLA, high leaf and fine root nitrogen (N) concentration, and low leaf dry matter content. The second axis reflected variation in seed mass and fine root morphology. Plants at the positive end of this spectrum were plants with large seeds and low specific root length (SRL). The third axis reflected variation in height and phenology. Plants at the positive end of this spectrum were tall species that flower late in the growing season. 4. Leaf N concentration was positively correlated with fine root N concentration. SRL was weakly positively correlated with SLA. SRL was not correlated with fine root N concentration. Leaf litter decomposition rate was positively correlated with the leaf economics spectrum and was negatively correlated with the height and phenology spectrum. 5. Leaf traits, seed mass, and height appear to be integrating properties of species that reflect much of the variation in plant function, including root function. Fine root N concentration was positively mirrored by the leaf economics spectrum, and SRL was inversely mirrored by seed mass. The leaf and height axes play a role in controlling leaf litter decomposability, indicating that these strategy axes have important consequences for ecosystem functioning.
 
Article
1. Changes of δ13C and its relation to leaf development, biochemical content and water stress were monitored over a 2 year period in two co-occurring Mediterranean oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex. 2. The time course of leaf δ13C showed different patterns in the two species. Young Q. pubescens leaves had a high δ13C and a marked decrease occurred during leaf growth. In contrast, leaves at budburst and maturity did not differ significantly in the case of Q. ilex. We suggest that the difference between δ13C of young leaves was linked to differential use of reserves of carbon compounds in the two species. 3.δ13C values of mature leaves were negatively correlated with minimum seasonal values of predawn water potential, suggesting that a functional adjustment to water resources occurred. 4. There was a significant correlation between individual δ13C values for two successive years. This interannual dependence showed that δ13C rankings between trees were constant through time.
 
Aquatic food-web isotope values for two ponds on our study site near Minnedosa, Manitoba, 1998, together with muscle values of arriving and incubating female Redhead Ducks (Aythya americana). This figure demonstrates the high δ13C and δD local food-web variability in the study area, thereby precluding the use of a simple mixing model approach to examining nutrient transfer to eggs. Also demonstrated is the large isotopic change in δD values through time due to evapotranspiration.
Changes in size-corrected body mass, body protein content and body lipid content of female Redhead Ducks (Aythya americana) on their breeding ground in southern Manitoba from 5 May (Day 0) to 18 July 1996 (Day 73). Data presented as residuals corresponding to expected values based on size estimates using a PCA1 score incorporating 3 mensural measurements.
Mean (± SE) carbon and hydrogen isotope ratios for muscle and abdominal fat from Redhead Duck (Aythya americana) females collected at Minnedosa, Manitoba, Canada during 1996
Mean (± SE) carbon and hydrogen isotope values for tissue and tissue fractions of redhead duck (Aythya americana) eggs collected with females at Minnedosa, Manitoba, Canada, during the laying period in 1996
Article
Summary Clutch formation represents a considerable energy expense for waterfowl, yet little evidence is available to quantify nutrient allocation from endogenous and exogenous sources. Here we investigated hydrogen and carbon stable isotope ratios (D and 13C) in female Redhead Ducks (Aythya americana) and their eggs to evaluate the use of D as an indicator of nutrient sources to reproduction. Females arrived with mean muscle tissue D and 13C values more positive than those of the local food web, reflecting marine dietary inputs from the wintering grounds. These values changed to the range of local food values by late incubation. 13C values from albumen and yolk protein were correlated, supporting the presence of a common exogenous carbon source for these egg components. There was no significant correlation between D or 13C values in egg tissues and abdominal fat or muscle from the corresponding laying female. No general population-level trends in isotope values from sequentially developing follicle yolks were found. Redhead females relied mainly on dietary lipids and proteins for egg production, and therefore endogenous reserves were used to satisfy female body maintenance and energy requirements. Functional Ecology (2004) 18, 737–745
 
Article
1. Quantitative genetic analysis of variation in host-use ability was performed in an extremely polyphagous species – the Gypsy Moth. Various life-history traits were investigated by applying a split-family two-environment experimental design, where 30 full-sibling families were reared on oak and Locust Tree leaves. 2. Feeding on Locust Tree leaves decreased preadult viability, prolonged development time, decreased pupal mass both in males and females, and decreased reproductive effort in females. 3. The majority of broad-sense heritabilities did not change across host plants. 4. Significant expression of genetic variation in diet breadth was observed for development time and pupal mass both in males and females, but not for female reproductive effort traits. The heritabilities of plasticities were, on average, lower than heritabilities of the traits themselves. 5. The majority of genetic correlations between the host plants were significantly positive. The only trade-off was found between reciprocal value of reproductive index and the average mass of a fertilized egg within oak. This means that selection for the decrease in relative reproductive investment (under starvation during gradation) will be followed by laying larger eggs. Given that the Gypsy Moth has a cyclic population dynamics, this negative genetic correlation could have a role in maintaining genetic variability in this species.
 
