Temporal stability in forest productivity increases with tree diversity due to asynchrony in species dynamics

Theory predicts a positive relationship between biodiversity and stability in ecosystem properties, while diversity is expected to have a negative impact on stability at the species level. We used virtual experiments based on a dynamic simulation model to test for the diversity–stability relationship and its underlying mechanisms in Central European forests. First our results show that variability in productivity between stands differing in species composition decreases as species richness and functional diversity increase. Second we show temporal stability increases with increasing diversity due to compensatory dynamics across species, supporting the biodiversity insurance hypothesis. We demonstrate that this pattern is mainly driven by the asynchrony of species responses to small disturbances rather than to environmental fluctuations, and is only weakly affected by the net biodiversity effect on productivity. Furthermore, our results suggest that compensatory dynamics between species may enhance ecosystem stability through an optimisation of canopy occupancy by coexisting species.     

Evidence of genetic influence on the flowering pattern of Ficus microcarpa

Flowering patterns result from the interactions between genetic and environmental factors. While the genetic basis for flowering time variation in commercial plants is often well understood, few studies have been conducted to investigate these patterns in plants without economic importance. Ficus microcarpa is a commonly introduced horticultural fig tree. Asynchrony in syconium development and the initiation, frequency, and size of crops may affect its fitness as well as the success of mutualism with its pollinating wasps. In order to identify genetically determined patterns in the flowering traits in F. microcarpa, a 14-month census was taken on the flowering characteristics of 28 trees growing in close proximity along an urban street in Taipei, Taiwan. Weekly surveys were taken on 7 characteristics: crop number, syconia per branch, crop asynchrony, as well as flowering onset and seed development duration for both the spring and summer crops. Post-census genotyping at microsatellite loci distinguished 16 genetic groups (5 clonal groups and 11 non-clone trees). All crop characteristics presented higher variation across different genotype groups than within groups except for seed development duration. We found no evidence of adjacency effects or spatial auto-correlation of flowering traits. The study offers the first evidence of genetic variations in the flowering patterns in a species of Ficus. These findings lend insight into the adaptive characteristics that potentially facilitate the local establishment of F. microcarpa in new locations.     

三种鹭异步孵化与雏鸟生长的比较研究

根据1996～1999年的野外工作和实验饲养,研究了池鹭、白鹭、夜鹭3种鹭的繁殖、雏鸟生长和异步孵化对雏鸟生长的影响.3种鹭于4月上、中旬迁到常山、余杭鹭保护区,9月下旬陆续迁离.孵卵期池鹭为23.0 d(n=26),白鹭23.9 d(n=32),夜鹭25.3 d(n=34);孵化率池鹭为76.32%,自鹭86.96%,夜鹭95.45%,池鹭繁殖力为3.21只,白鹭3.38只,夜鹭3.50只.雏鸟体重增长与成体体形大小呈负相关.幼雏体重增长与孵化顺序相关.在生长早期(≤8 d)全部雏鸟正常发育,之后差异显著.第1和第2孵化雏鸟生长曲线相似,但明显高于第4雏鸟,表明较早孵化者获得食物能力较强,而迟孵出雏鸟有食物不足现象.该3种鹭孵育幼雏能力的最适度估计为3只左右.     

Probabilistic measures of persistence and extinction in measles (meta)populations

Persistence and extinction are fundamental processes in ecological systems that are difficult to accurately measure due to stochasticity and incomplete observation. Moreover, these processes operate on multiple scales, from individual populations to metapopulations. Here, we examine an extensive new data set of measles case reports and associated demographics in pre‐vaccine era US cities, alongside a classic England & Wales data set. We first infer the per‐population quasi‐continuous distribution of log incidence. We then use stochastic, spatially implicit metapopulation models to explore the frequency of rescue events and apparent extinctions. We show that, unlike critical community size, the inferred distributions account for observational processes, allowing direct comparisons between metapopulations. The inferred distributions scale with population size. We use these scalings to estimate extinction boundary probabilities. We compare these predictions with measurements in individual populations and random aggregates of populations, highlighting the importance of medium‐sized populations in metapopulation persistence.     

Environmental fluctuations can stabilize food web dynamics by increasing synchrony

Natural food webs are species-rich, but classical theory suggests that they should be unstable and extinction-prone. Asynchronous fluctuations in the densities of competing consumers can stabilize food web dynamics in constant environments. However, environmental fluctuations often synchronize dynamics in nature. Using the same 'diamond-shape' food web model first used to demonstrate the stabilizing effects of asynchrony in constant environments, we show that weak-to-moderate environmentally induced fluctuations in consumer mortality rates stabilize food webs while disrupting asynchrony. Synchrony actually promotes stability because: (i) synchronous declines in consumer density reduce the maximum abundance of top predators and (ii) resource competition quickly converts synchronous increases in consumer density into synchronous declines. These results are robust to details of food web topology and the implementation of environmental fluctuations. The fluctuation strengths that enhance stability are within the range experienced naturally by many species, suggesting that stabilization via environmental fluctuations is a realistic possibility.     

