Influence of the number of queens on nest establishment: native and invasive ant species

Simple Summary : Nest establishment is a critical stage of the ant life cycle because it determines the chances of colony success. Here, we study the effect of different numbers of queens (i.e., one or six) on the position of queens and workers inside and outside the artificial nests of an invasive (Linepithema humile) and Mediterranean native (Tapinoma nigerrimum) species. Our results suggest that queens in nests with six queens entered the nest faster than single queens. Similarly, during nest establishment, workers in nests with six queens entered the nest faster, with this effect being more pronounced for the native species. Once nests were established, fewer workers were engaged in outside-nest tasks in nests with six queens. This was especially true for workers of the native species engaged in patrolling. These results suggest that the number of queens can influence both queen and worker behavior, and that invasive and native species have different responses.Abstract : As a critical stage in the life cycle of ant colonies, nest establishment depends on external and internal factors. This study investigates the effect of the number of queens on queen and worker behavior during nest establishment in invasive Argentine ants (Linepitema humile) and native Mediterranean Tapinoma nigerrimum. We set up experimental colonies with the same number of workers but with one or six queens. At different time points, we recorded the positions of queens and workers inside and outside the nest. Our results highlight the influence of the number of queens on the position of queens and workers with between-species differences. Queens of both species entered the nests more quickly when there were six queens. During nest establishment, more workers were inside nests with six queens for both species, with this effect being greater for T. nigerrimum. Once nests were established, fewer workers of both species were engaged in nest maintenance and feeding in nests with six queens; T. nigerrimum had fewer workers engaged in patrolling. These results suggest that the number of queens is a key factor driving queen and worker behavior during and after nest establishment with different species responses

Methods for comparing theoretical models parameterized with field data using biological criteria and Sobol analysis

Prey-predator models are frequently developed to investigate trophic webs and to predict the population dynamics of prey and predators. However, the parameters of these models are often implemented without empirical data and sometimes chosen arbitrarily. Furthermore, when the sensibility of the model to its parameter values is tested, only a few parameters are tested and different prey-predator models (in terms of predation function structure, for example) are rarely compared. Here, we propose a method to compare four prey-predator models for two populations and select the more biologically plausible one to model a simplified agricultural trophic system, including one predator compartment (the red fox Vulpes vulpes) and one prey group compartment (small mammals). These models are based on various Holling functional responses for the predation interaction and take the prey intrinsic growth into account through a Verhulst logistic function. Most parameters values (like attack rates or growth rates) were calculated from field data or based on literature review. Uncertainty quantification is a recent trend that has gained popularity in engineering fields. In this vein, we used Sobol indices to conduct parameter exploration around mean parameter values to investigate and compare the model dynamics responses. Our first results showed that under our assumptions, the two most relevant models for our study case are the saturated Holling I and II models. Furthermore, we were able to discriminate which were the most sensitive parameters in each model. These first encouraging results open the way for the next step, which will be to adapt this model construction to more complex prey-predator systems, with several predator and/or several prey compartments

Minimising trapping effort without affecting population density estimations for small mammals

Improving species community diversity studies needs population abundances to be calculated. Micromammal population densities are highly variable at small spatial scales. Mark-recapture methods based on grid trapping is the most reliable technique to study density in small rodents, albeit it is time-consuming because it necessitates increasing the number of spatial replicates. Here, we evaluated a live-trapping grid strategy to minimise field effort without decreasing the accuracy of small rodent population density estimations. We first computed spatially explicit estimates of population density using CMR histories from a large grid made by 100 traps set over 4 consecutive days and nights trapped twice per year between 2012 and 2015, and compared these estimates with those obtained from reduced session time and grid extent for two common rodent species: the wood mouse (Apodemus sylvaticus) and the bank vole (Myodes glareolus). We then compared density estimates to simpler catch-effort indexes of abundance for these rodents. Spatially explicit density estimates from capture-mark-recapture over 4 consecutive days from grids set with a single trap interspaced 5 m on a 10 × 10 square were highly correlated (R² = 0.945) with density estimates after 4 consecutive days on a 7 × 7 square arrangement. The best performance of catch-effort indexes relative to 4 days on 10 × 10 square grid spatial density estimates for these two rodents was found when using total trapping events recorded on 8 × 8 grids over 4 days or 9 × 9 over 3 days (R² = 0.947 and 0.945 respectively). Our results support the use of a reduced grid design over 4 days to obtain reliable spatially explicit density estimates. We also obtained a reduced duration of trapping at the expense of keeping larger grids when using catch-effort indexes.This paper is based on a study financed by the Conseil Général Hauts de Seine (CG92). The PhD student, leader of this paper I. Castañeda is funded by Region Ile de France, project R2DS 2014-02

Methods for comparing theoretical models parameterized with field data using biological criteria and Sobol analysis

Prey-predator models are frequently developed to investigate trophic webs and to predict the population dynamics of prey and predators. However, the parameters of these models are often implemented without empirical data and sometimes chosen arbitrarily. Furthermore, when the sensibility of the model to its parameter values is tested, only a few parameters are tested and different prey-predator models (in terms of predation function structure, for example) are rarely compared. Here, we propose a method to compare four prey-predator models for two populations and select the more biologically plausible one to model a simplified agricultural trophic system, including one predator compartment (the red fox Vulpes vulpes) and one prey group compartment (small mammals). These models are based on various Holling functional responses for the predation interaction and take the prey intrinsic growth into account through a Verhulst logistic function. Most parameters values (like attack rates or growth rates) were calculated from field data or based on literature review. Uncertainty quantification is a recent trend that has gained popularity in engineering fields. In this vein, we used Sobol indices to conduct parameter exploration around mean parameter values to investigate and compare the model dynamics responses. Our first results showed that under our assumptions, the two most relevant models for our study case are the saturated Holling I and II models. Furthermore, we were able to discriminate which were the most sensitive parameters in each model. These first encouraging results open the way for the next step, which will be to adapt this model construction to more complex prey-predator systems, with several predator and/or several prey compartments

Precision measurement of the structure of the CMS inner tracking system using nuclear interactions

The structure of the CMS inner tracking system has been studied using nuclear interactions of hadrons striking its material. Data from proton-proton collisions at a center-of-mass energy of 13 TeV recorded in 2015 at the LHC are used to reconstruct millions of secondary vertices from these nuclear interactions. Precise positions of the beam pipe and the inner tracking system elements, such as the pixel detector support tube, and barrel pixel detector inner shield and support rails, are determined using these vertices. These measurements are important for detector simulations, detector upgrades, and to identify any changes in the positions of inactive elements

Precision measurement of the structure of the CMS inner tracking system using nuclear interactions

The structure of the CMS inner tracking system has been studied using nuclear interactions of hadrons striking its material. Data from proton-proton collisions at a center-of-mass energy of 13 TeV recorded in 2015 at the LHC are used to reconstruct millions of secondary vertices from these nuclear interactions. Precise positions of the beam pipe and the inner tracking system elements, such as the pixel detector support tube, and barrel pixel detector inner shield and support rails, are determined using these vertices. These measurements are important for detector simulations, detector upgrades, and to identify any changes in the positions of inactive elements