Article
Summary • We propose that diets of consumers in a food web have various ages, where age is defined as the time elapsed since carbon (C) in the diet was fixed from atmospheric CO2 by primary producers. To examine the diet ages for primary consumers in a detrital food web, we measured the radiocarbon (14C) content of termites collected in Thailand in 1998 and 2004. Diet ages were estimated by comparing the 14C content of samples with records of atmospheric 14CO2, which doubled in the early 1960s as a result of nuclear weapons tests and decreased after the nuclear test ban treaty. For comparison, we measured the 14C content of bees as primary consumers in a grazing web at the same study site. Stable carbon and nitrogen (N) isotope ratios were also analysed. • The 14C contents of the same species of termites decreased during the sampling interval, indicating that they used organic matter produced after the peak in atmospheric 14CO2. The diet ages were estimated to be 12–18, 7–13 and 5–9 years for the wood-feeder (Microcerotermes crassus), the soil-feeders (Dicuspiditermes makhamensis and Termes comis) and the fungus-grower (Macrotermes carbonarius), respectively. One colony of soil-feeder (T. comis), which nested in a fallen tree trunk, had exceptionally low 14C content, and its diet age was estimated to be around 50 years. The two bee species had lower 14C contents compared with the termites, and their diet ages were estimated to be 0 (Apis florea) and 2–4 years (Trigona sp.). • Stable C and N isotope ratios of termites showed similar patterns as previously reported, and no clear difference was observed between 1998 and 2004. Although the bees and the fungus-growing termite had similar stable C and N isotope ratios, their diet ages differed. • Our study suggests that radiocarbon can be used to estimate the diet ages of consumers in terrestrial food webs. Diet age should provide new insight into the trophic positions of organisms in grazing and detrital food webs and the interactions between these two webs. Functional Ecology (2006) 20, 385–393 doi: 10.1111/j.1365-2435.2006.01081.x
 
Article
Summary • Stable nitrogen (N) isotope has been widely used to disentangle food webs and to infer trophic positions of organisms based on an assumption that the stepwise enrichment occurs along trophic levels. The enrichment of 15N in soil organisms with diet humification has also been reported, but the underlying mechanism has not been fully examined. • To examine the effect of diet humification on 15N, we estimated the stable N isotope ratios and diet ages of earthworms and termites. These organisms feed on organic matter with various degrees of humification, ranging from undecomposed plant materials to humified organic matter (soil organic matter), in a gallery forest and a savanna in the Ivory Coast. We defined diet age as the time elapsed since carbon (C) in the diet of earthworms and termites was fixed from atmospheric CO2 by photosynthesis; it was estimated by comparing the radiocarbon (14C) content of these organisms to atmospheric 14CO2 records. • Stable N isotope ratios increased along the humification gradient of diets, and values for earthworms and termites varied from 1·8‰ to 9·9‰ and from –1·5‰ to 15·9‰, respectively. Epigeic (litter-feeding) earthworms had younger diet ages (2–4 years), whereas endogeic (soil-feeding) earthworms generally exhibited older diet ages (5–9 years). Grass-feeding termites had young diet ages (2 years), and wood/soil-feeding termites had the oldest diet ages (c. 50 years). Soil-feeding termites were similar in diet age (7–12 years) to wood feeders (8–11 years), with the exception of one species (18–21 years) that consumes large-diameter wood. • A significant positive relationship was found between diet ages and stable N isotope ratios of the two groups in the savanna. This relationship held in the gallery forest when termites feeding on woody tissues were not considered. These results show that the stable N isotope ratios of organisms can increase with diet age, unless C in the diet has been stored as organic matter, such as woody tissue, that is able to age without being subject to humification processes. • Given that above-ground food webs are often sustained directly by material and energy flow from below-ground food webs, in addition to trophic interactions, gradual enrichment of 15N with the humification of below-ground diets should be considered when interpreting stable N isotope ratios of terrestrial food webs.
 
Article
1. About 10 years after establishment, plantations of Western Redcedar (Thuja plicata Donn ex D. Don) on northern Vancouver Island, British Columbia become nutrient deficient and chlorotic, grow slowly, and are susceptible to invasion by the ericaceous shrub Salal (Gaultheria shallon Pursh.). 2. To test the hypothesis that δ15N can be related to site histories (site disturbance, soil N dynamics and plant development), we measured soil and foliar δ15N in the summer of 1992 in 3-year-old (nutrient-sufficient) and 10-year-old (nutrient-deficient) plantations and in old-growth stands. The foliar and soil δ15N values of the plantations and old-growth forests were different and closely reflected site histories. Salal invasion and nutrient deficiency interacted to depress the growth of Redcedar in 10-year-old plantations. 3. Site preparation destroyed the top soil organic layers (fresh and decaying litter) and forced Salal (ecto- and ericoid mycorrhizal) into the humus layer, where it was in direct competition with Redcedar, thereby disadvantaging arbuscular mycorrhizal/non-mycorrhizal Redcedar in its nutrient acquisition during a period when N and P are severely limited. 4. There was a large seasonal range of foliar δ15N (5·5 and 4·3‰ for 10-year-old Redcedar and Salal, respectively), and there was no relationship between foliar δ15N and measured rooting depth, demonstrating that rooting depths cannot be used to explain foliar δ15N variation among coexisting woody taxa. 5. Foliar and soil δ15N declined with site age and with a presumed change from ‘open’ to ‘closed’ N cycling; the 15N-depleting effects of mycorrhizal N transformations contributed to the observed δ15N decline.
 
