Bai-an Li

Phase transition in spatial epidemics using cellular automata with noise

One of the central issues in studying the complex population patterns observed in nature is the role of stochasticity. In this paper, the effects of additive spatiotemporal random variations—noise—are introduced to an epidemic model. The no-noise model exhibits a phase transition from a disease-free state to an endemic state. However, this phase transition can revert in a resonance-like manner depending on noise intensity when introducing nonzero random variations to the model. On the other hand, given a regime where disease can persist, noise can induce disappearance of the phase transition. The results obtained show that noise plays a tremendous role in the spread of the disease state, which has implications for how we try to prevent, and eventually eradicate, disease.

Solving the pitfalls of pitfall trapping: a two‐circle method for density estimation of ground‐dwelling arthropods

Summary Pitfall traps are widely used for investigating ground-dwelling arthropods, but have been heavily criticized due to their species-, habitat- and attractant-specific trapping radius which produces unreliable estimation of species diversity and density. We developed a two-circle method (TCM) for simultaneously estimating densities of ground-dwelling arthropods and the effective trapping radius. Multiple pairs of traps are located different distances apart, and the intersection of trapping areas can be calculated using the inverse trigonometric function. The density and effective trapping radius can be estimated from a nonlinear regression of the change in the total number of individuals caught with the distance between the paired pitfall traps. We compared the performance of TCM with the estimator based on the nested-cross array (NCA) for arranging pitfall traps, by comparing predicted densities from these two methods with the real density obtained from the suction sampling method (SSM). Simulations with known arthropod densities and effective trapping radius suggested that TCM produced accurate density estimation, while NCA significantly underestimated the known density. Pitfall trapping of ground-dwelling arthropods on two habitats (crop field and desert steppe) confirmed this conclusion when comparing estimation from TCM and NCA with densities obtained from the SSM. TCM is a promising technique for the density estimation of ground-dwelling arthropods, especially for traps with liquid attractant and areas with relatively homogenous habitat and away from habitat edges.

Intrinsic Optimum Temperature of the Diamondback Moth and Its Ecological Meaning

ABSTRACT Temperature can notably affect development rate and intrinsic rate of increase of the diamondback moth, Plutella xylostella L. The intrinsic rate of increase is usually regarded as a good measure of fitness in insects, and the constant temperature at which the intrinsic rate of increase reaches its maximum is defined as the “optimal” temperature for an insect species to survive. The estimates of optimal temperature for some insects and mites are ≈30°C. However, the Sharpe— Schoolfield—Ikemoto model provides an estimate about the intrinsic optimum temperature at which the probability of an enzyme being in the active state is maximal. The intrinsic optimum temperature is considered to be the most suitable temperature for an insect species to survive. The estimates of intrinsic optimum temperature for some insects and mites are ≈20°C. The optimal temperature and the intrinsic optimum temperature of the diamondback moth were estimated in the current study. The former estimate is 28.4 (95% CI: 26.2–28.8°C), whereas the latter estimate is 19.4°C (95% CI: 17.9– 20.5°C). Considering the daily average air temperatures during the peaks of the diamondback moth in China, the intrinsic optimum temperature of 19.4°C might represent the most suitable temperature for this insect to survive. We also discussed whether it is sounded to use the intrinsic rate of increase as the fitness. Because the intrinsic rate of increase cannot reflect the density-dependence of population and the trade-off between individual body mass and population size, it is inappropriate to equate these two concepts.

ALLOMETRIC SCALING AS AN INDICATOR OF ECOSYSTEM STATE: A NEW APPROACH

It is argued that the problem of regional environmental security cannot in principle be solved without involving the regulatory environmental potential of the natural biota. Ecological allometry, i.e. the analysis of eco- logical and environmental phenomena based on body size and spatial scale regularities, is shown to provide clues to understanding the principles of envi- ronmental homeostasis in natural ecosystems.

Re-calibrating the snake palaeothermometer

Arising from: J. J. Head et al. 457, 715–717 (2009)10.1038/nature07671; Head et al. replyIn a recent study a new proxy for palaeoclimate reconstructions was proposed on the basis of a theoretical approach linking the largest body sizes to ambient temperature in extant taxa of air-breathing poikilotherms. The value of the largest fossil snake’s body length was used to estimate the mean annual temperature (MAT) for the Palaeocene neotropics of ΔT = 3.8–7.2 °C above the modern value. Here we argue that the reported temperature difference is a twofold overestimate and obtain a corrected estimate of ΔT = 1.9–3.7 °C using the taxon-specific metabolic scaling exponent α = 0.17 for boid snakes. The importance of using relevant taxon-specific information in case of one-taxon-based temperature reconstructions while leaving the theoretically derived generic α values (such as α = 0.33 used by Head et al.) for broad inter-taxonomic analyses is emphasized.

