Modelling periphyton in irrigation canals

Periphyton developments in water distribution canals induce major disturbances for system management, such as clogging problems when fixed algae are detached. Periphyton models can be used to simulate and improve canal management. The purpose of this paper is to review the periphyton models which integrate a hydrodynamic effect, and to discuss their relevance for application in open-channels. Afterwards, a new model of periphyton detachment that integrates the hydrodynamic factor is proposed. An experiment in semi-real conditions is performed to compare periphyton development under four different hydrodynamic regimes. The proposed model is compared on experimental results with two existing models. The new model reproduces well the periphyton dynamics in the four canals simultaneously.     

Development of a hydrothermal time seed germination model which uses the Weibull distribution to describe base water potential

Seed germination has been modelled extensively using hydrothermal time (HTT) models, that predict time to germination as a function of the extent to which seedbed temperature, T, and water potential, Ψ, exceed the base temperature, T_b, and base water potential, Ψ_b, of each seed percentile, g. Within a seed population the variation in time to germination arises from variation in Ψ_b(g) modelled by a normal distribution. We tested the assumption of normality in the distribution of Ψ_b(g) by germinating seed of two unrelated species with non-dormant seed (Buddleja davidii (Franch.) and Pinus radiata D. Don) across a range of constant Ψ at sub-optimal T. When incorporated into a HTT model the Weibull distribution more accurately described both the right skewed distribution of Ψ_b(g) and germination time course over sub-optimal T than the HTT based on the normal distribution, for both species. Given the flexibility of the Weibull distribution this model not only provides a useful method for predicting germination but also a means of determining the distribution of Ψ_b(g).     

A stage-structured, Aedes albopictus population model

Aedes albopictus has been the fastest spreading invasive animal species in the world from the mid-1980s until the mid-2000s. In areas it infests, it disrupts native mosquito ecology and can potentially vector up to 21 viruses. To better understand the population dynamics of this species, we created a temperature dependent population model. A stage-structured model was chosen to allow each life-stage to have different temperature dependent mortality and development rates, and each stage was modeled with an ordinary differential equation. Model parameters and distributions were based upon literature values. Initially, a basic model was constructed. This model then had parameters that were forced based upon daily average temperatures. Several criteria were used to evaluate the model, including a comparison to field data from Lubbock, TX. In a stochastic version of the model, a 95% confidence limit contained 70.7% of the field data points. Based upon these results, we feel reasonably confident that we have captured the role of temperature in driving the population dynamics of Ae. albopictus.     

An ecosystem model for estimating potential shellfish culture production in sheltered coastal waters

A generic ecosystem model has been developed for estimating the potential production of shellfish culture and the effect of that cultivation on the pelagic ecosystem in sheltered coastal waters. The model describes the dynamics of a simple food web, nutrient cycling and growth of shellfish. The design of the model is closely tied to the temporal and spatial scales that are important in determining the sustainable production level for a particular embayment. The pelagic ecosystem, mussel energetics, population dynamics and hydrodynamics are coupled to allow fully dynamic predictions of the effect of the shellfish density. When applied to Beatrix Bay, an intensive culture embayment in the Pelorus Sound of New Zealand, the model successfully captured main features of the observed system behaviour. The hydrodynamic regime of the bay controls mussel growth and production. Although high fluxes of water into the bay suppress nutrient and carbon cycling signals in the system, the model simulations demonstrated that the mussel cultivation can have considerable effects on the ecosystem of the bay including food depletion and nutrient cycling. One of the most obvious effects is nutrient enhancement through mussel excretion at low cultivation densities, which promotes primary production particularly during the N-limitation period in summer. The sensitivity analysis identified uncertainty in some parameters and indicated areas for which experimental studies could lead to model improvement. The modelling exercise has established a primary predictive tool for managing mussel aquaculture of a coastal embayment to estimate relationships between the stock level and the growth rate of mussels, and the potentially achievable harvest and stocking density.     