Article
Summary • Relationships of leaf traits with rainfall at the place of origin of seed (RPO) are a function of acclimation and adaptation. To disentangle these effects we studied 29 species of 16-year-old Eucalyptus at a productive and an unproductive common garden (mean annual increments of above-ground stem volume = 21 ± 11 and 8 ± 5 m3 ha−1 years−1, respectively).We tested three hypotheses: (i) leaf traits vary between sites, but relationships among them do not; (ii) relationships of leaf traits with RPO do not vary between sites; and (iii) ecotypes originating from low-rainfall areas allocate a small fraction of nitrogen to thylakoid proteins and Rubisco, and have small SLA, small and narrow leaves, and large water-use efficiency (WUE). • Eleven leaf traits (leaf area, leaf thickness, leaf width/length, specific leaf area, fresh weight/dry weight, N, chlorophyll a/b, carotenoids/chlorophyll, thylakoid N%, Rubisco N%, WUE derived from 13C content) were measured in 1-year-old sun leaves. • Site had a large effect on not only the absolute values of leaf traits, but also relationships between pairs of traits. There were 20 significant correlations between pairs of traits. Three of the correlations had different slopes between sites, while a further nine had different intercepts. Hence the majority of significant correlations were not independent of site. • Leaf area and leaf width/length were the only traits related to RPO. There was no evidence that N allocation to Rubisco or thylakoid proteins was related to RPO, or that WUE was greater in ecotypes from dry areas. • For Eucalyptus, and perhaps other genera, physiological leaf traits may play a minor role in adaptation to water availability. There is large phenotypic plasticity in many leaf traits affecting not only the absolute values of traits, but also relationships among them. Functional Ecology (2006) 20, 929–940 doi: 10.1111/j.1365-2435.2006.01198.x
 
Article
Summary The effects of nutrient enrichment on wetland vegetation may depend on the responses of different plant species to nutrient supply over several years, in waterlogged or flooded soils, and under either nitrogen- or phosphorus-limited conditions. However, most growth experiments comparing species from differently productive sites have focused on their short-term responses to variation in N supply. In this study we investigated whether increased N or P supply affects plant growth differently, whether these effects differ between the first and second year of growth, and whether they are modified by the water regime. Plants of 16 wetland species were grown during two seasons in tubes with sand under full light. Treatments combined three nutrient levels (low N and P, high N, high P) with three water regimes (constantly wet, periodically aerated, periodically flooded). In the first year, shoot biomass was enhanced by high N supply, particularly in species from nutrient-rich sites; this was associated with reduced shoot P concentration. In the second year, shoot biomass was generally enhanced by high P supply and reduced by high N supply; responses to high P were strongest in species with low shoot biomass and high N concentration but unrelated to the productivity of the species’ sites. The total biomass produced during both years was smaller at high N supply than at high P supply. A smaller fraction of the N and P supply was recovered in high-N plants, and these plants allocated less biomass to roots than those grown at high P supply or low N and P supply. Periodic flooding reduced biomass production and nutrient recovery, but hardly influenced the effects of nutrient supply on plant growth. Species from wet meadows were affected more by flooding than species from fens in the first season, but not in the second season. We propose that high N supply reduced second-year growth because strong P limitation increased below-ground nutrient losses from plants, whereas high P supply enhanced second-year growth by improving N retention in plants. Our results therefore suggest that N and P enrichment may have quite different effects on wetland vegetation.
 
Article
Summary 1. Inbreeding can negatively affect various fitness components. Here we examine how immune response and body size of a social insect are affected by inbreeding, sex and ploidy. 2. In the bumble-bee, Bombus terrestris (L.), the offspring of colonies resulting from brother-sister matings were compared with that of outbred colonies. Immune response was measured as the degree of encapsulation of a novel antigen, body size as the length of the radial cell in the forewings. 3. Inbreeding affected neither immune response nor body size in either workers or haploid males under laboratory conditions. However, fitness characteristics varied significantly among maternal families and colonies. The lack of detectable inbreeding depression for two fitness components might help explain why B. terrestris is a good colonizer in nature. 4. In addition, sex and ploidy strongly affected the fitness components studied: diploid males had a significantly lower immune response than haploid males, who in turn had a significantly lower immune response than workers of the same colony. The body size of diploid males was intermediate between the body size of workers and haploid males.
 
Article
1. Quantifying the amount of resources remaining under plant cover is essential for assessing plant–plant interactions or biological invasions. Although resource levels fluctuate in time, their quantification is performed mainly by instantaneous measurements. We investigated how instantaneous measurements are related to the amount of resources cumulated throughout one growing season, measuring parameters of both light and soil water depletion. 2. During a growing season, we measured regularly light and soil water levels under the cover of 18 plant species grown as monocultures in a common garden. The temporal dynamics of light and soil water depletion were assessed within each monoculture using mechanistic modelling approaches. 3. The total amounts of resources remaining over the year under the range of communities were best predicted by instantaneous measurements performed at critical periods, differing among resources. The significance of prediction decreased dramatically for other dates, including the period of peak production, but without changing the ranking of communities according to ability to deplete resources. We therefore recommend that such measurements should be limited to qualitative studies, and that mechanistic modelling for quantitative assessments should be developed.
 