Organization of biogeochemical nitrogen pathways with switch-like adjustment in fluctuating soil redox conditions

Nitrogen is cycled throughout ecosystems by a suite of biogeochemical processes. The high complexity of the nitrogen cycle resides in an intricate interplay between reversible biochemical pathways alternatively and specifically activated in response to diverse environmental cues. Despite aggressive research, how the fundamental nitrogen biochemical processes are assembled and maintained in fluctuating soil redox conditions remains elusive. Here, we address this question using a kinetic modelling approach coupled with dynamical systems theory and microbial genomics. We show that alternative biochemical pathways play a key role in keeping nitrogen conversion and conservation properties invariant in fluctuating environments. Our results indicate that the biochemical network holds inherent adaptive capacity to stabilize ammonium and nitrate availability, and that the bistability in the formation of ammonium is linked to the transient upregulation of the amo-hao mediated nitrification pathway. The bistability is maintained by a pair of complementary subsystems acting as either source or sink type systems in response to soil redox fluctuations. It is further shown how elevated anthropogenic pressure has the potential to break down the stability of the system, altering substantially ammonium and nitrate availability in the soil, with dramatic effects on biodiversity.

Effect of the high dose/refuge strategy on Bt-crop yield dynamics (mathematical simulation)

A mathematical model is presented that describes interactions between Bt-crops and insect pests taking into account the plant growth rate, consumption of plant biomass by pests, suppression of insect proliferation by Bt toxins, emergence of Bt-resistant insects and their mixing with the wild type. It is shown that migration of Bt-susceptible insects from “refuge plots” onto the Bt-crop field invaded by resistance-carrying insects improves the yield dynamics; being high enough, this inflow eventually eliminates the resistant pest population.

A Commensal Consumer-Induced Mediation Effects on Resource–Consumer Interactions

A general view of resource–consumer interactions is that resource intake by the consumers reduces the growth rate of resource population but it leads to an increase of consumer population. This view is proficiently interpreted with the classic Lotka–Volterra model that successfully describes the effects of changes in consumption rates due to changes in resource and consumer population densities. These effects are resulted in perpetual oscillatory dynamics of both the population densities, and the extent of the effects for given initial densities is measured by the oscillating frequency determined by the model parameters. But in many ecosystems, it has often observed a steep decline and delayed recovery in resource population that cannot be explained by the traditional Lotka–Volterra model. Foraging habits and behaviors of a consumer population may facilitate others, those usually do not affect them directly, to feed on the same resource and then to reproduce successfully. Such commensal consumers (facilitated population) can heavily influence the rate of resource exploitation and thereby affect the usual resource–consumer cycles. While involving such commensal consumer-induced effects, called here commensal mediation, into the Lotka–Volterra type models, it shows that the commensal mediation can have stabilizing or destabilizing effects on resource dynamics depending on the strength of interactions and the conditions in which the interactions occur. In the natural ecosystems where the growth rate of resource population depends on its own density even in absence of consumers, the commensal mediation provides a destabilizing effect on resource dynamics; increasing commensal population density increases the amplitude of resource fluctuations and the time laps from one peak to the next. On the other hand, in the managed ecosystems where the growth rate of resource population is expected to be maintained at a constant level in absence of consumers, the commensal mediation provides stabilizing effect at a certain condition; with a given restriction on the consumer population, decreasing mortality of the commensal population can stabilize the resource population dynamics at a stable, steady-state. Moreover, while the resource population experiences saturation effect, resource–consumer interactions with the commensal mediation exhibit a range of dynamical behaviours starting from stable equilibrium, then damped oscillation, to limit cycles as the resource carrying capacity increases from a critical level. In addition, commensal mediations with both controlling facilitator consumer population and resource harvesting are analyzed separately and the results are discussed for some exemplified managed and natural ecosystems.

Have Ecological Human Rights Been Globally Lost? A Conflict of Ecological Spatial Requirements and Cultural Landscape Opportunities in Modern Homo sapiens

The commonly respected set of human rights includes the right for food and water, which are direct consequences of the biological design of our species. However, as we argue, this list of inherent rights is not complete, as illustrated by the analysis of ecological space scaling and social group size in other mammalian species. The size of individually controlled territory (home range), which scales proportionally to body mass, is estimated to be of the order of 4 km2 per individual in a mammalian species equal in size to Homo sapiens. The urbanized landscapes of modern civilization, with concentrated living at high population densities, violate this inherent ecological demand of the species. The behavioral, biological, ecological, and social causes and consequences of this violation are discussed. It is argued that coping with the global ecological and environmental challenges will be impossible without focused scientific studies of the genetically encoded ecological requirements of our species.

Mathematical modeling of the spatial distribution of the pollen produced by genetically modified crops

We present and analyze the results of mathematical simulation of pollen spreading from a field sown with genetically modified plants. Factors responsible for genetic isolation of such fields are discussed.