Development and optimization of an Agro-BGC ecosystem model for C4 perennial grasses

Extrapolating simulations of bioenergy crop agro-ecosystems beyond data-rich sites requires biophysically accurate ecosystem models and careful estimation of model parameters not available in the literature. To increase biophysical accuracy we added C₄ perennial grass functionality and agricultural practices to the Biome-BGC (BioGeochemical Cycles) ecosystem model. This new model, Agro-BGC, includes enzyme-driven C₄ photosynthesis, individual live and dead leaf, stem, and root carbon and nitrogen pools, separate senescence and litter fall processes, fruit growth, optional annual seeding, flood irrigation, a growing degree day phenology with a killing frost option, and a disturbance handler that simulates nitrogen fertilization, harvest, fire, and incremental irrigation. To obtain spatially generalizable vegetation parameters we used a numerical method to optimize five unavailable parameters for Panicum virgatum (switchgrass) using biomass yield data from three sites: Mead, Nebraska, Rockspring, Pennsylvania, and Mandan, North Dakota. We then verified simulated switchgrass yields at three independent sites in Illinois (IL). Agro-BGC is more accurate than Biome-BGC in representing the physiology and dynamics of C₄ grass and management practices associated with agro-ecosystems. The simulated two-year average mature yields with single-site Rockspring optimization have Root Mean Square Errors (RMSE) of 70, 152, and 162 and biases of 43, −87, 156 g carbon m⁻² for Shabbona, Urbana, and Simpson IL, respectively. The simulated annual yields in June, August, October, December, and February have RMSEs of 114, 390, and 185 and biases of −19, −258, and 147 g carbon m⁻² for Shabbona, Urbana, and Simpson IL, respectively. These RMSE and bias values are all within the largest 90% confidence interval around respective IL site measurements. Twenty-four of twenty-six simulated annual yields with Rockspring optimization are within 95% confidence intervals of Illinois site measurements during the mature fourth and fifth years of growth. Ten of eleven simulated two-year average mature yields with Rockspring optimization are within 65% confidence intervals of Illinois site measurements and the eleventh is within the 95% confidence interval. Rockspring optimized Agro-BGC achieves accuracies comparable to those of two previously published models: Agricultural Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) and Integrated Farm System Model (IFSM). Agro-BGC suffers from static vegetation parameters that can change seasonally and as plants age. Using mature plant data for optimization mitigates this deficiency. Our results suggest that a multi-site optimization scheme using mature plant data from more sites would be adequate for generating spatially generalizable vegetation parameters for simulating mature bioenergy crop agro-ecosystems with Agro-BGC.     

Offspring sex ratios reflect lack of repayment by auxiliary males in a cooperatively breeding passerine

The repayment hypothesis posits that primary sex ratios in cooperative species should be biased towards the helping sex because these offspring “repay” a portion of their cost through helping behavior and therefore are less expensive to produce. However, many cooperatively breeding birds and mammals do not show the predicted bias in the primary sex ratio. Recent theoretical work has suggested that the repayment hypothesis should only hold when females gain a large fitness advantage from the presence of auxiliary adults in the group. When auxiliaries provide little or no fitness advantage, competition between relatives should lead to sex ratios biased towards the dispersing (non-helping) sex. We examined the benefits auxiliaries provide to females and corresponding offspring sex ratios in the red-backed fairy-wren (Malurus melanocephalus), a cooperatively breeding Australian bird with male auxiliary helpers. We found that auxiliaries provide little or no benefit to female reproductive success or survival. As predicted, the population primary sex ratio was biased towards daughters, the dispersing sex, and females with auxiliaries produced female-biased broods whereas females without auxiliaries produced unbiased broods. Moreover, offspring sex ratios were more strongly biased toward females in years when auxiliaries were more common in the population. These results suggest that offspring sex ratios are associated with competition among the non-dispersing sex in this species, and also that females may use cues to assess local breeding opportunities for their offspring.     

Aggressive thresholds in Dendropsophus ebraccatus: habituation and sensitization to different call types

Males in many chorusing anuran species use aggressive calls during defense of calling spaces from other males. The minimal intensity of another male’s vocalizations that elicits an aggressive call response has been termed the aggressive threshold. Previous studies of aggressive thresholds have shown that they are plastic: males habituated (increased their aggressive thresholds) in response to repeated presentation of stimuli above initial threshold levels. Habituation likely contributes to the stable chorus structure of these species, in which aggressive calling is rare compared to advertisement calls. I have observed high levels of aggressive calling in the treefrog Dendropsophus ebraccatus, suggesting that males of this species do not habituate. In this study, I investigated the plasticity of aggressive thresholds in D. ebraccatus. I measured the aggressive thresholds of males before and after suprathreshold stimulation by both advertisement and aggressive calls. I found that the different call types had different effects: males habituated to advertisement calls but lowered their aggressive thresholds in response to aggressive calls. I consider the latter response to be an example of sensitization, a behavior that has been documented infrequently in vocalizing anurans. Sensitization is a plausible mechanism responsible for the high levels of aggressive calling observed in this species. Given the high costs of aggressive calling, however, it is unclear why a mechanism that increases aggressive call output would be maintained.     