Frequency distributions for the medians of posterior distributions of tree architectural parameters (aH, bH, aF, bF, aW and bW). Vertical lines show median values of the community tendency. A grey bar shows species with significant variables whose 95% credible interval differed from the median of the community tendency. These frequency distributions nearly approximate the prior distribution of parameters.
Relationships between tree architectural variables for 200 species by applying medians of posterior distributions of architectural parameters; (a) tree height vs. stem diameter (H vs. D), (b) height of the lowest foliage vs. tree height (F vs. H) and (c) crown width vs. height (W1 vs. H). The maximum size for each species is the upper-diameter D* for stem diameter or upper-height estimated by D*. In the inset, the log–log relationships are shown.
Frequency histograms for life-history traits, (a) 95-percentile upper-diameter of all trees ≥0·1 × maximum dbh, D* and (b) median values of posterior distributions in sapling mortality, M. White bars show selected species, and vertical lines show median values for all species.
Relationships between tree architectural variables (tree height, height of the lowest foliage and crown width) and indices of life-history traits (upper-diameter D* and sapling mortality M) for trees of different reference diameters (upper panels) and heights (middle and lower panels). Left-hand panels (a–c) show Kendall’s correlation coefficients (τ) between posterior distributions of architectural variable and upper-diameter, and right-hand panels (d–f) show Kendall’s correlation coefficients (τ) between posterior distributions of architectural variable and sapling mortality for trees of different reference sizes. Solid symbols indicate significant correlations (95% interval of τ does not include zero); open symbols indicate non-significant correlations (95% interval of τ does includes zero). Solid lines show a decline in the number of species to compare with an increase in size, from 200 species (199 species for mortality) at the smallest reference size to 20 species at the largest reference size.
Article
1. Tree architecture is thought to allow species to partition horizontal and vertical light gradients in the forest canopy. Tree architecture is closely related to light capture, carbon gain and the efficiency with which trees reach the canopy. Previous studies that investigated how light gradients drive differentiation in tree architecture have produced inconsistent results, partially because of the differences in which tree species and ontogenetic stages were studied. 2. We examined the relationship between stem diameter, tree height, foliage height, crown width and life-history strategy over a broad size range of 200 randomly selected, co-occurring tree species in a lowland rainforest in Peninsular Malaysia. We developed a hierarchical Bayesian model to account for both intra- and interspecific variation and describe the relationships among tree architectural variables. We analysed interspecific variation in tree architectural variables in relation to adult stature and light requirement for species regeneration as a function of tree size. 3. There was little interspecific variation in architectural variables, this is partly because of large intraspecific variation in response to canopy heterogeneity, but it also suggests architectural convergence within this community. However, interspecific analyses showed that, for large-statured species, small size classes had thinner stems with narrow and shallow crowns, whereas large-size classes had wider crowns. Light-demanding species (as indicated by high sapling mortality in shaded conditions) showed weak trends in tree architecture and were only characterized by wide crowns at intermediate sizes. 4. In summary, tree architectural traits overlapped across the species community. This suggests that architectural convergence and equalizing effects occur in this diverse tropical forest and that community-wide allometric equations can be used to describe forest height and carbon storage. Light resource partitioning also occurs, indicating stabilizing effects. Interspecific architectural variation in relation to adult stature supports the theory of the trade-off between early reproduction and vegetative growth. In closed rainforests, adult stature imposes a stronger force on architectural differentiation of species than regeneration light requirements.
 
Article
Summary1. Climate change is predicted to bring earlier bud break and perhaps a greater risk of frost damage to developing leaves and flowers. Given the rarity and unpredictability of major frost events and limited community-level phenological observations, comparisons among deciduous forest species experiencing frost damage and refoliation are rare.2. This study used phenological observations ongoing at the time of a hard freeze to compare leaf and flower development, frost damage and leaf refoliation of 20 deciduous woody species in Trelease Woods, Champaign Co., IL, USA. Freezing temperatures from 5 to 9 April 2007 followed 22 days after very warm temperatures began in March.3. Bud break was the earliest in 17 years. Frost caused damage to leaf buds, developing shoots and/or expanding leaves of canopy trees of six species and saplings of two species. Undamaged species were inactive, or in bud break or shoot expansion. Among damaged species, 11–100% of individuals exhibited some frost damage. Mean damage level per individual ranged from 20% to 100% among species.4. Refoliation from dormant buds led to mean final canopy fullness that ranged from 46% to 99% among damaged species, but time of full leaf expansion was extended by 16–34 days for refoliating species.5. Frost damaged flowers, but not flower buds or developing fruit, of five of eight species that flowered during the frost period.6. The extent of frost damage in 2007 was unusual; damage was greater than any of the other 4 years with frost damage from 1993 to 2009 because record-breaking March temperatures in 2007 caused more species to be at later vulnerable stages with the advent of subfreezing temperatures in April.7. Differences among individuals and species in frost damage and ability to refoliate caused strong selection on individuals and differences in carbon gain that could, in the long-term, affect species’ abundances. The frost also reduced fruit/seed abundance for insects and mammals.
 