Asynchronous spatial evolutionary games

Over the past 50 years, much attention has been given to the Prisoner's Dilemma as a metaphor for problems surrounding the evolution and maintenance of cooperative and altruistic behavior. The bulk of this work has dealt with the successfulness and robustness of various strategies. Nowak and May (1992) considered an alternative approach to studying evolutionary games. They assumed that players were distributed across a two-dimensional (2D) lattice, interactions between players occurred locally, rather than at long range as in the well mixed situation. The resulting spatial evolutionary games display dynamics not seen in their well-mixed counterparts. An assumption underlying much of the work on spatial evolutionary games is that the state of all players is updated in unison or in synchrony. Using the framework outlined in Nowak and May (1992), we examine the effect of various asynchronous updating schemes on the dynamics of spatial evolutionary games. There are potential implications for the dynamics of a wide variety of spatially extended systems in biology, physics and chemistry.     

Survival of bisected rabbit morulae transferred to synchronous and asynchronous recipients

The rabbit was used as a model to test the concept that temporal asynchrony is required to establish physiological synchrony when embryos are bisected to produce demiembryos. In preliminary studies with intact embryos it was confirmed that embryos harvested on days 2, 3, 4, or 5 (day 0 = day of breeding) can be transferred with +/- 1 day of asynchrony to the uteri of recipient rabbits. Three experiments were conducted with bisected embryos. In experiment 1, 192 bisected and 194 control day 3 embryos were transferred to uteri of day 2, 2.5, and 3 recipients (ovulated 0, 12, and 24 h after the donors), with 14% of the bisected and 39% of the intact embryos (P less than .05) resulting in young. Only 4% (2/48) of the day 3 bisected embryos vs. 39% (P less than .05) of the intact day 3 embryos survived in the uteri of day 2 recipients. In experiment 2, day 3 bisected and intact embryos were transferred to the oviducts of day 3, 3.5, or 4 recipients, the speculation being that the oviduct might provide a more neutral environment than the uterus. However, embryo survival was very low, except for the intact embryos transferred to synchronized recipients (42% young born). In experiment 3, 150 intact and 162 (81 pairs) bisected day 3 embryos collected from uteri were transferred to uteri of day 2.5, 3.0, and 3.5 recipient does. Significantly more pregnancies (100% vs. 47%, P less than .01) and young born (56% vs. 19%, P less than .01) resulted from intact embryos than from bisected embryos, irrespective of the uterine age.(ABSTRACT TRUNCATED AT 250 WORDS)     

A landscape theory for food web architecture

Ecologists have long searched for structures and processes that impart stability in nature. In particular, food web ecology has held promise in tackling this issue. Empirical patterns in food webs have consistently shown that the distributions of species and interactions in nature are more likely to be stable than randomly constructed systems with the same number of species and interactions. Food web ecology still faces two fundamental challenges, however. First, the quantity and quality of food web data required to document both the species richness and the interaction strengths among all species within food webs is largely prohibitive. Second, where food webs have been well documented, spatial and temporal variation in food web structure has been ignored. Conversely, research that has addressed spatial and temporal variation in ecosystems has generally ignored the full complexity of food web architecture. Here, we incorporate empirical patterns, largely from macroecology and behavioural ecology, into a spatially implicit food web structure to construct a simple landscape theory of food web architecture. Such an approach both captures important architectural features of food webs and allows for an exploration of food web structure across a range of spatial scales. Finally, we demonstrated that food webs are hierarchically organized along the spatial and temporal niche axes of species and their utilization of food resources in ways that stabilize ecosystems.     

Flowering phenology of <Emphasis Type="Italic">Ulex europaeus</Emphasis>: ecological consequences of variation within and among populations

Reproductive phenology of gorse (Ulex europaeus L., Genisteae, Fabaceae) is unusual in that the onset and duration of flowering vary greatly among individuals within populations: some plants initiate flowering in autumn or winter and continue flowering through spring, others initiate flowering in early spring. To understand the origin of this diversity and its ecological consequences, we investigated flowering phenology of randomly sampled individuals from five different natural populations in Brittany (France). Reproductive success was evaluated for individuals with contrasting flowering patterns, from 16 natural populations. Flower production, pod production, seed production and seed predation were estimated. Plants initiating flowering in spring produced larger numbers of flowers and pods over a shorter period than plants flowering from winter to spring, which produced few flowers and pods at a time but over a longer period. Pod production of long-flowering plants did not differ significantly between winter and spring, but their pods were more intensively attacked by seed predators in spring than in winter. We discuss our results in relation to biotic and abiotic parameters. We postulate that long-flowering can be interpreted as a bet-hedging strategy, spreading the risk of pod failure (rotting or freezing) in winter and of seed predation in spring.     

Egg mass in an asynchronously hatching parrot: does variation offset constraints imposed by laying order?

Life history theory predicts phenotypic trade-offs between the number and quality of offspring produced. Intraspecific variation in egg mass is common in birds and increased egg size can have positive effects on offspring fitness. However, evidence of a trade-off with clutch size is limited. We analyzed variation in mass of 5,743 Green-rumped parrotlet (Forpus passerinus) eggs laid over 15 years to evaluate the potential for facultative adjustment of egg mass and factors governing variation. Heavier eggs had an increased probability of both hatching and fledging but egg mass did not affect postfledging recruitment. Offspring egg mass differed between populations and the potential for seasonal adjustment to egg mass may be related to environmental factors such as seed density. Egg mass was moderately heritable (h ²=0.42) which accounts for some of the individual variation detected, and these results are likely attributable to strong maternal effects. We found an effect of female age on egg mass, but no effects of previous reproductive experience. Finally, egg mass was strongly governed by position within the laying sequence, independent of clutch size, and such adjustment may facilitate brood reduction under some conditions in this highly asynchronous species.