Digit ratio (2D:4D) and dominance rank in female rhesus macaques (Macaca mulatta)

Female rhesus macaques exhibit matrilineal dominance structures, and high dominance rank confers fitness benefits across a lifetime and across generations. Rank effects are “inherited” through social processes that are well understood; however, biological mechanisms that might impact these processes are not well known. Recently, it has been shown that prenatal androgens appear to be implicated in supporting dominance rank hierarchies in some mammals. In humans, interindividual differences in the second (index) to fourth (ring) digit ratio (2D:4D) have been linked indirectly to variation in prenatal androgens, with low 2D:4D in both sexes associated with higher inferred prenatal androgen effects. 2D:4D has also been related to dominant social behavior and has been shown to co-vary with social systems across nonhuman primate species. Here, we investigate how 2D:4D co-varies with socially inherited dominance rank in female rhesus macaques. Low 2D:4D was associated with higher-ranking females, while higher 2D:4D was associated with lower-ranking females. Similar relationships were also shown between ranked families within matrilines. This is the first study to show such a relationship between 2D:4D and dominance rank in a nonhuman primate and suggests that prenatal androgen effects could be involved in the maintenance of dominance rank in female cercopithecine primates.     

Biodiversity Differences between Managed and Unmanaged Forests: Meta-Analysis of Species Richness in Europe

Abstract: Past and present pressures on forest resources have led to a drastic decrease in the surface area of unmanaged forests in Europe. Changes in forest structure, composition, and dynamics inevitably lead to changes in the biodiversity of forest‐dwelling species. The possible biodiversity gains and losses due to forest management (i.e., anthropogenic pressures related to direct forest resource use), however, have never been assessed at a pan‐European scale. We used meta‐analysis to review 49 published papers containing 120 individual comparisons of species richness between unmanaged and managed forests throughout Europe. We explored the response of different taxonomic groups and the variability of their response with respect to time since abandonment and intensity of forest management. Species richness was slightly higher in unmanaged than in managed forests. Species dependent on forest cover continuity, deadwood, and large trees (bryophytes, lichens, fungi, saproxylic beetles) and carabids were negatively affected by forest management. In contrast, vascular plant species were favored. The response for birds was heterogeneous and probably depended more on factors such as landscape patterns. The global difference in species richness between unmanaged and managed forests increased with time since abandonment and indicated a gradual recovery of biodiversity. Clearcut forests in which the composition of tree species changed had the strongest effect on species richness, but the effects of different types of management on taxa could not be assessed in a robust way because of low numbers of replications in the management‐intensity classes. Our results show that some taxa are more affected by forestry than others, but there is a need for research into poorly studied species groups in Europe and in particular locations. Our meta‐analysis supports the need for a coordinated European research network to study and monitor the biodiversity of different taxa in managed and unmanaged forests.     

Pheromone of the elm bark beetle Scolytus laevis (Coleoptera: Scolytidae): stereoisomers of 4-methyl-3-heptanol reduce interspecific competition

Stereoisomers of 4-methyl-3-heptanol (MH) are pheromone components of several Scolytus bark beetles. The elm bark beetle Scolytus laevis (Coleoptera: Scolytidae) has in previous studies been caught in traps baited with commercial MH containing all four stereoisomers, but the lure has been considered a weak attractant. In this study, we addressed the question whether stereospecific responses by S. laevis to stereoisomers of MH might contribute to its niche separation from other sympatric Scolytus species. Using GC–MS, we analyzed extracts of hindguts and abdomens from male and female S. laevis and the sympatric S. triarmatus. We also tested all four MH-stereoisomers individually and in combinations in the field to determine their role for S. laevis. All four stereoisomers were synthesized via a boronic ester method with 1,2-dicyclohexylethanediol as chiral director. In addition, the (3S,4R)-stereoisomer of MH was prepared through enantioselective, lipase-mediated transesterification of a mixture of the four stereoisomers of MH. Females of both species contained small amounts of syn-MH, and males contained trace amounts of anti-MH. The anti stereoisomer (3R,4S)-MH was attractive to male and female S. laevis, whereas the syn stereoisomer (3S,4S)-MH acted as an inhibitor or deterrent and reduced the catch when added to the attractive isomer. The syn isomer is the main aggregation pheromone component of the larger and sympatric S. scolytus and possibly also of S. triarmatus. The avoidance response of S. laevis to the (3S,4S)-stereoisomer may reduce interspecific competition for host trees.