Article
Summary 1. Genetic and environmental maternal effects can play an important role in the evo- lutionary dynamics of a population: they may have a substantial impact on the rate and direction of genetic change in response to selection, and they may generate immediate phenotypic change via phenotypic plasticity. Because of this potential to generate rapid phenotypic change in a population, maternal effects may be particularly important for evolution at ecological time-scales. 2. Despite an increased interest in the prevalence, composition and adaptive benefits of maternal effects, little is still known of their impact on ecological and evolutionary processes in natural populations. We consider here the insights that a quantitative genetic framework provides into the pathways by which maternal effects can influence trait evolution in wild populations. Widespread evidence for a genetic basis of a range of maternal effects traits reinforces the notion that they cannot be treated as purely environmental sources of variation. We also provide an overview of the impact of envir- onmental conditions on the expression and impact of maternal effects, and describe empirical evidence for their impact on evolution at ecological time-scales. 3. We emphasize the need for empirical work to quantify the associations between maternal and offspring phenotype and genotype, and the suite of selection pressures generated by maternal effects, as well as the relationship between maternal effects and environmental variation. Future work should aim to identify the conditions under which maternal effects are likely to play a role in evolution, as well as explicitly test the contribution of maternal effects to evolutionary responses.
 
Article
Summary 1. Dispersal and gene flow can have a variety of interacting effects on evolution. These effects can either promote or constrain adaptive divergence through either genetic or demographic routes. The relative importance of these effects is unknown because few attempts have been made to conceptually integrate and test them. 2. We draw a broad distinction between situations with vs. without strong coevolutionary dynamics. This distinction is important because the adaptive peak for a given population is more mobile in the former than in the latter. This difference makes ongoing evolu- tionary potential more important in the presence of strong coevolutionary dynamics than in their absence. 3. We advance a conceptual integration of the various effects of gene flow and dispersal on adaptive divergence. In line with other authors, but not necessarily for the same reasons, we suggest that an intermediate level of gene flow will allow the greatest adaptive divergence. 4. When dispersal is quite low, we predict that an increase will have positive effects on adaptive divergence, owing to genetic/demographic rescue and 'reinforcement.' The rescue effect may be more important in small populations and in homogeneous environments. The reinforcement effect may be more common in large populations and in heterogeneous environments. 5. Once a certain level of dispersal is reached, we predict that a further increase may have negative effects on adaptive divergence. These effects may arise if carrying capacity is exceeded or maladaptive genes are introduced. 6. Many additional effects remain to be integrated into this framework, and doing so may yield novel insights into the factors influencing evolution on ecological time-scales.
 
Article
1. Relative growth rate (RGR), proportional dry-mass content of leaf and stem tissues, and biomass-allocation pattern were assessed under controlled conditions for 22 populations of Dactylis glomerata s.l. from contrasting latitudes and altitudes in Europe, Israel and Kazakstan. Furthermore, width and thickness of leaves were measured in garden-grown mature plants. 2. All these parameters varied significantly among the populations. RGR correlated negatively with dry-mass content of leaves and stems, but not with biomass-allocation parameters, leaf thickness or leaf width. We argue that the close association of RGR with variation in dry-mass content among species and genetically distinct populations is a result of the larger volume of tissue, and correspondingly larger leaf area and longer root system, that a plant with a low tissue density can build per unit dry mass. 3. Leaf tissue dry-mass content decreased and RGR increased with increasing latitude and elevation of the originating site, indicating that a high growth rate may be an advantage in habitats with a short growing season. This contrasts with earlier findings of a negative correlation between inherent RGR and altitude.
 
Article
Summary 1. Classical evolutionary theory states that senescence should arise as a consequence of the declining force of selection late in life. Although the quantitative genetic predictions of hypotheses derived from this theory have been extensively tested in laboratory studies of invertebrate systems, relatively little is known about the genetics of ageing in the wild. 2. Data from long-term ecological studies is increasingly allowing quantitative genetic approaches to be used in studies of senescence in free-living populations of vertebrates. We review work to date and argue that the patterns are broadly consistent with theoretical predictions, although there is also a clear need for more empirical work. 3. We argue that further advances in this field of research might be facilitated by increased use of reaction norm models, and a decreased emphasis on attempting to discriminate between mutation accumulation and antagonistic pleiotropy models of senescence. We also suggest a framework for the better integration of environmental and genetic effects on ageing. 4. Finally, we discuss some of the difficulties in applying quantitative genetic models to studies of senescence outside the laboratory. In particular we highlight the problems that viability selection can cause for an accurate estimation of parameters used in the prediction of age-trajectory evolution.
 
Article
Summary 1. The chemical composition of plant litter is commonly considered to indicate its quality as a resource for decomposer organisms. Litter quality, defined in this way, has been shown to be a major determinant of litter decomposition rates both within and across terrestrial ecosystems. Notably, the structure of the microbial community that is directly responsible for primary decomposition is rarely considered as an empirical predictor of litter decay rates. 2. Microbial communities are generally assumed to perceive litters of the same chemical com- position to be of equivalent resource quality but evidence from field studies suggests that these same communities may adapt to the prevalent litter types at a given site. Here, we tested this assumption by assessing how microbial communities sourced from different forest- and herbaceous-dominated ecosystems perceive the quality of novel, foliar litters derived from a tree ( Rhododendron maximum ) and from a grass ( Panicum virgatum ) species. Based on chemical composition, we would expect R. maximum litter to be of lower quality than P. virgatum litter. 3. We used an experimental litter-soil system which employs a 'common garden' approach and measured rates of CO 2 production across 50 days; higher rates of production were assumed to indicate higher quality (i.e. more easily degradable) litter. 4. We found that communities sourced from habitats under differing plant cover perceived litter quality differently. Those communities sourced from herbaceous habitats perceived the grass litter to be of higher quality than the tree litter, whereas communities from forest habitats decomposed both litter types similarly. Within a litter type, differences in both community composition and nutrient availability of the source habitat were related to decomposition rates. 5. Our results suggest that litter quality cannot necessarily be predicted solely from chemical characteristics; instead the perceived quality is dependent on the quality of past resource inputs a community has experienced and the structure of those microbial communities responsible for the initial stages of litter decomposition.
 
Article
Summary • Experimental work in vertebrates shows that different forms of coloration – particularly carotenoid-based vs melanin-based ornaments – are differentially sensitive to stressors such as diet manipulations and parasitic infections. Comparative work also shows that historical patterns of ornament evolution depend on the proximate mechanisms of colour production. • Based on the results from vertebrates, it has been argued that melanin-based ornaments may not be good indicators of quality because, unlike carotenoid-based ornaments, melanin pigments can be synthesized from amino acid precursors, and therefore melanin synthesis is unlikely to be costly. • However, there is evidence for costly melanin synthesis in insects, which use melanin in some ways that vertebrates do not. Differences across taxa in the costs of melanin synthesis challenge the generality of the hypotheses relevant to these ornaments. • In general, all pigment-based ornaments are a function of precursor intake and processing. Differences in costs of melanin synthesis across taxa may reflect differences in one or both of these parameters. • I urge communication between researchers working on related questions in disparate taxa (vertebrates and invertebrates). This should facilitate the discovery of the most fundamental aspects of colour ornament evolution. Functional Ecology (2006) 20, 276–281 doi: 10.1111/j.1365-2435.2006.01090.x
 
Article
1. Seedling relative growth rate (RGR) is often decomposed into the product of specific leaf area (leaf area per leaf mass, SLA), net assimilation rate (rate of mass increase per unit leaf area per unit time, NARa) and leaf mass ratio (ratio of leaf to total dry mass, LMR). Commonly, most cross-species variation in RGR is accounted for by variation in SLA, while no general relationships occur between RGR and either NARa or LMR. NARa can be factored into the product of leaf nitrogen productivity (rate of mass increase per unit leaf nitrogen per unit time, LNP) and leaf nitrogen concentration (area basis, LNCa). In this way the influence on RGR of leaf nitrogen – how it is displayed, and how it is utilized – can be investigated.
 
Article
Summary 1. Our goal was to determine the relationships among ecophysiological, whole-plant and ecosystem traits of a wide variety of grassland species grown under field conditions in the long term. We measured 87 traits for 33 species (32 perennial, one annual) grown in monoculture for 5 years on sandy soils, and determined the relationship among traits and their correspondence with current functional classifications. 2. Among non-legumes, species that produced and maintained large amounts of biomass had tough, low-activity leaves and roots, high root : shoot ratios, and low extract- able inorganic nitrogen and N mineralization in their soils. The set of correlations among the functional traits of fine roots for non-legumes parallels the set of correla- tions for leaf functional traits. Low-N species maintained greater biomass than high- N species, more by producing tissues with low N concentrations and greater longevity than by acquiring more N. Greater relative production below ground, and the produc- tion of long-lived below-ground structures, were both important in determining the high root : shoot ratio of species. 3. For legumes, N 2 fixation not only led to greater above-ground biomass production, but also was associated with low fine root production; greater relative production of stem biomass; and accelerated ecosystem N cycling compared to non-legumes. 4. The measured traits, as condensed via principal components analysis, differentiated the 32 species into groups that corresponded with a common grassland functional clas- sification scheme (C 3 grasses, C 4 grasses, forbs, legumes, woody species) as well as an alternative, continuous approach. For all traits, species can be arrayed well along two continuous axes. The first axis separates cool-season and warm-season legumes; the second low-N and high-N non-legumes. 5. These continuous classifications show the generality of the two strategies for dealing with low nitrogen availability (N 2 fixation and the low-N suite of traits) and extends the strategies to span organ-level traits to ecosystem processes including roots, whole-plant patterns of productivity, and nutrient cycling. The correlations of traits among species will also be useful in predicting a large number of important parameters associated with plant growth from the measurement of a few, key traits.
 
Characteristics of the 38 study species
Two-way  with the effect of species (n = 38) and light level (n = 2; SH = shade, SU = sun) on leaf traits (total n
One-way  on crown exposure, maximum adult stature and plasticity in leaf traits for 38 tropical moist forest tree species
Article
1. The sun¿shade acclimation and plasticity of 16 functional leaf traits of 38 tropical tree species were studied in relation to their light demand, maximum adult stature and ontogenetic changes in crown exposure. 2. Species differed significantly in all leaf traits, which explained a large part of the observed variation (average R2 = 0·72). Light had a significant effect on 12 traits and species showed a similar proportional response to light, indicating that the species ranking in trait performance is largely maintained in different light environments. 3. Specific leaf area, leaf nutrient content and chlorophyll : nitrogen ratio showed the largest plasticity to irradiance. These traits are important for maximizing growth in different light conditions because they are closely linked to the photosynthetic capacity and carbon balance of the plant. 4. Plasticity is generally thought to be greatest for pioneer species that occupy early successional habitats with a large variation in irradiance. This hypothesis was rejected because short-lived pioneers showed the lowest plasticity to irradiance. 5. An alternative hypothesis states that plasticity is largest for tall species that experience large ontogenetic changes in irradiance during their life cycle. Yet plasticity was barely related to adult stature or ontogenetic changes in crown exposure. Short-lived pioneers that experience consistently high light levels did have low plasticity, but shade-tolerant species that experience consistently low light levels had high plasticity. 6. Tropical rainforest species show a large variation in plasticity. Plasticity is a compromise between many factors and constraints, and all of these may explain the observed patterns to some extent.
 
Article
1. A simple device called a ‘pocometer’ (POlar COordinate METER) was developed to measure three-dimensional structure of plants. It consists of a tape-measure to measure distance and two protractors to measure zenith angle and azimuth angle. 2. The pocometer can determine locations of points within a few metres distance with a resolution of less than 1cm. Location of any point on a plant can be measured in 10 to 30s depending on the ease of pulling the tape measure to the point of interest. 3. A system to use data obtained with the pocometer to calculate plant light capture was developed. The degree of shading at any point on a plant is estimated by checking obstruction by other plant parts of the view toward the sky at that point. 4. Photon flux density (PFD) on leaf surfaces was estimated for Aucuba japonica, a broad-leaved evergreen shrub, using the above system. The estimated PFDs for individual leaves of a plant corresponded to the sensor-measured PFDs with correlation coefficients of 0·67 to 0·92.
 
Article
Summary1. Hierarchical branching is a fundamental feature of trees. Understanding how tree architecture is linked to tissue nutrient concentrations, metabolic rates, and life cycles is important for predicting ecosystem processes such as respiration, module turnover, and organic matter decomposition.2. Here, we examined branch order–nutrient relationships in above- and belowground tree branching systems by analysing nitrogen (N), phosphorus (P), and N : P ratio in leaves, the first three orders of twigs, and the first five orders of roots in 49 tree species, including 21 temperate angiosperm species, six temperate gymnosperm species, and 22 subtropical-tropical angiosperm species.3. Tissue [N] and [P] declined linearly with increasing twig and root orders across all species. The slope of the linear regression between root order and root [N] was the same between temperate and subtropical-tropical angiosperms, but steeper in angiosperms than gymnosperms. In contrast, root order–[P] relationship differed between biomes but not between phylogenetic groups, probably due to the significantly lower P availability in subtropical-tropical soils. Additionally, the magnitude of change in tissue [N] and [P] between successive shoot and root branch orders was not constant across branching levels. Among all fine root orders, first order root tips had [N], [P], and N : P ratio most similar to those of leaves.4. These results demonstrate that there is a general inverse order–nutrient relationship in above- and belowground modules, though specific patterns of this relationship differed between N and P, and between species groups. Moreover, among all root orders within the fine root guild, root tips are the best parallels of leaves in nutrient concentrations. The order–nutrient relationships presented here advances our understanding of functional module construction in trees, and provide a basis for modelling tissue chemistry-regulated processes such as respiration and decomposition in forest ecosystems.
 
Article
1. Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of termites (Isoptera) were examined in Darwin, northern Australia. It is suggested that the stable isotope technique, together with phylogenetics, is a useful tool to understand the evolution of functional groups in detritivores.2. A high δ15N value was observed in the Termes-Capritermes branch of the subfamily Termitinae and the genus Amitermes, two distinct taxonomic groups that evolved from wood-feeding to soil-feeding in Australia. Among eight Termes-Capritermes branch species, only two species (Xylochomitermes melvillensis and Ephelotermes melachoma) were discernible as wood/soil interface feeders, the remaining six species analysed were soil-feeders, where the diet preference was identified by using δ15N of workers.3. The Termes-Capritermes group in Australia contains both wood/soil interface feeders and soil-feeders, whereas wood/soil interface feeders in Cameroon are from the Termes-Capritermes branch while soil-feeders are from Cubitermes group. The result confirmed that soil-feeding forms evolved both in Australia and Africa, but from different phylogenetic groups.
 
Article
Summary • Rising concentrations of atmospheric CO2 may have important consequences for reproductive allocation in forest trees. Changes in pollen production could influence population dynamics and is likely to have important consequences for human health. This is the first study to evaluate pollen production by forest trees in response to rising atmospheric CO2. • Our research objective was to quantify pollen production by Loblolly Pine (Pinus taeda L.) trees growing in elevated CO2 (ambient + 200 µl l−1) since 1996. • Trees grown in high-CO2 plots first began producing pollen while younger and at smaller sizes relative to ambient-grown trees. Pollen cone and airborne pollen grain abundances were significantly greater in the fumigated stands. We conclude that the greater number of mature trees in high-CO2 plots resulted in greater pollen production at the stand level. • Precocious pollen production has important implications for fertilization and pollen dispersal from young, dense stands. Increasing levels of airborne pollen raise concerns for escalating rates of human respiratory disease. Functional Ecology (2006) 20, 541–547 doi: 10.1111/j.1365-2435.2006.01133.x
 
Article
Summary • Above-ground structure was analysed in saplings of 56 sympatric species in a Bornean rain forest with consideration of the phylogenetic background to elucidate interspecific variation in the dry-mass cost and its ecological consequences. • The extension cost (total above-ground mass) in 1·5-m tall saplings varied eightfold among the 56 species. However, no significant differences in extension cost were observed among saplings of three crown types (branched, monoaxial simple-leaved, and monoaxial compound-leaved), although the monoaxial crown type has been considered an adaptation for achieving rapid height growth. The lack of differences arose because the advantages of monoaxial saplings in structural cost for displaying a given leaf area were unexpectedly small. • Understory species had a significantly higher extension cost than canopy species because of their thicker, and consequently, heavier trunks. This trend was common to the three crown types; thus, the higher extension cost was not caused by the prevalence of a specific crown type in understory species. • For all 56 species combined, the trade-off between height growth efficiency and light-interception-enhancing morphology was prominent. This structural trade-off, which makes efficient vertical growth incompatible with survival in the understory, potentially enables the stable coexistence of these species in a temporally heterogeneous light environment. Functional Ecology (2007) 21, 41–49 doi: 10.1111/j.1365-2435.2006.01217.x
 
Article
1. There are conflicting reports concerning the adaptive features of tree populations originating from cold, high-altitude environments. We hypothesize that such trees will possess adaptive features that will be demonstrated in a common environment, such as elevated rates of net CO2 exchange, elevated needle nitrogen concentration and high proportional biomass allocation to roots. To test this hypothesis we measured tree and seed properties of 54 populations of Norway spruce [Picea abies (L.) Karst.] located along eight altitudinal transects (from c.600 to 1500m) in southern Poland. We also measured growth, biomass partitioning, net photosynthetic capacity (Amax), needle dark respiration (RS) and carbohydrate, nitrogen (N) and chlorophyll concentration of seedlings originating from these populations grown for 2 to 7 years in a common garden at 150m elevation. Measured in situ along the elevational transects, there were linear declines in seed mass, average d.b.h. and height growth increment of seed trees with increased altitude or lower mean annual temperature.
 
Article
Summary 1. We studied the associations among growth rate, RNA content and P content at ∼ 12- h intervals during the larval stage in five species of Drosophilids that specialize on host foods that differ substantially in P content. 2. Consistent with expectations based on the 'growth rate hypothesis' (GRH), within each species there were significant positive correlations between growth rates and RNA and P contents and in each species variation in P content was largely determined by differences in RNA content. However, there was a significant difference among spe- cies in how these three parameters were associated with each other, primarily due to differences in the intercept of the relationships rather than in their slopes. 3. Consistent with the GRH, we also observed positive associations among the aver- age growth rates, RNA contents and P contents of the five species. Furthermore, these differences were broadly consistent with differences in the P content of their host resources: for example, Drosophila falleni , a species that specializes on P-rich mush- rooms, had the highest growth rates and P and RNA contents while D. pachea and D. mettleri , species that specialize in low-P exudates from necrotic cacti and trees, had the lowest growth rates and P and RNA contents. 4. While data for additional species are needed, our findings provide further evidence consistent with the GRH and highlight a potential role of P limitation in shaping growth rate evolution in the Drosophilids .
 
Article
1The allometric scaling relationship between lamina and lamina support has rarely been examined, such that its significance to plant life-history strategies has not been fully explored and understood so far. We investigated the sizes of leaf lamina and petiole for 93 temperate broad-leaved woody species at two altitudes of a southwestern mountain, and analysed the scaling relationship in relation to leaf habit (evergreen vs. deciduous), leaf form (simple- vs. compound-leaved species), and habitat type (low vs. high altitude).2Significant allometric scaling relationships were found between petiole mass and lamina mass, and between petiole mass and lamina area, with common slopes of 0·872 and 0·742, respectively, both significantly departed from the value of 1·0. The results of phylogenetic comparative analyses were in accordance with the observed positive scaling relationships.3The evergreen species were found to have a greater petiole mass than the deciduous at a given lamina area; whilst a contrasting pattern was observed between lamina mass and petiole mass, in which the evergreens had a greater biomass allocation to lamina for the same petiole mass relative to the deciduous.4The compound-leaved species were observed to be significantly greater in both lamina area and lamina support (including petioles, rachis and petiolules) than the simple-leaved species, whereas the former had a smaller lamina area or lamina mass at a given petiole mass than the latter.5The plants from the high altitude had less lamina area at a given petiole investment compared to those from the lower altitude, likely due to the large mechanic and transporting requirements of petioles in the species at high altitude.6Our results indicate that petioles serve as an adverse forcing on the maximization of lamina area and lamina biomass and that the allometric relationship between lamina and lamina support varies with leaf habit, leaf form and habitat.
 
Top-cited authors
Peter B Reich
  • University of Minnesota Twin Cities
Stephen C Stearns
  • Yale University
Andrew P Hendry
  • McGill University
Raoul Van Damme
  • University of Antwerp
Anthony Herrel
  • French National Centre for Scientific Research